Mechanical pulping methods

These first two mechanical methods of breaking down wood into pulp provide the bases for all of the further developments in the field of mechanical pulping. While all of the present mechanical pulping methods do produce different types of pulp, they still rely upon either... 

Apart from the fibers, the pulp contains a fraction of much smaller material, called the fines fraction. Different definitions of fines exist. For practical reasons, fines would be defined as all the particles smaller than 200 gm. The primary fines in the pulp are made up of ray cells, smaller pieces of broken fibers and thin parts of the fiber surface. Refining of the pulp creates secondary fines. The mechanical pulping method produces a large amount of fines. 

Refiner Mechanical Pulp was developed in 1929 and then used in 1938 for board products. Disk refiners began to be used in 1962 for pulp production. In this case, unlike SGW, small wood pieces or chips are broken down between rotating, grooved, or patterned metal disks at atmospheric pressure. The two methods for mechanically producing pulp are depicted in Fig. 4. One advantage of using refiners is that lowercost wood residues could be used as feedstock. Refiner mechanical pulp production totals about 3.5 x 106 tonnes/year. 

In Fig. 6 all of the methods are divided into purely mechanical pulps and chemically modified pulps. Under purely mechanical pulps the older methods, SGW, RMP, and TMP remain, but three new processes have been added to the list TRMP (thermo-refiner mechanical pulp), PGW (pressure ground wood) and PRMP (pressure refiner mechanical pulp). These purely mechanical methods are all very similar to the older processes. The differences are related to the temperature of either the wood before or during refining. Heat energy or pressure is not applied in the same manner in the different processes. 

There is a dearth of reliable methods available for determining ethylenic groups as components of quinonoid ring systems in lignin. A sensitive and specific method developed by Lebo et al. (1990), based on an addition reaction with trimethyl phosphite, has been used to determine o-quinonoid structures in situ in the lignin component of refiner mechanical pulp. 31P-NMR measurement capability is required for the analysis. 

Conductometric titrimetry can be applied to a wide range of pulp types with a wide range of sulfonate contents. The method has been applied to softwood chips treated with sulfite, softwood sulfite mechanical pulps, high-yield bisulfite pulps, low-yield acid sulfite pulp (Katz et al. 1984, Gummerus 1985, Heitner and Hattula 1988) and sulfite treated aspen wood (Beatson et al. 1985) with sulfonate contents ranging from 20 to 300 mmol kg-1. In addition, the method has been adapted to measure sulfonate content of sulfonated kraft lignin (Oster et al. 1988). 

Of the methods that measure total sulfur content, combustion/ion chromatography has several advantages over other methods. It is much simpler and faster than the standard gravimetric method and, when compared to titrimetric methods, is less prone to interference by other ions. The procedure has been applied to chemimechanical pulps with sulfur contents ranging from 0.1 to 1%. Measurements on a typical sulfite mechanical pulp gave a mean of 0.612%, with a standard deviation of 0.013%. 

U.S. 4,900,399 (to Eka AB) and U.S. 5,002,635 (to Scott Paper Co.) both describe chemical pretreatments that claim to improve the properties of mechanical pulp. Estimate the cost of these pretreatment processes for a world-scale mechanical pulping plant. Which method would you recommend ... 

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