Performance of the ENZA Z Pack apple carton under compression loading

Abstract

The ENZA Z Pack is a two-piece carton of corrugated paperboard construction, having an inner section that supports the fruit and an outer section that forms a lid. The telescopic design allows for the overfilling of the carton that occurs due to the range of fruit size categories that are required to be packed in this carton.

The carton design assumption is that the carton (inner) wall and the tray-layered fruit share the load of stacked cartons in a palletised system. Based on this assumption, the carton can be constructed to a lower compressive strength and is therefore less expensive than a carton designed to support the entire applied load.

To date, the amount of loadsharing occurring between the carton and fruit has not been quantified and there is not a good understanding of the factors that influence this relationship. Better definition of this relationship is important to the future design of improved packaging. There is a need to understand this interaction so that the performance and cost of the carton can be optimised. A key carton performance criterion is an acceptable level of bruising resulting from handling and storage within the international distribution channel.

A method has been developed to quantify the loadsharing between the fruit and the carton. This equipment has successfully measured the loadsharing relationship in current Z Pack export cartons and allowed investigation of the influence of variables, considered through industry observation, to have a major influence on apple bruising in the carton.

A study has also been carried out to provide industry-relevant bruising levels for compression loading in the Z Pack carton. A total of 120 cartons from three varieties and five fruit count sizes were compression tested under loads of 140kg, 300kg and 400kg, to replicate palletised stacking.

The results from the loadsharing and bruising studies have been combined in a nomograph to provide a preliminary prediction of bruising under carton loading conditions.

The most significant factors influencing bruising levels identified in this study were load, count size, carton overfill level and the moisture content of the packaging.

This thesis also includes a detailed overview of studies relevant to the Z Pack carton performance.