Abstract
The aim of this contribution is to assess the use poly(styrene-co-glycidyl methacrylate-b-styrene) copolymers synthesized by nitroxide mediated polymerization (NMP) as chain extenders in the recycling of poly(lactic acid) biopolyester. Concisely, the addition of such block copolymers during the melt processing of recycled poly(lactic acid) (rPLA) leads to important increases in the viscosity average molecular weight of modified polymeric materials. Molar masses increase from 31,000 g/mol for rPLA to 48,000 g mol−1 for the resulting rPLA/copolymer blends (bPLA). Fortuitously, this last value is nearly the same as the one for pristine PLA, which constitutes a first piece of evidence of the molar mass increase of the recycled biopolymer. Thermograms of chain extended rPLA show significant decreases in cold crystallization temperature and higher crystallinity degrees due to the chain extension process using NMP-synthesized copolymers. It was found that increasing epoxide content in the NMP-synthesized copolymers leads to increased degrees of crystallinity and lower cold crystallization temperatures. The rheological appraisal has shown that the addition of NMP synthesized copolymers markedly increases complex viscosity and elastic modulus of rPLA. Our results indicate that P(S-co-GMA)-b-S) copolymers act as efficient chain extenders of rPLA, likely due to the reaction between the epoxy groups present in P(S-co-GMA)-b-PS and the carboxyl acid groups present in rPLA. This reaction positively affects viscometric molar mass of PLA and its performance.
Highlights
Poly(lactic acid) (PLA) has attracted much attention in recent years as an environmentally biodegradable polymer which may serve as replacement of conventional petrochemical-based polymers [1]
In previous contributions from our group, we reported the chain extension of recycled PET by the addition of copolymers synthesized by reversible additionfragmentation transfer (RAFT), a type of reversible deactivation radical polymerization (RDRP) technique [40,41]
Formulations and experimental results for the macro-nitroxide mediated polymerization (NMP) precursors and P(S-co-GMA)-b-PS copolymers are summarized in Tables 1 and 2
Summary
Poly(lactic acid) (PLA) has attracted much attention in recent years as an environmentally biodegradable polymer which may serve as replacement of conventional petrochemical-based polymers [1]. PLA has good transparency, moderate toughness, barrier properties and biocompatibility, which lead to its wide applicability [3,4]. As stated earlier, such features make it suitable for substitution of some petroleum-based polymers. What really stands out with PLA is its biodegradability and the fact that it is completely derived from renewable resources. That is why this biopolymer has attracted substantial attention in recent years
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