Kraft Fibers Research Articles

Bulky paper with good strength and smoothness? Certainly!

Increasing bulk is the first step toward resource-lean papermaking. Increasing the bulk tends to reduce strength and increase porosity and roughness; however, loss in strength could be compensated for via an increase in the specific strength of bonds. The increase in total surface area can have a positive influence on the porosity and smoothness of the paper. Results suggest that the bulk of fine paper can be increased by 20% and the critical paper properties maintained through selection of the kraft fibre type, control of the degree of hornification, addition of xyloglucan, and use of fines-rich mechanical pulp. In general, the results reported on here suggest that increasing bulk or reducing grammage is a challenging task but can be accomplished through simultaneous application of several unconventional measures.

Carboxymethylation of Corncob Holocellulose and Its Influences on Paper Properties

Corncob is an underutilized agricultural by-product. In this work, corncob was treated with sodium chlorite to remove lignin, and the resulting holocellulose was optionally modified with sodium chloroacetate under alkaline conditions for different time periods to obtain five carboxymethylated corncob holocellulose samples. The derivatization products were investigated by infrared spectroscopy, elemental analysis, carboxyl content tests, and scanning electron microscope analysis. When added at the 1% level (time of carboxymethylation 140 minutes) to an unbleached triploid Populus tomentosa Carr kraft fiber suspension and made into paper, the tensile index, burst index, and folding endurance were increased by 46.4%, 34.2%, and 397.8%, respectively. The results demonstrated that simultaneous carboxymethylation of both hemicelluloses and cellulose in corncob can be an effective approach to preparing a novel dry-strength additive for paper.

Structure of swollen carboxylated cellulose fibers

Structural changes in cellulose fibers were elucidated for carboxymethylated fibers and fibers that are oxidized by periodate and chlorite. Non-fibrillated and partially fibrillated softwood, kraft fibers (SKF, m-SKF) were carboxymethylated to investigate the contribution of the S1 layer to the swollen fiber structures. Carboxymethylated non-fibrillated fibers (CMF) form balloon-like structures as they swell heterogeneously. When partially fibrillated SKF is carboxymethylated (m-CMF), the fibers do not exhibit this ballooning phenomenon due to the degradation of the S1 layer. Carboxymethylation disrupts the native cellulose crystalline structure without breaking the fibers apart. Periodate–chlorite oxidized fibers, on the other hand, swell homogeneously without disrupting the native cellulose I crystalline form. Periodate–chlorite oxidation damages all three secondary layers to the extent that any microfibril confinement caused by the swelling is removed. Each chemistry and mechanical treatment affects the cellulose fibers differently to yield various swollen structures.

Effects of Alkali Treatment and Polyisocyanate Crosslinking on the Mechanical Properties of Kraft Fiber-Reinforced Unsaturated Polyester Composites

The effects of alkali treatment and polyisocyanate crosslinking on the mechanical properties of kraft fiber-reinforced UPE composites were investigated by means of tensile evaluation, SEM analysis, and XRD analysis. The results indicated that the alkali treatment decreased the tensile strength of the prepared composite before aging from 121 MPa to 97 MPa due to the decreased degree of crystallinity of the alkali-treated kraft fiber. Polyisocyanate crosslinking could apparently improve the mechanical properties and stability in terms of a 43% increase of non-aged tensile strength and 52% increase of hydrothermal-aged tensile strength compared with the controlled composite without crosslinking modification, which was attributable to the formation of strong chemical bonding between the interfaces of kraft fiber and polyester.

Cationization of oat β-D glucan as a dry-strength additive for paper

Oat β-D glucan was treated with 3-chloro-2-hydroxypropyl-trimethyl ammonium chloride (10%, 20%, 30%, or 50% of beta glucan) to obtain a range of cationic β-D glucan samples. The derivatization was confirmed by the results of Fourier transform infrared (FTIR) tests and elemental analysis. Addition of 1% cationic β-D glucan based on the mass of unbleached pine kraft fiber increased burst, tensile, and folding endurance properties of the resulting paper. Similar effects were observed at pH 5 and pH 8.5, showing that the system can be considered robust relative to typical acidic and alkaline papermaking conditions. The strength benefits were also observed in recycled sheets made by reslurrying paper prepared with cationic β-D glucan, even when the initial drying conditions had been severe. The beneficial results of cationization, which can be explained by a more hydrophilic nature and better retention, hold promise as a means of improving the strength properties of virgin paper. The treatment of the initial paper also can enhance the dry-strength performance when the fibers are recovered and used again.

