Preparation and Investigation of Compatable and Tensile Properties of Entirely Biodegradable Polyester Blends

• Main Authors: Ching-Ju Wu, 吳京儒
• Other Authors: Ming-Chien Yang
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/87508288515655289056

博士 === 國立臺灣科技大學 === 高分子系 === 97 === Three mixture systems of biodegradable polymers were prepared through melt blending processes in this thesis including poly(lactic acid) (PLA)/poly(vinyl alcohol) (PVA), PLA/poly(ε-caprolactone ) (PCL), and PCL/modified multi-walled carbon nanotubes (MWNTs). The properties of these mixtures investigated are including tensile propteies, thermal properties, crystallinity, microstructures, and optical properties. In the first part, PLA and PVA were blended in various ratios by means of the melt blending method. The result of torque measurements and TGA tests showed that the addition of PLA can decrease the melt viscosity of PVA and that the second degradation step of PVA nearly disappeared for the PLA80PVA20 blend. The absorbance peaks of the carbonyl group and the hydroxyl group in the FTIR spectra of PLAxPVAy blends had significant shifts to lower wave numbers, indicating that there were interactions between these two groups. Combined with the result of DSC curves, this interaction would be favorable for improving miscibility. The XRD diffraction patterns and the PLM micrographs showed that PVA can serve as a nucleating agent to promote the crystallization of PLA in the PLAxPVAy blends. Moreover, the PLA80PVA20 blend gave the highest growth rate of PLA spherulite. In the second part, a series of blends of PLA and PCL with different mass ratio were prepared by means of the melt blending method to study their crystallization, miscibility, morphology, and thermal and mechanical properties. The result of DSC tests showed that the melting temperatures of PLA and PCL shifted toward each other, and that the largest shift appeared at the PLA70PCL30 blend. This result reveals that the PLA70PCL30 blend gives the strongest interaction between these two polymers. The results of dynamic mechanical analysis and SEM morphologies show that PLA and PCL form a partial miscible blend, in which an amount of amorphous PCL is dissolved in the PLA-rich phase, leading to a depression of the Tg value. The polarized optical micrographs showed that PCL can serve as a nucleating agent to promote PLA crystallization in the PLAxPCLy blend. Moreover, the PLA70PCL30 blend gave the highest growth rate of PLA spherulite. Finally, the mechanical property of PLAxPCLy blends indicated that PLA can easily be tuned from rigid to ductile by the addition of PCL. In the thord part, blends of PCL with MWNTs were prepared by means of a melt blending method. To cutail the poor compatibility between PCL and MWNTs, the acrylic acid grafted polycaprolactone (PCL-g-AA) and the multihydroxyl functionalized MWNTs (MWNTs-OH) were used as alternatives for the preparation of blends. As the comparison between PCL-g-AA/MWNTs-OH and PLA/MWNTs blends, the former gave much better thermal and mechanical properties than the latter; for example, the initial decomposition temperature was increased by 77°C with the addition of only 5wt%, owing to the formation of ester groups through the reaction between carboxyl groups of PCL-g-AA and hydroxyl groups of MWNTs-OH. Finally, the optimal amount of MWNTs-OH was 5wt% because excess MWNTs–OH caused separation of the organic and inorganic phases and lowering their compatibility.