Morphology, mechanical and thermal properties of poly(lactic acid) (PLA)/natural rubber (NR) blends compatibilized by NR
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Napida Hinchiranana) Department of Chemical Technology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand; and Center of Excellence on Petrochemical and Materials Technology, Chulalongkorn University, Bangkok 10330, Thailand (Received 15 August 2016; accepted 4 January 2017)
Natural rubber (NR) is expected to enhance impact strength of poly(lactic acid) (PLA). Because the polarity difference of NR and PLA leads PLA/NR blends having phase separation and poor mechanical properties, this research aimed to synthesize NR-graft-PLA (NR–PLA) via esterification of maleated NR (NR-MAH) with PLA. The role of NR–PLA used as a compatibilizer on mechanical and thermal properties of the PLA/NR blends was studied. Maximum grafted PLA level at 66.8% (w/w) was reached when NR-MAH was esterified with PLA [2/1 (w/w) PLA/NR-MAH] catalyzed by 0.05 M 4-dimethylaminopyridine at 140 °C. The addition of 5% (w/w) NR–PLA [36.6% (w/w) grafted PLA content] into PLA/NR blend [80/20 (w/w)] increased Izod impact strength of the neat PLA plate from 28.9 J/m to 62.7 J/m due to partial miscibility of blends attested by morphology analysis and Molau test. Hydrolytic degradation of PLA/NR blends with and without the addition of NR–PLA was also examined.
I. INTRODUCTION
Due to environmental concerns, the replacement of petroleum-based plastics by biodegradable and nonhazardous materials has been promoted. Among them is poly(lactic acid) (PLA), a biodegradable aliphatic polyester that is produced by the polymerization of lactic acid. Lactic acid itself is commercially obtained from the fermentation of carbohydrate sources, such as rice, sugar beet, sugarcane, wheat and sweet potato,1–3 including nonfood waste parts of these crops. Since PLA is naturally degraded to the nontoxic carbon dioxide and water within a few weeks under a typical compost condition, PLA is a great choice for the production of short-term packaging that would typically end up in landfill sites. Although PLA is transparent with a high flexural and tensile modulus, and so is able to compete with polystyrene,4 its application is limited by its inherent brittleness, low impact strength and low elongation at break due to its high glass transition temperature (Tg 5 55 °C) with low entanglement density and chain stiffness.5,6 It has previously been suggested that the brittleness of PLA could be improved by co-polymerization of PLA with polyisoprene7 or blending PLA with other polymers such as ethylene-co-acetate copolymer,8 poly(hydroxyl Contributing Editor: Tao Xie a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.9
butyrate) (PHB) plasticized by acetyl(tributyl citrate) (ATBC)9 or tributyrin (TBL)10 and block copolymers of ethylene glycol and propylene glycol.11 Moreover, it has been reported that the blending of PLA with natural rubber (NR) could produce the rubber-modified PLA with higher toughness and impact resistance properties and this method still maintained the bio-based characteristic product. The NR particles dis
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