Unbleached Softwood Kraft Pulp Research Articles

Manufacturing of Magnetic Papermaking Fibers and Paper (Part I)

(1) Magnetic papers were made from magnetite and ferrite lumen-loaded pulps. When the papers were made only from the magnetic pulps, its breaking strength and burst factor were 5.1km and 313kPa/g/m2, respectively. The breaking strength and burst factor of the papers increased to 6.5km and 461kPa/g/m2, respectively, by addition of 2-3% fibrous Polyvinyl Alcohol (PVA) binder. Thus, physical properties of the magnetic papers added with PVA were nearly equal or rather superior to those of papers from unbleached softwood kraft pulp (USKP). Saturation magnetization value of each paper prepared from manganese-ferrite and manganese-zinc-ferrite lumen-loaded pulps was 16.1, 15.7 and 21.2emu/g, respectively, and each remanent magnetization value was 3.5, 3.1 and 4.5emu/g, respectively.(2) In the next experiment, magnetic papers were made by mixing a magnetic pulps and USKP by changing the mixture ratios of 0, 40, 70 and 100%. Breaking strength of these papers decreased with the increase in the added amount of USKP to the pulps. When the 2% PVA binder was added to the magnetic pulps (without addition of USKP), breaking strength of the papers was almost same as that of USKP. Magnetic properties of the papers prepared by mixture of manganese-zinc-ferrite lumenloaded pulps and USKP decreased in both their saturation magnetization values and their remanent magnetization values with the decrease in the mixture ratio of the magnetic pulps.(3) Furthermore, combination papers were made from a magnetic papers prepared from pulps lumen- loaded with magnetite and ferrite and a bleached softwood kraft papers (BSKP). When the 1-2% PVA binder was added to the papers, the interlayer stripping strength of the combination papers having two or three layers was improved to 1.7N at the 50mm sample width, thus the composite papers having sufficient inter-layer strength were obtained.(4) Security papers endowed higher security were made by sparsely binding of magnetite, manganese-ferrite or manganese-zinc-ferrite lumen-loaded pulps and BSKP.

Distribution of strain to failure of single wood pulp fibres

The single-fibre composite test has been applied to characterize the distribution of strain to failure of individual fibres from unbleached softwood kraft pulp. The fibre was moulded into a thermos ...

Analysis of progress of oxidation reaction during oxygen-alkali treatment of lignin I: method and its application to lignin oxidation

A new method is applied to evaluate the progress of the oxidation reaction of lignin during oxygen-alkali treatment. This method employs the difference in permanganate consumption of the sample before and after the oxygen-alkali treatment as an indication for the lignin oxidation. When kraft lignin and residual lignin isolated from unbleached softwood kraft pulp were subjected to oxygen-alkali treatment up to 6000min, the progress of the oxidation expressed by this method was separated into clearly distinguished three phases. During the first and second phases, the progress of oxidation was well correlated to the loss of methoxyl group and to the decrease in the yield of nitrobenzene oxidation products. The addition of Mn+ to the oxygen-alkali treatment depressed oxidation during the second phase partly and that during the third phase almost completely. Calculations based on the change in the permanganate consumption revealed that the oxidation during the first phase corresponded to 4.2 electrons abstracted from one lignin structural unit on average. The oxidation process by oxygen-alkali treatment was hypothetically attributed to the direct reaction between molecular oxygen and the phenolic unit of lignin, which mainly took place during the first phase, and to the autooxidation-type oxidation during the second and third phases.

Effect of Xylanase and Dosage on the Refining Properties of Unbleached Softwood Kraft Pulp

Two xylanase preparations were compared at different doses for their abilities to enhance the refining properties of a never-dried, unbleached kraft pulp derived from radiata pine. These enzymes varied in their ability to solubilise xylan from pulp, and the selective removal of pulp xylan did not reduce intrinsic fibre strength. At low levels of xylan solubilisation, there were increases in sheet densification after PFI refining without change in tensile and tear strength at a given sheet density, indicating lower pulp refining requirements. At high levels of xylan solubilisation, the level of sheet densification was greater but there was a small decrease in tensile strength at a given sheet density and an increase in tear strength. One of the xylanases yielded a selective increase in tear strength at a given tensile strength.

Structural changes of residual lignin in softwood kraft pulp treated with manganese peroxidase

Structural changes of residual lignin in unbleached softwood kraft pulp (SWKP) during manganese peroxidase (MnP) treatment were investigated to obtain some understanding of the biobleaching action of SWKP with MnP treatment. Alkaline-extracted lignin from darkened SWKP by MnP showed more intense color and contained moreo-quinone than that from control SWKP. However, no difference in the conjugatedα-carbonyl was observed between the lignins from MnP-treated and control SWKP. The nitrobenzene oxidation analysis revealed that oxidative condensation of non-condensed lignin in SWKP occurs during an early stage of MnP treatment. These observations were supported by the model experiment in which the lignin prepared from control SWKP was subjected to MnP treatments three times, and the changes of color and functional groups in the lignin were determined after each treatment. These results suggested that an increase ino-quinone and the condensation reaction of non-condensed lignin in SWKP are responsible for the characteristic darkening of SWKP during MnP treatment. It was also ascertained that darkened lignin was degraded and brightened by repeated MnP treatments.

