Hardwood pulp production

Semichemical pulping comprised 6% of U.S. pulp production in 1993.1 Semichemical pulp is often very stiff, making this process common in corrugated container manufacture. This process primarily uses hardwood as furnish. 

Table 1.3 World-wide hardwood, softwood and non-wood pulp production (1988).

One of today s fastest growing segments of the wood composition board industry is production of medium density fiberboard (MDF) using a dry process similar to that used for particleboard. First mention of the possibility of utilizing bark for MDF came in a presentation by Brooks in 1971 (43). He described a process in which a homogenous board with superior properties could be made from such raw materials as mixed, unbarked hardwood pulp chips unbarked pine chips, if bark content was less than 30% forest thinnings, branches, and so on and hardwood bark. Furnish was prepared by double-disk pressurized refiners. Brooks concluded a plant could be built to operate on 100% hardwood bark. 

Extractive softest in hardwood pulping and ink production, magnetic tape solvent... 

The lignin residues from wood pulp production are another class of extractives currently receiving attention as phenolic resin additives. Substituted phenols, such as cresols and xylenols, have been used as glue mix additives for phenolic adhesive resins to improve assembly time tolerance. They are also used as solvents to remove oleo-resinous deposits on the surface of pitchy softwood veneers. They can be used as flow promoters in phenolic hardwood adhesives. To avoid interference with the rate of resin curing, the amount added should not exceed 3 to 4% of the phenolic resin solids content. 

As mentioned above, and despite the fact that suberin is widespread in plants [1], only two species produce suberin-rich biomass residues in amounts that justify the exploitation of this natural polyester as a renewable source of chemicals for polymer synthesis, namely, Quercus suber and Betula pendula. Betula pendula is one of the most important industrial hardwood species in Northern Europe, where it is mainly used as raw material in the pulp and paper industry, which generates considerable amounts of bark. Typically, a mill with a pulp production of 400 000 ton per year, leaves about 28000 ton per year of outer bark [37]. Considering a suberin content ranging from 32 to 59 per cent, [14], birch s outer bark has, like cork, an enormous potential as a source of suberin and suberin components. 

To compare the composite-formed sheets with standard products, a range of PCC morphologies available from the standard filler range were used in a further series of formed sheets. Refined pine softwood (23°SR) and birch hardwood pulp (18°SR) in a 30 70 ratio were used as the base furnish. C-PAM (250 g/t paper) was used as the retention aid in forming handsheets. No other additives were used. Conventional fillers were produced under similar conditions, in the absence of ceUulosic fibrils, as the composite PCCs were used in the reference experiments. 

Li H, Saeed A,Jahan MS, NiY, van Heiningen A. HemiceUulose removal from hardwood chips in the pre-hydrolysis step of the kraft-based dissolving pulp production process. J Wood Chem Technol 2010 30 48-60. 

Chemical charge, Hquor composition, time of heatup, and time at temperature of reaction are all functions of the wood species or species mix being digested and the intended use of the pulp. A typical set of conditions for southern pine chips in the production of bleachable-grade pulp for fine papers is active alkaH, 18% sulfidity, 25% and Hquor-to-wood ratio, 4 1. Time of heatup is 90 min to 170°C time at temperature of reaction, 90 min at 170°C. Hardwoods require less vigorous conditions primarily because of the lower initial lignin content. 

Although the hydrolysis of wood to produce simple sugars has not proved to be economically feasible, by-product sugars from sulfite pulping are used to produce ethanol and to feed yeast (107). Furthermore, a hemiceUulose molasses, obtained as a by-product in hardboard manufacture, can be used in catde feeds instead of blackstrap molasses (108). Furfural can be produced from a variety of wood processing byproducts, such as spent sulfite Hquor, bquors from the prehydrolysis of wood for kraft pulping, hardboard plants, and hardwood wastes (109). 

Triglycerides are important constituents of resin. In softwood, the triglycerides account for 20—40% of total resin content, and in hardwood, 40—50%. The paper industry uses the term pitch for resins that create problems in paper machines. Traditionally, pitch is controlled or reduced by aging the wood, by use of chemicals to avoid deposits on the roUs, or by intensive washing of the pulp. AH these methods add to the cost of paper production. An alternative is to add a Upase to the pulp in a reaction lasting about one hour with the help of agitation. Results from Japanese paper mills show substantial... 

Xylan-type polysaccharides are the main hemicellulose components of secondary cell walls constituting about 20-30% of the biomass of dicotyl plants (hardwoods and herbaceous plants). In some tissues of monocotyl plants (grasses and cereals) xylans occur up to 50% [6j. Xylans are thus available in huge and replenishable amoimts as by-products from forestry, the agriculture, wood, and pulp and paper industries. Nowadays, xylans of some seaweed represent a novel biopolymer resource [4j. The diversity and complexity of xylans suggest that many useful by-products can be potentially produced and, therefore, these polysaccharides are considered as possible biopolymer raw materials for various exploitations. As a renewable resource, xylans are... 

Attempts to remove hemicellulose for production of dissolving pulps with very low hemicellulose contents have shown that complete enzymatic hydrolysis of hemicellulose within the pulp is difficult to achieve. The xylan content in delignified mechanical aspen pulp was reduced from approximately 20 to 10%, whereas in bleached hardwood sulphite pulp the xylan content was decreased from 4 to only 3.5% even at very high enzyme dosages (50). The complete removal of residual hemicellulose seems thus unattainable, apparently due to modification of the substrate or to structural barriers. 

Mild chemical treatments are used to soften the wood chips and increase the amount of whole fibers. Some of the wood cell components are solubilized and the lignin is made more hydrophilic. The penalty paid for chemical addition is a reduction in yield, to levels of 80 to 90%. The benefits of chemical addition pulps are the increased ability to utilize hardwoods, lower energy requirements, stronger pulps, and increased process flexibility. Some of these pulps have been found to be suitable for products that generally require full chemical pulps. 

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