The melt compatibility between poly(L-lactide) (PLA) and polyamides (PAs) with related thermomechanical properties is addressed. A particular attention is paid to four commercial PAs with extrusion processing temperatures close to PLA (PA10-10 to PA12). PLA/PA blend morphologies without a compatibilizer are first revealed by scanning electron microscopy. PA12 displays the best droplet dispersion into PLA (D n 700 nm), whereas a poor interfacial adhesion is attested for PLA/PA10-10 blends. Interfacial tensions corroborate the PLA/PA10-10 incompatibility (γ 12 9 mN/m, 240 C) with decreasing γ 12 in the order PLA/PA10-10 > PLA/PA11 > PLA/PA12 (γ 12 2 mN/m). Surface tensions confirm the highest compatibility between PLA and PA12. Ductilities, toughnesses, and thermal resistances of PLA/PA blends are evaluated up to 40-wt % PA. Brittle-to-ductile transitions are observed for PA content higher than 30-wt % with the highest ductility for PLA/PA12, in accordance with their enhanced compatibility. Impact strengths display similar trends with a twofold increase for PLA/PA12. An outstanding synergy between PLA and PA is highlighted by dynamic mechanical analyses with heat deflection up to 130 C for PLA/PA blends. The synergy arises from a peculiar crystallization of PLA in the presence of PA. PLA/PA morphologies/interfaces can be consequently tuned by an appropriate PA choice with interesting improvements of thermomechanical properties for high-performance/durable applications.
Engineering properties of partially-biobased poly(L-Lactide)/poly(amide-12) (PLA/PA12) blends are here addressed using a functional compatibilizer, namely poly(L-Lactide) grafted maleic anhydride (PLA-g-MA). PLA/PA12 blends with compatibilizers are processed using twin-screw extrusion, and the amount of PLA-g-PMA is here optimized with respect to final blend properties such as ductility, impact toughness, and thermal resistance. Blend morphologies depict the enhanced PA12 dispersion into PLA-g-MA with strong interfacial adhesion, in accordance with a compatibilization effect of PLA-g-MA in PLA/PA12 blends. Ductility of the compatibilized blends shows remarkable improvements with the highest ductility close to 290% for an optimized PLA/PA12/PLA-g-MA weight composition (respectively, 69/30/1). The impact strength of compatibilized blends showed a similar twofold improvement for compatibilized blends. Morphology of injection molded samples revealed finer dispersion and stronger interfaces. The morphology of the transversal section displayed fibrillation of PA12 for PLA-g-MA content up to 2 wt.%. Fibrillation and lower droplet size seemed to play a key role in the improvement of ductility in compatibilized blends. Considerable synergy was detected in the dynamic mechanic analysis of the compatibilized blends. The thermal resistance of the PLA/PA12 blends showed improvement, and this behavior could be due to the formation of copolymer leading to additional interfacial crystallization. This study consequently indicates that PLA-g-MA is an efficient compatibilizer for partially biobased PLA/PA12 blends with potential applications in the automotive and electronic industry.
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