Cassava Starch-Based Biodegradable Foam Composited with Plant Fibers and Proteins

The development of starch foam trays has attracted an increasing amount of attention. However, starch foam trays exhibit poor physical and mechanical properties, and low water and oil resistance. This research aimed to improve the properties of baked composite cassava starch foam tray (CSF) by adding the leaf sheath of betel nut palm, coconut husk or kraft fibers, sunflower meal protein and gluten protein at concentrations of 0, 5 and 10%. All formulations of the CSF trays formed well-shaped trays. The addition of 10% kraft fiber and 10% gluten protein to the CSF trays exhibited the best properties for maximal flexural strength (4.8 MPa) and compressive strength (1.74 MPa). The water and oil absorptions of the trays were reduced by 43% and 72%, respectively. Moreover, composite CSF trays blended with 10% kraft fiber and 10% gluten protein were used as packaging for minimally processed durian (MPD) and kept at 4°C for 5 days. Results showed that compressive strength of the composite CSF slightly decreased from 1.74 to 1.51 MPa, while water and oil absorptions did not change during storage of MPD.

Enhancement of nanofibrillation of softwood cellulosic fibers by oxidation and sulfonation

In this study, sulfonic acid groups were introduced to milled softwood (SW) bleached kraft fibers by oxidation and sulfonation with sodium periodate followed by sodium bisulfite under relatively mild conditions. The effect of variable amount of sulfonated groups on nanofibrillation of sulfonated cellulose samples was investigated. The cellulose samples, with contents of sulfonated groups of 371–501μmol/g, were readily nanofibrillated by homogenization at relatively low pressure. These samples converted to viscous and transparent gels without clogging the homogenizer. By passing through the homogenizer one to four times, the transmittances of homogenized suspensions were up to 98%. SEM characterization of the homogenized and lyophilized fibril suspension indicates that the nanofibrillated fibrils are a network structure with lateral sizes of ∼15–45nm and lengths ˃1μm. The consecutive periodate oxidation and sulfonation with bisulfite was shown to be an effective pretreatment method to facilitate the nanofibrillation of softwood pulp cellulose and can be expectedly used with other cellulosic resources.

Characterization of cassava starch based foam blended with plant proteins, kraft fiber, and palm oil

Cassava starch foam (CSF) trays blended with zein, gluten, soy protein, kraft fiber, and palm oil at various concentrations: 0, 5, 10 and 15% by weight of starch, were characterized. The addition of zein and gluten into CSF resulted in consolidated and homogeneous structural foams compared to its controls. Moreover, the flexural and compressive strength increased with increasing kraft, zein and gluten. CSF containing 15% kraft gave the highest flexural and compressive strength. However, the addition of palm oil into CSF gave the lowest flexural strength and compressive strength. The observed water absorption and water solubility index of CSFs blended with 15% zein and 15% gluten protein was lowest. Although kraft, zein and gluten could improve mechanical properties, water absorption and water solubility were greater than the expanded polystyrene foam (EPS). The CSF trays in this study might be an alternative for packing low water content foods.

