Agro-residual fibers

Chapters 2-10 discuss in detail the different properties of natural lignocellulosic fibers, their processing and fabrication of polymer composites. Chapter 11 summarizes the structure, chemistry and properties of different agro-residual fibers such as wheat straw corn stalk, cob and husks okra stem banana stem, leaf, bxmch reed stalk nettle pineapple leaf sugarcane oil palm bunch and coconut husk along with their processing. 

Exploiting natural fibers from new sources, however, presents the new question of whether these fibers mechanical, morphological, and thermal characteristics would let them act as effective reinforcement elements for utilization in composites [15]. This necessitates the close study of agro-residual fibers. 

This chapter has been written in order to investigate agro-residual fibers in terms of their performance as reinforcing elements for polymer composites. This study excludes agro-residual fibers which replace wood fibers as fillers or are suitable for pulping applications rather than reinforcing polymer composites due to their small dimensions. Nevertheless, several representative examples are given. The chapter is... 

Agro-Residual Fibers as Potential Reinforcement Elements 235... 

Figure 11.1 Examples of some agro-residual fibers, (a) okra fiber (From 1. M. De Rosa et al. Composites Science and Technology, 2011 [14]. With Permission from Elsevier) (b) banana fiber (From A. V. R. Prasad, K. M. Rao, G. Ragavinirasulu, Indian Journal of Fibre and Textile Research, 2009 [30]. With permission from Indian Journal of Fibre and Textile Research)-, (c) corn husk fiber [31].

Table 11.1 List of Academic Literature on Agro-Residual Fibers, Extraction Methods, Studied Characterics. 

Waxes which constitute the secondary components together with pectin consist of different types of alcohols [8] that are water soluble and dissolve in acids [63]. Different kinds of agro residual fibers include varying amoimts of these chemical consitutents. Table 11.2 gives the chemical composition of agro residual fibers and compared it with conventional plant fibers. 

It is essential to know the fiber characteristics in order to expand the use of agro-residual fibers in biocomposites and to improve their performance [3]. 

Table 11.2 Chemical Composition of Agro-Residual Fibers Compared to Some Selected Conventional Fibers.

Mechanical properties of some agro residual fibers are compared with important bast, leaf and seed fibers in Table 11.4. 

De Rosa etal. [14] reported that the tensile tenacity and modulus of okra fibers presented a two-parameter Weibul distribution. They also reported a decrease in tensile tenacity and modulus with increase in okra fiber diameter, as Bodros and Baley [37] found for nettle stalk fibers. Having brittle structures, okra and nettle stalk fibers present straight stress-strain curves [14,37]. Mechanical properties of agro-residual fibers are listed in Table 11.3. 

Agro-residual fibers, similar to other plant fibers have moderate microbial resistance and thus they tend to decay. Microbial resistance is especially important during shipment and long-term storage [56], Microbial resistance of agro-residual fibers can be enhanced by increasing hydrophobicity [72]. 

The hydroxyl groups present in the cell wall, which are responsible of the moisture absorption problem, renders agro-residual fibers very reactive. This characteristic allows the fibers to undergo chemical modifications to improve durability and dimensional stability performance [6]. Some physical properties of agro-residual fibers are listed in Table 11.4 and characterization methods of agro-residuals fibers are given in Table 11.5. 

Alkalization leads to the loss of hemicellulose and lignin resulting in weight loss of fibers and increase in cellulose content. Properly applied alkalization enhances the tensile performance and thermal resistance of agro-residual fibers. Increasing the concentration, duration and temperature of alkalization treatment results in a decrease in fiber diameter. However, if the applied treatment is too strong that leads to strength loss of fibers [ 11 ]. Mahato et al. [55] reported decrease of crystallinity upon alkalization of coir fibers. 

Table 11.6 list of Characterization Methods Applied on Agro-Residual Fibers. 

The utilization of enzymes in the natural fiber modification field is rapidly increasing. This trend may be due to the environmentally-friendly nature of enzyme treatments as the catalyzed reactions are very specific and the performance is very focused [3]. Several enzymes have been used in order to enhance the effectiveness of extracting fibers from the agro-residue or fine-tune the properties of extracted fibers such as lowering their diameter. Xylanases, cellulases, pectinases are the enzyme types that have found more use in agro-residual fiber modification [12,13,38]. 

There have been limited amount of research devoted to enzymatic treatment of agro-residual fibers [12,13,58]. When comparing different extraction procedures including water retting, alkalization and enzyme treatment, Yilmaz [13] foimd the strongest and finest corn husk fibers to be produced by a fiber production route of water retting followed by enzyme treatment. 

N.D. Yihnaz, Agro-residual fibers as potential reinforcement elements for biocomposites, in Lignocellulosic Polymer Composites Processing Characterization, and Properties, Wiley-Scrivener, 2014. 

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