Kraft Fibers Research Articles

Effect of softwood kraft fiber coarseness on formation and strength efficiency in twin-wire roll forming

Abstract It has been unclear how fiber coarseness affect formation and the utilization of furnish strength in the machine-made paper (strength efficiency). In this work, the effect of softwood kraft fiber coarseness on formation and strength efficiency in twin-wire roll forming was examined in a pilot machine investigation. A reduction in softwood kraft fiber coarseness from 0.21 to 0.17 mg/m, associated with a reduction in fiber grammage from 6.2 to 5.2 g/m2, was found to have no significant effect on formation at the point of minimum shear during dewatering. The insignificant effect of reduced coarseness can be interpreted as the net result of two effects, namely, an increase in the number of fiber layers at a given grammage (favorable) and an increase in the flocculation tendency (unfavorable). While the effect of coarseness was negligible at the point of minimum shear, coarser fibers enabled larger improvement in formation through the jet-to-wire speed difference. In correspondence to the insignificant effect on formation, fiber coarseness had a negligible effect on tensile strength efficiency and Z-strength at the point of minimum shear. The larger improvement in formation through the jet-to-wire speed difference for the coarser fibers was reflected in a favorable effect on Z-strength efficiency.

Effect of chemical pretreatment on pulp and paper characteristics of bamboo gigantochloa scorthechinii kraft fibers

In chemical pulping process, lignin is targeted to be dissolved and eliminated as much as possible in order to obtain better fiber separation. A primary study was carried out to investigate the effect of sodium hydroxide pretreatment prior to bamboo chemical pulping. The selected bamboo species was Gigantochloa scortechinii which is a well-known bamboo in Malaysia. The bamboo chips were soaked in 2 % sodium hydroxide solution for 6 hours at 60 °C. These treated chips were cooked at 14 % and 18 % of alkali active via kraft pulping process. The unbleached pulp was obtained and made into paper. The pulp and paper were tested according to pulp yield, pulp freeness, paper optical, paper physical and paper mechanical properties. The results exhibited that by using treated bamboo chips, the value of pulp yield, freeness and paper brightness increasing. Slight decrement was observed for mechanical paper properties such as tensile, tear and burst strength. Chemical pretreatment prior to pulping process was investigated to offer significant effects to the pulp and paper properties of bamboo Gigantochloa scortechinii. Hence, mild kraft pulping can be carried out to produce bamboo unbleached pulps. In addition, dependency on bleaching sequences can also be declined.

Nanofibrillated Cellulose (NFC) as a Pore Size Mediator in the Preparation of Thermally Resistant Separators for Lithium Ion Batteries

Battery separators play a vital role in the safety, sustainability, and electrochemical performance of lithium ion batteries (LIBs). In this work, thermally resistant composite membranes were fabricated by a wet-laid process using northern bleached softwood kraft (NBSK) fibers, polysulfonamide (PSA) fibers, and nanofibrillated cellulose (NFC), for lithium ion battery applications. NFC functioned as a mediator to control and optimize pore size in the composite membranes, while the PSA fibers provided superior heat resistance to the membranes. The as-prepared composite separator membranes have more uniform micropores and superior thermal stability and electrolyte absorption in comparison with a commercial separator membrane (Celgard 2350).

