Unbleached Hardwood Research Articles

Model systems for clarifying the effects of surface modification on fibre–fibre joint strength and paper mechanical properties

The growing demand for sustainable products has spurred research into renewable materials, with cellulose-based materials emerging as prominent candidates due to their exceptional properties, abundance, and wide-ranging applications. In this context, there is a need to develop a better fundamental understanding of cellulose interactions such that we can continue to design and improve sustainable materials. Individual interactions can be difficult to assess in bulk fibre-based materials and therefore cellulose model materials have become indispensable tools for researchers as they can facilitate the study of cellulose interactions at a molecular level enabling the design of sustainable materials with enhanced properties.This study presents a new methodology for studying the effects of surface treatments on the individual fibre–fibre joint strength using wet-spun cellulose nanofiber (CNF) filaments as model materials. The Layer-by-Layer assembly technique is used to modify the surface chemistry of the model materials as well as bleached and unbleached hardwood Kraft fibres, demonstrating its potential to enhance adhesive properties and overall mechanical performance of papers made from these fibres. The study further explores the impact of increasing network density through wet-pressing during paper preparation, showcasing a comprehensive approach to molecularly tailor fibre-based materials to achieve superior mechanical properties. The proposed methodology provides a time-efficient evaluation of chemical additives in paper preparation.

Ergosterol and Its Metabolites Induce Ligninolytic Activity in the Lignin-Degrading Fungus Phanerochaete sordida YK-624.

White-rot fungi are the most important group of lignin biodegraders. Phanerochaete sordida YK-624 has higher ligninolytic activity than that of model white-rot fungi. However, the underlying mechanism responsible for lignin degradation by white-rot fungi remains unknown, and the induced compounds isolated from white-rot fungi for lignin degradation have never been studied. In the present study, we tried to screen ligninolytic-inducing compounds produced by P. sordida YK-624. After large-scale incubation of P. sordida YK-624, the culture and mycelium were separated by filtration. After the separation and purification, purified compounds were analyzed by high-resolution electrospray ionization mass spectrometry and nuclear magnetic resonance. The sterilized unbleached hardwood kraft pulp was used for the initial evaluation of ligninolytic activity. Ergosterol was isolated and identified and it induced the lignin-degrading activity of this fungus. Moreover, we investigated ergosterol metabolites from P. sordida YK-624, and the ergosterol metabolites ergosta-4,7,22-triene-3,6-dione and ergosta-4,6,8(14),22-tetraen-3-one were identified and then chemically synthesized. These compounds significantly improved the lignin-degrading activity of the fungus. This is the first report on the ligninolytic-inducing compounds produced by white-rot fungi.

Sustainable high-yield lignocellulosic fibers and modification technologies educing softness and strength for tissues and hygiene products for global health

Unbleached hardwood kraft pulp was treated with a non-ionic surfactant to decrease the concentration of a hydration shell by dislodging hard-to-remove water through a targeted reduction in surface tension. Energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry techniques were used to investigate and evaluate these fiber-surfactant interactions. Scanning electron microscopeimages were taken to observe the change in the morphology from the surfactant treatment. The surface tension was measured by using pendant drop tests, which reduced from 71.46 mN/m to ∼ 49–51 mN/m for different pretreatment techniques and hence, reduced the pulling force exerted by the liquid bridge water on the fibers by 28–31%. This consequently led to reduced fiber collapse, and the surfactant-treated fibers showed higher bulk and softness without a concomitant sacrifice of mechanical properties. The scanning electron microscopeimages confirmed a more cylindrical fiber structure and showed an unaffected fiber–fiber interaction because of which the tensile strength was not compromised with the increase of bulk. The surfactant-treated fibers showed better recovery or spring back, i.e. a return to their original form after compression relative to the untreated fibers. Therefore, it was possible to make tissue papers with higher bulk, softer hand-feel, and a higher absorbing capacity, without reducing the tensile strength by simple and green processes involving chemical and mechanical modifications.

Nanofibrillated Cellulose Extracted by Enzymatic Hydrolysis Followed by Mechanical Fibrillation

ABSTRACT In a comparison with certain one-step processes, enzymatic hydrolysis followed by mechanical defibrillation may avoid the use of nonrenewable resources, mitigate the generation of toxic effluents, and reduce the energy consumption related to a single mechanical process. In the present study, bleached and unbleached hardwood pulps were employed as raw materials for producing nanofibrillated cellulose (CNF) using a two-step process, in which a cellulase enzyme was inoculated to act as a pretreatment for a subsequent grinding process. The obtained CNF reached high crystallinity indexes (above 70%) and high thermal stability (degradation onset temperatures around 200°C). Increases in enzyme concentration yielded decreases in diameter and increases in both thermal stability and crystallinity index. These findings indicated that the enzymatic hydrolysis used as a pretreatment to a further grinding process can allow the production of valuable CNF-based products.

