Physical Properties of PHAs

Introduction of a co-monomer into the polymer backbone, as in the case of heteropolymers, greatly affects the polymer properties by increasing its flexibility, toughness and decreasing its stiffness. For example, a copolymer such 

Polymer Tensile strength Modulus Elongation to break (%) Reference  

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Physical properties of PHAs are determined by monomer units, which are predominantly responsible for the molecular interactions, the molecular weight, and the molecular weight distribution. In addition, different crystalline modifications and processing conditions have a considerable effect on the achievable property level of the samples. For this reason, only the basic material data are listed and compared the glass transition temperature (7 ), the equilibrium melting temperature of an infinite crystal (T ), the equilibrium heat of fusion (AH ), and the densities of the amorphous (yj and crystalline (yc) parts (Table 1). 

Aliphatic polyesters are the most representative examples of biodegradable polymeric materials. Poly(3-hydroxyalkanoate)s, PHA, are well known biocompatible and biodegradable polyesters that are produced by various microorganisms as carbon and energy reserves. The physical properties of PHAs vary from crystalline-brittle to soft-sticky materials depending on the length of the side aliphatic chain on p carbon ... 

Physical properties of PHAs and some polymer commodities, adapted from. Hazer and Steinbiichel. ° ... 

The side chain length strongly affects the physical properties of PHAs ic/-PHAs are rigid and brittle as semi-crystalline thermoplastics, while mcZ-PHAs behave as thermoplastic elastomers. The chemical structures of PHAs presented in this chapter are listed in Figure 6.1. 

Identifying inexpensive, renewable substrates and cosubstrates for PHA production, as well as novel feedstocks/monomers (e.g. tall oils produced as oleic and linoleic acid-rich byproducts from the wood pulping processes) to enhance the economics and physical properties of PHAs will help to advance PHA polymers to greater and more widespread appUcations. UtiUzation of renewable resources, such as those derived from forest biomass could contribute to substantial reductions in PHA production cost and creation of novel polymers and production processes. 

Poly(hydroxyalkanoates) (PHAs), of which poly(hydroxybutyrate) (PHB) is the most common, can be accumulated by a large number of bacteria as energy and carbon reserve. Due to their bio degradability and bio compatibility these optically active biopolyesters may find industrial applications. A general overview of the physical and material properties of PHAs, alongside with accomplished applications and new developments in this field is presented in this chapter. 

Polyhydric alcohols, 2 46-55 analysis, 2 52-53 chemical reactions, 2 46-50 economic aspects, 2 52 health and safety factors, 2 53 manufacture, 2 50-52 physical properties of, 2 48t uses of, 2 53-54 Polyhydroxyalkanoates (PHA),... 

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]. 

Table 13.5 Comparison of the physical properties of AsHa, SbHa and BiHa with those of NHa and PHa...

PHAs have rapidly gained interest both in research and industry due to their structural versatility and characteristics such as biodegradability, insolubility in water, nontoxicity, biocompatibility, piezoelectric property, thermoplasticity and or elastomeric properties, which make them favourable to be used in the packaging industry, medicine, pharmacy, agriculture, food industry and in the paint industry. The chemical and physical properties of the polymer are dependent on the monomeric composition which is determined by the producing microorganism and their nutrition. So far scl-PHAs are being studied extensively due to their easier... 

The functional architecture of this class of PHA copolymers is substantially different from that of more familiar types of PHAs, such as poly[(/ )-3-hydroxybutyrate] (PHB) homopolymer or poly[(/ )-3-hydroxybutyrate-c<9-(/ )-3-hydroxy valerate] (PHBV) copolymer. The size of the side groups in the conventional PHAs is limited only to short-side-chain types with no more than two carbon atoms. Although PHAs with only one or two carbon side groups may be viewed essentially as linear polymers, PHA copolymers with mcl side groups belong to a broad class of moderately branched polymers. The inclusion of a small amount of mcl-3HA units into the PHA polymer backbone leads to some profound changes in important physical properties of this class of copolymers. 

One way to obtain more hydrophilic PHAs consists in the introduction of specific functions into the macromolecular side chains. The combination of bioconversion and organic chemistry allows modulation of the physical properties of these bacterial polyesters, such as solubility, hydrophilic-hydrophobic balance, and water stability, from the perspective of biomedical applications. 

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