Chemically modified cellulose micro- and nanofibrils as paper-strength additives

Chemically modified cellulose micro- and nanofibrils were successfully used as paper strength additives. Three different kinds of cellulose nanofibrils (CNFs) were studied: carboxymethylated CNFs, periodate-oxidised carboxymethylated CNFs and dopamine-grafted carboxymethylated CNFs, all prepared from bleached chemical fibres of dissolving grade, and one microfibrillated cellulose from unbleached kraft fibres. In addition to mechanical characterization of the final paper sheets the fibril retention, sheet density and sheet morphology were also studied as a function of addition of the four different cellulose fibrils. In general, the cellulose fibrils, when used as additives, significantly increased the tensile strength, Young’s modulus and strain-at-break of the paper sheets. The effects of the different fibrils on these properties were compared and evaluated and used to analyse the underlying mechanisms behind the strengthening effect. The strength-enhancing effect was most pronounced for the periodate-oxidised CNFs when they were added together with polyvinyl amine (PVAm) or poly(dimethyldiallylammonium chloride) (pDADMAC). The addition of periodate-oxidised CNFs, with pDADMAC as retention aid, resulted in a 37% increase in tensile strength at a 2 wt% addition and an 89% increase at a 15 wt% addition (from 67 to 92 and 125 kNm/kg, respectively) compared to a reference with only pDADMAC. Wet-strong sheets with a wet tensile index of 30 kNm/kg were also obtained when periodate-oxidised CNFs and PVAm were combined. This significant increase in wet strength is suggested to be the result of a formation of cross-links between the aldehyde groups, introduced by the periodate oxidation, and hydroxyl groups on the lignocellulosic fibres and the primary amines of PVAm. Even though less significant, there was also an increase in wet tensile strength when pDADMAC was used together with periodate-oxidised fibrils which shows that the aldehyde groups are able to increase the wet strength without the presence of the primary amines of the PVAm. As an alternative method to strengthen the fibre network, carboxymethylated CNFs grafted with dopamine, by an ethyl dimethylaminopropyl carbodiimide coupling, were used as a strength additive. When used as an additive, these CNFs showed a strong propensity to form films on and around the fibres and significantly increased the mechanical properties of the sheets. Their addition resulted in an increase in the Young´s modulus by 41%, from 5.1 to 7.2 GPa, and an increase in the tensile strength index of 98% (from 53 to 105 kNm/kg) with 5 wt% retained dopamine-grafted CNFs.

Moisture transfer and pressure drop of humidifying elements made of non-woven fabric (Rayon/PET)

In modern buildings, humidity control is an essential constituent of the building management, where spray-type humidifying element is widely used. For the spray-type element, there is a concern about the durability and the resistance to formation of mold. In this study, we made new humidifying elements were made using non-woven fabric rayon/PET and investigated the moisture transfer and pressure drop characteristics. Samples consisted of two different rayon compositions (30 % and 50 %). From the results the sample with 50 % rayon and 50 % PET showed superior moisture transfer performance than the sample with 50 % Kraft fiber and 50 % PET, probably due to better water absorption characteristics of rayon over Kraft fiber. However, pressure drop of the rayon/PET sample was larger than Kraft fiber/PET sample due to increased surface roughness. The moisture transfer performance of the rayon/PET sample deteriorated as the rayon content decreased. The efficiency (jm/f1/3) was the largest for rayon/PET (5:5) sample, followed by Kraft fiber/PET and rayon/PET (3:7) sample. The efficiency of commercially available Glasdek was much lower than other samples.

Investigation of Nanofibrillated Cellulose for Hydrophobic Packaging Material: Examining Alternatives to Solvent Exchange and Lyophilization

A bio-based polyurethane and a thermosetting acrylic were tested in conjunction with nano-fibrillated cellulose and conventional kraft fiber to evaluate their use as a bio-derived, biodegradable packaging foam. Foams were evaluated for their density, water uptake, and compressive creep behavior. Bio-based urethane had a mean density of 68 kg/m3, mean water uptake of 4% in 24 h, and exceeded the 10% limit on compressive strain when tested at 71 °C and 22 °C, but remained below the limit when tested at -54 °C. The thermosetting acrylic had a mean density of 128 kg/m3, mean water uptake of 337% in 24 h, and showed less than 10% compressive creep at all three temperature conditions. The bio-derived urethane was able to incorporate 4% cellulose by mass, and the thermosetting acrylic was able to incorporate 48% cellulose by mass. In a 12-week test of biodegradation under fungal attack by Gloeophyllum trabeum and Rhodonia placenta, the urethane foam had < 3% mass loss and the acrylic foam had < 1% mass loss. The acrylic foams showed potential for durable packaging, particularly if they could be combined with a surface sealant that could be ruptured at the end of service life to promote degradation of the foam.