Biocatalysis of Industrial Kraft Pulps: Similarities and Differences between Hardwood and Softwood Pulps in Hydrolysis by Enzyme Complex of Penicillium verruculosum

Kraft pulp enzymatic hydrolysis is a promising method of woody biomass bioconversion. The influence of composition and structure of kraft fibers on their hydrolysis efficiency was evaluated while using four substrates, unbleached hardwood pulp (UHP), unbleached softwood pulp (USP), bleached hardwood pulp (BHP), and bleached softwood pulp (BSP). Hydrolysis was carried out with Penicillium verruculosum enzyme complex at a dosage of 10 filter paper units (FPU)/g pulp. The changes in fiber morphology and structure were visualized while using optical and electron microscopy. Fiber cutting and swelling and quick xylan destruction were the main processes at the beginning of hydrolysis. The negative effect of lignin content was more pronounced for USP. Drying decreased the sugar yield of dissolved hydrolysis products for all kraft pulps. Fiber morphology, different xylan and mannan content, and hemicelluloses localization in kraft fibers deeply affected the hydrolyzability of bleached pulps. The introduction of additional xylobiase, mannanase, and cellobiohydrolase activities to enzyme mixture will further improve the hydrolysis of bleached pulps. A high efficiency of never-dried bleached pulp bioconversion was shown. At 10% substrate concentration, hydrolysates with more than 50 g/L sugar concentration were obtained. The bioconversion of never-dried BHP and BSP could be integrated into working kraft pulp mills.

Refining Mechanism of Combined Refining Plates with Different Bar Angles

The refining plate is a key component of the disc refiner, which plays an important role in improving fiber morphology and its properties during pulp refining. In this study, the mixed pulps of bleached softwood and unbleached hardwood pulp was refined by the combined refining plates with different bar angles. Beating degree, fiber length, fiber width, fiber length distribution and fiber fibrillation were analyzed to explore the influences of different combinations of refining plates on the improvement of pulp and fiber properties. The results indicated that the combined refining plate of 0° and 5° had the more significant changes in fiber length distribution, beating degree and fiber morphology than that of the combined refining plate of 0° and 0° as refining proceeded. The influences of the combined refining plate of 0° and 39° on the fiber length components, beating degree and fiber morphology were weakest compared to the remaining two. This study is of positive significance for the design and the selection of refining plates.

Miscanthus × giganteus stalks as a potential non-wood raw material for the pulp and paper industry. Influence of pulping and beating conditions on the fibre and paper properties

This manuscript describes the relationship between the method of processing (soda and kraft pulping) of Miscanthus × giganteus stalks into unbleached pulps of different residual lignin content (1.5–8.7 wt. %) and their beatability and properties. It was found that Miscanthus soda pulps with low residual lignin content need to be beaten for longer to achieve the same level of SR-freeness compared with kraft pulps. In order to obtain higher values of mechanical properties of handsheets prepared from soda and kraft Miscanthus pulps they have to be beaten to SR-freeness higher than 35 °SR. The mechanical properties of Miscanthus kraft pulps determined in static conditions (e.g. tensile strength) are better than those of soda pulps. A decrease in the kappa number of Miscanthus soda pulps below 20, lowers these properties distinctly. The tear index of Miscanthus pulps is good, while Gurley air-resistance is comparable with birch kraft pulp. Soda Miscanthus pulps having a higher content of residual lignin and kraft Miscanthus pulps of low and high residual lignin contents, due to the similarity of their properties with unbleached hardwood kraft pulps (birch, poplar, hornbeam), could probably replace the latter pulps in the production of packaging papers (e.g. sack paper).

