Interactions between fibres, fines and fillers in papermaking:influence on dewatering and retention of pulp suspensions

Abstract Interactions between the components of papermaking suspensions (e.g. fibres, fillers, fines and polymers) have a remarkable effect on various unit processes in papermaking. The filterability of fibre suspensions, which is a crucial property for example in paper sheet forming and solid recovery, is also known to be depended on particle interactions. However, due to the complex nature of the interactions, the role of these phenomena in fibre suspension filtration is still not fully understood. The focus of this thesis was to find out how phenomena associated to fibre flocculation, fibre deflocculation and filler particle deposition affect the filterability of fibre suspensions in terms of their dewaterability and retention. It was shown that the influence of fibre flocculation on dewatering is closely related to the structure of fibre flocs. More importantly, the internal density of flocs and factors that impacted the packing structure of filter cakes, such as floc size, played a crucial role in fibre suspension dewaterability. Dense flocs with a low internal porosity particularly induces fast water flow by a mechanism termed as the “easiest path mechanism” through the large voids around the flocs. The effect of fibre suspension dispersing on dewaterability and particularly fines retention was found to be associated to the mechanism of action of the deflocculation agent. Carboxymethylcellulose (CMC), the deflocculant used in this study, had detrimental effects on the dewatering of a pulp suspension both when being adsorbed on fibre surfaces and when remained in the liquid phase. However, adsorbed CMC causes more plugging of the filter cake because it disperses the fines more profoundly. Thus the adsorbed CMC also reduces fines retention considerably more than CMC did in the liquid phase. Filler deposition and retention was found to be significantly higher on pulp fines fractions of mechanical and chemical pulp than on fibre fractions due to the higher external surface area of fines. The surface charge densities of pulp fractions also affected their ability to adsorb fillers. Cationic charges of filler particles was in turn observed to induce deposition of fillers on fibre surfaces which increased retention but also the dewaterability of a fibre suspension due to a decrease in total surface area of a suspension

Magnetic superabsorbents based on nanocellulose aerobeads for selective removal of oils and organic solvents

Abstract Superabsorbent aerogels are fascinating materials for oil and chemical spillage cleanup. However, the development of an economic and efficient superabsorbent is still highly challenging. In this study, we introduce a novel approach to prepare very low density (0.005 g/cm3), highly porous (>99.6%), economic, reusable, hydrophobic, and magnetic spherical cellulose nanofiber-derived aerogels (i.e., aerobeads) prepared from waste boxboards via a simple freeze-drying procedure. The spherical aerobeads were fabricated easily after dropping a hydrophobized nano-fibrillated cellulose solution containing magnetic Fe3O4 nanoparticles into liquid nitrogen. The aerobeads showed outstanding absorption efficiency for several oils and organic solvents (up to 279 g/g with castor oil) and demonstrated excellent selectivity for absorbing oil from an oil/water mixture. Moreover, they were easily collected by an external magnet, indicating excellent recyclability and reusable for at least 10 cycles while still retaining supreme absorption capacity (up to 101 g/g for diesel oil). This study proposes an economic and novel method for the large-scale preparation of spherical superabsorbent aerobeads, making them a promising candidate for the efficient and sustainable cleaning of oil and chemical spills

Enhancing packaging board properties using micro- and nanofibers prepared from recycled board

Abstract In this study, cellulose microfibers and cellulose nanofibers (CNF) prepared from recycled boxboard pulp using a mechanical fine friction grinder were used as reinforcements in a board sheet. Micro- and nanofibers manufactured by mechanical grinding have typically broad particle size distribution, and they can contain both micro- and nano-sized fibrils. Deep eutectic solvent of choline chloride and urea was used as a non-hydrolytic pretreatment medium for the CNF, and reference CNF were used without any chemical pretreatment. The CNF were ground using three grinding levels (grinding time) and their dosage in the board varied from 2 to 6 wt%. The results indicate that the board properties could be tailored to obtain a balance between the processability and quality of the products by adjusting the amount of CNF that was added (2–6 wt%). A preliminary cost assessment indicated that the most economical way to enhance the board strength properties was to add around 4% of CNF with a moderate grinding level (i.e., grinding energy of 3–4 kWh/kg). Overall, the strength properties of the manufactured board sheets improved by several dozen percentages when CNF was used as the reinforcement

