Challenges in primary processing of LFBC

Three major factors influencing the behavior of LFBC are depicted in Fig. 9.4. Thermal, physical, and chemical behavior of biopolymer matrix and lignocellulosic fibers play a significant role in determining the characteristics of biocomposites. As observed from Table 9.1 and Table 9.2, the physical properties as well as chemical

Natural Fiber-Reinforced Biodegradable and Bioresorbable Polymer Composites

166

Life cycle of lignocellulosic fiber-reinforced biocomposites

Figure 9.3 Life cycle of lignocellulosic fiber-reinforced biocomposites.

Major factors influencing behavior of biocomposites

Figure 9.4 Major factors influencing behavior of biocomposites.

composition of lignocellulosic fibers vary significantly for the same type of fiber. Lignocellulosic fibers exhibit variation in properties depending upon geographical regions of plant cultivation, age of plant, extraction process, the part of the plant from which the fiber is extracted, etc.

Fiber—fiber as well as fiber—matrix interactions within LFBC are crucial. Sometimes lignocellulosic fibers within the biocomposite do not act as effective reinforcement due to poor adhesion at the fiber—matrix interface. Lignocellulosic fibers, as discussed above, are comprised of hemicellulose, lignin, pectin, waxes, and cellulose. The presence of these noncellulosic substances on the fiber surface hinders an adequate fiber—matrix interaction and affects the wettability of fibers by the matrix (Petinakis et al., 2013). Lignocellulosic fibers are also prone to agglomeration due to strong interfiber hydrogen bonding. These fibers being hydrophilic have the tendency to absorb moisture, which in general can vary between 5 and 10% by weight. The presence of moisture during processing of LFBC can lead to dimensional variations,

Table 9.2 Properties of some lignocellulosic fibers and conventional fibers used in polymer composites

Lignocellulosic

fiber

Tensile strength (MPa)

Young’s modulus (Gpa)

Elongation

(%)

Density

(g/cm3)

Abaca

400

12

3—10

1.5

Flax

345—1500

27.6—80

1.2—3.2

1.4—1.5

Cotton

287—597

5.5—12.6

3—10

1.5—1.6

Jute

393—800

10—30

1.5—1.8

1.3—1.46

Kenaf

930

53

1.6

1.45

Coir

175—220

4—6

15—30

1.2

Bagasse

290

17

1.25

Sisal

400—700

9—38

2.0—14

1.33—1.5

Bamboo

140—230

11 — 17

0.6—1.1

Ramie

220—938

44—128

2.0—3.8

1.5

Pineapple

400—627

1.44

14.5

0.8—1.6

Hemp

550—900

70

2—4

1.48

Carbon

4000

230—240

1.4—1.8

1.4

E-glass

2000—3500

70

2.5—3.0

2.5

Aramid

3000—3150

63—67

3.3—3.7

1.4

Source: Faruk et al., 2012; Mohanty et al., 2000; Ramamoorthy et al., 2015.

porosity defects, and biopolymer degradation. Lignocellulosic fibers are prone to biological degradation due to the presence of carbohydrates present within the fiber structure. Exposure to ultraviolet radiation also results in biodegradation of lignin present in the lignocellulosic fibers. Lignocellulosic fibers are also prone to thermal degradation during processing. Thermogravimetric analysis of dry lignocellulosic fibers reveal that their thermal degradation is a typical two-stage process. The first stage of thermal degradation occurs between 190 and 360°C, wherein hemicellulose (190—280°C) and cellulose (280—360°C) degrades (Chaitanya and Singh, 2016a). Thermal degradation of lignin (second stage) occurs beyond 360°C. As the chemical composition of each type of lignocellulosic fiber differs, knowledge of their thermal degradation behavior prior to processing becomes imperative.

Apart from fiber—fiber and fiber—matrix interactions, the processing technique used and the interaction of tooling with the fiber—matrix melt mixture during processing also play significant roles in the behavior of the developed biocomposites. During processing fibers might experience high shear rates resulting in severe fiber attrition. Control of fiber attrition rate is one of the major challenges associated with the processing of biocomposites. The processing route followed also affects the fiber orientation and distribution behavior within the developed biocomposite. Fiber orientation and distribution influences the mechanical behavior of the biocomposites significantly. However, there is no set of standard guidelines available for the selection of processing route, preprocessing technique, and processing parameters to achieve the desired properties in the biocomposite.

 
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