**Plant Fibres for Textile and Technical Applications**

M. Sfiligoj Smole, S. Hribernik, K. Stana Kleinschek and T. Kreže

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/52372

## **1. Introduction**

Recently natural and made-man polymer fibres are used for preparation of functionalised textiles to achieve smart and intelligent properties. There are numerous application possibil‐ ities of these modified materials. Main pathways for functionalizaton of fibres are: inclusion of functional additives (inorganic particles, polymers, organic compounds); chemical graft‐ ing of additives on the surface of fibres and coating of fibres with layers of functional coat‐ ings. A new approach to produce new materials is by nanotechnology, which offers a wide variety of possibilities for development of materials with improved properties. Composites of cellulose fibres with nano-particles combine numerous advantageous properties of cellu‐ lose with functionality of inorganic particles, hence yielding new, intelligent materials. For preparing cellulose composite materials profound knowledge about fibres properties is needed. Besides, new fibre qualities are demanded to guaranty the modification efficiency. Therefore non-standard methods are involved to determine physical properties of fibres.

In addition to, manufacture, use and removal of traditional textile materials are now consid‐ ered more critically because of increasing environmental consciousness and the demands of legislative authorities. Natural cellulose fibres have successfully proven their qualities when also taking into account an ecological view of fibre materials. Different cellulose fibres can be used for textile and technical applications, e.g. bast or stem fibres, which form fibrous bundles in the inner bark (phloem or bast) of stems of dicotyledenous plants, leaf fibres which run lengthwise through the leaves of monocotyledenous plants and fibres of seeds and fruits. Flax, hemp, jute, ramie, sisal and coir are mainly used for technical purposes. Re‐ cently, the interest for renewable resources for fibres particularly of plant origin is increas‐ ing. Therefore several non-traditional plants are being studied with the aim to isolate fibres from plant leaves or stems.

© 2013 Smole et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Smole et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

A review of different conventional and non-conventional fibres is presented. For extraction of fibres different isolation procedures are possible, e.g. using bacteria and fungi, chemical and mechanical methods. The procedure used influences fibres surface morphology. By fi‐ bre isolation procedures mainly technical fibres are obtained, which means that cellulose fi‐ bres are multicellular structures with individual cells bound into fibre bundles.

Retting which is the process of separating fibres from non-fibre tissues in plants, involves bac‐ teria and fungi treatments and mechanical and chemical processes for fibres extraction. De‐ spite good quality of fibres, dew retting is usually replaced by other more economic methods because the process is very time consuming and weather dependent. Instead of atmospheric retting chemical methods and enzyme retting with pectinases, hemicellulases and cellulases is

Plant Fibres for Textile and Technical Applications

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Sclerenchyma cells possess fibre like form and are arranged longitudinally. The cells are long and narrowed at the cell ends and surrounded and protected by a cell wall which is a complex macromolecular structure. During cells growth the wall is thickened and further strengthened by addition of a secondary wall. Usually fibre cells are occurring in strands or bundles which are called technical fibres [Caffall 2009]. The cells are polygonal in transverse section and connected between themselves by sclerenchyma middle lamellas. The lumen or cavity inside mature, dead fibre cells is usually very small when viewed in cross section

The cellulose, hemicellulose and lignin content in plant fibres vary depending on the plant

Chemically unmodified cellulose is generally recognised to occur in four polymorphic forms. There is some evidence for the existence of others [Krässig1992, Lewin 1998]. The monoclinic spatial model for the unit cell of native cellulose is cellulose I crystal modifica‐ tion. The unit cell houses the cellobiose segments of two cellulose molecules, one being part of the 002 corner plane and the second being part of the 002 centre plane [Lewin 1998, Hu 1996]. The monoclinic unit cell has dimensions of 0.835 nm for the a – axis, 1.03 nm for the baxis or fibre period, 0.79 nm for the c-axis, and 840 for the ß angle according to Meyer, Mark and Misch [Krässig 1992]. For natural cellulose a typical x-ray diffraction diagram is ob‐ served, that is, three equatorial diffraction peaks at the angles of about 14°, 16° and the

However, the crystalline dimorphism of cellulose and the existence of two families of native cellulose were confirmed lately. The crystalline phases Iα and I<sup>β</sup> can occur in variable pro‐ portions according to the source of the cellulose. Phase Iβ is a monoclinic unit cell having space group P21 and dimensions a = 0.801nm, b = 0.817nm, c = 1.036 nm, ß = 97.3º and very close to the cell proposed by Meyer, Mark and Misch. Phase I<sup>α</sup> corresponds to a triclinic unit cell with space group P1 and dimensions *a* = 0.674nm, *b* = 0.593nm *c* = 1.036nm, α= 117º, γ = 113º and ß = 97.3º [O'Sullivan 1997]. The celluloses produced by primitive organisms (bacte‐ ria, algae etc.) are classified by the Iα phase whereas the cellulose of higher plants (woody tissues, cotton, ramie etc.) consists mainly of the Iβ phase. I<sup>α</sup> and Iβ were found to have the same conformation of the heavy atom skeleton, but to differ in their hydrogen bonding pat‐

used, however fibre properties depend on extraction conditions significantly.

**2.1. Morphology of lignocellulosic fibres**

species, origin, quality and conditioning [ Blackburn 2005].

strongest diffraction peak at an angle of 22° [Yueping 2010].

[ Lewin 1998, Cook, 1993].

**2.2. Fibre structure**

terns [O'Sullivan 1997].

## **2. Plant fibres**

Many useful fibres have been obtained from various parts of plants including leaves, stems (bast fibres), fruits and seeds. Geometrical dimensions of these fibres, especially the fibre length depends mainly on fibre location within the plant. Fibres from fruits and seeds are few centimetres long, whereas fibres from stems and leaves are much longer (longer than one meter) [Blackburn 2005].

With an exception of seeds' and fruits' fibres, plant fibres are sclerenchyma elongated cells which occur in different parts of plants, mainly in the stems and leaves. These are elongated cells with tapering ends and very thick, usually heavily lignified cell walls. Sclerenchyma gives mechanical strength and rigidity to the plant, since it is usually a supporting tissue in plants. Fibres are also associated with the xylem and phloem tissue of monocotyledonous and dicotyledonous plant stems and leaves.

All plant cells have a primary wall. During cell growth and after it has stopped, the cyto‐ plasm in sclerenchyma cells dries while the cell wall becomes thickened by addition of a thick and rigid secondary cell wall which is formed inwards of the primary cell wall and constructed of cellulose fibrils. The secondary cell wall is formed by successive deposition of cellulose layers, which are divided in three sub-layers (S1, S2 and S3), of which the middle layer is the most important for fibres mechanical properties. It consists of helically arranged microfibrils. The diameter of microfibrils is between 10-30nm [John 2008]. An important pa‐ rameter of the structure of the secondary wall is the angle that the cellulose microfibrils are making with the main fibre direction. Actually each of three fibres sub-layers has a different microfibrillar orientation [ Krässig 1992, John 2008, Cuissinat 2008] which is specific for the fibre type. Due to the formation of a thick secondary wall, the lumen becomes smaller.

The cell wall in a fibre is not a homogeneous layer. The walls of plant cells (the primary and the secondary cell wall) can be considered as a composite consisting of cellulose fibrils em‐ bedded within a matrix of lignin and hemicellulosic polysaccharides [Krässig 1992].

Vegetable fibres are generally composed of three structural polymers (the polysaccharides cellulose, and hemicelluloses and the aromatic polymer lignin) as well as by some minor non-structural components (i.e. proteins, extractives, minerals) [Marques 2010]. Cellulose forms a crystalline structure with regions of high order i.e. crystalline regions and regions of low order i.e. amorphous regions. Middle lamellas composed of pectic polysaccharides are connecting individual cells in bundles [Caffall 2009].

Retting which is the process of separating fibres from non-fibre tissues in plants, involves bac‐ teria and fungi treatments and mechanical and chemical processes for fibres extraction. De‐ spite good quality of fibres, dew retting is usually replaced by other more economic methods because the process is very time consuming and weather dependent. Instead of atmospheric retting chemical methods and enzyme retting with pectinases, hemicellulases and cellulases is used, however fibre properties depend on extraction conditions significantly.

## **2.1. Morphology of lignocellulosic fibres**

Sclerenchyma cells possess fibre like form and are arranged longitudinally. The cells are long and narrowed at the cell ends and surrounded and protected by a cell wall which is a complex macromolecular structure. During cells growth the wall is thickened and further strengthened by addition of a secondary wall. Usually fibre cells are occurring in strands or bundles which are called technical fibres [Caffall 2009]. The cells are polygonal in transverse section and connected between themselves by sclerenchyma middle lamellas. The lumen or cavity inside mature, dead fibre cells is usually very small when viewed in cross section [ Lewin 1998, Cook, 1993].

#### **2.2. Fibre structure**

A review of different conventional and non-conventional fibres is presented. For extraction of fibres different isolation procedures are possible, e.g. using bacteria and fungi, chemical and mechanical methods. The procedure used influences fibres surface morphology. By fi‐ bre isolation procedures mainly technical fibres are obtained, which means that cellulose fi‐

Many useful fibres have been obtained from various parts of plants including leaves, stems (bast fibres), fruits and seeds. Geometrical dimensions of these fibres, especially the fibre length depends mainly on fibre location within the plant. Fibres from fruits and seeds are few centimetres long, whereas fibres from stems and leaves are much longer (longer than

With an exception of seeds' and fruits' fibres, plant fibres are sclerenchyma elongated cells which occur in different parts of plants, mainly in the stems and leaves. These are elongated cells with tapering ends and very thick, usually heavily lignified cell walls. Sclerenchyma gives mechanical strength and rigidity to the plant, since it is usually a supporting tissue in plants. Fibres are also associated with the xylem and phloem tissue of monocotyledonous

All plant cells have a primary wall. During cell growth and after it has stopped, the cyto‐ plasm in sclerenchyma cells dries while the cell wall becomes thickened by addition of a thick and rigid secondary cell wall which is formed inwards of the primary cell wall and constructed of cellulose fibrils. The secondary cell wall is formed by successive deposition of cellulose layers, which are divided in three sub-layers (S1, S2 and S3), of which the middle layer is the most important for fibres mechanical properties. It consists of helically arranged microfibrils. The diameter of microfibrils is between 10-30nm [John 2008]. An important pa‐ rameter of the structure of the secondary wall is the angle that the cellulose microfibrils are making with the main fibre direction. Actually each of three fibres sub-layers has a different microfibrillar orientation [ Krässig 1992, John 2008, Cuissinat 2008] which is specific for the fibre type. Due to the formation of a thick secondary wall, the lumen becomes smaller.

The cell wall in a fibre is not a homogeneous layer. The walls of plant cells (the primary and the secondary cell wall) can be considered as a composite consisting of cellulose fibrils em‐

Vegetable fibres are generally composed of three structural polymers (the polysaccharides cellulose, and hemicelluloses and the aromatic polymer lignin) as well as by some minor non-structural components (i.e. proteins, extractives, minerals) [Marques 2010]. Cellulose forms a crystalline structure with regions of high order i.e. crystalline regions and regions of low order i.e. amorphous regions. Middle lamellas composed of pectic polysaccharides are

bedded within a matrix of lignin and hemicellulosic polysaccharides [Krässig 1992].

bres are multicellular structures with individual cells bound into fibre bundles.

**2. Plant fibres**

370 Advances in Agrophysical Research

one meter) [Blackburn 2005].

and dicotyledonous plant stems and leaves.

connecting individual cells in bundles [Caffall 2009].

The cellulose, hemicellulose and lignin content in plant fibres vary depending on the plant species, origin, quality and conditioning [ Blackburn 2005].

Chemically unmodified cellulose is generally recognised to occur in four polymorphic forms. There is some evidence for the existence of others [Krässig1992, Lewin 1998]. The monoclinic spatial model for the unit cell of native cellulose is cellulose I crystal modifica‐ tion. The unit cell houses the cellobiose segments of two cellulose molecules, one being part of the 002 corner plane and the second being part of the 002 centre plane [Lewin 1998, Hu 1996]. The monoclinic unit cell has dimensions of 0.835 nm for the a – axis, 1.03 nm for the baxis or fibre period, 0.79 nm for the c-axis, and 840 for the ß angle according to Meyer, Mark and Misch [Krässig 1992]. For natural cellulose a typical x-ray diffraction diagram is ob‐ served, that is, three equatorial diffraction peaks at the angles of about 14°, 16° and the strongest diffraction peak at an angle of 22° [Yueping 2010].

However, the crystalline dimorphism of cellulose and the existence of two families of native cellulose were confirmed lately. The crystalline phases Iα and I<sup>β</sup> can occur in variable pro‐ portions according to the source of the cellulose. Phase Iβ is a monoclinic unit cell having space group P21 and dimensions a = 0.801nm, b = 0.817nm, c = 1.036 nm, ß = 97.3º and very close to the cell proposed by Meyer, Mark and Misch. Phase I<sup>α</sup> corresponds to a triclinic unit cell with space group P1 and dimensions *a* = 0.674nm, *b* = 0.593nm *c* = 1.036nm, α= 117º, γ = 113º and ß = 97.3º [O'Sullivan 1997]. The celluloses produced by primitive organisms (bacte‐ ria, algae etc.) are classified by the Iα phase whereas the cellulose of higher plants (woody tissues, cotton, ramie etc.) consists mainly of the Iβ phase. I<sup>α</sup> and Iβ were found to have the same conformation of the heavy atom skeleton, but to differ in their hydrogen bonding pat‐ terns [O'Sullivan 1997].

Regenerated cellulose II is obtained when native cellulose is treated with strongly alkaline solutions or precipitated from solutions, such as when producing man-made cellulose fibres. The cellulose III crystal structure is formed after treating the cellulose with liquid ammonia and cellulose IV lattice structure is obtained by treating regenerated cellulose fibres in a hot bath under stretch.

gained economic importance and are now cultivated on a large scale globally [Blackburn

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Fibres that are produced on the seeds of various plants have been called seed hair or seed fibres. The most important fibre of this class is cotton. Other fibres of this group (kapok, floss from milkweed, dandelion, and thistle fibres) are not generally spun into yarns, but are

Due to fibres properties and low cost, cotton represents the most used textile fibre in the world. Fibres are obtained from seeds of the plant species *Gossypium*, which belongs to the *Malvaceae* family. Cotton fibres consist of unicellular seed hairs of the bolls of the cotton plant. Cotton fruit bursts when mature, revealing a tuft of fibres with the length from 25 to 60 mm and diameters varying between 12 and 45 μm. Cotton fibres have a pronounced three-wall structure. The cuticle layer consists of wax and pectin materials. This outer wax layer protects the primary wall, which is composed of cellulose crystalline fibrils. The secon‐ dary wall of the fibres consist of three distinct layers, which include closely packed parallel fibrils with spiral winding of 25 – 30° and represent the majority of cellulose within the fi‐ bres. Lumen is surrounded by the tertiary wall. The cross section of fibres is bean-shaped; however by swelling it is almost round when moisture absorption takes place (Figure 2).

utilized mainly as staffing in pillows and mattresses, and for life belts [Hearle1963].

