| An experimental study of the continuous PET foam extrusion process with environmentally benign CBA was conducted. The screening of CBAs for the selection of CBAs suitable for the production of low density PET foam was performed using thermal analysis and mechanical compatibility tests. From TG analyses for various CBAs, it was shown that Expandex 5 PT has superior decomposition characteristics compared to other CBAs. From mechanical compatibility analysis, Activex 331 and HK 40 B showed improved compatibilities over other CBAs. Expandex 5 PT was chosen considering its excellent decomposition characteristics and lack of any significant incompatibility with PET. The effects of material and processing conditions on foam properties were studied and the optimal parameters for the production of PET foam density were identified. The use of HMW PET reduced the PET foam density. It was shown that an increase in the CR of the screw (5:1) did not always increase the stock pressures in the metering and die sections, although the effect of CR on PET foam properties was not detected. As the concentration of CBA was increased, PET foam density was decreased, but it was increased above the CBA concentration of about 1% due to the shrinkage of the PET foam at high CBA concentration. The increase of CBA concentration caused the degradation of PET where higher molecular weight PET was more vulnerable to the degradation. It was observed that there is an optimal screw speed for the production of low-density PET foam with fine cell structure. At high screw speed, distortion of the cell shape was observed which was attributed to high shear. Using HMW PETs and Expandex 5 PT in a conventional extruder, PET foams with a density as low as 0.35 g/cm 3 were produced. The mechanical properties of PET foams were estimated. From tensile and flexural tests, it was seen that the modulus vs. density relationship follows the square law. The recommendations for further reductions in PET foam densities were presented. |
