Evaluation and optimization of the peel performance of a heat sealed topfilm and bottomweb undergoing cool processing

Abstract

Easy opening of heat sealable tray and topfilm food packaging concepts is often realized by using a peelable seal layer. Peel strength needs to be strong enough to prevent the package from opening during and after storage, transportation and handling at different environmental temperatures. It also needs to be weak enough to be convenient for an ageing population. When designing packaging concepts, a balance needs to be found assuring food quality, safety and convenience. This study presents a method to evaluate and optimize peel performance of a packaging concept with polyethylene seal layer undergoing cool processing at −18 C and 4 C. A design of experiment approach is used as a basis. With a limited amount of tests, models are fitted and experimentally validated to obtain an optimal peel strength of 0.5 N mm −1 at an environmental temperature of 23 C. When measured during thermal treatment at −18 C and 4 C, the peel strength increased but no effect was seen once the seals are tested at 23 C after treatment. Bending of the bottomweb during the peel test slightly decreased peel strength while bending stiffness increased at low temperatures, suggesting a minor impact of bending of the bottomweb related to environmental temperature on the observed peel performance. Increased peel strengths during cool processing were clearly related to a change in seal failure mechanism. Besides cohesive peeling, partial delamination occurred in these stronger seals. K E Y W O R D S cool processing, food packaging, heat seal, peel performance, polyethylene 1 | INTRODUCTION Tight packages are crucial to ensure food quality and food safety throughout the process chain. Perishable food products such as meat, cheese, ready meals and others are often packed in a rigid thermoformed tray, heat sealed with a thin flexible topfilm, in vacuum or with a modified atmosphere to extend the shelf life. In 90% of all thermoform fill and seal machines, only the bottomweb is formed. Besides heat sealability, materials are selected based on the barrier and mechanical properties. 1 These properties are determined by the chemical composition, production process and the thickness. The packed product undergoes thermal processing after sealing to extend the shelf life. At the food company, during transportation and storage, at the store and finally at the consumers' place, it can be cooled and/or heated. Cool processing can be differentiated in chilling at temperatures from 0 to 5 C and freezing at temperatures from −24 C to −18 C where the presence of H 2 O in a solid state extends the shelf life. Cool processing generally