**2.1 Fibrous layer extraction and characterizations: morphology, geometric dimensions, and mechanical behaviors**

The isolations of fibrous network layers from *Opuntia* (Cactaceae) trunk using a green process in relation to their multifunctional features and its use as a raw

material for novel ecological product was hardly studied for the first time by Mannai et al. [9]. **Figure 2** represents the fibrous networks (F-N) extraction steps which was performed manually and subsequently dried at room temperature for 7 days [9]. The obtained F-N layers (about 56 layers) represent a continuous phase (multidirectional fiber orientation angle) obtained from peripheral, middle, and central sections of the trunk, and **Table 1** displays their different characteristics.

**Figure 3** shows the microscopic photograph of *Opuntia* fibrous layer obtained from the brightfield microscope. The obtained microscopic views show clearly the presence of axial primary fibers cross-linked by secondary ones. The bifurcation of primary fibers forming an open woven texture with special network design is also worth noting. The dimensions and forms of fibers (primary and secondary) have been related to the distribution of the layers in the trunk.

The F-N properties towards bulk density, morphological parameters including width, angles of opening pores, and area of pores of both fibers (primary and secondary) before and after swelling test, as well as the mechanical properties are listed in **Table 1**.

The peripheral section of the trunk regroups the thicker F-N layers than other sections of the *Opuntia* trunk. The average fiber width increases from the central to peripheral trunk sections and varies proportionally to the thickness of the fibrous layer. The average pore angle increases proportionally with the F-N pore area [9]. The pore angle between the primary fibers for the central section (90°) is 36%

higher than the value obtained for primary fibers studied by Bouakba et al. [21] (about 57.5°); and for the secondary fibers, the pore angle of peripheral section is very acute (25°) compared to the other two sections (**Table 1**). The high obtained width with low pore area and low pore angle size of the outer layers of the trunk (peripheral section) confirm their dense structures which represent important fiber density with low porosity [9]. This finding is confirmed by the measured bulk density of these layers (see **Table 1**). The limited pore of the primary fibers of the

*Microscopic views of the surface of fibrous network layers from* Opuntia *(Cactaceae) [200 μm].*

*Novel Trend in the Use of* Opuntia *(Cactaceae) Fibers as Potential Feedstock…*

*DOI: http://dx.doi.org/10.5772/intechopen.92112*

peripheral layers, respectively [9]. It was higher than that of the fibrous layers

Otherwise, the swelling ratio and uptakes by peripheral layers are higher than the middle and central ones; this could be due to the internal morphological aspect of *Opuntia* fibers which represent a porous structure, the presence of large fibrovascular vessels [9, 25], and the high fiber density compared to those of the middle and central sections. The swelling of fibers can be explained by the hydrophilic nature of the Cactaceae plant, which can store a large amount of water [9]. Generally, the fiber hydration is noticed to be linked to the chemical composition of the fibers which have polar hydroxyl sites in their internal structures, which can form hydrogen bonds with water molecules [9]. The water-immersion process (applied for F-N extractions) could eliminate most of the water-soluble compounds (inorganic salts, ashes, coloring matter, etc.) from the fiber structure and favor the creation of void spaces, which could also explain the swelling of the fibers [9, 35]. The fiber water absorption can affect the geometric dimensions of *Opuntia* fibers by increasing the fiber width of both primary and secondary fibers (growth in size of the hydrated fibers) which can cause the decreasing of the pore areas and angles located between the primary and secondary fibers which may be explained by the occupation of the empty surfaces by the swelled fibers. Generally, highly hydrated fibers are characterized by their flexibility and ability to conform to fabric

The mechanical tensile and flexural behaviors of Cactaceae F-N were summarized in **Table 1**. It was found that the F-N tensile modulus increased from the central to the peripheral layers. The peripheral sections' tensile Young's modulus, uniaxial tensile strength, and deformation at breaks were found to increase compared to those obtained for the middle and central layers [9]. It is noted here that the peripheral layers have a favorably high Young's modulus compared to those of

The different flexural behaviors significantly increase from the central fiber layer to those of the peripheral F-N. This increase can be explained by the variation

) was 69% and 84.5% higher than that of the middle and

) studied by Bouakba et al. [21].

central section (18.58 mm<sup>2</sup>

**Figure 3.**

types [9].

