Assessment of non-ester monoterpenoids as biobased plasticizers for polylactide with improved ductile behaviour

Abstract

Poly(lactide) (PLA) is a biodegradable aliphatic polyester derived from renewable resources. This material is characterized by high strength and stiffness; however, it has a high brittleness which makes it difficult to use in certain applications. In the present work, the plasticizing effect of different non-ester monoterpenoids, namely carvone, citral, citronellal and eucalyptol, on the mechanical, thermal, morphological, physical and chemical properties of PLA has been studied. In this case, different amounts (10 and 20 wt%) of each monoterpenoid were mixed with PLA in a twin-screw extruder and standardized samples were obtained by injection molding. The obtained results show how the addition of 20 wt% of the different monoterpenoids significantly improves the elongation at break of PLA, reaching values of 335.7 % for 20 wt% citral content, which represents an increase of about 4044 % with respect to pure PLA (8.1 %). In addition, a significant reduction in the tensile strength and Young's modulus of PLA has also been observed with the presence of monoterpenoids. The addition of monoterpenoids also leads to a decrease in the glass transition temperature and crystallization temperature of PLA due to the increased mobility of the polymeric chains caused by the plasticizing effect of the monoterpenoids, this decrease being more noticeable in the case of citral and citronellal, which are the monoterpenoids with the highest miscibility with PLA. Finally, it has been observed that the addition of monoterpenoids hardly affects the transparency of PLA, obtaining materials that may have a high potential in sectors such as food packaging. Therefore, it has been demonstrated that these non-ester monoterpenoids, especially citral, have a great potential to obtain environmentally friendly PLA formulations with improved toughness.