SUPERFICIES

Tappi Journal (2008), 7(7), 15-21


Fiber trapping in refining has been defined by the fraction f of the bar edges that trap fibers as they cross, and by the no. of fibers i trapped under each section of bar. From these parameters, equations were derived to calc. the no. of impacts that a fiber undergoes during refining and the max. force experienced during each impact. Refiner power vs. gap was measured for a conical lab. refiner at max. peripheral speeds ranging from 4 m/s to 27 m/s and consistencies ranging from 1% to 6% for one softwood kraft pulp. The data were used to calc. relative changes in i and f as a function of consistency and speed. It was found that f was extremely sensitive both to an increase in refiner rotational speed and to a redn. in pulp consistency. A redn. in consistency from 4% to 2% at 20 m/s (3000 rpm) led to a decrease in the trapping fraction, f, by approx. 80%. The no. of fibers trapped under each section of bar also decreased, although to a lesser extent. The redn. in fiber trapping greatly increased the forces on the fibers, leading to enhanced fiber shortening and reduced refining efficiency.

Co-authors: Lundin, Tom; Batchelor, Warren

Nordic Pulp & Paper Research Journal (2008), 23(2), 181-188



The objective of this paper was to understand the effects of plasma activation, and thus influence of the surface energy and chem. changes on offset print quality. Pigment coated and surface sized papers were treated with corona and atm. plasma in pilot and lab. scales. The surface energy and surface chem. changes were evaluated by contact angle and XPS. Offset printing was performed in lab. scale with an IGT unit with predampening and in a pilot scale sheet-fed offset printing press. In addn., the ink setting rate was measured using an ink on paper tack tester. Plasma activation increased the surface energy of the papers. Furthermore, the polarity of the paper surface increased due to formed polar oxygen contg. mol. groups. Due to differences in treatment times lab. scale plasma treatment formed mainly carboxyl and ester groups, whereas pilot scale treatment induced mainly alc., ethers, aldehydes and/or ketones on paper surfaces. Printing evaluation showed that plasma activation influences both ink and water absorption properties. According to print tack results plasma activation led to faster ink-setting. With hydrophobic surface-sized paper plasma activation influenced the ink transfer, print gloss and d. by changing dampening water absorption properties. The difference in surface chem. with lab. scale plasma treated samples was also reflected in the print quality properties. SEM imaging showed that too intense plasma activation can cause topog. changes in addn. to of the surface chem. changes.

Co-authors: Pykonen, Maiju; Sundqvist, Henna; Tuominen, Mikko; Lahti, Johanna; Preston, Janet; Fardim, Pedro; Toivakka, Martti.

Holzforschung (2008), 62(4), 417-422


On damage of conifer trees, oleoresin is exuded onto the tree stem. The oleoresin is typically composed of monoterpenes and resin acids. It serves to protect the tree from dehydration and microbial attack. Callus resin, in the traditional German term "Uberwallungsharz", is a resin exuded from the callus tissue formed as the wound is closed by annual growth. These resins can usually be found as nodules or lumps on the rim of the closing wound. Both types of resin, collected from Picea abies, Pinus sylvestris, Larix decidua and Pseudotsuga menziesii, were analyzed sep. by GC/GC-MS. Expectedly, the oleoresin samples were composed of resin acids. However, the callus resins were of a completely different compn. as they are composed primarily of lignans and hydroxycinnamic acid derivs. In addn., the L. decidua sample contained significant amts. of abietol and abietadiene. The P. abies and L. decidua callus resins were found to be essentially resin acid-free. The components identified in the callus resin samples have previously been identified as minor components in oleoresin and bark samples. The potential for the inadvertent inclusion of callus resin in previously analyzed samples of oleoresin, bark and ingrown (dead) knots is highlighted.

Co-authors: Holmbom, Thomas; Reunanen, Markku

Papel (2008), 69(5), 56-73



A virtual pulp mill producing bleached soft-wood kraft pulp was examd. in this study and the amt. of wood chip screenings was estd. based on real pulp mill operating in the Nordic countries. Wood chip screenings are defined as undersize fraction that forms during wood chipping and it is screened out from the accept chip fraction. The generation of heat and steam and the amt. of bleached kraft pulp able to be produced from wood chip screenings were calcd. Chem. compn. of wood samples from softwood kraft pulp mill was detd. The prodn. of ethanol fuel and functional chems. from the analyzed wood materials was examd., based on existing and potential technologies. In addn., basic financial calcns. were done and the different processes were evaluated. We found that heat and steam generation is rather profitable, but not as profitable as producing bleached kraft pulp. Ethanol fuel prodn. is not profitable because of expensive pulpwood and sawmill chips and low ethanol price. We suggest that valuable wood residues should be utilized for prodn. of high-added valued functional chems. in Europe and esp. in Nordic countries, where wood is expensive. The prodn. of functional chems. can be almost 100 times more profitable than heat generation

Co-author: Korpinen, Risto

Appita Journal (2008), 61(3), 220-227



Fine wood particles (sawdust and chip screenings) and wood chips made of Scots pine were impregnated with kraft pulping liquor and the results were compared. The effect of removing the smallest fractions from the fine wood particles was also studied. The fine wood particles differed significantly from the chips. Some differences were obsd. even between sawdust and chip screenings but the removal of the smallest fractions had only minor effects on the impregnation. Pine chip screenings generated residual liquors with lower EA than sawdust in the beginning of the impregnation but with higher EA sorption and consumption. In addn., pine chip screenings produced lower impregnation yields than sawdust, indicated by lower residual liquor dry solids and TOC contents. Pine chips again generated residual liquors with higher EA than fine wood particles and the EA sorption and consumption were substantially lower.