Aqueous bifunctionalization of cellulose nanocrystals through amino and alkyl silylation:functionalization, characterization, and performance of nanocrystals in quartz microflotation

Abstract Surface modifications of cellulose nanomaterials can be used to tailor their surface charge and hydrophilicity-hydrophobicity characteristics. Additionally, it can facilitate the selective interaction of nanocelluloses with other solid particles to further expand their applicability in different fields. For instance, cellulose nanocrystals (CNC) with amphiphilic features are potential green alternatives in mineral processing such as particle flotation. In the present study, aqueous, one- and two-step silylation of CNCs with amino and alkyl silanes was considered to create a novel bifunctionalized CNCs that contained both positively charged amino silane moieties and hydrophobic alkyl chains. Especially, the effects of reaction conditions and different reaction routes on the silylation were investigated, and the electric surface potential and hydrophobicity of CNCs were determined. The bifunctionalization conducted by the simultaneous addition of an amino silane and alkyl silane led to a high reaction efficiency, and the grafting amount was notably higher than that obtained with the sequential reactions with individual reagents. After the functionalization, the hydrophobicity of the CNCs was strongly altered, leading to water contact angles of up to 135° on CNC films. However, the silylation with amino silanes slightly affected the ζ-potential of the functionalized CNCs. Due to the relatively low ζ-potential, the interaction and orthokinetic attachment of CNCs onto quartz surfaces were insufficient, resulting in a limited flotation recovery in microflotation using a Hallimond tube

Direct sulfation of cellulose fibers using a reactive deep eutectic solvent to produce highly charged cellulose nanofibers

Abstract Wood cellulose pulp was sulfated using a reactive deep eutectic solvent (DES). DES was prepared by heating sulfamic acid and urea together at 80 °C at a molar ratio of 1:4, 1:3, or 1:2. Sulfation of cellulose was performed by mixing dry cellulose fibers with DES at 80 °C, followed by heating at 150 °C for half an hour. Anionic charge as high as 3 mmol/g (degree of substitution of 0.68) was obtained with this simple chemical modification of cellulose at an elevated temperature using DES both as reaction media and reagent without any external solvent. The decrease in the urea content of DES improved the sulfation efficiency. In addition, the presence of urea led to the carbamation of cellulose to some extent. Cellulose sulfate (charge of 2.40 mmol/g) became a gel-like material in water, and after passing once through a microfluidizator, a highly transparent nanocellulose gel (transmittance of 0.1% solution at a visible light range was over 95%) was obtained. Sulfated cellulose nanofibers (SCNFs) exhibited a width of around 4 nm with a minor presence of elemental fibril aggregates (containing five or less elemental fibrils). SCNFs with high aspect ratio can have a potential end-use as a rheology modifier because of their high viscosity even at low concentrations or act as reinforcing additives

Cationic nanocelluloses in dewatering of municipal activated sludge

Abstract This study used cationic nanocelluloses (CNFC I and II) produced by nanofibrillizing periodate oxidized and aminoguanidine hydrochloride reacted wood cellulose as flocculation agents for municipal activated sludge. For both CNFC I and II, the diameters ranged from about 2–8 nm. Lengths ranged from hundreds of nanometers for CNFC I and about 50–100 nm for CNFC II. The charge densities for CNFC I and II were 1.07 and 1.70 meq g−1, respectively. The study examined the flocculation performance of the two CNFCs in the conditioning treatment of municipal activated sludge and compared the results with the performance of both a commercial coagulant and polyelectrolyte (polyacrylamide). Results showed that both CNFC I and II were able to flocculate activated sludge efficiently at effective doses similar to those of the commercial cationic polymer and at doses lower than the reference coagulant. Their efficiency in reducing turbidity was nearly as good as that of the synthetic reference polymer, and their COD was even better than that of the synthetic reference polymer. The performance of CNFC II was slightly better than that of CNFC I. In centrifugation analyses, the use of both CNFCs resulted in dense sludge cakes with moderate swelling and good colloidal-removal efficiency

