Peroxide-bleached Mechanical Pulps Research Articles

Purified pectinase lowers cationic demand in peroxide-bleached mechanical pulp

Pectinase, purified from the commercial enzyme mixture Novozym 863 by affinity chromatography, was able to lower the cationic demand of peroxide-bleached mechanical pulp. It was also able to enhance the ability of cationic polymers to increase fines and ash retention. A second purified pectinase, cloned polygalacturonase I from the fungus Aspergillus aculeatus, also produced these effects. However, when applied at the same pectinase activity, the crude pectinase increased retention more than the purified polygalacturonase. Apparently, other enzyme activities in Novozym 863 contribute to its effects on retention. This research expands our understanding of pectinase activity by proving that pectinase is responsible for both reducing cationic demand and improving the retention of peroxide-bleached thermomechanical pulps.

Sorption of spruce O-acetylated galactoglucomannans onto different pulp fibres

Sorption of spruce acetylated galactoglucomannans (GGM) onto different pulps, among which unbleached and peroxide-bleached mechanical pulps, and unbleached and bleached kraft (BK) pulps, was studied as a means of understanding the retention of acetylated GGMs in mechanical pulping and papermaking. The fibre surface coverage of lignin and carbohydrates was estimated by X-ray photoelectron spectroscopy (XPS) or electron spectroscopy for chemical analysis (ESCA). GGM sorption was clearly favoured on kraft pulps. Hardly any differences in sorption were, however, observed between unbleached and BK pulps, even if the surface coverage of lignin was lower on the bleached pulp. Neither thermomechanical pulp (TMP) nor chemithermomechanical pulp (CTMP) manufactured from spruce sorbed any acetylated GGMs. Peroxide bleaching of the pulp did not increase sorption. Only CTMP produced from aspen sorbed some GGMs. The anionic charge of neither chemical nor mechanical pulps influenced GGM sorption.

Pectinase in papermaking: solving retention problems in mechanical pulps bleached with hydrogen peroxide

Treatment with the enzyme pectinase has been reported to lower the cationic demand of thermomechanical pulp (TMP) bleached with alkaline peroxide in the laboratory. We have extended this discovery to bleached TMP produced industrially, and shown that commercial enzyme preparations can treat pulp within 15 min at the temperature and pH values prevalent in paper mills. About half of the cationic demand in the bleached pulp can be destroyed by pectinase. Dynamic drainage jar experiments show that the enzyme treatment improves the effectiveness of several cationic polymers to increase retention of fines and filler particles. It does not increase retention in the absence of retention aids or with nonionic polymers, and does not damage the strength properties of the pulp. Pectinase could be easily incorporated into paper machine stock preparation systems to lower the charges of cationic retention aids needed in furnishes containing peroxide-bleached mechanical pulp.

Photoyellowing of peroxide-bleached lignin-rich pulps: a photochemical study on stilbene-hydroquinone chromophores issued from β-5 units of lignin during refining and (or) bleaching

The contribution of stilbene-parahydroquinone structures, formed from β-5 units during refining and bleaching, in photoreversion of peroxide-bleached high-yield pulps, was studied using 4'-benzyloxy-2,5-dihydroxy-3,3'-dimethoxystilbene (I), as a model compound. The various photoproducts formed during irradiation of I in solution or adsorbed on cellulose paper were identified. Isomerization of the stilbene double bond and oxidation of the hydroquinone into quinone were observed in solution, whereas in the solid state only the formation of the quinone was found to operate. Our attempts to detect and quantify stilbene-hydroquinones forming from β-5 units created on peroxide bleached mechanical pulp were not met with success.Key words: lignin, stilbene, hydroquinone, lignin model compound, pulp, photoyellowing.

Light-Induced Yellowing of Mechanical and Ultra-High Yield Pulps. Part 3. Comparison of Softwood TMP, Softwood CTMP and Aspen CTMP

Abstract We have compared the light-induced yellowing of three peroxide-bleached mechanical pulps: softwood TMP (spruce/balsam fir mixture), softwood CTMP (spruce), and aspen CTMP. We attribute dissimilarities in the absorption difference spectra of softwood TMP and softwood CTMP to photobleaching of residual coniferaldehyde groups present in peroxide-bleached TMP. We also interpret an earlier report of photobleaching by ascorbic acid as coniferaldehyde photobleaching. Coniferaldehyde-free softwood pulps showed a broad absorption maximum at 360 nm and a shoulder at about 416 nm. The 360 nm peak resulted from the coalescence of two absorption peaks with Λmax ≈ 330 nm and 360 nm. Irradiated aspen CTMP had an absorption maximum at 360 nm, but no shoulder at wavelengths above 400 nm. The difference spectra of the irradiated pulps were compared with those for pulps where quinone groups were introduced by oxidation with either Fremy's salt or sodium periodate. These experiments suggested that even if one attributes all the absorption increase above 400 nm to formation of simple o-quinones, these quinones cannot account for the magnitude of the peak at 360 nm. The kinetics for increases in absorption coefficient were fit by a sum of two exponential terms. Within the error of the fitted parameters, all three pulps had identical rate constants.

Ir and uv spectroscopic study of borohydride reduced mechanical pulp during monochromatic and wide band irradiation

The fate of aromatic carbonyl groups during light-induced yellowing of peroxide-bleached mechanical pulps was investigated using infrared and uv-visible reflectance spectroscopies. If the interference of existing carbonyl groups is eliminated by borohydride reduction, both techniques indicate clearly that aromatic carbonyl groups are formed during irradiation. Methoxylated and unmethoxylatedortho-quinones were introduced into the pulp by treatment with sodium periodate or Fremy’s radical. Comparison with pulps which were discoloured by monochromatic near-uv irradiation (λ=320 nm) indicates that both types of quinones are formed during irradiation. The methoxylated quinones were bleached by 420 nm irradiation, but the unmethoxylated quinones seemed instead to sensitize destruction of aromatic groups.

Fluorescent Detection ofo-Quinones Formed in Lignin-Containing Pulps During Irradiation

Abstract o-Quinones are thought to play a key role in the photoyellowing of mechanical pulps. The facile reaction between o-quinones and o-phenylenediamine to give fluorescent phenazines is examined as a possible way to detect quinonoid intermediates in pulp sheets. The method was tested on o-quinone-rich mechanical pulp sheets prepared by chemical treatment with Fremy's salt (potassium nitrosodisulphonate). The presence of photochemically generated o-quinone groups in peroxide-bleached mechanical pulps was inferred from the fluorescence observed from o-phenylenediamine treated sheets. This fluorescence increased with increasing radiation time up to a limiting value. The quinones (but not their phenazine derivatives) are stable upon storage in the dark.