| Popis: |
Although loblolly pine (Pinus taeda) is less costly than northern softwoods, loblolly pine mechanical pulps tend to be of poor quality and are mainly used in low-value grades such as newsprint. We evaluated various mechanical pulping processes for mature and juvenile loblolly pine and their potential for use in value-added grades, especially in lightweight coated (LWC) paper. Results for black spruce were also included for comparison purposes. Pilot plant results have shown that loblolly pine is inferior to spruce in terms of sheet density, brightness ceiling, and long fiber coarseness. To some extent, the quality disadvantages of pine pulps could be offset by proper chemi-cal pre-treatment, high specific-energy application, or both, in the pulping process. With proper chemical pretreat-ment or refining, all the loblolly pine mechanical pulps should have adequate strength and light-scattering ability for LWC and supercalendered grades, compared with the general requirements reported in the literature. However, paper containing pine mechanical pulp is rougher on the surface, less dense, and has higher air permeability than the paper with spruce mechanical pulp. Therefore, proper papermaking strategies, such as precalendering, are essential to reduce sheet surface roughness and pore size before coating. This was confirmed by a LWC dynamic sheet former (DSF) sheet study that used three selected loblolly pine mechanical pulps. |