Co-authors: Korpinen, Risto I.; Hultholm, Tom E. M.; Lonnberg, Bruno K

Surface and Coatings Technology (2008), 202(16), 3777-3786


This work concerns the ageing effect of the atm. plasma and corona treatments when used to treat paper substrates. Pigment coated and surface sized papers were modified using two types of atm. plasma equipment; one at the pilot scale and one at the lab. scale. In addn., the plasma treatments were compared to conventional corona treatment. Surface energy was estd. by contact angle measurements and surface chem. by XPS as a function of the time during three months. The treatments increased surface energy and oxidn. level of surface for both papers. The ageing effect could be detected only in the surface energy, whereas the oxidn. level remained stable during the twelve weeks. The decay in surface energy was faster during the first weeks of storage and subsequently leveled off leading to a permanent change. The permanent change was explained as a contribution of oxygen contg. polar mol. groups, which were detected by XPS. The ageing effect was suggested to originate from already existing polar mol. groups, which have rotated on the surface by plasma-related process and then rotate back into the material in time. A part of the decay was also explained by the plasma cleaning model, in which the ageing effect occurred through re-contamination. Paper is a multicomponent system, where the constituents that have the lowest surface energy were suggested to migrate to paper surfaces.

Co-authors: Pykoenen, Maiju; Sundqvist, Henna; Kaukoniemi, Otto-Ville; Tuominen, Mikko; Lahti, Johanna; Toivakka, Martti.

Holzforschung (2007), 61(6), 647-655


The distribution of lignin, carbohydrates, and metal ions on the surface of spruce and aspen wood tissue sections was investigated by time-of-flight secondary ion mass spectrometry (ToF-SIMS). The distribution patterns of metals and lignin in ray cells, vessels, and fibers were different, whereas carbohydrates were uniformly distributed across the sections of all morphol. regions. In spruce sapwood, Ca, Mg, Na, K, Fe locations was more pronounced in the bordered pit tori and inner layer of ray parenchyma cells. Little lignin was detected in these regions. In spruce heartwood, the degree of lignification was low on the surfaces of bordered pit tori; however, Na and K were not detected here. In compression wood from spruce, the locations of p-hydroxyphenyl and guaiacyl units was different in cell wall layers. In aspen sapwood, the main locations of Ca, Mg, Na, K were in lumina of longitudinal parenchyma cells and in pits between vessels and ray cells. Low-intensity signals of the secondary ions assigned to lignin were found in the same morphol. regions.

Co-authors: Tokareva, Elena N.; Pranovich, Andrey V.; Daniel, Geoffrey; Holmbom, Bjarne.

Journal of Colloid and Interface Science (2007), 316(2), 360-366


The controlled heterogeneous modification of cellulose fibers with trifluoroacetic anhydride was investigated. The characterization of the ensuing materials was performed by elemental anal., FTIR spectroscopy, X-ray diffraction (XRD), thermogravimetry, and surface anal. (XPS, ToF-SIMS, and contact angles measurements). The trifluoroacetylation enhanced significantly the hydrophobic and lipophobic character of the fibers, whereas their thermal stability and crystallinity were only modestly affected by this treatment, except under the most severe conditions for the latter. Their hydrolytic stability to water vapor was also assessed as a function of the air humidity and shown to be lower than that of still liq. water in the case of a satd. atm.


Co-authors: Cunha, Ana G.; Freire, Carmen S. R.; Silvestre, Armando J. D.; Pascoal Neto, Carlos; Gandini, Alessandro; Orblin, Elina.

In Characterization of Lignocellulosic Materials, Edited by Thomas Hu, Blackwell Publishing,
(2008), 101-118


Chemical microscopy methods are nanoscale measurements that couples spatial resolution with chemical specificity. Between the techniques available, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) has unique capabilities of imaging combined with surface mass spectrometry while X-ray Photoelectron Spectroscopy (XPS) is useful for estimation of surface components and their different oxidation states. In this chapter we present our previous investigations on the distribution and composition of extractives in pulp fibres and newsprint papers using a combination of XPS and ToF-SIMS analyses. Our results suggested that extractives are usually evenly distributed on fiber and paper surfaces. However, the surface coverage by extractives is rather affected by the pulping and papermaking processes than only the wood used as raw material. We also suggest that extractives play an important contribution to the nanostructure and surface energy of fiber and paper surfaces and thus should be carefully investigated when innovative fibre and paper products are designed.

Co-author: Bjarne Holmbom

Papel (2007), 68(8), 98-108


Kraft pulp is a nanostructured material which is produced under chemical degradation
conditions where less ordered components are removed and new (supra)molecularly organized
systems are created. The effects of kraft pulping on the chemistry of eucalyptus pulp were investigated here by using X-ray Diffraction (XRD), Cross Polarization Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance (CP/MAS 13CNMR) and Near Infrared Spectrometry (NIR) combined with Principal Component Analysis (PCA). Cellulose, hemicelluloses, uronic acids, lignin and extractive amounts in pulp were determined using either chromatographic or different specific methods. The elastic modulus and tensile strength of pulp hand sheets and fiber morphological parameters such as length, width, cell wall thickness and lumen diameter were also measured. Pulping experiments were conducted varying the active alkali range while temperature, sulfidity, heating rate and liquor-to-wood ratio were kept constant. Two molecular assemblies were suggested and identified as function of active alkali used in pulping. Each molecular assembly had characteristic degree of crystallinity and affected the elastic modulus and tensile strength of the hand sheets. A transition point between the two assemblies was also identified and ascribed to hydrogen bond intermolecular interactions due to removal of lignin, hemicelluloses and bounded water. A mechanism of assembly of cellulose nanofibrils, driven by freeenergy of interaction, was proposed to affect the fibre morphology, decrease fibre wall flexibility and lower inter-fibre bonds. Our results also suggested that the variations in alkali charge usually present in industrial digesters can cause the formation of different molecular assemblies in a very sensitive limit. As a consequence, impacts on mechanical and physicochemical properties of fibres are expected.

