Recycling performance of softwood and hardwood unbleached kraft pulps for packaging papers

The scope of this work is to evaluate the recyclability potential of hardwood and softwood unbleached kraft pulps, leading to a sound basis for comparison and even to support a decision about fibers according to the performance achieved. The influence of successive recycling cycles (up to 10 cycles) on the fiber morphology, pulp suspension drainability, water retention capacity, and handsheet mechanical properties were studied for Eucalyptus globulus and Pinus sylvestris unbleached kraft pulps. The performance of these pulps as linerboard and corrugating medium for packaging was also evaluated. The requirements for brown kraftliner and for high performance recycled fluting grades is preserved for E. globulus pulp during all 10 recycling cycles, evidenced by the moderate decrease of burst index and crush resistance index and by the short-span compression index, whereas the P. sylvestris pulp loses this rating after the second cycle. These results strongly support the higher performance of E. globulus pulp for recycling as compared with softwood kraft pulp from the perspective of packaging papers.