Scott Bond Research Articles

Z-direction chemical analysis for new application methods

In conventional wet-end chemical addition during paper production, chemical distribution through the z-direction of the sheet is usually not considered an important characteristic. With a nontraditional chemical dosing approach, such as foam-assisted additive addition, the chemistry can appear at different concentrations throughout the sheet, typically in a z-direction gradient. To fully understand the strength properties of the sheet, it is helpful to view or quantify the chemical distribution through the sheet in the z-direction. One qualitative method uses a dye technique along with confocal laser scanning microscopy to generate an image where the relative chemical concentration can be observed. A quantitative method involves compiling nitrogen analyses of layered subsections of the sheet into a composite graph of relative chemical concentration vs. the z-direction of the sheet. Chemical distribution analysis can be paired with traditional z-direction strength tests, such as Scott bond and z-direction tensile, to help one understand and improve the chemical addition process and its effects.

Determining operating variables that impact internal fiber bonding using Wedge statistical analysis methods

In this study, Wedge statistical analysis tools were used to collect, collate, clean up, plot, and analyze several years of operational data from a commercial paper machine. The z-direction tensile (ZDT) and Scott Bond tests were chosen as representative of fiber bond strength. After analyzing thousands of operational parameters, the ones with the most significant impact upon ZDT involved starch application method, starch penetration, and the amount of starch applied. Scott bond was found to be significantly impacted by formation and refining. Final calendering of the paper web has also shown an impact on internal fiber bonding.

Multiple linear regression modelling of pulp and handsheet properties based on fiber morphology measurements and process data

A multiple regression model was evaluated to predict pulp and handsheet properties including z-directional tensile strength (z-strength) and Scott bond values. One hypothesis that was central for the model evaluation was that the crill content, as measured with ultraviolet and infrared lights, would improve the statistical models. A chemi-thermomechanical pulp (CTMP) mill designed with two parallel primary refining lines and a reject refiner was the basis for this study, and all process data and pulp samples were gathered from the specific process. Pulp was extracted from the process for an extended period from a position after the latency chest (primary refined pulp) and from the pulp-stream exiting the mill to the board machine (accept pulp). The crill content was positively correlated to the z-strength of the accept pulp, explaining 55% of the variance with a linear regression model with the crill content as the sole predictor. The estimation model of the z-strength of accept pulp was based on a combination of the crill content, freeness, fibril perimeter for longer fibers, and mean kink angle, and resulted in an R2 of 0.79. When applying cross-validation to determine the predictive model performance, the highest R2 obtained was 0.67. This latter model included the crill content, fibril perimeter, and mean kink angle as predictors.

Optimizing the mechanical properties of papers reinforced with refining and layer-by-layer treated recycled fibers using response surface methodology

Layer-by-layer (LbL) treated recycled fibers were investigated in mixtures with refined pulp relative to the mechanical properties of paper. The LbL treatments were conducted to assemble consecutive cationic and anionic starch layers on the fibers of old corrugated container (OCC) pulp. Fibers zeta potential was measured to examine the success of LbL treatment. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to reveal the differences between treated and untreated fibers surface and network. Subsequently, the LbL-treated fibers were added to the refined OCC pulps. Optimization of paper (60 ± 3 g m-2 basis weight) strength properties including: tensile index, Scott bond (internal bonding), and ring crush test (RCT) was carried out by response surface methodology (RSM). The meaningful change of zeta potential substantiated cationic/anionic starch layers construction. The AFM results showed that the surface of fibers were covered with starch, which was consistent with deposition of polyelectrolyte multi-layers (PEMs). The surfaces of the LbL-treated fibers were rough in comparison with untreated fibers. The optimization of mechanical parameters using RSM indicated that refining time significantly affected the paper’s mechanical properties. The property values of 44.5 N.m/g tensile index, 149 J/m2 Scott bond, 32 mN RCT, and 245% strain at break were achieved at optimal conditions of 16 min refining time and the addition ratio of 17.6% LbL treated pulp respectively.

