Chemithermomechanical Pulp Fibers Research Articles

Organosolv Lignin as a Green Sizing Agent for Thermoformed Pulp Products.

The purpose of this study was to investigate the use of organosolv lignin as a sizing agent for thermoformed pulp products as a sustainable material with improved water resistance. For this purpose, an in-house-produced organosolv lignin from softwood (Norway Spruce) was mixed with bleached and unbleached chemi-thermomechanical pulp fibers. In addition, the isolated organosolv lignin was characterized by ATR-FTIR spectroscopy, size-exclusion chromatography, and thermogravimetric analysis. The analysis showed that organosolv lignin was of a high purity and practically ash-free, exhibiting low molecular weight, a glass transition temperature below the thermoforming temperature, and a high content of phenolic OH groups. The mechanical properties and water resistance of the organosolv lignin-sized thermoformed pulp materials were measured. A small decrease in strength and an increase in stiffness and density were observed for the lignin-sized thermoformed materials compared to the reference, that is, unsized materials. The addition of organosolv lignin decreased the wettability and swelling of the thermoformed product. These results are due to the distribution of organosolv lignin on the surface, filling in the pores and cavities, and providing a tighter fit within the thermoformed materials. In conclusion, the results from our study encourage the use of organosolv lignin as a sizing additive to thermoformed products, which can improve the water resistance to use it in sustainable packaging applications.

Acoustic optimization of a flow through sonicator for fibrillation of cellulose fibers

Fibrillation is identified as the most energy intensive process step in pulp and paper manufacturing and improved energy efficiency is the motivation for development of alternative technologies. The aim of this study is to explore the potential of a new refining concept based on cavitation, focusing on the optimization of acoustic cavitation efficiency of the proposed flow-through sonicator concept. The simulations utilize the linearized wave equation in the frequency domain with an addition of nonlinear attenuation introduced by cavitation bubbles. Verification is made by pressure measurements, calorimetry, and foil tests. The fibrillation capability was validated on chemi-thermo mechanical pulp fibers at low consistencies. Fiber properties was characterized by ultrasonic spectroscopy, fiber analysis and SEM. The objective is to optimize the energy transfer efficiency from electrical input power to acoustic cavitation intensity for efficient fibrillation of cellulose fibers. Results showed changes in fiber dimensions and fiber morphology, however, improvements in tensile strength index, measured and predicted by ultrasonic spectroscopy, was limited to 20 % at an energy level of 804 kWh/bdt. To enhance energy efficiency and paper strength properties, it is suggested to add a hydrodynamic cavitation device prior to the sonicator to initiate cavitation bubbles and to increase turbulence intensity.

Air drying scalable production of hydrophobic, mechanically stable, and thermally insulating lignocellulosic foam

Demand for sustainable building thermal regulation is driving the development of low carbon-intensive, renewable, and safe-to-use materials to substitute the dominant synthetic polymers and inorganic mats. This study proposes a novel mild mechanical pretreatment strategy to fabricate high-performance, self-strengthening thermal insulation board in a low cost and scalable approach from chemi-thermomechanical pulp (CTMP), a type of high-yield wood pulp. CTMP fibers, after subject to a short period of disc milling, were found to gain abundant sub-fibrous structures at multiple scales. After foaming and air-drying, such micro-fibrillated fibers (MF-CTMP) formed robust, binder-free foam under capillary force with remarkedly stronger physical entanglement between fibers compared to that of pristine CTMP, achieving 3.7 folds Young’s modulus, 2.9 folds ultimate stress, and 1.9 folds toughness with respect to the latter. Palm wax coating further provided a sustainable hydrophobic protection for the foam (contact angle of ∼ 110°). The high porosity and structural tortuosity endowed the hydrophobic MF-CTMP foam with excellent thermal insulation property (thermal conductivity of 33.1 ± 2.3 mW/(m∙K)), demonstrating significantly better performance than a commercial glass fiber thermal insulator. Compared to other lignocellulosic boards prepared using freeze-drying or supercritical drying operations, the hydrophobic MF-CTMP foam represents a novel low cost, binder-free, and scalable technology for commercial sustainable thermal insulation applications.

