摘要:

The reaction of ethylene glycol dimercaptoacetate and pentaerythritol tetramercaptoacetate withp-benzoquinone have been investigated, both in solution and in the presence of cellulose fibers. In either system, Michael addition is the predominant reaction, leading to decolorization of the quinone by converting it to a substituted hydroquinone. This reaction accounts for the initial bleaching of high-yield pulp produced by these compounds. Handsheets impregnated with these compounds have been irradiated for extended periods of time, and are found ultimately to become more discolored than untreated handsheets. The darkening may be the result of photoinitiated redox chemistry between the Michael adducts and quinones produced in the photodegradation of lignin.

ISSN:0277-3813    

DOI:10.1080/02773810009349621

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Several metal catalysts were examined for their effectiveness in activating hydrogen peroxide and oxygen as oxidants for conversion of lignin models to benzoquinones. Good yields of quinones were observed when certain heteropolymetallates were used as catalysts in the presence of hydrogen peroxide. Oxygen was generally less effective. Oxidation of lignin samples gave 2-3 wt% yields of 2,6-dimethoxybenzoquinone.

ISSN:0277-3813    

DOI:10.1080/02773810009349622

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The process parameters affecting peroxyacetic acid delignification, i.e. temperature, pH and chemical charge, were studied in relation to their effect on carbohydrate depolymerization and dissolution for a softwood kraft pulp. Carbohydrate reactions were found to follow different paths in different pH regions. At low pH, acid hydrolysis was probably the main reason for carbohydrate depolymerization and dissolution. At neutral pH, however, carbohydrate depolymerization was probably caused by the decomposition products of peroxyacetic acid. Peroxyacetic acid may also react with dissolved monosaccharides to form aldonic acids with corresponding and shorter carbon chain lengths as well as aldoses with shorter carbon chains. These reactions were verified through model compound studies. Because of these reactions the amount of carbohydrates in spent liquor is not equal to that removed from pulp fibres during the treatment. These side reactions also consume a small amount of peroxyacetic acid during pulp bleaching.

ISSN:0277-3813    

DOI:10.1080/02773810009349623

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Attempts had been made to differentiate jack pine from some common eastern Canadian conifers (balsam fir, tamarack and black spruce) by analyzing the color appearance from three different chemical tests on wood. The tests conducted were based on either the major extractives (ferric chloride test), the pH (bromophenol blue test) or the resin acids (phenol/bromine test). The chemical tests work only on the heartwood; they do not work on sapwood. The results indicated that the measurement of CIE L*, a*, b,* color parameters is a useful and rapid means for differentiating jack pine from other conifers studied. The test results can be obtained in 10-15 min when wood flour is used.

ISSN:0277-3813    

DOI:10.1080/02773810009349624

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The distribution of anionic groups in fibres, fines, the colloidal fraction, and the dissolved fraction of thermomechanical pulp (TMP) suspensions was determined. The influence of extraction, alkaline treatment, and peroxide bleaching of spruce TMP were also studied.

ISSN:0277-3813    

DOI:10.1080/02773810009349625

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Rice husks (RH) were chemically modified with glycidyl methacrylate (GMA). The chemical loading of the GMA (weight percent gain, WPG) increased as the reaction time was increased. The modification of RH with GMA gave enhanced flexural, tensile and impact properties of rice husk-polystyrene (RH-PS) composites. These may be due to the increased interaction at the interfacial region between the surface of GMA-modified RH and PS. The modification improved dimensional stability and reduced water absorption of the composites.

ISSN:0277-3813    

DOI:10.1080/02773810009349626

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0277-3813    

DOI:10.1080/02773810009349627

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor