WOOD RESEARCH Volume 67, Number 2, 2022
Halaj Michal, Boháček Štefan, Pažitný Andrej, Monika Stankovská, and Albert Russ

Methods of preparation of nanofibrillated cellulose for special filter papers with effective air filtration. Short notes

Nanofibrillated cellulose was prepared from distillery refuse based on maize starch using the extraction with NaOH and HCl involving centrifugation. SEM images of bleached kraft pulp with/without the addition of nanofibrillated cellulose were compared. The results showed that the application of nanofibrillated cellulose caused a visible reduction in the surface porosity. Conversely, mixing of the pulp with the nanofibrillated cellulose resulted in large pores among the fibres. The effect of the cationic retention aid on porosity was not significant, observed in the fines retention. A minimal difference in porosity was found among of fine and coarse fibres. When lyophilisation as drying method was used it yielded nanofibrillated cellulose with a size in the range of approximately 100 to 150 nm.

WOOD RESEARCH Volume 61, Number 6, 2016
Juraj Gigac, Monika Stankovská, and Pažitný Andrej

Influence of the coating formulations and base papers on inkjet printability

At the coating were used two substrates, commercial base paper and base paper produced in pilot experimental paper machine. The printing quality varied at both base papers. The coating colours contain commercial silica and precipitated calcium carbonate pigments. As a binder was used polyvinyl alcohol and cationic starch combined with high-cationic polymer SMAI 1000. Colour gamut significantly improved when the inkjet ink contact angle decreased below 14° independently of the base paper. The order of coating colours effect on the base papers was similar. Application of silica pigment in the coating colour provided papers with the largest inkjet ink wetting, the best colour gamut area, print sharpness and smoothness. By using of polyvinyl alcohol, a high colour gamut area was reached but it resulted in a markedly low print sharpness in comparison with cationic starch. Coating of base paper produced in pilot experimental paper machine introduces papers with higher colour gamut and also print sharpness.

WOOD RESEARCH Volume 61, Number 5, 2016
Zuzana Brezániová, Mária Fišerová, Monika Stankovská, Juraj Gigac, Elena Opálená, and Jarmila Puškelová

Effect of prehydrolysis on enzymatic hydrolysis of two-stage pretreated wheat straw

The effect of water prehydrolysis conditions, which was used as the first stage of wheat straw pretreatment, on the composition of filtrates was analysed. Many of the substances that are present in the prehydrolysis filtrates are broadly used and thus they contribute to improvements in the efficiency of bioethanol production. Prehydrolysis was carried out at temperatures of 140, 160 and 180°C and times of 30, 60 and 120 min. Xylose and its oligomers were the most represented in prehydrolysis filtrates, their yields increased up to 12.1 % with increasing weight of wheat straw removed up to 28.6 %. Besides xylose and glucose, acetic acid, formic acid and the phenolic compounds were also present in the prehydrolysis filtrates. At 160 and 180°C, levulinic acid and furfural and hydroxymethylfurfural, respectively, were also present. The solid fractions of wheat straw were subjected to steam explosion under the same conditions at 200°C for 2 min. Two-stage pretreated wheat straw was subsequently enzymatically hydrolysed. The conditions of water prehydrolysis combined with steam explosion pretreatment had a significant effect on the results of enzymatic hydrolysis of wheat straw. The conversion of cellulose increased with increasing prehydrolysis temperature and time from 64.8 to 91.7 %. Similar results were observed for the conversion of xylan from 73.7 to 92.4 %. With increasing of prehydrolysis temperature and time, the amount of inhibitors in hydrolysates decreased. The recommended conditions for water prehydrolysis at two-stage pretreatment of wheat straw correspond to temperature of 160°C and time of 60 min.

WOOD RESEARCH Volume 61, Number 2, 2016
Juraj Gigac, Monika Stankovská, Elena Opálená, and Pažitný Andrej

The effect of pigments and binders on inkjet print quality

The effect of silica and calcium carbonate pigments, polyvinyl alcohol and cationic starch binders combined with high-cationic polymers on physical-chemical and printing properties of coated papers were studied. The best printing properties were obtained with coating colour based on silica. Colour gamut significantly improved when the inkjet ink contact angle decreased below 15°. The water fastness was influenced with specific charge density of coating colour. Application of silica provided papers with the largest inkjet ink wetting, colour gamut area, print sharpness and surface roughness. By using of polyvinyl alcohol a high colour gamut area was reached but it resulted in a low print sharpness in comparison with cationic starch. High-cationic polymer poly-DADMAC showed a more significant effect on all printing properties of coated paper in comparison with SMAI 1000. The final inkjet print quality depends on structural and chemical properties of coating.

