**2.2 Fibers supply chain**

The emerging trends and opportunities for natural fibers are broadening due to desirable attributes such as biodegradability, eco-friendly, sustainability and energy efficiency. Sustainability supply chain of natural fibers is assessed and rated based on the following criteria: water usage, CO2 emissions, cost, availability and any other impacts [16]. Moreover, in the fashion industry, businesses tend to identify the impacts of fibers on brands that contribute to the most impressive reduction in their impact on environmental footprint. Some of the preferred fibers include Linen, Tencel, Bamboo, Recycled Polyester, Recycled Wool, Cork, Organic Cotton and Hemp.

Perhaps the most important factor is the understanding of the entirety of the supply chain of natural fibers and the stages that contribute to having the biggest impacts. Consequently, a map of biodiversity quantitative impact indicators that help the companies determine where to focus their efforts in supply chain management to alleviate natural fiber environmental footprint was developed.

Nowadays, only 23% of companies take into account their environmental footprint when choosing their suppliers and between 40 and 60% of a company's environmental footprint actually comes from its supply chain. Hence, in developing the natural fiber supply strategy, it is critical to understand the role of supply chain management and the associated impacts of environmental footprint. Network analysis, optimization of transhipment costs and decision analysis on optimal solutions to minimize both the supply chain cost and environmental footprint are essential toolkits in the advancement and promotion of natural fibers industry.

Moreover, over the last two decades, the trends in production of plant fibers have been declining due to popularity of synthetic fibers as well as adverse drought conditions. The fiber production plants spread across all continents of the globe. **Table 1** illustrates the trends of different sources of fibers, production capacities and where they are produced.

In 2018, world production of all apparel and textile fibers reached 110 million tons, with natural fiber production estimated at 32 million metric tons. Natural fibers accounted for 29% of the total world fiber production capacity, with most of annual yield variation linked to dry weather conditions. Moreover, the decline in the amounts of natural fibers in total fiber production in the last decade is due to the exponential growth in polyester production, whose demands were triggered by the fast-fashion apparel industry.

## **2.3 Plant fibers' extraction methods**

## *2.3.1 Methods commonly used*

Cellulosic fibers originated from plants and trees such as cotton, flax, hemp, jute, ramie, kapok, coir and bamboo are termed natural PFs. Such fibers are derived from


#### **Table 1.**

*Fiber sources, country and annual production of plant fibers.*

various parts of plants including leaves, stems (bast fibers), fruits and seeds. Because all natural PFs are made up of mainly cellulose, they are categorized as 'natural cellulosic fibres', which may consist of one plant cell or an aggregate of cells bounded together by non-cellulose materials. Major commercially used PFs include: seed fibers (cotton, coir, kapok), bast fibers (flax, hemp, ramie, bamboo, banana), leaf fibers (sisal, kenaf, pineapple, abaca). To date, bast fibers are produced and utilized to manufacture a wide array of traditional and novel products including ropes, nets, carpets, mats, brushes, mattresses, paper and board materials. Generally, PFs are classified into two groups, namely soft fibers and hard fibers. Soft fibers are obtained through labour-intensive processes. It involves the following steps: selection of plant and harvesting the plant, partial drying, pounding with stone mallet, scraped with devices similar to comb to clean the fibers, wash the fibers, dry in the sun and finally

### *Extraction, Applications and Characterization of Plant Fibers DOI: http://dx.doi.org/10.5772/intechopen.103093*

comb the fibers. Subsequently, the fibers are ready to be spun or twisted into thread or cord. Soft fibers are often used to make ropes, string, nets, bags, and hammocks.

Hard fibers are processed through successive phases of cutting, drying, cleaning, and soaking before they can be woven. They are strong and naturally flexible fibers, thus suitable and utilized to make furniture, birdcages, toys, baskets, and mats.

**Figure 1(a)** and **(b)** shows the matured flax plants grown under a controlled greenhouse environment and a setup of bench-scale trouph for water retting of flax stems [17].

Historically, most plant fibers were extracted manually, supplemented by natural retting. Evidently, this process is tedious, time-consuming and the extracted quality of fibers depends on the skill of the labourer. Nowadays, these fibers are extracted by chemical, mechanical or biological methods.

Akubueze et al. [18], reviewed the chemical techniques employed to extract fibers from natural plants, which include alkali, acid and other reagents. The typical mechanical extraction methods involve the use of stripping the plant stem (typically known as Bacnis and Leonit processes). The latest mechanical extraction methods utilize the decortication process, whereby the plant stems are crushed between two drum rollers to obtain the fibers after removing the pulp. The use of decorticators increase fiber production by 20–25 times compared with the manual process. With biological processes, both consortium of microorganisms and enzymes are utilized to efficiently extract fibers from plant stems.

Overall, the mechanical extraction is incapable to remove the natural binding material (pectin) from the interspaces of the fibers within fiber bundle, chemical extraction is capable to remove the pectin within the fiber bundle but causes significant environmental pollution, whereas the biological extraction method provides increased fiber yield, with minimum detrimental effects to the environment.

