Unrefined Pulp Research Articles

Preparation of chitosan derivative and its application in papermaking

To improve the paper strength, a number of resins and polymeric materials are being used, which is not environmental friendly and sustainable. Therefore, bio-based paper additives for the papermaking industry are essential. In this investigation, a water soluble biopolymer like carboxymethyl chitosan (CMCh) was prepared. The degree of substitution of the prepared CMCh was 2.49. The solubility of the prepared CMCh was 2.0 (w/v) % at 50 °C, and the conductivity increased with the increase of CMCh concentration in water. The prepared CMCh was applied as dry and wet strength agent of unrefined and refined softwood pulps. Both pulp increased dry and wet strength with increasing CMCh dose. An addition of 2.0 % CMCh increased dry strength by 125 % and wet strength by 293 % of unrefined pulp. On the other hand, the dry and wet tensile index of refined pulp increased from 59.48 N·m/g to 66.11 N·m/g and 2.48 N·m/g to 3.47 N·m/g, respectively, with the addition of 1.0 % CMCh. The CMCh was also used in filler modification. The precipitated calcium carbonate (PCC) modified with CMCh increased the ash content in paper with improved strength properties. The CMCh can be used in papermaking both for improving paper strength and filler retention.

Xylan extraction strategies and the performance of the resulting high purity cellulose fiber to swelling and dissolution

In this study, we investigated the influence of hemicelluloses removal treatment on the reactivity of the resulting pulp. The idea was to develop treatment strategies consisting of mechanical refining (different refining technologies), chemical treatment (CCE), and xylanase treatment that enabled both quantitative xylan removal as well as good reactivity to dissolution without the need for additional post-extraction treatments (cellulose activation) to improve reactivity. Cellulose post-extraction treatments result in additional production costs. The reactivity of the extracted pulps was evaluated based on the degree of swelling in NaOH and dilute cupriethylene diamine solution (CUEN), the solubility in 8% NaOH at -10 °C, and the Fock reactivity. The result obtained showed that hemicelluloses removal strategies that included mechanical refining treatment led to better pulp reactivity than unrefined pulp. The best result was obtained with refined pulp extracted with 6% soda (cellulose II not detected). In addition, we obtained a Fock reactivity ranging from 60 to 70%. The good correlations found between fiber swelling, solubility in caustic soda, and Fock reactivity suggest that the tedious Fock test could be substituted by the much simpler swelling and solubility measurements. The negative impact of cellulose II on pulp reactivity is due to the higher number of hydrogen bonds formed under dewatering and drying. This problem would most likely be averted in the ideal case where pulp dissolution is integrated into the pulp mill.

ENERGY EFFICIENT NANOCELLULOSE SHEETS FOR PRODUCT APPLICATION

synthetic polymers and plastics which are currently used as barrier materials in the packaging industry are neither renewable nor biodegradable, creating a serious threat to the ecosystem. Nano cellulose which is obtained by breaking down cellulose fibers into nano-scale dimensions has unique properties with the potential to dramatically impact many commercial markets including packaging. This research investigates the refining of cellulose fiber to produce sustainable nano cellulose using a laboratory PFI mill and industrial Disc refiner. Refined pulp was made into nano cellulose sheets using standard laboratory paper making technique through vacuum filtration. The tensile index and sheet density for PFI mill refined BEK and Disc refined NBSK showed approximately five times and two times improvement over unrefined BEK and NBSK pulp respectively highlighting the role of refining in improving the mechanical structure of nano cellulose sheets. This strength enhancement comes at a cost of 17417 kWh/t specific refining energy in lab-scale PFI mill refining and 3346.3 kWh/t specific refining energy in industrial-scale Disc refining. Fines generation as a result of refining decreased the porosity by 37.972% and 48.939% in Disc refined NBSK and PFI mill refined BEK respectively which improved the water vapor and oxygen permeability. Refining decreased the water vapor permeability by approximately ten times for both BEK and NBSK making them very comparable with synthetic polymers such as polyethylene (PE). The lowest value of oxygen permeability achieved with PFI mill refined BEK and Disc refined NBSK was 0.533±0.098 and 0.762±0.03 (cc.µm)/(m2.day.kPa) which is very competitive with that of polymers used in plastics. Additionally, the surface roughness decreased by 77.05% and 52.8% for PFI mill refined BEK and Disc refined NBSK respectively which promises refining as an excellent tool to produce smooth nano cellulose sheets for printed electronics applications.

