Significant factors affecting horticultural corrugated fibreboard strength : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Engineering at Massey University, Palmerston North, New Zealand
The New Zealand kiwifruit and apple industries export the two largest horticultural crops by value and tonnage on long sea routes to distant markets. The long storage and shipping times, low temperature (~0°C) and high humidity (>70 %RH) conditions require boxes manufactured from high performance corrugated fibreboard. As the corrugated fibreboard boxes are a significant expense, improvements to reduce the weight and therefore the cost of the corrugated fibreboard, while maintaining their vertical compression strength, would increase the apple and kiwifruit industries profitability Through analysis of the literature it was established that the greatest contributor to box compression strength was the corrugated fibreboard edgewise compression strength, which is significantly affected by moisture. The strength of corrugated fibreboard decreases with increasing moisture content, which tends to be high in low-temperature high-humidity cool-stores. The literature also indicated that temperature and moisture content of the fluting medium could be optimised to reduce the damage caused during the fluting process. The objectives of this study included improving box compression strength predictions by measuring the effect of moisture and temperature on the strength of the corrugated fibreboard and measuring the relationship between temperature, humidity and corrugated fibreboard moisture content. The objectives also included developing a mathematical model to optimise the operations preceding the fluting process by predicting the fluting medium moisture content and temperature just prior to the fluting process. The measurements of corrugated fibreboard properties enabled the widely known McKee’s equation to be modified to enable the prediction of box compression strength over a range of moisture contents (7 to 30 %db), the valves of which could be estimated using the moisture sorption isotherms developed in this study over the temperature and relative humidity range of 0 to 20°C and 40 to 90 %RH. A mathematical model was developed to predict how the operation of the corrugator would affect the temperature and moisture content of the fluting medium just prior to the fluting process. The model was tested by running the corrugator at normal and extreme settings based on the model’s predictions, and measuring the strength properties of the corrugated fibreboard produced. The measured strength properties indicated that the machine speed and steam shower could have an effect but the too were inconsistent to established firm conclusions.