Abstract:

The strength, structural, optical and water absorption properties of bleached pulps from unprinted, low and high kappa number old corrugated containers (OCC) were determined. The results were compared with the properties of bleached birch pulp and pine pulp. It was found that old corrugated containers pulps show higher Shopper-Riegler freeness, distinctly lower tensile strength, and lower maximum short-span compressive strength (SCT) than birch and pine pulps. However, they also show quite good tear resistance, optical properties, bulk and water absorption. In order to explain the differences in the properties of bleached OCC pulps and birch and pine pulps, they were evaluated using image analysis. This study showed that OCC pulps contain both long softwood and short hardwood fibres, with a predominance of the former. An analysis of the lower tensile strength of OCC pulps was also made. It was established that it is mainly caused by the lower degree of polymerisation (DP) of cellulose and the higher degree of damage of OCC fibres.