Drying of thick foam formed mats comprising chemithermomechanical pulp fibers

This paper focuses on the drying studies of foam-formed wood fibre based relatively thick materials via infrared drying, impingement drying, and microwave drying. The drying experiments were carried out for materials with three initial moisture ratios and thickness levels. Material selection was guided by the possibility of using these kinds of materials in packaging and construction applications. The motivation for this study was the fact that in water-based manufacturing a lot of energy is consumed during the drying phase; therefore, the better understanding of drying kinetics is essential for improving the environmental friendliness and cost efficiency of material production. The results revealed differences in the results of drying methods and limitations for thick, porous wood fibre-based materials. The differences in these methods affected the drying rates and material quality, which both can arise as the limiting factor for material production. The highest drying rate was observed using microwave drying, the intermediate drying rate was achieved using impingement drying, and the lowest using infrared drying.

Relationship between wettability of pulp fibers and tensile strength of paper during recycling

The wettability of the paper surface is greatly affected by the wettability of the pulp fibers. We conducted this study in order to understand the relationship between the wettability of a single fiber of recycled pulp and the strength of recycled paper, as well as the inter-fiber bonding strength. The contact angle was determined from a series of photographs of the pulp fiber and the water silhouettes at the point of contact. The contact line and profile history were continuously photographed in every 1 s after the initial contact. The recycled softwood kraft pulp fibers were clearly much less hydrophilic than the original fibers, regardless of whether the fibers had been bleached or not. The contact angle of the original chemi-thermomechanical pulp fiber was much higher than that of the original softwood bleached kraft pulp fiber. Furthermore, increased number of recycling decreased the contact angle of the chemi-thermomechanical pulp fiber. The Page equation was used to evaluate the strength contributions of single fiber and fiber–fiber bonding to tensile strength of paper. As a result, an increase in weakness factor of fiber–fiber bonding strength was obtained for the recycled softwood kraft pulp handsheet. On the other hand, the weakness factor of the original chemi-thermomechanical pulp handsheet decreased with recycling. In addition, the weakness factor of fiber–fiber bonding strength and the contact angles of the provided softwood bleached kraft pulp fibers bore a proportional relationship to each other.

Effects of hydrophobic sizing on paper dry and wet-strength properties: A comparative study between AKD sizing of NBSK handsheets and rosin sizing of CTMP handsheets

Alkyl ketene dimer (AKD) and rosin sizing are used in papermaking to decrease paper’s tendency to absorb liquid water. Earlier information regarding the effects of internal sizing on paper dry strength is not consistent. In the present laboratory study, AKD sizing of handsheets made from Nordic bleached softwood pulp (NBSK), and rosin sizing of handsheets made from Nordic hardwood chemi-thermomechanical pulp (CTMP) were done via an internal sizing method, and by immersing handsheets in aqueous sizing agent dispersion. In the study, AKD sizing had no significant effect on the dry strength of NBSK handsheets. The result corresponds to practical experiences of papermakers. However, both AKD sizing methods resulted in a substantial and long-lasting increase of handsheet wet-strength. Unlike internal AKD sizing of NBSK handsheets, rosin internal sizing of CTMP handsheets resulted in decreased handsheet dry strength. The decrease indicates that, under the conditions present during the experiment, rosin sizing agents interfered with interfiber hydrogen bonding of CTMP fibers. Given that, in practice, no such undesired effects have been commonly linked to rosin sizing, the observed effect may be specific to sheet-making conditions. However, the effect of rosin sizing on strength properties and their variation cannot be ruled out completely.

