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While cationic cellulose has yet to find a place in the paper industry, manufacturers show certain interest in a more recent material: cellulose nanofibers (CNFs), generally with negative surface charge. This work suggests both to be combined to increase the mechanical properties of recycled paper while preventing the use of synthetic polyelectrolytes as retention agents. On one hand, a bleached pulp was cationized by etherification, both as-is and following mechanical refining (15,000 PFI revolutions) and submitted to high-pressure homogenization, generating two different kinds of cationic CNFs. On the other, the same pulp was submitted to an enzymatic pretreatment and high-pressure homogenization, producing a negatively charged cellulose micro/nanofiber (CMNF). Two different cellulose-based systems consisting of each type of cationic CNF and the enzymatic CMNF were applied in the papermaking of both virgin and recycled paper. This study demonstrates the effective use of the cationic CNFs as retention agents during sheet formation, which together with the enzymatic CMNFs significantly enhanced the mechanical properties of both types of paper. The study found that refining before cationization favored the retention effect, primarily due to increased surface area and charge of the cationic CNFs, where remarkable increases in the breaking length of virgin (125.1%) and recycled paper (46.5%) were reached. The synergy between cationic CNFs and enzymatic CMNFs outperformed the use of commercial polyacrylamide, a non-biodegradable polyelectrolyte. This research highlights the potential of tailored CNFs in producing high-performance papers, while promoting sustainability and offering a plausible strategy to increase paper recycling rates. [ABSTRACT FROM AUTHOR]

Paper is the largest renewable industrial substrate produced for various applications and can be recycled by disintegrating the fibers and reforming the paper. Paper and its fiber constituents lack functions such as electrical conductivity and papermaking itself has not been used for producing electronic devices. In this work, we show a potential industrially viable route for introducing cationic charges on the cellulose fibers and subsequently show how the adsorption of negatively charged ionically and electrically conductive materials onto these fibers from aqueous media can be applied at time scales relevant to industrial papermaking. This results in electroactive fibers, that can subsequently be used to prepare electroactive papers using standard papermaking procedures. Since fibers in the paper can selectively be coated with different active materials, various functions can be added into the paper. To demonstrate applications, we prepared electroactive papers using fibers with adsorbed carbon nanotubes (CNTs) and conducting polymers. We achieved conductivity of 21 S/m with only 1wt% CNT. We also prepared papers with CNTs and black phosphorus, used as paper-based lithium, and sodium ion battery (free-standing) anodes. They delivered a specific capacity of 642 mA h g−1 at 100 mA g−1 after 3500 cycles with 99.5% columbic efficiency. Furthermore, we recycled the papers, and as the disintegration of the fibers did not lead to removal of the ionic or electroactive materials from the fiber surface, the recycled papers showed similar electrical and mechanical properties to the original papers. This opens the path for recyclable paper-based electronics. [ABSTRACT FROM AUTHOR]

Nowadays, a high percentage (> 50%) of the paper produced in Europe uses recovered paper (secondary fibers) as raw material. In order to improve the mechanical properties of the paper produced, different kinds of additives are usually incorporated into the paper. Emerging renewable materials based on agricultural or forest residues, such as cellulose nanomaterials, have recently proved good capacities as reinforcing agents for different applications. In this work, pulp from wheat straw with a content of cellulose nanomaterial has been produced and tested as a mechanical reinforcing agent for paper production. A soda semi-chemical process was applied for the delignification of straw, to produce pulp with high cellulose content. Posteriorly, pulps with cellulose nanofibers were obtained in a high-pressure homogenizer, applying three different pretreatments to the cellulose pulp (acid hydrolysis, enzymatic hydrolysis and thermal treatment with glycerol) in order to facilitate the obtention of cellulose nanomaterial. Handsheets of paper were prepared from two sources of secondary fiber (fluting paper and old corrugated containers), adding different percentages of wheat straw derivatives (0, 3.5, 5 and 7%). The fibers' morphology and the papers' mechanical properties were investigated. Noticeable improvement rates (up to 25%) were observed for some mechanical properties of paper containing nanocellulose produced after the enzymatic and acid pretreatments. The quality of the secondary fibers source also affected the improvement rates achieved, with higher percentage changes for the lower-quality recycled paper. [ABSTRACT FROM AUTHOR]

