Studies on Reactive Blends of Poly (hydroxybutyrate-co-valerate) and Poly (butylene succinate) Bioplastics
Various commodity plastics used today are based on fossil fuels. Most of these plastics are non-biodegradable and will persist in the environment over a long time. The bioplastics from renewable resources have the potential to support a greener economy. The two of such renewably resourced bioplastics are poly (hydroxyl butyrate-co-valerate), PHBV and poly (butylene succinate), PBS. We have used petro-based PBS in our study, but renewable resource based PBS is expected to be available on a commercial scale in a very near future. These two bioplastics are both biodegradable. These two bioplastics are both biodegradable. In our study we have used PBS from petroleum resource but PHBV is a brittle bioplastic with a high modulus value and a low elongation at break while PBS is a low modulus bioplastic with a high elongation at break. Complementary properties can be obtained by blending PHBV and PBS. The direct melt blends showed poor mechanical properties due to limited interaction between PHBV and PBS phases. This research focuses on increasing the interaction between PHBV and PBS blends by using compatibilizers. The compatibilizers used in this thesis were dicumyl peroxide, DCP and trimethylolpropane triacrylate, TMPTA. Use of an in situ compatibilization method was done for the melt mixing of PHBV and PBS yielding blends with improved characteristics. The investigations were performed at three different ratios of PHBV and PBS blends. The increase in the compatibility between the two phases was demonstrated through various thermal, thermo-mechanical, rheological and morphological means. The increase in elongation at break was used as a primary marker for compatibilization. The optimization of DCP and TMPTA was carried out, which showed the enhanced interaction between PHBV and PBS phases, with the successful stress transfer from PHBV phase to the PBS phase resulting in increase in elongation at break. Inward shifts in tan delta peak on addition of DCP and TMPTA to the blends also showed increase in compatibility between the two phases. The interfacial adhesion between a brittle and ductile polymer, PHBV and PBS respectively was increased by using DCP and TMPTA. This opened gateways to various novel applications of PHBV and PBS blends via in situ reactive extrusion process.