2005, Mather 2011, Hearle 1963, Mwaikambo 2006].

**Figure 1.** Classification of textile fibres

**3.1. Seed fibres**

*3.1.1. Cotton*

Furthermore, cellulose molecules are, during the course of biosynthesis, arranged in mor‐ phological units elementary fibrils. The fibrillar structure model is accepted for cellulose na‐ tive and man made fibres however, there are some differences in the structural arrangement between different types of these fibres [Krässig 1992]. Elementary fibrils are strings of ele‐ mentary crystallites which are associated in a more or less random fashion into aggrega‐ tions. Isolated segments of the fibrils fringing from aggregations are forming a fibrillar network. By transition of cellulose molecules from crystallite to crystallite the longitudinal connections are achieved and coherence of the fibrils by hydrogen bonds at close contact points or by diverging molecules [Krässig 1992].

Microfibrillar orientation is different for different types of cellulose native fibres. It is a very important influence factor for fibres mechanical properties. Microfibrillar angle MFA of bamboo is 20 -100 , of coir 410 -450 , of flax 100 , of jute 80 , of ramie 7.50 , of sisal fibres 200 [Black‐ burn 2005] and of cotton 20-300 [Morton 1993]. Besides microfibrillar orientation, fibres strength and stiffness depend on fibres constitution, cellulose content, crystallinity and de‐ gree of polymerisation. In addition to, fibres maturity and part of the plant from which fi‐ bres are obtained plays an important role.

Due to the imperfect axial orientation of the fibrillar aggregates, interfibrillar and intrafibri‐ lar voids and less ordered interlinking regions between the crystallites inside the elementary fibrils the pore system of cellulose fibres is formed.

## **3. Conventional plant fibres**

Textile fibres are broadly classified as natural fibres and man-made fibres, as shown in Fig‐ ure 1. Natural fibres refer to fibres that occur within nature, and are found in vegetables re‐ spectively plants (cellulose fibres), animals (protein fibres) and minerals (asbestos). Manmade fibres are those that are not present in nature, although they may be composed of naturally-occurring materials. They are classified into three main groups: those made by transformation of natural polymers (regenerated fibres), those made from synthetic poly‐ mers (synthetic fibres), and those made from inorganic materials (fibres made of metal, ce‐ ramics, and carbon or glass) [BISFA.2006].

Nature in its abundance offers us a lot of materials that can be called fibrous. Plant fibres are obtained from various parts of plants, such as the seeds (cotton, kapok, milkweed), stems (flax, jute, hemp, ramie, kenaf, nettle, bamboo), and leaves (sisal, manila, abaca), fruit (coir) and other grass fibres. Fibres from these plants can be considered to be totally renewable and biodegradable. Plant fibres, which have a long history in human civilisation, have gained economic importance and are now cultivated on a large scale globally [Blackburn 2005, Mather 2011, Hearle 1963, Mwaikambo 2006].

Fibres that are produced on the seeds of various plants have been called seed hair or seed fibres. The most important fibre of this class is cotton. Other fibres of this group (kapok, floss from milkweed, dandelion, and thistle fibres) are not generally spun into yarns, but are utilized mainly as staffing in pillows and mattresses, and for life belts [Hearle1963].


#### **3.1. Seed fibres**

#### *3.1.1. Cotton*

Regenerated cellulose II is obtained when native cellulose is treated with strongly alkaline solutions or precipitated from solutions, such as when producing man-made cellulose fibres. The cellulose III crystal structure is formed after treating the cellulose with liquid ammonia and cellulose IV lattice structure is obtained by treating regenerated cellulose fibres in a hot

Furthermore, cellulose molecules are, during the course of biosynthesis, arranged in mor‐ phological units elementary fibrils. The fibrillar structure model is accepted for cellulose na‐ tive and man made fibres however, there are some differences in the structural arrangement between different types of these fibres [Krässig 1992]. Elementary fibrils are strings of ele‐ mentary crystallites which are associated in a more or less random fashion into aggrega‐ tions. Isolated segments of the fibrils fringing from aggregations are forming a fibrillar network. By transition of cellulose molecules from crystallite to crystallite the longitudinal connections are achieved and coherence of the fibrils by hydrogen bonds at close contact

Microfibrillar orientation is different for different types of cellulose native fibres. It is a very important influence factor for fibres mechanical properties. Microfibrillar angle MFA of

strength and stiffness depend on fibres constitution, cellulose content, crystallinity and de‐ gree of polymerisation. In addition to, fibres maturity and part of the plant from which fi‐

Due to the imperfect axial orientation of the fibrillar aggregates, interfibrillar and intrafibri‐ lar voids and less ordered interlinking regions between the crystallites inside the elementary

Textile fibres are broadly classified as natural fibres and man-made fibres, as shown in Fig‐ ure 1. Natural fibres refer to fibres that occur within nature, and are found in vegetables re‐ spectively plants (cellulose fibres), animals (protein fibres) and minerals (asbestos). Manmade fibres are those that are not present in nature, although they may be composed of naturally-occurring materials. They are classified into three main groups: those made by transformation of natural polymers (regenerated fibres), those made from synthetic poly‐ mers (synthetic fibres), and those made from inorganic materials (fibres made of metal, ce‐

Nature in its abundance offers us a lot of materials that can be called fibrous. Plant fibres are obtained from various parts of plants, such as the seeds (cotton, kapok, milkweed), stems (flax, jute, hemp, ramie, kenaf, nettle, bamboo), and leaves (sisal, manila, abaca), fruit (coir) and other grass fibres. Fibres from these plants can be considered to be totally renewable and biodegradable. Plant fibres, which have a long history in human civilisation, have

, of jute 80

, of ramie 7.50

[Morton 1993]. Besides microfibrillar orientation, fibres

, of sisal fibres 200 [Black‐

bath under stretch.

372 Advances in Agrophysical Research

bamboo is 20


burn 2005] and of cotton 20-300

**3. Conventional plant fibres**

ramics, and carbon or glass) [BISFA.2006].

points or by diverging molecules [Krässig 1992].

, of coir 410

bres are obtained plays an important role.

fibrils the pore system of cellulose fibres is formed.


, of flax 100

Due to fibres properties and low cost, cotton represents the most used textile fibre in the world. Fibres are obtained from seeds of the plant species *Gossypium*, which belongs to the *Malvaceae* family. Cotton fibres consist of unicellular seed hairs of the bolls of the cotton plant. Cotton fruit bursts when mature, revealing a tuft of fibres with the length from 25 to 60 mm and diameters varying between 12 and 45 μm. Cotton fibres have a pronounced three-wall structure. The cuticle layer consists of wax and pectin materials. This outer wax layer protects the primary wall, which is composed of cellulose crystalline fibrils. The secon‐ dary wall of the fibres consist of three distinct layers, which include closely packed parallel fibrils with spiral winding of 25 – 30° and represent the majority of cellulose within the fi‐ bres. Lumen is surrounded by the tertiary wall. The cross section of fibres is bean-shaped; however by swelling it is almost round when moisture absorption takes place (Figure 2). Cotton fibres consist of 80-90% cellulose, 6-8% water, 0.5-1% waxes and fats, 0-1.5% proteins, 4-6% hemicelluloses and pectins and 1-1,8% ash [Lewin 1998, Hu 1996].

of alpha cellulose, kapok is more like wood than flax and other plant fibres. The average de‐ gree of polymerisation is 6600 [Fengel 1986]. Kapok fibres are 10–35 mm long, with a diame‐ ter of 20–43 μm. The cell wall thickness is about 1–3 μm. The tensile strength is 0.84 cN/dtex (93.3 MPa), Young's module 4 GPa, and breaking elongation 1.2% [Mwaikamno 2001].

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Due to its wide lumen, kapok has an exceptional capability of liquids retention. Its excellent thermal and acoustic insulating properties, high buoyancy, and good oil and other non-po‐ lar liquids absorbency distinguish kapok from other cellulosic fibres. Kapok is mainly used in the form of stuffing and nonwovens; it is rarely used in yarns, mostly due to low cohesivi‐ ty of its fibres and their resilience, brittleness, and low strength. New potentials of kapok are in the field of technical textiles, yachts and boats furnishing, insulating materials in refriger‐ ation systems, acoustic insulation, industrial wastewaters filtration, removal of spilled oil from water surfaces, and reinforcement components in polymer composites [Rijavec 2008].

(a) (b)

**Figure 3.** SEM image of longitudinal view (a) and cross section (b) of kapok (2000× magnification) [Rijavec 2008].

Bast fibres i.e. flax, jute, hemp, ramie, kenaf, and abaca are soft woody fibres, which are ob‐ tained from stems or stalks of dicotyledonous plants. The fibres occur in bundles or aggre‐ gates [Hearle 1963]. The bundles consist of 10 to 25 elementary fibres, with the length of 2 to 5 mm and a diameter of 10 to 50 μm. The bundles are connected by lateral ramification, which forms a three dimensional network. The elementary fibrils and bundles are cemented by lignin and pectin intercellular substances, which must be removed during the processing of fibres extraction [Mohanty 2005]. Bast fibres have a long utilization tradition. They have been used for more than 8000 years. Currently bast fibres are raw materials not only used for the textile industry but also for modern environmentally friendly composites used in dif‐ ferent areas of applications like building materials, particle boards, insulation boards, food,

Flax fibres are obtained from the stems of the plant *Linum usitatissimum*. Fibres are running at the surface of the plant stem, which is about 1 m height and 2 – 3 mm thick in the diame‐

cosmetics, medicine and source for other biopolymers etc.

**3.2. Bast fibres**

*3.2.1. Flax*

**Figure 2.** a) Longitudinal view (5000× magnification) and b) cross-section of cotton fibre

Cotton is hydrophilic and the fibres swell considerably in water. Fibres are stable in water and its wet tenacity is up to 20% higher then its dry tenacity (25-40cN/tex). The toughness and initial modulus of cotton are lower compared to hemp fibres, whereas its elongation at break (5-10%) and its elastic recovery are higher. The fibres are resistant to alkali but de‐ graded by acids. The microbial resistance of cotton is low, it burns readily and quickly, can be boiled and sterilized, and does not cause skin irritation or other allergies [Lewin 1998, Cook 1993].

#### *3.1.2. Kapok*

Kapok *(Ceiba pentandra)* is a highly lignified organic seed fibre, containing 35-50% of cellu‐ lose, 22–45% of hemicelluloses, 15–22% of lignin and 2–3% of waxes. It also contains smaller quantities of starch, about 2.1% of proteins, and inorganic substances, notably iron (1.3– 2.5%). Kapok contains 70–80% of air and provides excellent thermal and acoustic insulation. The absolute density of a kapok cell wall is 1.474 g/cm3 , whilst the density of fibres by con‐ sidering about 74% of lumen is only 0.384 g/cm3 [Cook 2006]. Kapok is a smooth, unicellular, cylindrically shaped, twist less fibre. Its cell wall is thin and covered with a thick layer of wax. A wide lumen is filled with air and does not collapse like cotton. By the microscope observation kapok fibres are transparent with characteristic air bubbles in the lumen. The cross section of fibres (Figure 3) is oval to round. The kapok cell wall structure differs from other natural cellulosic fibres. A primary cell wall, which is directly related to the superficial properties of fibres, consists of short microfibrils, which are oriented rectangular to the sur‐ face of fibres. In the secondary cell wall microfibrils run almost parallel to the fibre axis. [Hearle 1963, Rijavec 2008, Fengel 1986, Khalili 2000, Fengel 1986/2]. Considering the content of alpha cellulose, kapok is more like wood than flax and other plant fibres. The average de‐ gree of polymerisation is 6600 [Fengel 1986]. Kapok fibres are 10–35 mm long, with a diame‐ ter of 20–43 μm. The cell wall thickness is about 1–3 μm. The tensile strength is 0.84 cN/dtex (93.3 MPa), Young's module 4 GPa, and breaking elongation 1.2% [Mwaikamno 2001].

Due to its wide lumen, kapok has an exceptional capability of liquids retention. Its excellent thermal and acoustic insulating properties, high buoyancy, and good oil and other non-po‐ lar liquids absorbency distinguish kapok from other cellulosic fibres. Kapok is mainly used in the form of stuffing and nonwovens; it is rarely used in yarns, mostly due to low cohesivi‐ ty of its fibres and their resilience, brittleness, and low strength. New potentials of kapok are in the field of technical textiles, yachts and boats furnishing, insulating materials in refriger‐ ation systems, acoustic insulation, industrial wastewaters filtration, removal of spilled oil from water surfaces, and reinforcement components in polymer composites [Rijavec 2008].

**Figure 3.** SEM image of longitudinal view (a) and cross section (b) of kapok (2000× magnification) [Rijavec 2008].

### **3.2. Bast fibres**

Cotton fibres consist of 80-90% cellulose, 6-8% water, 0.5-1% waxes and fats, 0-1.5% proteins,

Cotton is hydrophilic and the fibres swell considerably in water. Fibres are stable in water and its wet tenacity is up to 20% higher then its dry tenacity (25-40cN/tex). The toughness and initial modulus of cotton are lower compared to hemp fibres, whereas its elongation at break (5-10%) and its elastic recovery are higher. The fibres are resistant to alkali but de‐ graded by acids. The microbial resistance of cotton is low, it burns readily and quickly, can be boiled and sterilized, and does not cause skin irritation or other allergies [Lewin 1998,

Kapok *(Ceiba pentandra)* is a highly lignified organic seed fibre, containing 35-50% of cellu‐ lose, 22–45% of hemicelluloses, 15–22% of lignin and 2–3% of waxes. It also contains smaller quantities of starch, about 2.1% of proteins, and inorganic substances, notably iron (1.3– 2.5%). Kapok contains 70–80% of air and provides excellent thermal and acoustic insulation.

cylindrically shaped, twist less fibre. Its cell wall is thin and covered with a thick layer of wax. A wide lumen is filled with air and does not collapse like cotton. By the microscope observation kapok fibres are transparent with characteristic air bubbles in the lumen. The cross section of fibres (Figure 3) is oval to round. The kapok cell wall structure differs from other natural cellulosic fibres. A primary cell wall, which is directly related to the superficial properties of fibres, consists of short microfibrils, which are oriented rectangular to the sur‐ face of fibres. In the secondary cell wall microfibrils run almost parallel to the fibre axis. [Hearle 1963, Rijavec 2008, Fengel 1986, Khalili 2000, Fengel 1986/2]. Considering the content

, whilst the density of fibres by con‐

[Cook 2006]. Kapok is a smooth, unicellular,

4-6% hemicelluloses and pectins and 1-1,8% ash [Lewin 1998, Hu 1996].

