Chemithermomechanical Pulp Research Articles

Production and Characterization of Cellulose Nanofibrils from Different Chemical and Mechanical Pulps

In this study, mechanical fibrillation for the production of cellulose nanofibrils (CNF) from chemical and mechanical pulps with different chemical compositions was studied. To investigate the effect of nanofibrillation on wood pulps by the grinder, the nanofibrils obtained from grinded pulp were characterized with morphology, particle size distribution, apparent viscosity in aqueous solution, degree of crystallinity, and water retention capacity. The results showed that the low lignin-containing unbleached kraft pulp (UKP) exhibited good performance for fibrillation, resulting in CNF with high viscosity, high water retention value, and small particle size. However, the fibrillation of high lignin-containing chemi-thermomechanical pulp was the most inefficient which resulted in heterogeneous materials with relatively low viscosity, low water retention value, and large particle size compared to chemical pulps. Furthermore, bleached softwood pulp from radiata pine was found to be much faster and for easier fibrillation compared to the bleached hardwood pulp from acacia due to the more rigid structure of hardwood fibers.

The effect of delignification on the properties of cellulosic fiber material

Abstract The behavior of pressed poplar chemi-thermomechanical pulping (CTMP) without additive the focus of our study. Four CTMPs with decreasing lignin contents were prepared by the sodium chlorite/acetic acid method and the holocellulose, α-cellulose, pentosan and Klason lignin contents of the delignified CTMPs were determined. The surface composition, aggregation structure and microstructure of the delignified fibers were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscope (SEM), and the mechanical properties of the fiber material were investigated by means of tensile and bending tests. As shown by XPS, the lignin content of the Pr-CTMP surface layer firstly increased and then decreased as the lignin content of CTMP decreased. With the delignification time increased from 0 to 240 min, the crystallinity index (C r I) of CTMP increased from 60.1% to 65.7%. The C r I of all CTMPs at different delignification degrees showed significant elevated values after hot-pressing. The fiber cell wall became thinner and the cells were flattened and thus elevated the contact area among fibers and, as a consequence, the density of material gradually increased at higher delignification degrees. The tensile strength increased by ca. 10%, when the lignin content decreased from 24.9% to 13.1%, and by ca. 53%, when the lignin content decreased from 13.1% to nearly zero. The bending strength increased with increasing delignification. When the removal rate of lignin increased from 47% to 54%, the bending strength increased from 101 to 122 MPa.

Iso-concentration hydrogen peroxide bleaching of poplar chemi-thermomechanical pulp

Maintaining a constant chemical concentration (Iso-concentration, IC) has been found to be an effective method to improve peroxide bleaching efficiency for chemi-thermomechanical pulp (CTMP). In this study, the mechanism of IC bleaching was investigated. The concentrations of H 2 O 2 and total alkali in IC bleaching were monitored and compared with those in conventional bleaching processes. Control experiments without pulp were carried out to explore the effects of bleaching additives on H 2 O 2 decomposition. The results showed that the concentrations of H 2 O 2 and the total alkali at the early and later stages of IC bleaching were relatively low and high, respectively; thus, undesired decomposition of H 2 O 2 was inhibited, and brightness was improved. Moreover, the stabilizer played an important role in inhibiting the undesired H 2 O 2 decomposition. This may explain why high bleaching efficiency was achieved in IC bleaching. These findings would provide valuable insight for the production of high-brightness bleached chemi-thermomechanical pulp (BCTMP).

Modeling and prediction of methanol air release from bleached chemi-thermo mechanical pulp board.

This paper reports on the modeling, prediction and evaluation approaches of methanol release from bleached chemi-thermo mechanical pulp (BCTMP) board during storage. A pseudo-first order desorption kinetics model of methanol release was established for describing the desorption behavior of methanol from BCTMP, i.e., , in which the desorption constant (K) and rate constant (kdes) were well described by van't Hoff and Arrhenius equations. Based on the simulation experiments at various temperatures, the desorption activation energy of methanol and its adsorption enthalpy is calculated and is 53.7 and −86.2 kJ mol−1 K−1, respectively. With the developed model, the risk of methanol release for the storage of BCTMP board can be examined by either the time-dependent kinetics model or a two-step thermodynamic approach using the equilibrium concentration of methanol in indoor air. This paper provides a valuable tool to assess the risk of methanol release for the paper industry and related warehouse departments.

Mechanical Strength, Thermal Stability, and Hydrophobicity of Fiber Materials after Removal of Residual Lignin

The behaviors of the mechanical, hydrophobic, and thermal properties of the molded fiber product (MFP) were examined after the removal of residual lignin. The fibers resulting from the chemi-thermomechanical pulping and bleaching processes were treated by extended delignification, namely by their reaction with glacial acetic acid and sodium chlorite. The changes in surface composition, chemical structure, crystallinity, microstructure, and thermal stability of the MFP were investigated by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA), respectively. Results showed that the composition and structure of carbohydrates on the fiber surface were not changed significantly, the lignin in fibers was almost completely removed, the relative content of intermolecular hydrogen bonds in cellulose and the contact area between fibers was increased, and the crystallinity index increased from 79.5% to 81.4% after the extended delignification. When the content of lignin decreased from 5.78% to 0.02%, the tensile strength of the MFP increased 25.6%, but little changes were found in the bending strength. The onset thermal decomposition temperature of MFP increased from 242 °C to 250 °C and the maximum rate of degradation temperature increased from 347 °C to 350 °C.

