Degradable polymers, natural synthetic

Membranes used for the pressure driven separation processes, microfiltration (MF), ultrafiltration (UF) and reverse osmosis (RO), as well as those used for dialysis, are most commonly made of polymeric materials. Initially most such membranes were cellulosic in nature. These ate now being replaced by polyamide, polysulphone, polycarbonate and several other advanced polymers. These synthetic polymers have improved chemical stability and better resistance to microbial degradation. Membranes have most commonly been produced by a form of phase inversion known as immersion precipitation.11 This process has four main steps ... 

The material chosen to support Ti02 must withstand photocatalytic degradation. This condition excludes polymers, either synthetic (except those containing only C-F bonds) or natural, unless these materials can be used... 

The physical and mechanical properties of the degradable polymers can be controlled by blending with synthetic or natural polymers and copolymerization. 

In Chapters 15 and 16 the modification and degradation of respectively synthetic (e.g. PET, polyamides) and natural polymers (e.g. polysaccharides) are reviewed. It becomes obvious that biocatalytic modifications can offer advantages over chemical modifications therefore building a bridge between traditional polymerization techniques and enzymatic polymerizations. 

Several examples of biodegradable blends comprising either natural or synthetic degradable polymer are listed, respectively, in Tables 16.11 and 16.12 [Utracki, 1998]. 

As a partial solution to the global issue of plastic waste, in recent years much interest has been devoted to the formulation of environmentally degradable plastic materials. In particular the use of natural polymers presents several advantages such as biodegradability, utilizing of renewable resources, recyclability. At the same time water sensitivity and degradability of natural polymers limit their possible applications. Consequently bioplastics cannot replace synthetic plastics in every application but they can result appropriate in specific products especially for those applications in which recovery of plastics is not economically feasible, viable and... 

Abiotic hydrolysis is the most important reaction for initiating the environmental degradation of synthetic polymers (Gbpferich 1997) such as PE (Gu 2(X)3), PTT (Heidary and Gordon 1994), PLA, and their copolymers (Hiltunen et al. 1997 Nakayama et al. 1996). The degradation of most synthetic plastics in nature is slower than that of natural polyesters. This process involves environmental factors, followed by the action of microorganisms in their surroundings (Albertsson et al. 1994 Cruz-Pinto et al. 1994). 

Biodegradable composite materials are materials obtained from nature or by synthetic methods, whose chemical bonds can be cleaved by bacteria or other microorganisms present in the biosphere. Composites of biodegradable polyester can be classified as composites made of polyester reinforced by carbon and glass fibers, natural fibers, and degradable polymers. 

As discussed above, the results of a series of experiments carried out both outdoor and indoor indicate that chitin and chitosan are degradable polymers and very beneficial natural resources. But the elongation of chitin was impossible and the maximum draw ratio of chitosan film was two times. To extend further utilities of chitosan as industrial materials, their poor mechanical properties must be improved. As one of approaches to increase mechanical properties, drawing of chitosan and PVA blend films are carried out, since PVA is one of synthetic polymers with degradation and easy drawability. 

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