EFFECTS OF FILM BLOWING AND DRAWING CONDITIONS ON PROPERTIES OF POLY(LACTIC ACID)/NATURAL RUBBER FILMS

The aim of this research is to find the relationship between morphology, thermal and mechanical properties, and gas permeation property of poly(lactic acid) (PLA)/natural rubber (NR) films and film blowing conditions, such as take-up ratio (TUR) and blow-up ratio (BUR). The effect of uniaxial drawing at elevated temperature on the properties of drawn films was also investigated. PLA films containing 10 wt% NR were prepared by melt mixing in a twin screw extruder and then blown by a single screw extruder attached to a blown film line. It is found that increasing TUR and BUR shows the deformation of NR and enhanced orientation of polymer chains. The mechanical properties drop significantly, except tensile strength and Young’s modulus, which can be explained by a deformation of NR domains from spherical into elliptical after stretching. Moreover, oxygen permeation of PLA/NR blown films increases when TUR increases, resulting from the microvoid formation. Uniaxial drawing of the obtained blown films in machine direction (MD) and transverse direction (TD) at 65˚C and drawing rate of 150 mm/min was achieved in a tensile testing machine equipped with a temperature controlled environmental chamber. It is found that increasing drawing ratio in MD improves crystallinity from 3.42% to 11.52% at drawing ratio of 100%. In comparison with the blown PLA/NR films without drawing, the mechanical properties of films at drawing ratio of 100% are also enhanced as follows: tensile strength of 68%, Young’ modulus of 24%, elongation at break of 81% and tensile toughness of 114%. Furthermore, the oxygen permeation increases and reaches maximum value as a result of microvoid formation and gas barrier property of crystalline structure of PLA.