Influence of pulp bleaching and compatibilizer selection on performance of pulp fiber reinforced PLA biocomposites

ABSTRACTThis article focuses on the effect of pulp bleaching and emerging commercial compatibilizers on physical performance of pulp fiber reinforced poly(lactic acid) (PLA) biocomposites. Industrially bleached and unbleached hardwood kraft pulp fibers are treated with several additive types, and compounded with PLA to fiber content of 30 wt %. After injection molding, the produced biocomposites are evaluated by their mechanical performance and fiber–matrix adhesion. For selected materials, fiber surface and fiber properties are reflected to composite performance by analyzing the compositions, dimensions, and lignin coverage of original fibers, as well as fiber dispersion and dimensions after melt processing. As a conclusion, unbleached kraft pulp fibers provide significant improvement in physical properties of PLA/pulp fiber composites. Of the screened compatibilizers, epoxidated linseed oil has a clear positive effect on performance when bleached kraft pulp fibers are used. The improvements correspond to enhanced fiber–matrix adhesion and differences in remaining fiber length distributions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47955.

Micro-Chemical and Spectroscopic Study of Component Materials in 18th and 19th Century Sacred Books

AbstractThe Cyrillic books Menology for May (1705), The Bible (1822) and Mirror (1816) were consigned for conservation to the Conservation Laboratory at the National Library in Skopje. The first two books were printed in Moscow, while the third book was issued in Vienna, although it originates from the territory of the former Ottoman Empire, present-day Republic of Macedonia. In order to design a conservation protocol, papers and inks used in the books were characterized and their condition was assessed. Micro-chemical tests were used in order to identify the type of paper fibres and materials added to the paper pulp. FTIR was applied to confirm the findings for the sizing and fillers found in the paper support. Inorganic pigments were analysed by micro-Raman spectroscopy. The original paper in the Russian books was made of rags with less than 5 % lignin content present, whereas the paper in Mirror was made of raw and unbleached hardwood. Distinct types of sizing have been identified: gelatine/alum in Menology for May and Mirror and gelatine/rosin in The Bible. The pigments identified are lamp black, vermilion, Prussian blue and calcite. The study elucidates which internal and external factors could cause further decay of the books and will help in making informed decisions concerning the further preservation of the objects.

Hot water treatment of hardwood kraft pulp produces high-purity cellulose and polymeric xylan

Hot water treatments (HWTs) of unbleached hardwood kraft pulps under various process conditions were conducted to extract the xylan and thus produce a high-purity cellulosic pulp that could be used in dissolving applications. Increasing treatment temperature up to 240 °C increased the removal of xylan over the degradation of cellulose in birch pulp, but this effect was minor at higher temperatures. Addition of acetic acid lowered the treatment intensity needed to reach a certain degree of pulp purity, but did not improve the selectivity in xylan removal compared to water-only experiments. HWTs of eucalyptus pulp, with lower xylan content than birch pulp, produced cellulosic fibers with higher degree of polymerization at a given pulp purity. Under selected operational conditions (240 °C for 10 min) in a flow-through reactor, and provided that the HWTs were applied before bleaching, the chemical and macromolecular properties of water-treated pulps may be suitable for their conversion to viscose. Moreover, at high flow rates (200–400 mL/min), the extracted xylan was recovered from the aqueous hydrolysate in high yield and with relatively high molar mass (~10 kDa). Based on the results of this study, HWTs of hardwood kraft pulp are suggested as a simple and green method to produce high-purity cellulose and polymeric xylan for high value-added applications.

Accumulation of sugar from pulp and xylitol from xylose by pyruvate decarboxylase-negative white-rot fungus Phlebia sp. MG-60

Phlebia sp. MG-60 is a white-rot fungus that produces ethanol with high efficiency from lignocellulosic biomass without additional enzymes. Through engineering of this powerful metabolic pathway for fermentation in Phlebia sp. MG-60, chemical compounds other than ethanol could be produced. Here, we demonstrate sugar accumulation from unbleached hardwood kraft pulp and conversion of xylose to xylitol by pyruvate decarboxylase (pdc)-negative Phlebia sp. MG-60. We isolated Phlebia sp. strain MG-60-P2 from protoplasts to unify the protoplast phenotypes of the regenerated strains. Homologous recombination achieved a stable pdc-knockout line, designated KO77. The KO77 line produced traces of ethanol, but accumulated xylitol from xylose or glucose from unbleached hardwood kraft pulp. These metabolic changes in the pdc-knockout strain reflect the potential of metabolic engineering in Phlebia sp. MG-60 for direct production of chemical compounds from lignocellulosic biomass.

