Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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sulfate process ( sulfate pulp )

One of the two principal chemical methods of converting wood into pulp for papermaking, the other being the SULFITE PROCESS . Today, the terms "sulfate" and kraft, when applied to paper pulp, are generally used interchangeably, although there are slight differences between them. The term ' kraft" was first applied to the strong brown paper produced from pulp made by the sulfate process, and later to indicate the pulp itself. Originally, the term "sulfate" designated all paper pulps made by the sulfate process; later, it was used strictly with reference to special grades of pulp, such as bleachable sulfate pulp, bleached sulfate, etc., while "kraft" became restricted to that particular quality of unbleached sulfate pulp which had been cooked so as to produce a high yield or pulp of exceptional strength. Today, however, the term "sulfate" is generally used in the paper industry to indicate all grades of pulp produced by a process which utilizes sodium sulfate as it s principal chemical constituent. The only exceptions to this common practice are certain speciality grades of pulp, such as easy-bleaching sulfates made from both softwood and hardwood trees.

Sulfate pulps were first used primarily for the production of various grades of paper and board where physical strength was of greatest importance. Although the stronger grades are produced from the softwoods, very large quantities of hardwood sulfate pulps are also produced. Mixtures of hardwoods, with their longer fiber improve the formation and surface features of the paper or board. (17 , 72 , 143 , 198 , 320 )

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