Paper Dry Strength Research Articles

Effect of saturation adsorption of paper strength additives on the performance of paper

AbstractThe use of paper dry strength additives is one of the methods for producing packaging boards with a lower grammage while maintaining mechanical properties. In the present work, papers were formed using dissolving grade kraft fibres, kraft fibres and carboxymethylated cellulose (CMC) modified kraft fibres (C-kraft fibres), with either cationic starch (CS), anionic polyacrylamide (APAM) or anionic polyelectrolyte complexes (PECs). Fibres and sheets were characterized to evaluate how the saturation adsorption of the different strength additives influences the properties of the treated fibres and the final handsheets. The tensile index of papers made from C-kraft fibres was the highest due to the highest adsorption capacity of strength additives. Moreover, the strength additives increased the tensile index by 33–84 %, while z-directional tensile strength was increased dramatically by 46–139 %. Bending stiffness was improved by 2.6–25 %, and the combination of CS and APAM or PECs resulted in a significant improvement in bending stiffness compared to the addition of CS alone. Importantly, the strength improvement did not sacrifice the density significantly. In summary, the knowledge gained from the current study expands the understanding of strength additives and their relationship with fibres of different surface charge and the overall paper properties.

Effects of hydrophobic sizing on paper dry and wet-strength properties: A comparative study between AKD sizing of NBSK handsheets and rosin sizing of CTMP handsheets

Alkyl ketene dimer (AKD) and rosin sizing are used in papermaking to decrease paper’s tendency to absorb liquid water. Earlier information regarding the effects of internal sizing on paper dry strength is not consistent. In the present laboratory study, AKD sizing of handsheets made from Nordic bleached softwood pulp (NBSK), and rosin sizing of handsheets made from Nordic hardwood chemi-thermomechanical pulp (CTMP) were done via an internal sizing method, and by immersing handsheets in aqueous sizing agent dispersion. In the study, AKD sizing had no significant effect on the dry strength of NBSK handsheets. The result corresponds to practical experiences of papermakers. However, both AKD sizing methods resulted in a substantial and long-lasting increase of handsheet wet-strength. Unlike internal AKD sizing of NBSK handsheets, rosin internal sizing of CTMP handsheets resulted in decreased handsheet dry strength. The decrease indicates that, under the conditions present during the experiment, rosin sizing agents interfered with interfiber hydrogen bonding of CTMP fibers. Given that, in practice, no such undesired effects have been commonly linked to rosin sizing, the observed effect may be specific to sheet-making conditions. However, the effect of rosin sizing on strength properties and their variation cannot be ruled out completely.

Preparation and Characterization of Xylan Derivatives and Their Blends

Although hemicellulose is found widely in nature, it is currently under-utilized as a raw material for commercial applications. It would be desirable to find new uses for hemicellulose in order to add value to this agro-based material. A common type of hemicellulose is xylan, which is found in a number of wood species and in cotton. In this work we prepared cationic and anionic xylan derivatives and characterized them by 13C NMR, FT-IR, size exclusion chromatography (SEC), thermal analysis, and rheology. In particular, the 13C NMR spectra of carboxymethyl xylan (CMX) and quaternary ammonium-adducted xylan (QAX) were fully assigned with the help of samples with different degrees of substitution. SEC indicated that the beechwood xylan showed a bimodal molecular weight distribution, but with derivatization the distribution tended to become unimodal. Thermal analysis and rheology studies did not uncover any surprises; the solution of xylan and its derivatives exhibited mostly Newtonian behavior. The blends of CMX and QAX produced a precipitate at almost all ratios, indicating the formation of a polyelectrolyte complex. When cationic and anionic xylan samples were added together to paper, the paper dry strength increased. Thus, the combination of cationic/anionic xylan may be of interest in selected applications.

