Showing papers in "Appita Journal in 2003"

Estimation of air-dry density of increment cores by near infrared spectroscopy

Abstract: Eight Pinus radiata D. Don increment core samples were selected from a total of thirty-two increment cores for the development of an air-dry density calibration. Near infrared (NIR) spectra obtained from the radial - longitudinal face of each core in 10-mm increments were used to develop the calibration. The air-dry density calibration was developed using five factors giving an excellent relationship between SilviScan-2 determined air-dry density and NIR fitted air-dry density (coefficient of determination, R 2 = 0.90) with a standard error of calibration (SEC) of 23.5 kg/m 3 . To test the predictive ability of the air-dry density calibration, two intact P. radiata increment cores were selected from the same set as the calibration samples. NIR spectra were obtained in 10-mm sections from the radial - longitudinal face of both cores and the air-dry density of each section predicted. NIR predicted air-dry density was in good agreement with SilviScan-2 determined air-dry density, with R 2 of 0.95 (core A) and 0.92 (core B) and standard error of predictions (SEP) of 34.8 kg/m 3 (core A) and 62.3 kg/m 3 (core B). Several sections of core B had large negative residuals causing the large SEP. This study indicates that NIR spectroscopy provides a rapid method for the routine analysis of air-dry density in large numbers of core samples but particular attention must be paid to calibration sample selection.

A practical solution to the silica problem in straw pulping.

Abstract: In this study, the soda-oxygen, soda-anthraquinone and soda processes were evaluated for the pulping of wheat straw with respect to silica content, and chemical, physical and optical properties of the unbleached pulps. Soda-oxygen pulping gave the highest retention of silica by the pulp, and thus the least transfer of silica to the spent pulping liquor, with 80.4% of the silica remaining in the pulp. The addition of 1 to 3% oxides, CaO, MgO, and Al 2 O 3 , was also evaluated as a way of enhancing silica precipitation onto pulp. Results showed that 3% Al 2 O 3 added to the soda-oxygen process gave the best results among the methods studied, with 96.5% of the silica remaining with the pulp. Although the oxide-added soda-oxygen processes gave the best retention of silica they showed slightly inferior pulp physical properties. Overall, the oxide-added soda-oxygen process offers a highly practical and efficient solution to the non-wood pulping silica problem compared to the use of conventional desilication methods.

Performance and design of agitated pulp stock chests

Abstract: The chief purpose of agitated pulp stock chests is to reduce high frequency variability in pulp properties. Dynamic tests made on industrial stock chests have shown that mixing is far from ideal: channelling, recirculation and dead zones decrease the degree of upset attenuation. A scale-model stock chest has been built to study macroscale mixing and disturbance attenuation in a laboratory setting. The variables studied include chest dimensions, impeller speed and diameter, and suspension mass concentration. Initial tests in batch-mode confirmed established trends for chest behaviour, although existing literature correlations underpredict the power and momentum flux requirements needed for agitation at the laboratory scale. Tests have also shown that a liquid phase tracer (saline solution) can be used to trace the fibre phase provided the suspension mass concentration is ≥ 2%. The batch mixing-time was found to be a function of suspension mass concentration and impeller momentum flux.

Estimation of 'Eucalyptus nitens' Wood Properties by Near Infrared Spectroscopy

Abstract: To fully utilise the genetic potential of species grown in plantations, and to optimise wood consumption, a basic knowledge of the wood quality of plantation grown trees is required. To provide the necessary information, rapid, inexpensive methods for measuring wood properties are desirable. In this study the estimation of Eucalyptus nitens (Deane and Maiden) Maiden (Shining gum) wood properties by near infrared (NIR) spectroscopy was investigated. NIR spectra were obtained in 5 mm steps from the radial - longitudinal face of eight E. nitens radial strips characterised in terms of air-dry density, microfibril angle (MFA) and stiffness. Calibrations were developed for each wood property and coefficients of determination (R2) ranged from 0.69 (MFA) to 0.93 (air-dry density). The strong calibration statistics indicate that it is possible to develop calibrations using NIR spectra collected from the radial - longitudinal face of radial strips in 5 mm sections. Calibrations were tested on an individual test set. The air-dry density calibration provided the best results while the MFA calibration performed poorly. The poor performance of the MFA calibration was attributed to the limited MFA range of both the calibration and prediction sets.

