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Abstract
Poly(lactic acid) was melt-blended with epoxy resin without hardener and chitosan (CTS) to prepare modified PLA (PLAEC). Epoxy resin 5% and CTS 1–20% (wt/wt) were incorporated into PLA during melt mixing. PLAEC was melt-blended with an epoxidized natural rubber (ENR) 80/20 wt. The PLAEC CTS 1% blended with ENR (PLAEC1/ENR) showed a high tensile strength (30 MPa) and elongation at break (7%). The annealing process at 80 °C for 0–15 min maintained a tensile strength of approximately 30 MPa. SEM images of the PLAE/ENR blend showed phase inversion from co-continuous to ENR particle dispersion in the PLA matrix with the addition of CTS, whereas the annealing time reduced the hole sizes of the extracted ENR phase due to the shrinkage of PLA by crystallization. Thermal properties were observed by DSC and a Vicat softening test. The annealing process increased the crystallinity and Vicat softening temperature of the PLAEC1/ENR blend. Reactions of −COOH/epoxy groups and epoxy/−NH2 groups occurred during PLAE and PLAEC preparation, respectively. FTIR confirmed the reaction between the −NH2 groups of CTS in PLAEC and the epoxy groups of ENR. This reaction increased the mechanical properties, while the annealing process improved the morphology and thermal properties of the blend.
Highlights
Petroleum-based plastics are a major environmental concern owing to their inability to degrade naturally
It was confirmed that the epoxy resin reacted with −COOH of polylactic acid (PLA) and NH2 groups of CTS, whereas the interfacial reaction of the PLAEC20/epoxidized natural rubber (ENR) blend was due to a reaction between the NH2 groups of CTS and epoxy groups of ENR (Figure 3c)
PLA blends with epoxy resin, CTS, and ENR were successfully developed with improved morphology and mechanical properties
Summary
Petroleum-based plastics are a major environmental concern owing to their inability to degrade naturally. This lack of degradation affects organisms living on land and in the sea. Biodegradable polymers, such as polybutylene succinate (PBS) [1], polylactic acid (PLA) [2], polysaccharides [3], carboxymethyl cellulose [4–6], carboxymethyl bacterial cellulose [7], CTS [8], carboxymethyl chitosan [9], starch [10–12], thermoplastic starch (TPS) [13–15], keratin [16], and pectin [17,18], have been widely studied. It is transparent and has a high modulus and strength comparable to many petroleum-based plastics [19,20], such as polyethylene terephthalate and polystyrene. The use of polymer blends that react with their terminal carboxyl and hydroxyl groups [22,23] can improve the mechanical properties of bioplastics
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