Polymer rejuvenation of PET textile waste
Abstract: Thermomechanical recycling of polyethylene terephthalate (PET) typically includes a decrease in the polymer´s intrinsic viscosity and therefore a reduction of the molecular weight. Consequently, thermomechanical recycling is usually a downcycling of the product. However current methods to increase the molecular weight such as solid-state polymerization or the usage of chain extenders are time consuming or introduce foreign molecules into the PET´s molecular chain. Thus, the aim of this work was to try to increase the molecular weight in the molten state in an extruder, to decrease the processing times. The processing times are reduced compared to the solid-state polymerization because in the molten state the movability of the polymer chain is increased. Moreover, no supplementary substances are added for the processing so that no foreign structures are introduced during reprocessing. Virgin PET pellets were extruded at 285°C, 290°C and 295°C set temperature and 2rpm, 4rpm, and 7rpm screw rotation rate. Afterwards the PET´s properties were investigated by measuring their intrinsic viscosities, conducting a 1H NMR and a DSC measurement. Additionally, pre-experiments were conducted to explore the possibilities of feeding industrial scrap polyester fabrics into the extruder. The polymer characterization showed that the intrinsic viscosity and therefore the molecular weight of the processed samples decreased with the parameters chosen for this experiment. Samples processed at 285°C and 7 rpm showed in the average the highest intrinsic viscosities and therefore the highest molecular weight of all processed samples. Additionally, the results of the 1H NMR and the DSC indicated degradation reactions such as thermal degradation and hydrolysis. Thus, further research is necessary to find an easily accessible recycling method for polyester textiles and reduce the amount of polyester textile waste. However, it is possible to feed long textile stripes into the twin screw extruder and reprocess it to a strand which is an important step for further recycling.
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