**Figure 2.** a) Longitudinal view (5000× magnification) and b) cross-section of cotton fibre

The absolute density of a kapok cell wall is 1.474 g/cm3

sidering about 74% of lumen is only 0.384 g/cm3

Cook 1993].

374 Advances in Agrophysical Research

*3.1.2. Kapok*

Bast fibres i.e. flax, jute, hemp, ramie, kenaf, and abaca are soft woody fibres, which are ob‐ tained from stems or stalks of dicotyledonous plants. The fibres occur in bundles or aggre‐ gates [Hearle 1963]. The bundles consist of 10 to 25 elementary fibres, with the length of 2 to 5 mm and a diameter of 10 to 50 μm. The bundles are connected by lateral ramification, which forms a three dimensional network. The elementary fibrils and bundles are cemented by lignin and pectin intercellular substances, which must be removed during the processing of fibres extraction [Mohanty 2005]. Bast fibres have a long utilization tradition. They have been used for more than 8000 years. Currently bast fibres are raw materials not only used for the textile industry but also for modern environmentally friendly composites used in dif‐ ferent areas of applications like building materials, particle boards, insulation boards, food, cosmetics, medicine and source for other biopolymers etc.

#### *3.2.1. Flax*

Flax fibres are obtained from the stems of the plant *Linum usitatissimum*. Fibres are running at the surface of the plant stem, which is about 1 m height and 2 – 3 mm thick in the diame‐ ter [Blackburn 2005]. Like cotton, flax fibre is a cellulose fibre, however its structure is more crystalline, making it stronger, and stiffer to handle, and more easily wrinkled. Flax fibre properties are controlled by the molecular fine structure, which is affected by the plant growing conditions and the retting procedure that is applied.

(12-13%) and pectin (0.2%) [Mather 2011]. The cross-sections of bundles of jute fibres show a range in the size and number of fibres per bundle, in the thickness of the wall and in the shape and diameter of lumens. The fibre is generally smooth, with some dislocations. The individual fibres are mainly polygonal, with rounded corners and oval to round lumens (Figure 5) [Hearle 1963]. Jute has a moderate strength (30-45 cN/tex), however it is not as strong as flax or hemp. For fibres low extension at break (1-2%) is characteristic. Moisture regain of jute fibres is 12.6%, but it can absorb up to 23% of water under conditions of high humidity. Jute has high insulating and anti-static properties and low thermal conductivity

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(a) (b)

Hemp is the bast fibre obtained from stems of *Cannabis sativa* L plants. It grows easily to a height of 4 m without agrochemicals and captures large quantities of carbon. The most im‐ portant components of fibres are cellulose (77%), pectin (1.4%) and waxes (1.4%). Pectin is found in the middle lamellae and glues the elementary fibres to form bundles. The lignin (1.7%) is an incrusting component of the fibre. It is incrusting cellulose and contributes to the hardness and strength of fibres. It is located in the middle lamellae and fibre primary cell wall. Other components of hemp fibres are tannin, resins, fats, proteins etc. The content of

Therefore the processing of those fibres requires different technology [Blackburn 2005]. The diameter of the cell varies considerably from 16 to 50 μm, with broad flat lumen. The length of the individual or elementary fibres is ranging from 2 to 90 mm (average length is 15 mm). Elementary fibres are thick walled and the cross-section of fibres is polygonal with rounded edges (Figure 6). In longitudinal view, the fibre is roughly cylindrical, with surface irregu‐ larities and lengthwise deformations caused by dislocations. The ends of fibres are slightly tapered and blunt [Hearle 1963]. Hemp fibres are coarser when compared to flax and rather

**Figure 5.** a) Longitudinal view (5000× magnification) and b) cross-section (180× magnification) of jute fibre

these components is much higher in hemp than in cotton.

[Cook 1993, Mwaikamno 2009].

*3.2.3. Hemp*

The process of retting tends to separate the bundles of flax fibres into individual fibres, al‐ though many fibres remaining together in bundles [Hearle 1963]. Flax fibres are not as pure as cotton in terms cellulose content; indeed they contain only about 60 - 70% of cellulose. In addition they contain other substances such as hemicelluloses 17% and lignin 2-3%, as well as waxes 2%, pectins 10% and natural colouring matters [Mather 2011, Mohanty 2005]. Flax fibres have a soft handle and have fairly lustrous appearance. The length of fibres varies be‐ tween 6 – 65 mm, but on average they are about 20 mm long. Their diameter is about 20 μm. Flax fibres are not as twisted as cotton fibres, but both have a lumen in the centre. Several dislocations that are areas of the cell wall in natural fibres where the direction of the microfi‐ brils (the microfibril angle) differs from the microfibril angle of the surrounding cell wall, are observed on longitudinal images of fibres (Figure 4). These deformations are due to ex‐ traction procedures [Thygesen 2006]. The shape of fibres varies from polygonal to oval and irregular. Fibres cross-section form depends on variety, plant growth conditions and maturi‐ ty. Flax fibres are amongst the strongest in the group of naturally occurring fibres (55 cN/tex and about 20% stronger in wet state), but they do not stretch much. Flax fibres elongation at break is only 1.8% and their moisture regain is 12% [ Lewin 1998, Cook 1993].

**Figure 4.** a) Longitudinal view (10000× magnification) and b) cross-section (30× magnification) of flax fibre

#### *3.2.2. Jute*

Jute is a natural fibre obtained as an extract from the bark of the white jute plant *Corchorus capsularis* and to a lesser extent from tossa jute (*Corchorus olitorius*) [Mohanty 2005]. Jute is a long, soft and shiny fibre that can be spun into coarse, strong threads and is one of the cheapest natural fibres. It is also the most versatile, eco-friendly, natural, durable and anti‐ static fibre available. The plants are retted by the same method used for flax. The resulted jute strand, which are up to 3 m long, are composed of many very short fibres, elementary fibres (length between 0.5-6.0 mm, diameter 26-30 μm) held together by lignocelluloses. The fibres contain between 61-71% cellulose, large amount of hemicelluloses (14-20%) and lignin (12-13%) and pectin (0.2%) [Mather 2011]. The cross-sections of bundles of jute fibres show a range in the size and number of fibres per bundle, in the thickness of the wall and in the shape and diameter of lumens. The fibre is generally smooth, with some dislocations. The individual fibres are mainly polygonal, with rounded corners and oval to round lumens (Figure 5) [Hearle 1963]. Jute has a moderate strength (30-45 cN/tex), however it is not as strong as flax or hemp. For fibres low extension at break (1-2%) is characteristic. Moisture regain of jute fibres is 12.6%, but it can absorb up to 23% of water under conditions of high humidity. Jute has high insulating and anti-static properties and low thermal conductivity [Cook 1993, Mwaikamno 2009].

**Figure 5.** a) Longitudinal view (5000× magnification) and b) cross-section (180× magnification) of jute fibre

#### *3.2.3. Hemp*

ter [Blackburn 2005]. Like cotton, flax fibre is a cellulose fibre, however its structure is more crystalline, making it stronger, and stiffer to handle, and more easily wrinkled. Flax fibre properties are controlled by the molecular fine structure, which is affected by the plant

The process of retting tends to separate the bundles of flax fibres into individual fibres, al‐ though many fibres remaining together in bundles [Hearle 1963]. Flax fibres are not as pure as cotton in terms cellulose content; indeed they contain only about 60 - 70% of cellulose. In addition they contain other substances such as hemicelluloses 17% and lignin 2-3%, as well as waxes 2%, pectins 10% and natural colouring matters [Mather 2011, Mohanty 2005]. Flax fibres have a soft handle and have fairly lustrous appearance. The length of fibres varies be‐ tween 6 – 65 mm, but on average they are about 20 mm long. Their diameter is about 20 μm. Flax fibres are not as twisted as cotton fibres, but both have a lumen in the centre. Several dislocations that are areas of the cell wall in natural fibres where the direction of the microfi‐ brils (the microfibril angle) differs from the microfibril angle of the surrounding cell wall, are observed on longitudinal images of fibres (Figure 4). These deformations are due to ex‐ traction procedures [Thygesen 2006]. The shape of fibres varies from polygonal to oval and irregular. Fibres cross-section form depends on variety, plant growth conditions and maturi‐ ty. Flax fibres are amongst the strongest in the group of naturally occurring fibres (55 cN/tex and about 20% stronger in wet state), but they do not stretch much. Flax fibres elongation at

break is only 1.8% and their moisture regain is 12% [ Lewin 1998, Cook 1993].

(a) (b)

Jute is a natural fibre obtained as an extract from the bark of the white jute plant *Corchorus capsularis* and to a lesser extent from tossa jute (*Corchorus olitorius*) [Mohanty 2005]. Jute is a long, soft and shiny fibre that can be spun into coarse, strong threads and is one of the cheapest natural fibres. It is also the most versatile, eco-friendly, natural, durable and anti‐ static fibre available. The plants are retted by the same method used for flax. The resulted jute strand, which are up to 3 m long, are composed of many very short fibres, elementary fibres (length between 0.5-6.0 mm, diameter 26-30 μm) held together by lignocelluloses. The fibres contain between 61-71% cellulose, large amount of hemicelluloses (14-20%) and lignin

**Figure 4.** a) Longitudinal view (10000× magnification) and b) cross-section (30× magnification) of flax fibre

*3.2.2. Jute*

growing conditions and the retting procedure that is applied.

376 Advances in Agrophysical Research

Hemp is the bast fibre obtained from stems of *Cannabis sativa* L plants. It grows easily to a height of 4 m without agrochemicals and captures large quantities of carbon. The most im‐ portant components of fibres are cellulose (77%), pectin (1.4%) and waxes (1.4%). Pectin is found in the middle lamellae and glues the elementary fibres to form bundles. The lignin (1.7%) is an incrusting component of the fibre. It is incrusting cellulose and contributes to the hardness and strength of fibres. It is located in the middle lamellae and fibre primary cell wall. Other components of hemp fibres are tannin, resins, fats, proteins etc. The content of these components is much higher in hemp than in cotton.

Therefore the processing of those fibres requires different technology [Blackburn 2005]. The diameter of the cell varies considerably from 16 to 50 μm, with broad flat lumen. The length of the individual or elementary fibres is ranging from 2 to 90 mm (average length is 15 mm). Elementary fibres are thick walled and the cross-section of fibres is polygonal with rounded edges (Figure 6). In longitudinal view, the fibre is roughly cylindrical, with surface irregu‐ larities and lengthwise deformations caused by dislocations. The ends of fibres are slightly tapered and blunt [Hearle 1963]. Hemp fibres are coarser when compared to flax and rather difficult to bleach. The fibres have an excellent moisture resistance and rot only very slowly in water. Hemp fibres have high tenacity (53-62 cN/tex); about 20% higher than flax, but low elongation at break (only 1.5%) [Mohanty 2005].

resistance to bacteria, mildew and insect attack. The main disadvantage of ramie is its low elasticity (elongation at break is 3-7%), which means that it is stiff and brittle [Mather 2011]. Fibres are oval to cylindrical in shape and their colour is white and high lustrous. Fibres sur‐ face is rough and characterized by small ridges, striations, and deep fissures. Ramie fibre can be easily identified by its coarse, thick cell wall, lack of twist, and surface characteristics

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(a) (b)

Kenaf fibres are obtained from *Hibiscus cannabinus*. Kenaf contains two fibre types: long fibre bundles situated in the cortical layer and short fibres located in the ligneous zone. Elementa‐ ry fibres are short; their fibre length ranges from 3 to 7 mm, with average diameter of 21 μm. The cross-sections are polygonal with rounded edges and the lumens are predominantly large and oval to round in shape [Hearle 1963]. The lumen varies greatly in thickness along the cell length and it is several times interrupted. Kenaf fibres contain about 45-57% of cellu‐ lose, 21.5% hemicelluloses, 8-13% lignin and 3-5% pectin. Kenaf fibres are coarse, brittle and difficult to process. Their breaking strength is similar to that of low-grade jute and is weak‐ ened only slightly when wet. There are many potential specific utilization possibilities for kenaf whole stalk and outer bast fibres, including paper products, textiles, composites,

Leaf fibres are often referred to as hard fibres, and have limited commercial value, mainly because they are generally stiffer and coarser texture than the bast fibres. The fibres are usu‐ ally obtained from the leaves by mechanically scraping away the non fibrous material. Above all the leaves fibres are used for production of cordage and ropes. The most impor‐

**Figure 7.** a) Longitudinal view and b) cross-section (100× magnification) of ramie fibre

building materials, absorbents, etc. [Mohanty 2005].

tant fibres of this group are sisal, henequen and abaca.

[Hearle 1963].

*3.2.5. Kenaf*

**3.3. Leaf fibres**

**Figure 6.** a) Longitudinal view (10000× magnification) and b) cross-section (200× magnification) of hemp fibre

In recent years because of the interest for alternative renewable resources, hemp gained again relevance. Beside the traditional textile application of hemp numerous new directions emerge: building and isolation materials, composite materials, special cellulose materials (papers), technical textile, geotextiles and agricultural textile, oil based products, items for agriculture and horticulture etc. [Blackburn 2005].

#### *3.2.4. Ramie*

Ramie is a herbaceous perennial plant in the nettle family *Urticaceae*, native to eastern Asia. Ramie fibres are extracted from the stem of the plant *Boehmeria nivea* of the nettle family. In‐ dividual fibre cells in stems are bound together in fibre bundles by waxes, hemicelluloses, lignin and pectins that are difficult to remove (Figure 7). Therefore the efficiency of the re‐ tting process usually used for e.g. hemp fibres extraction is not sufficient to extract ramie fi‐ bres from stems. But, a combined microbial and chemical treatment is very effective and economical. Chemical composition of ramie fibres is: cellulose (91-93%), hemicelluloses (2.5%), pectin (0.63%) and lignin (0.65%). Ramie fibres exhibit excellent mechanical proper‐ ties, i.e. the best in the group of bast fibres (45-88 cN/tex) and, as most of the natural cellu‐ lose fibres the strength increases by 25% when fibres are wet. The ultimate fibre length is between 120-150mm and fibre diameter is 40-60 μm. Fibres are durable and they have good resistance to bacteria, mildew and insect attack. The main disadvantage of ramie is its low elasticity (elongation at break is 3-7%), which means that it is stiff and brittle [Mather 2011]. Fibres are oval to cylindrical in shape and their colour is white and high lustrous. Fibres sur‐ face is rough and characterized by small ridges, striations, and deep fissures. Ramie fibre can be easily identified by its coarse, thick cell wall, lack of twist, and surface characteristics [Hearle 1963].

