Torbjörn Reitberger

Study on the Selectivity of Bleaching with Oxygen-Containing Species

In the bleaching of pulp, the term Selectivity is widely used but poorly defined.This work is an attempt to quantify the selectivity of bleaching with Oxygen-containing species by generating hydroxil radicals and measuring their reaction rates with some lignin and carbohydrate models. Results of this investigation show that the selectivity factor defined as the ratio of the rate constants for a given pair of lignin and carbohydrate models, lies between 5 and 6.

Hydroxyl Radical Activity in Brown-Rot Fungi Studied by a New Chemiluminescence Method

A sensitive and selective Chemiluminescence method is used to detect hydroxyl radicals during growth of brown-rot fungi. The results show that hydroxyl radicals are generated after an incubation period in surprisingly high yields.The hydroxyl radicals are formed at different rates when brown-rot fungi grown liquid media, agar media or wood. Addition of glucose, veratryl alcohol or nutrient nitrogen to the culture media affects the formation of hydroxyl radicals in different ways.The initial degradation of wood, measured äs alkali solubility, closely follows the amount of hydroxyl radicals formed. Together, these observations indicate that hydroxyl radicals contribute significantly to the initial degradation of wood.

Chemiluminescence from oxidation of polypropylene: Correlation with peroxide concentration

Abstract The Chemiluminescence (CL) on heating in an inert atmosphere has been measured for samples taken at various times during oxidation of polypropylene (PP). Proportional relationships were obtained when the integrated emission (TLI) was plotted against peroxide concentration for all studied sets of parameters. Changes in melting temperature and molecular weight with ageing time were found to correlate with changes in the TLI. Oxidised PP was exposed to dimethylsulfide (DMS) for different periods with subsequent measurements of the CL and the peroxide concentration. The peroxide concentration has earlier been found to exhibit a two-step decay with DMS exposure time, indicating two fractions of peroxides with different reactivity. The CL was found to follow the same two-step decay, indicating that both peroxide fractions contribute to CL. The oxidative stability of PP, measured by CL induction times in oxygen, increases when the polymer is exposed to DMS.

Is cellobiose dehydrogenase from Phanerochaete chrysosporium a lignin degrading enzyme

Cellobiose dehydrogenase (CDH) is an extracellular redox enzyme of ping-pong type, i.e. it has separate oxidative and reductive half reactions. Several wood degrading fungi produce CDH, but the biological function of the enzyme is not known with certainty. It can, however, indirectly generate hydroxyl radicals by reducing Fe(3+) to Fe(2+) and O2 to H2O2. Hydroxyl radicals are then generated by a Fenton type reaction and they can react with various wood compounds, including lignin. In this work we study the effect of CDH on a non-phenolic lignin model compound (3,4-dimethoxyphenyl glycol). The results indicate that CDH can affect lignins in three important ways. (1) It breaks beta-ethers; (2) it demethoxylates aromatic structures in lignins; (3) it introduces hydroxyl groups in non-phenolic lignins. The gamma-irradiated model compound gave a similar pattern of products as the CDH treated model compound, when the samples were analyzed by HPLC, suggesting that hydroxyl radicals are the active component of the CDH system.

Radical Formation in Ozone Reactions with Lignin and Carbohydrate Model Compounds

Summary Using different independent methods, the kinetics of ozone consumption and the initial radical yield in reactions of ozone with lignin and carbohydrate model compounds were investigated. It was demonstrated that ozone reacts with phenolates several orders of magnitude more rapidly than with corresponding undissociated phenols. The pH dependence of the radical yield does not completely follow the pK a-value of the phenols. In fact, the radical yield starts to increase at pH 3 for all the phenolic model compounds investigated. Several indications suggest that superoxide rather than the hydroxyl radical is initially formed when ozone reacts with lignin model compounds. In contrast to lignin model compounds no radicals were detected in ozone reactions with carbohydrate model compounds or olefins. On the basis of this study, it may be concluded that ozone bleaching should preferably be performed at pH 3 and at a higher consistency. No significant effect of metal ions was observed.