Effect of cellulose microfibril (CMF) addition on strength properties of middle ply of board

Cellulose microfibrils (CMF) are a promising biobased material with unique nanospecific properties, giving them potential for use in numerous applications. Based on this, cost-effective and novel high-consistency enzymatic fibrillation (HefCel) technology was used to produce CMF, which was further used to reinforce middle ply of board structure and the results compared with those obtained without CMF addition and with addition of CMF produced by traditional Masuko grinding (VTT Native grade). The results showed an average increase in tensile index of middle ply of board of approximately 50% with VTT Native grade and approximately 15% with HefCel grade at 3% CMF dosage. According to special board measurements, ~100% improvement in Scott bond, ~117% improvement in Z-directional strength, as well as ~13% improvement in bending stiffness were achieved with VTT Native grade compared with the reference case, while addition of HefCel resulted in improvements of ~35% in Scott bond, ~40% in Z-directional strength, and ~20% in bending stiffness. Addition of HefCel CMF generated a bulkier handsheet structure compared with VTT Native CMF, which had a direct impact on the bending stiffness. The differences in the strengthening effect between HefCel CMF and VTT Native CMF are most probably due to the fibril morphology; VTT Native CMF with long and flexible fibrils provided tensile strength, while HefCel CMF consisting of short fibrils had a more substantial impact on the bending stiffness. The bending stiffness is one of the most important characteristics in board applications, indicating that HefCel CMF has potential for use as a reinforcement material in packaging applications.

Drying Temperature and Hornification of Industrial Never-Dried Pinus radiata Pulps. 1. Strength, Optical, and Water Holding Properties

Hornification and changes in properties of bleached Pinus radiata pulps were studied for oven-dried pulps and compared to never-dried pulps. Evaluation of unrefined and PFI-refined pulps showed an increase in strength loss with high drying temperature. The tensile index was reduced by 40 to 55%, the tear index was reduced by 14 to 31%, and the degree of hornification, measured as WRV, increased from 25 to 34% when the drying temperature was increased from 25 °C to 130 °C. The tensile stiffness index, Scott bond, and elongation were reduced, whereas the bulk, opacity, air permeability, and light scattering values increased at high drying temperatures. Neither fiber deformations nor damages were observed to justify such reductions in strength properties. In PFI refining, pulps dried at 130 °C required three times more revolutions than never-dried pulps to develop tensile index until 70 Nm/g. Dried pulps were found to have less capability to hold water into the fibers’ pore structure, as shown by water retention value. Changes in Scott bond, bulk, and water retention value suggested that besides irreversible pore closure and fibril microfibril aggregation, delamination can contribute to the observed strength loss in dried compared to never-dried pulps.

Correlation Analysis for Fiber Characteristics and Strength Properties of Softwood Kraft Pulps from Different Stages of a Bleaching Fiber Line

During sequential bleaching operations, pulp fiber properties are gradually changed due to mechanical and chemical treatments. In this study, the correlations between pulp or fiber properties such as kappa number, viscosity, total charge, fiber length, and zero-span tensile strength as well as Scott bond of elemental chlorine free (ECF) bleached softwood kraft pulps was investigated. The influence of zero-span tensile strength and Scott bond on tensile and tear strength was also discussed. The Scott bond and zero-span tensile strength showed a strong logarithmic correlation with pulp kappa number and pulp viscosity, while the regression coefficient for Scott bond was negative. An overall deterioration of paper tensile and tear strength from pulps whether beaten or not were observed along the multi-stage ECF bleaching operations. Changing contributions to sheet tensile or tear strength could be mostly attributed to changes in zero-span tensile strength rather than Scott bond during ECF bleaching.