**Figure 7.** a) Longitudinal view and b) cross-section (100× magnification) of ramie fibre

#### *3.2.5. Kenaf*

difficult to bleach. The fibres have an excellent moisture resistance and rot only very slowly in water. Hemp fibres have high tenacity (53-62 cN/tex); about 20% higher than flax, but low

(a) (b)

In recent years because of the interest for alternative renewable resources, hemp gained again relevance. Beside the traditional textile application of hemp numerous new directions emerge: building and isolation materials, composite materials, special cellulose materials (papers), technical textile, geotextiles and agricultural textile, oil based products, items for

Ramie is a herbaceous perennial plant in the nettle family *Urticaceae*, native to eastern Asia. Ramie fibres are extracted from the stem of the plant *Boehmeria nivea* of the nettle family. In‐ dividual fibre cells in stems are bound together in fibre bundles by waxes, hemicelluloses, lignin and pectins that are difficult to remove (Figure 7). Therefore the efficiency of the re‐ tting process usually used for e.g. hemp fibres extraction is not sufficient to extract ramie fi‐ bres from stems. But, a combined microbial and chemical treatment is very effective and economical. Chemical composition of ramie fibres is: cellulose (91-93%), hemicelluloses (2.5%), pectin (0.63%) and lignin (0.65%). Ramie fibres exhibit excellent mechanical proper‐ ties, i.e. the best in the group of bast fibres (45-88 cN/tex) and, as most of the natural cellu‐ lose fibres the strength increases by 25% when fibres are wet. The ultimate fibre length is between 120-150mm and fibre diameter is 40-60 μm. Fibres are durable and they have good

**Figure 6.** a) Longitudinal view (10000× magnification) and b) cross-section (200× magnification) of hemp fibre

elongation at break (only 1.5%) [Mohanty 2005].

378 Advances in Agrophysical Research

agriculture and horticulture etc. [Blackburn 2005].

*3.2.4. Ramie*

Kenaf fibres are obtained from *Hibiscus cannabinus*. Kenaf contains two fibre types: long fibre bundles situated in the cortical layer and short fibres located in the ligneous zone. Elementa‐ ry fibres are short; their fibre length ranges from 3 to 7 mm, with average diameter of 21 μm. The cross-sections are polygonal with rounded edges and the lumens are predominantly large and oval to round in shape [Hearle 1963]. The lumen varies greatly in thickness along the cell length and it is several times interrupted. Kenaf fibres contain about 45-57% of cellu‐ lose, 21.5% hemicelluloses, 8-13% lignin and 3-5% pectin. Kenaf fibres are coarse, brittle and difficult to process. Their breaking strength is similar to that of low-grade jute and is weak‐ ened only slightly when wet. There are many potential specific utilization possibilities for kenaf whole stalk and outer bast fibres, including paper products, textiles, composites, building materials, absorbents, etc. [Mohanty 2005].

#### **3.3. Leaf fibres**

Leaf fibres are often referred to as hard fibres, and have limited commercial value, mainly because they are generally stiffer and coarser texture than the bast fibres. The fibres are usu‐ ally obtained from the leaves by mechanically scraping away the non fibrous material. Above all the leaves fibres are used for production of cordage and ropes. The most impor‐ tant fibres of this group are sisal, henequen and abaca.

#### *3.3.1. Sisal*

The sisal fibre is a "hard" fibre extracted from fresh leaves of sisal plant *Agave sisalana*. It is usually obtained by a decortication process, in which the leaf is crushed between rollers and then mechanically scraped. The length of the sisal fibre varies between 0.6 and 1.5 m and its diameters range from 100 to 300 μm [Mohanty 2005]. Cellulose content in sisal fibres is about 70%. The fibre is composed of numerous elongated fibre cells that are narrowed to‐ wards both ends. Fibre cells are linked together by middle lamellae, which consist of hemi‐ celluloses, lignin and pectin. A sisal fibre in cross-section is built up of about 100 fibre cells. The cross section of sisal fibres is neither circular nor fairly uniform in dimension. The lu‐ men varies in size but is usually well defined. The longitudinal shape is approximately cy‐ lindrical. Longitudinal view and cross-section of sisal fibres is demonstrated on Fig.8. Physically, each fibre cell is made up of four main parts, namely the primary wall, the thick secondary wall, the tertiary wall and the lumen. The fibrils are, in turn, built up of microfibrils with a thickness of about 20 μm. The microfibrils are composed of cellulose molecular chains with a thickness of 0.7 μm and a length of a few μm [Joseph 1999]. Sisal fibre is fairly coarse and inflexible. The tensile properties of sisal fibres are not uniform along its length. The fibres extracted from the root or lower parts of the leaf have a lower tensile strength and modulus. The fibres become stronger and stiffer at midspan, and the fibres extracted from the tip have moderate properties. The lower grade fibre is processed by the paper industry because of its high content of cellulose and hemicelluloses. The medium grade fibre is used in the cordage industry for making ropes, baler and binders twine. The higher-grade fibre after treatment is converted into yarns and used by the carpet industry.

lumens are large in relation to wall thickness. Cross-marking is rare, and fibre tips pointed and often flat and ribbon –like. The technical fibres are 2 to 4 m long. The single fibres are relatively smooth and straight and have narrow pointed ends. Individual fibre diameters range from 14 to 50 μm and the lengths from 2.5 to 13 mm [Hearle 1963]. Chemically, abaca comprises 76.6% cellulose, 14.6% hemicelluloses, 8.4% lignin, 0.3% pectin and 0.1% wax and fat. Abaca is considered as one of the strongest of all natural fibres, being three times stron‐ ger than cotton and twice that of sisal, and is far more resistant to saltwater decomposition than most of the vegetable fibres. Abaca is a lustrous fibre and yellowish white in colour. Abaca fibres are used manly to manufacture ropes and handicraft goods [Blackburn 2005].

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Henequen (*Agave fourcroydes*) plant of the family agave is a close relative to the sisal plant. The henequen plant is native to Mexico, where it has been a source of textile fibre since pre-Columbian times. Many factors can influence the properties of the fibre including weather conditions, age of the plant, type of soil, extraction method, etc. Henequen fibre is composed of approximately 77% cellulose, 4-8% hemicelluloses, 13% lignin and 2-6% pectin and waxes by weight [Blackburn 2005, Aguilarvega 1995]. Fibres have variable diameter, being larger at the butt end and the smaller at the tip end of the fibre. Also, the diameter is connected with the fibre's origin, fibres cultivated at different locations have different diameters. The fibre cross-section changes from a beanlike shape at the butt end to rounded form at the tip end of the fibres. Like sisal, henequen fibres are smooth, straight, yellow, and easily degraded in salt water. Compared to other leaf fibres, henequen has low elongation at break and low modulus, but relatively high tenacity which makes them suitable as reinforcement for poly‐

Lignocellulosic agricultural by-products are a promising and beneficial source for cellulose fibres. Due to the chemical and physical properties, composition and sustainability agrobased biofibres represent a potential for use in textile and paper industry for fibres, chemi‐ cals, enzymes and other industrial products. Annually renewable resources, e.g. corn, wheat, rice, sorghum, barley, sugarcane, pineapple, banana and coconut, etc. by-products

Also in non-conventional fibre plants elongated sclerenchyma cells are organized in a simi‐ lar manner than traditional fibre cells like flax, hemp etc. These cells provide strength and support and are located next to the outer bark in the bast or phloem and serve to strengthen

To extract the fibre strands from other plant tissues the natural gum binding them must be removed by retting. The most common way is a biological treatment by an enzymatic or

*3.3.3. Henequen*

mers [Blackburn 2005].

**4. Non-conventional plant fibres**

are utilized as agro-based biofibres [Reddy 2005].

bacterial action on the pectinous matter of the stem.

the stems. The fibres are in strands running the length of the stem.

**Figure 8.** a) Longitudinal view (2500× magnification) and b) cross-section of sisal fibre

#### *3.3.2. Abaca*

Abaca or Manila hemp is extracted from the leaf sheath around the trunk of the abaca plant (*Musa textilis*). The commercial fibres are utilized in the form of strands, and the strands in turn are composed of bundles of individual fibres. Individual fibres, when removed from the strands by boiling in an alkali solution, are smooth and fairly uniform in diameter. The lumens are large in relation to wall thickness. Cross-marking is rare, and fibre tips pointed and often flat and ribbon –like. The technical fibres are 2 to 4 m long. The single fibres are relatively smooth and straight and have narrow pointed ends. Individual fibre diameters range from 14 to 50 μm and the lengths from 2.5 to 13 mm [Hearle 1963]. Chemically, abaca comprises 76.6% cellulose, 14.6% hemicelluloses, 8.4% lignin, 0.3% pectin and 0.1% wax and fat. Abaca is considered as one of the strongest of all natural fibres, being three times stron‐ ger than cotton and twice that of sisal, and is far more resistant to saltwater decomposition than most of the vegetable fibres. Abaca is a lustrous fibre and yellowish white in colour. Abaca fibres are used manly to manufacture ropes and handicraft goods [Blackburn 2005].

#### *3.3.3. Henequen*

*3.3.1. Sisal*

380 Advances in Agrophysical Research

*3.3.2. Abaca*

The sisal fibre is a "hard" fibre extracted from fresh leaves of sisal plant *Agave sisalana*. It is usually obtained by a decortication process, in which the leaf is crushed between rollers and then mechanically scraped. The length of the sisal fibre varies between 0.6 and 1.5 m and its diameters range from 100 to 300 μm [Mohanty 2005]. Cellulose content in sisal fibres is about 70%. The fibre is composed of numerous elongated fibre cells that are narrowed to‐ wards both ends. Fibre cells are linked together by middle lamellae, which consist of hemi‐ celluloses, lignin and pectin. A sisal fibre in cross-section is built up of about 100 fibre cells. The cross section of sisal fibres is neither circular nor fairly uniform in dimension. The lu‐ men varies in size but is usually well defined. The longitudinal shape is approximately cy‐ lindrical. Longitudinal view and cross-section of sisal fibres is demonstrated on Fig.8. Physically, each fibre cell is made up of four main parts, namely the primary wall, the thick secondary wall, the tertiary wall and the lumen. The fibrils are, in turn, built up of microfibrils with a thickness of about 20 μm. The microfibrils are composed of cellulose molecular chains with a thickness of 0.7 μm and a length of a few μm [Joseph 1999]. Sisal fibre is fairly coarse and inflexible. The tensile properties of sisal fibres are not uniform along its length. The fibres extracted from the root or lower parts of the leaf have a lower tensile strength and modulus. The fibres become stronger and stiffer at midspan, and the fibres extracted from the tip have moderate properties. The lower grade fibre is processed by the paper industry because of its high content of cellulose and hemicelluloses. The medium grade fibre is used in the cordage industry for making ropes, baler and binders twine. The higher-grade fibre

after treatment is converted into yarns and used by the carpet industry.

**Figure 8.** a) Longitudinal view (2500× magnification) and b) cross-section of sisal fibre

(a) (b)

Abaca or Manila hemp is extracted from the leaf sheath around the trunk of the abaca plant (*Musa textilis*). The commercial fibres are utilized in the form of strands, and the strands in turn are composed of bundles of individual fibres. Individual fibres, when removed from the strands by boiling in an alkali solution, are smooth and fairly uniform in diameter. The

Henequen (*Agave fourcroydes*) plant of the family agave is a close relative to the sisal plant. The henequen plant is native to Mexico, where it has been a source of textile fibre since pre-Columbian times. Many factors can influence the properties of the fibre including weather conditions, age of the plant, type of soil, extraction method, etc. Henequen fibre is composed of approximately 77% cellulose, 4-8% hemicelluloses, 13% lignin and 2-6% pectin and waxes by weight [Blackburn 2005, Aguilarvega 1995]. Fibres have variable diameter, being larger at the butt end and the smaller at the tip end of the fibre. Also, the diameter is connected with the fibre's origin, fibres cultivated at different locations have different diameters. The fibre cross-section changes from a beanlike shape at the butt end to rounded form at the tip end of the fibres. Like sisal, henequen fibres are smooth, straight, yellow, and easily degraded in salt water. Compared to other leaf fibres, henequen has low elongation at break and low modulus, but relatively high tenacity which makes them suitable as reinforcement for poly‐ mers [Blackburn 2005].

## **4. Non-conventional plant fibres**

Lignocellulosic agricultural by-products are a promising and beneficial source for cellulose fibres. Due to the chemical and physical properties, composition and sustainability agrobased biofibres represent a potential for use in textile and paper industry for fibres, chemi‐ cals, enzymes and other industrial products. Annually renewable resources, e.g. corn, wheat, rice, sorghum, barley, sugarcane, pineapple, banana and coconut, etc. by-products are utilized as agro-based biofibres [Reddy 2005].

Also in non-conventional fibre plants elongated sclerenchyma cells are organized in a simi‐ lar manner than traditional fibre cells like flax, hemp etc. These cells provide strength and support and are located next to the outer bark in the bast or phloem and serve to strengthen the stems. The fibres are in strands running the length of the stem.

To extract the fibre strands from other plant tissues the natural gum binding them must be removed by retting. The most common way is a biological treatment by an enzymatic or bacterial action on the pectinous matter of the stem.

