Recycling of poly(ethylene terephthalate) into closed-cell foams

The increase of the elongational viscosity of recycled poly(ethylene tereph thalate) (PET) is investigated with the aim of producing closed-cell foams by means of a cost-effective reactive extrusion technique. A recycled PET g rade containing controlled contamination levels of polyvinyl chloride (PVC) and poylethylene (PE) is selected, and compared with virgin bottle-grade P ET as a reference. Reactive processing with a tetrafunctional epoxy additiv e induces randomly branched molecules with a lower degree of branching in r ecycled PET than in virgin PET, as shown by a molecular structure analysis. The corresponding increase in elongational viscosity is related to foaming experiments performed using supercritical CO2 in a pressurized vessel. Obs ervations of foam microstructures reveal that modified virgin PET forms clo sed-cell structures under a large variety of foaming conditions, as opposed to unmodified virgin and recycled PM, which collapse as a result of insuff icient elongational resistance. Closed-cell foams are also obtained using m odified recycled PET, providing that the temperature at which the pressure is released is lowered to 260 degrees C. Recycling of PET into closed-cell foams is thus achieved, although the processing window is slightly reduced compared to virgin PET.