Biodegradable polymers physical properties

Poly (butylene adipate-co-terephthalate) (PBAT) is an interesting polymer [116,117] and has attracted more attention. PBAT is also a biodegradable poljmier, which has proper viscosity and elasticity. Moreover, the balance of biodegradability (e.g., life time) and its physical properties (e.g., thermal and mechanical properties) can be adjusted by controlling the molar ratio of comonomers in the copolymer [118,119]. It has been reported that the aliphatic/aromatic copolyester with aromatic units within the range of 35 - 55 mol% offers an optimal compromise of its biodegradability and physical properties. 

The extent of biodegradation is usually measured using respirometric methods, which detect CO2 evolution. Other parameters to assess are the rate of MW loss, the loss of polymer physical properties (e.g., tensile strength per ASTM standard D3826-98 [5]), the rate of increase of the microbial culture colony size in contact with the material, O2 uptake (e.g., biochemical oxygen demand) and radioactive tracer techniques that use labelling. 

PHAs can consist of a diverse set of repeating unit structures and have been studied intensely because the physical properties of these biopolyesters can be similar to petrochemical-derived plastics such as polypropylene (see Table 1). These biologically produced polyesters have already found application as bulk commodity plastics, fishing lines, and for medical use. PHAs have also attracted much attention as biodegradable polymers that can be produced from biorenewable resources. Many excellent reviews on the in vivo or in vitro synthesis of PHAs and their properties and applications exist, underlining the importance of this class of polymers [2, 6, 7, 12, 26-32]. 

The environment is an important factor affecting the rate and degree of biodegradation of polymer substrates. The other key aspects determining biodegradability are related to the chemical composition of the polymer. The polymer chemistry governs the chemical and physical properties of the material and its interaction with the physical environment, which in turn affects the material s compostability with particular degradation mechanisms. 

While, synthetic biodegradable polymers are more costly than either starch-based or PLA polymers, they often have better physical and mechanical properties than types of biodegradable polymers based on renewable resource. These include higher strength, better clarity, better barrier properties and a greater ease of processing. 

Japan s Dainippon Ink and Chemicals (DIC) has pursued the alternate approach of combining polyester and PLA properties into one polymer. DIC developed a biodegradable copolymer called CPLA based on a co-polyester plus lactic acid. A higher ratio of co-polyester increases flexibility, while more lactic acid adds stiffness. One version of CPLA is reported to combine PS-like clarity with PP-like physical properties. 

Alicagenes eutropha produces a copolymer of hydroxyvalerate and hydroxybutyrate when deprived of key nutrients, such as amino acids and minerals. The product, biopol, represents up to 90 percent of the dry weight of the bacterium. It is comparable to polypropene in physical properties, has better flexibility at low temperatures, and is biodegradable to CO2 and water within months. However, the polymer (trade name Biopol) is not currently cost-competitive with synthetic polymers because of the high costs of the fermentation substrates and the fermentation plants. 

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