Polymer blends copolymer with PLLA

In particular, a microporous poly(/-lactide) (PLLA) composition can be prepared using poly(styrene) (PS) and as compatibilizer a copolymer from a lactide and styrene. Binary blends and compatibilized ternary blends are prepared by melt mixing the polymers and copolymer in a Brabender internal mixer with roller blades, under a constant high flow of dry nitrogen. Dry nitrogen is required to avoid a dramatic melt degradation of the PLLA. Prior to blending, PLLA and PS are dried for 48 /z in a vacuum oven at 70°C. 

Commercial PLA is a blend of PLLA and PDLA or copolymer PDLLA, obtained by the polymerization of LLA and DLLA, respectively [1]. Many important properties of PLA are controlled by the ratio of d- to L-enantiomers used and the sequence of arrangement of the enantiomers in the polymers. PLLA constitutes the main fraction of PLA derived from renewable sources since the majority of lactic acid obtained from biological sources exists as LLA. PLA with PLLA content higher than 90% tends to be crystalline while that with lower optical purity is amorphous. The melting temperature (Tm), glass transition temperature (Tg), and crystallinity of PLA decrease with decreasing amounts of PLLA [2-5]. 

However, a reactive styrene acrylonitrile copolymer (SAN)/gly-cidl methacrylate copolymer was found to be an effective reactive compatibilizer for the blends. Ethyltriphenyl phosphonium bromide was used as the catalyst. Probably, the epoxide groups react either with carboxyl or with hydroxyl groups of the PLLA end groups. This so modified polymer acts as the compatibilizer. Compatibilized PLLA/ABS blends exhibit an improved impact strength and an im-... 

Y. Li and H. Shimizu, Improvement in toughness of poly(l-lactide) (PLLA) through reactive blending with acrylonitrile-butadiene-styrene copolymer (ABS) Morphology and properties, Eur. Polym. J., 45 (3) 738-746, March 2009. 

Pandey et al. [174] claimed that microwave radiation blending was a clean, fast, and effective way of blending. Blends were produced with PGA/PLLA ratios of 33/67, 50/ 50, and 67/33 in chloroform and then subjected to radiation. The chloroform helped maintain the temperature of the process and was quickly evaporated. The resulting blends were compatible, especially the 50/50 blend, as determined by EUR, NMR, and DSC. The blends had linkages between the carboxylic acids of PGA and PLLA (according to FTIR). In addition, the blends mostly had one Tm. The linkages of the two polymers, which were determined by the CH2 peak absorption, showed that the blends were actually copolymers. 

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