Biodegradability, wood-polymer composites

JL HE POLYMERIZATION OF VINYL MONOMERS in the void spaces of bulk wood results in wood—polymer composites of increased strength properties and dimensional stability see Chapter 6). Because the different environmental conditions expose in-service timber to attack by numerous wood-deteriorating microorganisms, it is desirable to enhance the biodegradation resistance of wood, with simultaneous improvements in mechanical behavior. This chapter summarizes the formation of bioactive wood-polymer composites (1-4). The basic approach is still in situ polymerization of vinyl monomers in wood, with the appropriate choice of a bioactive, toxic, functional group incorporated in the monomer, and with other modifications based on wood-polymer reactions. 

It is difficult to make a distinct classification of biodegradable polymers. Many authors have classified them according to their origin as natural or synthetic polymers. Both of these are subdivided into different classes based on the main linkages present in their structure. Thus completely biodegradable natural polymer subclasses include polysaccharides, polypeptides, polyesters, lipids, natural rubber and natural composites (wood). Partially biodegradable synthetic polymer subclasses include polyesters, polyur eas, polyurethanes, polyamides, poly( vinyl alcohol) and poly (ethylene glycol). 

Due to the increasing commercial interest for natural fiber-reinforced polymer composites as well as demands for environment friendly materials, the development of fully biodegradable plant fiber-PLA composites is on the rise. Different natural plant fibers have been employed with PLA to produce composites. The most studied natural fiber reinforcements for PLA were kenaf [10, 21-23], flax [24, 25], hemp [26], bamboo [27], jute [28], abaca [29], pineapple leaf [9], and wood fibers (WF) [30, 31]. In addition to these conventional plant fibers, recently reed fibers have been used for preparation of PLA composites [31]. 

Hazarika A, Maji TK (2014c) Strain sensing behavior and dynamic mechanical properties of carbon nanotubes/nanoclay reinforced wood polymCT nanocomposite. Chem Eng J 247 33-41 Hazarika A, Maji TK (2014d) Thermal decomposition kinetics, flammability, and mechanical property smdy of wood polymtar nanocomposite. J Therm Anal Calorim 115 1679-1691 Hazarika A, Mandal M, Maji TK (2014) Dynamic mechanical analysis, biodegradability and thermal stability of wood polymer nanocomposites. Compos Part B 60 568-576 Hetzer M, Kee D (2008) Wootl/polymer/nanoclay composites, environmentally friendly sustainable technology a review. Chem Eng Res Des 86 1083-1093 Hill CAS, Abdirl KHPS, Hale MD (1998) A study of the potential of acetylation to improve the properties of plant fibres, frrd Crops Prod 8 53-63 Hoffmann MR, Martin ST, Choi WY, Bahnemann W (1995) Environmental application of semiconductm photocatalysis. Chem Rev 95 69-96 Huda MS, Drzal LT, Misra M, Mohanty AK (2(K)6) Wood-fiber-reinforced poly(lactic acid) composites evaluation of the physicomechanical and morphological properties. J AppI Polym Sci 102 4856-4869... 

In this chapter, several classes of biopolymers are discussed. First, biobased and biodegradable polymers are considered, together with wood plastic composites (WPCs) (Section 8.2). A field of increasing importance is the application of polymers in medicine, particularly their use in the human body (Section 8.3). 

These materials are from renewable sources and are often made from plant materials that can be grown year after year and should come from agricultural nonfood crops. Biodegradable polymers are broken down into CO 2 and water by microorganisms. Although biopolymers may be able to help solve the disposal problems of current plastic packaging, it is not clear if they can really deliver on this promise and whether there is possible competition with the food chain. Cellulose is the most common biopolymer and organic compound on Earth. Other examples are starch, PHB (polyhydroxybutyrate), natural fibers, silk, and wood plastic composites (WPC). 

Lu, X., Zhang, M.Q., Rong, M.Z., Shi, G., and Yang, G.C. (2003) All-plant fiber composites II. Water absorption behavior and biodegradability of unidirectional sisal fiber reinforced benzylated wood. Polym. Compos., 24, 367-379. 

Cellulose, which is more fibrous than wood flour, is used as a filler for urea and melamine plastics. Melamine dishware is a laminated structure consisting of molded resin-impregnated paper. Starch and soybean derivatives are biodegradable, and the rate of disintegration of resin composites containing these fillers may be controlled by the amount of these fillers present in polymers. 

---