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Polymers 2014, 6(12), 3019-3043; doi:10.3390/polym6123019

Evaluation of the Thickness and Oxygen Transmission Rate before and after Thermoforming Mono- and Multi-layer Sheets into Trays with Variable Depth

1
Research Group Packaging Center, Institute for Materials Research–Institute for Materials Research in Microelectronics (IMO–IMOMEC), University Hasselt, Wetenschapspark 27, 3590 Diepenbeek, Belgium
2
Research Group Applied and Analytical Chemistry, Institute for Materials Research–Institute for Materials Research in Microelectronics (IMO–IMOMEC)/Centre for Environmental Sciences (CMK), University Hasselt, Agoralaan building D, 3590 Diepenbeek, Belgium
*
Author to whom correspondence should be addressed.
Received: 22 September 2014 / Revised: 6 December 2014 / Accepted: 12 December 2014 / Published: 22 December 2014
(This article belongs to the Special Issue Packaging Films)
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Abstract

During thermoforming, plastic sheets are heated and subsequently deformed through the application of mechanical stretching and/or pressure. This process directly impacts sheet properties such as material thickness in walls, corners, and bottom, crystallinity in the constituent layers, and particularly the oxygen gas permeability. The aim of this study was to quantify the impact of thermoforming on thickness and oxygen transmission rate (OTR) of selected packaging materials (polypropylene (PP); PP/ethylene-vinyl alcohol co-polymer/PP (PP/EVOH/PP); polystyrene/EVOH/polyethylene (PS/EVOH/PE); amorphous polyethylene terephtalate/PE (APET/PE); APET/PE/EVOH/PE; polyamide/PE (PA/PE); and (PE/)PA/EVOH/PA/PE). These materials were extruded in two different thicknesses and thermoformed into trays with the same top dimensions and variable depths of 25, 50, and/or 75 mm and a 50 mm tray with a variable radius of the corners. The distribution of the material thickness in the trays was visualized, showing the locations that were most affected by the deep drawn process. The OTR results indicate that the calculated OTR, based on a homogeneous material distribution, can be used as a rough approximation of the measured OTR. However, detailed analysis of crystallization and unequal thinning, which is also related to the tray design, remains necessary to explain the deviation of the measured OTR as compared to the predicted one. View Full-Text
Keywords: thermoforming; oxygen transmission rate; gas barrier; EVOH; semi-rigid food packaging; flexible food packaging film thermoforming; oxygen transmission rate; gas barrier; EVOH; semi-rigid food packaging; flexible food packaging film
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Buntinx, M.; Willems, G.; Knockaert, G.; Adons, D.; Yperman, J.; Carleer, R.; Peeters, R. Evaluation of the Thickness and Oxygen Transmission Rate before and after Thermoforming Mono- and Multi-layer Sheets into Trays with Variable Depth. Polymers 2014, 6, 3019-3043.

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