{"id":237,"date":"2020-09-20T02:17:02","date_gmt":"2020-09-20T02:17:02","guid":{"rendered":"http:\/\/wordpress.kpu.ca\/najikad93\/?page_id=237"},"modified":"2020-09-29T03:00:53","modified_gmt":"2020-09-29T03:00:53","slug":"materials","status":"publish","type":"page","link":"https:\/\/wordpress.kpu.ca\/najikad93\/materials\/","title":{"rendered":"Materials"},"content":{"rendered":"\n
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Softwoods<\/p>\n<\/div><\/div>\n\n\n\n

Softwoods are the preferred raw material for \u2018strong\u2019 papers, primarily because of the length and slenderness of its fibers<\/strong>. In other papers, it is typically used as a \u2018reinforcement\u2019 component. Low-density softwoods<\/strong> (various spruces, firs, scots pine, lodgepole pine, etc.) in which thin-walled fibers normally are predominant are preferred for papers with high demands for bonding-related strength characteristics, such as tensile, burst, and surface strength<\/strong>. <\/p>\n\n\n\n

Denser softwood<\/strong>s, such as the southern pines (slash pine, loblolly pine, longleaf pine, and shortleaf pine) and some US western species, such as the Douglas fir, give more tear strength and bulk, which are essential when paper with a high bending stiffness is required. Juvenile wood is characterized by having slightly smaller fibers and a somewhat lower density than the average of a mature tree.<\/p>\n\n\n\n

In mechanical pulping<\/strong>, softwoods, especially spruce, are the preferred raw material, since most hardwoods are too dense. Exceptions in this respect are Populus species (aspen, cottonwood, etc.)<\/p>\n\n\n\n

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Hardwoods<\/p>\n<\/div><\/div>\n\n\n\n

Hardwoods are the preferred raw material for pulp used in printing papers. The desirable feature of hardwood pulp in this context is the small dimensions of its fibers<\/strong>. This implies a high number of fibers per unit mass of pulp, which in turn is beneficial for formation characteristics, such as small-scale uniformity, opacity, and surface smoothness<\/strong>, all of which are important for printing paper.<\/p>\n\n\n\n

Hardwood fibers should also be slender and not too thick-walled. The short hardwood fibers, especially in eucalyptus pulp, are also preferred in soft tissue, where they improve the tactile softness of the product.<\/p>\n\n\n\n

Hardwoods contain more cellulose and extractives, and less lignin, than softwoods; as well, they usually have a higher initial brightness. For pulp purposes, softwood fibers are, on average, more than three times the length of those contained in hardwoods <\/strong>(thus the origin of the terms \u201clong-fiber pulp\u201d and \u201cshort-fiber pulp\u201d). And since increasing fiber length usually translates into more inter-fiber bonding, softwood pulps impart greater strength to the products into which they are made, than do hardwood pulps manufactured by the same process.<\/strong> As an example, bleached softwood kraft (BSK) is considerably stronger than bleached hardwood kraft (BHK).<\/p>\n\n\n\n

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Pulpwood Fibers<\/p>\n<\/div><\/div>\n\n\n\n

Wood fibers are natural composite structures in which cellulose fibrils are held together by lignin and hemicellulose. The major constituents of wood fibers are lignin, cellulose, hemicellulose, and extractives. <\/p>\n\n\n\n

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