The development of thermally responsive packaging materials for transporting perishable food

Abstract

Unwanted warming can adversely affect the quality and export value of chilled perishable food products and often occurs when the packages are exposed to warm temperatures on airport tarmacs and in temporary (unrefrigerated) storage in transit during air transportation. The warm temperature spikes are for durations typically up to one hour or so, but can be up to several hours and this is sufficient time to cause spoilage of the perishable produce in the package due to the limited thermal insulation and poor thermal buffering capacity of the paperboard containers that are typically used. Insulating food packaging helps to minimise temperature fluctuations in the food product at all stages during transportation. The optimum packaging system is one that utilises phase change materials in combination with thermal insulation materials to provide sufficient thermal buffering capacity to prevent the unwanted warming of perishable goods. This thesis presents the results of a quantitative analysis of the thermal properties of suitable phase change materials for new responsive thermal packaging. This included investigating the effects of alkane phase change materials and their heat storage capacities following their incorporation into corrugated plastic (Corroplast TM) packaging materials and the characterising the thermal conductivities and thermal buffering properties of the composite PCM packaging materials. The thermal properties of a range of existing packaging materials and insulation materials were also evaluated for comparative purposes. This investigation involved the characterization of the thermal conductivities and insulation properties of a number of paperboard, expanded polystyrene, bubble-wrap, and corrugated plastic (Corroplast TM) packaging materials. The characterisation of the thermal conductivities and thermal buffering properties of composite nano-structured calcium silicate - alkane phase change materials (NCS - PCM) was also carried out. This involved the incorporation of NCS - PCMs into corrugated paperboard packaging materials and the characterisation of the thermal conductivities and thermal buffering properties of the composite PCM packaging materials. It was determined that the packaging materials with the lowest thermal conductivity generally had the highest thermal resistance and thus the best insulating properties. The best insulating packaging material evaluated was expanded polystyrene (EPS). This material in combination with an alkane phase change material with a melting point of 6 - 8°C (contained in corrugated plastic) exhibited good thermal buffering properties. The best overall results however, were obtained from the calcium silicate - alkane phase change materials (NCS - PCM) materials which had excellent thermal buffering capacities particularly when evaluated in combination with insulation packaging materials. The results provide a quantitative approach for fabricating a combined thermal insulation / thermal buffering material to provide effective temperature control for the safe transport of temperature sensitive chilled foods from New Zealand to international markets.