A Review: the Process of, and Products from Kraft Pulping of Southern Pine

Pertinent and available information on the title subject is reviewed. The influence of process variables and wood quality on yield and papermaking properties of the pulps are especially emphasized. Specific gravity seems to be the best single property for characterization of pulpwood quality. It is concluded that the papermaking properties of the pine pulps in the different southern mills are mainly dependent on the age of the wood, the climate where the wood has grown, the heritage of the wood, and the lignin content of the pulps. Wood species seem to have minor influence, but as the different pine species are limited to, or concentrated in, specific climatic zones, they appear to give pulps with definite paper-making characteristics. Properties of southern pulpwood are listed and pulping literature for the different species is given. The desired papermaking properties of a pulp are dependent on the product made from it. For linerboard, where a burst factor of only 39 to 40 is required, high density wood can be used that will also be favorable for producing high stiffness and good runnability on the paper machine. Wrapping, bag, and sack paper require moderate to high tensile, tear, and bursting strengths (high toughness). Wood of moderate density (0.45 to 0.55) should therefore be best suited for these products. The same applies to bleached board, magazine, book, printing, writing, tissue, and sanitary paper, where the pine pulps are added in an amount of approximately 20 to 60 percent in order to improve strength. For newsprint, where the pine pulp is added (15 to 30 percent) for improving tensile strength, low density wood would be best. It should be possible for mills producing pulps that require different papermaking properties to select wood according to density. Purchased sawmill chips, which are predominantly from the outer parts of the tree (slabs), would be best suited for linerboard pulps. Low diameter wood (juvenile wood) could be used for pulps from which products are made with especially high tensile and burst requirements.

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