Several techniques are used for extraction of conventional bast fibres: (i) Dew retting by the action of dew, sun, and fungi on the plants spread out on the ground, (ii) Water retting is conducted in rivers or pools through bacterial action and takes 2–4 weeks, (iii) For chemical retting solutions of different chemicals are used, e.g. sodium hydroxide, sodium carbonate, soaps, or mineral acids. The process takes only a few hours, (iiii) controlled biological or biochemical retting by addition of enzymes. The differences between the procedures are not on‐ ly in expenses and process duration but the most important the quality and uniformity of retted fibres.

in single cells that are too small to be used for high value fibrous applications. Elementary fibres with the length of 0.7 -1.5mm and cell diameter of 15 – 35 μm which is comparable to rice and wheat straw fibres were extracted and analysed. Fibres contain about 80% cellulose, 8% lignin and 8% moisture. The rest are minerals and pectin. The most important parame‐ ters for fibres properties, i.e. crystallinity and microfibrillar angle MFA condition fibres properties. The typical cellulose I structure is observed with the crystallinity of 52% and MFA of about 110. MFA is lower than that of cotton which has MFA in the range of 20–300 depending on the maturity and cotton species. Due to high fibrils orientation tensile proper‐ ties of fibres are good, i.e. they have high strength but low elongation. Elementary fibres form bundles with mechanical properties similar to that of kenaf and with moisture regain of about 7.9%, which is similar to that of cotton but lower than flax (12%) and kenaf (17%), respectively, are suitable for blending and processing with other common textile fibres to

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Although fibre properties of corn stover have been studied for decades, the first systematic investigation of cell morphology and fibre quality of different corn stover fractions was per‐ formed by Li et al. [Li 2012]. Individual fibres were connected in bundles by middle lamella with the highest lignin concentration. Obvious differences in cell morphologies and chemi‐ cal compositions between four different plant fractions, i.e. stalk rind and stalk pith, and leaf blade and leaf sheath were observed. Fibres were shorter and finer in stalk pith and paren‐ chyma and vessel content was the highest in this part of the plant. Therefore it was not suit‐ able for papermaking, while morphological characteristics of fibres from corn stalk rind were appropriate as papermaking materials. There were also differences in lignification and hemicellulose content. Sclerenchyma cells in stalk rind were more lignified than those in

other tissues. The lowest hemicellulose content was observed in stalk rind [Li 2012].

strength and elastic modulus decreased with increasing temperature up to 2000

The microstructure, thermal and mechanical properties of wheat straw fibres have been ex‐ amined and compared to flax straw fibres with an idea of using these natural fibres as rein‐ forcing additives for thermoplastics [Hornsby 1997]. Of crucial importance in this regard is the manner by which their inherent mechanical properties alter on exposure to elevated temperatures, which are encountered during melt processing of the polymer. Under all test conditions flax straw was significantly stronger and stiffer than wheat straw. The tensile

was minor for wheat straw than flax straw. The differences are due to fibres structural form. The form of wheat straw is much more cellular than flax. Due to different lignin content the thermal stability of flax fibres was significantly higher than it was for wheat straw [Hornsby

Hop (*Humulus lupulus* L.) belongs to the family *Cannabaceae* and genus cannabis that in‐ cludes hemp. The use, production or properties of natural cellulose fibres from hop stems

C. This effect

produce various products [Reddy 2005/2].

**4.2. Wheat straw fibres**

**4.3. Fibres from hop stems**

was studied by Reddy and Yang [Reddy 2009].

1997].

Ultimate fibres extracted from agricultural by-products are round, polygonal or elliptical in cross section and have a lumen in the centre. Their geometrical properties are conditioned by fibres origin and are different.

Reddy and Yang have collected structural characteristics and biofibres properties (Table1) [Reddy 2005]. Fibres obtained from pineapple leaves are the longest in this group and be‐ cause of high crystallinity and high content of cellulose (70-82%) they express good mechan‐ ical properties (Young's modulus 400–627 MPa) [John 2008].


**Table 1.** Properties of some non-conventional plant fibres [Reddy 2005]

#### **4.1. Fibres from corn stover**

As a kind of abundant and renewable agricultural residue, corn (Zea mays L.) stover, that refers a combination of corn stalk (stem) and leaf, could be a low-cost and sustainable source for energy and chemicals in future. For a long time (since 1929) fibres obtained from corn waste materials have been studied and utilized for pulp and papermaking [Li 2012].

Cornstalks as a potential for fibres extraction were studied by Reddy and Yang [Reddy 2005/2]. They have found, that natural cellulose fibres obtained from cornstalks have the structure and properties required for textile and other industrial applications.

The fibres obtained from cornstalks are composed of single cells bound together in cell bun‐ dles. Stronger fibres extraction conditions remove most of the binding substances resulting in single cells that are too small to be used for high value fibrous applications. Elementary fibres with the length of 0.7 -1.5mm and cell diameter of 15 – 35 μm which is comparable to rice and wheat straw fibres were extracted and analysed. Fibres contain about 80% cellulose, 8% lignin and 8% moisture. The rest are minerals and pectin. The most important parame‐ ters for fibres properties, i.e. crystallinity and microfibrillar angle MFA condition fibres properties. The typical cellulose I structure is observed with the crystallinity of 52% and MFA of about 110. MFA is lower than that of cotton which has MFA in the range of 20–300 depending on the maturity and cotton species. Due to high fibrils orientation tensile proper‐ ties of fibres are good, i.e. they have high strength but low elongation. Elementary fibres form bundles with mechanical properties similar to that of kenaf and with moisture regain of about 7.9%, which is similar to that of cotton but lower than flax (12%) and kenaf (17%), respectively, are suitable for blending and processing with other common textile fibres to produce various products [Reddy 2005/2].

Although fibre properties of corn stover have been studied for decades, the first systematic investigation of cell morphology and fibre quality of different corn stover fractions was per‐ formed by Li et al. [Li 2012]. Individual fibres were connected in bundles by middle lamella with the highest lignin concentration. Obvious differences in cell morphologies and chemi‐ cal compositions between four different plant fractions, i.e. stalk rind and stalk pith, and leaf blade and leaf sheath were observed. Fibres were shorter and finer in stalk pith and paren‐ chyma and vessel content was the highest in this part of the plant. Therefore it was not suit‐ able for papermaking, while morphological characteristics of fibres from corn stalk rind were appropriate as papermaking materials. There were also differences in lignification and hemicellulose content. Sclerenchyma cells in stalk rind were more lignified than those in other tissues. The lowest hemicellulose content was observed in stalk rind [Li 2012].

#### **4.2. Wheat straw fibres**

Several techniques are used for extraction of conventional bast fibres: (i) Dew retting by the action of dew, sun, and fungi on the plants spread out on the ground, (ii) Water retting is conducted in rivers or pools through bacterial action and takes 2–4 weeks, (iii) For chemical retting solutions of different chemicals are used, e.g. sodium hydroxide, sodium carbonate, soaps, or mineral acids. The process takes only a few hours, (iiii) controlled biological or biochemical retting by addition of enzymes. The differences between the procedures are not on‐ ly in expenses and process duration but the most important the quality and uniformity of

Ultimate fibres extracted from agricultural by-products are round, polygonal or elliptical in cross section and have a lumen in the centre. Their geometrical properties are conditioned

Reddy and Yang have collected structural characteristics and biofibres properties (Table1) [Reddy 2005]. Fibres obtained from pineapple leaves are the longest in this group and be‐ cause of high crystallinity and high content of cellulose (70-82%) they express good mechan‐

As a kind of abundant and renewable agricultural residue, corn (Zea mays L.) stover, that refers a combination of corn stalk (stem) and leaf, could be a low-cost and sustainable source for energy and chemicals in future. For a long time (since 1929) fibres obtained from corn

Cornstalks as a potential for fibres extraction were studied by Reddy and Yang [Reddy 2005/2]. They have found, that natural cellulose fibres obtained from cornstalks have the

The fibres obtained from cornstalks are composed of single cells bound together in cell bun‐ dles. Stronger fibres extraction conditions remove most of the binding substances resulting

waste materials have been studied and utilized for pulp and papermaking [Li 2012].

structure and properties required for textile and other industrial applications.

**Fibre Length (mm) Width (μm) Crystallinity (%)**

cornhusk 0.5-1.5 10-20 48-50 pineapple leaf fibre 3-9 20-80 44-60 coir 0.3-1.0 100-450 27-33 bagasse 0.8-2.8 10-34 banana 0.9-4.0 80-250 45 wheat straw 0.4-3.2 8-34 55-65 rice straw 0.4-3.4 4-16 40 sorghum stalks 0.8-1.2 30-80 barley straw 0.7-3.1 7-24 -

retted fibres.

382 Advances in Agrophysical Research

by fibres origin and are different.

ical properties (Young's modulus 400–627 MPa) [John 2008].

**Table 1.** Properties of some non-conventional plant fibres [Reddy 2005]

**4.1. Fibres from corn stover**

The microstructure, thermal and mechanical properties of wheat straw fibres have been ex‐ amined and compared to flax straw fibres with an idea of using these natural fibres as rein‐ forcing additives for thermoplastics [Hornsby 1997]. Of crucial importance in this regard is the manner by which their inherent mechanical properties alter on exposure to elevated temperatures, which are encountered during melt processing of the polymer. Under all test conditions flax straw was significantly stronger and stiffer than wheat straw. The tensile strength and elastic modulus decreased with increasing temperature up to 2000 C. This effect was minor for wheat straw than flax straw. The differences are due to fibres structural form. The form of wheat straw is much more cellular than flax. Due to different lignin content the thermal stability of flax fibres was significantly higher than it was for wheat straw [Hornsby 1997].

#### **4.3. Fibres from hop stems**

Hop (*Humulus lupulus* L.) belongs to the family *Cannabaceae* and genus cannabis that in‐ cludes hemp. The use, production or properties of natural cellulose fibres from hop stems was studied by Reddy and Yang [Reddy 2009].

The single sclerenchyma cells in hop stem fibres are small. Their length is 2.0 ± 1.0 mm and width 16.5 ± 5.5μm. Fibres extracted from hop stems contain 84% of cellulose, 6% of lignin in 2% of ash. From the diffraction patterns of cellulose in hop stem fibres cellulose crystalline structure was determined. The crystallinity index is 44 ± 5% (65–70% for cotton and 81–89% for hemp cellulose) and microfibrillar angle of cellulose fibrils 8 ± 0.70 . The diffraction pat‐ tern is very similar to the diffraction pattern of hemp. Cellulose crystallites in hop and hemp fibres are regularly distributed and are also parallel to the fibre axis and to each other.

A high content of lignin was observed for all types of fibres (17.44%±0.19% Banana, 23.33% ±0.02% Bagasse and 15.46%±0.02% Sponge gourd). Sorption properties of these fibres (banana and bagasse: 8.57±0.19 and 9.21±0.01, respectively ) are very similar as cotton fibres, however moisture content in Sponge gourd fibres at standard climate conditions is significantly lower

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Bamboo is an abundant resource and it has always been used in agriculture, handicraft, pa‐ per-making, furniture and architecture. Recently attempts have been made to produce tex‐ tile fibre from bamboo. Since a single bamboo fibre is 2 mm in length, it is used in textile production in the form of a fibre bundle. Bamboo is a very-fast growing grass. Environmen‐ tal friendly fibres extracted from bamboo, which is renewable, fast growing, degradable, and does not occupy cultivated land are economically efficient and especially useful to grow

After degumming through a chemical treatment, the cellulose content in the bamboo fibre reached more than 70%. Comparing chemical structure of hemp, jute and bamboo, lignin and hemicellulose contents in bamboo are far higher than that of the flax fibres, and almost as much as that of the jute fibres (Hemicellulose content: bamboo 12.49%, jute 13.53%, flax 11.62; lignin content: bamboo: 10.15%, jute 13.30%, flax 2.78%). Lignin in bamboo fibre bun‐

Cross section of single bamboo fibre is round with a small round lumen. The bamboo single fibre width is 6–12 μm and the length 2–3 mm and it is smaller than that of flax (12–20 μm,

By the x-ray analysis of bamboo fibres a similar x-ray diffraction pattern is obtained as it is of jute fibres. Two diffraction peaks are observed at the angles of 15–16° and 22° for the bamboo fibre and jute fibre. It is known that the crystalline structure of natural cellulose from various plants belongs to cellulose I with typical diffraction maxima at scattering an‐ gles 14°, 16° and 22°, respectively. Due to a high content of amorphous hemicellulose and lignin in the bamboo fibre and jute fibre an overlapping of the two peaks at angles of 14°

The fine structure and mechanical properties of fibres within a maturing vascular bundle of moso bamboo Phyllostachys pubescens was studied by Wang with co-workers [Wang 2012].

Almost axially oriented cellulose fibrils were found in the fibre cell walls. This fibrilar ar‐ rangement maximizes the longitudinal elastic modulus of the fibres and their lignification

Because of high and different content of non-cellulose substances in various plant fibres the fibres' crystallinity is different. When comparing crystallinities of some plant fibres, the crys‐ tallinity of ramie is the highest, follows flax and cotton and the lowest crystallinity is ob‐ served for bamboo fibres and jute fibres. These structural differences are reflected on fibre

dles is reason for yellow colour of fibres and coarse fibre fineness [Yueping 2010].

( 4.79±0.02) [Guimarăes 2009].

17–20 mm, respectively) [Yueping 2010].

increases the transverse rigidity [Wang 2012].

and 16° on the diffraction pattern is observed [Yueping 2010].

**4.5. Bamboo fibres**

in hilly areas.

Mechanical properties of hop stem fibres are close to that of hemp fibres. Shorter single cells and low crystallinity of cellulose in the fibres should be the major reasons for the lower breaking tenacity of hop fibres compared to hemp. Sorption properties of hop fibres are comparable to cotton properties and slightly lower than that of hemp [Reddy 2009].

### **4.4. Banana, sugarcane bagasse and sponge gourd fibers**

Fibres from *Musaceae maturate rachis:* The fibrous structure of agro-industrial residues of two different types of *Musaceae* maturate waste rachises (banana -Musa AAA, cv 'Valery' and Musa AAB, cv 'Dominico Harton') has been studied by Gañán et al. Using an up-bottom ap‐ proach, rachises, fibre bundles and conducting tissues, elementary or ultimate fibres, micro‐ fibrils bundles and cellulose microfibrils have been isolated [Gañán 2008]. For fibre bundles extraction biological retting followed by chemical treatment was used.

An important amount of vascular bundles that were formed by conducting tissues and fibre bundles was observed on rachis cross sections. Researchers are suggesting two groups of fi‐ brous structures: the first at the microscopic level formed by conducting tissues, fibre bun‐ dles and their elementary fibres, and the second at nanoscopic or ultrastructural level where cellulose microfibrils are grouped in microfibril bundles. In addition to, on fibre surface cal‐ cium oxalates crystal structures were observed. Their occurrence on residue surfaces is relat‐ ed to the maturate state of samples.

The diameter of elementary fibres was 10-20μm and diameter of macrofibrils with helicoidal arrangement inside the secondary cell wall was less than 1μm. In addition to microfibril bundles with the diameter 40 – 60nm and cellulose microfibrils with the diameter 5-10nm were identified [Gañán 2008].

Three types of fibres, namely banana fibres (*Musa sapientum*) obtained from the pseudo stem of the plant, sugarcane (*Saccharum officinarum*) bagasse fibres and Brazil sponge gourd (*Luffa cylindrica*) fibre were studied by Guimarăes and co-workers [Guimarăes 2009].

The chemical structure of extracted fibres was determined. The cellulose content is the high‐ est in Sponge gourd (66.59%±0.61%), Bagasse follows (54.87%±0.53%) and the lowest cellu‐ lose content was determined for Banana fibres (50.15%±1.09%). Cellulose crystallinity degree was between 39% and 50% for the analysed fibres. The most crystalline structure was ob‐ served in Sponge gourd fibres (50%), cellulose in Bagase was 48% crystalline and in banana fibres only 39%.