Fractionation of pulp and precipitated CaCO3\u2013pulp composites: effects on sheet properties of selective CaCO3 precipitation onto fiber size fractions

CaCO3-pulp composite was prepared via precipitation of calcium hydroxide in the presence of pulp. In order to investigate the precipitation selectivity and mechanism, the substrate pulps and the obtained composites were fractionated (R30, R100, R200, R400 and a sedimented fraction that passed the 400 mesh wire) using a Bauer-McNett unit. The main fractionation criterion was therefore fiber length. The pulp used was CTMP (chemithermomechanical pulp), yielding a precipitated calcium carbonate-chemithermomechanical pulp (PCC-CTMP) composite with a targeted PCC-to-CTMP ratio of 1:1. The PCC consisted primarily of nano-sized primary particles which formed aggregates and clusters on the fibers. When the fiber morphology, zeta potential and surface charge density of the fractions were determined, a correlation was found between the surface charge density of the CTMP and the ash content of the corresponding PCC-CTMP fractions. This supports the hypothesis that the precipitation on the CTMP fiber is driven by the charge interparticle interaction. The use of refined CTMP furnishes and fractionation of the PCC-CTMP furnishes demonstrates that PCC is preferably fixed on fines and fibrils since it appears at a higher content in the fines fractions. Fiber activation via fiber split, removal of primary wall and surface defibrillation enhanced the affinity of the PCC for the fibrils. The laboratory handsheets prepared from the material demonstrated the importance of controlling the substrate fiber properties for the mineral-fiber composite, e.g. via refining, as differences between the refining levels and fractions were found to lead to differences in both optical properties and bonding.Graphic abstract

Preparing lignin-rich microcrystalline cellulose from spruce chemithermomechanical pulp fiber by Fe3+ enhanced high temperature liquid water treatment

Preparing lignin-rich microcrystalline cellulose from spruce chemithermomechanical pulp fiber by Fe3+ enhanced high temperature liquid water treatment

Bioconversion of Waste Fiber Sludge to Bacterial Nanocellulose and Use for Reinforcement of CTMP Paper Sheets.

Utilization of bacterial nanocellulose (BNC) for large-scale applications is restricted by low productivity in static cultures and by the high cost of the medium. Fiber sludge, a waste stream from pulp and paper mills, was enzymatically hydrolyzed to sugar, which was used for the production of BNC by the submerged cultivation of Komagataeibacter xylinus. Compared with a synthetic glucose-based medium, the productivity of purified BNC from the fiber sludge hydrolysate using shake-flasks was enhanced from 0.11 to 0.17 g/(L × d), although the average viscometric degree of polymerization (DPv) decreased from 6760 to 6050. The cultivation conditions used in stirred-tank reactors (STRs), including the stirring speed, the airflow, and the pH, were also investigated. Using STRs, the BNC productivity in fiber-sludge medium was increased to 0.32 g/(L × d) and the DPv was increased to 6650. BNC produced from the fiber sludge hydrolysate was used as an additive in papermaking based on the chemithermomechanical pulp (CTMP) of birch. The introduction of BNC resulted in a significant enhancement of the mechanical strength of the paper sheets. With 10% (w/w) BNC in the CTMP/BNC mixture, the tear resistance was enhanced by 140%. SEM images showed that the BNC cross-linked and covered the surface of the CTMP fibers, resulting in enhanced mechanical strength.

Effect of Compound Surface Treatment on the Performance of Poly(butylene succinate)/Chemithermomechanical Pulp Fiber Composites

ABSTRACTChemithermomechanical pulp fiber was pretreated by alkali solution to alter the surface characteristics of fibers. The untreated and treated fibers were used to prepare poly(butylene succinate)/chemithermomechanical pulp fiber composites with or without the incorporation of cellulose fatty acid ester (hydroxyethyl cellulose lauric acid ester). X-ray photoelectron spectrum analysis shows that the O/C ratio on the fiber surface increased after alkali treatment, indicating that part of lignin was removed during alkali treatment process. Scanning electron microcopy images indicate that the fiber surface was changed to rough after alkali treatment. The modification effect of hydroxyethyl cellulose lauric acid ester reflects as the improvement of fiber order in matrix, together with the enhancement of interfacial bonding, whereas, the modification effect of alkali treatment is mainly due to the enhancement of interfacial bonding. The integrated mechanical properties of composite prepared by alkali-treated fibers are superior to those of composite prepared by hydroxyethyl cellulose lauric acid ester-treated fibers. The combination of these two modification methods favors the enhancement of tensile and impact strengths of composite. However, in comparison with the composite prepared only by alkali treatment, the flexural strength and modulus would be despaired in a certain degree. When fibers were alkali treated, the shear viscosity of composite exhibited a larger increase, whereas the shear viscosity of composite prepared fibers with hydroxyethyl cellulose lauric acid ester treatment exhibits a slight decrease.