FORMATION AND INVOLVEMENT OF RADICALS IN OXYGEN DELIGNIFICATION STUDIED BY THE AUTOXIDATION OF LIGNIN AND CARBOHYDRATE MODEL COMPOUNDS

The formation of superoxide and hydroxyl radicals under the conditions of oxygen bleaching and their involvement in the oxidative degradation of lignin and carbohydrate structures have been demonstrated using simple model compounds. It was found that: 1. The first step of autoxidation is a one-electron transfer process yielding a substrate radical and superoxide. Direct coupling between these species in the initial solvent cage is of minor importance. 2. Hydroxyl radicals are formed by a superoxide driven Fenton reaction with a pH-maximum in the range 11–11.5. 3. Of the heavy metal salts investigated CuSO4 and MnSO4 facilitate both the degradation of phenolic substrates and the formation of hydroxyl radicals, whereas FeSO4 has no significant effect. 4. Striking mechanistic analogies between the autoxidative degradation of lignin and carbohydrate model compounds determine the fundamental selectivity of the process, while formation of hydroxyl radicals determine the conditional selectivity imposed on oxygen delignification processes.

Imaging chemiluminescence instrument for the study of heterogeneous oxidation effects in polymers

Abstract An imaging Chemiluminescence equipment used for studies of diffusion controlled oxidation effects in polymers is presented. The design involves an imaging photon counting system mounted on a cylindrical oven with a controlled atmosphere. The overshoot on heating is less than 2 °C and the temperature during isothermal conditions is maintained at ±0.4 °C, thus, a stable thermal environment is attained. To point out possible applications, the monitoring of oxidation profiles from aged nylon specimens and oxygen-barrier properties of an inorganic coating by chemical plasma deposition on a hydroxyl terminated polybutadiene substrate are presented. The results demonstrate the feasibility of studying diffusion controlled oxidation and also the possibility of the technique to estimate the function and durability of surface treatments on elastomers.

Detection of Hydroxyl Radicals by a Chemiluminescence Method - A Critical Review

A chemiluminescence (CL) method for the sensitive and selective detection of free hydroxyl radicals has been investigated. The CL method is based on hydroxylation of non-chemiluminescent phthalic hydrazide by hydroxyl radicals to give the strongly chemiluminescent 3-hydroxyphthalic hydrazide. The selectivity of the method was tested against some one-electron oxidants, including the highly reactive sulphate anion radical. No hydroxylation of phthalic hydrazide was observed with these oxidants, showing that the method is selective for the hydroxyl radical. The CL method showed a high sensitivity : detection at a level of 0.1 picomole 3-hydroxyphthalic hydrazide was reached. In our studies on the role of the hydroxyl radical in the fungal degradation of wood and in the bleaching of pulp the method has proven to be reliable and has contributed in a crucial way to the results obtained. The method may also be suitable for in vivo studies.

Oxidation profiles of polyamide 6,6 studied by imaging chemiluminescence and FTIR

Abstract Injection moulded test specimens of polyamide 6,6 have been subjected to ageing in ambient atmosphere at temperatures ranging from 100 to 130 °C for different times. Skin-core oxidation was observed and evaluated by infrared spectroscopy in terms of carbonyl index depth profiles and by imaging chemiluminescence as peroxide depth profiles. The oxidation depth profiles determined by the two techniques showed good agreement with respect to ageing time and temperature. The oxidation depth was shown to decrease with increasing ageing temperature. The results clearly indicate a diffusioncontrolled oxidation process.

Thermal oxidation of hydroxyl-terminated polybutadiene rubber. I. Chemiluminescence studies

The chemiluminescence (CL) intensity from a hydroxyl-terminated polybutadiene (HTPB) rubber was measured during isothermal oxidation at temperatures ranging from 70 to 130°C. The CL isotherms were characterised by an approximately constant level of intensity followed by a rapid increase to a maximum intensity. The initial intensity as well as the maximum intensity levels of the different isotherms obeyed an Arrhenius expression, suggesting an invariable overall oxidation mechanism. Total luminous intensity (TLI) values in nitrogen atmosphere were obtained at selected times during the isothermal oxidation. The TLI data showed a good correlation with the CL isotherm, indicating that the time course of the isotherm can be explained in terms of peroxide build-up and decomposition. The build up of peroxides during oxidation was shown from FTIR data to be accompanied by a build-up of carbonyl groups. Above a certain TLI level, FTIR data showed a significant decrease in unsaturation, while swelling measurements showed an increase in the apparent crosslink density. This formation of a secondary network later accelerated, with gradual depletion of oxygen in the specimen, causing sever embrittlement of the rubber.