Direct Fungal Production of Ethanol from High-Solids Pulps by the Ethanol-fermenting White-rot Fungus Phlebia sp. MG-60

A white-rot fungus, Phlebia sp. MG-60, was applied to the fermentation of high-solid loadings of unbleached hardwood kraft pulp (UHKP) without the addition of commercial cellulase. From 4.7% UHKP, 19.6 g L-1 ethanol was produced, equivalent to 61.7% of the theoretical maximum. The highest ethanol concentration (25.9 g L-1, or 46.7% of the theoretical maximum) was observed in the culture containing 9.1% UHKP. The highest filter paper activity (FPase) was observed in the culture containing 4.7% UHKP, while the production of FPase in the 16.5% UHKP culture was very low. Temporarily removing the silicone plug from Erlenmeyer flasks, which relieved the pressure and allowed a small amount of aeration, improved the yield of ethanol produced from the 9.1% UHKP, which reached as high as 37.3 g L-1. These results indicated that production of cellulase and ensuing saccharification and fermentation by Phlebia sp. MG-60 is affected by water content and benefits from a small amount of aeration.

All-cellulose composites from unbleached hardwood kraft pulp reinforced with nanofibrillated cellulose

In the present work, nanofibrillated cellulose (NFC) from bleached eucalyptus pulp was prepared, characterized and used as reinforcement in an unbleached eucalyptus fiber matrix. First, the NFC was fabricated through TEMPO-mediated oxidation and characterized for the degree of polymerization, water retention value, cationic demand and carboxyl content. Intrinsic mechanical properties were also calculated by applying the rule of mixtures, which determines the coupling (f c) and efficiency factor (η e) of cellulose nanofibrils within the matrix. The results showed that the average intrinsic tensile strength and Young’s modulus of NFC are estimated to be 6,919 MPa and 161 GPa, respectively. After characterization, the NFC was used as reinforcement in the preparation of biocomposites in the form of paper handsheets, which were physically and mechanically analyzed. The presence of NFC induced an increase in the density of biocomposites and significant enhancement of the mechanical properties as well as an important reduction in porosity. Finally, f c and η e were determined from the mean intrinsic properties.

Direct ethanol production from cellulosic materials by the hypersaline-tolerant white-rot fungus Phlebia sp. MG-60

White-rot fungus Phlebia sp. MG-60 was identified as a good producer of ethanol from several cellulosic materials containing lignin. When this fungus was cultured with 20g/L unbleached hardwood kraft pulp (UHKP), 8.4g/L ethanol was produced after 168h of incubation giving yields of ethanol of 0.42g/g UHKP, 71.8% of the theoretical maximum. When this fungus was cultured with waste newspaper, 4.2g/L ethanol was produced after 216h of incubation giving yields of ethanol of 0.20g/g newspaper, 51.1% of the theoretical maximum. Glucose, mannose, galactose, fructose and xylose were completely assimilated by Phlebia sp. MG-60 with ethanol yields of 0.44, 0.41, 0.40, 0.41 and 0.33g/g of sugar respectively. These results indicated that Phlebia sp. MG-60 was a good candidate for bioethanol production from cellulosic materials.

Novel blend of biorenewable wet-end paper agents

Recent studies have shown potential for a designed biorefinery product, polylactic acid (PLA), to increase the strength-to-weight ratio of paper produced from conventional kraft pulp and kraft pulp made from hot-water extracted hardwoods (biorefinery pulp). These results indicated that, after surface-treatment with 2 % PLA (per ovendry [o.d.] fiber basis), paper made from sugar maple biorefinery pulp could be equivalent to or even greater in strength than paper made from sugar maple conventional kraft pulp, while retaining its higher bulk. In the current study, we present the results of reinforcement of the pulps with PLA applied in the wet-end in combination with a known environmentally friendly dry strength agent, cationic starch. The preliminary results obtained with amylopectin-based starch of relatively high nitrogen content (starch B) were encouraging since strength, including wet strength and stretch, of paper reinforced with a blend of 0.5% starch B and 0.5% PLA was higher than strength of paper reinforced with 1% starch B. Moreover, based on the compatible strengths of paper reinforced with 0.6 % PLA-starch B blend (1/5) and of paper reinforced with 1% starch B, we hypothesize that there is a synergistic effect of PLA and starch B on tensile strength of paper. The hypothesis was tested using pulps of different lignin content (Norway spruce thermomechanical pulp [TMP], hardwood unbleached kraft pulp, and softwood bleached kraft pulp). Tensile strength increased for papers made from these pulps. The effect was pronounced in the case of lignin-rich pulps, where tensile strength in the presence of 0.6% PLA-starch blend (1/5) exceeded that in the presence of 1% starch B. This result is in accordance with a higher attraction of lignin-rich fibers to hydrophobic PLA and indicates a promising approach in increasing strength-to-weight ratio of paper made from relatively hydrophobic pulps like TMP or unbleached kraft pulp. Accordingly, paper made from unbleached hardwood kraft pulp with 0.6% PLA-starch B blend (1/5) exhibited an improved resistance to water penetration.