Removal of Lignin-rich Surface Material from Unbleached Kraft Fibres

The composition and structure of the surface material of kraft fibres can affect properties of the pulp such as the reactivity in, for example, bleaching processes. In order to study the nature of the surface material, conditions for a gentle removal of fibre surface material from unbleached kraft fibres have been evaluated. An unbleached softwood kraft pulp with a lignin content of 6.2% (kappa number 32) was treated mechanically using three different types of laboratory equipment : a PFI-mill, a high intensity mixer, and a disintegrator. The number of revolutions and the pulp concentration were varied and the removal of surface material was followed by chemical and microscopical analyses. These analyses revealed that there is lignin-rich material present on the fibre surface which can be removed by a mild mechanical treatment. The lignin content of the surface material abstracted was between 2.5 and 4.5 times higher than that of the fibres. The primary fines (obtained by fractionation of unbeaten pulp, 20μm), also originating from the fibre surface, had a lignin content almost 5 times higher than that recorded in the fibres. For analytical studies of the surface material, a mechanical treatment of the kraft fibres in a disintegrator at a pulp concentration of 4.5% and at 20.000-200.000 revolutions is an efficient and suitable treatment for gradual removal of material from the fibre surface.

Metal Ion Content of Material Removed from the Surface of Unbleached Kraft Fibres

Distribution and attachment of metal ions to the pulp components in kraft pulps can affect the possibilities to achieve a metal ion profile favourable for total chlorine free bleaching. By enrichment and analysis of different morphological fractions of the pulp, such as material from the fibre surface and ray cells, the metal ion distribution (Fe, Cu, Mn. Mg and Ca) in a commercial unbleached softwood kraft pulp (kappa number 32) was investigated. Material removed from the surface of unbleached kraft fibres and the fraction containing the ray cells were found to have a considerably higher metal ion content than the rest of the pulp. There was good correlation between the content of manganese and calcium and the content of lignin and carboxy groups. Distribution patterns of metal ions in the pulp appear to resemble those found in the wood. The metal profile in the pulp was studied also following EDTA treatment. Metal ions remaining in the pulp after the EDTA treatment were still unevenly distributed, with high levels in the surface material and the ray cell enriched fraction

Surface characterization of unbleached kraft pulps by means of ESCA

The effect of digestion conditions (amount of effective alkali, digestion time) on the surface compositions of unbleached softwood (Pinus sylvestris) kraft pulp has been investigated by electron spectroscopy for chemical analysis (ESCA). The quantities monitored were the angular dependence of the total O/C ratio, the relative amounts of carbons in different states of oxidation and the adsorption of Al and Ca ions to the carboxyl groups in the surface. Examination of the angular dependence of ESCA intensities shows that the concentration of alkyl carbon is high in a very thin surface layer and that it decreases linearly with decreasing kappa number. The concentration of alkyl carbon is decreased by extraction of the fibres with dichloromethane, but the amount remaining in the surface after extraction still decreases linearly with decreasing kappa number (i.e. it decreases with increasing digestion time). It is suggested that the observed enrichment of alkyl carbon in the outermost surface layers most probably is due to reprecipitation of lignin. In pulp that has not been extracted, there is also strong enrichment of extractives in the surface. This amount increases with increasing effective alkali but is relatively independent of digestion time. ESCA analysis of the Al and Ca bound to the carboxyl groups shows that the amount depends on digestion time; the results are consistent with the notion that the reprecipitated lignin contains carboxyl groups.

Structural and Concentration Effects on the Diffuse Reflectance Ftir Spectra of Cellulose, Lignin and Pulp

Abstract 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.

Transverse dimensions of wood pulp fibres by confocal laser scanning microscopy and image analysis

Cross-sectional images of wood-pulp fibres were generated using optical sectioning by a confocal laser scanning microscope. The technique has a distinct advantage over mechanical sectioning with a microtome, as it simplifies specimen preparation. Cross-sectional images were obtained for unbleached softwood kraft pulp fibres using epifluorescence mode. The accuracy of cross-sectional images was verified by imaging fluorescent microspheres. An image analysis procedure, in which the boundaries of fibre cross-sections were defined with a maximum-gradient edge-finding technique, was developed for measuring fibre cross-sectional area and wall thickness rapidly and accurately. The measurements were insensitive to the confocal microscope's asymmetric resolution, signal deterioration through the specimen thickness, overall image quality and operator bias.

Effect of fibre curl on the properties of wood pulp fibre-cement and silica sheets

Curl has been induced in unbleached softwood kraft pulp fibres by treatment in the laboratory at 20% consistency in a planetary mixer. Steam treatment of the fibres to set the curl more strongly was found to be detrimental to fibre properties as deduced from handsheet properties. A means of producing two-ply specimens in the laboratory was devised and a tensile test for interlaminar bond strength was developed. The use of curly fibres in reinforced cement and silica sheets gave sheets with improved wet interlaminar bond strengths, relative to sheets prepared from conventionally treated fibres but had little effect on the values of modulus of rupture and fracture toughness.