WOOD RESEARCH Volume 62, Number 6, 2017
Juraj Gigac, Mária Fišerová, Monika Stankovská, and Pažitný Andrej

Enzymatic hydrolysis of extruded wheat straw with addition of sodium hydroxide and calcium hydroxide

Extrusion pretreatment of wheat straw in a single screw extruder was investigated in terms of effectiveness of enzymatic hydrolysis and the formation of fermentation inhibitors. The effect of sodium hydroxide in extrusion pretreatment was compared with calcium hydroxide. The accessibility of wheat straw structure to hydrolytic enzymes increased with NaOH and Ca(OH)2 loadings, whereby more with the addition of NaOH. With 6% w/w of NaOH loading, the conversion of polysaccharides was 76.1% and with the same Ca(OH)2 loading it was 47.3%. The conversion of polysaccharides with 12% w/w of Ca(OH)2 loading was 66.6%. Without alkali in extrusion pretreatment, the conversion of polysaccharides was only 36.7%. The polysaccharides conversion of original extruded wheat straw was about 1.5 to 3.3% higher in comparison to washed extruded wheat straw. Fermentation inhibitors such as lignin, acetic and formic acid are primarily formed in the presence of alkali during extrusion pretreatment, most of which was lignin. Alkaline extrusion is a suitable method for pretreatment of lignocellulosic biomass.

WOOD RESEARCH Volume 62, Number 4, 2017
Juraj Gigac, Monika Stankovská, and Mária Fišerová

Comparison of capillary flow porometry and mercury intrusion porosimetry in determination pore size distribution of papers

Capillary flow porometry and mercury intrusion porosimetry achieved a good agreement in determining the pore size distribution in papers for the top layers of corrugated board. Differences in the papers composition as well as structure can be easily detected by changes in the measured parameters, thus allowing a better understanding their behaviour at processing and use. Water absorption is mainly dependent on the diameter of the large pore and to a lesser extent from the diameter of medium pore, surface free energy of paper and the swelling ability of recycled and bleached pulp fibres.

WOOD RESEARCH Volume 63, Number 5, 2018
Juraj Gigac, Monika Stankovská, and Mária Fišerová

Improvement of oil and grease resistance of cellulosic materials

The oil and grease resistance of paper after surface sizing with aqueous dispersions composed of film forming polymers, their mixtures with fluorinated polymer or fluorinated polymer and silver nanoparticles was compared. The oil and grease resistance of paper was regulated by changing the composition and intake of aqueous dispersions and paper grade, and it was evaluated by the content of fine surface pores, contact angle, oil absorptiveness, grease resistance, oil repellency on the inclined surface and oil penetration time. The aqueous dispersions were applied on one side and on both sides of paper surface in the size press. The film forming polymer has created a physical barrier against oil and grease, while combination with the fluorinated polymer developed a physical and chemical barrier. The papers sized with aqueous dispersions containing a mixture of film forming and fluorinated polymer with the addition of silver nanoparticles, achieved high oil and grease resistance even with lower consumption of the fluorinated polymer, and also achieved an antimicrobial surface. The more porous paper has achieved the required oil and grease resistance at higher polymers intake.

WOOD RESEARCH Volume 63, Number 4, 2018
Mária Fišerová, Elena Opálená, Juraj Gigac, and Monika Stankovská

Oxidative and reductive bleaching of deinked pulp

Deinked pulps for hygienic paper production were bleached with hydrogen peroxide and sodium dithionite in single and two-stage bleaching. The brightness gain of high brightness deinked pulp in the peroxide stage was 5.7% ISO and of low brightness 4.4% ISO. In sodium dithionite stage, the brightness gain of high brightness deinked pulp was 4.0% ISO and of low brightness deinked pulp 3.8% ISO. The two-stage oxidative-reductive bleaching sequence resulted in an increase of brightness by 9.7% ISO for high brightness deinked pulp and by 9.1% ISO for low brightness deinked pulp. Brightness gain in the two-stage reductive-oxidative bleaching sequence was 6.7% ISO for high brightness deinked pulp and 5.6% ISO for low brightness deinked pulp. The coordinate b* value and yellowness of deinked pulps decreased in sodium dithionite bleaching stage more than in hydrogen peroxide stage. The two-stage oxidative-reductive bleaching sequence is more preferred than reductive-oxidative sequence regardless of the fibre composition. The tensile index and the tensile energy absorption index of deinked pulps slightly decreased after single-stage and two-stage bleaching sequences, their reduction in the peroxide stage was greater than in the dithionite stage. The fibre strength and fibre length characteristics of deinked pulps decreased after bleaching, while fibre bonding ability increased. The water absorption and bulk softness increased after bleaching, the increase was higher after peroxide stage than dithionite stage.