Effect of a solvent‐free acetylation treatment on reinforcements permeability and tensile behaviour of flax/epoxy and flax/wood fibre/epoxy composites

ABSTRACTAcetylation is a common way to enhance interfacial adhesion between natural fibres and polymeric matrices in composites. This work investigates the effect of a solvent‐free environmentally friendly acetylation treatment of short flax and kraft fibres on the impregnation behaviour and tensile properties of flax fibre/epoxy composites. Untreated and acetylated fibres have been used to prepare fibre mats, which were next studied for their morphology, their permeability to liquid epoxy, and their ability to adhere to the epoxy matrix after cure. The results show that acetylation enhances the roughness of flax fibres and improves fibre‐matrix interaction, but reduces the permeability of the fibre mats and the intrinsic properties of fibres, thus leading to slightly lower composite modulus and strength. The proposed treatment is an interesting option to improve the affinity between natural fibres and polymeric matrices, but more work will be required to improve the interfacial adhesion without damaging the fibres.

Esterification of industrial lignin and its effect on the resulting poly(3-hydroxybutyrate-co-3-hydroxyvalerate) or polypropylene blends

Utilisation of lignin in plastic based blends offers a sustainable alternative to non-renewable materials as well as value-added use of technical lignin obtained from pulping operations. To overcome poor compatibility between lignin and plastic, in this study, two industrial lignins (softwood Kraft and agricultural fiber soda) were esterified (with acetic, propionic, butyric, and hexanoic anhydrides) and subsequently blended with poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) or polypropylene (PP) at a weight ratio of 3:7. This paper systematically characterized C2–C6 anhydrides esterified lignins (molar mass, glass transition temperature (Tg), hydrophobicity, and polarity), and provides a comprehensive evaluation of the effect of different lignin esters in the blends on tensile properties, water absorption, thermal transitions, for the first time, spherulite morphology, and dynamic rheological behaviour. Generally, compared to blends with unmodified lignin, a progressive increase of tensile strength (25%) and elongation at break (26%) could be observed with increasing ester carbon chain length in PHBV based systems, while no improvement was seen in PP based systems. Water absorption of PHBV and PP blends decreased by about 50% after lignin esterification. The effect of lignin esterification on the crystallization process was matrix dependent: depression of melting crystallization and occurrence of cold crystallization was observed in PHBV based blends, while the melting crystallization shifted to higher temperature in PP based blends. The lignin acetate and propionate blends were partially miscible showing two-stage glass transitions by thermal mechanical analysis. Esterification led to more uniform dispersion of lignin in the plastic matrix. The frequency of PHBV spherulites increased and their size decreased from 700μm to less than 100μm with addition of lignin acetate and propionate. Lignin hexanoate blends showed a Tg depression and smaller dynamic elastic and viscous moduli than the other lignin esters, suggesting that it acted as a plasticizer.

Development of smart colourimetric starch–based indicator for liberated volatiles during durian ripeness

The mechanical, physical and barrier properties of colourimetric starch–based films (CSBFs) were developed by adding natural polymers (chitosan, citric acid, carboxymethylcellulose, and kraft fibre). Novel volatile compound indicator films were prepared from starch (as a film matrix with 30% w/w sorbitol) using the casting method and adding natural polymers, and pH–dye (methyl red and bromothymol blue as indicators). CSBFs mixed with 0.1% chitosan improved the mechanical and barrier properties with a significant decrease in water vapour transmission rate, water solubility, and oxygen transmission rate, as well as improved tensile strength. Trials using liberated fruit aromas verified that CSBFs resulted in visible colour changes in the presence of mixed sulphur and ethyl alcohol aromas. Colour change in terms of the total colour difference of CSBFs was related to mixed sulphur and ethyl alcohol levels, thereby enabling CSBFs could be used to monitor real–time ripeness of durian volatiles.