A high content of lignin was observed for all types of fibres (17.44%±0.19% Banana, 23.33% ±0.02% Bagasse and 15.46%±0.02% Sponge gourd). Sorption properties of these fibres (banana and bagasse: 8.57±0.19 and 9.21±0.01, respectively ) are very similar as cotton fibres, however moisture content in Sponge gourd fibres at standard climate conditions is significantly lower ( 4.79±0.02) [Guimarăes 2009].

#### **4.5. Bamboo fibres**

The single sclerenchyma cells in hop stem fibres are small. Their length is 2.0 ± 1.0 mm and width 16.5 ± 5.5μm. Fibres extracted from hop stems contain 84% of cellulose, 6% of lignin in 2% of ash. From the diffraction patterns of cellulose in hop stem fibres cellulose crystalline structure was determined. The crystallinity index is 44 ± 5% (65–70% for cotton and 81–89%

tern is very similar to the diffraction pattern of hemp. Cellulose crystallites in hop and hemp fibres are regularly distributed and are also parallel to the fibre axis and to each other.

Mechanical properties of hop stem fibres are close to that of hemp fibres. Shorter single cells and low crystallinity of cellulose in the fibres should be the major reasons for the lower breaking tenacity of hop fibres compared to hemp. Sorption properties of hop fibres are

Fibres from *Musaceae maturate rachis:* The fibrous structure of agro-industrial residues of two different types of *Musaceae* maturate waste rachises (banana -Musa AAA, cv 'Valery' and Musa AAB, cv 'Dominico Harton') has been studied by Gañán et al. Using an up-bottom ap‐ proach, rachises, fibre bundles and conducting tissues, elementary or ultimate fibres, micro‐ fibrils bundles and cellulose microfibrils have been isolated [Gañán 2008]. For fibre bundles

An important amount of vascular bundles that were formed by conducting tissues and fibre bundles was observed on rachis cross sections. Researchers are suggesting two groups of fi‐ brous structures: the first at the microscopic level formed by conducting tissues, fibre bun‐ dles and their elementary fibres, and the second at nanoscopic or ultrastructural level where cellulose microfibrils are grouped in microfibril bundles. In addition to, on fibre surface cal‐ cium oxalates crystal structures were observed. Their occurrence on residue surfaces is relat‐

The diameter of elementary fibres was 10-20μm and diameter of macrofibrils with helicoidal arrangement inside the secondary cell wall was less than 1μm. In addition to microfibril bundles with the diameter 40 – 60nm and cellulose microfibrils with the diameter 5-10nm

Three types of fibres, namely banana fibres (*Musa sapientum*) obtained from the pseudo stem of the plant, sugarcane (*Saccharum officinarum*) bagasse fibres and Brazil sponge gourd (*Luffa*

The chemical structure of extracted fibres was determined. The cellulose content is the high‐ est in Sponge gourd (66.59%±0.61%), Bagasse follows (54.87%±0.53%) and the lowest cellu‐ lose content was determined for Banana fibres (50.15%±1.09%). Cellulose crystallinity degree was between 39% and 50% for the analysed fibres. The most crystalline structure was ob‐ served in Sponge gourd fibres (50%), cellulose in Bagase was 48% crystalline and in banana

*cylindrica*) fibre were studied by Guimarăes and co-workers [Guimarăes 2009].

comparable to cotton properties and slightly lower than that of hemp [Reddy 2009].

. The diffraction pat‐

for hemp cellulose) and microfibrillar angle of cellulose fibrils 8 ± 0.70

extraction biological retting followed by chemical treatment was used.

**4.4. Banana, sugarcane bagasse and sponge gourd fibers**

ed to the maturate state of samples.

384 Advances in Agrophysical Research

were identified [Gañán 2008].

fibres only 39%.

Bamboo is an abundant resource and it has always been used in agriculture, handicraft, pa‐ per-making, furniture and architecture. Recently attempts have been made to produce tex‐ tile fibre from bamboo. Since a single bamboo fibre is 2 mm in length, it is used in textile production in the form of a fibre bundle. Bamboo is a very-fast growing grass. Environmen‐ tal friendly fibres extracted from bamboo, which is renewable, fast growing, degradable, and does not occupy cultivated land are economically efficient and especially useful to grow in hilly areas.

After degumming through a chemical treatment, the cellulose content in the bamboo fibre reached more than 70%. Comparing chemical structure of hemp, jute and bamboo, lignin and hemicellulose contents in bamboo are far higher than that of the flax fibres, and almost as much as that of the jute fibres (Hemicellulose content: bamboo 12.49%, jute 13.53%, flax 11.62; lignin content: bamboo: 10.15%, jute 13.30%, flax 2.78%). Lignin in bamboo fibre bun‐ dles is reason for yellow colour of fibres and coarse fibre fineness [Yueping 2010].

Cross section of single bamboo fibre is round with a small round lumen. The bamboo single fibre width is 6–12 μm and the length 2–3 mm and it is smaller than that of flax (12–20 μm, 17–20 mm, respectively) [Yueping 2010].

By the x-ray analysis of bamboo fibres a similar x-ray diffraction pattern is obtained as it is of jute fibres. Two diffraction peaks are observed at the angles of 15–16° and 22° for the bamboo fibre and jute fibre. It is known that the crystalline structure of natural cellulose from various plants belongs to cellulose I with typical diffraction maxima at scattering an‐ gles 14°, 16° and 22°, respectively. Due to a high content of amorphous hemicellulose and lignin in the bamboo fibre and jute fibre an overlapping of the two peaks at angles of 14° and 16° on the diffraction pattern is observed [Yueping 2010].

The fine structure and mechanical properties of fibres within a maturing vascular bundle of moso bamboo Phyllostachys pubescens was studied by Wang with co-workers [Wang 2012].

Almost axially oriented cellulose fibrils were found in the fibre cell walls. This fibrilar ar‐ rangement maximizes the longitudinal elastic modulus of the fibres and their lignification increases the transverse rigidity [Wang 2012].

Because of high and different content of non-cellulose substances in various plant fibres the fibres' crystallinity is different. When comparing crystallinities of some plant fibres, the crys‐ tallinity of ramie is the highest, follows flax and cotton and the lowest crystallinity is ob‐ served for bamboo fibres and jute fibres. These structural differences are reflected on fibre properties, i.e. density, moisture regain, tenacity, dyeing and thermal properties, etc. [Yuep‐ ing 2010].

### **4.6. Quinoa fibres**

Quinoa originates from Andes in South America and it belongs to the family Chenopodia‐ ceae (Chenopodium quinoa Willd). It is a grain-like crop grown primarily for its edible seeds and it has become highly appreciated for its nutritional value. It has been recognized as a complete food due to its protein quality. It has remarkable nutritional properties; not only from its protein content (15%) but also from its great amino acid balance. It is an impor‐ tant source of minerals and vitamins, and has also been found to contain compounds like polyphenols, phytosterols, and flavonoids with possible nutraceutical benefits [Abugoch 2009]. The plant is not problematic and it can be cultivated everywhere. Quinoa has a high nutritional value and has recently been used as a novel functional food because of all these properties; it is a promising alternative cultivar.

The elementary fibres can be isolated from Quinoa stems. It is possible to use different proc‐ esses for fibre isolation. Sfiligoj et al. reported about fibres which were obtained from un‐ treated stems by mechanical isolation. Besides, stems were subjected to chemical treatment in alkaline medium (1%NaOH; different treatment times and temperatures were used; sam‐ ple A – 1day treatment, room temperature; sample B – 11days treatment, room temperature; sample C – 1 hour T = 1000 C). In addition to they were water treated, respectively. Thereby the pectin structures connecting fibres with other plant tissues were loosed and the mechan‐ ical separation of the elementary fibres or fibre bundles was performed [Sfiligoj-Smole 2011].

**Figure 11.** SEM image of surface morphology of isolated fibres from quinoa (fibres obtained by decortication from

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The fibre bundles were mainly inhomogeneous and sclerenchyma cells were often accompa‐ nied by tracheary elements. Fibres surface morphology was strongly dependent on isolation process (Fig. 11, 12, 13 and 14). Fibres obtained by decortication, i.e. by only mechanical iso‐ lation show totally different surface morphology when compared to the fibres obtained from water and alkaline treated stems. In addition to, thermal conditions of the treatment

**Figure 12.** SEM images of surface morphology of differently isolated fibres from quinoa (fibres from water treated

influenced the surface morphology (cf. Fig. 13 and Fig.14).

untreated stems)

**Figure 10.** Cross – section of the quinoa stem

stems)

Morphological characteristics of fibres were microscopically observed. Light microscopy tests were performed on whole stems and on ultimate fibres and fibre bundles. Different structures were observed on cross- sections and on longitudinal views of stems. Quinoa plant and its stem are shown on Figure 9. In addition to, stem's cross-section is demonstrat‐ ed on Figure 10. Quinoa technical fibres, i.e. bundles of elementary cells were isolated from untreated and differently treated stems.

**Figure 10.** Cross – section of the quinoa stem

properties, i.e. density, moisture regain, tenacity, dyeing and thermal properties, etc. [Yuep‐

Quinoa originates from Andes in South America and it belongs to the family Chenopodia‐ ceae (Chenopodium quinoa Willd). It is a grain-like crop grown primarily for its edible seeds and it has become highly appreciated for its nutritional value. It has been recognized as a complete food due to its protein quality. It has remarkable nutritional properties; not only from its protein content (15%) but also from its great amino acid balance. It is an impor‐ tant source of minerals and vitamins, and has also been found to contain compounds like polyphenols, phytosterols, and flavonoids with possible nutraceutical benefits [Abugoch 2009]. The plant is not problematic and it can be cultivated everywhere. Quinoa has a high nutritional value and has recently been used as a novel functional food because of all these

The elementary fibres can be isolated from Quinoa stems. It is possible to use different proc‐ esses for fibre isolation. Sfiligoj et al. reported about fibres which were obtained from un‐ treated stems by mechanical isolation. Besides, stems were subjected to chemical treatment in alkaline medium (1%NaOH; different treatment times and temperatures were used; sam‐ ple A – 1day treatment, room temperature; sample B – 11days treatment, room temperature;

the pectin structures connecting fibres with other plant tissues were loosed and the mechan‐ ical separation of the elementary fibres or fibre bundles was performed [Sfiligoj-Smole 2011].

Morphological characteristics of fibres were microscopically observed. Light microscopy tests were performed on whole stems and on ultimate fibres and fibre bundles. Different structures were observed on cross- sections and on longitudinal views of stems. Quinoa plant and its stem are shown on Figure 9. In addition to, stem's cross-section is demonstrat‐ ed on Figure 10. Quinoa technical fibres, i.e. bundles of elementary cells were isolated from

C). In addition to they were water treated, respectively. Thereby

ing 2010].

**4.6. Quinoa fibres**

386 Advances in Agrophysical Research

properties; it is a promising alternative cultivar.

sample C – 1 hour T = 1000

**Figure 9.** Quinoa – ripe plant and the stem

untreated and differently treated stems.

**Figure 11.** SEM image of surface morphology of isolated fibres from quinoa (fibres obtained by decortication from untreated stems)

The fibre bundles were mainly inhomogeneous and sclerenchyma cells were often accompa‐ nied by tracheary elements. Fibres surface morphology was strongly dependent on isolation process (Fig. 11, 12, 13 and 14). Fibres obtained by decortication, i.e. by only mechanical iso‐ lation show totally different surface morphology when compared to the fibres obtained from water and alkaline treated stems. In addition to, thermal conditions of the treatment influenced the surface morphology (cf. Fig. 13 and Fig.14).

**Figure 12.** SEM images of surface morphology of differently isolated fibres from quinoa (fibres from water treated stems)

Fibres' elongation is low and breaking strength high. The elongations vary between 1.41 % to 2.11 % and tenacities from 13.78 to 32.19cN/tex. The obtained values are comparable with the mechanical properties of some textile bast fibres, e.g. jute, hemp or coir. Ultimate fibre cell in hemp is 13 – 26 mm long; its diameter is between 5 and 32 μm, tenacity 29 – 47 cN/tex

In addition to, the powder X-ray diffraction spectra of quinoa fibres, which were obtained by the fibres extraction by water treatment and mechanical isolation, exhibit a diffraction pattern

to the 002 reflection. However, the two diffraction maxima of 101, 10-1 reflections at diffrac‐

fraction pattern is very similar to the pattern obtained by x-ray scattering of bamboo and jute fibres [Yueping 2010]. It is assumed that accompanying substances were not removed suffi‐ ciently and therefore the remaining amorphous hemicellulose and lignin are origin of overlap‐

Grass because of its huge available amounts represents a great potential. It is an annual plant with bundles of elementary fibre cells bound by pectin middle lamellae. Parenchyma

The most important representatives in the group of grasses are: Perennial Ryegrass (*Lolium perenne*), Italian ryegrass (*Lolium multiflorum*), Hybrid ryegrasses (*Lolium perenne x multiflo‐ rum*), tetraploid varieties of perennial and Italian ryegrass, Timothy (*Phleum pratense*), Cocksfoot (*Dactylis glomerata*), Fescues (Meadow fescue - *Festuca pratensis*; tall fescue – *F.ar‐ undinasea*; red fescue – *F.rubra*), Bromes (*Bromus willdenowii*) [Holmes 1989, Petersen 1981]. Legumes are presented by: White clover (*Trifolium repens*), Red clover (*Trifolium pratense*),

The elementary grass fibres were studied. They were isolated from different grass and le‐ gumes sorts, i.e. Ryegrass (*Lolium hybridum* Gumpenstein), Trefoil (*Trifolium pratense*) and Lu‐ cerne (*Medicago sativa*) [Sfiligoj-Smole 2005, Sfiligoj-Smole 2004]. The fibre-samples were obtained in a bio-refinery, after the liquid phase containing proteins and lactic acid was elimi‐ nated from the ensiled and green grasses, respectively. For the isolation of elementary grass fi‐ bres different processes were used. Cross section of a Trefoil stem is presented on Fig.15.

On the microscopy images of grasses cross sections stem area, lumen area, fibre area and fi‐ bre content was determined. A high content of fibres was detected in stems regardless the fibres origin. The highest fibre content was determined in Ryegrasses (39.5%), Lucerne fol‐ lowed (34.5%) and the lowest content of fibres was observed in the cross-section of Trefoil

Esparto fibres, esparto grass or Alfa are cellulose based fibres extracted from esparto *Stipa tenacissima* leaves. It is a fast growing perennial plant from poaceae family that grows in

, respectively, typical for native cellulose are not pronounced. The dif‐

, which can be assigned

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typical of cellulose I, with a diffraction peak of the 2θ angle at about 22<sup>0</sup>

and elongation 1.8% [Sfiligoj-Smole in press].

ping of these two peaks [Sfiligoj-Smole in press].

cells separate fibre bundles from each other.

Lucerne (*Medicago sativa*) [Holmes 1989].

(20.2%) [Sfiligoj-Smole 2005, Sfiligoj-Smole 2004].

