摘要:

Syringylalcohol (1), α-methyl syringylalcohol (2), 3, 4, 5-trime-thoxyphenyl methylcarbinol (3) were dispersed onto filter paper pulp or linter pulp, and treated, respectively, with a ceramic ball mill (CBM) or a vibration ball mill (VBM-1 or -2) under air for 1h. Mechanical treatment of VBM-2, having the more rigid surface of linter pulp, furnished thep-carbonylphenols (5), (6), and 3, 5-dimethoxy-p-benzoquinone (7). Mechanical treatments of syringylgl-ycerol-β-guaiacyl ether (4) with CBM, VBM, and a laboratory refiner provided α-(2-methoxyphenoxy)-β-hydroxypropiosyringone (8) in the highest yield and a less yield ofp-quinone derivative (7) and others as shown in TABLE 2 and FIGURE 3. When treated the resultant mixture with alkaline H202, the chromophore (III) can be decomposed, but remarkable amounts of the leucochromophre (IV) are produced as shown in FIGURE 4.

ISSN:0277-3813    

DOI:10.1080/02773819308020529

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Experiments were conducted to determine the effect of sample type and concentration on the diffuse reflectance infrared fourier transform (DRIFT) spectra of unbleached softwood kraft and thermomechanical pulps, microcrystalline cellulose (Avicel) and kraft lignin (Indulin AT). The absorption of characteristic bands, in Kubelka-Munk units, was followed as a function of sample concentration in potassium bromide, and, in the case of the two pulps, was also determined on handsheets. Anomalous dispersion occurred at concentrations of 1% or below. This phenomenon resulted in a decrease of absorption of specific bands with increasing concentration and was particularly significant for kraft pulp, less important for thermomechanical pulp and microcrystalline cellulose, and practically absent in pure kraft lignin. These effects of specular reflectance could not be completely eliminated by diluting the sample in a non-absorbing matrix, as previously claimed, but could only be minimized at low concentrations.

ISSN:0277-3813    

DOI:10.1080/02773819308020530

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Chlorinated organic matter is formed during chlorine bleaching of carbohydrate. After chlorine bleaching of various cellulosic materials, organochlorine is found in the cellulose substrate (e.g., about 490 μg Cl/g substrate for cotton cellulose) as well as in the spent bleaching liquor. Some organochlorine is mineralized by alkali treatment of the cellulose and some is dissolved. Some organochlorine is not removed by exhaustive extraction with organic solvents, i.e., is inextractable. The carbohydrate-originated organochlorine accounts for part of the inextractable organochlorine in fully-bleached chemical pulp (previously ascribed entirely to a lignin origin). Chlorination of unmodified simple sugars results in some organochlorine (17 to 83 μg Cl/g sugar), while chlorination of “kraft-cooked” glucose precipitate results in 6150 μg organochlorine as Cl/g substrate. Household hypochlorite bleaching of cotton fabric also results in formation of inextractable organochlorine.

ISSN:0277-3813    

DOI:10.1080/02773819308020531

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

This report presents a method to characterize underivatized lignin by Capillary Zone Electrophoresis (CZE), in which separation is achieved by differences in mobility due to differences in the charge-to-size ratios of the solutes.

ISSN:0277-3813    

DOI:10.1080/02773819308020532

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Absolute molecular weights of several commercially and semi-commercially available lignins were determined by gel permeation chromatography (GPC with a differential viscosity detector (DV). Solubility in THF was assured by acetylation. Polystyrene molecular weight standards were used for establishing a universal calibration curve. The lignins included those from hardwood, softwood, and sugar cane bagasse; and these were isolated by the kraft or organosolv pulping process, or by steam explosion/autohydrolysis. All lignins exhibited more or less uniform distributions with weight average molecular weights (Mw) between 3, 000 and 20, 000; with polydispersities (Mw/Mn)between 2 and 12; with Mark-Houwink-Sakurada exponential factors (α) between 0.17 and 0.35; and with intrinsic viscosities between 0.037 and 0.08 dLg−1. A significant relationship between Mw/Mnand Mwwas discovered that had a correlation factor of 0.92. This relationship has the form of Mw/Mn= 0.45 (Mw10−3+ 0.85.

ISSN:0277-3813    

DOI:10.1080/02773819308020533

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The formation of hydroxyl radicals from hydrogen peroxide in alkaline solutions and under the conditions of hydrogen peroxide bleaching of pulps was investigated. The results lend support to the generally accepted view that the decomposition of alkaline hydrogen peroxide is catalyzed by redox processes involving transition metal ion species. The formation of hydroxyl radicals by one-electron reduction of hydrogen peroxide in this process is believed to be catalyzed primarily by mononuclear transition metal ion complexes, polynuclear species being far less efficient in this respect. It was found that a certain formation of hydroxyl radicals during alkaline hydrogen peroxide bleaching of pulp may have a beneficial effect on the final brightness. This finding is ascribed to the cleavage of crosslinks in the rigid lignin matrix which facilitates penetration of the bleaching reagent(s). Silicate does not appreciably suppress the formation of hydroxyl radicals in alkaline hydrogen peroxide solution. The stabilizing effect of this additive is probably due to deactivation of finely dispersed colloidal particles of metal hydroxides and hydrated oxides which decompose hydrogen peroxide to give mainly molecular oxygen and water.

ISSN:0277-3813    

DOI:10.1080/02773819308020534

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Model studies suggest that vinyl ethers are in equilibrium with quinone methides at 170°C in aqueous NaOH and that 25–30% of the vinyl ethers undergo fragmentation during kraft and AQ pulping.

ISSN:0277-3813    

DOI:10.1080/02773819308020535

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Several lignin model precursors have been submitted to zinc borohydride reductions and their resultant stereochemistries determined by NMR spectroscopy. Benzoyl carbonyls of α-aryloxy-β-hydroxy systems were reduced without significant stereoselectivity to produce boththreoanderythroisomers. However, protection of the β-hydroxyl with either an acyl, alkyl, or silyl group and subsequent reduction gaveerythzro-specificities of up to 97%. A mechanism where competition for zinc cation complexation between the β-hydroxyl and the α-aryloxy substituent is invoked to explain the observed results. Protection of the β-hydroxyl prevents its complexation with the zinc cation; complexation occurs solely with the α-aryloxy substituent, affording theerythro-isomers.

ISSN:0277-3813    

DOI:10.1080/02773819308020536

出版商:Taylor & Francis Group    

年代:1993

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:10.1080/02773819308020528

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor