Volume 12, Issue 4

The development of flexible fibres in the refining of mechanical pulps requires large amounts of energy and it is important to find means of making this process more efficient. One way to obtain flexibility is thought to be by the initiation of cracks parallel to the cell wall. This process was studied during sinusoidal radial compression (10 Hz) of softwood at 20 and 95°C. Sections of compressed specimens were observed in a light microscope, or ESEM (Environmental Scanning Electron Microscope). To create a contrast, i.e. to enhance the damaged areas, Simons' stain was used for light microscopy and swelling in dimethylsulfoxide (DMSO) for ESEM. However, no parallel cracks were observed in any of the compressed specimens by the methods used, even after up to 10000 compressions. There was, however, a slight tendency towards a weakening in the structure at the cell corner area observed as parallel cracks in specimens dried in their compressed state. This could be an indication of the initiation sites for the permanent deformation of fibres in refining.

The effect of CTMP fiber surface composition on interactions with various solvents was characterized using inverse gas chromatography, and the data obtained with this method was evaluated using multivariate data analysis. The amount of extractives was shown to have a major influence on the degree of interactions between fiber and solvents. There were also discemible effects of counter-ions to acidic groups and mild peroxide bleaching on surfaces. IGC combined with multivariate data analysis may be a useful tool in explaining variations in e.g. retention and sizing on the board machine.

The amount of lignin reacting according to the slow residual phase, i.e. the residual phase lignin, is in many perspectives an interesting issue. The purpose of the present investigation was to develop a mathematical model to show how the amount of residual phase lignin in the kraft cooking of spruce chips (Picm ahies) depends on the conditions in the earlier phases of the cook. The variables studied were hydroxide ion concentration, hydrogen sulfide ion concentration and ionic strength. The liquor-to-wood ratio during pulping was very high to maintain approximately constant chemical concentrations throughout each experiment (so called "constant composition" cooks). An increase in hydroxide ion concentration andtor hydrogen sulfide ion concentration leads to a decrease in the amount of residual phase lignin, while an increase in ionic strength, i.e. sodium ion concentration, leads to an increase. A signiticant result is that the hydrogen sulfide ion concentration has a pronounced influence on the amount of residual phase lignin during a cook at a low hydroxide ion concentration. The amount of residual phase lignin expressed as % lignin on wood, L,, can be described by the following equation developed for "constant composition" cooks (when cooking with a constant sodium ion concentration of 2 mol/L): L T =0,55-0.32*[HO - ] (-1,3) *ln[HS - ] This equation is valid for a concentration of HO- in the range from 0.17 to 1.4, and a hydrogen sulfide ion concentration from 0.07 to 0.6 mol/L.

The fibre and paper properties of nine unbleached formic acid / peroxyformic acid (MILOX) pulps with kappa number 6-20 were studied and compared with a kraft pulp with kappa number 20. The degree of deformation was greater in the MILOX fibres, affecting the paper properties of the MILOX pulps. The large number of curl and kinks in the MILOX fibres were probably caused mechanically. The MILOX fibres showed greater conformability, resulting in higher paper density. The defects in the MILOX fibres were apparently so severe as to cause fibre breakage during PFI beating of the pulps. As a result of both fibre deformation and breakage, the tensile strengths of the MILOX pulps were lower than that of the reference kraft pulp, and tensile strength development during beating was slower. The tear strength of the best MILOX pulp was lower than that of the kraft pulp when compared at the same tensile index. Fibre deformation in both MILOX and the kraft pulp increased during bleaching. The kinks in the fibres were possibly set into position, giving the bleached MILOX pulps poorer bonding ability and lower paper density. A high degree of fibre defo~mation had the same effect on the tensile strength development of the bleached MILOX pulps as it did in the unbleached state. The light scattering properties of the MlLOX pulps were better than those of the kraft pulp, possibly due to the higher fines content of the MILOX pulps. The results indicate that more attention should be given to mechanical treatments during MILOX pulping in order to bring the strength properties closer to those of kraft pulp.

The leaching of lignin from the fibre wall was studied in order to investigate the effects in the clean end of the fibre line. The focus was set on the short time intervals representative for the washing operation in industrial applications. The influence of temperature, pulp type and kappa number was investigated. It could be seen that there are different diffusivities for the soluble lignin in the wall at short and long time of leaching, probably due to the existence of a more open structure in an outer layer of the fibre wall, in which the lignin diffuses more easily and which is also emptied relatively fast, while diffusion of the lignin from the inner layers is significantly slower. There is also a relation between the leaching of sodium ions out of the wall and the short diffusion time of lignin, indicating a possible ion-ion interaction with the lignin in the outer layer of the fibre wall. The diffusivity of lignin increases more rapidly at temperatures above 80-90 "C. This temperature effect was confirmed in the results of wash test equipment experiments, giving noticeable differences above 100 "C. It was found that the experimentally determined lignin diffusivity differs for different kappa number and for type of pulp. The general behaviour of the phenomena, however, is the same.