Qualitative evaluation of microfibrillated cellulose using the crill method and some aspects of microscopy

It has been a challenge to develop rapid online characterisation techniques for nanocellulose given the fibrillar structure of the nanoparticles. The crill optical analyser uses optical response signals in the infrared (IR) and ultraviolet (UV) wavelength ranges to evaluate the particle size properties of micro/nanofibrillar cellulosic materials. In this work, the crill analyser was used to measure the projected areas of UV and IR light sources by measuring the light blocked by nanocellulosic particles. This work uses the crill methodology as a new, simplified technique to characterise the particle size distribution of nanocellulosic material based on chemi-thermomechanical pulp (CTMP), thermomechanical pulp (TMP), and sulphite pulp (SP). In the first part, hydrogen peroxide pretreatment of CTMP and TMP in a wing mill refiner followed by high-pressure homogenisation to produce microfibrillated cellulose (MFC) was evaluated using the crill method. In the second part, TEMPO oxidation of CTMP and SP combined with high-shear homogenisation to produce MFC was studied using the crill method. With 4 % hydrogen peroxide pretreatment, the crill values of the unhomogenised samples were 218 and 214 for the TMP and CTMP, respectively, improving to 234 and 229 after 18 homogenisation passes. The results of the TEMPO method indicated that, for the 5 mmol NaClO SP-MFC, the crill value was 108 units at 0 min and 355 units after 90 min of treatment, a 228 % improvement. The CTMP and TMP fibres and the MFC were freeze dried and fibrillar structure of the fibres and microfibrils was visualised using scanning electron and transmission electron microscopy.

Upgrading poly(butylene succinate)/wood fiber composites by esterified lignin

Aliphatic chains were introduced into the macromolecule of kraft lignin using aliphatic chlorides as esterification reagents. The hydrophobicity of esterified lignin (EL) was enhanced as compared to the original lignin. EL was further used as a macromolecular coupling agent in poly(butylene succinate)/chemi-thermomechanical pulp fiber composites. As a result, the composites with enhanced mechanical performance were obtained, and the tensile strength, impact strength, and bending strength were increased by 25.1, 22.4, and 19.3%, respectively, under 2 wt% EL-treatment (synthesized by palmitoyl chloride, –COCl/–OH = 1.5:1) in comparison with those of the specimen without any coupling agent treatment. Furthermore, the composite prepared with EL-treated fibers shows significant lower water absorption ratio than that of untreated one. A significant increase in storage modulus (E′) was observed upon the incorporation of treated fibers. Furthermore, the improved interfacial bonding between treated fibers and matrix was verified by SEM images. The shear viscosity of composite was increased by the incorporation of EL, but in general, the rheological behaviors of composites are not significantly changed.

