Abstract
The solidification and melting behaviour of quasi-binary systems formed by poly( l-lactic acid) (PLLA) and respectively the diluents parahydroxybenzoic acid (PHBA) and hexamethylbenzene (HMB) have been investigated. For both quasi-binary systems the effect of diluent concentration on the measured melting temperatures was in reasonable agreement with the theoretical values calculated according to the Flory-Huggins theory of melting point depression. The PLLA-PHBA system formed an eutectic composition for 84% w/w of PLLA in the mixture. Its eutectic melting temperature is 437K. For the PLLA-HMB system the eutectic composition was 65% w/w of PLLA in the mixture and the eutectic melting temperaturre of 432K. The morphology of the PLLA-diluent mixtures was strongly dependent on the diluent concentration. Fracture surfaces of the mixtures of PLLA and PHBA exhibited faceted crystals of various shape, formed by the diluent. They could not be removed from the polymer by sublimation, probably because of the intermolecular hydrogen bonds formed by PHBA itself and/or PHBA and the PLLA matrix. Sublimation of diluent from PLLA-HMB quasi-binary system led to a highly porous material of varying morphology.
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