Electrospray Deposition of Cellulose Nanofibers on Paper: Overcoming the Limitations of Conventional Coating.

While the potential of cellulose nanofibers to enhance the mechanical and barrier properties of paper is well-known, there are many uncertainties with respect to how to apply them. In this study, we use not only bulk addition of micro-/nanofibers and bar coating with oxidized nanofibers, but also a combination of these and, as a novel element, electrospray deposition of nanofiber dispersions. Characterization involved testing the strength of uncoated and coated paper sheets, their resistance to air flow, their Bendtsen roughness, and their apparent density, plus visualization of their surface and cross-sections by scanning electron microscopy. As expected, bulk addition to the unrefined pulp was sufficient to attain substantial strengthening, but this enhancement was limited to approximately 124%. Following this, surface addition by bar coating improved air resistance, but not strength, since, as applying nanocellulose at high consistency was technically unfeasible, this was performed several times with detrimental drying stages in between. However, replacing bar coating with electrospraying helped us overcome these apparent limitations, producing enhancements in both barrier and tensile properties. It is concluded that electrosprayed nanofibers, owing to their uniform deposition and favorable interactions, operate as an effective binder between fibers (and/or fines).

Influence of Hollander beater refining on xylan extraction from hardwood paper pulp by cold caustic extraction and xylanase treatment

Cellulose fibers’ complex and compact structure hinders the quantitative extraction of residual hemicelluloses from the fiber wall. In this study, hardwood kraft paper pulp was subjected to refining with a Hollander beater at different refining loads (3, 4.5, and 5.5 kg) in order to assess the impact of refining load on xylan removal by cold caustic extraction. The refined pulp showed high water retention values and specific surface area, which increased accessibility and a correspondingly high degree of xylan removal. Coupling refining and cold caustic extraction (100 g/L soda) achieved over 50% more xylan removal than the unrefined pulp (3% against 7%, respectively). Furthermore, an improvement in xylan removal (79%) was achieved by implementing a one-pot simultaneous refining and cold caustic extraction treatment at half the time required for the sequential treatment and low soda concentration (60 g/L). Finally, the benefit of beating was also observed for xylanase treatment. Overall, the combined extractions made it possible to remove 85% of xylan from a conventional hardwood paper pulp giving rise to a high purity cellulose pulp with unimodal and narrow molecular mass distribution.

Production of fines from refined kraft pulp by fractionation with micro-perforated screens

Abstract The objective in this work was to obtain a fine fraction of kraft pulp, with as high concentration as possible, in a pilot-scale fractionation with micro-perforated screen baskets. The influence of screen basket surface, hole size, feed concentration, pulp type and refining segment design was investigated. The results showed that a smooth screen basket surface improved the fractionation efficiency of the unrefined pulp compared to a profiled screen basket, despite a larger hole size. A significantly higher fine fraction concentration was obtained when using refined hardwood pulp compared to when using softwood pulp, which was explained with its lower average fibre length and narrower and thus more flexible fibre fragments. The pilot trials also showed that the screening process could be operated at feed concentrations similar to those directly after a refiner, 30–40 g/l. This was demonstrated in a process layout with partial recirculation where a refiner and a micro-perforated screen basket were operated in series in pilot scale.

TOGA feature selection and the prediction of mechanical properties of paper from the Raman spectra of unrefined pulp.

