Processed cellulosic fibers derived from hardwoods, softwoods, and other plants. There are two major types of pulp: (1) Ground wood or mechanical pulp, which is merely finely divided wood without purification and is made into newsprint, cheap manila papers, and nonpermanent tissues. (2) Chemical pulp, of which there are three kinds: (a) soda process pulp obtained from the digestion of wood chips (mostly poplar) by caustic soda; (b) sulfite process pulp (mostly spruce and other coniferous woods), obtained by digestion with a solution of magnesium, ammonium, or calcium disulfite containing free sulfur dioxide; and (c) sulfate process (kraft) pulp, in which sodium sulfate is added to the caustic liquors but is reduced by the carbon present to the sulfide, which becomes a digesting agent. Sulfite and sulfate pulps (chiefly from softwoods) compose the bulk of paper pulps. Sulfate pulps are known as kraft pulps because of their strength (“Kraft” is the German word for strength), and are used for wrapping, packaging, container board, etc. A relatively new process called holopulping replaces sodium sulfate with oxidants. A synthetic pulp based on polyolefins(styrene copolymer fibers) has been developed to the production stage in Japan.See Holopulping; Paper; Digestion.
