Polybutylene Succinate / Poly Blend The Structure And Properties Of Materials

As typical biodegradable polymer materials, thermoplastic aliphatic polyesters such as poly(butylene succinate)(PBS) and polylactide (PLA) have generated great interest recently in the material research field. PBS with high toughness, high thermal stability and slow degradation rate shows low strength, while PLA with high strength and fast degradation rate shows poor toughness and poor thermal stability. Therefore, to blend them together is a convenient strategy to obtain new biodegradable materials with high performance due to their property complementarity. However, the two polymer components are incompatible thermodynamically and the poor interface adhesion restrains the property improvement on their blends. To design and to fabricate biodegradable polymer blends with excellent performance, it is hence necessary to explore the aspects influencing phase morphology and to establish the relation between phase structure and performance of PBS/PLA blends.In this work, therefore, the PBS/PLA blends with various blending ratios and viscosity ratios were prepared by melt mixing for the structure-property relation study. The phase morphology and rheological properties of the blend systems were then studie in order to describe the effects of blending ratio and viscosity ratio as well as temperature on the morphological formation and evolution. Several approaches were employed to evaluate interfacial tensions between PLA and PBS to further relate the phase morphology and its viscoelastic responses. Based on those observations, dicumyl peroxide (DCP) was used as a reactive compatibilizer to improve phase morphology and properties of PBS/PLA blends. The relation between morphology and properties of the compatibilized systems was then studied, aiming at providing useful experimental and theoritical information on fabrication of biodegradable PBS/PLA blends with high performance. The obtained results are as follows.PBS and PLA are incompatible thermodynamically. The morphology of their blends highly depends on the viscosity ratio and blending ratio between them. Three typical immiscible morphologies, i.e., spherical droplet, fibrous and co-continuous structure can be seen at various compositions. As the viscosity ratio and blending ratio value is closed to1, the co-continuous structure of blends is more obvious. Among all blends, the blend with co-continuous structure presents the highest modulus at the terminal frequency zone. This is because the inter-connected network structure formed by the two phases contributes additional elastic. However, with increasing temperature, the partial co-continuous structure will transform into a "sea-island" one, which indicates that the principle of time-temperature superposition (TTS) is invalid for the blends with partial co-continuous structure.The contact angle measurement can be used to measure the interfacial tension between PBS and PLA at room temperature. However, this approach might not be appropriate for determining the interfacial tension at high temperature because the temperature coefficient used to extrapolate high-temperature values of interfacial tension is hard to be obtained. To obtain accurate values of interfacial tension at high temperature, the imbedded fiber retraction method is much better than the contact angle measurement because the temperature and viscoelasticity dependence of the interfacial tension are fully considered by the former. Besides, the Palierne and G-M models can also be used to evaluate the interfacial tension through rheological responses, but the obtained values of interfacial tension show blending ratio and morphology dependence more or less.Using DCP as a reactive compatibilizer, the morphology of PBS/PLA blends is improved evidently. The radii of discrete PBS domain reduce, accompanied by sharply enhanced interface adhesion. But the addition of DCP will not change the carbon chain structure of PBS and PLA, despite the crosslinking and grafting reactions between PBS and PLA on the phase interface. Compared with those of the pristine blend, the impact strength and tensile strength of the compatibilized blends are improved sharply because of reduced interfacial tension and thickened interface layer. Besides, the reactive compatibilization has large influence on the thermal behaviors of the blend systems. With the addition of DCP, the glass transition temperature of PLA decreases, and the crystallization ability of two polymer components reduces more or less.