The rate of adoption of the polylactide (PLA) polymer as a commodity plastic has been slow due to its inherently low toughness, low heat deflection temperature, slow rate of crystallization and poor melt strength. In the current work, we have focused on addressing these critical issues with PLA via four specific approaches, with the ultimate goal of expanding its portfolio of commercial applications. First, the incorporation of a novel Polylactide-Polydimethylsiloxane (PLA-PDMS) block copolymer for application as an impact modifier for injection molded PLA articles was studied. The PLA-PDMS copolymer was synthesized via a transesterification chemistry using reactive extrusion as a facile technique. The copolymer was added to neat PLA during the injection molding process at varying loading levels. Thermal annealing of the injection molded part was carried out to increase the percent crystallinity and subsequently the heat deflection temperature. The addition of the copolymer and the subsequent annealing was found to have an unprecedented synergistic effect on both the tensile and impact toughness of the PLA, which were improved by up to 200 and 500% respectively. A model was proposed to explain the unique behavior shown by the annealed PLA-PDMS system. Optimization of molding and annealing conditions were performed to ensure a cost-effective route towards commercialization.Second, the use of a biobased mono-epoxy-functionalized cardanol molecule, derived from cashew nut shell liquid (CNSL), is explored as a "green" plasticizer. Reactive blends of the modifier with PLA, produced via twin-screw extrusion, was found to successfully reduce glass transition temperature of the PLA resulting in enhanced flexibility of the injection molded PLA specimens. Thermal annealing of these specimens was found to improve heat deflection temperature by 200303 °C and the percent crystallinity by 1003030%. Mechanical properties of the annealed samples were observed to closely mimic the unique synergistic trend shown by the PLA-PDMS system. The model developed for the PLA-PDMS system was appropriately modified to take into account the behavior of the PLA-epoxy system.Third, multifunctional epoxy-based chain extenders were reactively blended with PLA via twin-screw extrusion to improve its melt strength for applications in processing techniques such as blown films. A fossil-fuel based epoxy modifier and a biobased substitute derived from cardanol were used for the study. The effects of varying molar ratios and the type of processing used on the final rheological properties were first evaluated using model compounds to simulate PLA and then validated by reactions with PLA. Improvements in melt strength were characterized using dynamic oscillatory shear and uniaxial extensional viscosity measurements. The presence and type of chain extension evolved with each modifier was established.The last section of the work involves the use of basalt and glass fibers to reinforce the PLA matrix for automotive interior applications. The PLA-based fiber composite materials were produced by adopting the Direct-Long Fiber Thermoplastic (D-LFT) approach, wherein continuous rovings of the fibers were directly fed into a twin-screw extruder. The D-LFT technique allows for a higher aspect ratio of the fiber in the matrix leading to improved load transfer at the fiber-matrix interface. Optimization of the process parameters, including screw configuration, was performed to ensure desired level of fiber breakage and dispersion, and to maximize the fiber content in the final composite material. PLA-based short fiber composites were prepared under similar processing conditions to demonstrate the efficacy of the D-LFT technique at preparing composite samples with a higher aspect ratio and improved mechanical performance over using short fiber.
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