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 Ultrasonic-assisted Cold Caustic Extraction on the Properties of CTMP Poplar Fibers

Chemithermo-mechanical pulp (CTMP) has been widely utilized in papermaking industry because of its high yield. However, the poor strength properties arising from the high contents of hemicellulose and lignin have limited its applications. In this study, ultrasonicassisted cold caustic extraction (CCE) on hemicellulose removal was applied to ascertain its influence on the properties of CTMP. It was found to have a positive effect on hemicellulose removal and resultant pulp properties. At the same alkali concentration (3 wt%), hemicellulose removal and Canadian Standard Freeness (CSF) in ultrasonic-assisted CCE (360 W, 10 min) increased 53.4% and 9.6%, respectively. Ultrasonic-assisted CCE reduces alkali concentration from 5 wt% to 2 wt% to obtain similar hemicelluloses removal, whereas the pulp yield at 2 wt% NaOH was higher than that of CCE alone at 5 wt% NaOH. In addition, at the same alkali concentration (3 wt%), the tensile index, bursting index and tearing index of CTMP in ultrasonic-assisted CCE (120 W, 10 min) increased by 12.7%, 11.34% and 3.0%, respectively. Ultrasonic-assisted CCE enhanced the fibrillation of fibers at optimal conditions, as determined by SEM.

Effect of Sodium Hydroxide and Magnesium Dihydroxide on Bleaching of Chemithermomechanical Pulp Made from Pinus densiflora

Effect of Sodium Hydroxide and Magnesium Dihydroxide on Bleaching of Chemithermomechanical Pulp Made from Pinus densiflora

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.

Cellulose fiber based fungal and water resistant insulation materials

AbstractThe development of thermal insulation materials from sustainable, natural fibrous materials is desirable. In the present study, cellulose fiber based insulation foams made of bleached chemi thermo mechanical pulp (CTMP) have been investigated. To improve water resistance, the foams were impregnated with hydrophobic extractives from the outer bark of birch (Betula verrucosa) and dried. The surface morphology of the foams and the distribution of the deposited particles from the extractives were observed by scanning electron microscopy (SEM). The modified foams showed improved water resistance, as they did not disintegrate after immersion in water for 7 days, whereas the unmodified foam did. Compared to the unmodified foam, the modified foams absorbed 50% less moisture within 24 h. The modification had no negative effects on the thermal insulation properties, fungal resistance or compressive strength of the foams. The proposed approach is simple and can be easily integrated into plants working based on the biorefinery concept.

Characterization of hemicelluloses in process streams in thermomechanical and chemi-thermomechanical pulp mills

Increased interest in hemicelluloses as a renewable source of biopolymers has resulted in an interest in hemicelluloses in process streams in pulp mills. The aim of this study was to compare potential positions for the withdrawal of hemicelluloses from mechanical pulp mills. Samples were withdrawn at a total of fourteen positions from two thermomechanical and two chemi-thermomechanical pulp mills. The molecular mass distributions of hemicelluloses and lignin were determined by size-exclusion chromatography. Hemicelluloses showed peaks in the molecular mass interval of 0.2–2 kDa and 4–60 kDa, whereas lignin showed peaks in the range of 0.5–4 kDa, but no peak in the high-molecular-mass region. Glucomannan accounts for approximately two-thirds of the hemicellulose content of softwood, and mannan and glucan were thus the dominating saccharides in all samples. Mannan was preferentially found in fractions with a molecular mass ranging from 4 to 22 kDa.

Modeling for output fiber length distribution of refining process using wavelet neural networks trained by NSGA II and gradient based two-stage hybrid algorithm

The chemi-thermo-mechanical pulping (CTMP) is an important process that produces fibers for paper-making, whose output fiber length distribution (FLD) directly determines the energy consumption and product quality of the subsequent papermaking production. Therefore, study on modeling and control of the output FLD is essential for improving pulp quality and saving energy in refining process. However, the output FLD of refining process has non-Gaussian stochastic distribution property, making it difficult to use conventional methods to establish the output FLD model effectively. Under the framework of stochastic distribution control theory, this paper presents a novel modeling approach for output probability density function (PDF) of fiber length in CTMP by combining with the improved wavelet neural network (WNN). In this context, the square root B-spline approximation principle is firstly adopted to extract the B-spline weights of fiber length PDF shape as the target outputs for the WNN based B-spline weights model. Secondly, a novel two-stage hybrid learning algorithm is proposed to establish the parameters system for the WNN based weighs model by defining a multi-objective evaluation index for modeling accuracy in advance. This learning algorithm integrates multi-objective NSGA II algorithm in the first stage for better initial solutions at a global scope, and gradient descent method is employed in the second stage for accurate solutions of WNN model parameters inside a local range. As a result, the final output PDF of fiber length is reconstructed by the estimated B-spline weights using the B-spline approximation principle again. Experiments using actual industrial data have demonstrated the superiority and practicability of the proposed method.