As a kind of chemical additives, surfactants are widely used in the processes of papermaking, which played roles of wetting, dispersing, emulsifying etc. to adjust and maintain the product performance. However, there are few reports about the effect of surfactants on fiber properties, especially during paper recycling. This work investigated the effects of three types of surfactants on the cellulosic fibers and paper properties during five-time recycling. Properties of recycled paper with five times were presented as the index of papermaking potential. The results showed that cetyl trimethyl ammonium bromide (CTAB), a cationic surfactant, had an obvious negative effect on paper properties. For continuous surfactant supplements, the burst, tearing, and tensile index decreased by 50.2%, 41.6%, and 43.6%, respectively. Sodium dodecyl benzene sulfonate (SDBS), an anionic surfactant, had a significant positive effect on fibers' WRV and inhibited the fibers' hornification to some extent. However, it had a negative effect on paper properties by affecting the bonding between the fibers. Triton X-100 (TX-100), a nonionic surfactant, improved paper properties according to the papermaking potential. For adding surfactant only once, the burst, tearing, and tensile index increased by 15.0%, 8.59%, and 7.2%, respectively. For these three types of surfactants, TX-100 was generally more beneficial for fiber and paper. This paper revealed the effects of surfactants on the fiber and paper properties and perfected the theory of surfactants applied for fiber and paper in papermaking. [ABSTRACT FROM AUTHOR]

In this work, the efficiency of a polyelectrolyte complex (PEC) to retain different cellulose micro/nanofibers (CMNFs) during paper formation and to improve the physical properties of recycled unbleached fiber paper was analyzed. CMNFs were obtained from a commercial bleached eucalyptus pulp (BEP) using a PFI refiner followed by a chemical treatment with oxalic acid at two different concentrations. Finally, the pulp was fibrillated using a high-pressure homogenizer at three different intensities. The PEC was formed by addition of the xylan (Xyl) solution on chitosan (CH) solution with a Xyl/CH mass ratio of 80/20. The required dosages of PEC solution to neutralize the charges of different nanocellulose fractions were determined by ζ-potential measurements, and the CMNF retentions on recycled unbleached fibers were evaluated in a Britt Dynamic Drainage Jar. The results showed that the maximum retention was obtained when the neutral PEC-CMNF system was added to pulp. Besides, a significant decrease on °SR was observed when PEC and PEC-CMNF systems were added to the untreated pulp, limiting the negative effects of nanocellulose addition on pulp drainability. The incorporation of PEC-CMNF systems to the handsheets increased the tensile index (up to 28%), Mullen index (up to 40%) and internal bonding (up to 255%). Finally, the compressive strength of the handsheets, namely SCT and CMT, increased up to 30 and 70%, respectively. These simultaneous improvement on drainability and mechanical properties makes the proposed PEC-CMNF system a promising solution for the production of packaging paper. [ABSTRACT FROM AUTHOR]

Sustainable and low-cost old corrugated container (OCC) paper has been extensively employed in packaging materials for shipping and handling different products to substitute petroleum-based plastics. However, the poor mechanical strength and wet stability of OCC papers impede their general use. To solve these problems, we proposed constructing a dense carboxymethyl cellulose (CMC)-Mn+ (Mn+: Ca2+, Al3+) crosslinked network in the OCC papers' interior, allowing outstanding mechanical performance and waterproof. The resulting OCC-CMC-Al3+ paper demonstrated a superior tensile strength of 49.6 MPa and Young's modulus of 1.9 GPa, substantially higher than that of original OCC paper (tensile strength of 15 MPa, Young's modulus of 0.7 GPa) and comparable to commercial plastics. More significantly, the OCC-CMC-Al3+ paper demonstrated a superior wet strength of 13.0 MPa to the original OCC paper of 0.6 MPa. Additionally, the OCC-CMC-Al3+ paper exhibited excellent thermal stability, durability, and biodegradability. Generally, the biodegradable, strong, and water-resistant OCC-CMC-Al3+ paper is a potential and ecofriendly material for substituting nonbiodegradable plastics. [ABSTRACT FROM AUTHOR]