Co-author. Nelson Duran

Appl. Surf. Sci. (2007), 253(18), 7569-7577

Tissue of Norway spruce wood was investigated by time-of-flight secondary-ion mass spectrometry (ToF-SIMS) and field-emission SEM (FE-SEM). Different sample prepn. techniques (including sectioning and drying) traditionally used for SEM anal. were compared and critically evaluated. A high contamination of wood surfaces by polytetrafluoroethylene (PTFE) introduced onto the sample during sectioning was detected by ToF-SIMS. A new protocol was developed and images of wood sections dried in different ways were compared. Main location of Mg, Na, K and Ca, but no lignin in membranes of bordered pits in spruce section surfaces was detected by ToF-SIMS imaging if crit. point drying (CPD) or acetone extn. followed by drying under nitrogen flow (AEND) was applied. No specific locations of wood components as well as low signals from metal ions (Mg and Na) were obsd. on the wood surfaces of freeze-dried (FD) or air-dried (AD) sections. It was found that extractive substances, presenting on surfaces of FD and AD wood section, were evenly distributed on the surfaces and interfered with ToF-SIMS anal. Our results indicated that ToF-SIMS imaging was critically sensitive to the sample prepn. technique and a strict protocol for characterization of metals, lignin and polysaccharides in wood was suggested.

co-authors: Tokareva, E. N.; Pranovich, A. V.; Fagerholm, H.-P.; Daniel, G.; Holmbom, B.

Langmuir (2007), 23(21), 10801-10806


The surface modification of cellulose fibers with 3,3,3-trifluoropropanoyl chloride (TFP) was studied in a toluene suspension. The characterization of the modified fibers was performed by elemental anal., Fourier transform IR (FTIR), 13C-solid-state NMR, X-ray diffraction, thermogravimetry, and surface anal. (XPS, ToF-SIMS, and contact angles measurements). The degree of substitution (DS) of the ensuing trifluoropropanoylated fibers ranged from less than 0.006 to 0.30, and in all instances the fibers' surface acquired a high hydrophobicity and lipophobicity resulting from a drastic redn. in its energy. The hydrolytic stability of these cellulose derivs. was also evaluated and shown to be permanent in time in the presence of neutral water, still appreciable in basic aq. soln. at pH 9, but, as expected quite poor at pH 12.

Co-authors: Cunha, Ana G.; Freire, Carmen S. R.; Silvestre, Armando J. D.; Neto, Carlos Pascoal; Gandini, Alessandro; Orblin, Elina

Biomacromolecules (2007), 8(4), 1347-1352

New highly hydrophobic/lipophobic biopolymers were prepd. by the controlled heterogeneous pentafluorobenzoylation of cellulose substrates, i.e., plant and bacterial cellulose fibers. The characterization of the modified fibers was performed by elemental anal., FTIR spectroscopy, x-ray diffraction, thermogravimetry, and surface anal. (XPS, ToF-SIMS, and contact angle measurements). The degree of substitution of the ensuing pentafluorobenzoylated fibers ranged from 0.014 to 0.39. The hydrolytic stability of these perfluorinated cellulose derivs. was also evaluated and showed that they were quite water stable, although of course the fluorinated moieties could readily be removed by hydrolysis in an aq. alk. medium.

Co-authors: Cunha, Ana G.; Freire, Carmen S. R.; Silvestre, Armando J. D.; Pascoal Neto, Carlos; Gandini, Alessandro; Orblin, Elina

Colloids Surf. A, (2007) 296(1-3), 1-7.

The amount of total anionic groups (TAGs) in laboratory-scale chemithermomechanical pulps (CTMP) were assessed by methylene blue (MB) and quinoline sorption. The amounts of surface anionic groups (SAGs) were determined by MB sorption followed by X-ray photoelectron spectroscopy (XPS) and by polyelectrolyte (PE) titration. The content of uronic acids in the pulps was determined by acid methanolysis and GC and the methyl-esterification degree of pectins by alkaline hydrolysis. Pulps were produced by chemical pretreatments of sapwood chips of Norway spruce (Picea abies) prior to refining in a small-scale batch refiner. The chips were pretreated with alkaline, sulphite, alkaline sulphite and alkaline peroxide liquors. The TAGs in the pulps increased linearly with alkali and sulphite dosages. Sulphonic groups in lignin and new carboxyl groups formed in pectins accounted for a major part of the new anionic groups. New anionic groups were also created in thefibre material due to lignin oxidation in alkaline peroxide treatment. Pretreatment with sulphite resulted in a lower surface lignin content compared to pretreatment with alkali or alkaline sulphite. This may indicate more preferential fibre separation in the primary wall layers than in the middle lamella or be a result of redeposition of alkali dissolved lignin onto fibre surfaces. The amount of SAGs, determined by XPS, was doubled for the chemically pretreated pulps compared to a reference TMP. This is probably a result of primary wall exposure and substantial pectin demethylation. Sulphonation did not result in more SAGs.


Keywords: Chemithermomechanical pulping; Anionic groups; Sulphonation; Pectin
demethylation; Surface chemistry.

My co-authors were Jonas Konn, Andrej Pranovich and Bjarne Holmbom

Nord. Pulp Paper Res. J. (2007), 22(1), 131-135

The surface chemistry of starch-coated fine and
LWC papers was studied using Time-of-Flight Secondary Ion
Mass Spectrometry (ToF-SIMS). The starch was modified by
varying the degree of acetylation and cationization and spread
onto paper surfaces by spraying or bar coating. ToF-SIMS imaging
showed a substantially more uniform coating layer of
starch when bar coating was used. The spatial distributions of
acetyl and quaternary nitrogen functional groups were also
assessed. A direct relation between the theoretical cationization/
acetylation ratio and the peak ratios obtained by ToF-SIMS
indicated that the starch characteristics can significantly influence
the surface chemistry of paper. Furthermore, some benefits
and drawbacks of this novel characterization technique,
especially with regard to quantification of the spectral information,
are discussed.

