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21.
Using time-resolved CIDEP and conventional ESR as well as optical studies much can be elucidated concerning the initial photochemical
reactions of lignin model compounds such as α-guaiacoxyacetoveratrone and α-guaiacoxy-β-propioveratrone. The resulting transient
radicals are models for intermediates in the processes of photoyellowing of lignin containing mechanical pulps and papers.
Model solution experiments which produce evidence for the roles of free radicals in reductive bleaching of mechanical pulps
and in the oxidative aging of papers are also described. The more thorough understanding of these complex processes allows
the development of strategies to try to “protect” mechanical pulps and papers from light and thermally induced damage and
to “repair” any damage which invevitably occurs. 相似文献
22.
T. R. J. Dinesen M. Y. Tse M. C. Depew J. K. S. Wan 《Research on Chemical Intermediates》1991,15(2):113-127
A series of model organic haliae compounds were decomposed by the technique of microwave catalysis. The reactions were 100%
efficient which were followed and characterized by gas chromatography, mass spectrometry, and direct electron spin resonance
detection. The results clearly establish the primary free radical mechanisms of the decomposition by breaking selectively
the C-X bond, leading to an organic fragment/radical and a stable form of solid metal halides. Many of the non-halogenated
organic products are of economic and chemical value and can be recovered in the microwave processing. 相似文献
23.
R. S. Pemberton M. C. Depew S. D. Pollington J. K. S. Wan 《Research on Chemical Intermediates》1995,21(3-5):425-439
The reactions of alkyl peroxyl radicals with cellulosic and lignin-containing papers have significance in both the problems of brightness reversion and paper aging phenomena. Since transient peroxyl radicals are elusive to ESR and other spectroscopic detection, we have explored the controlled study of the interactions of nitrogen oxides with paper and some model lignin compounds in solution as a comparable model of free radical oxidation. Formations of intermediate iminoxyl and nitroxide radicals are identified by ESR with products in some model systems analysed by GC/MS to elucidate the primary mechanisms of the interactions of these gaseous free radicals with papers and with some simple organic model lignin compounds. 相似文献
24.
Theories explaining the clinically proven efficacies of 5-aminosalicylic acid and its derivatives sulfasalazine and olsalazine in the treatment of inflammatory bowel disease have invoked the neutralization or scavenging of reactive free radicals. This is a preliminary study comparing the relative scavenging abilities of these 5-ASA derivatives towards the stable free radicals 2,2-diphenyl-1-picrylhydrazyl (DPPH) and galvinoxyl with several compounds including phenols, acetaminophen and vitamins C, K and E which have well documented antioxidant and radical scavenging capabilities both in solution and in biological systems. 相似文献
25.
The effects on the radiation response of Harwell polymethylmethacrylate (PMMA) dosimeters of dose-rate, radiation type, temperature during irradiation and post-irradiation storage, and post-irradiation stability, are of importance to the operators of commercial irradiation facilities.
This paper describes recent studies of the effects of some of these parameters on the radiation response of Harwell Red 4034, Amber 3042, and Gammachrome YR Perspex dosimeters, and provides data on batch to batch variation and shelf-life. 相似文献
26.
M. C. Depew 《Research on Chemical Intermediates》1991,16(3):279-279
27.
The photoyellowing of lignin-rich papers has been demonstrated to depend on the formation of phenoxyl radical intermediates and their ultimate conversion into various products, including quinones. Molecular oxygen has also been observed as a necessary adjunct to this process, although the mechanism is not understood. This work demonstrates the requirement for the reaction of O2 with active radical intermediates (in processes analogous to autoxidation reactions) in order for the photoyellowing of the phenolic moieties to occur. Photo-oxidations of a variety of alkoxyphenols and their reactions with model alkyl, alkoxy and alkylperoxy radicals are studied by CIDEP. 相似文献
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30.
Jeffrey K. S. Wan Ivan Kalatchev Janusz Dziak M. Catherine Depew 《Research on Chemical Intermediates》2001,27(9):917-926
Non-alkaline bleaching of thermo-mechanical pulps using 40 MHz RF dielectric capacitor heating is described. Experimental data obtained under RF irradiation are compared with non-alkaline bleaching under pulsed microwave at 2.45 GHz. Optimal processing time is determined. Effectiveness of non-alkaline bleaching of TMP in RF is shown to be close to that in microwave. Neither microwave nor RF irradiation, under non-alkaline bleaching conditions, is shown to result in detriment to the physical properties of the pulp. 相似文献