Thermal behavior of PLA plasticized by commercial and cardanol-derived plasticizers and the effect on the mechanical pro
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Thermal behavior of PLA plasticized by commercial and cardanol‑derived plasticizers and the effect on the mechanical properties Antonio Greco1 · Francesca Ferrari1 Received: 19 June 2020 / Accepted: 11 November 2020 © The Author(s) 2020
Abstract This paper is aimed at studying the thermal properties of poly(lactic acid), PLA with different plasticizers. Plasticized PLA was obtained by mixing and extruding PLA with 20 mass% of neat cardanol, epoxidized cardanol acetate (ECA) and poly(ethylene glycol) (PEG) 400. The glass transition of completely amorphous samples, melting and crystallization behavior of plasticized PLA were analyzed by differential scanning calorimetry. Results obtained show that, below Tg, a higher enthalpy relaxation occurs for PLA plasticized by cardanol derivatives. This is indicative of a faster mobility of PLA chains below Tg, when cardanol derivatives are used as plasticizers. On the other hand, an opposite behavior was observed for the crystallization studies. In facts, a much faster crystallization was found for PLA plasticized by PEG, which in turn indicates a much higher mobility of PLA chains above Tg compared to PLA plasticized by cardanol derivatives. Mechanical properties obtained on completely amorphous samples show that PLA plasticized by ECA is characterized by lower modulus, which is indicative of a more efficient plasticization. On the other hand, the thicker crystals formed during crystallization of PLA plasticized by ECA involve a more relevant increase in the modulus in semicrystalline samples. Keywords PLA · Plasticizer · Glass transition · Crystallization · Modulus
Introduction Recently, environmental concerns and a decrease in petroleum availability led to bulk production of bio-based materials [1, 2]. Among them, poly(lactic acid) (PLA), a biodegradable, aliphatic polyester derived from lactic acid, is a promising polymer for the replacement of petroleum derivatives [3]; PLA main features, such as high biodegradability and good mechanical response, with stiffness and strength comparable to those of polystyrene, allowed its use for several industrial applications [4]. Moreover, thermal and rheological properties of PLA allow its processing with a wide range of industrial techniques, such as injection molding, extrusion, thermoforming, fiber spinning and calendaring [5, 6].
* Antonio Greco [email protected] 1
Department of Engineering for Innovation, University of Salento, via per Arnesano, 73100 Lecce, Italy
Nevertheless, PLA usage can be limited because of its high brittleness, which poses severe limitations in terms of processability and end-use mechanical performances. On the other hand, the ductility of PLA can be improved by copolymerization, or by the addition of plasticizers [7]. Being the addition of plasticizers much more cost-effective, it is often preferred to copolymerization; in particular, plasticizer addition allows a decrease in glass transition temperature and an increase in toughness of the polymer [8, 9]. Although several plasticizers
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