Stone Groundwood Pulp Research Articles

Silane-modified high-yield lignocellulosic fibers as reinforcement of polylactic acid: Enhancement of interfacial adhesion for high-performance biocomposites

This study investigates the enhancement of PLA-based biocomposites using high-yield mechanical stone groundwood (SGW) pulp, with a focus on reinforcing fiber-matrix interactions through silane-coupling fiber modification. Different fractions of SGW (20 and 30 wt%) and (3-glycidyloxypropyl)trimethoxysilane (GPS) as a coupling agent (3, 5, 7, and 10 wt%) were incorporated into the PLA matrix. Thermo-mechanical properties including melt flow index, melt rheology, tensile strength, and Young’s modulus were evaluated, along with thermal degradation behavior via TGA and DSC. Non-modified and partially modified SGW fractions (20 and 30 wt%) improved PLA-SGW interface, resulting in increased tensile strength (14 % and 27 % respectively). Biocomposites with 30 wt% SGW modified with 5 and 7 wt% GPS exhibited the highest tensile strength improvement, along with the rest of the properties, attributed to GPS influence on melt flow index and processability. The obtained biocomposites showcased properties comparable to commodity polypropylene composites.

Development of a fast brightness testing method for mechanical pulp based on microwave oven drying

Brightness is an important quality parameter for pulp products, and it is important to have reliable measurement of pulp brightness in a timely manner for process control and/or quality control purposes. In these circumstances, a quick testing method for pulp brightness is highly desirable. A rapid handsheet brightness testing method for lignin-rich mechanical pulp has been developed, which is based on the use of tap water to make handsheets and microwave ovens to rapidly dry the handsheet. Microwave oven fast drying decreased the handsheet brightness of mechanical pulp by 5–6 points due to the lignin-originated discoloration reactions. The spray of ascorbic acid and ethylenediaminetetraacetic acid (EDTA) solutions to the handsheet can effectively inhibit these lignin discoloration reactions. With 0.2% ascorbic acid and 0.2% EDTA spraying on the wet pulp handsheet, the brightness of the handsheet from a peroxide-bleached stone groundwood pulp after the microwave oven fast drying method was similar to that obtained from the same pulp but following TAPPI Standard Test Method T 272 sp-12 “Forming handsheets for reflectance testing of pulp (sheet machine procedure)”. The effect of handsheet dryness on the handsheet brightness was also studied, and the results showed that the brightness reading was almost constant in the dry-ness range of 70% to 90%. The method developed is a reliable, fast brightness testing method for lignin-rich pulp that is of practical interest in industrial operations.

Research on the Strengthening Advantages on Using Cellulose Nanofibers as Polyvinyl Alcohol Reinforcement.

The present work aims to combine the unique properties of cellulose nanofibers (CNF) with polyvinyl alcohol (PVA) to obtain high-performance nanocomposites. CNF were obtained by means of TEMPO-mediated ((2,2,6,6-Tetramethylpiperidin-1-yl)oxyl) oxidation, incorporated into the PVA matrix by means of compounding in a single-screw co-rotating internal mixer and then processed by means of injection molding. It was found that CNF were able to improve the tensile strength of PVA in 85% when 4.50 wt % of CNF were added. In addition, the incorporation of a 2.25 wt % of CNF enhanced the tensile strength to the same level that when 40 wt % of microsized fibers (stone groundwood pulp, SGW) were incorporated, which indicated that CNF possessed significantly higher intrinsic mechanical properties than microsized fibers. SGW was selected as reference for microsized fibers due to their extended use in wood plastic composites. Finally, a micromechanical analysis was performed, obtaining coupling factors near to 0.2, indicating good interphase between CNF and PVA. Overall, it was found that the use of CNF is clearly advantageous to the use of common cellulosic fibers if superior mechanical properties are desired, but there are still some limitations that are related to processing that restrict the reinforcement content at low contents.