WOOD RESEARCH Volume 65, Number 4, 2020
Pažitný Andrej, Albert Russ, Boháček Štefan, Monika Stankovská, Vladimír Ihnát, and Štefan Šutý

Effect of steam explosion on enzymatic hydrolysis of various parts of poplar tree

The effect of steam explosion on enzymatic hydrolysis of various parts of poplar tree (heartwood, sapwood and 1-year coppice) was investigated. These parts were milled, the obtained sawdust was chemically analysed and then steam explosion of 0.7 mm poplar particles at temperature of 205°C was performed. Concentration of monomers obtained after enzymatic hydrolysis was considered as the main indicator for cellulose accessibility. Analysis of high performance liquid chromatography showed that non-treated poplar sawdust does not enable sufficient cellulose accessibility, while excessively high temperature and rapid pressure release resulted in substantial breakdown of polysaccharides and lignin and formation of inhibitors. The concentration of monomers increased gradually in the order of coppice, sapwood and heartwood. Steam exploded heartwood gave the maximum monosaccharides concentration of 90.0 g.L-1 after 72 hours of enzymatic hydrolysis. However, glucose concentration culminated after 48 hours of this hydrolysis. This corresponds to the best holocellulose accessibility for enzymes. The maximum concentration of inhibitors (9.3 g.L-1) was determined for poplar coppice after 24 hours of enzymatic hydrolysis.

WOOD RESEARCH Volume 65, Number 3, 2020
Monika Stankovská, Mária Fišerová, Juraj Gigac, and Elena Opálená

Blending impact of hardwood pulps with softwood pulp on tissue paper properties

The influence of proportions of bleached birch, eucalyptus, beech kraft pulps as well as the bleached aspen chemi-thermomechanical pulp (BCTMP) in the mixture with bleached pine kraft pulp on tissue paper properties was compared. Increase of bleached beech kraft pulp and aspen BCTMP proportion in a mixture with bleached pine kraft pulp leads to significant rise of porosity ε as well as bulk. The water absorption after immersion increased significantly with increase of aspen BCTMP content in the mixture while other hardwood pulps in the mixture had only moderate impact. Increasing of bleached beech and eucalyptus kraft pulps content in the mixture continually increased initial water absorption. As a result of blending of bleached birch kraft pulp with bleached pine kraft pulp, bulk softness improved and the tensile index increased slightly. The increased content of bleached birch and beech kraft pulp in the mixture increased the brightness while the addition of aspen BCTMP and bleached eucalyptus kraft pulp increased of coordinate b* value. Mixed pulps with properties suitable for different types of hygienic products were selected.

WOOD RESEARCH Volume 65, Number 1, 2020
Juraj Gigac, Mária Fišerová, Maroš Kováč, and Monika Stankovská

Paper substrates for inkjet printing of uhf rfid antennas

Conventional papers are not suitable for printed electronics because they have a rougher surface than the plastic film commonly used for electronics printing. The paper surfaces were modified by coating and calendering processes to reduce surface roughness and electrical resistance of inkjet-printed UHF RFID antennas. The composition of coatings, the main component which included aluminum oxide pigment, had an influence on the surface roughness, the surface pore content and the electrical resistance of the inkjet-printed UHF RFID antennas on coated papers. Papers coated with a mixture containing 25% polyvinyl alcohol binder in combination with the cationic polymer PDADMAC without glyoxal crosslinker had the lowest surface roughnesses and the lowest electrical resistances of the inkjet-printed antennas. As the coating basis weight increased, the electrical resistance of the antennas increased. Reduction of the electrical resistance of the antennas was achieved after calendering coated paper. The design of the antennas had a significant effect on their electrical resistance, which increased with the length of the antenna.

WOOD RESEARCH Volume 64, Number 3, 2019
Pažitný Andrej, Albert Russ, Boháček Štefan, Monika Stankovská, Vladimír Ihnát, and Štefan Šutý

Various lignocellulosic raw materials pretreatment processes utilizable for increasing holocellulose accessibility for hydrolytic enzymes Part II. Effect of steam explosion temperature on beech enzymatic hydrolysis

Beech wood is one of the most abundant species and the most harvested hardwood in Slovak Republic. The structure and chemical composition predetermines beech wood for the second generation bioethanol production. Steam explosion of beech wood from industrial treatment was investigated as a suitable pretreatment method. The effect of steam explosion temperature on beech sawdust enzymatic hydrolysis was investigated. Optimum steam explosion temperature at around 180°C was determined based on concentration of monosaccharides in hydrolysates and concentration of enzymatic hydrolysis inhibitors such as formic acid and acetic acid from beech sawdust. This corresponds to creating conditions resulting in good disintegration to the lignocellulosic structure which leads to increased cellulose accessibility. Non-treated beech sawdust does not enable sufficient cellulose accessibility while excessively high temperature results in significant breakdown of monosaccharides and lignin and formation of inhibitors. The concentration of inhibitors was also determined for each studied steam explosion temperature. Based on steam explosion of beech sawdust, the effect of severity factors was investigated to find the optimum conditions of steam explosion pretreatment on cellulose and xylan recovery of beech wood. The obtained optimum steam explosion temperature corresponds to severity factor R0 = 3.36 (180°C, 10 minutes).

