Crystallization Behavior Of Poly (3-hydroxybutyrate-co-4-hydroxybutyrate) And Its Composites

In this article, the crystallization behavior of biodegradable polyester of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) and its composites with microcrystalline cellulose (MCC) were investigated. The results in detail were as follows.(1) Crystallization kinetics and morphology of P(3HB-co-4HB) were investigated. The samples were prepared by solvent-casting method. Isothermal and non-isothermal crystallization kinetics and subsequent melting behavior of P(3HB-co-4HB) were investigated by differential scanning calorimetry (DSC). It was demonstrated that the Avrami equation was suitable for describing the isothermal and non-isothermal crystallization process of P(3HB-co-4HB). The nucleation constant Kg value obtained from Lauritzen-Hoffman model was (1.92±0.16)×105 K2. Compared with Kg value of PHB, that of P(3HB-co-4HB) is lower, which indicated that the crystallization ability of P(3HB-co-4HB) was lower than that of PHB. In addition, the melting curves of P(3HB-co-4HB) samples for isothermal and non-isothermal crystallization showed multiple peaks. The wide angle X-ray diffraction (WAXD) results showed that P(3HB-co-4HB) samples crystallized non-isothermally had the same crystal forms as that of P(3HB). The small angle X-ray scattering (SAXS) results further demonstrated that two population of lamellae were formed during nonisothermal crystallization of P(3HB-co-4HB), which should be responsible to the double melting peaks observed in DSC curves.(2) Crystallization behavior of fully biodegradable P(3HB-co-4HB)/MCC composites were investigated. The samples of different components were prepared by melt blending. Dynamic mechanical properties and crystallization behavior of composites were investigated. It was demonstrated by dynamic mechanical analysis (DMA) testing results that storage modulus of P(3HB-co-4HB) were improved with increased MCC content from 0 to 40%. It was demonstrated by WAXD testing results that the crystal structure of P(3HB-co-4HB) did not change after blending. It was demonstrated by DSC testing results that the adding of MCC reduced the crystallization of the P(3HB-co-4HB). At the same time, Avrami equation was suitable for describing the non-isothermal cold crystallization process of composites. The Avrami exponent n values were hardly changed, which indicated that the nucleation mechanism of P(3HB-co-4HB) was not affected by adding MCC.