Wood, pulp and handsheet relationships in plantation grown Eucalyptus globulus

Abstract: Eucalyptus globulus trees, representing a range of wood densities, were harvested from three sites at eight percentage heights per tree, kraft pulped and handsheets prepared for testing. Two laboratories provided kraft pulp evaluations; the third used bisulfite pulping. SilviScan 2 was used to determine radial profiles of density and microfibril angle from each height. Longitudinal density variation differed between trees, but generally increased on all sites. Microfibril angle remained constant with height apart from an initial reduction between 0 and 0.5 m above ground. Data from 0% height was therefore considered atypical, probably resulting from buttressing effects close to the ground. Density and microfibril angle data explained greater than 70% of kraft pulp variance in bulk, burst, stretch, TEA index and tensile strength. No significant variance was explained in bisulfite pulps. Refining the pulps improved the predictions of wood properties.

The influence of spacing on wood properties for Eucalyptus globulus Labill pulpwood

Abstract: Wood properties relevant for pulping were measured in Eucalyptus globulus trees from plantations with different spacings (3x2, 3x3, 3x4, 4x4 and 4x5 m), at 18 years of age, on discs taken at breast height. The wood density varied from 565kg/m 3 to 594 kg/m 3 , respectively, in the closer (3x2) and the wider (4x5) spacings. There was no effect of spacing on mean fibre length (on average 1.02 mm), fibre width (21.3m) and wall thickness (5.7m). The wood chemical composition was similar for all spacings except for extractives, which increased from 5.4% to 8.7% with increasing spacing. Pulp yield (% on o.d. wood) in the closer spacings was higher and with lower residual lignin than in wider spacings (e.g. 57.0% and 54.1% at Kappa 15 for 3x2 and 4x5, respectively). The chemical quality of wood therefore decreased in the wider spacings and management for pulping should take this into account.

A Microscopic Study of Fibre-Fibre Contacts in Paper

Abstract: Confocal microscopy is used to acquire images of paper cross-sections in which some longitudinally sectioned fibres are chosen as fibres of interest. The properties of fibre-fibre contacts including the number of fibre-fibre contacts per unit length of fibre, the nature of the contacts, the free fibre lengths and the out-of-plane deflection angles of the free fibre segments with respect to those fibres of interest are determined directly in these images. It is found that both the shape of fibre cross-section and the length of fibre have no significant effects on the properties of fibre-fibre contacts. The measured distributions of free fibre lengths cannot be fitted to the negative exponential distribution proposed by Kallmes and Bernier. However a two-parameter Weibull probability density function seems to provide an acceptable fit to the measured distributions. It is demonstrated that model structures of fibre-fibre contacts can be reconstructed using the measured data.

The pore radius distribution in paper. Part I: the effect of formation and grammage

Abstract: The pore radius distribution in paper is known to be influenced by changes in the mean grammage and formation. Experimental data are presented that confirm the established result that the standard deviation of pore radii is proportional to the mean. The data show also that this proportionality is the same for changes in grammage and formation and that, contrary to results reported in the literature, the coefficient of variation of pore radii is approximately constant. This property of the pore radius distribution confirms that the gamma distribution is appropriate for its characterisation. We find that the mean pore radius increases with worsening formation but the effect is weak compared to that of changing grammage. Of the formation indices examined, the mean pore radius is most strongly correlated to a weighted index of floc grammage.

Fibre suspension flow in small diameter pipes

Abstract: Pipe friction loss measurements for a TMP pulp suspension were obtained from a flow loop with three small-diameter, hydraulically-smooth pipes (3.77mm, 4.74 mm, and 7.50 mm internal diameter). Data are presented at stock concentrations up to 1.88% and velocities in excess of 10 m/s. Below about one per cent fibre concentration the friction loss data surprisingly correspond with data for water even though classical laminar and turbulent flow could not exist. Between 1.0 and 1.88 per cent, the curves are slightly below the water curve at higher flow rates. Turbulence damping could not cause this, as the friction loss reduction would also have been more pronounced at lower fibre concentrations. The friction loss curves are very different from those obtained for large diameter pipes where friction loss is much higher than water at low flow rates, and much lower than water at high flow rates. The results provide new insights into mechanistic differences between fibre suspension flow in small and large conduits.

