Effect Of Polyhydric Acid On The Properties Of Poly(Lactic Acid) Composites

Polylactic acid(PLA) is a new kind of green biodegradable polymer material that can be derived from renewable plant resources, compared with the traditional plastic in daily life, it exhibits good biocompatibility, excellent mechanical properties. However, inherent brittleness characteristics of PLA and its low crystallization rate have been the major limitation for its use in variety of application. So the modification of PLA has become necessary. In this paper, we selected corn starch, poly(butylene adipate-co-terephthalate) and polyhydric acid to modify PLA respectively. A series of PLA composite materials were prepared by melt blending using a twin screw-extruder, meanwhile the influence of polyhydric acid(PHA) content on the properties of composite materials were discussed. The effects of content of PHA on rheological properties and phase morphology of PLA composite materials were investigated by rotational rheometer and scanning electron microscope(SEM). The impact of content of PHA on thermal properties and mechanical properties of PLA composite materials were characterized and analysed by thermogravimetry(TG), differential scanning calorimetry(DSC), charpy impact testing machine and electronic universal testing machine.For PLA/starch-PHA composite materials, rheological properties test and SEM micrographs results showed that starch particles dispersed poorly in PLA matrix and easy agglomeration, which made the molten state of PLA/starch composites exhibit pseudoplastic fluid. The introduction of PHA into PLA/starch composites made the storage modulus, loss modulus and complex viscosity increase significantly, meanwhile starch distributed evenly and embedded better in PLA matrix. The fractured surface was rough, so the compatibility of PLA and starch were improved. TG test analysis indicated that PHA could enhance the thermal stability of composite materials. DSC test demonstrated that suitable amount of PHA was conducive to the crystallization of PLA. Mechanical testing showed that PHA was helpful to improve the toughness of PLA/starch composite materials.For PLA/PBAT-PHA composite materials, rheological properties test and SEM micrographs test revealed that proper amount of PHA could improve the storage modulus, loss modulus and complex viscosity of PLA/PBAT composites, so PHA had good compatibilization for PLA/PBAT composites. TG and DSC test results showed that the thermostability and crystallinity could be increased by the addition of proper amount of PHA. When 1.5wt% PHA was added, PLA/PBAT composite had better heat resistance and higher degree of crystallinity. It was found that the toughness of PLA/PBAT composites was improved with the introduction of PHA.For PLA/starch/PBAT-PHA composite materials, rheological properties test and SEM micrographs test showed that the addition of PHA could make the storage modulus, loss modulus and complex viscosity of PLA/starch/PBAT composites increase significantly and improve the compatibility among PLA, starch and PBAT. TG test analysis indicated that PHA could significantly improve the thermostability of PLA/starch/PBAT composites. DSC test results demonstrated that PHA could promote the crystallization of PLA. Mechanical properties testing results showed that PHA could improve the toughness of PLA/starch/PBAT composites. It presented the better comprehensive performance of PLA/starch/PBAT composite when the content of PHA was 1.5 wt %.