Process-monitoring laboratories in the pulp and paper industry generally use a combination of wet chemical analyses and physical measurements to certify the fitness of a production pulp for a specific end-use. These laboratory tests require time and the effort of trained personnel, limiting their utility for real-time process control. Here we show that Raman probes of unrefined cellulosic pulps, well-suited to the online measurement of in-process materials, can predict the quality attributes of manufactured papers. The accuracy of prediction improves when the covariance is modelled in a reduced measurement space selected by a data-driven, feature-selection technique referred to as a Template Oriented Genetic Algorithm (TOGA). TOGA, combined with discrete wavelet transform (DWT), isolates functional-group features that correlate best with mechanical properties paper derived from refined pulp. Paper makers refine market pulps to build sheet strength using a beating process that decreases freeness as it increases fibre-fibre bonding. Methods demonstrated here predict manufactured sheet properties obtainable after any specified degree of refining from the Raman spectrum of an unrefined pulp. This analysis capacity will enable both vendors of market pulp and makers of sheet paper to specify in advance the amount of beating required to produce a desired product, thereby saving cost and conserving resources.

Production of a fine fraction using micro-perforated screens

Abstract The objective for this work was to investigate the possibility to use a pressure screen equipped with a micro-perforated screen basket to produce a fine fraction from bleached chemical pulp. Trials were performed with unrefined bleached chemical hardwood pulp, and with unrefined and refined bleached chemical softwood pulp. The effect of feed concentration, feed flow, and volumetric fine fraction flow was evaluated. The difference between the fine fraction (i. e. the particles passing the screen) and the feed was analysed by studying the fibre morphology. The results showed that high feed concentration was positive for both the fine fraction concentration and the separation efficiency. A higher fine fraction concentration was also obtained when using hardwood pulp, which was explained by the shorter fibre length. Refining of the pulp prior to the fractionation proved beneficial, as a larger share of the refined pulp passed the screen, resulting in a twice as high concentration of the fine fraction when compared to unrefined pulp.

The shear and compressive yield stress of fibrillated acacia pulp fiber suspensions

Abstract The degree of interactions between fibers and the tendency of fibers to form flocs play an important role in effective unit operation in pulp and paper industry. Mechanical treatments may damage the structure of the fiber cell wall and geometrical properties, and ultimately change the fiber-fiber interactions. In this study, the gel crowding number, compressive and shear yield stress of fibrillated acacia pulps were investigated, and the results showed that the gel crowding number of the refined pulp samples ranged from 8.7 to 10.7, which were much lower than that of un-refined pulps. As the concentration increased, both the compressive yield stress P y {P_{y}} and shear yield stress τ y {\tau _{y}} of all suspensions increased accordingly, and the yield stress was found to depend on a power law of the crowding number. Moreover, the values of τ y / P y {\tau _{y}}/{P_{y}} were also examined and the variation of τ y / P y {\tau _{y}}/{P_{y}} became largely dependent on the fiber morphology and mass concentration.

Potassium hydroxide pulping of four non-woods

Four non-woods such as, dhaincha (Sesbania bispinosa), jute stick (Corchorus capsularis), wheat straw (Triticum aestivum) and corn stalks (Zea mays) were cooked by potassium hydroxide (KOH) at the optimum conditions of soda pulping. Dhaincha, wheat straw and corn stalks were delignified to kappa number 19.4, 13.6 and 19, respectively, while jute stick was not delignified sufficiently (kappa number 32.5). All these four raw materials maintained good yield in KOH process. Dhaincha produced the highest pulp yield (50.5%) and wheat straw had the lowest pulp yield (44.7). All pulps were bleached by D0EpD1 bleaching sequences in identical bleaching conditions. Final pulp brightness reached to above 80% ISO except jute stick pulp. Jute stick pulp reached to 74.9% brightness only after the consumption of 30 kg ClO2/ ton of pulp. The overall bleaching yields were 92.6%, 88.4%, 90.1 and 90.8% for dhaincha, jute stick, wheat straw and corn stalks pulps, respectively. The oSR of these four non-wood bleached pulps was above 20, consequently improved papermaking in the unrefined state. Beating rapidly increased papermaking properties, as for example, the tensile index of dhaincha pulps increased from 49 N.m/g in the unrefined pulp to 90 N.m/g in the beaten 50 oSR. It can be seen that KOH is a good substitute to soda process for non-wood.Bangladesh J. Sci. Ind. Res.53(1), 1-6, 2018