Keywords: ToF-SIMS, Sizing, Spraying, Coating,
Acetylated cationic starch, Degree of substitution, Degree of acetylation

My co-authors were: Jyrki Juhanoja, Heidi Fagerholm, Sari Hyvärinen, Soili Peltonen, Kirsi Kataja and Henna Lampinen

Tappi J. 5(8) 2006, 31-35

Softwood kraft pulps at consistencies from 1% to 6% were refined in a conical laboratory refiner. For each consistency, the refiner power was measured as a function of the gap between the rotor and stator. The data were analyzed for no-load power, and the net refining power was fitted with a negative exponential function. The fitted functions for no-load and net-refining power were then used to estimate the gap at which the fibers first take up load. The number of fibers trapped was assumed to be proportional to this gap. The value of this gap was used to convert the measured gaps into fiber mat strains, or the strains of compression for the fiber mats. The net refining power versus fiber strain was a direct function of the pulp consistency. This finding indicates that the fraction of the refiner bars that trap fibers is proportional to the pulp consistency. A reduction in bar coverage during lower fiber trapping increased the harshness of the refining on the fibers.
Application: Refining efficiency can be considered in terms of how fiber mat trapping is affected by changes in pulp consistency, the degree of refining, the average fiber length, the peripheral speed, and the bar edge wear.

My co-authors were: Warren Batchelor and Tom Lundin.

J. Colloid Interf. Sci 301(1), 2006 205-209

The topochemistry of the controlled heterogeneous esterification of cellulose fibers with fatty acid chlorides of different chain length, both in swelling and non-swelling media, was assessed by X-ray Photoelectron Spectroscopy (XPS), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and contact angle measurements. On the one hand, the results provided by the combined use of these three powerful techniques showed unambiguously the occurrence of the reaction at the fibers' surface and, on the other hand, the XPS results showed that the surface coverage with the fatty acid moieties increased with their chain length, but was only modestly affected by the degree of substitution (DS), suggesting that when the esterification yield was increased (higher DS values), an in-depth reaction also occurred, particularly when DMF was used as a cellulose swelling medium, involving the OH groups buried below the fibers' surface.

Carmen S.R. Freire is the first author. I did the XPS and ToF-SIMS characterization. A. J.D. Silvestre, C.P. Neto, A. Gandini and B. Holmbom are other co-authors.

Holzforschung 60(2) 2006, 149-155

Different methods for estimation of surface coverage by extractives and lignin have been critically compared. For data collection, four state-of-the-art X-Ray Photoelectron Spectroscopy (XPS) instruments located in four different laboratories were used. Hand sheets of one mechanical and two chemical pulp samples were prepared in one laboratory and distributed among the other participants. The XPS results based on O/C ratios and curve fitting of C1s peak had very good intra- and interlaboratory variation for extracted and non extracted pulp samples. The estimations of surface coverage by extractives and lignin also had acceptable intra- and interlaboratory variation. However, significant differences were observed between the results of the various methods. Estimation of surface coverage by extractives based on O/C ratios was much higher than that based on the C1 component analysis in the case of mechanical and unbleached chemical pulp. The surface coverage by lignin of mechanical pulp was detected reproducibly based on O/C ratios, C1 component analysis and by labelling with mercury acetate. The same data were, however, rather scattered if they were collected with these three methods for bleached and unbleached chemical pulp. In spite of the differences, similar trends regarding the pulp type could be observed. We interpret the results that the surface coverage neither by extractives nor by lignin should be considered as absolute "true" values rather than relative values, which are reliable only for comparison of samples by the same instrument. Even for relative comparisons, we recommend selected a strict experimental set-up for the spectral acquisition and data treatment when applying any of the instruments and calculation models currently available.

Keywords: Chemical pulp, ESCA, Lignin, Surface Chemistry, Spectrometry, Thermo mechanical pulp, Wood extractives, XPS

My co-authors were:
Anette Heijnesson Hultén, Jean-Phillippe Boisvert, Leena-Sisko Johansson, Marie Ernstsson, Joseph M. Campbell, Agnes Lejeune, Bjarne Holmbom, Janne Laine and Derek Gray

J. Wood Chem. Technol. 25(4) 2005, 267-279

Multivariate data analysis and NIR spectrometry were used to determine the mechanical and optical properties of eucalyptus kraft pulps with different chemical composition and refined to different levels. Tear (TrID), tensile (TsID), burst (BuID), and bending (BeID) indexes and elastic modulus (EM), stretch (ST), and breaking length (BL) were the mechanical properties measured. Measurement of beating degree (SR) was also achieved. Light scattering (LS) and light absorption (LA) coefficients were the optical properties measured. Mechanical and optical properties were modeled using NIR spectra obtained on pulp hand sheets by diffuse reflectance and application of the partial least squares (PLS) method. Models with two to seven PLS components and very good predictive ability were stablished after testing the first derivative, Kubelka-Munk, or a combination of both as pre-processing techniques. Models were validated by using cross-validation methodology and a comparison of measurements using conventional methods for new samples. The predictive models can reduce time in traditional measurements in the pulp and paper industry and are suitable for direct application using "at-line" conditions. As an additional benefit, improvements in process monitoring and paper quality can be achieved.

J. Wood Chem Technol. 25, 2005

My co-authors were: M. Ferreira and N. Durán

The effects of kraft pulping on the interfacial properties of eucalypt pulp fibres were investigated using polyelectrolyte titration (PT) and contact angle measurements. Changes on surface composition were assessed by FTIR-ATR spectrometry combined with principal component analysis (PCA). Surface lignin was removed by increase in active alkali in pulping as indicated by FTIR-ATR and PCA. In parallel, the surface charge decreased while the surface energy and work of adhesion with water (Wap) increased. The acid-base component (Wap-AB) explained the increase of Wap. Our results suggested that the removal of surface lignin, exposure of carbohydrates and surface mobility of extractives are the main contributors to modifications of interfacial properties by kraft pulping. The role of interfacial properties on development of bleaching sequences and new pulp products was also briefly discussed.