On estimating local defects of softwood kraft fibers stained with congo red and assessed with a novel fiber analyzer

The fiber deformations of once-dried, bleached and never-dried unbleached kraft pulps were studied with respect to their behavior in high- and low-consistency refining. The pulps were stained with congo red to experimentally highlight areas where the arrangement of the fibrils was altered by refining such as dislocated zones or slip planes. The stained fibers were analyzed with conventional Metso Fiberlab but also with a novel prototype measurement device utilizing a color imaging setup. The local intensity of the stain in the fiber was expressed as degree of overall damage (Overall fiber damage index, OFDI). The rewetted zero span tensile index (RWZSTI) was used to verify the OFDI with respect to the pulp strength. High consistency refining resulted in a clear increase in the number of kinks which negatively influenced the pulp strength. The OFDI which was used to detect the intensity of local fiber defects also responded accordingly. A higher OFDI resulted in a lower pulp strength. Low consistency refining removed a significant amount of kinks and resulted in an increase in fiber swelling. A slight increase in fibrillation and a significant increase in flake-like fines were also observed. The OFDI, however, was not reduced in low consistency refining as it would be expected by the removal of less severe dislocations. One reason proposed here is that low consistency refining created new fiber pores that allowed the dye to penetrate into the fiber wall similarly as it does in the zones of the dislocations.

Phosphorylation of Kraft fibers with phosphate esters

Phosphate esters, derived from two different long-chain aliphatic alcohols, were used as phosphorylating reagents for Kraft pulp fibers. High phosphorus contents and almost non-degraded fibers were obtained by following this pathway. The phosphorylation efficiency was influenced by the alkyl chain length of PEs since the phosphorus content in modified fibers was higher for the shorter chain reagent. Due to the heterogeneous reaction environment, the amount of grafted phosphorus was found to be almost three times higher at the surface than in the bulk of the fibers. Analyses also indicated that the phosphorus was bonded to fibers as a phosphate-like structure. Furthermore, the situation seemed to be different for the fiber surface where significant amounts of phosphorus were present in more complex structures like pyrophosphate or even oligo-phosphate.

A Novel Process for the Production of Unidirectional Hybrid Flax/Paper Reinforcement for Eco-composite Materials

In this paper a new process to manufacture unidirectional reinforcements for eco-composite materials, made of natural fibers, is presented. Starting with flax rovings of different sizes, an apparatus was developed to feed and align the rovings over the wet-end section of a paper machine. The short kraft paper fibers are therefore mixed with the long flax roving as the machine is running, and at the end of the process, a sheet of the hybrid dry reinforcement is obtained and cut to size for impregnation with various resins, using different processes. This novel manufacturing process allows for high volume production of reinforcement. It is very flexible, and many different combinations of long and short fibers can be exploited for the production of a vast variety of dry reinforcements. In this paper, composite samples are obtained out of these reinforcements, using the resin infusion (RI) molding process with a commercial epoxy resin. The results are compared with those of usual glass fiber reinforcement. An interesting aspect is that the large variability, typical for natural fibers, is largely reduced when the short kraft fibers are present in the composite. In terms of permeability to resin, reasonably comparable values can be obtained compared to that of glass fabrics, if a low surface density of reinforcement is chosen.

In situ generated cellulose nanoparticles to enhance the hydrophobicity of paper

Handsheets with in situ generated cellulose nanoparticles were made from oxidized pulp fibers prepared by 2,2,6,6-tetramethylpiperidinyl-1-oxyl-mediated oxidation of kraft fiber with sodium hypochlorite and sodium bromide. The oxidized pulp fibers were blended prior to handsheet formation for short times (1–3 min). From gravimetric analysis of the supernatant, yield of cellulose nanoparticles generated from this blending process were up to 9.5 dry wt%. Scanning electron microscopy showed that the handsheets fabricated in a wetlay process had increased smoothness with increased blending time. A significant decrease in water vapor transmission rate for the sheets supported the hypothesis that cellulose nanoparticles fill the empty spaces between pulp fibers throughout the handsheet affording a more dense structure. Oxidation significantly enhanced the tensile index of the handsheets and this value was further improved by blending for 2 min. The handsheets were treated with a solution of octadecylamine (ODA) modifying the surface chemistry of the paper. Irreversibly adsorbed ODA on the oxidized cellulose surfaces after extensive extraction was confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Sessile drop contact angle tests for modified handsheets illustrated its enhanced hydrophobicity with contact angles over 90°. Overall the study developed a novel route to make paper with enhanced functionality without the need to separately deposit nanocellulose onto the paper surface.