**147**

other cactus fibers [33–37].

derived from the *O. ficus-indica* (11.3 mm<sup>2</sup>

#### **Figure 2.**

*Water-immersion process for fibrous networks layer extraction from the trunk of* Opuntia *(Cactaceae).*


#### **Table 1.**

*Apparent density, swelling ratio, and their effect on geometric dimensions before swelling (Bs) and after swelling (As) and mechanical strength properties obtained for fibrous networks obtained from peripheral, middle, and central sections of* Opuntia *(Cactaceae) trunk.*

*Novel Trend in the Use of* Opuntia *(Cactaceae) Fibers as Potential Feedstock… DOI: http://dx.doi.org/10.5772/intechopen.92112*

**Figure 3.** *Microscopic views of the surface of fibrous network layers from* Opuntia *(Cactaceae) [200 μm].*

higher than the value obtained for primary fibers studied by Bouakba et al. [21] (about 57.5°); and for the secondary fibers, the pore angle of peripheral section is very acute (25°) compared to the other two sections (**Table 1**). The high obtained width with low pore area and low pore angle size of the outer layers of the trunk (peripheral section) confirm their dense structures which represent important fiber density with low porosity [9]. This finding is confirmed by the measured bulk density of these layers (see **Table 1**). The limited pore of the primary fibers of the central section (18.58 mm<sup>2</sup> ) was 69% and 84.5% higher than that of the middle and peripheral layers, respectively [9]. It was higher than that of the fibrous layers derived from the *O. ficus-indica* (11.3 mm<sup>2</sup> ) studied by Bouakba et al. [21].

Otherwise, the swelling ratio and uptakes by peripheral layers are higher than the middle and central ones; this could be due to the internal morphological aspect of *Opuntia* fibers which represent a porous structure, the presence of large fibrovascular vessels [9, 25], and the high fiber density compared to those of the middle and central sections. The swelling of fibers can be explained by the hydrophilic nature of the Cactaceae plant, which can store a large amount of water [9]. Generally, the fiber hydration is noticed to be linked to the chemical composition of the fibers which have polar hydroxyl sites in their internal structures, which can form hydrogen bonds with water molecules [9]. The water-immersion process (applied for F-N extractions) could eliminate most of the water-soluble compounds (inorganic salts, ashes, coloring matter, etc.) from the fiber structure and favor the creation of void spaces, which could also explain the swelling of the fibers [9, 35].

The fiber water absorption can affect the geometric dimensions of *Opuntia* fibers by increasing the fiber width of both primary and secondary fibers (growth in size of the hydrated fibers) which can cause the decreasing of the pore areas and angles located between the primary and secondary fibers which may be explained by the occupation of the empty surfaces by the swelled fibers. Generally, highly hydrated fibers are characterized by their flexibility and ability to conform to fabric types [9].

The mechanical tensile and flexural behaviors of Cactaceae F-N were summarized in **Table 1**. It was found that the F-N tensile modulus increased from the central to the peripheral layers. The peripheral sections' tensile Young's modulus, uniaxial tensile strength, and deformation at breaks were found to increase compared to those obtained for the middle and central layers [9]. It is noted here that the peripheral layers have a favorably high Young's modulus compared to those of other cactus fibers [33–37].

The different flexural behaviors significantly increase from the central fiber layer to those of the peripheral F-N. This increase can be explained by the variation

material for novel ecological product was hardly studied for the first time by Mannai et al. [9]. **Figure 2** represents the fibrous networks (F-N) extraction steps which was performed manually and subsequently dried at room temperature for 7 days [9]. The obtained F-N layers (about 56 layers) represent a continuous phase (multidirectional fiber orientation angle) obtained from peripheral, middle, and central sections of the trunk, and **Table 1** displays their different characteristics. **Figure 3** shows the microscopic photograph of *Opuntia* fibrous layer obtained from the brightfield microscope. The obtained microscopic views show clearly the presence of axial primary fibers cross-linked by secondary ones. The bifurcation of primary fibers forming an open woven texture with special network design is also worth noting. The dimensions and forms of fibers (primary and secondary) have

*Invasive Species - Introduction Pathways, Economic Impact, and Possible Management Options*

The F-N properties towards bulk density, morphological parameters including

The peripheral section of the trunk regroups the thicker F-N layers than other sections of the *Opuntia* trunk. The average fiber width increases from the central to peripheral trunk sections and varies proportionally to the thickness of the fibrous layer. The average pore angle increases proportionally with the F-N pore area [9]. The pore angle between the primary fibers for the central section (90°) is 36%

width, angles of opening pores, and area of pores of both fibers (primary and secondary) before and after swelling test, as well as the mechanical properties are

*Water-immersion process for fibrous networks layer extraction from the trunk of* Opuntia *(Cactaceae).*

**Layer sections Peripheral Middle Central**

Thickness (mm) 2.3–3.75 1.5–2.15 0.41–1.26 Swelling ratio (%) 180 12 135 3 115 5

Width (mm) 1.7 3.2 0.64 0.9 1.3 1.25 0.5 0.64 1 1.3 0.4 0.62 Pore angle (°) 54 42 25 20 80.3 68.3 41.1 37 90.7 59 41 26

**Mechanical structure Tensile Flexural Tensile Flexural Tensile Flexural** Elastic modulus (GPa) 2.93 2.36 2.11 1.21 1.5 0.99 Strength (MPa) 14.3 9.7 9.7 8.8 5.2 7.36 Deformation at break (%) 5.04 6.18 1.7 4 1.4 2.9

*Apparent density, swelling ratio, and their effect on geometric dimensions before swelling (Bs) and after swelling (As) and mechanical strength properties obtained for fibrous networks obtained from peripheral,*

*middle, and central sections of* Opuntia *(Cactaceae) trunk.*

) 688–740 486–500 290–320

) 2.8 1. 2 1.33 0.5 5.74 2.6 0.9 0.45 18.5 8 0.5 0.3

**Primary Secondary Primary Secondary Primary Secondary Bs As Bs As Bs As Bs As Bs As Bs As**

been related to the distribution of the layers in the trunk.

listed in **Table 1**.