Inglês

Inglês

Amphoteric polymers to improve paper dry strength

The objective of the present work is to evaluate the application of an amphoteric polymer, with acidic and basic groups on the polymer chain, as a paper dry strength additive. The polymer studied here is random terpolymer of high electrostatic charge density, and high molecular weight. The results of our work showed that the balance between the charge densities of the surface and the polymer structures is an important factor to be considered when using this polymer. The highest paper strength value, measured by tensile index, was found at the polyampholyte’s isoelectric point (ca. pH of 7.3) when the charge of the fiber surface was negative and the polymer structure charge was symmetric. This observation agrees with our dynamic light scattering results which, demonstrated that at the isoelectric point there was a maximum in association among polyampholyte molecules, leading to a maximum in size of molecular aggregates. When adsorbed on an electrically charged surface, the maximum amount of adsorbed polymer, measured by the shift in resonance frequency in a quartz crystal microgravimetric balance, was observed for the same isoelectric point. Better results for paper dry strength were found when the fiber surface and the polymer structures were oppositely charged or at the isoelectric point of the polymer. Less effective addition strategies were found in the case when the fiber surfaces and the polymer structures had same sign of charge. DOI: 2446941601022015065

A New Class of Biobased Paper Dry Strength Agents: Synthesis and Characterization of Soy-Based Polymers

The goal of the current effort was to develop a new soy-based (soy flour) derivative to impart high fiber–fiber strength improvements to two-dimensional paper sheets. The success of the research hinged on successful proliferation of carboxylic and/or amine functionalities onto the polymeric backbone of the soy flour to significantly contribute to improved interfiber bonding of the paper–fiber sheets. Diethylenetriaminepentaacetic acid (DTPA) was reacted with soy flour in the presence of sodium hypophosphite and complexed with chitosan for the development of a new class of dry strength agents to improve integration into pulp fibers and thus increase interfiber bonding. The synthetic conditions including surface modifier concentration, time, temperature, pH, and material-to-liquor ratio were optimized. The paper materials incorporating the DTPA cross-linked (modified) soy flour agent demonstrated unprecedented tensile strength increases. A 1% soy protein flour–DTPA–-chitosan agent by mass of pulp-based slurry was thoroughly mixed before generating two-dimensional hand sheets whose tensile indices increased 52.6%, 53%, and 57.8% for recovered (OCC, old corrugated containerboard), NSSC (virgin) pulp, and kraft (virgin) pulp sheets, respectively. The modified soy flour agent-treated pulp sheets also provided significantly increased gloss and water repellency with diminished surface roughness.

A Survey of Soy Protein as a Novel Dry Strength Agent for Papermaking

In this paper, soy protein papermaking process conditions as dry strength agents were studied. The results show that a part of the three parts of soy protein and a mixed system with a cationic starch alone, or cationic starch, soy protein, as compared to dry strength additives will significantly increase the strength. The optimum conditions were: pulp types E, defatted soy protein, dry vacuum drying method is 105°C, adding ways to add the pulp, the best reaction time was 10min, the optimum dosage of 2%. Soy protein sources are widely readily available, and environmentally friendly and easily biodegradable, paper dry strength agents as a good material.

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

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

Paper dry strength improvement by xyloglucan addition: Wet-end application, spray coating and synergism with borate

AbstractThe polysaccharide xyloglucan as a wet-end additive improves paper properties. In the present study, paper strength improvement was analysed for dry handsheets made from chemical, mechanical and recycled pulps coated with xyloglucan in a spray application. Results are compared with sheets made from the same pulps treated with xyloglucan in the wet-end. Kraft pulp handsheets of bleached hardwood and softwood showed significant improvements of tensile, tear and Z-strength by xyloglucan spray treatment versus wet-end application, whereas handsheets of de-inked and thermomechanical pulp were improved only slightly. In both wet-end and spray applications, the effect of xyloglucan addition was intimately related to the presence of non-cellulosic components on the fibre surface. Further strength improvements were obtained for chemical pulps by addition of borax to the spray solution, which were likely to be due to the formation of borate-mediated xyloglucan cross-links. Spray coating of xyloglucan, with or without borax, thus represents a potential new application of this polysaccharide to increase paper dry strength.

Influence of retention system and curing on paper wet strength improvement by a copolymer containing glycidyl groups

AbstractThe copolymer (PGS) synthesized by polymerization of glycidyl methacrylate with styrene had a significant effect on paper wet strength. Factors such as retention aids, curing temperature, and curing time were investigated. The results showed that among four kinds of partially aminated poly N‐vinylformamide (APNVF), APNVF‐4 that had the highest charge density was the most effective for strengthening paper. The effectiveness of the retention systems increased with their wet functionality in the order APNVF‐4 > C‐PAM ≈ PAAm > PEI > PDADMAC. The curing temperature and curing time had little influence on paper dry strength, but they influenced paper wet strength greatly. The FTIR studies on model reactions showed that glycidyl groups could react with amino groups and carboxyl groups under common curing conditions. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2791–2797, 2001