Medium density boards made of groundwood fibres: an analysis of their mechanical and physical properties

The use of stone groundwood (SGW) pulp in paper manufacturing has constantly decreased in the last decades due to the increasing recycling of paper. The production capacity for SGW fibres is however still available in many paper mills, which could be exploited for alternative applications, like for example medium density fibreboards (MDF). Thin SGW MDF of 800 kg/m3 in density, 2 mm in thickness and bonded with polydiphenilmethan-4,4′-diisocyanate (PMDI) or urea–formaldehyde (UF) adhesives were produced with varying resin contents, raw fibres moisture content and hot-pressing parameters. Their mechanical characteristics, dimensional stability and optical properties were investigated and compared to MDF made of coarser Asplund fibres. SGW MDF bonded with PMDI adhesive showed higher internal bonding (IB = 1.5–2.6 N/mm2), lower thickness swelling (TS = 22–24%) and whiter surfaces (distance from white E = 28–30) than Asplund MDF (IB = 1.3, TS = 42%, E = 42). The possible development of covalent links between SGW fibres and PMDI adhesive was indicated by Fourier transform infrared spectroscopy (FTIR). Bending properties of SGW MDF remained however inferior to Asplund MDF. SGW MDF might represent a suitable product for non-load bearing applications requiring low moisture susceptibility and the possibility for surface decoration, for example flooring and furniture elements.

The key role of lignin in the production of low-cost lignocellulosic nanofibres for papermaking applications

The use of cellulose nanofibres (CNF) for the enhancement of paper’s mechanical properties has been reported by many authors. Concretely, the available literature is mainly focused on TEMPO-oxidized cellulose nanofibres. However, recent industrial research projects, in which LEPAMAP group has been involved, have demonstrated that this type of nanocellulose has unaffordable production costs for the papermaking industry. In this sense, the present work aims to produce low-cost lignocellulosic nanofibres (LCNF), finding some strong alternatives to TEMPO-mediated oxidation. For that, lignocellulosic nanofibres (LCNF) were produced from stone groundwood pulp (SGW) from pine after a chemical pulping process (sodium hydroxide and antraquinone). The effect of lignin content was studied and controlled through bleaching steps and quantified. It was found that high lignin content makes nanofibrillation difficult. The reinforcing effect of CNF was mechanically characterized by the addition of 3wt% of CNF into different papermaking pulps. The results showed that it is possible to obtain low-cost LCNF that provide the same increase in mechanical properties than TEMPO-oxidized CNF when they are used for paper reinforcement. It was also found that lignin plays an important role in the obtaining of LCNF by fully mechanical treatments, where lower lignin contents expedite the nanofibrillation.

Impact and flexural properties of stone‐ground wood pulp‐reinforced polypropylene composites

This study analyses the flexural and impact strength of polypropylene reinforced with stone ground wood pulp (SGWP) and the effect of a maleated‐polypropylene (MAPP) coupling agent on the mechanical properties of these composites. Composites prepared in the absence of the coupling agent showed a very light positive linear evolution of the flexural strength with the percentage of reinforcing fiber. In contrast, composites that included MAPP in their formulation presented highly noticeable improvements with fiber content. By applying mathematical modeling strategies, the flexural modulus has been analyzed using the Cox–Krenchel model. Similarly, the flexural and tensile strength factors for the reinforcing fiber have been defined and utterly allowed for the determination of intrinsic fiber flexural strength. POLYM. COMPOS., 34:842–848, 2013. © 2013 Society of Plastics Engineers

STONE-GROUND WOOD PULP-REINFORCED POLYPROPYLENE COMPOSITES: WATER UPTAKE AND THERMAL PROPERTIES

Two of the drawbacks of using natural-based composites in industrial applications are thermal instability and water uptake capacity. In this work, mechanical wood pulp was used to reinforce polypropylene at a level of 20 to 50 wt. %. Composites were mixed by means of a Brabender internal mixer for both non-coupled and coupled formulations. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to determine the thermal properties of the composites. The water uptake behavior was evaluated by immersion of the composites in water until an equilibrium state was reached. Results of water absorption tests revealed that the amount of water absorption was clearly dependent upon the fiber content. The coupled composites showed lower water absorption compared to the uncoupled composites. The incorporation of mechanical wood pulp into the polypropylene matrix produced a clear nucleating effect by increasing the crystallinity degree of the polymer and also increasing the temperature of polymer degradation. The maximum degradation temperature for stone ground wood pulp–reinforced composites was in the range of 330 to 345 oC.

