Research On Blown Film Extrusion Of Polylactic Acid

Poly(lactic acid) (PLA) is a kind of environmentally friendly biocompatibility polymer, its blown film products have high strength, high modulus and high permeability compared with common plastic film. However, the melt strength of PLA is quite low, which limites its application in the blown film extrusion. PLA also presents poor toughness, brittleness, low crystallinity and poor heat resistance. All these drawbacks restrict the use of PLA blown film seriously.In this study, in order to overcome these drawbacks above, chain extender is applied to enhance melt strength to promote the film-forming property; some kind of toughening agent is applied to enhance toughness to process the blown film successfully; blending modification of PLA with Talc is applied to improve its crystallinity and heat resistance. The influences of bulking agent type and content on the mechanical properties of PLA blown film were analyzed. At the same time, the influences of the process parameters of the extruder on the mechanical properties of the blending film were studied. The reasons for these results were also discussed. The main conclusions are as below:(1) The melt strength of PL A is a key factor on the properties of PLA blown film in the process of preparation of blown film. The use of chain extension can enhance the melt strength, which results in the obtention of the blown film successfully and the increased tensile strength and tensile modulus as well.(2) The toughness of PLA blown film was greatly improved by adding polyethylene glycol (PEG). The elongation at break and tear strength were greatly improved with PEG added. However, the tensile strength and modulus decreased. The optimum adding amount of PEG is 10wt.%in the experiment.(3) The crystallinity, heat distortion temperature, heat resistance and surface layer structure of PLA were improved by adding Talc. The maximum blowup ratio and mechanical properties of PLA blown film were also promoted.(4) The effects of screw speed, head-temperature, blowup ratio and drawing ratio of PLA blown film extrusion on mechanical properties were studied, and the optimum technologies among the blown film extrusion processes was determined.