Increase of the filler content in papermaking by using a silica-coated PCC filler

Abstract The increase of filler content in paper without significantly sacrificing the paper mechanical resistances is of high interest for papermakers. In this work, precipitated calcium carbonate (PCC) modified with silica was used as filler for papermaking. Handsheets based on a eucalyptus kraft pulp furnish with different amounts of the modified filler, ranging from 16 to 40%, were produced. For similar levels of filler content it was found that the strength properties of the handsheets produced with the modified PCC were always significantly better than those obtained with the unmodified PCC. In particular, for handsheets with a filler content of 30%, the tensile index and the Scott bond internal resistance improved by ca. 20% and 39%, respectively. Some decrease of the light scattering and opacity values was noted when using the modified PCC, but the brightness was roughly the same, for each filler level evaluated. The enhanced fibre-tofiller bonding can be due to the hydrogen bonding between the cellulosic fibres and the hydroxyl groups of the silica film coating the calcium carbonate crystals, during the sheet formation. The present results with the new modified PCC provide a possibility to increase the filler amount in the papermaking industry.

A Cry for Justice: Daniel Rudd and His Life in Black Catholicism, Journalism, and Activism, 1854–1933 (review)

A Cry for Justice: Daniel Rudd and His Life in Black Catholicism, Journalism, and Activism, 1854-1933- By Gary B. Agee. (Fayetteville: University of Arkansas Press. 2011. Pp. xv, 237. $39.95. ISBN 978-1-55728975-9.)This biography of Daniel A. Rudd, an Afro-American Catholic who rose from slavery to become an important figure in nineteenth-century Catholicism, is based on a doctoral dissertation that Gary B. Agee completed for the University of Dayton, and it reads as such. As the author acknowledges, it builds on earlier scholarship of Cyprian Davis, O.S.B., and others.Agee calls attention to material in the American Catholic Tribune, the journal edited and published by Rudd, that has not been discussed in print. Among this material are comments on employment opportunities for blacks and the emergence of the New Woman. In addition, he fills in some details about Rudd's life from the demise of the newspaper to his work on the biography of Scott Bond, a wealthy black Arkansas farmer and merchant. The picture of Rudd is enriched as we see him described as an inventor, businessman, lumber mill manager, accountant, and teacher, as well as a writer, political activist, and publisher. Finally, Agee records Rudd's participation as a speaker in a Cleveland meeting of the NAACP in 1919 and notes his good relationship with Bishop John B. Morris of Little Rock. On the other hand, he does not indicate that some who were initially close to Rudd found him contentious.The words conceivable, plausible, and perhaps occur throughout the text. Sometimes the conjectures seem fair, but they are educated guesses. Others seem less than plausible. For example, on the basis of the fact that Elizabeth Rudd and her children were listed as mulatto, he suggests that she or her mother may have been victims of sexual violence (p. 8). There is no indication in anything that Rudd ever wrote that such may be the case. In commenting on the marriage of Elizabeth and Robert Rudd, he mentions that legally the master could dissolve a marriage, but he does not qualify the statement by noting that a sacramental marriage could not be dissolved in the eyes of the Church. Throughout the work there are issues like this one that need more nuance.At the same time, it seems that material extraneous to the main topic is sometimes introduced. For example, Agee devotes a chapter to Archbishop John Ireland. Clearly, Ireland was a great champion of African Americans, and Rudd admired and quoted his words. But a chapter is not necessary to make the point.In some things Agee is simply wrong. For example, he writes ... Rudd appears to have been the initiator of the interracial lay Catholic congress movement (pp. xiiii-xiv). As a matter of fact, Henry E Brownson made the suggestion for the Lay Catholic Congress, and Cardinal James Gibbons eventually accepted. Rudd was invited to be a member of the Committee on Organization by William Onaham, its chair. …

Effect of Hemicellulose Pre-extraction on the Properties and Bleachability of Aspen (Populus tremuloides) Chemithermomechanical Pulp

Pre-extraction of hemicelluloses prior to pulping and conversion of the extracted hemicelluloses to other byproducts will provide additional revenue to the traditional pulp and paper industry. The effect of hemicelluloses pre-extraction with dilute sulfuric acid on the properties and bleachability of aspen (Populus tremuloides) chemithermomechanical pulp (CTMP) was investigated. The acid pre-extraction significantly reduced refining energy consumption to a given freeness. However, at the same freeness, the acid pre-extraction resulted in the reduction of bulk, tensile index, and zero-span breaking length, fewer long fibers and more fines, but an increase of the Scott bond strength. Alkaline peroxide bleaching can compensate the strength loss, but the bleachability of pulps with acid pre-extraction was lower than that of the control.