My co-author was Nelson Durán

Click on the title to download the article in pdf format.

Pulp fibres and papers are complex materials with remarkable heterogeneity in chemistry and morphology. The chemistry of fibre interfaces determines important interactions in pulping, bleaching and papermaking. Lignin, carbohydrates and extractives are removed, re-deposited or modified in different processes affecting the fibre interface chemistry. Anionic groups are also generated or liberated, and metals, colloidal and dissolved substances can be attached to them or simply sorbed onto the fibre wall. Fibre interfaces are usually characterized by different spectrometric, imaging and sorption methods. Additionally, contact angle and inverse chromatography methods give information about interactions with different liquid probes. In this work, we present recent advances in characterization of fibre interfaces by using modern and state-of-art techniques such as Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), X-ray Photoelectron Spectroscopy (XPS), Electron Microscopy (EM), Atomic Force Microscopy (AFM), Attenuated Total Reflectance Infrared (ATR-IR), measurement of apparent contact angle and sorption of different molecular probes. Our results show that a combination of techniques was a key factor in the evolution of understating of chemistry of fibre interfaces in the latest five years. The relevance of methods that combine chemical specificity and imaging capability to localize different components in interfaces is highlighted. Challenges regarding contaminations, interpretation of results and application of new molecular level insights into process chemistry are critically discussed. Our research in the development of new on-line methods for fibre and papermaking processes is also presented and briefly discussed.

You can download the powerpoint slides in .pdf format by clicking on the title. Questions are welcome.

Pedro

Anionic groups (AG) on different cellulosic fibre surfaces were investigated by methylene blue (MB) and polyelectrolyte (PE) sorption, X-ray photoelectron spectroscopy (XPS or ESCA) and total attenuated reflectance infrared spectrometry (FTIR-ATR). The MB sorption isotherms well fitted the Langmuir equation that gave consistent estimations of sorption capacities. FTIR-ATR showed that MB molecules had extensive accessibility to the fibre wall pores. Estimation of surface AGs by PE sorption gave much higher values than a new method combining MB sorption and XPS measurements (MB-XPS). The surface AGs in different cellulosic fibres accounted for 1-3 % of the total AG content as revealed by MB-XPS. It was suggested that PE molecules can penetrate the fibre wall and form loops or unattached segments at external fibre surfaces that disrupts the PE sorption stoichiometry. The competition of MB and PE for the anionic sites in papermaking was assessed and it was showed that MB ions have a much stronger affinity to AGs than PE molecules.

Keywords: Pulp fibres, surface chemistry, carboxyl groups, papermaking, paper formulation, interactions, Langmuir, Freundlich, equilibrium, competition

My co-authors were: T. Moreno and B. Holmbom

XPS has been applied to pulp and paper research for decades. However, there has been no attempt to standardise or even systematically compare exptl. and anal. procedures, even though it is known that fibrous, nature-derived and insulating fiber materials pose remarkable challenges to reliable surface anal. The exptl. problems are mainly linked with neutralisation, energy resoln., contamination and X-ray induced degrdn. We have tested applicability, reliability and reproducibility of XPS anal. on real pulp samples with varying lignin and extractives contents in a small round robin investigation. We also tested the instrumental set-ups with an acetone-extd. filter paper, used as a ref. sample. The data, collected at four different labs. with state-of-the-art instruments indicate that reproducible results can be obtained, despite minor differences in exptl. and anal. procedures. However, we found that a specified sample handling procedure and limited X-ray exposure are crucial for reproducible, reliable data. Based on the round robin data we recommend dose restricted monochromatic measurements, a cellulosic in situ ref. and a consistent sample handling procedure. The data confirms that a paper-based ref. material and the correlation of high-resoln. C 1s data with O/C at. ratios can be used in testing instruments and exptl. set-ups for pulp and paper materials.


My co-authors were: L. S. Johansson, J. Campbell, A. Heijnesson-Hulten, J-P. Boisvert, M. Ernstsson.

The effects of bulk and surface composition on the mechanical properties (MP) of eucalyptus kraft pulp were investigated using Liquid Chromatography (HPLC), Scanning Electron Microscopy (SEM), X-ray Photolectron Spectroscopy (XPS) and Principal Component Analysis (PCA). SEM images of fractured regions during tear (TrID), tensile (TsID) and burst (BuID) tests of refined pulps showed fibre deformation and low proportion of broken fibres, indicating an inter-fibre failure in the sheet network. TrID of unrefined samples was affected by lignin surface coverage (SLig) while TsID and BuID were affected by surface coverage of extractives (SExt) and carbohydrates (SCar). After refining, TrID was affected by uronic acids (UA) in xylan and the influence of bulk composition was more pronounced. Our results also indicated that the fibre-to-fibre bonding rather than the individual fribre strength was the limit factor for MP. A strategy combining surface modification and preservation of polysaccharides in pulping was suggested to improve the MP of this material.


Keywords: eucalyptus, cellulosic fibre, surface composition, mechanical properties, XPS, PCA

My co-author was Nelson Durán

J. Braz. Chem. Soc. 16 (2) 2005 163-170

Click on the title to download the article from the journal website

The distribution of papermaking chemicals on the surface of various uncoated and coated papers was investigated by ToF-SIMS, FE-SEM, EDS, and XPS. Four paper samples, two office papers, one matte-coated and one traditionally coated paperboard were investigated with the aim of evaluation of chemical microscopy methods for examination of morphological and chemical heterogeneities on paper surfaces. Distribution of fillers, pigment particles, size, optical brightener, latex and other paper and coating components was assessed. Application of Au–Pd treatment on paper and coating surfaces prior to ToF-SIMS imaging increased the secondary ion counts for the region of low intensity peaks and improved the chemical mapping of papermaking and coating chemicals. ToF-SIMS imaging is shown to be a valuable and promising technique for chemical microscopy of paper surfaces.