High-rate anaerobic co-digestion of kraft mill fibre sludge and activated sludge by CSTRs with sludge recirculation

Kraft fibre sludge from the pulp and paper industry constitutes a new, widely available substrate for the biogas production industry, with high methane potential. In this study, anaerobic digestion of kraft fibre sludge was examined by applying continuously stirred tank reactors (CSTR) with sludge recirculation. Two lab-scale reactors (4L) were run for 800days, one on fibre sludge (R1), and the other on fibre sludge and activated sludge (R2). Additions of Mg, K and S stabilized reactor performance. Furthermore, the Ca:Mg ratio was important, and a stable process was achieved at a ratio below 16:1. Foaming was abated by short but frequent mixing. Co-digestion of fibre sludge and activated sludge resulted in more robust conditions, and high-rate operation at stable conditions was achieved at an organic loading rate of 4g volatile solids (VS)L−1day−1, a hydraulic retention time of 4days and a methane production of 230±10NmL per g VS.

Experimental Investigation of the Effect of Short Flax Fibers on the Permeability Behavior of a New Unidirectional Flax/Paper Composite

A new type of reinforcement for unidirectional natural fiber composites has been developed, where a paper layer is assembled with a layer of unidirectional flax yarns. The paper layer chemically and mechanically bonds to the loose yarns to maintain their alignment and enables better manipulability of the reinforcement during stacking in the mold. Unfortunately, the paper layer adversely affects the permeability of the whole reinforcement to liquid resin and thus limits the impregnation quality of the final part. In this paper, a technique is adopted to increase the impregnation performance by modifying the architecture of the fibrous network in the paper layer. In particular, a method has been developed to replace a proportion of the Kraft fibers by short flax fibers in the paper layer, in an attempt to open the structure and increase the paper permeability. Permeability measurements show a major improvement in global reinforcement permeability. Basic mechanical properties of resulting composites were also analysed. Results show a slight decrease in modulus and strength when the paper layer is present. This is compensated by an important reduction in variability. Furthermore, increasing the flax proportion in the paper layer limits the loss of mechanical properties, while reducing variability even further.

Improving strength properties of recycled and virgin pulp mixtures with dry strength agents

In the paper industry, the increasing use of recycled fibers as a substitute for virgin fibers has resulted in decreased strength properties. In this study, old corrugated container fibers were added in different ratios to virgin kraft fibers, and the effects on paper properties were investigated. Furthermore, 0.75% cationic starch and 0.75% Luredur® with respect to oven‐dry fibers were added separately to old corrugated container fiber‐containing/fiber‐free suspensions, and the effects on handsheet strength properties were determined. Starch is the oldest and most common additive for improving the strength of paper. Luredur®, a cationic polymer‐based vinyl amine and N‐vinylformamide, is used for the same purpose in papermaking. Results indicated that, except for the tear index, old corrugated container fiber addition decreased handsheet strength properties in the agent‐free samples. The cationic starch addition was more efficient than the Luredur® with regard to tensile index, stretch, tensile energy absorption, and burst index. However, the effect of Luredur® on the tear index was more pronounced compared to that of the cationic starch. Consequently, comparable handsheets strength was achieved in the 100% virgin and dry strength additive‐free fibers with the addition of 0.75% cationic starch to a suspension containing 20% old corrugated containers and 80% virgin fiber.

Porous structure of fibre networks formed by a foaming process: a comparative study of different characterization techniques.

Recent developments in making fibre materials using the foam-forming technology have raised a need to characterize the porous structure at low material density. In order to find an effective choice among all structure-characterization methods, both two-dimensional and three-dimensional techniques were used to explore the porous structure of foam-formed samples made with two different types of cellulose fibre. These techniques included X-ray microtomography, scanning electron microscopy, light microscopy, direct surface imaging using a CCD camera and mercury intrusion porosimetry. The mean pore radius for a varying type of fibre and for varying foam properties was described similarly by all imaging methods. X-ray microtomography provided the most extensive information about the sheet structure, and showed more pronounced effects of varying foam properties than the two-dimensional imaging techniques. The two-dimensional methods slightly underestimated the mean pore size of samples containing stiff CTMP fibres with void radii exceeding 100 μm, and overestimated the pore size for the samples containing flexible kraft fibres with all void radii below 100 μm. The direct rapid surface imaging with a CCD camera showed surprisingly strong agreement with the other imaging techniques. Mercury intrusion porosimetry was able to characterize pore sizes also in the submicron region and led to an increased relative volume of the pores in the range of the mean bubble size of the foam. This may be related to the penetration channels created by the foam-fibre interaction.

