Caustic Treatment of Old Corrugated Containers (OCC) for Strength Improvement During Recycling, 1993 Pulping Conference Proceedings
Caustic soaking is being used commercially to improve the strength of secondary fiber. This study was designed to investigate whether a soaking tower is necessary for optimum utilization of this technology when applied to old corrugated containers (OCC).
Optimum process parameters for soaking were found to be 4 hours in 2% sodium hydroxide at 52°C and 14% consistency. It was found that the pH of sheet formation is as important as caustic soaking in the OCC strength improvement. With the optimum conditions found for OCC soaking, adjustment of the pH to 5.5 resulted in a maximum strength (short span compression index) increase of 11% over untreated pulp. If however, the pH of sheet formation is 11, the short span compression index increase is 22%. It was determined that the components of OCC behave differently during sodium hydroxide treatment. When treated with optimum conditions, the OCC short span compression index increases 10.6% whereas the linerboard increases 20.4% and the medium increases 11.3%.