Softwood pulp

Figure 4.11 Flocculation and formation effects in a chemically pulped bleached softwood pulp (slightly refined). Fibre suspensions settled for 40 min. Sheets (60 gm 2) photographed in transmitted light, (a) no additives, (b) polyelectrolyte added to induce flocculation. Scale bar = 2 cm.

Figure 5.8 2H NMR quadrupole splittings for D20 adsorbed on to never dried bleached Kraft softwood pulp refined to different degrees (25000 and 500 revolutions in a PFI mill).

Table 10.3 Occurrence and toxicity of chlorinated phenolics from the bleaching of hardwood and softwood pulps.

The only very slight photochromic behaviour obtained upon irradiation of bleached aspen CTMP may be due to the presence of syringyl instead of guaiacyl units in hardwood lignin. These structures are less able to form orr/to-quinones during irradiation than softwood pulps (8). 

Industrial scale continuous fermentations on rotoevaporated spent sulfite liquor (hardwood pulping, y softwood pulping). 

Some classes of pulp such as the sulfites or bisulfites are relatively easy to bleach. These pulps can be bleached with as few as three to five steps (e.g., CEH, CEHEH). Kraft softwood pulps are difficult to bleach to high brightness. From five to seven steps may be required (e.g., CEHEH, CEHDEDP). Kraft hardwood pulps generally are regarded as intermediate in difficulty. 

Dependence of grafting on initial pH is illustrated in Figure 1. Grafting efficiency is not much affected by pH, even though the optimum value seems to be between pH 4 and 7. This is a little lower than the values obtained for mechanical softwood pulp, for which maximum grafting efficiency was in the proximity of pH 6-9 (4). In case of softwood kraft semibleached pulp (2% lignin),... 

Method pH range "Base" alternatives Active reagents Max. temp. (°C) Time at max. temp, (hr) Softwood pulp yield (%)... 

Holton, H., Soda additive softwood pulping - Major new process. Pulp Paper-Canada 1977, 78 (10), 19-24. 

Chlorine (hypo) number = Roe chlorine number x 1 052 Softwood pulps... 

Alkyl-polychlorofluorenes (RPCFL) were detected at sub-ng 1 1 levels in effluents, at a few ng g 1 dw levels in biosludge and < ng g 1 dw concentrations in softwood pulp product of a kraft mill. The structures were deduced from high resolution mass spectra and verified by comparison to GC/HRMS/SIM of model substance mixtures from chlorination of methyl- and dimethylfluorenes... 

This conclusion is not contrary to other recognized facts relating to the mannan of wood. Even the most severely refined, softwood pulps still retain a certain amount of mannan. Wise and Ratliff extracted slash-pine holo-cellulose with 16% potassium hydroxide, and treated the residue repeatedly with fresh charges of boiling 5% sulfuric acid. A large part of the origina... 

Evidence for a chemical linkage between cellulose and mannan, at least in softwood pulps, continues to accumulate. In this connection, Steinmann and coworkers have observed that, during the normal preparation of cellulose acetate, a considerable part of the xylan may be lost (30 to 60%), whereas the mannan content is not greatly affected. These authors suggest that this may indicate that the mannan is bound to the anhydroglucose chain. According to these workers, certain differences in properties of cellulose acetate prepared from different samples of cellulose can be explained if a mannan-to-cellulose bond actually does exist. However, it must be realized that no definitive proof has been presented of a mannan-to-cellulose linkage in any preparation of wood cellulose. 

Tall oil, derived from the Swedish tallolja meaning pine oil, is recovered from the black liquor of softwood pulping. It is taken out at an intermediate stage of the multiple-effect evaporation when the liquor contains about 30% total solids, after it is allowed to stand [21]. The soaps (sodium salts of fatty acids present) are insoluble, cream to the top of the vessel, and are skimmed off. The residual black liquor is returned to the evaporators to continue chemical recovery. The soap yield, which can range from 10 to 200 kg/tonne of pulp (or even higher for pine), is then acidified and the free fatty acids and resin acids obtained are separated by distillation. The fatty acids recovered consist mainly of oleic and linoleic acids and are employed in soap manufacture and as the drying oil components of paints and varnishes [22] (Chap. 19). Resin acids consist of terpene acids such as abietic acid and its positional and reductive variants, and are mainly employed in paper sizing. 

The response of hardwood and softwood pulps to beating is very different. 

Lightly beaten softwood pulps show an initial inerease in tear strength but as the fibres become better bonded they show a steady deeline in tear strength. 

Figure 2. ESCA spectra for filter paper and for a handsheet of mechanically refined softwood pulp. The binding energies associated with classes C, Clt and Cs carbon atoms are indicated. Binding energies are not corrected for sample charging effects. (Reproduced, with permission, from Ref. 21. Copyright 1978, Cellulose Chemistry and Technology.)...

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