Research On The Chain Extension /branching And Foaming Of Pet

Polyethylene terephthalate (PET) has excellent physical properties and is widely used in manufacture of textile fibers, bottles and packaging films. The recycled PET (R-PET) is increasing day by day as a result of the broad use of PET. This thesis is based on the use of R-PET. As the degradation reactions during melt processing of R-PET will lead to the decreasein intrinsic viscosity and molecular weight, so this study, in which the influence of temperature and screw speed on intrinsic viscosity is mainly investigated, began with the processing parameters which effect the degradation reaction of R-PET. Then a study on chain extension /branching modification of R-PET under the best processing parameters was carried out. Batch mixer experimental results showed that a certain amount of PMDA could increase the chain extension /branching degree of R-PET, which led to the decrease in melt flow rate, crystallization temperature and melting temperature. In reactive extrusion process, intrinsic viscosity and molecular weight of R-PET decreased with the increase of processing temperature and screw speed. Experimental results showed that PMDA and BASF chain extender (ADR- 4370S) are effective chain extenders in increasing intrinsic viscosity and molecular weight of R-PET, in which the effect of ADR-4370S is better than PMDA.To improve the foaming properties of PET, the chain extension /branching modification of PET was studied in the experiment. Shear rheological data showed that the apparent viscosity increased with the addition of a certain amount of chain extenders.PET was foamed using the simulative foaming apparatus designed by ourselves, with supercritical CO2 as the foaming agent. This study began with the investigation of the influence of temperature on cell morphology of PET foam. Experimental results showed that due to the low melt strength of PET at high temperature, cell coalescence happened, resulting in large cell size of the foamed samples. With the decrease of foaming temperature, cell coalescence decreased and cell size decreased with the increase of melt strength. The influences of processing parameters including foaming temperature, temperature drop rate and saturation pressure on cell size, cell morphology and cell–population density of PMDA modified PET foamed samples were still studied. From the experimental study, several conclusions were drawn as follows: foamed samples with better cell morphology could be obtained with the decrease in foaming temperature; the temperature drop rate was increased by air cooling, which could improve the cell morphology and decrease cell size; with the increase in gas saturation pressure, the solubility and diffusion coefficient of supercritical CO2 in PET increased, which was propitious to increase of cell-population density. Foamability of PET was improved with chain extending/branching modification to a certain degree. Further study needs to be carried out with the improvement of our equipment.