Keywords: Pulp fibres; Coating; Latex; Sizing; FE-SEM; XPS; EDS; ToF-SIMS

My co-author was B. Holmbom

The composition, nanostructure and distribution of extractives on fiber surfaces of a birch bleached kraft pulp (BKP) and a recycled deinked pulp (DIP) was investigated using X-ray photoelectron spectroscopy (XPS or ESCA), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and atomic force microscopy (AFM). Effects of different extraction methods on the fiber surfaces were also investigated, in addition to the analyses of extractives by gas chromatography (GC). Traces of surface extractives were observed by XPS, ToF-SIMS and AFM in the BKP after extraction using an acetone–phosphate method (AcP). This method improved the extraction yield of palmitic and stearic acids in DIP, but the removal of surface extractives was not as effective as for BKP. Contaminants, identified as siloxanes and phthalates by ToF-SIMS were observed for DIP and BKP, even after AcP extraction. Stearic acid and its calcium salts were found to form aggregates with a diameter of 100–500 nm, while oleic acid formed a uniform layer. Estimations of extractive surface coverage by XPS were consistent with qualitative observations by ToF-SIMS and AFM. The combinations of different techniques strengthen the value of XPS, ToF-SIMS and AFM for fiber surface investigation.

Keywords: Pulp fibers; Recycled pulp; Fatty acids; Nanostructure; ToF-SIMS; AFM

My co-authors were J. Gustafsson, S. von Schoultz, J. Peltonen and B. Holmbom

The origin and character of anionic groups (AGs) in a broad selection of papermaking fibres comprising chemical, mechanical and chemimechanical pulps was investigated using methylene blue sorption (MB) and determination of uronic and hexenuronic acid contents by different chromatographic methods. The amount of AGs on the fibre surfaces was estimated by labeling with Mg2+ and MB, and subsequent analysis using techniques with different depth resolution, i.e., energy dispersive spectrometry (EDS) and X-ray photoelectron spectroscopy (XPS or ESCA). Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was also used to study the surface distribution of AGs. A significant part of AGs in chemical pulps was found being introduced during pulping and bleaching, independently of the wood used as raw material. In case of mechanical and chemimechanical pulps, a larger portion of AGs were from uronic acids already present in wood. Effects of different pulping and bleaching processes on the formation, depth profile and surface distribution of AGs were assessed. The content of AGs for different pulps at depths of 1000 and 10 nm were in the range of 60–97 and 1–3% of the total AG amounts, respectively.

Keywords: Chemical pulps; Anionic groups; Surface chemistry; XPS; ToF-SIMS

My co-author was B. Holmbom

GO PLACIDLY AMID THE NOISE & HASTE, & REMEMBER WHAT PEACE THERE MAY BE IN SILENCE. AS FAR AS POSSIBLE WITHOUT surrender be on good terms with all persons. Speak your truth quietly & clearly; and listen to others, even the dull & ignorant; they too have their story. Avoid loud & aggressive persons, they are vexations to the spirit. If you compare yourself with others, you may become vain & bitter; for always there will be greater & lesser persons than yourself. Enjoy your achievements as well as your plans. Keep interested in your own carrier, however humble; it is a real possession in the changing fortunes of time. Exercise caution in your business affairs; for the world is full of trickery. But let this not blind you to what virtue there is: many persons strive for high ideals; and everywhere life is full of heroism. Be yourself. Especially, do not feign affection. Neither be cynical about love; for in the face of all aridity & disenchantment it is perennial as the grass. Take kindly the counsel of the years, gracefully surrendering the things of youth. Nurture strength of spirit to shield you in sudden misfortune. But do not distress yourself with imaginings. Many fears are born of fatigue & loneliness. Beyond a wholesome discipline, be gentle with yourself. You are a child of the universe, no less than the trees & stars; you have a right to be here. And whether or not it is clear to you, no doubt the universe is unfolding as it should. Therefore be at peace with God, whatever you conceive Him to be, and whatever your labours & aspirations, in the noisy confusion of life keep peace with your soul. With all its sham, drudgery & broken dreams, it is still a beautiful world. Be cheerful. Strive to be happy.

Desiderata is Latin for "Things to be Desired". This poem was written by Max Ehrmann in 1920s.

ECF (DEDED)-bleached kraft pulps were prepared from five hardwoods: Acacia mangium (Indonesia), Betula pendula (Scandinavia), Eucalyptus globulus (Portugal), Eucalyptus urograndis (Brazil) and Eucalyptus grandis (Brazil).The bleached pulps were investigated by detailed bulk chemical analysis including lignin content, carboxyl groups content and compostion of carbohydrates and lipophilic extractives. The five pulps showed remarkable differences in xylan/cellulose ratio, content of carboxyl groups and, particularly, in the amount and compostion of lipophilic extractives. Such differecnes were assigned to the different wood compositions and to the diverse pulping and bleaching conditions required to fully bleach the pulps. The surface composition of pulp fibres was analysed by X-ray Photoelectron Spectroscopy (XPS) and by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The XPS analysis showed that the extractives content of the surface is much higher than in the inner parts of fibres. The Acacia pulp had a surface coverage of extractives around five times higher than the other pulps investigated. The ToF-SIMS spectra showed that fatty acids are the dominant extractives of the surface of Acacia fibres while sterols dominate at the surface of Eucalyptus fibres. The influence of the diverse compositions on the behavior of fibres in papermaking is discussed.

