Woodpulping processes

In 1839, Payen discovered that wood was not homogeneous but contained cellulose and an incrusting material (32-34) for which Schultze coined the term lignin in 1865 (35). As shown in Table I, chemical woodpulping processes were developed to dissolve away lignin, hemicelluloses, and extractives (30). These represent the major woodpulping processes in operation today. 

Sulphite Pulping. This is a generic term used to describe various sulphite chemical woodpulping processes carried out at different pH s and pulp yields (37). (The term yield refers to the quantity of fiber recovered from the original wood.)... 

It is worthwhile to review the U.S. market size for the four principal resins currently used in wood-panel products today (4 )- These are phenol-formaldehyde (PF), urea-formaldehyde (UF), melamine-formaldehyde (MF), and resorcinol-formaldehyde (RF) (Table III). When these production figures are compared to the quantities of lignin potentially available (Table II), it is immediately obvious that all wood adhesives could be replaced by only a very small fraction of the lignin produced annually during chemical woodpulping processes. 

The beater additive process starts with a very dilute aqueous slurry of fibrous nitrocellulose, kraft process woodpulp, and a stabilizer such as diphenylamine in a felting tank. A solution of resin such as poly(vinyl acetate) is added to the slurry of these components. The next step, felting, involves use of a fine metal screen in the shape of the inner dimensions of the final molded part. The screen is lowered into the slurry. A vacuum is appHed which causes the fibrous materials to be deposited on the form. The form is pulled out after a required thickness of felt is deposited, and the wet, low density felt removed from the form. The felt is then molded in a matched metal mold by the appHcation of heat and pressure which serves to remove moisture, set the resin, and press the fibers into near final shape (180—182). 

Practically the only commercial successful innovations made by Finnish chemists in the early 20th century were related to tall oil soap and some other byproducts of woodpulping. The Finnish scholar Alfons Hellstrom discovered two more natural terpenes from juniper resin, invented methods for distilling tall oil under vacuum from sulphate pulping waste, and developed commercially applicable processes for the manufacture of tall oil soap and the use of rosin acids from tall oil for paper sizing. Such distillations of tall oil became an important industry not only in Finland but also in many other countries. By 1939, the sales of tall oil soap conquered a third of the Finnish detergent market. ... 

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