The sizing mechanism of AKD and its effect on paper friction

Abstract: The AKD sizing mechanism and reasons for the lowering of frictional properties of AKD sized papers were studied. It was found that machine drying increases the reaction between AKD and the furnish, which results in paper sizing. The amount of unbound AKD retained in paper has a negligible effect on sizing but was found to be responsible for lower paper friction. PCC had a negative effect on sizing and was found to improve paper friction properties.

Changes in Density and Wood-fibre Properties with Height Position in 15/16-year-old Eucalyptus nitens and E. Fastigata

Abstract: Variation among trees in wood density and wood-fibre properties with height position was assessed for 29 trees each of E. fastigata and E. nitens from 15/16-year-old stands. Seven properties were measured, namely density, vessel-free density, microfibril angle, fibre perimeter, coarseness, wall thickness and the perimeter/wall thickness ratio (P/Tw ratio), all using SilviScan technology. The changes in species wood properties with percentage height were found to be significantly different for the two species. It was concluded that: - Wood density, vessel-free density and the P/Tw ratio changed only slightly with increasing height position for E. fastigata, but markedly increased (decreased for P/Tw) for E. nitens. - Fibre wall thickness increased with increasing height position for E. nitens and decreased for E. fastigata, in accordance with their different coarseness and perimeter. - Species trends in chip density and kraft fibre dimensions with height showed similar trends to those of wood-fibre properties, except for coarseness. This difference was explained by the high lignin content of the E. fastigata (30.6 %) compared to that of the E. nitens (27.6 %) chips.

A new non-wood pulping process for high silicon content raw materials. Application to rice straw

Abstract: The cooking of rice straw is carried out at atmospheric pressure using a mixture of formic acid/acetic acid/water. The chemical and mechanical properties of the pulp obtained are similar to pulp obtained with a mixture of caustic soda/anthraquinone. The majority of the silica derivatives are retained in the pulp because of the acid cooking conditions. However the cooking chemicals are easily recyclable, because of the absence of mineral reagents, without the need for combustion of the black liquor.

Total Approach to Deposit Control on Newsprint Machine Using TMP and DIP Pulp Mix - from Specialized Fixation of Individual Pulps to Retention

Abstract: Efficiency of a newsprint paper machine and the quality of produced paper are often affected by deposition of detrimental substances known as pitch, originating from wood extractable materials, or stickies, hydrophobic contaminants introduced through de-inking raw materials. Review of the most typical detrimental substances and available control strategies are provided in the introduction of our paper. For machines that use blended TMP and DIP pulps, complex chemical equilibrium occurring during the process of their blending potentially leads to higher deposition propensity when compared to machines that operate with TMP or DIP furnish only. We will discuss some of these interactions and propose steps that allow the reduction of their negative impact on machine runnability and paper quality. We will also discuss parameters that affect the stability of machine performance, understanding that any instability in pH, conductivity or cationic demand may trigger an outbreak of deposit. Finally, we will discuss the total chemical application on the machine: chemistry, feed points optimization and control strategy. This chemical application includes fixation with specific fixatives for TMP and DIP and with turbidity measurement as control strategy. We will also describe the chemistry and mechanism of operation of HYBRID coagulant as a fixative agent and as a component of a retention program when dosed in a pre-mix mode with a typical high molecular weight flocculant.

Improving the printability of paper with long-chain quaternaries

Abstract: Long-chain quaternary trimethyl ammonium chloride, a mixture of fatty acid esters (TMACFE), quaternary ditallow methyl epoxypropyl ammonium halogens (EPK2-chemicals) and EPK2 oligomers (EPK2P-chemicals) were synthesised and their effect on the printability properties (e.g. ink-jet) in different papermaking systems was investigated. The use of these chemicals enabled the creation of a hydrophobic layer on the fibre surface that improved ink-jet printability. The results showed that TMACFE-chemicals and EPK-chemicals improved printability at least as well as or better than corresponding synthetic chemicals currently used.

The use of nonionic galactomannan polysaccharides for stabilisation of ASA emulsions

Abstract: Alkenyl succinic anhydride (ASA)-galactomannan (guar gum) emulsions with different ASA/galactomannan ratios and different ASA concentrations were prepared under controlled conditions. These ASA-guar gum emulsions were subjected to various treatments using a deposition rotor to evaluate their stability. Deposition experiments showed that the more guar gum used in the emulsion, the more stable was the emulsion. Furthermore, the use of a surfactant in this combination resulted in even less deposition, and a much smaller average particle size of the emulsion. The stability of these ASA emulsions has been studied and compared to ASA emulsions with two cationic starch derivatives as stabilisers. Internal sizing tests using ASA-guar gum emulsions as a sizing agent indicates that these emulsions are usable as a stock sizing agent as well.

