The Modification Of Biodegradable Poly(ε-caprolactone) By Blend And Nano-hybrid

Poly(e-caprolactone) (PCL) is a kind of polymer material withexcellent biocompatibility and biodegradability. Its final product afterdegradation in vivo is water and carbon dioxide, and won't assemble(?)in the main organs. Therefore, PCL has great applied value in biomedicalengineering and tissue engineering. But its lower crystallizationtemperature makes it difficult to be melt-spun in the industrial production.Furthermore, since the existing of the long methylene chain segment,PCL has lower degradation rate. In my research, the modification byblend and nano-hybrid was applied to PCL to improve its performance.First of all, a novel way using glacial acetic acid, acetic anhydride and methylsulfonic acid as esterification catalyst was applied to synthesize starch acetate. The starch acetate has been mixed with PCL in melting state to form poly-blends. The crystallization behavior of the blends has been studied by DSC analysis. It has been found that with the increase of the starch acetate content, the melting points of the blends decrease. The relative crystallization degrees of the blends show non-linear relation with the starch acetate content. The starch acetate in the blends plays a role of nucleation agent, which increases the crystallization temperature and crystallization rate of PCL in the blends.Subsequently, electrospinning of PCL/ starch acetate in acetone was Studied. SEM observation showed that beads would show up in the samples after the adding of starch acetate. From XRD analyses, we found that electrospinning was propitious to the crystallization of PCL and also changed its crystal structure. This is because the electrostatic field produced during electrospinning can facilitate the tropism of the polymer molecule. But the adding of starch acetate will reduce this effect.Finally, nanocomposites based on PCL and attapulgite (AT) were prepared by solution mixing. The non-isothermal crystallization of the pure PCL and PCL/AT nanocomposites at different AT contents and different cooling rates were investigated by DSC. There are significant dependence of non-isothermal crystallization behavior and kinetics of PCL/AT nanocomposites on the AT content and cooling rate. The Jeziorny method has been employed to analyze the DSC data. The results show that attapulgite can be used as an effective nucleating agent and has effects on the growth of crystallites in the crystallization process of PCL matrix. SEM observation showed that AT nano-rods were well dispersed in the PCL matrix in a nanometer scale at low AT content and a severe aggregation would happen at high AT content. The rheological analysis found that because of the aggregation of AT, the nanocomposite with high AT content displayed notable shear thickening behavior at low frequency and had much higher complex viscosity. The storage modulus and relaxation time of our nanocomposites showed a monotonic increase with AT content in low frequency region due to the interaction between the PCL matrix and AT, which was consistent with the structure changes found in the Cole - Cole plot.