This study was aimed at developing a single-step process that efficiently incorporates epoxidised soybean oil (ESO) into a poly (lactic acid) or PLA matrix in order to manufacture PLA sheet/film with improved flexibility without affecting other package characteristics. To achieve this goal, a processing system in which an extruder and a peristaltic injector pump attached in tandem was developed for a continuous and accurate incorporation of the plasticizer into the molten matrix.The effect of ESO addition levels on impact and tensile properties of plasticized PLA sheets was examined. The flexibility of plasticized specimens and the phase morphology between the plasticizer and the matrix were characterized through glass transition measurement and scanning electron microscopy, respectively. Additionally, this study examined the effect of plasticizer on the heat sealability of PLA film during pouch manufacture by measuring both the burst pressure and seal strength of the flexible pouches sealed at different sealing temperatures. Finally, the tensile properties of plasticized PLA blown films as a function of storage time over a span of 125 days was examined.The impact strength of plasticized sheets increased significantly with increasing ESO content, indicative of the toughening capacity of ESO as a plasticizer. The experimental results suggested approximately 15 wt % as the optimum concentration of ESO in plasticized sheet. The ductility of plasticized PLA sheets followed similar trends and the brittle-to-ductile transition occurred in the range of 5-10 wt % ESO content, in agreement with the impact strength results. In contrast, both the tensile strength and the modulus of the sheets decreased with increasing ESO content. This was expected due to the plasticization effect, which induced a decrease in the glass transition temperature resulting in mobility of the PLA polymer chains.Burst pressure and seal strength of PLA films were not affected by the addition of plasticizer or by the sealing temperature range studied. The tensile properties of blown film plasticized with 15 wt % ESO, tested at periodic intervals of storage time, indicated no significant change in the ductility and the tensile strength at yield as the storage time increased, implying the good permanence of ESO in the plasticized PLA films over a period of time tested. In contrast, the tensile modulus showed a slight but a statistically significant increase in stiffness after only 7 storage days, indicating a possible loss of plasticizer from the film as the storage time increased. This contradictory trend will be investigated further.
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