Study On Blown Film Extrusion Of Polyethylene Terephthalate(PET)

PET films have high strength, good heat resistance and high transparency,widely used in packaging industry. Nowadays, almost all the PET film products are casting film, which equipment investment is high; and blowing film has low investment in equipment, film size can be adjusted. So, the study on blown film extrusion of PET had very important significance for reducing costs of film and expanding product applications.But the melt strength of PET is very low, resulting in blow molding difficult. And the Material toughness is poor, resulting in blown film products brittle. These shortcomings seriously affect the PET blown film processing and application. Faced with these drawbacks, PET is modified by chain extension to improve the material processing performance. And then PET is toughened and modified to improve the toughness of the material, thereby improving the flexibility of the film. The effects of chain extenders and toughener and blow molding process on the bubble stability, maximum blow ratio film strength, mechanical properties, heat resistance and transparency were studied systematically. The optimum formula and blown film process parameters were studied. High strength, good flexibility, heat resistance and high quantity of PET blown film were prepared. The main work and conclusions are as follows:(1) Improved PET molding performance by blending modification. The results show that the amorphous polymer PETG with better processing performance can improve the blow molding performance of the material, and the elongation at break of the blended film can be improved.(2) The melt strength and the maximum blowing ratio of the blown film were greatly improved by the extended chain modification, and the tensile strength and elongation at break of the blown film were improved.(3) using two tougheners (PEG, POE) toughening of PET material, studies have shown that, POE better toughening effect on the PET film. The addition of POE greatly improved the flexibility of the blown film, the elongation at break of the film product was improved significantly, and the tensile fracture was changed from brittle fracture to ductile fracture, and the PET blown film with high flexibility, low wrinkle and high surface roughness .(4) The effect of extrusion blown film process on the mechanical properties of the film, in order to determine the superior process parameters:The blow up ratio 3.7, 5.0 pulling speed, die temperature of 270℃. Finally, the transverse / longitudinal tensile strength and elongation at break of PET blown film products were 36.9MPa / 41MPa and 150.3% / 131.8%, respectively.