Studies on melt processing and rheology of poly (lactic acid) and its efficacy in recyclable bionanocomposite, biodiesel and biolubricant

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The overall aim of the present study is to focus on the melt processing and rheology of poly (lactic acid) (PLA) and its efficacy towards the fabrication of recyclable bionanocomposite and its end use application as a biolubricant and biodiesel additive. PLA is known to have poor melt strength, which is a major limitation for melt processing and recycling using the conversional technologies. In this thesis, melt stabilization of PLA has been attained through melt extrusion with thermally stable and crystalline silk. Over the assessment, the impact of silk nanocrystals (SNC) on melt degradation of PLA during thermomechanical process is investigated at melting temperatures (185 ºC and 200 ºC) under shear (40 and 100 rpm). The rate of degradation is studied through the estimation of molecular weight distribution at different residence times (up to 30 min) using gel permeation chromatography (GPC). Simplified two-parameter model which accounts for degradation and recombination is used to predict the kinetic parameters by coupling with Arrhenius equation. The impact of SNC and processing condition on macromolecular change of PLA matrix is also investigated using melt rheology. The incorporation of SNC in PLA matrix is observed to hinder the melt degradation which is confirmed by the increment in degradation activation energy and reduction in degradation rate constant. FTIR results confirm the formation of weak interaction between the SNC and PLA, which can be considered to be the reason for the stabilizing effect of SNC. The morphology of the SNC-PLA composite captured by field emission scanning electron microscope (FESEM) shows network formation, which is absent in neat PLA (NPLA) matrix. Crystallinity is improved and the reduction in number average molecular weight (Mn) and weight average molecular weight (Mw) with increasing residence time is minimized as compared to pristine PLA.
Supervisor: Vimal Katiyar