Natural fibers hemicellulose

Lignocellulosics are three-dimensional, polymeric composites made up primarily of cellulose, hemicelluloses, and lignin. Table 1 shows the chemical composition of several different types of natural fibers. It is interesting to... 

These are covered with a sheath of para-crystaUine polyglucosan material surrounded by hemicellulose [29]. In most natural fibers, these micro-fibrils orient themselves at an angle to the fiber axis called the micro-fibril angle. The ultimate mechanical properties of natural fibers are found to be dependent on the microfibrillar angle. Gassan et al. have performed calculations on the elastic properties of natural fibers [30]. 

Cellulosic fiber reinforced polymeric composites find applications in many fields ranging from the construction industry to the automotive industry. The reinforcing efficiency of natural fiber is related to the namre of cellulose and its crystallinity. The main components of natural fibers are cellulose (a-cellulose), hemicelluloses, lignin, pectins, and waxes. For example, biopolymers or synthetic polymers reinforced with natural or biofibers (termed biocomposites) are a viable alternative to glass fiber composites. The term biocomposite is now being applied to a staggering range of materials derived wholly or in part from renewable biomass resources [23]. 

This is one of the most important natural fibers. It is produced in India, Bangladesh, Thailand, Vietnam, and other countries. It contains 56-64 wt% cellulose, 29-25% hemicellulose, 11-14% lignin, and a small proportion of fats, pectin, ash, and waxes. Application of jute fiber in RPs with matrices of TS resins such as unsaturated polyester or vinyl ester resins has been widely studied. To date the poor adhesion to hydrophobic TPs, such as polyethylene and polypropylene, has to date limited application in TPs. 

Jute fiber (JF) has been popular since the start of this century, principally as a filler and as a reinforcement with TP matrices. These low-cost natural fibers consist mainly of cellulose and hemicellulose chains running parallel to the fiber direction and lignin. High performance, average unidirectional-oriented tensile strength (T ) is 500 MPa, elastic modulus (E) is 40 GPa, and elongation is 1.7%. Other fiber properties are density 1.45 and weight 0.21 g/m. 

Natural fiber Type of fiber Density Composition (%) Cellulose Hemicellulose Lignin Degradation peak temperature (°C) (First derivative) (Ref.) Tensile strength (MPa) Young s modulus (GPa)... 

Chemical decomposition of hemicellulose and lignin, causing embrittlement and decreasing reinforce capacity of natural fibers because break the link between elementary fibers [31,40,41]. Chemical decomposition of these compounds, is caused because they are solubilized in the calcium hydroxide and in other alkalis produced during hydration reaction. 

Taking into account their stoichiometry, both reactions are similar and produce the same products in different proportions [30, 65, 66]. Hydrated calcium silicate (3Ca0.2Si0, AY[ O) is the principal hydration product and is the component that provides resistance to cement matrix and is formed on the surface of cement particles. The calcium hydroxide (Ca(OH)2) is responsible for the pH 12 of the cement matrix and is critical in protecting the steel reinforcement against corrosion however it deg-radates the hemicellulose and lignin of natural fibers decreasing the properties of the composite material. 

The structure and chemical makeup of natural fibers varies greatly and depends on the source and many processing variables. However, some generalizations are possible. Natural fibers are complex, three-dimensional, polymer composites made up primarily of cellulose, hemicellulose, pectins, and lignin [12]. These hydroxyl-containing polymers are distributed throughout the fiber wall. The major chemical components of selected natural fibers are listed in Table 11.1. 

Chemical or physical treatments can be applied to natural fibers to modify their surface (polar groups) and/or their composition (lignin, cellulose and hemicellulose content). Several treatments may enhance the interaction between the phenolic matrix and natural fibers, such as mercerization, succinic anhydride, ionized air, and others (Leao, 1997 Mu et al., 2009 Trindade et al., 2008). Barreto et al. (2010) prepared composites of a phenolic matrix. 

Plant based natural fibers are lignocellulosic, consisting of cellulose micro fibrils in an amorphous matrix of lignin and hemicellulose. To improve the incorporation of natural fibers into polymers and to have higher fiber/matrix interfacial adhesion, natural fibers can be altered by different physical and chemical treatments. 

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