Chemimechanical pulp

We thank the Natural Sciences and Engineering Research Council of Canada for financial support via Mechanical and Chemimechanical Pulps Network and Strategic grants, and Colonial Metals Inc. for loans of RuC13 -3 H20. 

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 3. UV-VIS difference reflectance spectra (unirradiated minus irradiated) of untreated chemimechanical pulp (CMP) after irradiation with light at selected wavelengths.

Figure 9. Kinetics of irradiation of peroxide-bleached chemimechanical pulp (CMPB) at selected wavelengths analyzed by measuring the reflectance at 457 nm.

Coniferaldehyde structures are the major leucochromophore present in spruce lignin. These end groups are also present to a large extent in unbleached mechanical pulps and are responsible for a major portion of the absorption of UV-radiation above 350 nm. Mild sulfite treatment leads to a considerable reduction in the content of coniferaldehyde structures. After bleaching of mechanical and chemimechanical pulps with alkaline hydrogen peroxide, coniferaldehyde structures are to a large extent eliminated and they cannot be considered to be major contributor to the photo-... 

Pulp Samples. The samples used in the study were commercial unbleached and peroxide-bleached spruce (Picea abies) groundwood (GW), unbleached and peroxide-bleached spruce, and unbleached and peroxide-bleached aspen chemimechanical pulp (CTMP). 

In a series of experiments with a spruce chemimechanical pulp, it was established that, regardless of the initial irradiation time, a second irradiation period of five minutes with UV-containing radiation after 24 hours storage was sufficient to eliminate the photochromic brightness increase, as shown in Figure 4. If the chromophoric structures are present in the pulp from beginning in their uncoloured or potential chromophore form or whether they are formed by reactions during the initial irradiation is not known and may in fact also depend on the prehistory or the type of pulp. 

It is relevant to note that the effect has been observed in all the high-yield pulps that we have studied. The study included commercial unbleached and peroxide-bleached spruce groundwood, unbleached and peroxide-bleached spruce and aspen chemimechanical pulp (Table I). 

In a previous communication [2] it was shown that the irradiation of chemimechanical pulps with monochromatic light at selected wavelengths can be used to obtain new information on the wavelengths that most readily cause photochemical... 

Chemimechanical pulps usually are produced by soaking the chips in solutions of NaOH or Na2S03, and then refining in disc refiners to produce a groundwood-type pulp. Chemical consumption is very low, and yields are usually 85-95 percent. 

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%. 

Fig. 7.7.4. Relationship between the sulfonate contents of chemimechanical pulps obtained by conductometric titration and those obtained by magnesium exchange. (Katz et al. 1984)...

Fig. 7.7.5. Relationship between sulfur content of chemimechanical pulps obtained by combustion/ion chromatography and by CPPA standard gravimetric method G28. (Douek and fng 1989)...

Forsskahl and Tylli [116] constructed action spectra for irradiation of softwood chemimechanical pulp (CMP) and CTMP by measuring the changes in PC number at 457 nm and 557 nm. The spectra for peroxide-bleached chemimechanical pulp are shown in Figure 3.12. Both action spectra have a maximum response at 325 mn, although the response for PC number at 457 nm is significantly broader, perhaps due to a hidden maximum at 350 nm. 

Porsskahl and J Janson. Sequential Treatment of Mechanical and Chemimechanical Pulps with Light and Heat. Part 1. UV-VIS Reflectance Spectroscopy. Nordic Pulp Paper J. 6 118-126, 1991. 

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