Short-Chain-Length PHA

Short-chain-length PHAs (scl PHA) include PHB, PHBV and copolymers of 3-hydroxybutyrate and 4-hydroxybutyrate (P3HB4HB), copolymers of 3-hy-droxypropionate (3HP) and 3HB (PHPHB) as well as copolymers of P3HP4HB. 

Company Types of PHA Production scale (t/a) Period Applications 

Chemie Linz, Austria PHB 20-100 1980s Packaging and drug delivery 

Biomers, Germany PHB Unknown 1990s to present Packaging and drug delivery 

Germany PHB,PHBV Pilot scale 1980s to 2005 Blending with Ecoflex 

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Short-Chain-Length-PHAs Containing Repeating Units other than... 

First, the short chain length PHAs, poly(HASCL), are composed of monomeric units containing up to 5 carbon atoms. The most well-known representatives are poly(3-hydroxybutyrate) (PHB), and its copolymers with hydroxyvalerate. Of all the PHAs, PHB is by far the most commonly encountered in nature [18]. It is the simplest PHA with respect to chemical structure, having a methylene (-CH3) group as the pendent R-unit in Fig. 1. Owing to its enzymatic synthesis, PHB has an exceptional stereochemical regularity. The chains are linear and the chiral centers all are in the R-stereochemical conformation, which implies that this polymer is completely isotactic. 

Applications from Short Chain Length PHAs... 

Polyhydroxybutyrate [PHB] is the most common type of polymer that falls in the category of polyhydroxyalkanoates. PHAs are generally classified into short-chain-length PHA (sCL-PHA) and medium-chain-length PHA (mCL-PHA) by the different number of carbons in their repeating units. 

Notes PHB Poly-3-hydroxybutyrate 3HB 3-hydroxybutyrate 3HV 3-hydroxyvalerate 4HB 4-hydroxybutyrate 3HH 3-hydroxyhexanoate 3HO 3-hydroxyoctanoate sc/-PHA short chain length PHA mc/-PHA medium chain length PHA. 

Several PHA producing microorganisms as well as several types of PHA were discovered. " The whole PHA family can be sub-divided into three main categories the short-chain length PHA (PHAscl), the medium-chain length PHA (PHAmcl) and rarer PHA (Figure 1.1). The structural differences inside the PHA family imply deep differences in their thermo-mechanical... 

Two major classes of PHAs are known to exist. PHAs whose polymeric units are predominantly five carbons or less are classified as short-chain-length PHAs (SCL PHAs) while all others are referred to as medium-chain-length PHAs (MCL PHAs). The term MCL was coined because the number of carbons in the monomers roughly corresponds to those of medium-chain-length carboxylic acids. PHA nomenclatme may still be in a state of flux as new stnictmes continue to be discovered. 

Figure 10.3 Chemical structure of PHAs. Side chain = CH3 to C2H5 are short chain length PHAs. Side chain = C3H7 to C11H23 are medium chain length PHAs. Side chain >Ci4H2g are long chain length PHAs.

PHAs are classified into three classes short chain length PHA (PHAscl). medium chain length PHA (PHAmcl) and long chain length PHA (PHAlcl) (Figure 10.3). PHAs are thermoplastic and/or elastomeric, insoluble in water, enantiomerically pure, non-toxic, biocompatible, piezoelectric compounds that exhibit high degree of polymerization. 

Figure 1. General molecular structure of polyhydroxyalkanoates. m = 1, 2, 3, yet m = 1 is most common, n can range from 100 to several thousands. R is variable. When m=, R-CH3, the monomer structure is 3-hydroxybutyrate, while m = 1 and R = C3H7, it is a 3-hydroxyhexanoate monomer. If R > C3H7, the PHA are called medium-chain-length PHA If R < C3H7, the PHA are referred to as short-chain-length PHA.

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