478308 Improving Crystallization Behavior and Morphology of Polylactic Acid (PLA) with Solid-State Shear Pulverization (SSSP) and Solid-State Melt Extrusion (SSME)
Ethan Blumer and Katsuyuki Wakabayashi
Department of Chemical Engineering, Bucknell University, Lewisburg PA 17837
Polylactic acid (PLA) is a bio-based polymer derived from corn, sugar beets, and other natural sources. Products made from PLA have recently become of interest due its biodegradability and similarity in properties to other petroleum-based polymers. However, the widespread use of PLA is currently hindered by its inherently slow crystallization kinetics relative to other commercial polymers. The desired semi-crystalline structure is difficult to achieve in a reasonable amount of time when extrusion and other melt-molding techniques are used.
Many different methods have been attempted in enhancing the crystallization kinetics of PLA, like the addition of nucleating agents. While effective, this method is not environmentally friendly and can be cumbersome and costly. An alternative is processing via solid-state shear pulverization (SSSP) and solid-state melt extrusion (SSME), both twin-screw extruder-based, mechanochemical processing techniques. Each has been shown to lead to faster crystallization kinetics in both PLA without any additives or blend components.
This study explores the crystallization behavior and morphology of PLA processed via SSSP and SSME. The effectiveness of processing was assessed by comparing the properties of SSSP and SSME-processed samples to unprocessed PLA pellets and samples processed by industry standard twin screw extrusion. The rate and level of crystallization was measured by differential scanning calorimetry (DSC), while the crystal morphologies were analyzed with an x-ray diffractometer (XRD) and a polarized optical microscope (POM). Static flexural testing and dynamic mechanical analysis (DMA) were conducted to determine the effect of crystallization on the physical properties of PLA.
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