A comparative study of hot versus conventional chlorine dioxide bleaching for different wood species

Abstract: Hot chlorine dioxide bleaching is a very promising emerging technology for the bleaching of hardwood kraft pulp. In this study a general approach to hot chlorine dioxide bleaching was taken. The effect of hot chlorine dioxide bleaching was compared to that of conventional D 0 technology for a large number of different wood raw materials, including eucalypt, birch, beech, acacia and mixed tropical hardwood (MTH) from all over the world. A Scandinavian softwood kraft pulp was also included in the study. It was concluded that savings in chlorine dioxide of about 2% to reach target brightness are typically achieved by replacing the D 0 -stage by a D * -stage. Moreover the yellowing tendency was reduced by some 15%. The viscosity of the D * -pulp was typically 5 to 10% lower than the viscosity of a conventional pulp.

Interrelationships between Kraft Handsheet, and Wood Fibre and Chemical Properties for the Trees and Logs of 29 Eucalyptus fastigata and 29 E. nitens

Abstract: Interrelationships between kraft handsheet, and wood-fibre and chemical properties of 15/16 year-old Eucalyptus fastigata and E. nitens were estimated for 29 individual trees per species, as well as for 5.5 m log-height portions of ninetree subsets. Kraft pulp qualities of individual-trees of E. fastigata and E. nitens (and logs), can be effectively predicted by glucose content and wood-microstructure characteristics (fibre perimeter, wall thickness, fibre length, and microfibral angle (MFA)). Also, fibre perimeter and wall thickness can be replaced in the predictive models by fibre coarseness and wood basic density. The inclusion of coarseness (with wood density) ensures fibre number per unit mass is taken into account. Predictions of handsheet density, log of air resistance, tensile index, stretch and T.E.A. index were consistent, and moderate to high (R 0.57-0.91) for the various species, individual-tree and individual-log data sets. The separate influences of fibre perimeter and wall thickness, versus fibre coarseness and wood density, were quantified and explained by the different within-tree property distributions of E. fastigata and E. nitens.

The pore radius distribution in paper. Part II: The effect laboratory beating.

Abstract: An experimental investigation into the effects of different beating processes on the pore radius distribution in paper is presented. Standard handsheets were formed from fibres beaten in four laboratory beaters with different actions. The relationship between the mean pore radius and the standard deviation of pore radii was found to be linear and to pass close to the origin such that the coefficient of variation of pore radii was insensitive to beating type or duration. Changing the formation of sheets formed from one beating condition did not affect the relationship between the mean pore radius and the standard deviation of pore radii. The relationship between mean pore radius and density was found to be dependent on beater type and very sensitive to the presence of fines. The dependence of air permeability and light scattering coefficient on mean pore radius exhibited some dependence on beater type, reinforcing the importance of coupling pore radius distributions with porosity when considering the influence of void structure on the physical properties of paper.

Fracture Mechanism in Inter-fiber Bond Failure - Microscopic Observations

Abstract: A fracture area of an inter-fiber bond between two fibers was evaluated using a scanning electron microscope (SEM), a confocal laser scanning microscope (CLSM) and an atomic force microscope (AFM). The objective was to obtain a better insight into the fracture mechanism of fiber bond failure and into the properties of inter-fiber bonds. Some fibrils were found to rise from the fracture area while the rest of the fracture area was densified, which may imply uneven distribution of the mechanical interaction between fibril elements in the contact area. As the degree of beating increased, the number of fibrils raised in the fracture area also increased. External fibrils produced by beating may play an important role in the bonding layer during fiber bond failure. By combining different microscopic techniques, the fracture area can be observed in greater detail for qualitative and quantitative analysis.

