Development of Polylactic Acid (PLA) based Durable Blends and Biocomposites: Routes for Improving Performance
Use of synthetic plastics derived from petroleum is challenged due to extremely well-known issues of greenhouse gas (GHG) emissions causing climate change. Bioplastics are emerging as a new paradigm, focusing on renewability and sustainability. Replacing the fossil carbon present in plastics and products with renewable carbon allow to reduce the carbon footprint and GHG emissions. Polylactic acid (PLA) is one of the widely studied renewable resource based bioplastic with huge potential to be on a par with synthetic plastics. However, common commercial grades of neat PLA is yet to gain a strong commercial standpoint in applications other than cold food packaging due to its poor toughness and low heat resistance. This thesis demonstrated feasible routes to fabricate PLA based blends and biocomposites with desirable morphology and crystallinity for durable applications. Two promising directions were considered; one based on PLA as a major phase and the other based on PLA as a minor phase. A three step approach was followed while pursuing both research directions. First, binary blends were studied to have a fundamental understanding regarding how the properties of the blends change by varying the blend ratio. Next, a suitable compatibilizer containing a reactive functional group was added to the optimum binary blend to achieve better properties through a reactive extrusion technique. The developed ternary blends showed improvement in toughness depending on the type of functionalized terpolymer. In the third and final step, fabrication of biocomposites and the effect of addition of different fillers, additives, and processing strategies were investigated in an aim to increase the crystallinity and heat resistance. Through a combination of univariate and statistical optimizations, biocomposites containing PLA either as a major or minor phase, having a stiffness-toughness balance and a higher heat resistance were developed. Successful property improvements obtained in the developed materials has so far been unattainable for injection molded PLA biocomposites. Polymer and additive combinations investigated in this thesis are novel. Property attainment elaborated here enriches the existing body of literature concerning PLA based durable materials.