Abstract
Crystalline morphology and phase structure play a decisive role in determining the properties of polymer blends. In this research, biodegradable blends of poly(l-lactic acid) (PLLA) and poly(butylene succinate) (PBS) have been prepared by melt-extrusion and molded into specimens with rapid cooling. The crystalline morphology (e.g., crystallinity, crystal type and perfection) is manipulated by annealing the molded products from solid-state within a short time. This work emphasizes on the effects of annealing conditions on crystallization and properties of the blends, especially impact toughness and thermal stability. Phase-separation morphology with PBS dispersed particles smaller than 1 μm is created in the blends. The blend properties are successfully dictated by controlling the crystalline morphology. Increasing crystallinity alone does not ensure the enhancement of impact toughness. A great improvement of impact strength and heat resistance is achieved when the PLLA/PBS (80/20) blends are plasticized with 5% medium molecular-weight poly(ethylene glycol), and simultaneously heat-treated at a temperature close to the cold-crystallization of PLLA. The plasticized blend annealed at 92 °C for only 10 min exhibits ten-fold impact strength over the starting PLLA and slightly higher heat distortion temperature. The microscopic study demonstrates the fracture mechanism changes from crazing to shear yielding in this annealed sample.
Highlights
Over the past decade, poly(L-lactic acid) (PLLA) has attracted attention in many applications such as biodegradable medical devices, healthcare products, and single-use packaging
The addition of 20% Poly(butylene succinate) (PBS) is very effective for overcoming the brittleness of PLLA, resulting in a significant increase in elongation at break
The results of this study clearly demonstrate that the brittleness of PLLA can be overcome by manipulating the crystallization and morphology of PLLA via a combined melt-blending and thermal annealing approach
Summary
Poly(L-lactic acid) (PLLA) has attracted attention in many applications such as biodegradable medical devices, healthcare products, and single-use packaging. The application of PLLA has expanded to three-dimensional (3D) printing where individually customized products are produced. Biocompatibility, and biodegradability, PLLA has a relatively low heat resistance and is considered brittle for some applications requiring high mechanical strength levels, high resistance to temperature, and good impact performance [1,2]. Simultaneous improvements of impact toughness and heat resistance of PLLA need to be made while preserving its biodegradability and sustainability. Blending PLLA with PBS is suggested to obtain the fully biodegradable blend with improved thermal stability and toughness [5,6,7,8]. Even though remarkably enhanced tensile toughness and elongation can be obtained, [5,6]
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