Cellulase-assisted refining of bleached softwood kraft pulp for making water vapor barrier and grease-resistant paper

The effect of cellulase pretreatment of bleached softwood kraft fiber before laboratory refining on the water vapor barrier and grease resistance properties of handsheets was investigated in this work. In contrast to no cellulase pretreatment, cellulase pretreatment at 0.5 filter paper units (FPU) combined with refining for 7500 revolutions was effective in reducing the water vapor transmission rate (WVTR, 50 % RH and 23 °C) of the paper by 83 % and achieving 100 % grease resistance over a 24-h test period. After cellulase pretreatment, the fiber morphology and hydrophobicity changed dramatically as a function of refining intensity. The role of cellulase pretreatment in reducing the WVTR and grease-stained areas was revealed on morphological observation by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, as well as water contact angle testing.

Development of PLA/cellulosic fiber composite foams using injection molding: Crystallization and foaming behaviors

Poly(lactic acid) (PLA) and northern bleached softwood kraft (NBSK) or black spruce medium density fiberboard (MDF) fibers were melt compounded using a co-rotating twin screw extruder and subsequently microcellular injection molded. Poly(ethlylene glycol) (PEG) was used as a lubricant. The microcellular structure, thermal properties, and crystallization behaviors were characterized using scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, and wide angle X-ray diffraction. Results show that cellulosic fibers, acting as crystal nucleating agents, increased the crystallization temperature and the crystallinity and decreased the crystallization half time. The dissolved N2, the shear stress, and biaxial stretching during foaming also enhanced the crystallinity of PLA. Compared to PLA/PEG, a finer and more uniform cell structure was achieved in the cellulosic fiber composite foams. The improved foam morphology was attributed to the cell nucleating effects of the fibers and the increased melt strength by the addition of cellulosic fibers and by the gas- and fiber- induced crystallization.

Effects of charge ratios of xylan-poly(allylamine hydrochloride) complexes on their adsorption onto different surfaces

The adsorption behavior of polyelectrolyte complexes (PECs) of poly(allylamine hydrochloride) (PAH) and 4-O-methylglucuronoxylan (Xyl) onto silica surface, cellulose nanofibrils (CNFs) model surfaces, and unbleached softwood kraft fibers was studied. Different charge ratios and ionic strengths of the liquid medium (q − /q +: 0.3, 0.5 and 0.8 in 1 mM NaCl, and q − /q +: 0.2, 0.3 and 0.5 in 10 mM NaCl), at pH 7.5 were considered. First, the complexes obtained were characterized by measuring the charge density, the particle size and the zeta potential. Then, the adsorption of PAH alone and PECs on silica and CNF model surfaces were studied by quartz crystal microbalance with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR). The QCM-D test indicated that: (a) adsorbed cationic layers of PECs were soft in 10 mM NaCl, (b) higher adsorption was observed at higher ionic strength and (c) the highest adsorption of complex and coupled water was found at a charge ratio of 0.3. The SPR results analyzed together with the corresponding QCM-D results revealed that a significant portion of the adsorbed layers corresponded to coupled water on the cationic PEC structures. Morphology and structures of the adsorbed PEC layers studied using atomic force microscopy showed that the majority of the PECs were spherical, while some bigger aggregates were also found. Finally, the retention of different PECs on an unbleached softwood pulp was determined and the maximum retention was obtained when the PEC charge ratio was 0.5 in a 10 mM NaCl solution.

