The thermo-mechanical degradation of an unstabilized polypropylene copolymer during extrusion at different temperatures (from 180 to 240 °C) and the production of volatile organic compounds (VOC) were studied. VOC's were collected via a volatile condenser, fitted at the degassing exit of the extruder and analyzed via infrared spectroscopy (FTIR-ATR). The polymer degradation was followed via size exclusion chromatography and FTIR. At low extrusion temperatures (180 °C) the PP degradation produces undetectable quantities of VOC's. On the other hand, starting from 200 °C, there is the formation of olefinic compounds of molecular weight not volatile at room temperature, which increase in quantity with the rise of the extrusion temperature. The Chain Scission Distribution Function (CSDF) shows that at low temperatures (180 and 200 °C) the PP degradation mechanism is preferentially via chain scission with some branching and/or crosslinking in the lower molecular weight. At higher extrusion temperatures (220 and 240 °C) the degradation mechanism is exclusively via chain scission and it is preferential, i.e., the number of chain scission increases with the increase in the initial molecular weight of the original polymeric chain.
Polypropylene; thermo-mechanical degradation; molecular weight distribution; chain scission; FTIR; CSDF