Organic sticky contaminants represent one of the biggest technical challenges in the paper recycling process. These contaminants reduce paper strength, cause plugging of wires and felts, and stick to or deposit on machine parts affecting the runnability of the paper machine. The removal of these sticky contaminants is difficult to achieve along the process due to the heterogeneous nature of these organic contaminants. In this study, the nature of sticky contaminants in multiple wastepaper grades was analyzed and characterized using screening, solvent extraction with subsequent analysis such as FT-IR, GC-MS, and SEM. The content of stickies in wastepaper varies among different paper grades and their recovery methods. The wastepaper from curb side collection contains nearly 4 times the amount of stickies than most of the wastepaper grades collected from a local paper recycling mill. Polyvinyl acetate polymers, styrene butadiene rubber (SBR), paraffin waxes and polyamines are the major components in the extracted sticky contaminants. In addition, these stickies deposit heavily on fibers surface leading to high negative charge in fibers suspension ranging between 2 and 4.5 µeq/L. It is expected that these findings will assist addressing the knowledge gaps in understanding the nature of stickies and their behaviors, and to eventually develop highly efficient technologies for contamination removal in the paper recycling process. [ABSTRACT FROM AUTHOR]

The mechanical strength degradation of recycled paper (RP) caused by the keratinization of recycled fibers is a basic problem to be solved urgently in the waste paper recycling industry. Compensating RP strength in a sustainable pathway is imperative and challenging. Cellulose nanofibrils with a three-dimensional interpenetrating network structure (3DIPN-CNFs) developed as a new family of strength additives for RP were demonstrated herein. The 3DIPN-CNFs were obtained from bagasse in a single bath treatment with H3PO4 and H2O2 under mild aqueous conditions. The tensile index and tear index of the RP with 3DIPN-CNFs were increased by 78% and 39%, respectively. 3DIPN-CNFs are less expensive and easier to obtain than Isolated-CNFs because homogenizing mechanical treatment is not required and are expected to become a sustainable strength additive for RP. [ABSTRACT FROM AUTHOR]

This paper develops a novel paper additive for effectively recycling old corrugated container (OCC) by functionalizing nanocellulose (NC) with diethylenetriaminepentaacetic acid (DTPA) and chitosan (CS), and investigate the reinforcing mechanisms and effect of the developed additive on the physical properties of recycled OCC pulp handsheets. The tensile, tear and burst index, air permeability, tensile energy absorption (TEA), and drainage performance of the recycled OCC handsheets are examined. Fourier transform infrared FTIR) spectroscopy, thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM) are used for the chemical and microstructure characterization of both NC based additives and paper from recycled OCC pulp. The results show that functional groups on the NC based additive, such as carboxyl, amino and hydroxyl groups, can bond with the hydroxyl groups on the recycled OCC fibres to generate a chemical bond. This leads to an increase in the crosslinks and bonding area between the fibres, which increases their tensile strength and improves their recycling rate. SEM shows that the paper with NC based additives had tighter inter-fibre bonds and smaller paper pore structure. Addition of 0.3% NC-DTPA-CS additive results in optimal properties of the recycled OCC paper with an increase by 31.64%, 22.28% and 36.6% of tensile index, tear index, burst index respectively, and the air permeability decreases by 36.92%. [ABSTRACT FROM AUTHOR]

The addition of nanofibrillated cellulose in paper production requires attention to its dispersion and retention during the paper forming process, and this is commonly facilitated by the use of retention agents. The performance of retention agents, which commonly have a cationic charge, is affected by the presence of dissolved and colloidal substances in the process water. In the process of paper production at an industrial level, especially when using recycled paper, there are a large amount of dissolved and colloidal substances in the water. A high proportion of these substances are negatively charged and are commonly referred to as anionic trash. Its presence increases the conductivity and charge density of the water, and this has a negative influence on the retention of cellulose nanofibers. In brown line paper production, some fibers have already been refined in at least one previous papermaking cycle. In this sense, recycled fibers have a reduced capacity to benefit from refining as they have suffered morphological damage. On the other hand, the addition of lignocellulosic nanofibers in the production of brown line paper has been found helpful to improve its properties and extend its lifespan. In this work the influence on the retention of nanofibers of different anionic trash levels in the water has been evaluated. The results showed its viability as a reinforcing agent in waters with high anionic trash content, through the addition of an anionic trash catching system. [ABSTRACT FROM AUTHOR]