**Figure 2.**

Apparent density (kg/m<sup>3</sup>

**Geometric fiber dimensions**

Pore areas (mm2

**Table 1.**

**146**

similar to that found in *olive trimmings*, hardwood, softwood, vine stems, and some annual plants; and it was clearly higher than those obtained for carrot leaves, amaranth, banana stems, and *Posidonia oceanica* balls; but it was lower than the holocellulose content measured for date palm rachis, rapeseed straw, and Alfa stems. In general, the holocellulose content can provide information about the quality and quantity of the produced pulp and paper [52]. The measured α-cellulose rate was surprisingly higher in the trunk (around 53.6 wt%) than those obtained for cladode (21.6 wt%) and other plants (**Table 2**); it was slightly lower than in *olive trimmings*. Non-wood fibers are handled in ways specific to their composition, and it was also acceptable for papermaking applications and corresponded to paper with enhanced strength [22]. For this reason, the processes used for the delignification of lignocellulosic fibers from *Opuntia* were adapted in very soft conditions to mini-

*Novel Trend in the Use of* Opuntia *(Cactaceae) Fibers as Potential Feedstock…*

*DOI: http://dx.doi.org/10.5772/intechopen.92112*

A very small fraction of inorganic compound (5.5 wt%) was observed in the trunk compared to the total mineral amount in the cladode, *Posidonia oceanica balls*, and banana stems; however, it was comparable to the values estimated for date palm rachis; but it was significantly higher than the ash contents measured for rapeseed straw, *olive trimmings*, Alfa stems, *Eucalyptus citriodora* and vine stems, and some annual plants (**Table 3**). The lower fraction of minerals in lignocellulosic fibers from the *Opuntia* trunk presents a major advantage, and the utilized raw material was silica free, which was extremely important for papermaking [25]. The chemical composition of ash was determined with elemental analysis and reported for the first time by Mannai et al. [25]. The resulting proportions, as seen in **Table 3**, are compared with other plants (amaranth, *Astragalus armatus*, date palm rachis, and banana pseudo stems) and have shown that the elemental composition of mineral contents in *Opuntia* can vary considerably from one species to another. A very low fraction of silicon (0.2 wt%) observed for *Opuntia* than those of other raw materials led to good separation after chemical delignification. It is clear that calcium and magnesium are the predominant inorganic materials in the Cactaceae family (18.33 and 16.54 wt%). The high presence of calcium due to the calcium oxalate crystals present naturally in *Opuntia* species [9, 25, 26]. The mineral elements present in this raw material do not present any counterindication for chemical pulping, composite manufacturing, and the area of the extraction of various

mize degradation of the fibers and thus maximize pulp yield.

cellulosic derivatives.

**(%)** *Opuntia*

**Table 3.**

**149**

**(Cactaceae) [25]**

**Amaranth [43]**

*Astragalus armatus* **[53]**

*Ash composition of* Opuntia *(Cactaceae) trunk in comparison with data from previously published studies.*

Si 0.2 0.25 18.42 2.8 2.7 Ca 18.33 4.17 11 21.5 7.5 Mg 16.54 0.035 2.90 3.53 4.3 Fe 399 ppm — 0.29 240 ppm — Cu 192 ppm 0.01 ˂0.1 360 ppm — K 11.1 36.67 0.59 10.2 33.4 P 0.24 — 8.11 0.7 2.2 S 2.51 — 0.94 1.69 — C 3.84 — 4.1 1.5 — Na 0.6 — 1.8 6.79 —

**Date palm rachis [40]** **Banana pseudo stems [49]**

in geometric shape, layer thicknesses, fiber width, pore area distributions, fiber density, and bifurcation of primary fibers. It is worth noting that the flexural properties measured from the peripheral F-N layers are higher than those *O. ficusindica* studied by Greco and Maffezzoli [34] and are lower than those found for *Myrtillocactus geometrizans* studied by Schwager et al. [36]. As expected, the F-N structural and geometric aspects modify the tensile and flexural states in such a way that the maximum elastic modulus shifts in an axial direction. This shift can be explained by the primary fiber orientation, which is axially aligned in most of the regions in the direction of the principal stresses and primary fiber density, on a macroscopic level. Mannai et al. [9] and El Oudiani et al. [38] affirmed and confirmed that the major factors that influence the F-N tenacity and elongation and give good mechanical properties include (i) the hierarchical structure; (ii) the unit cell dimensions (large and thick-wall parenchyma cells, long fiber bundles, and the densely distributed periderm with thick cell edges); and, on a microscopic level, (iii) the degree of crystallinity and (iv) the chemical composition of the fibers.