Comparative study of cellulose nanofiber blending effect on properties of paper made from bleached bagasse, hardwood and softwood pulps

Cellulose nanofibers (CNFs) offer the motivational prospective for a native fibrous constituent that can exceed the mechanical performance of plant fibers in current use for commercial products. In this research work, CNFs were prepared with an increased extent of mechanical refining from bleached bagasse, hardwood and softwood pulp fibers. These prepared CNFs were investigated by using the FE-SEM technique. During the increased refining process, partial fibrillation on the fiber surfaces was created, and these fibers were converted from the micro- to nano-scale through nanofibrillation. This shows the significant effect on the tensile, burst and tear strengths of paper made from unrefined and refined fibers. However, the optical properties remained almost constant with increases of the percentage of CNF and decreased significantly with increases of the refining intensity due to fiber damage. The strength properties of reinforced paper sheets were greater than those of paper sheets without reinforcement. The main drawback of this process is that the drainage time is longer with an increasing percentage of CNF in refined and unrefined pulp fibers.

Effects of Modified Cooking on Fiber Wall Structure of E. globulus and E. nitens

This work examined the impact of SuperBatch™ (SB), CompactCooking™ (CC), and Lo-Solids™ (LS) modified kraft pulping on the fiber wall structure of unbleached and bleached unrefined pulps of E. globulus and E. nitens. The kappa number target for all pulps was 17 ± 0.5. It was found that E. nitens had higher water retention values (WRVs) and fiber saturation point (FSP) for both bleached and unbleached pulps versus E. globulus. Fibril lateral aggregates width of unbleached pulps increased as WRV increased. After bleaching there was an inverse trend in correlation of WRV versus the lateral fibril aggregate width. The modified cooking methods or wood species did not have an influence on lateral fibril aggregate width. The higher WRV and FSP values for E. nitens were not reflected in the cumulative pore volume measurements including pore widths below 216 nm.

Chemical characterisation and suitability for papermaking applications studied on four species naturally growing in Tunisia

Four plants species namely Astragalus armatus, Retama raetam, Pituranthos chloranthus and Nitraria retusa were collected from Kasserine (Tunisia) to study their suitability for pulp and papermaking. Their chemical composition revealed that the α-cellulose content in R. raetam was lower than the normal range of hardwood, but the others were acceptable for pulp production. The Klason lignin content in these species was lower than 20%, except for N. retusa (26%). The amount of extractives in organic solvents was quite high (close to 10%) in R. reatam and P. chloranthus. The previous raw materials were pulped by using the soda-anthraquinone cooking process, the morphological properties, kappa number and the degree of polymerisation of the pulps obtained were determined. Finally, laboratory handmade standard sheets were prepared from the unrefined pulps of P. chloranthus and A. armatus. Their characterisation showed that the prepared papers present low density values and quite good mechanical properties particularly for the unbleached pulp. This study demonstrates the high potentiality of these two species for papermaking applications.