Characteristics of residual lignin from sulfate pulp

The residual lignin from samples of unbleached and bleached hardwood sulfate pulp was isolated by an aqueous acetic acid solution in the presence of zinc chloride. The resulting lignin was analyzed by 13C NMR and infrared Fourier spectroscopy, potentiometric titration, and cryoscopy. Physicochemical and spectral characteristics provide some insight into the structure of the residual lignin from sulfate pulp.

Binding affinities of different metal ions to unbleached hardwood kraft pulp

No abstract available

A comparative study of energy consumption and physical properties of microfibrillated cellulose produced by different processing methods

Microfibrillated celluloses (MFCs) with diameters predominantly in the range of 10–100 nm liberated from larger plant-based fibers have garnered much attention for the use in composites, coatings, and films due to large specific surface areas, renewability, and unique mechanical properties. Energy consumption during production is an important aspect in the determination of the “green” nature of these MFC-based materials. Bleached and unbleached hardwood pulp samples were processed by homogenization, microfluidization, and micro-grinding, to determine the effect of processing on microfibril and film properties, relative to energy consumption. Processing with these different methods affected the specific surface area of the MFCs, and the film characteristics such as opacity, roughness, density, water interaction properties, and tensile properties. Apparent film densities were approximately 900 kg/m3 for all samples and the specific surface area of the processed materials ranged from approximately 30 to 70 m2/g for bleached hardwood and 50 to 110 m2/g for unbleached hardwood. The microfluidizer resulted in films with higher tensile indices than both micro-grinding and homogenization (148 Nm/g vs. 105 Nm/g and 109 Nm/g, respectively for unbleached hardwood). Microfluidization and micro-grinding resulted in films with higher toughness values than homogenization and required less energy to obtain these properties, offering promise for producing MFC materials with lower energy input. It was also determined that a refining pretreatment required for microfluidization or homogenization can be reduced or eliminated when producing MFCs with the micro-grinder. A summary of the fiber and mechanical energy costs for different fibers and processing conditions with economic potential is presented.

On-line predictions of the aspen fibre and birch bark content in unbleached hardwood pulp, using NIR spectroscopy and multivariate data analysis

An on-line fibre-based near-infrared (NIR) spectrometric analyser was adapted for on-site process analysis at an integrated paperboard mill. The analyser uses multivariate techniques for the quantitative predication of the aspen fibre (aspen) and the birch bark contents of sheets of unbleached hardwood pulp. The NIR analyser is a prototype constructed from standard NIR components. The spectroscopic data was processed by using principal component analysis (PCA) and partial least square (PLS) regression. Three sample sets were collected from three experimental designs, each composed of known pulp contents of birch, aspen and birch bark. Sets 1 and 2 were used for model calibration and set 3 was used to validate the models. The PLS model that produced the best predictions gave an error of prediction (RMSEP) of 13% for aspen and less than 2% for birch bark. Eight components resulted in an R 2 X of 99.3%, R 2 Y of 99.6%, and Q 2 of 95.3%. For additional validation of aspen, three unbleached hardwood samples from the mill's production were calculated to lie between − 7% and + 6%, regarding to the PLS model. When vessel cells were counted under a light microscope a value for the aspen content of 4.7% was obtained. The predictive models evaluated were suitable for quality assessments rather than quantitative determination.

Nanoindentation of single pulp fibre cell walls

Unrefined chemical pulps of bleached and unbleached softwood (Scots pine, Pinus sylvestris) and hardwood (Eucalyptus, Eucalyptus globulus) were subjected to indentation tests using a nanoindenter equipped with an AFM scanner. Tests on unbleached pulps revealed no difference in hardness values between softwood and hardwood, but bleaching treatment decreased the hardness values of both pulps. Indentation modulus of 12 GPa was observed for unbleached softwood pulps, which is 25% higher than unbleached hardwood pulps. Bleaching treatment again decreased the indentation modulus of the softwood pulps, whereas it slightly increased the indentation modulus of the hardwood pulps. After bleaching and drying processes, only negligible difference was observed in cell wall mechanical properties (hardness and indentation modulus) between hardwood and softwood pulps. This study is based on latewood pulp fibres.