A Study on the Measurement of Volume and Surface Electrical Conductivity of Cryogenic Insulants for DC HTS Equipment

For the insulation design of dc high-temperature superconducting (HTS) equipment, dc electric field analysis should be performed. As the dc electric field distribution is mainly determined by the relative electrical conductivities of the various insulating materials used, the conductivities of these materials should be precisely measured. In particular, in cryogenic environment, the measurement of electrical conductivity could not be easily conducted due to the difficulty of measuring extremely low leakage current. In this paper, investigation on the measurement of volume and surface electrical conductivity of various cryogenic insulants, including polypropylene laminated paper (PPLP), Kraft, and glass fiber reinforced plastic (GFRP), was carried out. For the measurement of volume electrical conductivity in LN2, the infiltration of LN 2 into the specimen should be considered in order to avoid inaccurate measuring data. Thus, in order to increase the reliability for volume electrical conductivity, the PPLP specimen deposited by copper was adopted, and the comparison between ordinary PPLP and PPLP with copper deposition was made. As a result, it was suggested that the copper deposition could be a valid method to prevent the infiltration of LN 2 when the electrical conductivity of thin paper was measured. Consequently, volume and surface electrical conductivity values of PPLP, Kraft, and GFRP have been measured and summarized.

The Properties of Phosphorylated Kraft Fibers

The properties of phosphorylated kraft fibers, including their flame retardancy and behavior in water, such as electrical charge and swelling capacity, were investigated in this study. Two different phosphorus contents and three forms of phosphorylated fibers (ammonium, acid, and sodium) were analyzed. All types of phosphorylated fibers exhibited high char formation and limiting oxygen index (LOI) values, indicating good flame retardancy. In particular, the ammonium form exhibited the best flame retardancy behavior and the highest LOI value. The charge density and swelling capacity of the kraft fibers were significantly increased by phosphorylation. Alkaline treatment following the phosphorylation reaction further increased the water retention value (WRV) and surface charge of the kraft fibers. Compared to unmodified kraft fibers, the phosphorylated fibers had lower absolute values of the negative zeta potentials, and these values were less affected by conductivity.

Production of recycled cellulose fibers from waste paper via ultrasonic wave processing

ABSTRACTRecycling waste paper can be considered as a means to displace the use of natural cellulose fibers applied in building materials, because it is composed mostly of cellulose. The water absorption and special surface area of cellulose fibers are the key properties for their use in building materials. The objective of this article was to study the production of recycled cellulose fibers from waste paper using ultrasonic wave processing. The physical and chemical properties of recycled cellulose fibers, such as water absorption, specific surface area and pore characteristics, etc., were investigated with various testing methods. The results indicated that the ultrasonic cavitation effect was feasible for the preparation of the secondary fibers. When the ultrasonic treatment time lasted for 10 min, the water absorptions of both newsprint fibers and kraft fibers increased significantly and reached the highest values of 12.5 g/g and 11.2 g/g, respectively, which were nearly two times than that of fibers without ultrasonic treatment. With a pretreatment of 20 min, the average length and fineness of recycled cellulose fibers decreased by 4% and 25%, respectively, and the length‐diameter ratio of the recycled cellulose fibers was 1.28 times than that of the untreated fibers, which greatly increased the special surface area of the recycled cellulose fibers. This work also determined that NaOH was useful to improve the physical properties of the recycled cellulose fibers. Because the recycled cellulose fibers after processing, fulfilled several technical indexes, they can be considered as a filling material for used in cement‐based materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41962.

How xylan effects the breaking load of individual fiber–fiber joints and the single fiber tensile strength

Bleached and unrefined softwood kraft fibers were treated with aqueous solutions of xylans and potassium hydroxide (KOH) to vary the amount of xylan present on the fiber surface and within the fiber wall. This was done in order to directly measure the influence of xylan on the joint strength of individual fiber–fiber joints as well as the tensile strength of individual fibers to determine the elastic modulus. The results were compared with two unbleached and unrefined softwood kraft pulps (Kappa 42 and 54). Additional xylan had a statistically significant effect on the mean values of the breaking load of individual fiber crossings. Moreover, the breaking load was strongly affected by the cooking time during pulping. However, no correlation between the optical bonded area and the joint strength was observed. The modulus of elasticity of individual fibers was not influenced by additional xylan or alkaline extraction. The elastic modulus was influenced more by chemical pulping and bleaching. The results indicate that additional xylan on the fiber surface has a strength-enhancing effect on the joint strength individual fiber crossings which also depends on the distribution of xylan. On the other hand, the elasticity of a fiber seems to be more influenced by the morphology and the composition of the fiber walls, especially in the secondary S2 wall.