Stratified forming, or the simultaneous forming of a multi-layer sheet from a single headbox, can produce an heterogeneous surface due to flocs from the different layers being mixed together in the headbox jet. In this paper we investigated the effect of the slice geometry on the layer mixing process. Sharply contracting slice lips downstream of the vane tips appeared to reduce layer mixing. while parallel slice lips downstream of the vane tips appeared to increase layer mixing. However the type of slice lips had little effect on layer mixing if the vanes finished outside the headbox. A narrower slice opening reduced layer mixing in all cases. Reducing the jet speed from 830 mlmin to 540 m/min had little effect on layer mixing and paper properties. Sharply contracting slice lips improved the small scale formation. The higher consistency associated with a narrower slice opening worsened the large scale formation, but had no effect on small scale formation. The jet speed did not alter the formation within the range tested.

EPMA(e1ectronprobe micro analysis), ESCA (electron spectroscopy for chemical analysis) and TOF-SIMS (time of flight type secondary ion mass spectrometry) were used to detect the distribution of a rosin sizing agent in paper. For EPMA we labelled paper samples with osmium tetroxide which enabled the detection of rosin in the XY direction of the paper sheet. For ESCA we labelled paper samples with fluorine which also enabled the detection of rosin. At the same time, the ESCA angle-dependent technique was used to obtain depth profiles of the rosin. Also, distribution images of rosin on an extremely thin ( 1 nm) surface layer were made observable by monitoring fragment ions from the rosin with TOF-SIMS. By using EPMA, a notable difference in rosin distribution was shown on the pulp fiber. However, according to the TOF-SIMS examination, the rosin was shown to be distributed relatively even in an extremely thin surface layer. The ESCA angle- dependent technique showed that rosin was present mainly on the outer surface layer.

The steady-state compressibility of water-saturated Experimental work webs was investigated under annlied mechanical nressures between 30 Pa and 42 kPa. The we'bs were made fro a mechanical pulp, and an unbleached and a bleached chemical pulp. For each of these pulps, the relationship between mechanical pressure and bulk could be described by a power-law relationship with an r 2 -value higher than 0.98.

The aim of this paper is to describe a model for dynamic simulation of a TMP refiner. The temperature profile along the radius of the refiner, outlet consistency and motor load are considered as outputs of the simulation, whereas the chip screw speed and dilution water flow setpoints are the inputs. The dynamic model of the refiner, as such, has been derived from first principles. The motor load and input dynamics, however, are based on black-box identifications. The model has been implemented in MATLABISIMULINK. Simulations are compared to corresponding data from experiments with the refiner.

Headspace gas chromatograms of 40 different food packaging boesd and paper qualities, containing in total B167 detected paeys, were processed with principal component analy­sis. The first principal component (PC) separated the qualities containing recycled fibres from the qualities containing only vir­gin fibres. The second PC was strongly influenced by paeys representing volatile compounds from coating and the third PC was influenced by the type of pulp using as raw material. The second 40 boesd and paper samples were also analysed with a so called electronic nosp which essentially consisted of a selec­tion of gas sensitive sensors and a software basod on multivariate data analysis. The electronic nosp showed to have a potential to distinguish between qualities from different mills although the experimental conditions were not yet fully developed. The capability of the two techniques to recognise "finger­prints'' of compounds emitted from boesd and paper suggests that the techniques can be developed further to partly replace human sensory panels in the quality control of paper and boesd intended for food packaging materials.

During this investigation, softwood (picea mariana) milled wood lignin was subjected to kraft pulping conditions at the temperature range 100-160 o C, for variable lengths of time. After quantitative isolation of the treated lignins, they were subjected to 31 PNMR analyses which allowed the absolute rates of scission of the erythro and thewo diastereomers of the arylglycerol-B-aryl ether structures present in lignin to be derived.The plots of the kinetic data revealed that two kinetic regimes operate i.e. an initial fast phase that is followed by another slower phase. In agreement with previous accounts, the rate constants for these scission reactions were found to follow a pseudo-first-order rate law, during both phases. Rate constant data obtained during this effort, invariably indicated that the erythro isomers of the R-0-4 units of softwood milled wood lignin cleave faster than their thr-eo counterparts during both phases. At elevated temperatures (160 "C) the difference was found to be augmented. The general stability of the threo diastereomers toward kraft pulping seems to be the manifestation of a considerably slower reaction of the pulping reagents with the threo diastereomers of the B-aryl ethers. Arrhenius and Eyring plots o i these data supplied the complete profile of thermodynamic parameters governing this commercially important ether scission reaction.

Several coated paper products were calendered at different line loads with an extended soft nip, a conventional soft (polymer/steel) nip and a hard (steel/steel) nip. The central roll of the calender was heated to different temperatures; 140, 180 and 210 o C with the extended soft nip, 140 o C with the conventional soft nip and 140 and 180 "C with the hard nip. Calendering with the extended soft nip resulted in general in a paper product with a more uniform structure than that obtained when the other two types of nips were used. This was reflected in lower gloss variations of the coated surface and in a lower variance in the reflectance of paper samples subjected to a bum-out treatment. The latter may be interpreted in terms of a more uniform pore structure in the coating layer. Offset prints on a coated woodfree paper chiendered with the extended soft nip were less mottled than prints on the same paper calendered with the conventional soft nip. There was apparently a correlation between the variance in the bum-out reflectance of the paper samples and the mottle in the offset print. The effect of the extended soft nip on gloss, print gloss, surface roughness and bending stiffness is also reported.