Effect of the Addition of Natural Rice Bran Oil on the Thermal, Mechanical, Morphological and Viscoelastic Properties of Poly(Lactic Acid)

For the first time in this study, the utilization of rice bran oil (RBO) as possible totally eco-friendly plasticizer for poly(lactic acid) (PLA) has been investigated. For comparison, the behavior of soybean oil (SO) has also been analyzed. Both oils are not completely miscible with PLA. However, certain compatibility exists between PLA and (i) RBO and (ii) SO, because demixing is not complete. Although not totally miscible, RBO and SO are able to reduce the viscosity of the PLA+RBO and PLA+SO mixtures, which attests that a small amount of RBO or SO can be successfully added to PLA to improve its processability. Additionally, the mechanical properties of the PLA+RBO and PLA+SO mixtures exhibit trends typical of plasticizer-polymer systems. More interestingly, RBO was found to accelerate the growth of PLA alpha'-crystals at a low crystallization temperature. This feature is appealing, because the alpha'-phase presents lower elastic modulus and higher permeability to water vapor in comparison to the alpha-phase, which grows at high temperatures. Thus, this study demonstrates that the addition of RBO to PLA in small percentages is a useful solution for a faster preparation of PLA materials containing mainly the alpha'-phase.