Enhancement of paper dry strength by carboxymethylated β-d-glucan from oat as additive

Abstract The hypothesis has been tested that a carboxymethyl hemicellulose improves more effectively the dry strength of papers than a native hemicellulose. To that end, β-d-glucan from oat was treated with an alkaline ethanolic solution of sodium chloroacetate for different times to obtain a range of carboxymethylated β-d-glucan (CM-glucan) samples. The derivatization was confirmed by Fourier transform infrared spectroscopy and elemental analysis. The physical properties of paper concerning burst and tensile strength as well as folding endurance were essentially improved if CM-glucan was added to unbleached kraft fiber suspension from pine before papermaking. The effects could be maximized by a proper selection of carboxymethylation time and the amount of CM-glucan added to the suspension. The effect was also beneficial in the case of recycled fibers.

Pulping-tailored fiber properties from a novel Brazilian Eucalyptus hybrid

Abstract The chemical composition and morphology of pulp fibers have a significant impact on the properties of fiber products. Pulp samples from a novel unique Eucalyptus triple hybrid [Eucalyptus grandis × (Eucalyptus urophylla × Eucalyptus globulus)] were obtained by various pulping processes – kraft, soda-anthraquinone (NaOH-AQ), and thermomechanical pulping (TMP). The chemical composition of the fiber surfaces was evaluated by X-ray photoelectron spectroscopy (XPS). The surface lignin content of NaOH-AQ pulp fibers was lower than that of the kraft counterpart. However, kraft pulp handsheets showed better physical and mechanical properties. XPS data strongly suggests that together with the pulp bulk chemical composition the xylan is more abundant on the surface of kraft fibers, which is reflected on their better mechanical properties. Moreover, the relatively low surface lignin content in TMP pulp compared to wood suggests that defibration takes place in the secondary wall, where lignin is less concentrated.

TEMPO-mediated oxidation of oat β-d-glucan and its influences on paper properties

An enhanced bonding agent for papermaking was prepared by selective oxidation of a hemicellulose-rich byproduct of oat processing, which will be identified here by its primary component, β-d-glucan. The β-d-glucan was treated sequentially with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) and sodium hypochlorite, or alternatively just with sodium hydroxide. When added to a slurry of unbleached softwood kraft fibers, in combination with an optimal dosage of aluminum sulfate, the oxidized β-d-glucan yielded greater increases in tensile strength and folding endurance in comparison to untreated β-d-glucan. NaOH treatment also improved dry-strength performance of the β-d-glucan, except for folding endurance. The improvements were attributed to increased charge density of the treated polyelectrolytes, leading to better distribution and retention on fibers prior to sheet formation. Modified β-d-glucan also enhanced the strength of recycled sheets when the treated paper was repulped and formed into recycled paper with no further chemical addition.

Enzymatic strategies to improve removal of hexenuronic acids and lignin from cellulosic fibers

Abstract Different enzymatic strategies were applied to improve lignin and hexenuronic acid (HexA) removal. Three laccases (L) with different redox potentials were applied in combination with 1-hydroxybenzotriazole or methyl syringate to softwood sulfite and hardwood kraft fibers. The enzymes with a high-redox potential from Pycnoporus cinnabarinus and Trametes villosa were found to be the most efficient. The bleaching efficiency was not significantly influenced by the presence or absence of HexA in the different types of lignocellulosic fibers. Subsequently, the lignin or HexA removal in the presence of different mediators was evaluated in eucalyptus fibers with the T. villosa laccase (TvL). Natural mediators removed only lignin, whereas the combinations of TvL with synthetic mediators removed both HexA and lignin. The mediator violuric acid (VA) was the most efficient as judged by the properties of fiber and effluent. A xylanase pretreatment stage was found to boost the access of the LVA system to HexA without affecting lignin in the pulp.