**4.8. Alfa or esparto fibres**

tion angles 14 and 160

**4.7. Grass fibres**

**Figure 13.** SEM images of surface morphology of differently isolated fibres from quinoa (fibres from NaOH treated stems)

Fibre dimensions were measured on microscopy images. Fibres' diameters are dependent on the procedure of fibres isolation. When untreated stems were processed fibre bundles were formed from a bigger number of cells and a mean diameter of 164μm was determined for these fibres. Pre-treatment of stems facilitates sclerenchyma cells separation from other plant tissues, and fibres' diameter for fibres isolated from pre-treated stems was 42.61μm. The variation of fibres' diameter is very high (variation coefficient is 43.76%).

In addition to, geometrical and mechanical properties of isolated fibres and fibre bundles were determined. The measurements were performed on Lenzing apparatus Vibrodyn and Vibroskop according to standard test methods. Ten parallel samples were measured. Fine‐ ness of fibre bundles was between 24.66 and 96.84 dtex depending on the isolation method used for fibres extraction. The fineness variation is related to different number of cells in the bundle and quality of fibre extraction process which is connected with the presence of dif‐ ferent non-cellulose compounds on fibres.

It was important to obtain a representative sample for testing due to the inherent variability of most biological materials and extensive mechanical damage due to the isolation process. As mechanical and geometrical properties vary considerably according to temperature and humidity, all samples for testing were conditioned and prepared in the ISO standard atmos‐ phere for textile testing of 65 ±2% relative humidity and 20 ±2ºC according to ISO 5079 was used [ISO 5079 (1995)].

**Figure 14.** SEM images of surface morphology of differently isolated fibres from quinoa (fibres from stems, treated in NaOH at T = 1000C)

Fibres' elongation is low and breaking strength high. The elongations vary between 1.41 % to 2.11 % and tenacities from 13.78 to 32.19cN/tex. The obtained values are comparable with the mechanical properties of some textile bast fibres, e.g. jute, hemp or coir. Ultimate fibre cell in hemp is 13 – 26 mm long; its diameter is between 5 and 32 μm, tenacity 29 – 47 cN/tex and elongation 1.8% [Sfiligoj-Smole in press].

In addition to, the powder X-ray diffraction spectra of quinoa fibres, which were obtained by the fibres extraction by water treatment and mechanical isolation, exhibit a diffraction pattern typical of cellulose I, with a diffraction peak of the 2θ angle at about 22<sup>0</sup> , which can be assigned to the 002 reflection. However, the two diffraction maxima of 101, 10-1 reflections at diffrac‐ tion angles 14 and 160 , respectively, typical for native cellulose are not pronounced. The dif‐ fraction pattern is very similar to the pattern obtained by x-ray scattering of bamboo and jute fibres [Yueping 2010]. It is assumed that accompanying substances were not removed suffi‐ ciently and therefore the remaining amorphous hemicellulose and lignin are origin of overlap‐ ping of these two peaks [Sfiligoj-Smole in press].

#### **4.7. Grass fibres**

**Figure 13.** SEM images of surface morphology of differently isolated fibres from quinoa (fibres from NaOH treated

Fibre dimensions were measured on microscopy images. Fibres' diameters are dependent on the procedure of fibres isolation. When untreated stems were processed fibre bundles were formed from a bigger number of cells and a mean diameter of 164μm was determined for these fibres. Pre-treatment of stems facilitates sclerenchyma cells separation from other plant tissues, and fibres' diameter for fibres isolated from pre-treated stems was 42.61μm.

In addition to, geometrical and mechanical properties of isolated fibres and fibre bundles were determined. The measurements were performed on Lenzing apparatus Vibrodyn and Vibroskop according to standard test methods. Ten parallel samples were measured. Fine‐ ness of fibre bundles was between 24.66 and 96.84 dtex depending on the isolation method used for fibres extraction. The fineness variation is related to different number of cells in the bundle and quality of fibre extraction process which is connected with the presence of dif‐

It was important to obtain a representative sample for testing due to the inherent variability of most biological materials and extensive mechanical damage due to the isolation process. As mechanical and geometrical properties vary considerably according to temperature and humidity, all samples for testing were conditioned and prepared in the ISO standard atmos‐ phere for textile testing of 65 ±2% relative humidity and 20 ±2ºC according to ISO 5079 was

**Figure 14.** SEM images of surface morphology of differently isolated fibres from quinoa (fibres from stems, treated in

The variation of fibres' diameter is very high (variation coefficient is 43.76%).

ferent non-cellulose compounds on fibres.

used [ISO 5079 (1995)].

NaOH at T = 1000C)

stems)

388 Advances in Agrophysical Research

Grass because of its huge available amounts represents a great potential. It is an annual plant with bundles of elementary fibre cells bound by pectin middle lamellae. Parenchyma cells separate fibre bundles from each other.

The most important representatives in the group of grasses are: Perennial Ryegrass (*Lolium perenne*), Italian ryegrass (*Lolium multiflorum*), Hybrid ryegrasses (*Lolium perenne x multiflo‐ rum*), tetraploid varieties of perennial and Italian ryegrass, Timothy (*Phleum pratense*), Cocksfoot (*Dactylis glomerata*), Fescues (Meadow fescue - *Festuca pratensis*; tall fescue – *F.ar‐ undinasea*; red fescue – *F.rubra*), Bromes (*Bromus willdenowii*) [Holmes 1989, Petersen 1981]. Legumes are presented by: White clover (*Trifolium repens*), Red clover (*Trifolium pratense*), Lucerne (*Medicago sativa*) [Holmes 1989].

The elementary grass fibres were studied. They were isolated from different grass and le‐ gumes sorts, i.e. Ryegrass (*Lolium hybridum* Gumpenstein), Trefoil (*Trifolium pratense*) and Lu‐ cerne (*Medicago sativa*) [Sfiligoj-Smole 2005, Sfiligoj-Smole 2004]. The fibre-samples were obtained in a bio-refinery, after the liquid phase containing proteins and lactic acid was elimi‐ nated from the ensiled and green grasses, respectively. For the isolation of elementary grass fi‐ bres different processes were used. Cross section of a Trefoil stem is presented on Fig.15.

On the microscopy images of grasses cross sections stem area, lumen area, fibre area and fi‐ bre content was determined. A high content of fibres was detected in stems regardless the fibres origin. The highest fibre content was determined in Ryegrasses (39.5%), Lucerne fol‐ lowed (34.5%) and the lowest content of fibres was observed in the cross-section of Trefoil (20.2%) [Sfiligoj-Smole 2005, Sfiligoj-Smole 2004].

#### **4.8. Alfa or esparto fibres**

Esparto fibres, esparto grass or Alfa are cellulose based fibres extracted from esparto *Stipa tenacissima* leaves. It is a fast growing perennial plant from poaceae family that grows in

duces the bulk density, thereby acoustic and thermal insulation properties of biofibres are increased and therefore these fibres are preferable for lightweight composites for noise and

Plant Fibres for Textile and Technical Applications

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391

In addition to insulation, these materials are used in Civil Engineering as building materials. From industrial hemp Cannabis Sativa L useful cellulose fibres to manufacture fibre cement products for roofing are obtained. The disadvantages of some cellulose fibres are: lower modulus of elasticity, high moisture absorption, decomposition in alkaline environments, they are susceptible to biological attack, variable mechanical and physical properties. Hemp fibres with a higher durability than traditional cellulose fibres are more suited for this kind of application, and therefore a lot of research was performed about the use of hemp fibres as reinforcement for building materials based on cement. In addition to, hemp core fibres from agricultural waste industrial hemp straw with the length between 5-10 mm were studied by

An important aspect of natural fibres is associated with their hierarchically built anatomies developed and optimized in a long term evolution process. A variety of non-wood plants offer multiple possibilities in dimensions, composition and morphology of fibrous structures that can be useful for pulp and paper making industries [Gañán 2008]. Therefore based on high cellulose content they are replacing wood pulp in paper and fibres production. Grass

Natural fibres are currently attracting a lot of attention for reinforcement. Fibre reinforced composites consists of fibre as reinforcement and a polymer as a matrix. Their special ad‐ vantage is their low cost, low density, good mechanical properties, biodegradability, etc. The advantage of natural fibre composites includes lack of health hazards and non-abrasive nature [Sreenivasan 2012]. Natural fibres provide stiffness and strength to the composite and are easily recyclable. Hemp fibres represent a good potential for this utilization. The use of hemp fibres as reinforcement in composite materials has increased in recent years as a re‐ sponse to the increasing demand for developing biodegradable, sustainable and recyclable materials [Shahzad 2012]. Hemp fibres are used for reinforced thermoplastics (composites hemp fibres - polypropylene PP, polyethylene PE, polystyrene PS, hemp fibres - maleated polypropylene MAPP, kenaf-hemp nonwoven impregnated with acrylic matrix., etc.), ther‐ mosets ( polyester, epoxy resin, vinylester, phenolics) [Shahzad 2012] and biodegradable polymers (thermoplastic starch, polyhydroalkanoates (PHA), polyactides (PLA), lignin

Also other natural cellulose fibres have been used for composite preparation. Polymers in‐ cluding high density polyethylene (HDPE), low density polyethylene (LDPE) polypropylene

A major disadvantage of cellulose fibres is their highly polar nature which makes them in‐ compatible with non-polar polymers. These fibres therefore are inherently incompatible with hydrophobic thermoplastics, such as polyolefins [John 2008]. This characteristic results in compounding difficulties leading to non-uniform dispersion of fibres within the matrix which influences composite properties. To achieve strong adhesion at the interfaces which is

(PP) polyether ether ketone (PEEK), have been reported as matrices [Li 2007].

stems and leafs fibres could be utilized for this purpose [Saijonkari – Pahkala 2001].

thermal automobile insulators.

Jarabo et al. [Jarabo 2012].

based epoxy, soy based resin, etc [Shahzad 2012].

**Figure 15.** Cross section of a Trefoil stem [Sfiligoj-Smole 2005].

North Africa and southeast Spain. Leaves which reach up to 1m are rich with fibres [Belkhir 2012]. Fibres are extracted for cellulose pulp and paper manufacturing and therefore fibres and pulp were extensively studied. Pulp properties, chemical composition and cell wall ar‐ chitecture was researched. It was found that fibres morphological variability (length and width) is related to growth conditions, i.e. growth location, season and leaf level. Average length of fibres is 1-2 mm and fibres width varies from 14-17μm [Belkhir 2012].

#### **4.9. Sea grass – Zostera marina**

Researchers report about different new cellulose sources, however mainly from terrestrial plant origin. But fibres from marine sources offer addition options when appropriate species are identified. Sea grasses belong to angiosperm and are found in most of the oceans. Among sixty different species *Zostera marina* called eel-grass is the most widespread. [Da‐ vies 2007].

P.Davis et al. reported about Baltic species of *Zostera marina* which was collected on the Ger‐ man Baltic coast. The diameter of the plant stem was about 2-5 mm and it was 3-8 times branched. The plant was up to 1.2 m long.

In *Zostera marina* a very interesting plant structure was observed. Fibres were reinforcing a matrix and thereby forming a composite structure. Fibres were organized in bundles. Indi‐ vidual fibres with the diameter around 5μm and approximately circular cross section were mechanically extracted from sea grass *Zostera marina*. Fibres are composed of 57% cellulose, 38% of non-cellulosic polysaccharides (10%pectins and 28% hemicellulose) and 5% of resid‐ ual matter [Davies 2007]. Single fibre stiffness was determined. It was 28 GPa [Davies 2007].

Due to sea-grass fibres mechanical properties and its low density fibres present an attractive reinforcement for composite materials, especially when bio-degradability is required.

## **5. Applications of non-conventional cellulose fibres**

Depending on their physical properties and cellulose content lingocellulose fibres can be used for various applications. The typical fibre morphology with a lumen in the centre, re‐ duces the bulk density, thereby acoustic and thermal insulation properties of biofibres are increased and therefore these fibres are preferable for lightweight composites for noise and thermal automobile insulators.

In addition to insulation, these materials are used in Civil Engineering as building materials. From industrial hemp Cannabis Sativa L useful cellulose fibres to manufacture fibre cement products for roofing are obtained. The disadvantages of some cellulose fibres are: lower modulus of elasticity, high moisture absorption, decomposition in alkaline environments, they are susceptible to biological attack, variable mechanical and physical properties. Hemp fibres with a higher durability than traditional cellulose fibres are more suited for this kind of application, and therefore a lot of research was performed about the use of hemp fibres as reinforcement for building materials based on cement. In addition to, hemp core fibres from agricultural waste industrial hemp straw with the length between 5-10 mm were studied by Jarabo et al. [Jarabo 2012].

North Africa and southeast Spain. Leaves which reach up to 1m are rich with fibres [Belkhir 2012]. Fibres are extracted for cellulose pulp and paper manufacturing and therefore fibres and pulp were extensively studied. Pulp properties, chemical composition and cell wall ar‐ chitecture was researched. It was found that fibres morphological variability (length and width) is related to growth conditions, i.e. growth location, season and leaf level. Average

Researchers report about different new cellulose sources, however mainly from terrestrial plant origin. But fibres from marine sources offer addition options when appropriate species are identified. Sea grasses belong to angiosperm and are found in most of the oceans. Among sixty different species *Zostera marina* called eel-grass is the most widespread. [Da‐

P.Davis et al. reported about Baltic species of *Zostera marina* which was collected on the Ger‐ man Baltic coast. The diameter of the plant stem was about 2-5 mm and it was 3-8 times

In *Zostera marina* a very interesting plant structure was observed. Fibres were reinforcing a matrix and thereby forming a composite structure. Fibres were organized in bundles. Indi‐ vidual fibres with the diameter around 5μm and approximately circular cross section were mechanically extracted from sea grass *Zostera marina*. Fibres are composed of 57% cellulose, 38% of non-cellulosic polysaccharides (10%pectins and 28% hemicellulose) and 5% of resid‐ ual matter [Davies 2007]. Single fibre stiffness was determined. It was 28 GPa [Davies 2007].

Due to sea-grass fibres mechanical properties and its low density fibres present an attractive

Depending on their physical properties and cellulose content lingocellulose fibres can be used for various applications. The typical fibre morphology with a lumen in the centre, re‐

reinforcement for composite materials, especially when bio-degradability is required.

**5. Applications of non-conventional cellulose fibres**

length of fibres is 1-2 mm and fibres width varies from 14-17μm [Belkhir 2012].

**4.9. Sea grass – Zostera marina**

390 Advances in Agrophysical Research

**Figure 15.** Cross section of a Trefoil stem [Sfiligoj-Smole 2005].

branched. The plant was up to 1.2 m long.

vies 2007].

