Thermal, mechanical and morphological characterization of plasticized PLA-PHB blends

A blend of poly(lactic acid) (PLA) (75% by weight) and poly(3-hydroxybutyrate) (PHB) (25% by weight) with a polyester plasticizer (Lapol 108) at two different concentrations (5 and 7% by weight per 100 parts of the blends) were investigated by TGA, DSC, XRD, SEM, mechanical testing and biodegradation studies. PLA/PHB blends showed a good distribution of the major components and absence of phase separation. XRD showed that the original crystal structure of PHB in the PLA75/PHB25 blend had been disturbed. DSC curves of PLA or PHB with plasticizer exhibited one Tg value, indicating that both major blend components are miscible. The Tg values also decreased with increased amount of plasticizer and showed good correlation to the Fox Equation, The melting temperature of PLA and PHB blends mostly did not change with an increase in plasticizer content, and the thermal stability of PLA and PHB was not affected. Also, the elongation at break of the PLA/PHB blend was greatly improved with the addition of plasticizer. In addition, in preliminary biodegradation studies carried in natural compost neat PHB showed some biodegradation, whereas the samples containing PLA did not experience a substantial biodegradation. This last aspect is worthy of further investigation in a more comprehensive and detailed approach.