Ultrasonic-assisted ionic liquid treatment of chemithermomechanical pulp fibers

Enhancing the swelling of chemithermomechanical pulp is essential for improving its physical properties and thus broadening its end-use applications. In this work, ionic liquid (IL) using 1-allyl-3-metheylimidazolium chloride ([Amim]Cl) was used for reducing hydrogen bonding within the fiber wall, and ultrasonic treatment was used for improving the performance of IL treatment. Mixing IL with pulp fibers at 5 ml/g concentration decreased the Canadian standard freeness (CSF) of pulp from 760 to 570 ml at room temperature, and the pretreatment with ultrasonic treatment for 20 min reduced its CSF to 545 ml. The ultrasonic-assisted IL treatment improved the tensile, tear and burst indices as well as the folding endurance of the cellulosic network by 41, 36, 12 and 150%, respectively. The surface charge density and area of fibers were improved, but the lignin and hemicellulose contents of the fibers were reduced via ultrasonic-assisted IL treatment.

Xylanase Treatment Suppresses Light- and Heat-Induced Yellowing of Pulp.

Xylanase is commonly applied in pulp and paper industries to ease cost-related and environmental pressures. The effect of xylanase treatment on pulp bleaching is well-established, however, few studies were conducted on the effects of xylanase treatment in pulp yellowing, especially the mechanism of pulp yellowing inhibition by xylanase treatment. In this study, pure xylanase (EC 3.2.1.8) was applied to treat wheat straw chemical pulp (CP) and poplar chemi-thermo-mechanical pulp (CTMP) to determine their effects on pulp brightness and on light- and heat-induced yellowing. The xylanase treatment decreased the post-color number of the pulps during light- and heat-induced yellowing. However, differences were observed in the yellowing inhibition between the wheat straw CP and poplar CTMP. The changes in chemical components of pulps after the xylanase treatment, for example, lignin, hemicellulose, and HexA contents, and analysis of UV–vis absorption spectra and Fourier transform infrared-attenuated total reflectance spectrum were used to explore the pulp yellowing inhibition causes by the xylanase treatment.

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.

Fibrillation of Aspen by Alkaline Cold Pre-treatment and Vibration Milling

In this article an attempt to fibrillate aspen bleached chemi-thermo mechanical pulp (BCTMP) fibre in an environmentally friendly way is reported. The effects of various NaOH, KOH, urea and ethanol aqueous solutions at lowered temperature were tested for pre-treatment. The pre-treatment was followed by vibration milling aiming to peel off outer cell wall layers and to fibrillate S2 layer of the aspen wood fibre. The effects of the treatments were evaluated by scanning electron microscopy (SEM). The results show that it is possible to fibrillate BCTMP aspen fibres by using alkaline aqueous solutions at low temperatures followed by a mechanical treatment. A strong dependence on fibrillation of cellulose on temperature, time and alkali concentration was established. DOI: http://dx.doi.org/10.5755/j01.ms.22.3.7412

Fibre Stress-Strain Response of High-Temperature Chemi-Thermomechanical Pulp Treated with Switchable Ionic Liquids

The removal of lignin from a high-temperature chemi-thermomechanical pulp (HT-CTMP) using a switchable ionic liquid prepared from an organic superbase (1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU)), ...

Characteristics of high yield pulp fibers by xylanase treatment

The effects of xylanase treatment on the fiber surface properties of high yield pulp (chemithermomechanical pulp, alkaline peroxide mechanical pulp, and bleached chemithermomechanical pulp) were studied. Fibers surface composition and surface structure were investigated by X-ray photoelectron spectroscopy and scanning electron microscopy, respectively. The former demonstrated an increase in the atomic oxygen to carbon ratio, a decrease in the lignin content, and variation in the C1s on the fiber surface of enzymatically treated samples. An enrichment of a large proportion of open and fibrillated fibers was visualized by the latter, resulting in an improvement in the pulp’s physical strength-related properties. Surface modification using enzymatic treatments allow for improved fiber surface properties to obtain new products through sustainable technologies.

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.

Characterizing latency removal in mechanical pulping processes part I: Kinetics

Latency removal in the mechanical pulping process occurs in a continuous stirred-tank reactor and non-ideal mixing lowers the performance. In order to optimize the latency removal process and reduce the energy consumption in the operation, a kinetic study was carried out. In the study, the phenomenon of latency and knowledge related to latency removal were critically reviewed and discussed. Latency removal was characterized by the change of Canadian Standard Freeness (or freeness), and its dependences on treatment conditions, i.e., disintegration temperature, power input, pulp consistency and time, were determined. Kinetic models of latency removal for secondary refiner thermomechanical (TMP) and bleached chemithermomechanical (BCTMP) pulps have been developed, which were based on the rate of latency elimination characterized by the decrease of freeness.