Research On Extrusion Foaming Of Polyethylene Terephthalate (PET)

Polyethylene terephthalate(PET) foamed material has excellent thermost-ability, thermal insulation, waterproofness and well mechanical properties, as well as its low density, well recyclability and little environmental impact which make it available in many fields with extensive market foreground. Nevertheless, foaming of PET is creating challenges due to its strong sensibility to moisture,high melting point,narrow forming temperature range and low melt strength. At present, several PET foaming products were produced abroad while little research of PET foaming was carried out in our country. Continous fabrication of PET foam can come true by extrusion foaming, which meet the requirement of industrialization. In this paper, PET foaming materials with low apparent density and fine uniform cells were gained by chemical extrusion foaming method, which would make great significance to improve PET foaming industrialization in our country.In this paper, PET extrusion foaming process routes were established, specialized screw was designed on the basis of characteristics of PET, melt strength of PET was enhanced, and rheological properties of PET were analysed. On that basis, effect of formula, equipment and processing parameters on foaming effects of samples were systematically studied, the optimal formula, and technological parameters were summarized finally. Conclusions were gained as follow:(1) According to rheological properties analysis of melt strength modified PET, it was indicated that melt strength of PET was improved effectively by chain extender KLA and thermoplastic elastomer added, and chain extender KLA was more efficient than chain extender PMDA.(2) According to the effect of formula on foaming effects of samples, it was indicated that chain extender KLA was more efficient to improve the foaming effects of samples; samples of best foaming effect were gained with 0.8phr chain extender KLA and 2.0phr endothermic chemical foaming agent C-1; Sink marks of samples were reduced when extruded, shapes of samples were kept and cell structures were improve further by thermoplastic elastomer added of fair amount.(3) According to comparison between specialized screw designed and general type screw, it was indicated that structure design of specialized screw was reasonable and foaming effects were better by specialized screw. According to comparison between two process routes, it was indicated that samples by two-step extrusion foming method present better foaming effects with smoother surface, more uniform distrubution of cell size and cell position.(4) According to effect of screw speed, barrel temperature and die temperature on PET foaming effects, it was indicated that foaming effects were improved by increasing screw speed or decreasing barrel temperature and die temperature. Samples of best foaming effect were gained with barrel temperature of 265℃, die temperature of 220℃and screw speed of 30 r/min.(5) Fine PET foaming samples were gained with apparent density range from 0.53g/cm3 to 0.83g/cm3 and cell size range from 55μ.m to 77μm. This foaming level has reach or even exceeded that abroad by chemical extrusion foaming with cell mean size of 65μm and apparent density range from 0.5 g/cm3 to 0.83g/cm3.