Random aliphatic copolyesters as new biodegradable impact modifiers for polylactide materials

In this work, amorphous poly(ε-caprolactone-co-δ-valerolactone) (P[CL-co-VL]) random aliphatic copolyesters were synthesized and investigated as biodegradable impact modifiers for PLA in order to enhance the low brittleness of renewable and biodegradable polylactide (PLA). The random copolyesters were produced by ring-opening polymerization between δ-valerolactone (VL) and ε-caprolactone (CL) in bulk (absence of solvent) at 160 °C using tin(II) octoate as catalyst. The copolyesters were added at 10 wt.% into a commercially available PLA matrix using a microcompounder. The influence of the composition and the molar masses of the resulting copolyesters were investigated on the PLA toughness in relation with the type of molding techniques, i.e., via melt injection or compression moulding. It came out that the use of a high molar mass copolyester (Mn¯=ca.60,000) with a molar composition of 45/55 mol% (CL/VL) results in a significant improvement in toughness for compression-molded PLA materials, actually reaching almost a threefold increase in impact strength. This improvement in toughness was related to the mean size and size distribution of the dispersed copolymer microdomains throughout the PLA matrix.

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► P[CL-co-VL] copolyesters were investigated as biodegradable impact modifiers for PLA.
► Molecular parameters and molding techniques were investigated on the PLA toughness.
► The mechanical and morphological properties of the blends were evaluated.
► The influence of rubbery character of the dispersed phase was highlighted.
► Improvement in toughness was related to the morphological issues.