Polyesters biodegradation mechanisms

Keywords biodegradable, biobased, polyester, polylactide, mechanical properties, dispersion, environmentally friendly. 

PBS is a semicrystalline polyester. Its mechanical properties such as tensile strength, impact strength, and flexibility and its transparency and biodegradability depend on the crystal structures and the degree of crystallinity to some extent. 

Poly(e-caprolactone) (PCL) is a synthetic polymer which has many advantages biodegradability mechanical properties similar to polyolefins hydrolysability similar to polyesters compatibility with many other polymers ease of melt... 

In this chapter, information on the different types of aliphatic polyesters, aliphatic-aromatic copolyesters and their biodegradable mechanisms will be disclosed. 

Polyesters, polycarbonates and poly(amino acids)s can be synthesized and chemically recycled by novel enzyme-catalyzed polymerization and degradation methods, and these technologies will be realized as a sustainable chemical industry in the near future (Fig. 14.26). Based on these considerations, extensive studies of the biodegradation mechanisms should be further carried out in detail. 

Biodegradable plastics have been used on an industrial scale since the end of the 1990s when BASF launched Ecoflex . This is a fossil-based, man-made polyester but yet is completely biodegradable due to its chemical structure. This structure is also the reason why Ecoflex combines excellent mechanical properties with the good processability of synthetic thermoplastics. Ecoflex is the preferred blend partner for bio-based and biodegradable polymers, which typically do not exhibit good mechanics and processability for film applications by themselves. Ecoflex therefore is a synthetic polymer that enables the extensive use of renewable raw materials (e.g., starch). 

At the end of the 1990s, BASF commercialized Ecoflex F, a completely biodegradable statistical copolyester based on the fossil monomers 1,4-butanediol (BDO), adipic acid and terephthalic acid (see Fig. 3). Ecoflex F combines the good biodegradability known from aliphatic polyesters with the good mechanical properties of aromatic polyesters. 

Ecoflex FS A Biodegradable Polyester with New Mechanical Properties and a High Content of Renewable Resources... 

Eilm products with good mechanical characteristics are only obtained if thermoplastic, plasticized starch has been used. If no plasticizer is used, biodegradable polymers with limited mechanical properties will be obtained. In this case, coextmsion with the base polyester or another polymer is the way to upgrade the mechanical and/or moisture barrier properties (for comparison see Table 6). 

Aliphatic polyesters occupy a key position in the field of polymer science because they exhibit the remarkable properties of biodegradability and biocompatibihty, which opens up a wide range of applications as environmentally friendly thermoplastics and biomaterials. Three different mechanisms of polymerization can be implemented to synthesize aliphatic polyesters (1) the ring-opening polymerization (ROP) of cyclic ketene acetals, (2) the step-growth polymerization of lactones, and (3) the ROP of lactones (Fig. 1). 

The polymerization of substituted lactones is an attractive strategy for extending the range of aliphatic polyesters and for tailoring important properties such as biodegradation rate, bioadherence, crystallinity, hydrophilicity, and mechanical properties [100]. Moreover, the substituent can bear a functional group, which can be very useful for the covalent attachment of drugs, probes, or control units. 

Aliphatic polyesters are the most economically competitive of the biodegradable polymers moreover, synthetic polyesters are expected to be degraded nonspecifi-cally by lipases. Although these polyesters are biodegradable, they often lack good thermal and mechanical properties. On the other hand, aromatic polyesters - such as... 

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