Improving the strength of recycled liner for corrugated packaging by adding virgin fibres: Effect of refrigerated storage on paper properties

The high humidity produced by the ripening of fruit and vegetables during refrigerated storage and transport leads to a noticeable loss of strength of corrugated board packaging. Increasing use of recycled fibres in the manufacture of corrugated board further reduces box compression strength. Adding virgin fibres to the furnish composition of liner paper could solve this problem. Various proportions of unbleached virgin eucalyptus and pine fibres were added to a recycled furnish used to manufacture liner paper for corrugated board. Laboratory sheets of each fibre blend were characterised by tensile, bursting and compressive strength. The change in the strength properties and moisture content of the sheets during refrigerated storage at 6 degrees C and high relative humidity (90% RH) was also studied. The results showed that paper strength improved with the proportion of virgin fibres added. Pine fibres yielded higher increments than eucalyptus fibres in tensile and burst indices, whereas both fibres improved compression strength at a similar rate. After 4 h of exposure at refrigerated storage, the paper strength properties decreased considerably, in particular compression strength, which showed a loss of about 70% compared to the reference value. The percentage of strength lost compared to the value in standard conditions was influenced only by exposure time at low temperature and high RH. However, an increase in the amount of pine fibres added enhanced the remaining tensile and burst indices.