Mechanical Pulping: High consistency hydrogen peroxide bleaching of a Norway spruce stone groundwood pulp: Influence of heat treatment and iron content

The objective of this work was to improve the understanding on how thermal treatments of mechanical pulps containing iron influence the unbleached brightness and hydrogen peroxide bleachability at ...

Analysis of printing and writing papers by using direct analysis in real time mass spectrometry

A quick and direct method for identifying organic components of papers in library and archival collections with minimal destructive sampling is needed for preservation, forensic, and general purposes. Direct analysis in real time mass spectrometry (DART-MS) is used for characterizing 16 reference papers of known manufacture in terms of their pulp composition and pitch contaminants. Unique mass spectra are obtained from bleached kraft, chemithermomechanical, and stone groundwood pulp papers in real time without extractions, derivatizations, chromatographic separations, and other time- and chemical-consuming sample preparations. Phytosteroids are volatilized from bleached hardwood kraft but not from bleached softwood kraft papers, which differentiates the two of them. The kraft papers are in turn differentiated from chemithermomechanical pulp papers by lignin-derived thermolyis products: syringyl products arise from hardwood, but guaiacyl and coumaryl products arise from softwood, chemithermomechanical pulp papers. Stone groundwood papers contain a number of extractives that are volatilized, which serve to differentiate them from all the other papers. Papers that contain rosin vs. alkyl ketene dimer (AKD) sizings are immediately differentiated. The DART-MS methodology is fast and simple, and the spectra are repeatable. Microsamples as small as ∼10 μg tweezed from the paper surface may be analyzed. These benchmark spectra are the prelude to further applications of DART-MS in paper research and the beginning of the development of a searchable library of DART-MS spectra of printing and writing papers by the Library of Congress.

An industrial evaluation of a stand level grading system forPinus patula

Abstract This paperreports on progress madein the development and implementation ofa standlevel woodquality grading system for P. patula identified for processing in Mondi Merebank's stone ground wood and thermo-mechanical pulp lines. The grading system stratified the resource using fiber collapsibility as the selection criteria. The paper evaluates the impact of the grading system on the process parameters and the basic characteristics of pulp produced by the different pulp lines. The grading system was found to have a positive impact on desired pulp quality criteria. Variability inherent in the resource and the production process declined significantly upon implementation of the grading system. The results indicate the level of improvement that can be realized from a simple wood quality grading system. It is anticipated that a more detailed understanding of factors impacting on wood and pulp characteristics, and resource and process variation will support a process of continuous pulp quality improvement...

Attempt to photostabilize paper made from high-yield pulp by application of UV screens in conjunction with thiols

The stabilization against photoinduced brightness reversion of peroxide-bleached stoneground wood pulp by two phenolic UV screens (methyl 3-hydroxy-4-benzoylphenoxy acetate (DHBE) and methyl 3-(2″-benzotriazinyl)-4′-hydroxy-5′-terbutylphenyl propanoate HBTE) and two polyethyleneoxythiols (2-(2′-methoxyethoxy)ethanethiol (MSH) and 2,2′-oxydiethanethiol (DSH), individually or in combination (DHBE + MSH and HBTE + DSH), was investigated. A synergistic photostabilization effect was observed between the thiol and the UV absorber, but was not retained during irradiation due to thiol consumption probably by Michael-type addition on the quinones, generated by light. Moreover, during the irradiation, the HBTE derivative was found to be very stable on paper in contrast with the DHBE compound. This effect was related to the presence in HBTE of a bulky substituent (tert-butyl) adjacent to the phenolic group which locks the molecule in a favorable conformation for proton transfer in the ground and excited states.

