The paper deals with gel permeation chromatography (GPC) monitoring of the behaviour of PET (polyethylene terephthalate) after repeated extrusions. Virgin PET was submitted to three successive extrusion/drying cycles and then the samples were swelled with hexafluoroisopropanol and treated with chloroform. GPC analysis was carried out at room temperature on a B.C.S. Serial LC 2000 GPC system equipped with a series of four GPC columns with UV detection at 254 nm and chloroform as eluent. GPC results showed that after each extrusion step the molecular weight distribution of the PET was different and Mw, Mn and Mz decreased. These findings suggest that during each extrusion degradation occurs and that repeated extrusions, as in the case of the recycling PET, may cause an alteration of the molecular weight distribution of the original PET.
In this work the relationships between processing, structure and migration properties of recycled polypropylene (PP) were analysed in relation to the possible use of recycled PP in food packaging applications. PP containers used in food packaging were contaminated with food and then washed, reduced into a processable size, dried and reprocessed by injection moulding. Gel Permeation Chromatography (GPC) analysis, mechanical, and total migration tests were performed on injection moulded samples to verify the effect of the recycling process on the structure and properties of PP. In order to evaluate the effect of the molecular weight on the properties of the recycled polymer, the study was conducted on containers produced by injection moulding made from a low molecular weight (LMW) PP and on containers produced by thermoforming made from a high molecular weight (HMW) PP.
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