摘要:

This paper reports the structural investigation of a series ofin situspruce lignins in wood, thermomechanical pulp (TMP) and the corresponding bleached (BTMP) and photoyellowed (YBTMP) samples. This was achieved by using an original two-step degradative technique, thioacidolysis followed by Raney nickel desulfuration. The determination of thioacidolysis monomeric and dimeric products allowed an estimate of various lignin building units and interunit bonds, respectively. It was observed that the thermomechanical and bleaching treatments did not affect spruce lignin structure to an appreciable extent. On the contrary, the photoyellowing treatment caused marked structural changes in lignin, particularly when run in severe conditions. These changes were essentially a decrease in the amount of β-O-4 and β-1 interunit bonds and a relative increase in catechol units and in vanillin end-groups.

ISSN:0277-3813    

DOI:10.1080/02773819208545075

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The pH of sulfite treatments has a profound influence on the efficiency of fiber sulfonation of Norway spruce. Compared at the same pulp yield, the extent of sulfonation decreases in the order of pH value 7·5 > 9·5 > 4·5; the sulfonation reaction is improved significantly by using a two-stage treatment at pH 4·5 and 7·5. The degree of fiber sulfonation plays a dominant role in the tensile and tear strength improvement of these high-yield pulps.

ISSN:0277-3813    

DOI:10.1080/02773819208545076

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The chemical properties and performance of aspen percarbonate (P) and sulfite (S) chemimechanical pulp (CMP) fibers are very comparable. The PCMP, when compared with SCMP of the same yield, has a slightly higher tear index, same beatability and light scattering coefficient, but a lower tensile index and brightness. The strength properties of these fibers are closely related to the total acidic group content resulting from lignin oxidation (carboxyls) and sulfonation (sulfonate).

ISSN:0277-3813    

DOI:10.1080/02773819208545077

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Interaction of sunlight and UV light with thermomechanical (TMP) pulps, milled wood lignin (MWL) and various lignin model compounds in solid state was studied. It was found that TMP fibers were sensitive to these lights. During exposure, TMP lost its brightness as a function of irradiation time and increased its yellowness. The α-carbonyl group functioned as a light absorption center to promote photocleavage of Cα—Cβand β–0–4 linkages. Electron spin resonance (ESR) studies demonstrated that free radicals were generated in the interim. Phenoxy radicals appeared to be important radical intermediates that ultimately transformed into o—quinonoid structures.

ISSN:0277-3813    

DOI:10.1080/02773819208545078

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Hybrid willow (Salix spp.) is a potential source of pulp as demonstrated by its fibre morphology, chemical composition and pulping kinetics. Fibre length and cell wall thickness measurements on one and two years old clones ranged from 0·49 mm to 0·70 mm and 2·5 μm to 3·6 μm respectively. Fibre length variation by annual growth layer varied from 0·5 mm in the first growth layer to about 1·1 mm in the last growth layer and the maximum growth rate occurred in the first two to three years for fourteen years old clones. The clones were producing more fibre fraction as indicated by volumetric composition. The UV absorptfvities of milled wood lignin was found in the range of 12·17 -14·31 Lg−1cm−1at 278 nm and the presence of syringyl and guaiacyl lignin was observed.13C-NMR results of acetylated milled wood lignin showed clonal structural variations during lignification process and the Klason lignin content of one and two years old clones ranged from 20·8% to 26·1%. Bulk kraft delignification of mature wood resulted in 5–6% higher yield than juvenile wood from the same clone and the pulping activation energy ranged from 98 kJ.mol−1to 120 kJ.mor−1.

ISSN:0277-3813    

DOI:10.1080/02773819208545079

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The fractionation of wood consists of the separation of the fibrous material into its constitutive polymers (i.e. extractives, hemicellulose, cellulose and lignin) in a sequential and selective way. The thermochemical or biochemical upgrading of each fraction leads to the production of common and fine chemicals. The first step of the fractionation process is the pretreatment which permits the solubilization of extractives and hemicellulose. The residue thus obtained is more accessible to chemicals and enzymes. The goal of this paper is to prove that a thermomechanical pretreatment in aqueous phase (without adding any chemical) may solubilize, in a relatively selective way, the hemicellulose. This process consists of the following steps: 1) Steeping of aspen sawdust (0·25–0.·50 mm) in water at 7% consistency for 16 h; 2) Cooking at 165–235°C; 3) Rapid discharge (i.e explosion) at δp=6·9 MPa; 4) Quenching. The extent (i.e conversion) and selectivity (i.e. hemicellulose removal vs delignification) of wood solubilization have been studied as a function of cooking temperature in a batch reactor system.

ISSN:0277-3813    

DOI:10.1080/02773819208545080

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A high level of control over grafting reactions onto cellulose derivatives was achieved by an acyl transfer reaction mechanism. Ethylene/maleic anhydride copolymer (EMA) and styrene/maleic anhydride copolymer (SMA) were grafted onto cellulose acetate (CA) and methyl cellulose (MC) in a simple and effective way under homogeneous reaction conditions. While pyridine, a commonly used catalyst for the reaction of an anhydride with an alcohol to form an ester, gave an inconveniently long reaction time, N-methylimidazole (NMID) and 4-(N,N-dimethylamino)pyridine (DMAP) were found to increase greatly the rate of esterification.

ISSN:0277-3813    

DOI:10.1080/02773819208545081

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0277-3813    

DOI:10.1080/02773819208545082

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor