John A. Schmidt

Lignin and lignans : advances in chemistry

Overview D. Dimmel Determining Lignin Structure by Chemical Degradations C. Lapierre Electronic Spectroscopy of Lignins J. A. Schmidt Vibrational Spectroscopy U. P. Agarwal and R. H. Atalla NMR of Lignins J. Ralph and L. L. Landucci Heteronuclear NMR Spectroscopy of Lignins D. S. Argyropoulos Functional Groups and Bonding Patterns in Lignin (Including the Lignin-Carbohydrate Complexes) G. Brunow and K. Lundquist Thermal Properties of Isolated and in situ Lignin H. Hatakeyama and T. Hatakeyama Reactivity of Lignin-Correlation with Molecular Orbital Calculations T. Elder and R. C. Fort, Jr. Chemistry of Alkaline Pulping D. Dimmel and G. Gellerstedt Chemistry of Pulp Bleaching G. Gellerstedt The Chemistry of Lignin-Retaining Bleaching: Oxidative Bleaching Agents G. Leary and J. A. Schmidt The Chemistry of Lignin-Retaining Bleaching: Reductive Bleaching Agents S. Robert Lignin Biodegradation K-E. L. Eriksson Biopulping and Biobleaching I. D. Reid, R. Bourbonnais, and M. G. Paice The Photochemistry of Lignin C. Heitner Pharmacological Properties of Lignans T. Deyama and S. Nishibe

Light-Induced Yellowing of Mechanical and Ultrahigh Yield Pulps. Part 2. Radical-Induced Cleavage of Etherified Guaiacylglycerol-β-Arylether Groups is the Main Degradative Pathway

Abstract Bleached softwood mechanical pulp was treated with sodium borohydride to reduce carbonyl groups and dimethyl sulphate to block phenolic hydroxyl groups. Upon irradiation with near ultra-violet light, new phenolic hydroxyl groups and aromatic carbonyl groups formed. Existing mechanisms for photoyellowing require that either aromatic ketones or phenolic hydroxyls be initially present in the pulp, and cannot explain these observations. We interpret our results in terms of light-induced breakdown of etherified arylglycerol-β-arylether structures in lignin. Degradation occurs via the corresponding ketyl radicals, which cleave rapidly at the β-O-4 bond to give a phenoxy radical and an acetophenone enol. The enol tautomerizes to a ketone, while the phenoxy radical is oxidized to coloured groups. We believe that the ketyl route is the main lignin degradative pathway, and estimate that up to 70% of the colour formed during light-induced yellowing is attributable to this reaction.

Light-Induced Yellowing of Mechanical and Ultra-High Yield Pulps. I. Effect of Methylation, NaBH4, Reduction and Ascorbic Acid on Chromophore Formation

Abstract Absorption difference spectra of bleached TMP irradiated with near-uv light exhibited two apparent absorption maxima at π 410 nm and 330 nm. Experiments with borohydride-reduced pulp suggest that photochemical formation of aromatic carbonyls contributes to the λ = 330 nm peak. Chromophore formation followed an apparently first-order rate law, and the rate was unaffected by methylation of phenolic hydroxyl groups, or by exhaustive reduction of carbonyl groups with NaBH4. Methylation of phenolic hydroxyl, while having no effect on the kinetics of chromophore formation, did decrease the maximum change in absorption coefficient, ΔK∞. Treatment of bleached TMP with ascorbic acid slowed light-induced yellowing substantially; significant yellowing occurred only after 2 hours. Light-induced bleaching of a chromophore with λmax π 350 nm, possibly a stilbene, occurred during the first 90 minutes of irradiation.

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 Fremys salt or sodium periodate. These experiments suggested that even if one attrib...

A dramatic solvent effect on high-yield pulp yellowing inhibition for a benzophenone-based ultraviolet absorber

Abstract UV screens used to photostabilise high-yield pulp do not work as well when deposited from water as they do when deposited from organic solvents. For a water-soluble ultraviolet absorber (UVA) based on 2-hydroxybenzophenone, the water-effect is dramatic. For example, during light exposure a 78% ISO brightness paper sheet made from lignin-containing peroxide bleached softwood thermomechanical pulp (BTMP) lost 27 brightness points. A BTMP sheet treated with 0.5% by weight of the UVA 5-benzoyl-4-hydroxy-2-methoxy-benzenesulfonic acid, 1 (Uvinul MS40™) delivered from ethanol lost only 19 brightness points. However, a sheet treated with 0.5% of the same UVA from water lost 25 brightness points. For a benzotriazole UVA, 5-benzotriazolyl-4-hydroxy-3- sec -butyl-benzenesulfonic acid, 2 (Cibafast W™) the adverse water-effect is smaller. Our experiments suggest several reasons for the poor performance of aqueous-delivered 1 : attenuation and broadening of the absorption spectra on paper when the additive is delivered from water, disruption of the internal hydrogen bond, partial formation of phenolate ion, and changes in the distribution of the additive through the thickness of the paper sheet. This effect has been found to be general across several water-soluble benzophenone- and benzotriazole-type UVAs. One exception to the rule is found for a benzotriazole that has a PEO side chain on the hydroxyphenyl ring. Thus, choice of solvent used in testing new paper stabilisers is of central importance to stabiliser performance.

Diffuse-reflectance laser flash photolysis studies of the photochemistry of bleached thermomechanical pulp

Abstract Diffuse-reflectance laser flash photolysis was used to study the photochemistry of bleached, black spruce mechanical pulp. Following laser excitation of bleached pulp samples at 354 nm, a transient absorption spectrum was observed with λ max = 450 nm. Oxygen and the phenolic hydroxyl groups in lignin reduced the detected amount of transient by static quenching, and the intensity of the transient spectrum also decreased in pulps reduced with sodium borohydride. The transient was assigned as the electronic triplet state of the aryl ketone group in lignin. Computer simulations indicated that the concentration of the ketone triplet states varied exponentially with depth into the sample, and kinetic analysis was carried out on this basis. The decay of the transient was remarkably long, and was not described by either simple first-order or higher-order kinetics. We interpret this as a manifestation of the heteogeneity of lignin; the aromatic ketone group is distributed over a variety of structurally or chemically distinct sites in the macromolecule.