In the recent years, several methods for producing cellulose nanofibers (CNF) have appeared. Depending on the type of treatment and its conditions, the source of cellulose and the fibrillation method, different properties and characteristics can be obtained. TEMPO-mediated oxidation has been extensively used for CNF production and it is considered as one of the most suitable treatments to obtain high-performance CNF with superior properties and reduced size. However, the recovery of the catalyst and its cost is still a challenge. In the recent years, the oxidation by means of ammonium persulfate (APS) has appeared as a potential alternative, although it is commonly used for cellulose nanocrystals production. The present work aims at comparing the properties of CNF obtained by means of TEMPO-mediated oxidation (TOCNF) and ammonium persulfate oxidation (APSCNF). For this, a similar oxidation degree was selected, adjusting the treatment conditions of both oxidative methods. The obtained results exhibited that similar properties can be obtained with different production costs associated. In addition, the APSCNF exhibited a significantly lower degree of polymerization and slightly higher transmittance, indicating the presence of higher crystalline regions. Finally, both types of CNF were tested over a recycled paper substrate, revealing that both APSCNF and TOCNF significantly increased the mechanical properties of paper with low effect on pulp drainability, representing a great advantage for the paper industry. [ABSTRACT FROM AUTHOR]

The degradation of paper-based materials involves several and complex mechanisms, such as hydrolysis and oxidation. The behaviour of different types of pulps can be very variable. In this study, the difference upon oxidation of contemporary non-recycled and recycled papers, which now constitute a considerable fibre source, is investigated. A 0.015 M potassium periodate solution is used to oxidise five types of paper, two non-recycled and three recycled, for 0.5, 1, 2 and 4 h. The effects of such oxidation treatments are evaluated in terms of carbonyl content and degree of polymerisation (DP). A modified procedure of the Szabolcs's method and viscometry are used to measure the carbonyl content and DP, respectively. The carbonyl groups are found to increase more rapidly in the recycled papers than in the non-recycled ones. On the contrary, oxidation causes a larger decrease of the DP values in the non-recycled papers, the paper made of pure cellulose being the most sensitive in terms of depolymerisation. The DP values measured for pure cellulose paper are in line with previously reported data. Moreover, in accordance with the Ekenstam equation, the plots of the reciprocal of DP as a function of oxidation time show good linear correlations for all types of paper investigated. Pseudo rate constants are thus calculated from the slopes of these plots, those of the non-recycled papers being found to be higher than those of the recycled papers. [ABSTRACT FROM AUTHOR]

Bacterial nanocellulose (BNC) is a unique natural nanomaterial that shares very few similarities with other natural or industrially produced nanomaterials. BNC can be produced by a variety of bacteria, as a survival aid in different ecological niches. BNC is traditionally produced by static or shaking culture methods, and the 'mother vinegar', or biofilm, is a typical example of this product after static vinegar fermentation. BNC has great potential in biomedicine, and recent studies have also demonstrated its use in the papermaking industry. It has nanoscale fiber size and large numbers of free hydroxyl groups, which ensure high inter-fiber hydrogen bonding. Thus, BNC has great potential as a reinforcing material, and is especially applicable for recycled paper and for paper made of nonwoody cellulose fiber. As well as enhancing the strength and durability of paper, modified BNC shows great potential for production of fire resistant and specialized papers. However, the biotechnological aspects of BNC need to be improved to minimize the cost of its production, and to thus make this process economically feasible. [ABSTRACT FROM AUTHOR]

