Extrusion blown films of poly(lactic acid) chain‐extended with food grade multifunctional epoxies

The effectiveness and efficiency of two food grade multifunctional epoxies with low and high epoxy equivalent weights in chain extending/branching poly(lactic acid) (PLA) were studied in a torque rheometer. Processing PLA and chain extender (CE) at 200°C for 300 s not only chain‐extended PLA effectively as indicated by a significant increase in the mixing torque as well as PLA's melt viscosity and molecular weight, but also branched it leading to its reduced crystallinity. Chain extension occurred through the ring opening reaction of epoxy groups in the CE with PLA's hydroxyl and/or carboxyl groups. CE with lower epoxy equivalent weight was more efficient due to its higher reactivity. Secondly, the processabilities of PLA films chain‐extended and branched with various amounts of the most efficient CE were assessed. Like in torque rheometer, chain extension and branching also occurred during film production as indicated by PLA's increased molecular weight and decreased crystallinity when blended with CE. However, film manufacture was feasible only for blends with up to 0.5% CE, becoming unprocessable above this content due to chain entanglement leading to increased viscosity. Chain extension/branching of PLA was beneficial in overcoming film's brittleness since its impact strength increased almost linearly with the CE content. POLYM. ENG. SCI., 59:2211–2219, 2019. © 2019 Society of Plastics Engineers