Evaluation of a Novel Hydrocyclone Design for Pulp Fractionation

Abstract The fractionation efficiency and operating conditions of a novel hydrocyclone design were evaluated. The novel design comprised a modified inlet section, where the pulp suspension had to pass a narrow ring-shaped opening, and a very compact fractionation zone. The effect of feed concentration and fine fraction mass ratio was studied. The experiments were performed with fully bleached, unrefined and never-dried chemical softwood pulp. Fractionation efficiency was evaluated in terms of change in surface roughness of handsheets. Feed concentration had a large influence on the fractionation results, with a lower feed concentration resulting in improved fractionation efficiency. Furthermore, the surface roughness improved considerably for very low fine fraction mass ratios. Surprisingly, these ratios were much lower compared to the share of earlywood fibres in the pulp. The novel hydrocyclone design showed a lower thickening of the coarse fraction when compared with previous experiences with conventional hydrocyclones. Based on these results a hypothesis on the separation mechanism in a hydrocyclone was proposed. It suggests the existence of a radial variation in suspension composition in the fractionation zone, and most likely also a layer of unfractionated feed pulp along the outer wall. The existence of the gradient and the layer could explain that, especially at higher feed concentrations, a significant improvement in surface roughness was only obtained when the fine fraction ratio was significantly below the earlywood fibre share in the pulp.

Investigation of the effect of drying and refining on the fiber–fiber shear bond strength measured using tensile fracture line analysis of sheets weakened by acid gas exposure

No reliable method exists for measuring the cellulose fiber–fiber shear bond strength in paper. This paper reports a simple method for measuring the fiber–fiber shear bond strength by weakening the fibers independently of the bonds in a sheet of paper, using acid vapor, until all the fibers break across the fracture line. The bond strength is then calculated from the fiber strength, as measured by the zero span test, at the point where the fibers first are weakened such that they all break. The method was used to calculate the average bond strength of handsheets made out of two different pulps. The first pulp was a never dried, 60% yield, unbleached radiata pine. The bond strength was 25.0 ± 3.3 MPa. Drying the fibers before reslushing and making sheets reduced the bond strength by up to 33%, with the reduction depending on the severity of the drying treatment. The second pulp was a bleached dried softwood kraft and was used to investigate the effect of low consistency refining on bond strength. The bond strength increased from 13.7 ± 1.0 MPa for the sheets made from the unrefined pulp to 37.0 ± 1.0 MPa, for the sheets made from the most heavily refined pulp. The bond strength measurements are considerably higher than previous literature estimates for the shear bond strength. The causes for the discrepancy include stress concentrations in tests of single fiber–fiber bonds.

Studying the effects of laccase-catalysed grafting of ferulic acid on sisal pulp fibers

Functionalization of sisal specialty pulp fibers by laccase-catalysed grafting of ferulic acid (FRC) was investigated. To this end, the extent of phenol coupling to fibers under different reaction conditions (laccase and FRC rates, and time) was evaluated in terms of pulp properties including kappa number (expressed as the combined contributions of lignin and hexenuronic acids), brightness, Klason lignin and surface anionic charge after Soxhlet extraction of acetone-treated pulp. The specific treatment resulting in the highest degree of grafting was then used in a comparative study of the effects of applying the laccase–FRC system to refined and unrefined pulp with a view to confirming whether the increased surface area obtained by effect of fibrillation would lead to enhanced grafting. Based on the results, refining the pulp prior to the enzyme treatment resulted in increased grafting which in turn led to handsheets with improved strength-related properties (particularly wet tensile strength) relative to control samples.

Chemical composition and pulping of date palm rachis and Posidonia oceanica – A comparison with other wood and non-wood fibre sources

In the present paper, the valorisation of two residues: Posidonia oceanica and date palm rachis was investigated. First, their chemical composition was studied and showed that they present amounts of holocellulose, lignin and cellulose similar to those encountered in softwood and hardwood. Extractives in different solvents and ash contents are relatively high. Moreover, ash composition assessment showed that silicon is the major component (17.7%) for P. oceanica. The high ash quantity and the low DP (about 370) may be considered as serious disadvantages of P. oceanica, in the pulping and papermaking context. Oppositely, the properties of rachis date palm and those of the ensuing pulp, obtained from a classical soda-anthraquinone cooking, demonstrated the suitability of this agricultural by-product for papermaking. Preliminary tests conducted on unrefined pulp suspensions and handsheets from date palm rachis in terms of freeness, Water Retention Value and mechanical properties allowed confirming the good quality of date palm rachis fibres.

