Degradation of low density polyethylene during extrusion. I. Volatile compounds in smoke from extruded films

Many problems with odor and taste in food packaging can be traced to degradation of the packaging materials during processing. From this starting point, the degradation of polyethylene in a commercial extrusion coating process was studied by analyzing degradation products present in smoke sampled at the extruder die orifice. Two low-density polyethylenes, A and B, with similar melt flow indexes and densities and obtained from different producers, were investigated. A third polymer, C, consisting of recycled material B, was also investigated. More than 40 aliphatic aldehydes and ketones, together with 14 different carboxylic acids, were identified in the smoke. The highest concentration was found for acetaldehyde, regardless of polymer and processing conditions. Increasing the extrusion temperatures in the range 280-325 degreesC increased the amounts of the oxidized products in the smoke. The extruded film thickness, 12 and 25 mum, influenced the concentrations of degradation products, With the thicker film giving higher amounts of product. The recycled polymer C generally gave lower concentrations of degradation products compared with the virgin polymer B. Difference ill the product spectrum between the two virgin polymers may be related to differences in the manufacturing process, Many of the identified compounds have very characteristic taste and smell and are consequently of interest fron on odor and taste point of view in food packaging applications. (C) 2002 Wiley Periodicals, Inc.