According to the Centre for Learning and Teaching in Art and Design (CLTAD), bast fibers, for example, are generally obtained from the phloem, an inner skin of a plant. These fibers support the cells of the phloem to provide strength to the stem. During processing, the fibers need to be separated from both the interior (xylem) and exterior (epidermis) which is the outermost layer of cells. The processes for separating these fibers from plant stalks are known as retting and decortication. Bast fiber

**Figure 1.**

*Greenhouse controlled experiments for flax plants [17]. (a) Matured flax plants in Phytotron and (b) matured flax stems undergoing water retting.*

bundles are typically several feet long, composed of overlapping cellulose fibers and a cohesive gum (or pectin), which strengthens the stem of the plant. The processes with which the bast fibers are separated significantly influence the quality of fibers as there are many stages involved. Kumar et al. [19], reported that the processing of sustainable fiber starts with fiber extraction and yarn production followed by bleaching, dyeing, softening, printing and drying.

Moreover, the process that separates the fibers into smaller bundles and elementary fibers is known as retting. Fiber retting is a key process and is an important criterion that most industries value because it determines the ultimate properties of the fibers produced. Traditional retting methods include dew and water retting. Dew retting depends on ambient weather conditions, typically takes several weeks and hence the quality of fibers produced varies considerably. Similarly, water retting has been a primary method for low-cost production of bast fibers. The process involves submerging bast straws into water and then the decomposition of the pectic is effected by the activity of anaerobic microorganisms. The quality of retting is assessed by the weight, degumming rate and the fiber properties. The faster rate of weight loss is preferred, the degumming rate is evaluated as the percentage change in pectin content of phloem regions in the raw plant to those in water-retted plant, whereas the desired fiber properties include color, linear density and tensile strength. Ruan et al. [20], reported that water retting improved both whiteness and fineness as well as the mechanical properties of fibers.

Although water retting is capable to produce good quality fibers, the inherent long duration of 7–14 days and associated odor has made it less attractive. The retting period can be reduced to 100 h by using warm water (35°C), but high water consumption and unpleasant odor limit its use to some developing countries. Retting is the process by which pectin gets dissolved or softened from the fiber bundles and separates the fibers from stems through microbial activity. As such, a group of Clostridium microorganism is commonly known to play a significant role in the process by hydrolysing the pectin as it produces pectinase enzyme. These enzymes initially attack the cambium layer and then the other thin-walled cells in the cortex. This phenomenon takes place in most plant bast fibers as they have similar long filament structures, except those from cotton fibers which are single plant cells. As an example, for the retting process conducted in a bench-scale trouph under no-flow process water conditions, there were distinct features on how the fibers separate from bundles. **Figure 2(a)** and **(b)** show the scanning electron microscopy of the unretted and retted fibers of flax.

**Figure 3(a)** shows that cellulosic fiber production accounted for 6% of the total in 2018, synthetic filament accounted for 45% and synthetic staple 20%. Similarly, **Figure 3(b)** depicts that cotton accounted for 81% of natural fiber production by weight in 2018, jute accounted for 7%, while coir and wool each accounted for 3%.

The synthetic fibers are dominated by polyester, which accounts for nearly 90% of world filament production and 70% of world synthetic staple production. The remaining synthetic fibers are composed mostly of nylon, acrylic and polypropylene.

Perhaps a key factor is to consider the role and contribution of human capital and household social economics. Employment statistics in natural fiber industries is difficult to estimate because households do not engage in consistent annual production. In Ref. [21] it is estimated that about 60 million households worldwide are engaged in natural fiber production, and hence the total employment, reflecting both full-time year-round employment and part-time or seasonal employment, is around 300 million, which represents about 4% of the world's population.

*Extraction, Applications and Characterization of Plant Fibers DOI: http://dx.doi.org/10.5772/intechopen.103093*

**Figure 2.**

*A SEM shows the microstructure of flax fibers (a) before retting and (b) after the retting process [17].*

**Figure 3.** *World total fiber production and natural fiber production [21].*

Natural fibers possess superior advantages over synthetic fibers including widespread availability, low cost, low density, moderate strength modulus to weight ratio, high acoustic damping, low manufacturing energy consumption, low carbon footprint and biodegradability. Consequently, there are emerging concerted research initiatives that explore and promote the understanding of the characteristics of natural fibers [15, 22].

### *2.3.2 Other methods*

As discussed in Section 2.3.1 above, dew and water retting are the most common processes for fiber retting. Plant fibers can also be extracted using chemical and enzymatic retting, which provide better control than dew and water retting. Unfortunately, chemical retting while effective in extraction of fibers, causes significant pollution challenges due to higher amount of chemicals utilized. For the chemical extraction methods, alkali and selected reagents have been employed. Alkali treatments promote

the fibrillation, whereby the composite fiber bundle is degraded into smaller fibers. Sodium hydroxide (NaOH) is popularly used to reduce the fiber roughness, but also produces good quality fiber. Reagents such as sulfuric acid, hydrogen peroxide, protease and sodium citrate can also be used for chemical extraction [23].

Similarly, enzymatic retting is relatively expensive despite its shorter retting time, yet it produces acceptable fiber quality and is advantageous over other retting processes. In the enzymatic method, the selection of enzymes depends on the type of substrate, composition, size and lignin content. The most common enzymes utilized are cellulases and pectinases. Cellulase enzymes enhance the fiber smoothness by removing fibrils from the outer layer. As such, this results in reduction in the mechanical properties due to the damage caused in the fibers. Pectinases remove the inter-lamellar pectin, which is a natural adhesive compound between fibers.