Hairy cellulose nanocrystalloids (HNC) are a brand new family of nanocellulose characterized by having functionalized amorphous poles joined by a crystalline shaft. In this paper we hypothesize that cationic HNC (CNCC) could be used as an effective retention agent in papermaking. To investigate this, we first flocculated a suspension of only fillers, namely kaolinite and CaCO3, and second, a suspension of recycled fibers, with CNCC. It was monitored by photometric dispersion analysis and laser focused beam reflectance. The flocculation mechanism was assessed by means of zeta potential, reflocculation efficiency, flocculation stability and optical microscopy. Finally, the effect of CNCC on drainage, retention and paper mechanical properties was studied. CNCC were found to heteroflocculate fillers at a wide range of dosages, finding a maximum floc size at a dosage of 30 mg/g. On the other hand, the maximum floc size when flocculating the pulp suspension, was found at a lower CNCC dosage (20 mg/g). In this case, fillers were being attached to the exterior surface of the fibers. In both systems, the maximum size increment was observed at the isoelectric point, so a charge neutralization mechanism was proposed. The addition of CNCC not only improved filler retention, but also pulp drainage by reducing these times. Moreover, although mechanical properties of the handsheets were affected by the presence of CNCC, this effect was much lighter than that caused by traditionally used retention systems. Hence, CNCC could replace many additives used in the wet-end of a paper machine, thus simplifying its operation. [ABSTRACT FROM AUTHOR]

A novel procedure based on the addition of polyelectrolyte complexes (PECs) onto the pulp containing lignocellulosic micro/nanofibers (LCMNF) is presented. This procedure allows increasing paper strength avoiding an excessive loss in drainability. LCMNF were obtained from partially delignified kraft pine sawdust using a high-pressure homogenizer. Cationic complexes (CatPECs) were prepared by adding the anionic polyelectrolyte solution (polyacrylic acid) on the cationic polyelectrolyte solution (poly(allylamine hydrochloride)). According to turbidity and surface morphology changes, an interaction between CatPECs and LCMNF could be established. Different CatPEC dosages (from 0.3 to 1.0% on pulp) were added on a recycled unbleached softwood kraft pulp containing 3% of LCMNF. For a PEC dosage of 0.75% on pulp, an optimum balances between negatively and positively charged materials [near to zero value of the logarithm of the colloidal titration ratio (logCTR)] was found. Britt Dynamic Drainage Jar test showed a high retention of fines and LCMNF for all PEC dosages. A maximum in retention value was obtained for the addition of 0.75% of PECs on pulp, dosage that was suggested as optimum by the logCTR. In addition, the best drainability value (18°SR) was obtained for this PEC addition level. Papermaking properties were clearly improved for all dosage of PECs. Particularly for a dosage of 0.75% of PECs on pulp, tensile strength was noticeably increased (+48%) and both compressive resistance Concora Medium Test (CMT) and Short-span Compressive Test (SCT) were markedly increased (+64% and +39%, respectively). These results suggest that PECs are a possible alternative to assist the application of LCMNF in papermaking. [ABSTRACT FROM AUTHOR]

Abstract: Paper is still regarded as the most common carrier of information. Encouraged by environmental policies, the papermaking technology recently changed, resulting in an increased production of recycled paper. Two types of contemporary paper, non-recycled and recycled, were thus investigated to evaluate possible differences in their rate of degradation. The analyses were carried out using unaged paper to evaluate acidity, dry matter and ash content, lignin presence, and fibre furnish. Accelerated ageing experiments were performed at different temperatures (50-80 °C) and water vapour pressures (90.5-227.5 torr). Viscometric measurements were carried out to evaluate the extent of paper degradation as a function of time, upon various accelerated ageing conditions. The results indicate that the rates of degradation follow first-order kinetics with respect to scission of glycosidic bonds, the rate constants for recycled paper being found to be slightly higher than the corresponding constants for non-recycled paper, but comparable within experimental limits. The kinetic constants did not display a monotonic trend with increasing water vapour pressures. The Arrhenius dependence of the rate constants on temperature for both kinds of paper supplied the activation energies, which fall in the typical range expected for paper degradation. Finally, the measured rate constants fit fairly well the recently modelled dose-response function for historic paper. Colour changes were found to be visible to the human eye for samples aged for more than 40 days at 60, 70 and 80 °C.Graphical abstract: [ABSTRACT FROM AUTHOR]