Pyrolysis-GC-MS analysis of ASA-sized papers by on-line butylation with tetrabutylammonium hydroxide

Abstract: Structures of size components in paper prepared by internal addition of alkenyl-succinic anhydride (ASA) were studied by pyrolysis-gas chromatography-mass spectroscopic (Py-GC-MS) analysis of model compounds and handsheets. ASAcid components having free carboxyl groups or carboxylic acid salts are converted to ASAcid dibutyl esters by Py-GC analysis combined with on-line butylation using tetrabutylammonium hydroxide (TBAH). On the other hand, cellulose-ASA half esters having free carboxyl groups or carboxylic acid salts are converted to ASA by the pyrolysis, irrespective of the addition of TBAH. These results obtained for model compounds were then applied to handsheet samples. ASAcid components having free carboxyl groups were predominantly present in ASA-sized handsheets prepared without alum or CaCO 3 filler, while significant amounts of ASAcid having carboxylic acid Ca salts were present in handsheets prepared with CaCO 3 filler. The stability of ASA-cellulose esters under alkaline conditions was also investigated using the model compounds.

Some effects of fibre properties on formation and strength of paper

Abstract: Different pulp fractions were produced using a Bauer McNett fractionator. Handsheets were made from each fraction using a Finnish Standard laboratory sheet former ('SH former') and a sheet former making handsheets at headbox consistency ('HC former'). The handsheets made from shorter fibre length fractions yielded better formation and higher tensile strength. The shorter fibres were also the finer fibres (i.e. less coarse fibres). Increasing pulp stock concentration resulted in deterioration of formation and strength properties of the handsheets.

Effect of harvesting age on the quality of Eucalyptus camaldulensis bleached kraft pulp

Abstract: The effect of harvesting age of Eucalyptus camaldulensis on wood, pulp and papermaking properties was studied. Bleached kraft pulp was prepared from 4-, 6- and 8-year-old trees, which came from the same clone and area located in eastern Thailand. The basic density at breast height increased with increasing tree age. Holocellulose, lignin and ash contents were not affected; the pentosan content decreased while extractive content increased with increasing tree age. Older trees had longer and coarser fibres. The vessel area was constant from 4- to 6-growth rings and then increased from 6- to 8-growth rings, while the parenchyma area was constant. Consequently, fibre area increased from 6- to 8-growth rings. The 4- to 6-year-old trees gave better pulp quality than the 8-year-old in terms of higher pulp yield, lower Kappa number, better bleachability, and brighter and stronger pulps.

Effect of Precipitated Gas Bubbles in Papermaking

Abstract: The gas present in a papermaking fibre suspension is divided into dissolved and entrained gas. Entrained gas is divided into free and bound gas bubbles. Bound gas bubbles are attached to fibres, fines or pigments. The adverse effects of entrained gas in papermaking, such as pinholes, foam spots and impaired drainage, are well known. Dissolved gas is not believed to have any effects on the papermaking process, as long as the gas remains dissolved. However, it can precipitate into free and bound gas, if the temperature and pressure of the fibre suspension change. In most previous studies concerning the effect of entrained gas in papermaking, the gas has been formed from gas bubbles dispersed into the fibre suspension. In laboratory conditions, dispersed gas is rarely transformed into bound gas bubbles, unlike the precipitated gas, which, according to some research results, is formed on fibres and fillers. The dissolved gas present in the papermaking process is quite easily precipitated into entrained gas bubbles, if the temperature or pressure vary, for example due to pressure changes before and after pumps. Recent research had been designed to determine if precipitated gas bubbles affect the papermaking process in a different way compared with dispersed gas bubbles. The present study was performed using a furnish with different air contents made by precipitated air in a Moving Belt Drainage Tester (MBDT), which has been found to simulate a Fourdriner paper machine quite well. In the MBDT, drainage is pulsed, as on a commercial paper machine. A headbox stock from a commercial paper machine was used in the study. Gas bubbles were found to have adverse effects on tensile strength, retention, sheet density and drainage. The results clearly show how precipitated gas bubbles affect papermaking in quantitative terms. The results are quite similar to those obtained with the same furnish with dispersed air. However, differences were found in the effects on tear and wet tensile strength.

Fibre loading using an aluminium compound

Abstract: Fibre loading offers two advantages in paper production: the filler distribution of the final product does not depend upon the sheet forming conditions and the strength properties at a given filler level are better than with conventional filler loading. As a result fibre loading opens up a wide variety of potential uses for paper products. In this study the fibre loading was done using alum and sodium silicate as raw materials. These chemicals are widely used in paper production. The fibre loading was achieved by adding alum solution into a mixing vessel containing a mechanical pulp at a stock concentration of 15%. Sodium silicate and sodium hydroxide were then added into the vessel, some initially and the remainder slowly over a period of time, increasing the pH from 4 to >8.0 thereby precipitating an aluminium compound through the fibres. The results were promising in terms of retention, paper properties and process simplicity.