Cationic Alkoxylated Amine Surfactant as a Debonding Agent for Papers Made of Sulfite-Bleached Fibers

Today, there is a steadily increasing demand for the application of surfactants as debonding agents in tissue manufacturing. The work presented herein focused on evaluating the debonding ability of cationic alkoxylated amine surfactant on unrefined and refined fibers. The results showed that, as the dosage of the surfactant was increased to 10 mg/g on unrefined pulps, the adsorption of the surfactant on the fibers increased to 5 mg/g, and the tensile and burst indices of the papers made of the modified fibers decreased by as much as 12.6% and 14.9%, respectively. Also, the roughness, strain, and moisture content of the papers were enhanced, whereas the apparent density was reduced. Furthermore, the tear index of the papers increased upon the application of surfactant (10 mg/g) at the expense of reductions in tensile and burst indices, as well as the apparent density at any pressure applied in wet pressing. Also, as the pressure was increased, the surfactant impacted the fiber bonding more significantly. O...

Characterization of hairs and pappi from Cynara cardunculus capitula and their suitability for paper production

The capitula of Cynara cardunculus contain hairs and pappi representing 7% of the total plant biomass. These low density biomass components could be mechanically separated without apparent losses using a whole-plant processing prototype. Hairs and pappi are filamentous structures made up of longitudinally aligned fibre cells, without intercellular voids or pitting, with the following dimensions regarding length, width and wall thickness: 1.35 mm, 19.8, and 4.8 μm for hairs and 1.78 mm, 10.4, and 2.9 μm for pappi. Chemically hairs and pappi have low content of ash (1.9% and 1.1%, respectively), extractives (5.4% and 6.0%) and lignin (10.6% and 17.8%), and high content of holocellulose (77.5% and 72.8%) and α-cellulose (55.2% and 46.8%). Pulps could be produced using a conventional kraft process with high yields and low residual lignin, e.g. 63% at Kappa 7 for hairs and 48% at Kappa 11 for pappi, low coarseness values (0.04 and 0.03 mg m −1) and adequate pulp properties for paper (40 and 42 N mg −1 tensile index; 3.6 and 3.4 kPa m 2 g −1 burst index in unrefined pulps of hairs and pappi, respectively). The results also indicated that there is scope for improving pulp quality by optimising pulping conditions to this type of new raw materials. The differences between hairs and pappi may also be further exploited namely the lower lignin content of hairs and the higher slenderness and wall thickness of pappi fibres. The utilization of hairs and pappi may strengthen the differentiated use of biomass fractions of the Cynara plant and its potential as a bioenergy crop.

A comparison of kraft, PS, kraft-AQ and kraft-NaBH 4 pulps of Brutia pine

The aim of this work was to study the effect of adding PS, AQ and NaBH 4 into kraft pulping with special attention given to NaBH 4. Kraft, kraft-AQ, PS, and kraft-NaBH 4 pulps were produced under the same cooking conditions and the pulps produced were compared in terms of pulp and paper properties. Kraft method was modified by adding 0.1% AQ, 4% PS and 2% and 4% NaBH 4 and the resultant pulps displayed an increase in pulp yield and reduction in both kappa number and screening rejects. On the other hand, there observed an increase in both pulp yield and kappa number when the kraft was modified to PS method. The benefits of NaBH 4 addition into kraft pulping was a significant reduction in kappa number and screening rejects and a significant increase in pulp yield. The most notable outcome of NaBH 4 was 66.6% increase in pulp brightness when 4% NaBH 4 was added into kraft pulping. Of unrefined pulps, unrefined kraft pulp displayed the highest strength of pulp, which is described as tear index at a constant tensile index. Of refined pulps, kraft-AQ showed the highest pulp strength when refined to 6000 and 12,000 revs in PFI mill.