Succinate polyesters, melting point

Pranamuda, H., Tokiwa, Y. Tanaka, H. (1995). Microbial degradation of an aliphatic polyester with a high-melting point, poly(tetramethylene succinate). Applied and Environmental Microbiology, 61, 1828-32. 

The saturated polyesters that find conunercial applications are mostly linear, except for some specially prepared branched polymers used in the preparation of polyurethanes. The linear polyesters became commercially important materials early in this century and still find many uses in industry. The earliest studies reported condensations of ethylene, trimethylene, hexamethylene, and de-camethylene glycols with malonic, succinic, adipic, sebacic, and orthophthalic acids. Later studies showed that such condensations yield high molecular weight compounds. Nevertheless, these polyesters exhibit poor hydrolytic stability and are generally low-melting. Subsequently, however, it was found that aromatic dicarboxylic acids yield polymers with high melting points, and poly(ethylene terephthalate), which melts at 265 C, is now an important commercial material. 

Another class of soft aliphatic polyesters are based on repeating succinate units such as PBSU, poly(butylene succinate adipate) (PBSA), and poly(ethylene succinate) (PES). Each of these succinate-based aliphatic polyesters are manufactured by Showa High Polymer, Ltd. and are sold imder the trade name Bionolle . Glass transition temperatures (Tg) and melting points (T ) of tree types are shown in Table 4.6. 

Here, the a low-melting component is poly(butylene succinate) (PBSU). The low melting point polyesters may contain a minor portion of other monomer constituents, such as aromatic monomers. 

PCL -OCH CH CH CH CH CO-ln) is a partially-crystalline polyester that is biodegraded by microbial lipases and esterases. The plastic is made from petrochemical feedstocks. It has too low a melting point (60°C) to be useful in any packaging applications. Higher aliphatic polyesters such as poly(butylene succinate) (PBS) (-0(CH2) OC(CH2)2CO-)n and poly(ethylene succinate) (PES) (-OCCH l OOCCCH l CO-) are also biodegradable at a rate that depends on environmental factors (Kasuya et al., 1997). They have higher melting points of 112-114°C and 103-106°C, respectively, and the properties compare well to those of polyolefins. As succinic acid can be derived from plant sources, the polysuccinates can be potentially a bio-based polymer. 

Blending of starch with aliphatic polyesters improves their processability and biodegradability Particularly suitable polyesters are poly(s caprolactone) and its copolymers, or polymers of higher melting point formed by the reaction of 1,4-butandiol with succinic acid or with sebacic acid, azelaic acid, or polydactic acid), poly(hydroxyalkanoates), and aliphatic-aromatic polyesters. 

Crystallization and melting behaviour of polyesters based on succinic acid and respective ahphatic diols, with 2-4 methylene groups were studied by Papageoigiou et al. [80]. The equi-libriiun melting points were foimd to be 114, 133.5 and 58°C for poly(ethylene succinate), polyfbutylene succinate) and poly(propylene succinate), respectively. The corresponding values... 

Unfortunately, apart from aliphatic polyesters of this group based on succinic acid, the majority have a very low melting point, which can range from nearly 40-70 °C depending on the diol/dicarboxylic acid coupling. This characteristic precludes their use at an industrial level. 

The most common industrial products are polyesters and copolyesters of succinic acid, as having a high melting point makes them suitable for applications requiring high temperature resistance. 

Blends of biodegradable synthetic aUphatic polyesters and starch are used to produce sheets and films for packaging by film extmsion or blown film methods. Up to 50% of the synthetic polyester can be replaced with starch. A polyester synthesised from the poly-condensation of 1,4-butanediol and a mixture of adipic and succinic acids has been blended with wheat starch by Lim (1999) (Nolan-ITU Pty Ltd, 2002). The blends were found to have melting points near that of the polyester alone. Plasticisers were also added to the starch to improve flexibiUty and processability of the blend. The modified blends were found to retain a high tensile strength and elongation, even at high starch concentrations. 

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