Suitability of Acacia Pulp for Wood Free Coating Base Papers

Abstract: The suitability of bleached acacia (Acacia mangium) kraft pulp for making wood free coating (WFC) base paper was studied in laboratory. Despite the slow strength development in refining, results indicate that acacia is an excellent raw material for WFC base paper. Compared to Nordic birch and Iberian eucalyptus pulps, it produces paper with excellent formation and smoothness (before calendering), outstanding bulk and bending stiffness, high light scattering coefficient, good tear strength, acceptable porosity and oil absorbency.

Methods to decrease manganese-induced decomposition of peroxide

Abstract: Previous studies have shown that transition metal ions in the higher oxidation state, (e.g. Mn(+III)), are much more catalytically active in decomposing alkaline peroxide solutions than the same transition metal ions in a lower oxidation states (e.g. Mn(+II)). Potential techniques to decrease manganese-induced peroxide decomposition by minimising the oxidation of Mn(+II) by air/oxygen to Mn(+III) under alkaline conditions were studied. Two methods were evaluated, namely: (1) adding a neutralised Na 2 SiO 3 -MgSO 4 mixture, followed by the addition of sodium hydroxide and then hydrogen peroxide to reach the desired conditions for alkaline peroxide bleaching, and (2) removal of air/oxygen in the system by purging with nitrogen. The results showed that both techniques were successful.

A Mechanistic Creep Model and Test Procedure

Abstract: Compressive creep failure is a major reason for corrugated box failure in service. It is accelerated by conditions of changing humidity. Creep has been difficult to measure because of mechanistic complexity, high variability and long testing times. It is consequently poorly understood. PAPRO has developed a multi-module testing rig and an accompanying hyperbolic model that allows much faster testing with significantly reduced variability. The rig and test model provides feedback times that will considerably speed the development of creep resistant corrugated board.

An estimate of the level of fibre crowding for polydisperse suspensions

Abstract: An expression is developed to extend the concept of the crowding number N, as defined by Kerekes et al., to fibre suspensions having a distribution in fibre lengths. The utility of the expression was tested against direct measurement of the number of fibres present in both softwood and hardwood flocs; the expression was found to be valid to within approximately 12% of the experimentally determined values. The derived expression was compared to other estimates of N found in the literature and found to be a better estimator.

Optimisation of the use of calcium carbonate as filler in mechanical pulps

Abstract: The formation of calcium-phosphorus (Ca-P) containing overgrowths on the surface of ground calcium carbonate (GCC) treated with phosphoric acid was studied. During GCC dissolution in water containing H 3 PO 4 , the rate of phosphorus precipitation gradually increased and reached equilibrium in 15 hours. Energy-dispersive X-ray (EDX) analysis of the GCC treated with H 3 PO 4 showed that the kinetics of formation of Ca-P overgrowths on the GCC surface follows a profile similar to phosphorus precipitation. X-ray photoelectron spectroscopy and EDX show that increasing H 3 PO 4 concentration increases the formation of Ca-P overgrowths on GCC. Scanning electron microscopic scans revealed a different morphology on the GCC surface because of the overgrowths, which are believed to inhibit GCC dissolution. When GCC was added to a pulp suspension containing H 3 PO 4 , the pH rise was suppressed. Finally, handsheets were made and the brightness and scattering coefficient were found to slightly improve with increasing H 3 PO 4 concentration.

Effect of mechanical pretreatment on fibre properties

Abstract: Improvements in water retention value at a given freeness without loss of fibre length were obtained using a Hobart mixer to apply a controlled mechanical pretreatment to BCTMP and white ledger furnishes prior to refining. These improvements were similar to those obtained in an earlier study where softwood kraft, hardwood kraft and OCC furnishes were given the same type of mechanical pretreatment. Electron microscope analysis and measurement of fibre surface area confirmed that the mechanical pretreatment resulted in extensive internal delamination of the pulp fibres. The fibre property changes that occurred before refining were maintained throughout the refining process. The degree of change differed for the different pulp furnishes. The effectiveness of the pretreatment appears to depend on the mean fibre length, chemical composition and wet fibre flexibility of the furnish. The design of the mechanical device may be another important factor in determining the effectiveness of the pretreatment.