Structure, Crystallization Behavior, And Properties Of Biodegradable Poly(ε-caprolactone) And Polyhedral Oligomeric Silsesquioxanes Nanocomposites

In this dissertation, poly(ε-caprolactone)(PCL) and polyhedraloligomeric silsesquioxanes(POSS) nanocomposites were prepared bysolution-casting method. The microstructure, crystallization behavior,spherulitic morphology, crystal structure, mechanical properties, andthermal stability of PCL and its nanocomposites were investigated withvarious techniques. The relationships between microstructure andproperties of PCL and its nanocomposites were also analyzed. The mainresults are as follows:1. In the PCL/ovi-POSS nanocomposites, ovi-POSS were distributeduniformly throughout the PCL matrix with crystalline regular hexahedronfrom80to120nm. The ovi-POSS acted as nucleating agent for thecrystallization of PCL, enhanced melt crystallization rates of PCL in thenanocomposites, reduced the size, and blurred the boundaries of PCLspherulitics without changing the crystal structure of PCL. Meanwhile,the Young’s modules and storage modules of PCL and its nanocompositeswere improved by ovi-POSS. The presence of ovi-POSS reduced the elongation at break of PCL in the nanocomposites. Thermal analysisindicated that though ovi-POSS decomposed at200oC，its decompositiondid not change the thermal stability of PCL in the nanocomposites. Thecharacterization results indicated that the interaction between PCL andovi-POSS was rather weak.2. In the PCL/oap-POSS nanocomposites, oap-POSS were alsodistributed uniformly throughout the PCL matrix as nanoscale sphereswhich coated with PCL with diameter from70to140nm. The oap-POSSacted as nucleating agent for the crystallization of PCL, but limited themotion of molecule chain of PCL, decelerated the spherulite growth rate.Like ovi-POSS, oap-POSS reduced the size and blurred the boundaries ofPCL spherulite without changing the crystal structure of PCL. Moreover,when the weight percent of oap-POSS was2%, the Young’s modules andstorage modules of PCL nanocomposites improved by oap-POSSremarkably. It even improved the yield strength and the elongation atbreak of the nanocomposites compared to neat PCL. Thermal analysisindicated that oap-POSS reduced the thermal stability of PCL in thenanocomposites slightly. The interaction between PCL and oap-POSSwas much stronger than that in PCL/ovi-POSS.3. Compared microstructures and properties of PCL/ovi-POSS andPCL/oap-POSS nanocomposites, we could conclude that the dispersionmorphology of POSS was related to its crystallization ability. POSS with strong crystallization ability tend to form nanocrystals during theevaporation of the solvent, while POSS with poor crystallization abilitytend to form amorphous nanospheres. More importantly, if the interactionbetween PCL and POSS is stronger, POSS could enhance the mechanicalproperties of PCL more significantly.