My co-authors were B. Holmbom, C. Pascoal Neto, A. Silvestre, D. Evtuguin, C. Freire, P. Pinto, A. Santiago.

The surface distribution of extractives on Norway spruce TMP hand sheets was studied by Electron Spectroscopy for Chemical Analysis (ESCA), Attenuated Total Reflectance-Infrared Spectrometry (ATR-IR), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Environmental Scanning Electron Microscopy (ESEM). The contact angle of water was also determined. Different model compounds of extractives and TMP resins were added to an acetone-extracted TMP. Unextracted and extracted TMP were also compared. The surface coverage of extractives analyzed by ESCA differed depending on the model compound added. The surface coverage increased in the following order: unsaturated fatty acids < saturated fatty acids < resin acids < sterols < steryl esters. Samples with a higher surface coverage of extractives also had a higher contact angle of water. ToF-SIMS imaging indicated that the extractives were evenly distributed on the sheet surfaces except for a few aggregates observed for stearic acid. No aggregates or other morphological effects by extractive addition were observed using ESEM, probably due to its higher depth resolution and poorer surface sensitivity compared to ToF-SIMS imaging. No specific IR peaks from the different extractives were observed in the ATR spectra, indicating that either the sensitivity of this technique is not high enough to detect small amounts of extractives or that aggregates were located less than 1 mum below the surface.

My co-authors were P. Kokkonen and B. Holmbom

Effects of pulping variables on the retention of carbohydrates and lignin in fast kraft pulping of eucalyptus were investigated using a complete factorial design. Influences of pulp chemical composition on physicochemical and mechanical properties were evaluated using Principal Component Analysis. Active alkali ( AA) significantly affected the macromolecular degradation of cellulose and retention of xylan and lignin. Cellulose retention was unaffected. The use of low AA in pulping improved all mechanical properties, but increased the kappa number and reduced ISO brightness. The degree of polymerization of cellulose was related to tensile index and elastic modulus while xylan affected the apparent sheet density. Tear index had a positive influence of fiber length and uronic acid groups, which were preserved in xylan by a combination of low AA, thin wood chips and a short pulping cycle. The characteristics, rather than the content of xylan, were suggested to be relevant to tear index.

My co-author was N. Durán

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Sorption of spruce acetylated galactoglucomannans (GGM) onto different pulps, among which unbleached and peroxide-bleached mechanical pulps, and unbleached and bleached kraft (BK) pulps, was studied as a means of understanding the retention of acetylated GGMs in mechanical pulping and papermaking. The fibre surface coverage of lignin and carbohydrates was estimated by X-ray photoelectron spectroscopy (XPS) or electron spectroscopy for chemical analysis (ESCA). GGM sorption was clearly favoured on kraft pulps. Hardly any differences in sorption were, however, observed between unbleached and BK pulps, even if the surface coverage of lignin was lower on the bleached pulp. Neither thermomechanical pulp (TMP) nor chemithermomechanical pulp (CTMP) manufactured from spruce sorbed any acetylated GGMs. Peroxide bleaching of the pulp did not increase sorption. Only CTMP produced from aspen sorbed some GGMs. The anionic charge of neither chemical nor mechanical pulps influenced GGM sorption.

Note: My co-authors were T. Hannuksela and B. Holmbom.

The effects of laboratory pulping and refining on the surface properties of eucalyptus kraft pulp fibres were investigated using Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS or ESCA) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). Refining affected fibre structure, surface morphology, lignin (phi(lig)), carbohydrate (phi(carb)) and extractive (phi(ext)) surface coverage. The phi(lig) and phi(carb), estimated with XPS, decreased and increased with refining, respectively. The phi(ext) changed according to the pulping conditions. Cellulose, xylan, lignin, sterols, fatty acids and their salts were identified by ToF-SIMS. Significant changes in the normalized ToF-SIMS peak intensities were observed after refining. The release of xylan and fatty acid salt aggregates formed in pulping and entrapped in the cell wall pores with subsequent adhesion to the fibre external surfaces was suggested as a source of surface chemical modification by refining.

My co-author was N. Durán

Methylene blue (MB) sorption can be used to determine anionic groups (AGs) in chemical, chemimechanical, and mechanical pulps. Fast sorption performed in 5 min under vigorous agitation gave similar results as obtained using 20 h sorption time, with no observed effects of AG counter ions. The MB sorption isotherm showed different plateaus according to the amount of free MB in solution. We also identified regions related to chemisorption and physisorption. For analytical purposes, the saturation level in the chemisorption process must be the target for performing MB sorption. The isotherm in the chemisorption region for this study was of the Langmuir type, according to experimental data fitting and as observed by X-ray photoelectron spectroscopy (XPS) analyses. Based on our results, we suggest that pulp and paper mills can use MB sorption as a fast and reliable method applied to "on-line" and "at-line" process control.

My co-author was B. Holmbom

Anionic or acidic groups in pulp fibres are important for many interactions in pulping and papermaking. The total amount of anionic groups can be determined by acid-base titration, as well as different sorption and ion-exchange techniques. In this study, different methods for determination of total anionic groups were compared on a broad selection of pulps. Conductometric titration with NaOH and methylene blue sorption gave very similar results on all pulps, and both methods had a good repeatability. The methylene blue technique is especially attractive because of its simplicity. Polyelectrolyte adsorption with polybrene generally gave higher readings, was less repeatable, and was also a very laborious method. Uronic acids, including hexenuronic acid, determined by enzymatic hydrolysis and HPLC (High Pressure Liquid Chromatography), represented only 20-60% of the total anionic groups in the kraft pulps. Uronic acids analysed by acid methanolysis and GC (Gas Chromatography) usually represents 70-100% of the anionic groups in mechanical pulps.

