Study On Microstructure Changes And Hydrolytic Degradation Behaviors Of Poly(Butylene Succinate) Induced By Dispersed Phase

Poly(butylene succinate) has been increasingly researched and used during the past decades because of its outstanding biocompatibility and biodegradability and comprehensive mechanical properties. However, the strength and modulus of PBS are not high enough and the hydrolytic degradation rate of PBS is relatively slow, which restrict the application of PBS in more fields. It will lay the foundation for further improving the mechanical properties of PBS to investigate its crystallization behaviors, for many reports showing a substantial connection between the mechanical properties and crystallization behaviors of PBS which possesses very good crystallization capacity. Besides, to enhance the hydrolytic degradation rate of PBS has been one of the key matters just because PBS serves as a kind of degradable polymer. It is shown that polar dispersed phase helps improve the hydrophilicity of polymers, so it is meaningful to promote the hydrolytic degradation behaviors of PBS by adding polar dispersed phase into it. In this work, different dispersed phases were introduced into PBS matrix to study the effects of dispersed phases on the crystallization, hydrolytic degradation behaviors and structure changes of PBS, and the obtained results are as the follows:(1) PBS/Graphene oxides (GOs) nanocomposites with different contents of GOs were prepared by means of solution blending, and the rheology, nonisothermal crystallization and subsequent melting, and isothermal behaviors were systematically investigated. It was found that GOs served as heterogeneous nucleating agents for PBS and enhanced the crystallization of PBS. During the nonisothermal crystallization process, the nucleating effect of GOs was related to the content of GOs and the cooling rate. The crystallization of PBS was promoted most remarkably when adding 0.5 wt% GOs, and hindered by the physical network formed by GOs sheets when its content was high enough. During the isothermal crystallization process, the nucleating effect of GOs was only related to the content of GOs. The more content of GOs added, the higher density of nucleation was, and the shorter time was needed to complete crystallization for PBS.(2) The structures and hydrolytic degradation behaviors of PBS/GO nanocomposites were investigated. It was found that the hydrophilicity of PBS/GO nanocomposites increased with increasing content of GOs. Although the degree of crystallinity increased for some samples such as PBS/GO-0.2, the hydrophilicity played a dominant role in the hydrolytic degradation process, thus resulting in the hydrolytic degradation rate of PBS enhancement with the increasing of GOs content. The hydrolytic degradation of PBS/GO was a kind of surface corrosion process, and started from amorphous region followed by crystalline region. Besides, the crystal form of PBS was constant during the whole hydrolytic degradation process.(3) The effect of temperature on the hydrolytic degradation behaviors of PBS/GO nanocomposites was researched by increasing the temperature of environment, and it was found that increasing temperature could enhance the hydrolytic degradation without changing the mechanism of degradation.(4) PBS/Poly(ethylene oxide) (PEO) blends with different component ratios was prepared through melt-blending. The crystallization behaviors of PBS/PEO blends were studied and it was shown that there was a critical value xc (5 wt%) of the content of PEO in promoting the crystallization of PBS, below which PEO enhance the crystallization of PBS and above which PEO hindered the crystallization of PBS.(5) The hydrolytic degradation behaviors of PBS/PEO blends was researched and it was found that the hydrolytic degradation rate of PBS also increased with the content of PEO resulted from the enhanced hydrophilicity, the minished crystal size and the decreased of degree of crystallinity when containing enough PEO. The mechanism of degradation is illustrated as follows:firstly PEO molecular chains located in the boundaries of PBS spherulites dissolved in water, thus making the structure in the boundaries of PBS spherulites looser; secondly abundant water moleculars intruded in the boundaries of PBS spherulites, resulting in hydrolytic degradation starting from these regions; finally, hydrolytic degradation expanded to the inside of PBS spherulites. Adding PEO into PBS matrix changed the hydrolytic degradation mechanism of PBS into body corrosion from the surface corrosion.