摘要:

Wood-polymer composites (WPC) of 13 different Malaysian tropical hardwoods and 10 vinyl monomers and mixtures of monomers were prepared byin situpolymerisation using gamma radiation or the catalyst-heat treatment.

ISSN:0277-3813    

DOI:10.1080/02773819008050224

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

This study was designed to indicate how well direct-scan X-raying predicts preservative retention and distribution of chromated copper arsenate (CCA) in wafers of conifer sapwood. The intensity of X-rays passed through western hemlock wafers treated with varying concentrations of CCA solutions was inversely proportional to preservative concentration. X-ray intensities predicted 98% of the variation in preservative retention among the wafers. Intensity of direct-scan X-rays passed through selected test materials was consistent over a 9-month span. X-ray intensity over 1000 readings at a single scan point had a coefficient of variation of 0.1%. The strong relationship between direct-scan X-ray intensity and preservative retention, as well as the repeatability of intensity readings over time and the small variation in intensity readings at each data point, indicate that direct-scan X-ray techniques can be used to assess preservative retention and distribution in wood treated with inorganic arsenicals such as CCA.

ISSN:0277-3813    

DOI:10.1080/02773819008050225

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

APinus radiatarefiner mechanical pulp (RMP) sample and a range of lignin model compounds were treated with a solution of 25% w/w acetyl bromide (AcBr) in acetic acid to assess the reactions which take place during the dissolution of wood with the AcBr solution. The lignin model reactions were also carried out in solutions to which 4% w/w perchloric acid was added. The RMP sample gave a product which contained 9.2% bromine, and was severely degraded to low molecular weight products, the polysaccharides more so than the lignin fraction. The reactions of the lignin model compounds with AcBr included O-acetylation of phenolic and aliphatic hydroxyl groups, cleavage of β-ether bonds, C-acetylation of aromatic rings, particularly in positionsparato methoxyl groups, demethylation of aromatic methoxyl groups and probable replacement of benzyl alcohol groups by bromine functions. The reactions were accelerated by perchloric acid, and the rates appeared to decrease in the order O-acetylation π bromine substitution >> β-ether cleavage π C-acetylation > demethylation. It is concluded that dissolution of wood in the AcBr solution is a consequence of depolymerisation of the polysaccharides and lignin, and acetylation to give products which would be soluble in the reaction medium.

ISSN:0277-3813    

DOI:10.1080/02773819008050226

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Four regiospecifically methylated condensed tannin derivatives were synthesized by the condensation of regiospecifically methylated flavan-3, 4-diols protected by benzyl groups, and subsequent debenzylation. The monomeric flavan-3,4-diols were obtainedviafour reaction steps starting from phloroacetophenone derivatives and protocatechualdehyde derivatives. Protein—precipitating capacity of these synthetic condensed tannin derivatives was tested and a comparision of these capacity suggests the following results: 1) Phenolic hydroxyl groups in tannins are essential sites for protein precipitation. 2) Although the A-ring has been considered not to be important for tannin—protein interactions, it was proved that the A-ring also plays an important role together with the B-ring. 3) Both hydroxyl groups of A- and B-rings may synergistically interact with proteins.

ISSN:0277-3813    

DOI:10.1080/02773819008050227

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Milled Bamboo Lignin (MBL) fromPhyllostachys pubescens (Bambuseae)was found to containp-hydroxycinnamic acid (PC), guaiacylpropane and syringylpropane units in an approximate molar ratio of 1:4:3 on the basis of chemical and spectroscopic analyses. In addition, the MBL is comprised of a guaiacylsyringyl type lignin-core and PC type peripheral groups. At least 9 PC type units/100 C9-units were chemically bonded to the lignincore in the form of ester linkages at C-a and C-γ, and the remainder in the form of aryl ether linkages at C-a. Bamboo kraft lignin (BKL) was found to be a lignin of the guaiacyl-syringyl type, having a higher degree of condensation and a higher phenolic hydroxyl content than the MBL. The major low-molecular-weight constituents of bamboo kraft black liquor were determined to be acetosyringone, syringic acid, acetoguaiacone and vanillic acid. Structural change in bamboo lignin during kraft cooking are discussed on the basis of the observed results.

ISSN:0277-3813    

DOI:10.1080/02773819008050228

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Two new lignin model quinone methides (QMs) have been characterised by1H and13C NMR techniques. It was shown that the QMs existed in solution as non-interconvertingsynandantiisomers, in a ratio of 2:1. Evaluation of chemical shift data and nuclear Overhauser effects from these and previously synthesised QMs showed that theantiisomer was under greater steric strain than thesynisomer. Additional evidence for the increased steric strain was obtained from a relative kinetic study of the addition of primary amines to the QMs.

ISSN:0277-3813    

DOI:10.1080/02773819008050229

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The effect of the degree of acetylation on the enzymatic digestibility of acetylated xylans has been investigated. Oatspelts xylans were reacetylated to degrees of 0.26 to 1.67 moles acetyl groups per mole of anhydroxylose units. These acetylated samples were then used to study the effect of acetylation on the xylanase (EC 3.2.1.8) and acetyl esterase (EC 3.1.1.6) activities of a commercialTrichoderma reeseicellulase preparation. The enzymatic digestibility was dramatically affected by the degree of acetylation. The onset of resistance is similar for both the xylanase and acetyl esterase enzymes, and both enzymes were completely inhibited by a degree of acetylation of 1.5 moles acetyl groups per mole anhydroxylose units at all enzyme loadings.

ISSN:0277-3813    

DOI:10.1080/02773819008050230

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The hemicelluloses of the fossil tree (Metasequoia glyptostroboides) were isolated from a mildly-prepared acid chlorite holocellulose. Arabinoxylan, glucomannan, and galactoglucomannan were isolated from the holocellulose by extraction and fractionation techniques. The sugar compositions of the polysaccharides were analyzed by quantitative thin layer chromatography and gas chromatography. The hemicelluloses accounted for 21–22% of the wood; the arabinoxylan about 10%, the glucomannan about 6.3%, and the galactoglucomannan about 4.8%. The glucose:mannose ratio for the glucomannan and galactoglucomannan were approximately 1:1.6 and 1:1.7, respectively, in contrast to a ratio of 1:3 commonly found in coniferous woods.

ISSN:0277-3813    

DOI:10.1080/02773819008050231

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0277-3813    

DOI:10.1080/02773819008050223

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor