Preparation,crystallization Behavior And Properties Of Biodegradable Polyesters/polyhedral Oligomeric Silsesquioxane Composites

Due to the arising environmental and resource problems,biodegradable polyesters have attracted more and more attentions as environmental friendly materials in both industrial and academic fields.The preparation of biodegradable polyesters based composites can regulate the properties of the polyesters and further broaden their application.In this dissertation,solution casting and melt compounding methods were used to prepare biodegradable polyesters/polyhedral oligomeric silsesquioxane(POSS)composites containing POSS with different loadings and different cage structures.The influence rules of POSS loadings,POSS structures and preparation methods on POSS dispersion,the crystallization behavior,mechanical and degradation properties of the composites were investigated.1.Octaisobutyl-POSS(oib-POSS)and octavinyl-POSS(ovi-POSS)were introduced into poly(ethylene succinate)(PES)and poly(ethylene succinate-co-diethylene succinate)(PEDEGS).At the loadings of 0.5 and 1 wt%,POSS dispersed finely at nanoscale in the matrix.POSS enhanced the crystallization process of the matrix under different conditions without changing the crystallization mechanisms or the crystal structures.The spherulites growth rate of the matrix remained unchanged while the nucleation density was higher,proving the heterogeneous nucleating effect of POSS.The heterogeneous nucleating effect was stronger at higher POSS loading.Oib-POSS as rigid nanoparticle strengthened the matrix and increased the Young’s modulus as well as the tensile strength of PES.Ovi-POSS lubricated the polymer chains because of its small aggregate size and decreased the storage modulus of PEDEGS.2.Open cage trisilanolisobutyl-POSS(tsib-POSS)and close cage oib-POSS were added into PES and poly(ε-caprolactone)(PCL)via solution casting at the same loading(1 wt%).Two kinds of POSS both dispersed at nanoscale in the matrix,but tsib-POSS aggregates sizes were smaller because the solubility parameters were closer between tsib-POSS and the polymer matrix.Both tsib-POSS and oib-POSS could enhance the crystallization process of the matrix as heterogeneous nucleating agents without changing the crystallization mechanism or the crystal structure of the matrix.In addition,oib-POSS had better nucleating effect because of its stronger nucleation ability and the lattice matching with the matrix.Oib-POSS acted as plasticizer for the matrix;tsib-POSS strengthened the matrix because of the hydrogen bonding between the-OH group of tsib-POSS and the matrix.The dispersion of POSS increased the roughness of the composites surface and consequently accelerated the enzyme degradation of the composites;furthermore,the hydrogen bonding between-OH group in tsib-POSS and the solution could better increase the degradation rate of the composites.3.Oib-POSS at higher loadings(2 wt%)was introduced into PCL by solution casting and melt compounding.The oib-POSS aggregates sizes in the solution casting sample(sPCL/oib-POSS)were smaller than that in the melt compounding sample(mPCL/oib-POSS).Oib-POSS enhanced the crystallization process of PCL without changing its crystallization mechanism or its crystal structure.The crystallization enhancement by oib-POSS was more obvious in sPCL/oib-POSS due to the better dispersion of oib-POSS in solution casting sample.Oib-POSS at higher contents with larger aggregate size strengthened the PCL composites.The degradation rates of the composites were increased because the surface roughness of the composites was higher due to the dispersion of oib-POSS on the sample surface.In this dissertation,biodegradable polyesters/POSS composites were prepared via solution casting and melt compounding methods and were characterized and tested with various means.The effects of POSS loadings,POSS structures and preparation methods on the POSS dispersion in the matrix were studied.Furthermore,the influence rule of POSS dispersion,lattice matching between POSS and the matrix,and hydrogen bonding on the properties of composites were discussed.The research results could provide important reference value for the basic research and practical applications of biodegradable polyester based composites.