Effect of tempo and periodate-chlorite oxidized nanofibrils on ground calcium carbonate flocculation and retention in sheet forming and on the physical properties of sheets

Nanofibrils (NFC) or microfibrils (MFC) are potential candidates for high filler-loaded papers and board as they are able to compensate for strength loss caused by the filler itself. However, the interaction of nanofibrils and the filler during sheet forming is not yet well understood. The aim here was to examine 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) and periodate-chlorite oxidized (DCC) anionic nanofibrils during sheet forming in order to determine their effects on flocculation, filler retention and the strength and optical properties of the handsheets. The experiments were carried out by manufacturing filler-loaded sheets from refined kraft fibres and ground calcium carbonate (GCC) with various added levels of TEMPO and DCC nanofibrils. The results showed that both types of nanofibril caused pronounced agglomeration of the GCC filler, which increased its retention in the paper web. Given the same filler content, the strength properties were the same or slightly better than in a sheet formed without any chemical agent, while light scattering was slightly inferior. Poorer formation seemed to be the explanation for why the increased bonding induced by NFCs was not reflected in obviously better sheet strengths. The physical properties of sheets containing NFC were superior to those of sheets formed with cationic polyacrylamide as a retention aid with the same filler content and level of formation. Thus NFCs seem to be potential retention aids for use in fine paper production instead of traditional polymers.

Crystallization behavior of organo-nanoclay treated and untreated kraft fiber–HDPE composites

Both non-isothermal and isothermal crystallization behaviors of neat HDPE and organo-nanoclay treated and untreated kraft fiber–high density polyethylene (HDPE) or HDPE–maleic anhydride polyethylene (MAPE) composites were analyzed using differential scanning calorimetry (DSC). The isothermal crystallization process was studied by the Avrami model. The crystallization patterns and organo-nanoclay distribution was characterized by X-ray diffraction (XRD). It was found that both organo-nanoclay treated and untreated kraft fibers could act as nucleating agent for the HDPE polymer when the fiber length was comparatively small. All composites crystallized much faster than the neat HDPE, while their crystallinity levels were lower. The organo-nanoclay treatment of kraft fibers made the crystallinity level lower, but the nucleation rate increased in the composites compared to the untreated kraft fiber–HDPE composites. But both the crystallinity level and the nucleation rate of the composites were increased by adding MAPE compatibilizer to the composites. MAPE increased the d-spacing of the organo-nanoclay layers in the composites and resulted in exfoliated clay platelets when the fiber loading was as high as 40wt%.

Pulp fiber-reinforced thermoset polymer composites: Effects of the pulp fibers and polymer

In this study, composites were fabricated with four types of pulp fibers and two types of thermoset polymers. Four pulp fibers included hardwood and softwood high-yield pulp (HYP), Kraft pulp, and Whatman cellulose fibers and two polymers included unsaturated polyester (UPE) and vinyl ester (VE). FTIR and TGA results showed the chemical differences among the four pulp fibers and confirmed the existence of lignin on the HYP pulp fibers. The two HYP fibers were more compatible to the UPE resin, while the Kraft and Whatman cellulose fibers were more compatible to the VE resin as indicated by the tensile properties. Lignin on the two HYP fibers acted as a natural coupling agent for the natural fiber and the more hydrophobic UPE resin. The two cellulose-rich pulp fibers performed better when the VE resin was used. Composite storage moduli were significantly improved as compared with those of the neat UPE and VE resins. Only a slight increase in glass transition temperature was noted for the composites.

Mechanical properties and dimensional stability of organo-nanoclay modified biofiber polymer composites

In this study, hydrophobic Kraft fibers were obtained by organo-nanoclay modification. The treated fibers were used as reinforcements for improving mechanical performance and dimensional stability of high density polyethylene (HDPE) composites. After the organo-nanoclay treatment, Kraft fibers had a more uniform dispersion in the HDPE matrix and the resulting composites had a higher Young’s modulus and thermal stability than the composites containing untreated fibers. The addition of 5wt% of maleic anhydride polyethylene (MAPE) compatibilizer improved fiber and matrix adhesion and resulted in increased tensile strength and Young’s modulus as well as thermal stability of both treated and untreated fiber composites. However, this improvement was more significant for the composites with the treated fibers. In addition, water absorption of the organo-nanoclay treated Kraft fiber–HDPE composites decreased after adding the compatibilizer.