The production of high filler-loaded recycled papers is often affected by high values of linting and low values of strength. In the first case, the accumulation of lint particles from paper’s surface on the printing blanket affects the quality of the printed paper and the pressroom’s productivity. In the second case, increasing the use of fillers and recycling cycles lead to poor paper strength. Cellulose nanofibers (CNFs) are receiving a great deal of attention due to their potential as a reinforcement aid for high filler-loaded papers through filler–fiber interaction and interfiber bonding. It is already proven that high quality CNFs can reduce linting, although their industrial application is limited by their high production cost. The objective of this research is, therefore, to quantify the effect of applying lower grade, more sustainable CNFs on linting phenomena and on the mechanical properties of recycled papers. Eucalyptus, pine and triticale residues were used as cellulose sources, and the CNFs were produced minimizing the chemical pretreatment before homogenization. Addition of 3 wt% of CNFs from pine residues into the recycled paper with 15.7 wt% of total filler reduced linting by 40% and increased tensile strength by 15.1%; further improvements on linting and mechanical properties were achieved at 5 wt%. Moreover, the increase in drainage time can be overcome by the addition of a retention aid, in this case a coagulant-cationic polyacrylamide-bentonite system, commonly used in paper mills. [ABSTRACT FROM AUTHOR]

The use of nanocelluloses as strength-enhancing additives in papermaking is widely known since both cellulose nanofibers (CNF) and nanocrystals (CNC) present similar composition than paper but their exceptional properties in the nanometer scale confers a paper quality enhancement. However, some agglomeration problems in CNF and CNC through hydrogen bonding cause a lower improvement of mechanical properties of paper. Therefore, a better dispersion of both nanocelluloses can maximize their effect on paper properties, thus reducing the needed dose to get the same increment in tensile strength and then reducing material costs. To ease the implementation of these nanocelluloses in the production process of recycled paper, typically used operations of these industries have been used. Among them, those devoted to improve the homogeneous mixture of nanocellulose in the pulp suspension have been assessed. Firstly, pulping conditions were studied, including pulping time, temperature and need for soaking as variables. Secondly, some dispersing agents used in papermaking were considered, studying the effect of different types and doses. The highest tensile strength of paper was achieved by applying long pulping times (60 min), getting increments up to 30% with the use of soaking and polyacrylamide as retention system. However, with the use of a low dose of a dispersing agent (0.003%), tensile index can be still increased up to 20.6% avoiding these long times. This study can be of great interest of those researchers trying to implement the use of nanocelluloses as strength additive in papermaking. [ABSTRACT FROM AUTHOR]

The development of paper-based analytical platforms has brought a requirement on easily creating patterned paper sensors. This article describes a facile method of fabricating patterned paper sensors using a combination of wettability-controlled paper and the precipitation assays between analytes and sensing elements. Different from common fabrication processes in which patterned channels are defined by creating hydrophobic barriers, herein the direct deposition of the patterns of sensing elements onto paper is performed by simple writing and stamping. Without hydrophobic treatment, the patterned sensing components can remain in place on the paper substrate whose wettability is tuned via bovine serum albumin (BSA) modification. After exposure to the analytes, the precipitates of sensing reactions are not delocalized, giving a simple and successful patterned signal readout. The results of typical colorimetric assays show that slow capillary flow and insoluble products together on paper provide an extremely easy route for fabricating multifunctional patterned paper sensors. [ABSTRACT FROM AUTHOR]

The present work shows the suitability of using industrial fluting papers as raw material for the development of four different substrates, enzymatically refined and/or containing cellulose nanofibers (CNF) in bulk. These four substrates were deeply studied and treated with different coating formulations, containing CNF, polyvinyl alcohol (PVA), native starch and alkyl ketene dimer, with the purpose of evaluating the benefits of using fiber-based packaging paper with improved mechanical, physical and barrier properties. The results showed that if CNF are coated in combination with PVA the tensile properties of paper can be significantly improved, as well as the grease resistance, whereas the air permeability and water vapor transmission rate decrease. The obtained papers present interesting vapor and air barrier properties, at the same time that unconceivable limits of breaking length are achieved (6.44 km). In addition, when a second layer of alkyl ketene dimer was coated on both sides of paper, the water contact angle was significantly improved, being higher than 115°. Overall, the present work shows the feasibility of recycled fibers for the production of high value-added papers that can be used for packaging purposes due to their improved barrier and mechanical properties, and contributes therefore for the bio-based circular economy. [ABSTRACT FROM AUTHOR]

