Chemi-mechanical pulping

Continuous digester, displacement heating/batch digesters, chemi-mechanical pulping... 

Figure 13. Action spectra for the photoyellowing measured at 457 nm of untreated (CMP) and peroxide-bleached (CMPB) chemi-mechanical pulp constructed after irradiation at selected wavelengths for 2 h.

Wood resin is the water-insoluble material that is soluble in neutral, non-polar organic solvents. Large amounts of it pass through mill systems that utilize softwoods and some of the hardwoods. This resin can cause pitch problems, particularly with sulfite pulping and the manufacture of unbleached sulfite pulps and to a lesser extent with mechanical and chemi-mechanical pulping. Problems are less frequently encountered with kraft pulping and usually they are less severe and of a different type. 

Pulp manufacture by stone groundwood, mechanical refiner, thermo-mechanical, chemi-mechanical, or chemi-thermomechanical means for newsprint, coarse papers, tissue, molded fiber products, and fine papers... 

Mechanical pulping aqueous environments are similar to paper machine white waters. In chemi-thermo mechanical pulping, however, the addition of sulfur ions can increase corrosivity. Pressurized presteaming of wood chips from seaborne logs can result in environments conducive to chloride SCC and also to the evolution of wood acids that can cause corrosion in the vapor phase. Wear is a more significant problem than corrosion in mechanical pulping environments. 

Pulps have since been made by various chemical processes, covering the full pH range from acid to neutral to alkaline. Each pulping method produces characteristic pulp properties, depending on the type of wood used, and each pulp type lends itself to a different end use. The most widely used chemical cooking process in North America today is the alkaline kraft process . The kraft process was invented in 1884, and the first U.S. kraft mill started production in 1909. As will be detailed later, semi-chemical, chemi-mechanical, and non-suUur cooking processes are also used. These methods are often considered more environmentally friendly than some of the older processes. 

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