An important aspect of natural fibres is associated with their hierarchically built anatomies developed and optimized in a long term evolution process. A variety of non-wood plants offer multiple possibilities in dimensions, composition and morphology of fibrous structures that can be useful for pulp and paper making industries [Gañán 2008]. Therefore based on high cellulose content they are replacing wood pulp in paper and fibres production. Grass stems and leafs fibres could be utilized for this purpose [Saijonkari – Pahkala 2001].

Natural fibres are currently attracting a lot of attention for reinforcement. Fibre reinforced composites consists of fibre as reinforcement and a polymer as a matrix. Their special ad‐ vantage is their low cost, low density, good mechanical properties, biodegradability, etc. The advantage of natural fibre composites includes lack of health hazards and non-abrasive nature [Sreenivasan 2012]. Natural fibres provide stiffness and strength to the composite and are easily recyclable. Hemp fibres represent a good potential for this utilization. The use of hemp fibres as reinforcement in composite materials has increased in recent years as a re‐ sponse to the increasing demand for developing biodegradable, sustainable and recyclable materials [Shahzad 2012]. Hemp fibres are used for reinforced thermoplastics (composites hemp fibres - polypropylene PP, polyethylene PE, polystyrene PS, hemp fibres - maleated polypropylene MAPP, kenaf-hemp nonwoven impregnated with acrylic matrix., etc.), ther‐ mosets ( polyester, epoxy resin, vinylester, phenolics) [Shahzad 2012] and biodegradable polymers (thermoplastic starch, polyhydroalkanoates (PHA), polyactides (PLA), lignin based epoxy, soy based resin, etc [Shahzad 2012].

Also other natural cellulose fibres have been used for composite preparation. Polymers in‐ cluding high density polyethylene (HDPE), low density polyethylene (LDPE) polypropylene (PP) polyether ether ketone (PEEK), have been reported as matrices [Li 2007].

A major disadvantage of cellulose fibres is their highly polar nature which makes them in‐ compatible with non-polar polymers. These fibres therefore are inherently incompatible with hydrophobic thermoplastics, such as polyolefins [John 2008]. This characteristic results in compounding difficulties leading to non-uniform dispersion of fibres within the matrix which influences composite properties. To achieve strong adhesion at the interfaces which is needed for an effective transfer of stress and load distribution through out the interface, sometimes surface modification is needed. Surface modifications include (i) physical treat‐ ments, such as solvent extraction; (ii) physico-chemical treatments, like the use of corona and plasma discharges or laser, and UV bombardment; and (iii) chemical modifications, both by direct condensation of the coupling agents onto the cellulose surface and by its grafting by free-radical or ionic polymerizations [John 2008].Therefore different coupling agents which introduce chemical bonds between the matrix and fibre are involved (e.g. si‐ lane, isocyanate and titanate based products, alkaline treatment, acetylation, benzoylation, acrylation, maleated coupling agents, permanganate, etc) [51]. or methods of physical fibre treatments (e.g. surface fibrillation, plasma treatment) are used [George 2001]. An additional possibility is to impregnate cellulose fibres in monomer solution, follows the in-situ catalyst, heat or UV polymerisation [George 2001].

Cellulose nanofibres and crystals have gained a large interest, not only in the academic re‐

Plant Fibres for Textile and Technical Applications

http://dx.doi.org/10.5772/52372

393

It is well known that isolation of nanocrystals from cellulose is possible by strong acid hy‐ drolysis. Under controlled conditions, acid hydrolysis allows removal of the amorphous re‐ gions of cellulose fibres whilst keeping the crystalline domains intact in the form of

The diamensons of nanofibres are usually around 20–30 nm in diameter with the length of few μm. Nanocrystals are much smaller. Their length is about 200nm and diameter about 3– 5 nm [Oksman 2012]. Cellulosic nanomaterials are obtained form different resources, i.e. wood, bioresidues and annual plants, e.g. wood fibres, sisal, pineapple leaves, coconut husk fibres and bananas, mengkuang leaves (*Pandanus tectorius*) [Sheltami 2012], mulberry bark [Li 2009]. The use of isolated cellulose nanocrystals as reinforcements in the field of nano‐ composites has attracted considerable attention since it was first reported in 1995 [Sheltami 2012]. Natural fibre reinforced composites can be applied in the plastic, automobile and

Lignocellulosic natural fibres have a very long tradition for textile materials manufacturing. Especially are these fibres important for technical textiles production. The series of plants yielding conventional textile fibres, e.g. flax, hemp, etc. has been recently extended by sever‐ al abundant plant species traditionally not-connected with fibres extraction. Of huge interest are especially agricultural wastes from cultures which are primary grown for food industry, and their plant wastes additionally containing fibres. Different fibres have been studied by several authors; their properties were determined and compared to the properties of con‐ ventional fibres. Regardless of the origin fibre cells are elongated sclerenchyma cells of dif‐ ferent geometrical characteristics, associated in fibre bundles with adequate mechanical properties. Several plant species were suggested for utilization from different geographic

Natural fibres from conventional and unconventional source are considered as potential re‐ placement for man-made fibres in composite materials for their reinforcement. Natural fi‐ bres from annual plants have advantages of being low cost and low density and therefore they are light. They are a renewable material. In addition to, an important advantage of these materials is their biodegradability and low toxicity. It was confirmed by many re‐ searchers that properties of natural fibres of different origin improve composites properties, e.g. the mechanical properties of natural fibres - polymer composites are superior to those of

search society but also in industries, during the last few years [Oksman 2012].

crystalline nanoparticles [Sheltami 2012].

packaging industries [Li 2007].

**6. Conclusions**

areas.

the unreinforced materials.

Different natural fibres species have been used for preparation of composites. Some exam‐ ples are: aspen fibre, abaca fibre, bagasse fibres, bamboo fibre (BF), banana fibre, etc.

Unidirectional isora fibre reinforced polyester composites were prepared by compression moulding. Isora is a natural bast fibre separated from the *Helicteres isora* plant by a retting process. Untreated and alkali treated fibres were used for composite preparation and influ‐ ence of fibre content on composite properties was studied. It was observed that the pretreatment process conditions the fibre content for achieving optimum composites mechanical properties [Joshy 2007].

Green composites were prepared from pineapple leaf fibres and soy-based resin. The addi‐ tion of polyester amide grafted glycidyl methacrylate (PEA-g-GMA) as compatibilizer in‐ creased the mechanical properties of composites. For preparing composites from pineapple leaf fibres in natural rubber fibres were pre-treated in NaOH solutions and benzoyl peroxide (BPO) of different concentrations. It was found that all surface modifications enhanced ad‐ hesion and tensile properties [Joshy 2007].

Elephant grass (*Pennisetum purpureum*) is available abundantly in nature and is renewable. It is a tall grass growing in dense clumps along lake and riverbeds up to 3 m height. The diam‐ eter of the stem is 25 mm and leaves are 0.6 to 0.9 m long and about 25 mm wide. It repre‐ sents a potential and economic source compared to other natural fibers, however it is still underutilized, therefore K. Murali Mohan Rao with co-workers suggest fibres from the grass for reinforcement of polyester composites [55]. The density of the elephant grass fiberres is very low compared to other lignocellulose fibres.

This property is a good base for designing lightweight material from these fibres. The diam‐ eter of fibers is between 70 lm to 400 μm. Fibres mechanical properties are: tensile strengh is 185 MPA, tensile modulus is 7.40 GPa and elongation at break 2.50% [55]. The positive im‐ pact of elephant grass fibres on tensile strength of fiber reinforced

composites was determined and it was found that composite mechanical properies increase with percentage volume of fibers. Whereas the fibre extraction is simple, fibres are cheap and of appropriate properties elephant grass is also suitable for composites used for light‐ weight structures preparation [55].

Cellulose nanofibres and crystals have gained a large interest, not only in the academic re‐ search society but also in industries, during the last few years [Oksman 2012].

It is well known that isolation of nanocrystals from cellulose is possible by strong acid hy‐ drolysis. Under controlled conditions, acid hydrolysis allows removal of the amorphous re‐ gions of cellulose fibres whilst keeping the crystalline domains intact in the form of crystalline nanoparticles [Sheltami 2012].

The diamensons of nanofibres are usually around 20–30 nm in diameter with the length of few μm. Nanocrystals are much smaller. Their length is about 200nm and diameter about 3– 5 nm [Oksman 2012]. Cellulosic nanomaterials are obtained form different resources, i.e. wood, bioresidues and annual plants, e.g. wood fibres, sisal, pineapple leaves, coconut husk fibres and bananas, mengkuang leaves (*Pandanus tectorius*) [Sheltami 2012], mulberry bark [Li 2009]. The use of isolated cellulose nanocrystals as reinforcements in the field of nano‐ composites has attracted considerable attention since it was first reported in 1995 [Sheltami 2012]. Natural fibre reinforced composites can be applied in the plastic, automobile and packaging industries [Li 2007].

## **6. Conclusions**

needed for an effective transfer of stress and load distribution through out the interface, sometimes surface modification is needed. Surface modifications include (i) physical treat‐ ments, such as solvent extraction; (ii) physico-chemical treatments, like the use of corona and plasma discharges or laser, and UV bombardment; and (iii) chemical modifications, both by direct condensation of the coupling agents onto the cellulose surface and by its grafting by free-radical or ionic polymerizations [John 2008].Therefore different coupling agents which introduce chemical bonds between the matrix and fibre are involved (e.g. si‐ lane, isocyanate and titanate based products, alkaline treatment, acetylation, benzoylation, acrylation, maleated coupling agents, permanganate, etc) [51]. or methods of physical fibre treatments (e.g. surface fibrillation, plasma treatment) are used [George 2001]. An additional possibility is to impregnate cellulose fibres in monomer solution, follows the in-situ catalyst,

Different natural fibres species have been used for preparation of composites. Some exam‐

Unidirectional isora fibre reinforced polyester composites were prepared by compression moulding. Isora is a natural bast fibre separated from the *Helicteres isora* plant by a retting process. Untreated and alkali treated fibres were used for composite preparation and influ‐ ence of fibre content on composite properties was studied. It was observed that the pretreatment process conditions the fibre content for achieving optimum composites

Green composites were prepared from pineapple leaf fibres and soy-based resin. The addi‐ tion of polyester amide grafted glycidyl methacrylate (PEA-g-GMA) as compatibilizer in‐ creased the mechanical properties of composites. For preparing composites from pineapple leaf fibres in natural rubber fibres were pre-treated in NaOH solutions and benzoyl peroxide (BPO) of different concentrations. It was found that all surface modifications enhanced ad‐

Elephant grass (*Pennisetum purpureum*) is available abundantly in nature and is renewable. It is a tall grass growing in dense clumps along lake and riverbeds up to 3 m height. The diam‐ eter of the stem is 25 mm and leaves are 0.6 to 0.9 m long and about 25 mm wide. It repre‐ sents a potential and economic source compared to other natural fibers, however it is still underutilized, therefore K. Murali Mohan Rao with co-workers suggest fibres from the grass for reinforcement of polyester composites [55]. The density of the elephant grass fiberres is

This property is a good base for designing lightweight material from these fibres. The diam‐ eter of fibers is between 70 lm to 400 μm. Fibres mechanical properties are: tensile strengh is 185 MPA, tensile modulus is 7.40 GPa and elongation at break 2.50% [55]. The positive im‐

composites was determined and it was found that composite mechanical properies increase with percentage volume of fibers. Whereas the fibre extraction is simple, fibres are cheap and of appropriate properties elephant grass is also suitable for composites used for light‐

ples are: aspen fibre, abaca fibre, bagasse fibres, bamboo fibre (BF), banana fibre, etc.

heat or UV polymerisation [George 2001].

392 Advances in Agrophysical Research

mechanical properties [Joshy 2007].

hesion and tensile properties [Joshy 2007].

very low compared to other lignocellulose fibres.

weight structures preparation [55].

pact of elephant grass fibres on tensile strength of fiber reinforced

Lignocellulosic natural fibres have a very long tradition for textile materials manufacturing. Especially are these fibres important for technical textiles production. The series of plants yielding conventional textile fibres, e.g. flax, hemp, etc. has been recently extended by sever‐ al abundant plant species traditionally not-connected with fibres extraction. Of huge interest are especially agricultural wastes from cultures which are primary grown for food industry, and their plant wastes additionally containing fibres. Different fibres have been studied by several authors; their properties were determined and compared to the properties of con‐ ventional fibres. Regardless of the origin fibre cells are elongated sclerenchyma cells of dif‐ ferent geometrical characteristics, associated in fibre bundles with adequate mechanical properties. Several plant species were suggested for utilization from different geographic areas.

Natural fibres from conventional and unconventional source are considered as potential re‐ placement for man-made fibres in composite materials for their reinforcement. Natural fi‐ bres from annual plants have advantages of being low cost and low density and therefore they are light. They are a renewable material. In addition to, an important advantage of these materials is their biodegradability and low toxicity. It was confirmed by many re‐ searchers that properties of natural fibres of different origin improve composites properties, e.g. the mechanical properties of natural fibres - polymer composites are superior to those of the unreinforced materials.

## **Author details**

M. Sfiligoj Smole\* , S. Hribernik, K. Stana Kleinschek and T. Kreže

\*Address all correspondence to: majda.sfiligoj@uni-mb.si

University of Maribor, Faculty of Mechanical Engineering, Department for Textile Materials and Design, Maribor, Slovenia

[13] George J., Sreekala M. S., Thomas S. A Review on Interface Modification and Charac‐ terization of Natural Fiber Reinforced Plastic Composites. Polymer Engineering and

Plant Fibres for Textile and Technical Applications

http://dx.doi.org/10.5772/52372

395

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**Author details**

394 Advances in Agrophysical Research

M. Sfiligoj Smole\*

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*Edited by Stanisław Grundas and Andrzej Stępniewski*

The idea of this book was born due to the rapid increase of the interest in excellence of agricultural production in the aspect of both – the quality of raw material for food production as well as in the aspect of environment protection. Agrophysics is a field of science that focuses on the quality of agriculture as a whole i.e. the interaction between human and environment, especially the interaction between soil, plant, atmosphere and machine. Physics with its laws, principles and rules is a good tool for description of the interactions, as well as of the results of these interactions. Some aspects of chemistry, biology and other fields of science are also taken under consideration. This interdisciplinary approach can result in holistic description of processes which should lead to improvement of the efficiency of obtaining the raw materials to ensure a sufficient amount of food, safe for human health. This book could be regarded as the contribution to this description. The reader can find some basic as well, as more particular aspects of the contemporary agriculture, starting with the soil characteristics and treatment, plant growth and agricultural products' properties and processing.

Advances in Agrophysical Research

Advances in

Agrophysical Research

*Edited by Stanisław Grundas* 

*and Andrzej Stępniewski*

Photo by Milkos / iStock