Evaluation of the Scott bond test method

Abstract The Scott bond test is the most commonly used test method for quantifying the delamination resistance of paper and board. The objective of this investigation was to validate the hypothesis that the Scott bond value would be dominated by the total energy under the force elongation curve in a z-directional tensile test. The investigation comprised three types of hand sheets with comparatively low strength values. Three test methods were used to obtain the energy for delamination: 1) Z-test, a z-directional tensile test, 2) Scott bond test, and 3) Simulated Scott bond test, a Scott bond type of test performed in a hydraulic tensile tester. The test data were expressed as a correlation between the failure energy obtained from the Z-test and the other two tests. The results showed that the Scott bond test gave slightly higher values than the Z-test for the weakest paper, but that the value tended to be much higher for the stronger papers. On the other hand the Simulated Scott bond test tended to give lower values than the Z-test. High speed photography was used to reveal several energy consuming mechanisms in the Scott bond test that can explain why this test gave higher values than the Ztest. The lower values from the Simulated Scott bond values are more difficult to explain. At this stage we can suggest that the failure mechanism is different if the paper is delaminated by pure tension or by a gradual delamination as in the Scott bond test.

Increasing the Use of High-Yield Pulp in Coated High-Quality Wood-Free Papers: From Laboratory Demonstration to Mill Trials

Although high-yield pulps (HYP) are gaining increasing use to replace hardwood kraft pulp in paper grades such as uncoated and coated fine papers, the amount has been typically limited to less than 20% because there are concerns about its potential impact on papermaking operation and product quality. To address these concerns, laboratory experiments that mimic the actual paper machine operation were carried out and coated paper samples from mill trials were examined to clarify the impact of high-level HYP substitution on the properties of coated wood-free papers. Results showed that the HYP substitution, even at 40%, did not yield negative effects on strength properties such as tensile and tear; in fact the Scott bond increased with the HYP addition. The small increase in the surface roughness from the HYP addition can be eliminated by the filler addition, precalendering, and coating process. The lower brightness and CIE (Commission Internationale d'Eclairage) whiteness of the HYP can be compensated for by the addition of optical brightening agents (OBAs) and dyes, as well as pigments in the coating color. The analysis of samples collected from mill trials indicated that coated paper containing 40% HYP has lower coating penetration than that containing 40% HYP content paper samples. This was attributed to the smaller pore size created by HYP substitution. No significant differences were found between the samples containing 17 and 40% HYP on print gloss, color gamut, and print gloss uniformity. The implication from this study is that the HYP substitution level can be increased up to 40% in the production of coated wood-free paper without significant negative effect on the paper quality.

The Impact of Lignin Content on Paper Physical Strength of CTMP

The research reported here gives some new insights into the influence of lignin content on paper strength properties. The relative amount of total lignin in CTMP was varied by using multistage ClO2 bleaching method. Few differences were observed in fiber morphology charcteristics of CTMP during ClO2 treatments. Linear correlations greater than 99% were found between total lignin content and paper strength properties. The influences of lignin content on Scott bond and tensile strength were greater than that of tear and burst strength.