Note: Anionic groups are very important for interface chemistry of fibres!
My co-authors were B. Holmbom, A. Ivaska, J. Karhu, G. Mortha and J. Laine

The surface chemistry of Eucalyptus grandis wood pulp fibres was investigated using the sessile drop apparent contact angle, XPS and TOF-SIMS techniques. Pulp fibres were studied using different chemical pulping conditions. The pulping affected the surface coverage of lignin and extractives, as indicated by XPS, and the work of adhesion with water, as estimated from contact angle determinations. The amount of surface lignin decreased while surface extractives and work of adhesion with water increased in relation to the amount of active alkali used in the pulping. Desorption and analysis of surface extractives by TOF-SIMS showed sterols, fatty acid calcium and sodium salts. After acetone extraction the spectra obtained by TOF-SIMS showed changes. However, calcium and sodium salts of fatty acids were still detected, indicating their resistance to solvent extraction. This resistance to extraction can affect the lignin and extractive surface coverage estimations using XPS due to the contribution of the carbon content after extraction. The extent of interference was, however, uncertain.

Note: My co-author was Prof. Nelson Durán

Near infrared spectrometry and multivariate data analysis were applied to predict the chemical composition and physico-chemical characteristics of eucalypt unbleached kraft pulps obtained at different laboratory pulping conditions. Viscosity, degree of polymerization (DP), kappa, brightness and contents of glucan, xylan, uronic acids, and lignin were the modeled variables using diffuse reflectance near infrared spectra obtained on pulp handsheets and the partial least squares (PLS) method. Models with two to four PLS components and good predictive ability were established after first derivative spectra pre-processing and application of cross-validation methodology. The predictive models can reduce the time consuming traditional analyses in the pulping industry laboratories, and also lead to a better process monitoring for suitable applications.

Note: In this work my co-authors were Prof. Marcia M.C. Ferreira and Prof. Nelson Durán

Surface chemical interactions are important in many steps of paper manufacturing and converting. Most of the interactions are complex and not very well understood. Thus, many paper and coating formulations are designed through an empirical trial-and-error approach. This work is the second part of a critical literature review concerning some interactions present in papermaking, coating, and printing. The first part reviewed interactions relating fiber surfaces and wet end chemicals. This second part discusses surface phenomena present in coating formulation and printing.
Paper manufacturing creates a surface. Different treatments, either mechanical such as calendering or chemical such as coating, are applied to the paper surfaces to improve printability, optical properties, and strength. Coating is a mixture of minerals, colloidal particles and dissolved polymers. The mixture is applied onto the base paper surfaces requiring optimum flow properties, usually achieved with low solids and viscosity. However, high solids and viscosity are needed to obtain good printability and a uniform coating layer. Finding a balance between coating application and printability requires an understanding of surface chemical phenomena within coating formulation and rheology.
This paper provides a review of interactions between mineral particles with the dispersion media and adhesion with latex particles. It also discusses the influence of interactions between minerals, binder, and co-binder on coating water retention. Rheological properties and changes in coating viscosity are interpreted using the DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory. The discussion also relates the theory to formation and deposition of white pitch in paper machines. Interactions between printing inks, paper surfaces, and penetration of the ink vehicle into coating layer are discussed in terms of Lucas-Washburn capillary model and thermodynamic work of adhesion. The concept of surface engineering offer potential for developing coating formulations that may improve adhesion with the paper base and eliminate problems such as varnish rejection, spots, cutting powder, and non-uniform printability. The knowledge of surface chemical phenomena can be useful for the pulp and paper industry, not only for patents and product development, but also for improving in troubleshooting and customer support.
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Paper manufacturing and converting involves a multitude of surface chemical interactions. Beating, stock preparation, coating, and converting processes are steps where surface phenomena play an important role for product consolidation and performance. Interactions between fibers and colloidal particles, polymers, minerals, and dyes are fundamental in papermaking. Most of those interactions are complex and not very well understood. Thus, many paper formulations are designed according to an empirical trial-and-error approach. This work is a critical literature review of some of the interactions present in papermaking, coating, and printing. The first part discusses the current models for fiber surfaces and their interactions in the wet end. It highlights limitations concerning the fiber surface definition and the available models based on direct observation, DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory, and a combination of qualitative and quantitative approaches. Complexity factors such as surface composition heterogeneity, contamination from manufacturing processes, and surface mobility are noted for consideration. The paper also discusses surface interactions present in the wet end, with a focus on reversible and irreversible flocculation and the flocculation mechanisms concerning fibers, polymers and micro-particles. The paper reviews the role of the fiber surface chemical composition on flocculation and flock size and the influence from the chemical medium in the paper machine. Papermaking is suggested as being a fiber surface modification process once polymers and other chemicals are used to change the surface energy and chemical composition. Modification by formation of cellulose esters or attachment of aluminum abietate onto surface anionic groups is believed to occur during sizing. Modification, which affects the fiber-fiber bond with the aim of improving the wet and dry strength properties, is also discussed. Accessibility of anionic groups in pulp fibers to the chemicals during the short time scale of the papermaking process and competition for the same charged sites are still not clear. This report notes the implications of that, and comments on the limitations regarding the present process monitoring using measurements with no specificity. A combination of different sorption and chemical microscopy methods is suggested as a suitable approach to clarify surface interactions. Why does a paper formulation need such a number of additives? Where are they attached on the fiber? Questions of this nature are challenges not only in the scientific point of view, but also to market perspectives, demanding critical research work.
Another idea presented in this review is the application of surface engineering to pulp fibers. Surface engineering is a concept traditionally applied to development of coating for metals and its main goal is the modification of material surfaces in order to achieve desired properties. This concept has a good potential for eucalyptus-based pulp and paper, especially for improving strength and absorbing properties. The strategic application of surface chemistry in the pulp and paper industry also can be a useful tool, not only for patents and product development, but also to improve troubleshooting and customer support.

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