Comparative study of stone-ground wood pulp and native wood 3. Application of fluorescence spectroscopy to a study of the weathering of stone-ground pulp and native wood

Abstract The fluorescence spectra of chemically treated and weathered paper made from stone-ground wood pulp (SGWP) and thin sections of wood treated in a similar manner have been recorded. Very little difference was found between the paper and wood samples. Chemical treatment included reduction with sodium borohydride and photochemical bleaching with thiourea dioxide. The samples were subjected to photobleaching of the fluorescent chromophores, and the wood samples and paper exhibited a photochromic effect. Of particular significance was the observation that borohydride-reduced and thiourea-dioxide-photobleached wood perform differently in the photobleaching experiments from their paper counterparts. These differences are attributed to the mechanochemistry which occurs during pulping, producing species such as stilbenes which are present in the paper but not in the wood. When borohydride-reduced SGWP and wood are weathered, much of the short-wavelength fluorescence is lost and in increase in longer wavelength emission is observed. Reduction by borohydride of the weathered samples leads to partial recovery of the shorter wavelength fluorescence. These observations are interpreted as being due to photoreactions of 4-hydroxy-3-methoxycinnamyl alcohol residues.

Comparative study of stone-ground wood pulp and native wood 2. Comparison of the fluorescence of stone-ground wood pulp and native wood

Abstract The fluorescence spectra of paper made from high yield pulp (stone-ground wood pulp (SGWP)) and of thin sections of a softwood (Abies) were recorded and shown to be very similar. The fluorescence from a wood sample, previously reduced with sodium borohydride, shows a biexponential decay, with the magnitude and contribution of the components being dependent on wavelength. From the bleaching kinetics of the chromophores producing the fluorescence, it is concluded that the emission observed for paper made from high yield pulp and for wood originates mainly from lignin and not as previously suggested from cellulose. The steady state and dynamic fluorescence of some lignin model molecules adsorbed on cellulose indicates that the fluorescence of wood, which has been reduced by sodium borohydride, might originate to some extent from coniferyl alcohol and biphenyl-type structures.

FT-IR Study of UV-Irradiated Stoneground Wood Pulp

The photo-induced colour reversion of handsheets of unbleached and bleached stoneground wood pulp was studied by FT-IR transmission spectroscopy. Changes in the chemical structure of thin handsheets were monitored quantitatively as a function of repeated exposures to UV irradiation at 320 nm followed by storage in the dark. A slight loss of carbohydrate structures was observed throughout the cycles, while a pronounced loss in lignin aromaticity was produced by the UV irradiation.

Bleaching of Eucalypt Pulps Studied by Carbon-13 N.M.R. Spectroscopy

Abstract Cross polarization, magic-angle spinning, interrupted decoupling and paramagnetic doping techniques have been combined to provide the sensitivity needed for detection of chemical functional groups involved in pulp bleaching reactions. Cold soda pulp and stone groundwood pulp were bleached by calcium hypochlorite and hydrogen peroxide respectively. These treatments had little effect on ketonic structures and no effect on etherified aryl units, but hypochlorite degraded most lignin units not linked in beta-0–4 ethers. This work provides direct confirmation of published predictions based on bleaching of model compounds in solution.

Study on Pulp Bleaching Hydrogen Peroxide Spray Bleaching of Unbleached Pulp and Bleached Pulp

A laboratory scale study and experiments on the operating machine were made on bleaching many kinds of pulp by using Hydrogen Peroxide spray bleaching. Pulp sheet machine is quite conformable to Hydrogen Peroxide spray bleaching method. Basical conditions required for Hydrogen Peroxide bleaching process, such as low temperature, fairly long reaction period and high consistency were all satisfied with pulp sheet machine. Experiments have shown that much higher brightness is obtained by this method than with the equal rate of chemical cost. The presence of Hydrogen Peroxide residue in the finished pulp increased the brightness of the pulp while it was stored. However, this method was not available for stone groundwood pulp. Such as low temperature and long bleaching process time are not effective for stone groundwood pulp compared with the tower bleaching process. High charge of Hydrogen Peroxide is required for stone groundwood pulp, chemimechanical pulp and unbleached sulphite pulp compared with semibleached sulphite pulp and bleached sulphate pulp.