Mechanical Pulping: Birch pulp fractions for fine paper and board

SUMMARY: Mill birch kraft pulp was fractionated using hydrocyclones and a pressure screen equipped with smooth-hole screen basket. Through hydrocyclone fractionation a coarse fraction was obtained having a high tensile stiffness and no extractives. The fine fraction had a high bonding ability and a high xylan and extractives content. The coarse fraction could be used in the top layer of board or in fine paper. The fine fraction obtained by hydrocyclone and pressure screen fractionation could be used for bonding in board middle layer or as a source of xylan. The tensile stiffness and Scott bond of the fractions could be improved further by optimized refining, using lower specific edge load and higher refining consistency. ADDRESSES OF THE AUTHORS: Sari Asikainen (sari.asikainen@vtt.fi) and Agneta Fuhrmann fractionation according to the fiber length wou(agneta.fuhrmann@vtt.fi): VTT, P.O. Box 1000, FIN -02044 VTT, Finland. Leif Robertsen (leif.robertsen@kemira.com): Kemira Oyj, Espoo Research Center, P.O Box 44, FIN-02271 Espoo, Finland.

A Simplified Treatise of the Scott Bond Testing Method

The Scott bond test method has been used extensively in the paper industry over the years as a means to assess the bond strength of paper. The method has been a subject of some controversy lately since it does not always correlate to the sensitivity of the material to fracture by delamination. To gain some further insight into which parameters govern the fracture process in a Scott bond test a simplified approach has been chosen in order to formulate an analytical mathematical/mechanical model of the test. The model is dynamic in the sense that inertia effects are included. The material model utilised is a simple cohesive theory that assumes a linear behaviour between stress and crack opening when the material has started to degrade. This choice of material model makes the mathematical model very nonlinear. In fact, a system of three coupled nonlinear second order partial differential equations have to be solved and adjusted to the correct initial conditions. The material parameters needed for the model are the elastic modulus in the thickness direction, the transverse shear (elastic) modulus, the tensile strength (in the thickness direction) and the fracture work (per unit area) for a delamination crack. To investigate the ability of the model, a Scott bond testing apparatus have been equipped with a piezoelectric load sensor. The load cell was mounted on the apparatus’ pendulum so that the load acting on the sample holder could be recorded during the whole impact stage. This was done for a number of different initial velocities of the pendulum and it is found that the model gives a fair prediction of the contact load.

Tailoring softwood kraft pulp properties by fractionation and refining

Fractionation of softwood pulp offers potential for different products with different strength properties. In this study, fractionation was done in two stages: coarse screening with a 1.6mm-diameter hole screen, followed by a 0.15mm slot screen. The rejects of first-stage coarse screening, which have the highest average fiber length and coarseness, were tested with low and high SEL refining. Refining with a low specific edge load was beneficial for preserving the fiber length and tear index of the rejects. The refining energy input was higher, however, than in refining with a high specific edge load, when compared at a certain tensile index. The rejects from the two screens were mixed to test optimum filling and refining conditions. Conical filling with low bar-edge cutting speed resulted in gentle treatment with less fiber cutting and better tear index, but required more refining energy for a certain tensile index level. Narrow-bar disc filling with high cutting speed was more energy efficient and low SEL refining produced less fiber cutting. The accept fraction had a low average fiber length and contained more short and thin fibers and fines. The accepts were used to modify once-dried kraft pulp before refining by replacing a certain percentage of the pulp. The modified pulp consumed less energy when refined to the same tensile index and increased the internal Scott bond strength of the original pulp. Fractionation shows good potential for tailoring soft-wood pulp for different products with different strength properties and can serve as a flexible tool in getting the most out of available raw materials.

Laccase-initiated cross-linking of lignocellulose fibres using a ultra-filtered lignin isolated from kraft black liquor