WOOD RESEARCH Volume 64, Number 2, 2019
Monika Stankovská, Juraj Gigac, Mária Fišerová, and Elena Opálená

Relationship between structural parameters and water absorption of bleached softwood and hardwood kraft pulps

The influence of porosity, relative bonded area and air permeability on water absorption of unbeaten and beaten bleached kraft pulps from different wood species used for tissue paper production was investigated. The water absorption was determined by four different methods such as absorption of water after immersion, initial water absorption, water absorption capacity and saturation rate with water. Linear dependences between water absorption parameters and the structural parameters of individual pulps as well as all tested pulps were obtained. The correlation coefficients obtained within individual bleached kraft pulps were from 0.95 to 1.00 and within the whole group of pulps were from 0.86 to 0.98. Relative bonded area and air permeability were found to be the most suitable parameters for predicting of initial water absorption and saturation rate with water.

WOOD RESEARCH Volume 64, Number 1, 2019
Pažitný Andrej, Albert Russ, Boháček Štefan, Monika Stankovská, and Štefan Šutý

Various lignocellulosic raw materials pretreatment processes utilizable for increasing holocellulose accessibility for hydrolytic enzymes Part I: Evaluation of wheat straw pretreatment processes

New requirements for the biofuels industry force individual enterprises to develop various procedures for newly selected substrates pretreatments that could be applicable in processing of large quantities of raw materials. Even greater pressures are on second-generation biofuels producers justified by selection of waste lignocellulosic substrates and methods of substrate processing. Among the most suitable lignocellulosic raw materials in Slovak Republic (SR) for 2G bioethanol production is wheat straw. This raw material (Senec region, SR) for enzymatic hydrolysis was pretreated by dry milling (Brabender), cyclic freezing and thawing, wet milling (Sprout Waldron), two-step process of steam explosion at 180°C and extrusion at 145°C and one-step process of steam explosion at different temperatures. Wheat straw holocellulose accessibility was tested by adsorption of three commercially available dyes (Pylam Products Company, Inc., USA). Absorptivity coefficient of each dye at its maximum wavelength was determined from individual calibration curves of dyes and their values resulted ranging from 13.78 to 19.52 dm3.g-1.cm-1. The absorption of solution was measured and concentration of residual dye was calculated at given wavelength. The accessibility of holocellulose contained in wheat straw pretreated by steam explosion was controlled by SEM (scanning electron microscope) in correlation with the ratio of adsorbed dyes according to the modified Simons’ method.

WOOD RESEARCH Volume 66, Number 3, 2021
Monika Stankovská, Mária Fišerová, Juraj Gigac, and Elena Opálená

Effect of addition of deinked pulp to bleached kraft pulp on tissue paper properties

The influence of addition of deinked pulps with low and high brightness to bleached eucalyptus and pine kraft pulps on functional tissue paper properties was studied. Deinked pulps with low and high brightness had some different functional properties. Deinked pulp with high brightness has higher bulk, porosity, water absorption after immersion, initial water absorption, bulk softness as well as brightness. On the contrary, the difference in relative bonded area and porosity e between deinked pulps with low and high brightness was moderate. The mixed pulps laboratory pulp sheets from bleached eucalyptus kraft pulp or bleached pine kraft pulp with addition of 20, 40 and 80% of deinked pulp with low brightness or deinked pulp with high brightness were prepared. The addition of the deinked pulp with high or low brightness to bleached kraft pulp leads to increasing of bulk, bulk softness as well as high water absorption after immersion and initial water absorption. The tensile index rapidly decreased by the addition of deinked pulps with high brightness to bleached eucalyptus and pine kraft pulps. Similarly, the addition of deinked pulp with low brightness to bleached pine kraft pulp led to rapid decreasing of tensile index. On contrary, with the addition of deinked pulp with low brightness to eucalyptus kraft pulp, the decreasing of tensile index was less pronounced. Mixed pulp from bleached eucalyptus kraft pulp with a small content of deinked pulp with low brightness with functional properties suitable for production of tissue papers was found as optimal.