EFFECTS OF MASTICATION TIME AND TYPE OF NATURAL RUBBER ON PROPERTIES OF POLY(LACTIC ACID)/NATURAL RUBBER BLOWN FILMS

In order to enhance the properties of poly(lactic acid) (PLA) blown film, the different kinds of natural rubbers (NRs) were considered. Air dried sheet (ADS) and Standard Thai Rubber 5L (STR5L) were used in this research. Non-rubber content and plasticity of natural rubbers (NRs) were characterized before using. Plasticity after ageing (P30) and plasticity retention index (PRI) values of STR5L were much lower than those of ADS, indicating that STR5L is vary thermally sensitive. Mastication sufficiently induced the breaking up of the long rubber molecules into short ones via thermal oxidation and shear force. Viscosity average molecular weight and Mooney viscosity of masticated NRs intensely decreased with increasing mastication time, especially STR5L. The properties of PLA/NR blown films were then studied. Masticated NR/PLA blown film’s surface is much smoother and the film is much transparent than those of virgin NR/PLA blown films. As mastication time increased, numerous small rubber domains in PLA matrix were clearly evident by scanning electron microscope (SEM). The mechanical properties of blown films are outstandingly improved by the addition of masticated NRs into PLA matrix phase, especially toughness, tear strength and impact strength. Consequently, blending PLA with masticated NRs containing short rubber molecules is an effective approach to improve the properties of blown films for using in food and green packaging applications.