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

Abstract

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°C increased the amounts of the oxidized products in the smoke. The extruded film thickness, 12 and 25 m, 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. Differences in 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 from an odor and taste point of view in food packaging applications.

Degradation of low density polyethylene during extrusion. III. Volatile compounds in extruded films creating off‐flavor

“…In our previous work 4,8,15 it was discussed how the degradation of polyethylene is initiated at temperatures of 260 -325°C. We identified the type of volatile degradation products being formed and where in the process most of the oxidative degradation occurs.…”

“…Although the amounts of volatiles increase with extrusion temperature, 4,8,15 they do not all contribute to off-flavor. Ratings: 0 ϭ No off-flavor, 1 ϭ Very weak off-flavor, 2 ϭ Weak off-flavor, 3 ϭ Average off-flavor, 4 ϭ Strong off-flavor, 5 ϭ Very strong off-flavor.…”

“…They also reported a synergistic behavior of aldehydes, ketones, and acids, giving offflavor sensations even though the different components were below their threshold concentrations. Based on our previous work regarding degradation products found in extruder smoke 4 and in extruded PE films, 8 the present study was aimed at finding a correlation between the experienced off-flavor in packaged foods and the presence of specific degradation products in PE packaging films. In the present work, the possibilities to trap degradation products by chemical reactions with scavengers, thus preventing these components from migrating to the polymer film surface, and further into food in contact with the film, were investigated.…”

Investigation of volatile low molecular weight compounds formed during continuous reclaiming of ground tire rubber

“…poly(lactic acid)) processed with using extruders. In published papers on/in-line [16,17] as well as off-line [18e21] measurement of VOCs were described. Unfortunately, it is hard to find detailed reports about identification of the gas phase of waste rubber reclaimed using a co-rotating twin screw extruders.…”

Taste

“…Many aldehydes (formaldehyde, acetaldehyde, propanal, propenal, butanal, and other higher aldehydes) are found in smoke from extruded polyethylene. 3 Also, various ketones (propanone, 2-butanone, 2,4-pentadione, 2-pentanone, 3-methyl-3-pentene-2-one, 3-pentanone, 2-methyl-3-hexanone, 2-methylcyclohexanone, 3-hexanone, 3methylcyclohexanone, 4-methylcyclohexanone, 2-heptanone, 4-hepatanone, 3-heptanone, 3-methyl-3 heptanone, 4-heptanone, 2-octanone, 3-octanone, 2-nonanone, 5nonanone, 3-decanone, 3-undecanone, and 3-dodecanone) are found in smoke at the die orifice for extruded films of polyethylene. 3 Some carboxylic acids (acetic acid, propionic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, and dodecanoic acid) are also identified in smoke coming from die orifice for extruded films of polyethylene.…”