A surface-modified form of cellulose nanocrystals (CNC) was employed to explore mechanisms related to the release of water from cellulosic fiber suspensions during papermaking. The CNC surface was rendered partly cationic (forming CCNC) by adsorption of poly-(diallyldimethylammonium chloride) (poly-DADMAC), a high charge density cationic polymer. Meanwhile, a suspension of cellulosic fibers and calcium carbonate particles was prepared from recycled copy paper, which was treated sequentially with poly-DADMAC and a very-high-mass anionic acrylamide copolymer (aPAM). Subsequent addition of CCNC strongly promoted water release, whereas ordinary CNC had the opposite effect. The effect of the CCNC was achieved with ten times less poly-DADMAC, as the final additive, compared to when adding the polymer alone. Results were consistent with a model of nanoparticle-enabled bridging, based on an assumption of non-equilibrium or slowly equilibrating processes of adsorption. [ABSTRACT FROM AUTHOR]

Cellulose nanofibers (CNF) have increasing relevance in different applications, for instance, in the paper industry as a sustainable strength additive. This application is especially beneficial for recycled paper, which reaches higher product quality despite its limitations. CNF change paper properties and also can affect the production process, especially the drainage stage, in which retention additives (RA) are commonly used to promote interaction of cellulose fibers. CNF probably interact with fibers and RA, affecting the drainage stage. However, these interactions vary depending on the type and flocculation mechanism of RA. This research is aimed at establishing possible synergies between CNF and RA to improve paper strength, avoiding negative effects on the drainage process. No further RA were used to retain CNF, taking advantage of the RA already used in the process. Polyvinylamine, chitosan, cationic starch, C-PAM, and C-PAM-B were selected as RA. CNF from eucalyptus kraft pulp and corn stalk organosolv pulp were tested. Strength properties of laboratory sheets were studied, and interactions were assessed by measuring Z-potential. Synergies between PVA, chitosan, C-PAM, and C-PAM-B with CNF were found. Drainage time decreased ranging between 30 and more than 40% using CNF. Strength depended on RA and formation quality. Among the studied options, CNF with C-PAM-B or chitosan resulted in the best formation and higher strengths with a significant drainage time reduction. [ABSTRACT FROM AUTHOR]

Although the positive effect that cellulose nanofibers (CNF) can have on paper strength is known, their effect on flocculation during papermaking is not well understood, and most relevant studies have been carried out in presence of only cationic starch. Flocculation is the key to ensuring retention of fibers, fines, and fillers, and furthermore floc properties have a great influence on paper quality. The aim of this research is to study the interactions between CNF and flocculants by assessing the effect of two types of CNF, from eucalyptus and corn, on the flocculation process induced by three different retention systems [a dual system, polyvinylamine (PVA), and cationic starch as reference]. The results showed that CNF interacted with the flocculants in different ways, affecting flocculation efficiency and floc properties. In general, addition of CNF increased floc stability and minimized overdosing effects. Moreover, presence of CNF increased floc size for given PVA dose; therefore, CNF addition could contribute to improve the wet end in the paper machine if combined with the optimal flocculant and dose. [ABSTRACT FROM AUTHOR]

During their recycling, cellulosic fibres suffer irreversible damage caused by repeated wetting and drying cycles, beating stages and bleaching reactions. This damage decreases the mechanical properties of the paper prepared from recycled pulp. Soft beating of the pulp is a simple way to partially recover the original mechanical properties, but it is limited by the high degradation of fibres, fines generation and decrease in drainage rate that recycled fibres already present. The present research studies the use of nanofibrillated cellulose (CNF) as an alternative to mechanical beating to improve the strength properties of paper produced from a deinked recycled pulp obtained by disintegration and flotation of a mixture of old newspapers and magazines. Different percentages of CNF were added to this mixture with a retention aid. A fraction of the same pulp without CNF was also beaten at different intensities in a PFI mill. Morphological properties of both beaten and CNF-reinforced pulp suspensions, as well as structural and mechanical properties of handsheets made thereof, were analysed and their results compared. Paper containing 1.5 % of CNF presented a higher tensile strength and stiffness than paper from beaten pulp with similar freeness and water retention values. A higher amount of CNF further improved the mechanical properties, up to double the tensile index, which opens new possibilities of use for recycled paper. [ABSTRACT FROM AUTHOR]