Synthesis of imidazolium-crosslinked chitosan aerogel and its prospect as a dye removing adsorbent

Abstract The potential utility of Debus–Radziszewski imidazole synthesis in the fabrication of crosslinked chitosan was studied. Three-component crosslinkingwas achieved by using glyoxal and propionaldehyde to connect amine groups of chitosan via imidazolium crosslinking. A water-insoluble (at pH range of 2–10) chitosan was obtained at room temperature with a degree of substitution of 0.45 and aerogel was obtained after freezedrying. The ability of the imidazolium-crosslinked chitosan (ICC) aerogel to absorb an anionic dye, Direct Yellow 27, from a model water was then studied. Based on the Langmuir isotherm, at a pH of 4, an adsorption maximum of 2340 mg g⁻¹ (3.5 mmol g⁻¹) was obtained. In addition, due to the permanent cationic charge of imidazolium group, ICC exhibited excellent adsorption capacity, even under alkaline conditions. Methylglyoxal and benzaldehyde were also used to obtain other types of ICC, demonstrating the versatility of Debus–Radziszewski imidazole synthesis for fabrication of modified chitosan

Fast and filtration-free method to prepare lactic acid-modified cellulose nanopaper

Abstract Dewatering in the preparation of cellulose nanopapers can take up to a few hours, which is a notable bottleneck in the commercialization of nanopapers. As a solution, we report a filtration-free method that is capable of preparing lactic acid-modified cellulose nanopapers within a few minutes. The bleached cellulose nanofibers (CNFs), obtained using a Masuko grinder, were functionalized by sonication-assisted lactic acid modification and centrifuged at 14 000 rpm to achieve a doughlike, concentrated mass. The concentrated CNFs were rolled into a wet sheet and dried in a vacuum drier to obtain nanopapers. The nanopaper preparation time was 10 min, which is significantly faster than the earlier time period reported in the literature (up to a few hours of preparation time). The mechanical properties of nanopaper were comparable to the previous values reported for nanopapers. In addition, the method was successfully used to prepare highly conductive functional nanopapers containing carboxylated multiwalled carbon nanotubes

Pine sawdust modification using Fenton oxidation for enhanced production of high-yield lignin-containing microfibrillated cellulose

Abstract Sawdust is an abundant high-quality residue from sawmills, representing 20–30 % of sawn products by volume. In this study, the chemical pre-treatment of pine sawdust with Fenton’s reagent, formed from hydrogen peroxide and iron catalyst under moderately acidic conditions, was found to intensify the microfibrillation process in terms of energy consumption and improve the grade of the high-yield lignin-containing microfibrillated cellulose (LMFC) produced. With a minor yield loss of 5.5 wt.%, Fenton pre-treatment increased the microfibrillation rate and bonding potential of LMFC, indicating that the ultrastructure of the lignocellulose cell walls had been modified. Linear dependency between the growth of specific surface area and energy consumption was seen, i.e. microfibrillation followed Rittinger’s law of comminution. In comparison with the reference without any pretreatment,the total grinding energy consumption to a particle size of 14 µm was about 30 % lower (10.7 vs. 15 MWh/t) while the tensile strength and stiffness of LMFC films were 50 % (100 vs. 66 MPa) and 35 % higher (6.6 vs. 4.9 GPa), respectively. The advantageous effects of Fenton chemistry were assumed to originate from the cleavage of lignin-carbohydrate bonds, mainly between lignin and hemicelluloses. This phenomenon was supported by the substantially increased solubility of polysaccharides in dilute alkali. The calculated manufacturing costs of LMFCs (using the above-mentioned specifications) was € 850/t, of which the raw material, chemical and electricity costs accounted for 10 %, 2 % and 88 %, respectively. Without any chemical pre-treatment, manufacturing costs were € 1100/t of which raw material accounted for 7 % and electricity 93 %