Performance enhancement of poly(butylene succinate)/chemithermomechanical pulp fiber composites by debonder treatment

Debonder, a kind of weak combination reagent usually used in the production process of fluff pulp, was used as interfacial modifier in poly(butylene succinate)/chemithermomechanical pulp fiber composites. Physical properties of handsheets prepared by treated fibers indicated that the bonding strength between fibers was sharply decreased by the debonder treatment. The mechanical performance of composites prepared from treated fiber showed significant enhancement. In comparison with untreated one, the tensile strength, impact strength, and bending strength of composite containing 40 wt% of chemithermomechanical pulp fiber treated with 0.5 wt% debonder increased by 21.9, 22.3, and 35.4%, respectively. Furthermore, the data of rheological behavior measurement exhibited that the incorporation of debonder lowered the shear viscosity of composite and favored the processing process of composite. Besides, debonder played a role of hydrophobic agent in composites. A significant increase in storage modulus (E’) was observed upon the incorporation of treated chemithermomechanical pulp fiber. Scanning electron microcopy images showed that the interfacial bonding between treated fibers and poly(butylene succinate) matrix was improved.

Changes in the microstructure and properties of aspen chemithermomechanical pulp fibres during recycling.

The effects of recycling on the microstructure and properties of bleached aspen chemithermomechanical pulp (CTMP) fibres were systematically investigated. The low-temperature nitrogen adsorption and atomic force microscopy results showed that a substantial amount of large pores and most of the very small pores in the fibre wall closed and the fibre surface became less coarse and porous during recycling. The partial cocrystallisation of cellulose microfibrils took place, as reflected in the increment of the cellulose crystallinity and the width of the crystallite in the 0 0 2 lattice plane. These irreversible structural changes caused significant hornification of the recycled fibres, leading to the loss of swelling and bonding capability. The decrease of the tensile index, burst index, and tear index further demonstrated the deterioration of the fibre properties. However, the single-fibre strength considerably increased after recycling, which was mainly due to the enlarged cellulose aggregates in the fibre wall.

CTMP-based cellulose fibers modified with core–shell latex for reinforcing biocomposites

The toughening of cellulose fiber reinforced polypropylene (PP) was performed via adsorbing the cationic latex with core–shell structure onto chemithermomechanical pulp (CTMP) fibers as reinforcements, which is a novel approach for rendering the surface of cellulose fibers elastomeric. The mechanical, morphological and thermal properties of the resulting biocomposites, containing 40% (wt) of the modified fibers, were investigated. The results showed that with the increasing of the latex dosage up to 2% (wt on dry CTMP fibers), the impact, tensile and flexural strengths of the modified CTMP/PP biocomposites were significantly increased. The toughening mechanism was discussed based on the retarding of crack propagation and the promoting of crystallization of PP matrix (as revealed by DSC characterization). The overall performance of the biocomposite demonstrated that cationic latex-modified CTMP fiber is very effective in reinforcing thermoplastic-based biocomposites along with the synergetic effect on enhancing crystallinity of polymer matrix.

Location and fate of carboxyl groups in aspen alkaline peroxide-impregnated chemithermomechanical pulp fibres during alkaline peroxide bleaching

The origin and kinetic changes of carboxyl groups in aspen chemithermomechanical pulp (CTMP) fibres during alkaline peroxide bleaching were evaluated. The results showed that the major contributors of carboxyl groups in aspen CTMP fibres were the 4-O-methylglucuronic acid, galacturonic acid and the carboxyl groups in oxidized lignin. Alkaline peroxide bleaching could increase the total carboxyl groups, surface charge and dissolved anionic substances. However, the excess degradation by superfluous hydroxide and peroxide could result in the reduction of carboxyl groups in fibres because of the production and dissolution of low-molar-mass substances. The total carboxyl groups from polysaccharides in fibres remained constant, and the increase of carboxyl groups in fibres should result from the carboxyl groups newly formed by the lignin oxidation during peroxide bleaching. Alkaline peroxide bleaching could also result in the removal of a large part of extractives and a small fraction of lignin on the fibre surface.

