Biodegradable polymers obtained from natural polysaccharides

4 Biodegradable polymers obtained from natural polysaccharides 

3 Completion ofthe carbon cycle for renewable resource based materials, but not for petroleum based polymers (adapted from E. Chiellini, Proceedings of UNIDO-ICS International Workshop on Environmentally Degradable Polymers, Nov. 10-15, (1997), p. 32). 

Three-dimensional moldings from plant fibers (up to 80%) and polyolefins have been developed for applications as containers, shock absorbers, and heat insulators (Takasaki and Naito, 2002). Instead of the plant fiber, lignins have also been used as fillers with biodegradable polymers like poly(l-lactic acid), and the resulting blend was found to be promising due to the good material properties and economics (Li et al, 2003). 

A very novel study that could be of importance for the future is that of functionalized cellulose nanofibers and nanocrystals blended with biodegradable polyesters and acrylic acid polymers (Winter and Bhattacharya, 2003). The nanocrystals were found to be markedly superior reinforcing agents than wood flour, and their behavior was similar to the exfoliated clays in terms of reinforcing properties (Winter and Bhattacharya, 2003). These continued new developments bode well for the future role of plant fiber based composite materials. 

Native and modified industrial starches, and the advantages of specific industrial starches focusing on application in biodegradable packaging, have 

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Starch is a natural polymer available in large quantities from various sources. It can be obtained from different plants for which it is the most common source of polysaccharides of energetic reserve. In its native state, starch consists of semicrystalline granules insoluble in water. It is composed of two polysaccharides, branched amylopectin and essentially linear amylose. Starch is cheap, environmentally friendly and a completely biodegradable biopolymer, which has been also used to reinforce NR composites as filler. 

Chitosan is a water-insoluble, nontoxic, edible, biodegradable polymer (polysaccharide) that is obtained commercially from chitin by alkaline deacetylation [103]. Chitosan is the second most abundant biopolymer in nature after cellulose. Since chitosan is a polycationic polymer, its high sensitivity to moisture limits its applications. One way to overcome this drawback is to blend the material with humidity resistant polymers such has PLA. Suyatma et al. [104] combined hydrophilic chitosan with hydrophobic PLA (92% L-lactide and 8% mesolactide, Mw = 49,000 Da) by solution and film mixing, resulting in improved water barrier properties and decreased water sensitivity of the chitosan films. However, testing of mechanical and thermal properties revealed that chitosan and PLA blends are incompatible. 

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