In this work, the effect of Trametes pubescens laccase (TpL) used in combination with a low-molecular-weight ultra-filtered lignin (UFL) to improve mechanical properties of kraft liner pulp and chemi-thermo-mechanical pulp was studied. UFL was isolated by ultra-filtration from the kraft cooking black liquor obtained from softwood pulping. This by-product from the pulp industry contains an oligomeric lignin with almost twice the amount of free phenolic moieties than residual kraft pulp lignin. The reactivity of TpL on UFL and kraft pulp was studied by nuclear magnetic resonance spectroscopy and size exclusion chromatography. Laccase was shown to polymerise UFL and residual kraft pulp lignin in the fibres, seen by the increase in their average molecular weight and in the case of UFL as a decrease in the amount of phenolic hydroxyls. The laccase initiated cross-linking of lignin, mediated by UFL, which gives rise to more than a twofold increase in wet strength of kraft liner pulp handsheets without loosing other critical mechanical properties. Hence, this could be an interesting path to decrease mechano-sorptive creep that has been reported to lessen in extent as wet strength is given to papers. The laccase/2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) mediator system showed a greater increase in wet tensile strength of the resulting pulp sheets than the laccase/UFL system. However, other mechanical properties such as dry tensile strength, compression strength and Scott Bond internal strength were negatively affected by the laccase/ABTS system.

New mechanical treatment for chemical pulp

This study presents a new method to modify chemical pulp mechanically using an ultra-fine friction grinder, which works in a different way compared with conventional refiners. It consists of two grinding stones: a lower rotating one and an upper stationary one. The pulp passing through the gap between the stone plates is subjected to compressive and shear forces. The results showed that the gap clearance of the grinder plays an important role in controlling the fibrillation of fibres and the specific energy. External fibrillation became a dominant effect at a larger gap, whereas internal fibrillation developed faster at a smaller gap. Fibres were modified mostly into fibrils at a much smaller gap. Scott bond strength of pulps treated in the grinder was better than that of Valley-beaten pulps. Pulp properties can be varied by adjusting the pulp consistency, rotating speed, grit size, the dullness of the plate surface, and the number of pulp recirculations.

The use of polyelectrolyte multilayers of cationic starch and CMC to enhance strength properties of papers formed from mixtures of unbleached chemical pulp and CTMP. Part I

The construction of alternating multilayers of cationic potato starch and anionic carboxymethylcellulose (CMC) was investigated in two parts. In the first part, stagnation point adsorption reflectometry (SPAR) showed that the chosen chemicals formed polyelectrolyte multilayers (PEM) upon adsorption to the silicon oxide surface. This was in accordance with earlier work. The chosen polyelectrolytes adsorbed to similar extents on the silicon oxide surface and recharged the surface enough to allow for adsorption of a consecutive layer. In the second part, the multilayer concept was tested on 80/20, 20/80% of total in mixture of mixed spruce CTMP and bleached chemical pulp in order to enhance the sheet strength properties of a typical packaging board furnish.. The multilayers yielded a significant improvement in Scott Bond values and tensile index and a marginal improvement in tensile stiffness index. The Scott Bond values were improved more than 150% for papers prepared from a furnish consisting of 80% spruce CTMP and 20% chemical pulp. Polyelectrolyte multilayers treatment also led to a slight densification of the sheets, but the polyelectrolyte multilayers treatment resulted in a more favourable density/strength relationship than that achieved with a change in the amount of chemical pulp.

Paper properties affecting pressure-sensitive tape adhesion

The interaction between paper and pressure-sensitive adhesive was investigated by peel adhesion testing. The paper/adhesive peel curves were analyzed by plotting the logarithm of the peak peel force (i.e. the maximum value) against the logarithm of the peel rate, yielding two linear segments: a peel-rate-dependent interfacial failure domain and a rate-independent paper failure domain. Three independent parameters were extracted from these plots, namely, the interfacial peel force (F in) at a low peel rate of 1 mm/min, the maximum peel force (F c) and the slope (S p) in the plot of log (interfacial peel force) versus log (peel rate). The linkages between paper and its peel responses were analyzed using the multivariate statistical methods. The paper properties influencing peel force in interfacial failure domain were found to be primarily the paper surface chemistry, characterized by oxygen/carbon ratio (determined by XPS), and secondarily paper surface roughness. The peel force increased with oxygen/carbon ratio and with the surface roughness. The log–log slope in the interfacial failure domain was found to be independent of paper properties; it is determined by the adhesive rheology. The governing paper property in the paper failure domain was found to be the paper internal bond strength as measured by an internal (Scott) bond tester.