PACKAGING TECHNOLOGY AND SCIENCE Packag. Technol. Sci. 2004; 17: 43–52 DOI:10.1002/pts.642 Oxygen Barrier Properties of Thermoformed Trays Manufactured with Different Drawing Methods and Drawing Depths By Marit Kvalvåg Pettersen, 1,2 * Mikael Gällstedt 3 and Thomas Eie 1,2 1 Matforsk AS – Norwegian Food Research Institute, Osloveien 1, N-1430 Ås, Norway 2 Department of Chemistry, Biotechnology and Food Science, Agricultural University of Norway, PO Box 5003, N- 1432 Ås, Norway 3 Packforsk – The Institute for Packaging and Logistics, AB Box 9, SE-164 93 Kista, Sweden A comparison was made of oxygen barrier properties and wall thickness distribution of different thermoformed trays. The thermoformed trays were manufactured with three drawing depths and two different thermoforming methods; with and without plug-assist. Four different polymer combinations were evaluated. The oxygen transmission rate (OTR) [cm 3 /(package/day)] was measured at three conditions (23°C/50% relative humidity (RH) with 0% RH inside, 6°C/80% RH with 0% RH inside, and 6°C/80% RH with 100% RH inside. Wall thickness was measured at five different positions in the trays. In general, temperature had more influence on the oxygen transmission rate (OTR) than the humidity. The OTR in the packages increased with increasing drawing depth, but the increase was not linear. Other effects besides thinning, such as orientation, may have influenced the OTR, since the relationship between OTR, given as cm 3 /(m 2 /day), and the drawing depth was not linear. Plug-assisted thermoforming only had an effect on the OTR in trays with 70mm drawing depth made of 600mm thick laminate of PP/PE, which was probably due to exceeding the maximum drawing depth of this material. There was no correlation between the OTR value in the packages and the wall thickness in either of the positions, but a quite high correlation between the drawing depth and the relative wall thickness in all measured positions was observed. Copyright © 2004 John Wiley & Sons, Ltd. Accepted 22 December 2003 KEY WORDS : thermoforming; drawing depth; oxygen transmission; thickness * Correspondence to: M. K. Pettersen, Matforsk AS – Norwegian Food Research Institute, Osloveien 1, N-1430 Ås, Norwa Email: marit.kvalvag.pettersen@matforsk.no Contract/grant sponsor: Norwegian Research Council. Copyright © 2004 John Wiley & Sons, Ltd. INTRODUCTION Thermoformed trays are used for several kinds of food products. Due to the relative ease of produc- tion filling and sealing, such trays are popular both among consumers and in the food industry. 1 The most commonly used methods of thermoforming are vacuum, plug-assist and plug-assist vacuum thermoforming, reverse draw forming, and drape forming. 1–3 A co-extruded sheet may in some systems be supplied directly from the extruder to the thermoform/fill/seal machine. 1,5 This method has high capacity and since the thermoforming moulds can be made fairly quickly and at rela- tively low cost, it is a popular process also for short runs. 1 The slowest stage, and therefore also the