摘要:

Two series of pine kraft lignins were prepared by a) normal kraft cooks to different pulp yield levels and precipitation of the lignins from the black liquors by acidification and b) by successive acidification of the black liquor obtained from a flow-through cook. All the lignins were extensively purified, subjected to elemental and methoxyl analysis and subsequently acetylated.

ISSN:0277-3813    

DOI:10.1080/02773818408070647

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

90.7 MHz Carbon-13 NMR spectra of spruce and beech milled wood lignins (MWLs) and comparison with the spectra of their acetates as well as acetylated dehydrogenation polymer (DHP) from coniferyl alcohol reveals detailed information on the constitution of the two lignins. The signals indicative of β-0-4 units are split, due to the occurrence oferythroandthreoisomers. In beech ligninerythroβ-0-syringyl ethers by far prevail in the β-0-4-linkages. The spectra also provide unequivocal evidence for the occurrence of β-5 and β-β linkages in both spruce and beech lignins, while some anomalies remain in the case of β-1 and α,β-bis-0-4 units. Two-dimensional13C-J(1H)-NMR spectra of acetylated DHP corroborate the assignment of signals in the spectra of acetylated MWLs.

ISSN:0277-3813    

DOI:10.1080/02773818408070648

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Two models of lignin structure are compared and discussed with respect to experimentally measured molecular weight data. The model of polycondensation of f-functional monomers appears to give incorrect results. A generalized model is presented based upon the concept of a crosslinked polymer formed with randomly distributed pre-polymers. Molecular weight data support a tetrafunctional branch point in the lignin preparation studied. However, viscometry data do not support a tetrafunctional or trifunctional functionality. Number- and weight-average DP measurements give important information concerning the characteristics of degraded lignin fractions.

ISSN:0277-3813    

DOI:10.1080/02773818408070649

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The formation and subsequent disappearance of coniferyl alcohol during kraft and soda-AQ (anthraquinone) pulping of western hemlock wood meal have been studied under isothermal condition. At 140°C, the amount of coniferyl alcohol generated increases to a sharp maximum (0.4% of total lignin in kraft and 1.9% in soda-AQ pulping) and then declines rapidly to low values. It was found that the disappearance of coniferyl alcohol was mainly due to condensation with other components of dissolved lignin. Nearly identical activation energies, 125 kJ mole−1for kraft and 128 kJ mole−1for soda-AQ pulping, were derived from the initial rates of coniferyl alcohol formation, conforming closely with the value 121 kJ mole−1for the cleavage of phenolic β-ether model compounds in the kraft process.

ISSN:0277-3813    

DOI:10.1080/02773818408070650

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The molecular weights of lignin fractions leached from an unbleached kraft pulp were found to increase from 230,000 to 410,000 as washing of the pulp proceeded. The free diffusion coefficients for both a spherical and a disk-like conformation were calculated and were found to be seven orders of magnitude higher than the observed intrafiber diffusion coefficient. Also the change in the free diffusion coefficient with molecular weight was far less than the 100-fold polydispersity observed previously. A comparison of the molecular dimensions with the pore size indicated that a flat, disk-like conformation, rather than a spherical conformation, is appropriate for the lignin macromolecule.

ISSN:0277-3813    

DOI:10.1080/02773818408070651

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The Klason method–dissolution of carbohydrates in sulfuric acid–has been widely used for the determination of lignin content in woody materials. It was an unsolved problem, however, whether Klason lignin still contains carbohydrates. We observed previously that Klason lignin becomes almost completely soluble in water after ozone treatment. In this work, the residual sugar content of Klason lignin was determined on the basis of the above observation.

ISSN:0277-3813    

DOI:10.1080/02773818408070652

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A linear relationship between the enthalpy relaxation and the logarithm of time was observed for a variety of lignins and lignin derivatives annealed at temperatures below their glass transition temperature. While the behavior is noticeably affected by differences in lignin structure in terms of origin, chemical functionality and molecular weight, the sub-Tg annealing temperatures were found to be the primary factor determining the rate d ER/d log t (where ER represents enthalpy relaxation and t time), and this ranged from 0.2 to 0.4. This time dependent reduction in enthalpy is the result of a non-equilibrium chain conformation and has been shown to correlate with mechanical and several other physical properties for a number of material systems.

ISSN:0277-3813    

DOI:10.1080/02773818408070653

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The stress-strain properties of a NSSC-fluting medium plasticized with various amounts of ethylene glycol have been measured over a temperature range up to 250°C. By comparison with delignified and hemicellulose-extracted samples it is concluded that the major softening is to a large extent caused by the lignin. It is shown that the Kaelble equation provides a good estimate of the glass transition temperature in lignin plasticizer systems. A reasonable correlation is also found between the measured softening in NSSC-papers containing ethylene glycol and the predictions of the plasticizing effect on lignin and carbohydrates based on the Kaelble approach. On this basis, the thermal softening of a NSSC-fluting medium and its lignin and carbohydrate polymers when plasticized by water is discussed, particularly in relation to the hot corrugating process.

ISSN:0277-3813    

DOI:10.1080/02773818408070654

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Ozone was found to be reasonably stable at moderately low pH (∼pH 3) and ambient temperature in acetic, sulfuric and nitric acid solutions. In these cases, the exact kinetic order of ozone decomposition could not be established. However, second order with respect to ozone was preferred on the basis of statistical analysis of the data. At pH 3, the ozone decomposition rate was found to be slightly higher at 15°C and moderately higher at 35°C than at 25°C for all three buffer systems. At lower concentration level (∼ 0.5 ppm), only Co(II) ion enhanced decomposition of ozone in sulfuric acid solution at pH 3 and 25°C. In contrast, at the higher concentration level (∼ 3.0 ppm), Ca(II), Cr(III), Fe(II), Fe(III), Co(II), Ni(II) and Cu(II) ions were found to contribute the decomposition of ozone; the effect of Co(II) and Fe(II) ions was very pronounced as compared to the other ions. Using acetic acid instead of sulfuric acid as buffer reagent resulted in drastic and moderate reductions of the ozone decomposition catalyzed by Co(II) and Fe(II) ions, respectively. These indicate that acetic acid acts as radical scavenger for hydroxyl radical as postulated by Walling et al. Thus, the drastic increase in the ozone decomposition in the sulfuric acid solution with the presence of Co(II) or Fe(II) ion is caused by free radical chain reactions initiated by free radicals produced in the process.

ISSN:0277-3813    

DOI:10.1080/02773818408070655

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

This paper is a description of the present state of knowledge on the nature and properties of the compounds present in spent bleach liquors known to have acute toxic, mutagenic and/or carcinogenic effects. Included is also a discussion concerning bioaccumulation of spent bleach liquor material. Furthermore, the eventual risks involved in releasing such liquors into the rivers and lakes are briefly discussed.

ISSN:0277-3813    

DOI:10.1080/02773818408070656

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor