Chemithermomechanical pulps

A cross-sectional view of kenaf is shown in Figure 3d. The ultimate cells are nearly cylindrical with thick cell walls. Kenaf fibers are shorter and coarser than those of jute. Both chemical (kraft) and mechanical pulps have been produced from kenaf, and successful demonstration mns of newsprint have been made for the Dallas Morning Nem, the St. Petersburg Times, and the Bakersfield Californian with a furnish of 82% kenaf chemithermomechanical pulp and 18% softwood kraft pulp. Kenaf fiber is also considered a substitute for jute and used in sacking, rope, twine, bags, and as papermaking pulp in India, Thailand, and the former Yugoslavia. RoseUe bleached pulp is marketed in Thailand. 

Certain chemical treatments can be employed during the TMP process to achieve improved strength. Sodium sulfite and hydrogen peroxide have been used either for chip pre- or post-treatment of the TMP pulp such pulp is called chemithermomechanical pulp (CTMP). The strength improvements, which may be 50%, are obtained at some sacrifice to yield and opacity. The yields of mechanical pulps are 90—95% the lower yields are associated with chemical treatment. No principal commercial pulps are produced in the next lower yield range, ie, 80—90%. 

Aspen Wood Treated with Chemical-Thermomechanical Process. Aspen wood was pulverized into "chemithermomechanical pulp (CTMP) by a chemical-thermomechanical process 24), During this process, very little hemicellulose and lignin are removed. The CTMP was used without any... 

The purpose of this work was to investigate the nature of lignin in bleached mechanical pulp and sulfonated chemithermomechanical pulp (CTMP). Specifically, the purpose was to identify structures that may be responsible for photoyellowing. 

Pulps. Chemimechanical pulp (CMP) was made from fresh spruce chips on a laboratory scale and the pulp was bleached with 4% hydrogen peroxide as previously reported [77]. Chemithermomechanical pulp (CTMP) was made in a full-scale refiner (at KCL) after pretreatment of industrial spruce chips (Picea abies) with sodium sulfite solution (30 g/1) at 130°C for 5-10 min, followed by pressurized refining. 

Figure 5. UV-VIS difference reflectance spectra (unirradiated minus irradiated) of untreated chemithermomechanical pulp (CTMP) after irradiation with light at selected wavelengths.

Figure 8. Post-color values (PC) of pre-yellowed chemithermomechanical pulp (CTMP-Y), measured at 457 and 557 nm after irradiation for 7 h with light at selected wavelengths, as a function of wavelength.

Agnemo (29) in his patent application describes the effect of treatment of bleached aspen chemithermomechanical pulp with ascorbic acid and sodium sulphite. Figure 3 is a plot of the specific absorption at 457 nm against the time of irradiation. It appears that relative to the initial specific absorption, adding NaaSC and ascorbic... 

Castellan, A., Nourmamode, A., Noutary, C. and Lachenal, D., "Improvement of the Photostability of Peroxide Bleached Chemithermomechanical Pulps Using Cationic Phase transfer Catalysts and Hydroxyl Blocking agents", Cellulose Chem. Technol., 1992, 26, 451. 

Fomier de Violet, P., Nourmamode, A., Colombo, N., and Castellan, A., "Study of Brightness Reversion of Bleached Chemithermomechanical Pulp by Solid State Electronic Spectroscopy", Cellulose Chem. Technol., 1989, 23, 535. 

Chemically modified pulps, as the name implies, are pulps produced by either subjecting wood chips to a mild chemical treatment or using chemical treatment at some point during or after refining. Often steam is injected with the chemicals to yield a chemithermomechanical pulp (CTMP) with good strength properties. This approach has been adopted by many Canadian mills in recent years. 

Table 13.3. Typical data for specific energy demand of mechanical pulps from radiata pine and for some of their properties (unpuhhshed Dr. J.M. Uprichard). The pulps are of the same freeness, 100 CSF, which would he suitahle for newsprint. Pulps of higher freeness require less refining and would have a lower specific energy demand. There is a general increase in strength from stone groundwood to chemithermomechanical pulp. 1 kWh = 3600 kJ.

ID Suckling. The Effect of Coniferaldehyde Sulfonation on the Brightness and Absorption Spectra of Chemithermomechanical Pulps. 6th International Symposium on Wood and Pulping Chemistry, Melbourne, 1991, 1, pp. 587-593. 

U.S. Pat. No. 5,120,776 [64] also discloses using of maleic anhydride (0-4%) to improve the bonding and dispersibility of an extruded mixture of 60-90% of HOPE and 40-10% of wood flour (or chemithermomechanical pulp). 

Thermomechanical pulping of whole kenaf was done, but the resulting pulp had very low strength properties [71]. Chemithermomechanical pulping has also been done using alkaline hydrogen peroxide [72]. Table 7.18 shows the properties of paper made from whole kenaf using either TMP and CTMP. 

The first commercial installation of a steam dryer in Sweden for a chemithermomechanical pulp (CTMP) line with a capacity of 150 t/day showed a 30% reduction in overall drying costs per ton of market pulp compared with an equivalent-size flash dryer [90]. 

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