Improved surface properties of CTMP fibers with enzymatic pretreatment of wood chips prior to refining

Surface properties of chemithermomechanical pulp (CTMP) fibers produced from enzymatically pretreated eucalyptus wood chips prior to refining were investigated by Field Emission Scanning Electron Microscope (FE-SEM), Transmission Electron Microscope (TEM) and X-ray Photoelectron Spectroscopy (XPS). The results showed that in a traditional CTMP refining process most fiber disruptions occur in the middle lamella (ML) leaving behind a significant amount of hydrophobic materials on the resulting fiber surface. However, in a Bio-CTMP refining process, fiber fractures preferentially take place in the primary (P) and secondary 1 (S1) layers or the S1 and secondary 2 (S2) layers, which results in more fibrillation being generated in the subsequent refining thus improving inter-fiber bonding strength and paper strength. XPS chemical composition analysis together with pulp physical strength property showed that the surfaces of Bio-CTMP fibers become enriched with a greater proportion of carbohydrates in comparison with CTMP fiber surface, which supports FE-SEM and TEM observations.

Oil Spills Abatement: Factors Affecting Oil Uptake by Cellulosic Fibers

Wood-derived cellulosic fibers prepared in different ways were successfully employed to absorb simulated crude oil, demonstrating their possible use as absorbents in the case of oil spills. When dry fibers were used, the highest sorption capacity (six parts of oil per unit mass of fiber) was shown by bleached softwood kraft fibers, compared to hardwood bleached kraft and softwood chemithermomechanical pulp(CTMP) fibers. Increased refining of CTMP fibers decreased their oil uptake capacity. When the fibers were soaked in water before exposure to the oil, the ability of the unmodified kraft fibers to sorb oil was markedly reduced, whereas the wet CTMP fibers were generally more effective than the wet kraft fibers. Predeposition of lignin onto the surfaces of the bleached kraft fibers improved their ability to take up oil when wet. Superior ability to sorb oil in the wet state was achieved by pretreating the kraft fibers with a hydrophobic sizing agent, alkenylsuccinic anhydride (ASA). Contact angle tests on a model cellulose surface showed that some of the sorption results onto wetted fibers could be attributed to the more hydrophobic nature of the fibers after treatment with either lignin or ASA.

Changes of anionic groups in alkaline peroxide-impregnated aspen chemithermomechanical pulp during subsequent alkaline peroxide bleaching

The effect of alkaline peroxide bleaching on the total anionic groups (AGs) and surface AGs in aspen chemithermomechanical pulp (CTMP) fibers was investigated. Alkaline treatment, especially alkaline peroxide bleaching resulted in the formation of new AGs and surface AGs in the CTMP fibers. The carboxylic groups in uronic acid units, including 4-O-methylglucuronic acid, galacturonic acid, and glucuronic acid units were the main contributors to the AGs in the fibers. However, the oxidized lignin accounting for more than 30% of the total AGs in the bleached CTMP fibers, was the main origin of the new AGs formed during the peroxide bleaching. In addition, the new AGs were also formed by extensive deesterification of the residual esterified uronic acids in pectins and lignin-carbohydrate complexes (LCCs). Although some uronic acid units were dissolved in the process water, both the total AGs and surface AGs in the fibers increased after alkaline peroxide bleaching.

Increased Water Resistance of CTMP Fibers by Oat (Avena sativa L.) Husk Lignin

The insertion of oat husk lignin onto chemithermomechanical pulp (CTMP) fibers was studied to increase fiber hydrophobicity. The pretreated pulp samples were subsequently used for preparation of handsheets for characterization. Treatment of CTMP with laccase in the presence of oat husk lignin resulted in a significant increase in hydrophobicity of the handsheet surface, as indicated by dynamic contact angle analysis. Water absorption time of 8 s was obtained with initial contact angle of 118°. Although the handsheet's brightness was reduced by 33%, tensile index was only subtly decreased. Neither laccase nor oat husk lignin alone gave much improved water absorption times. Therefore, handsheets made of laccase-treated pulp with and without oat husk lignin were further examined by XPS, which suggested that both laccase and oat husk lignin were inserted onto CTMP fibers. The oat husk lignin was distributed as heterogeneous aggregates on the handsheet surface whereas laccase was uniformly distributed. Evidence was obtained that the adsorbed laccase layer formed a noncovalent base for the insertion of oat husk lignin onto fiber surfaces.