Study On Crystallization And Degradation Properties Of P(3HB-co-4HB)/PLA Blends

In this study, the crystallization properties and degradation properties of poly (3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)], poly(L-lactic acid)[PLA] and their blends with different weight ratios. Their crystal structure, crystallization kinetics and morphology were determined by wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and polarized optical microscopy (POM) respectively. The isothermal crystallization kinetics and the non-isothermal crystallization kinetics were dealt with Avrami equation, Jeziorny and MO models. The weight loss, molecular weight and surface morphology change during degradation process were investigated by capillary viscometry, scanning electron microscope (SEM), thermal weight analysis and so on.(1) Crystal structure is mainly dependent on the proportion of PLA in these blends. According to Bragg equation, when its weight proportion is smaller (WPLA<20%), the crystal structure of P(3HB-co-4HB) do not change, but its regular pattern is broken; when the proportion of PLA is more (WPLA>20%), P(3HB-co-4HB) and PLA crystallize at the same time and the laws of their regular patterns are lower.(2) The crystallization kinetics of P(3HB-co-4HB)/PLA blends were remarkably affected by crystallization temperature (Tc), weight proportion of PLA (WPLA) and the cooling rates. At the study, the isothermal crystallization rate decreases with increasing Tc and WPLA-With increasing WPLA, the melting double peaks becomes single peak and PLA appears cold crystallization; during the non-isothermal crystallization process, the crystallization peak and the melting peak move to lower temperatures with adding WPLA and the cooling rate. When WPLA is during 0-80%, the crystallization difficulty degree of P (3HB-co-4HB)/PLA blends increases first, then decreases, then increases, at last decreases.(3) Crystallization morphology depends on Tc, WPLA and the time for isothermal crystallization. And at different Tc, the effects of addition of PLA on morphology are different. When the Tc is lower, the PLA is unformed and it acts as the defects in the crystal of the blend. And the morphology of system is similar to that of PLA at higher temperature(110,120℃). And the two composites form co-crystal at most cases.(4) Degradation mechanisms of P(3HB-co-4HB)/PLA blends are different in different mediums. The soil and enzyme degradations give first place to enzyme degradation mechanism while the buffer solution and hot alkali water degradations appear mainly the hydrolysis mechanism. WPLA , the degradation condition, mechanism and the time play important effects on the degradation rate and surface morphology.