Wood pulp preparation

For the purpose of conversion to textile fibers, dispersions or solutions of cellulose or its derivatives are achieved by various means, in order to make possible the extrusion of the fiber-forming material through the small orifices of the spinning jets. Wood pulps prepared for these and similar uses (such as the manufacture of cellophane) are known as dissolving pulps. The manufacture of dissolving pulps is a highly developed art, with processes protected by patents or, more effectively, within company files. The purification of sulfite pulps to a degree suitable for manufacture of textile rayon (90 to 94% alpha-cellulose), tire cord (94 to 9.5% alpha-cellulose), and cellulose acetate (9.5 to 90% alpha-cellulose) requires some kind of... 

On the other hand, certain types of wood pulp, prepared by se((uences involving both acidic and alkaline treatments, show a linear relationship between gamma-cellulose and non-cellulosic polyoses. This may be illus-strated from the studies of White, Steinman and Work on acetylation pulps. Acetylation-grade pulps are usually prepared from softwoods by sulfite cooking followed by hot-caustic refining. When the total polyose content of a number of such pulps was compared with their gamma-cellulose content, a linear relationship was obtained (see Fig. 3). In spite of this excellent correlation, it cannot be assumed that all of the non-cellulosic polyoses are contained in the gamma fraction of these pulps (see below). 

Gray K, Crosby HL, Steinberg JC. Recovery of chemicals in wood pulp preparation. U.S. Patent 24,293 June 13,1956. 

Microcrystalline ceUulose (MCC) is a partiaUy depolymeri2ed from of ceUulose prepared by the hydrolysis of wood pulp with hydrochloric acid. 

Calcium sulfite [10257-55-3] and acid sulfite may be prepared by reaction of SO2 and hydrated lime or limestone. Calcium acid sulfite [13780-03-5] Ca(HS02)2, has been used to remove lignin (qv) from wood pulp in paper manufacture (6) (see Paper Pulp). 

Cellulose acetate with improved solubiUty properties can be prepared from low quaUty wood pulps by multistage addition of the components (97) or by intermpting the reaction in the early stages, filtering, and continuing the acetylation with fresh reactants (98,99). 

Adsorption. Adsorption (qv) is an effective means of lowering the concentration of dissolved organics in effluent. Activated carbon is the most widely used and effective adsorbent for dyes (4) and, it has been extensively studied in the waste treatment of the different classes of dyes, ie, acid, direct, basic, reactive, disperse, etc (5—22). Commercial activated carbon can be prepared from lignite and bituminous coal, wood, pulp mill residue, coconut shell, and blood and have a surface area ranging from 500—1400 m /g (23). The feasibiUty of adsorption on carbon for the removal of dissolved organic pollutants has been demonstrated by adsorption isotherms (24) (see Carbon, activated carbon). Several pilot-plant and commercial-scale systems using activated carbon adsorption columns have been developed (25—27). 

Filter aids should have low bulk density to minimize settling and aid good distribution on a filter-medium surface that may not be horizontal. They should also be porous and capable of forming a porous cake to minimize flow resistance, and they must be chemically inert to the filtrate. These characteristics are all found in the two most popular commercial filter aids diatomaceous silica (also called diatomite, or diatomaceous earth), which is an almost pure silica prepared from deposits of diatom skeletons and expanded perhte, particles of puffed lava that are principally aluminum alkali siheate. Cellulosic fibers (ground wood pulp) are sometimes used when siliceous materials cannot be used but are much more compressible. The use of other less effective aids (e.g., carbon and gypsum) may be justified in special cases. Sometimes a combination or carbon and diatomaceous silica permits adsorption in addition to filter-aid performance. Various other materials, such as salt, fine sand, starch, and precipitated calcium carbonate, are employed in specific industries where they represent either waste material or inexpensive alternatives to conventional filter aids. 

Alternatively cellulose is produced from wood via wood pulp. A number of processes are used in which the overall effect is the removal of the bulk of the non-cellulosic matter. The most widely used are the sulphite process, which uses a solution of calcium bisulphite and sulphur dioxide, the soda process using sodium hydroxide and the sulphate process using a solution of sodium hydroxide and sodium sulphide. (The term sulphate process is used since sodium sulphate is the source of the sulphide.) For chemical purposes the sulphite process is most commonly used. As normally prepared these pulps contain about 88-90% alpha-cellulose but this may be increased by alkaline purification and bleaching. 

Much of the CI2O manufactured industrially is used to make hypochlorites, particularly Ca(OCl)2, and it is an effective bleach for wood-pulp and textiles. CI2O is also used to prepare chloroisocyanurates (p. 324) and chlorinated solvents (via mixed chain reactions in which Cl and OCl are the chain-propagating species).Its reactions with inorganic reagents are summarized in the scheme opposite. 

Refs 1) A.J. Phillips, Characteristics of Wood Pulps and their Preparation for Nitration , PATR 19 (1931) 2) A.J. Phillips, Study of the... 

Suitability of Wood Pulps for the Preparation of Guncotton , PATR 24 (1931) 3) A.J. Phillips,... 

Use of Sulfur-35 to Characterize the Sulfate Content in Nitrocellulose (NC). Military grades f NC are prepared by nitrating a suitable grade of cellulose, either cotton linters or wood pulp,... 

Hackh s Diet (1944), p 357-L defines "freeness as die extent to which a pulp for the manuf of paper has not been hydrated by beating. Accdg to J.N. Stephenson, Edit, "Preparation and Treatment of Wood Pulp", McGraw-Hill, NY, Vol 1(1950), pp 943-56,... 

Alkaline-extracted/steam-exploded (AESE) aspen lignin samples were prepared from steam exploded wood samples (55 s residence time at 240°C) obtained from Iotech Corp. Exploded wood pulp was treated with a series of carbon tetrachloride and alkaline extractions (12). 

The gas is used in various chemical industries. For example, it forms an intermediate stage in the production of sulphuric acid and of sulphites it is also applied in the preparation of chemical substances such as selenium, tellurium, quinol, etc. To some extent sulphur dioxide finds application for fire-prevention and -extinguishing, and much is used in the form of alkali sulphite in the production of wood pulp for paper and artificial silk manufacture. 

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