Polymeric Wet-Strength Agents in the Paper Industry: An Overview of Mechanisms and Current Challenges

Multiple cross-linked cellulosic paper-based waterproof and biodegradable mulch film for "green" agriculture

Biodegradable cellulosic mulch has been demonstrated as the promising alternative to traditional plastic mulch film in agriculture, whereas the highly hydrophilic property and poor wet strength severely restricted their practical application. Herein, a new waterproof dialdehyde cellulose (OR)-polyamide epichlorohydrin (P)-alkyl ketene dimer (A) (OR-P-A) was carefully designed as the green mulch film. The hydrogen bonds and Schiff base reaction between -CHO on dialdehyde cellulose fibers and -NH2 on PAE reinforced the interfacial interaction of cellulosic fibers. Furthermore, the formed β-keto ester bonds of -OH on cellulose with AKD improved the water resistance of paper fiber. Compared with the pristine cellulose film, the dry and wet tensile strength of OR-P-A2 were increased to 17 MPa and 3 MPa, respectively. Moreover, the water contact angle was increased from 25° for pristine cellulose film to 124° for OR-P-A2. In addition, the germination rate of cabbage seeds covered by OR-P-A2 was similar to that of commercial polyethylene film in practical application. This strategy proposed a novel method to improve the hydrophobicity of cellulose film, which boosting the development of biodegradable mulch film and "green" agriculture.

Lignin microparticle coatings for enhanced wet resistance in lignocellulosic materials

The widespread use of synthetic plastics in packaging materials poses significant environmental challenges, prompting the search for biobased, biodegradable, and non-toxic alternatives. This study focuses on improving high-yield pulps (HYPs) as sustainable materials for packaging. Enhancing wet strength and barrier properties of papers from bleached chemi-thermomechanical pulps (BCTMPs) is crucial for their application in water- and air- resistant wrappers. Traditional wet strength agents raise environmental and health concerns; therefore, this research explores the use of lignin, in the form of microparticles (LMPs), as a natural biopolymer that offers a safer alternative. However, the low viscosity of LMPs hampers their dispersion as a coating, requiring thickening agents (such as cationic starch (CS), chitosan (CH) or sodium alginate) for an effective coating formulation. Results demonstrate a synergistic effect of LMP coatings with CH or CS, enhanced by hot-pressing at 260 °C for 30 s, which improves dry and wet mechanical properties and decreases air permeability. The use of LMPs as a water-resistant interlayer between BCTMP paper sheets further improves the wet tensile index to 40 kN·m/kg for CH + LMPs and 23 kN·m/kg for CS + LMPs interlayer, representing 55 and 38 % of their respective dry tensile indices.

Study on the enhancement of paper tensile strength and hydrophobicity by adding PEI-KH560 in pulp suspension

Novel eco-friendly strength agent has inspired much attention of researchers. Herein, the PEI-KH560 prepared by PEI (polyethyleneimine) and KH560 (γ-glycidyl ether propyl trimethoxysilane) was added in the pulp suspension to enhance the paper performance. The results showed that the m(PEI):m(KH560) ratio and PEI's molecular weight were closely related with the paper strength and hydrophobicity. The SEM morphology of paper surface showed that the fiber-fiber crosslinking reached the tightest, at the optimal m(PEI):m(KH560) ratio and PEI's molecular weight. The results showed that when the Mw (molecular weight) of PEI was 10,000 and the m(PEI):m(KH560) ratio was 1:2, the PEI-KH560 presented the best strengthening performance on the paper strength and hydrophobicity. Dry tensile index and wet tensile index could reach 29.9 N·m/g and 1.37 N·m/g after adding the PEI10000-KH560 in pulp suspension before the paper formation. Further, the effect of process conditions (temperature, time, the addition amount, and pulp concentration) on the strength and hydrophobicity of paper network structure was investigated, after adding PEI-KH560 into the pulp suspension. It was of great significance for studying the mechanism between the chemical structures of PEI-KH560 and paper performance, which provided valuable theoretical practice on the preparation of novel strength agent.

Cationic polymer-mediated interbacterial aggregation: A novel approach for rapid aerobic granules development

This study introduces a novel approach to aerobic granular sludge technology that minimizes the start-up time and guarantees the formation of stable granules. This is achieved by seeding the reactor with a cationic polymer without using inoculated sludge. Three cationic polymers (Hydrofloc C4400SA, C8896, and polyelectrolyte emulsion) were tested to determine the most appropriate polymer for aerobic granular sludge (AGS) startup based on the optimal dose and formation of aerobic granules. Hydrofloc cationic polymer C4400SA has excellent granule-forming properties in the AGS reactor compared to their counterparts. The formation of granules was boosted by adding 15 ppm of polymer, resulting in densely packed aerobic granules after 10 days. This improvement can be due to the more cationic properties of hydrofloc, which play a key role in bridging between cells and particles because the cationic charges of hydrofloc attract negatively charged bacteria in wastewater, thereby promoting aggregation and the formation of initial flocs. These flocs serve as the foundation for the development of granules. After 80 days of operation, 40-50% of particles with an average size range from 0.6 to 0.9 mm were observed. The AGS SBR operation was closely monitored and showed consistent efficiency in removing solids, where TP, TN, NH+4 -N, and the total soluble COD were removed at average efficiencies of 62%, 73%, 97%, 93%, and 79% respectively, during steady-state cycles conducted at room temperature. Overall, this study highlights the potential of hydrofloc cationic polymer C4400SA to enhance the performance and resilience of AGS in wastewater treatment applications.

Effect of molecular weight of PEI on the strength and hydrophobic performance of fiber-based papers via PEI-KH560 surface sizing

In recent years, researchers have put much attention on the improvements and upgrades of novel wet strength agent in the papermaking fields, especially in the usage of household paper. Herein, PEIM-KH560 by polyethyleneimine (PEI) and γ-glycidyl ether propyl trimethoxysilane (KH560) was synthesized with five molecular weights (Mw) of PEI at 600, 1800, 10,000, 70,000 and 750,000. Results showed that the molecular weight greatly influenced the physicochemical properties of PEI-KH560, such as the size and thermal stability. The intrinsic cationic charge of PEI-KH560 provided the bonding sites with the paper fibers, forming strengthened fiber-fiber joints. It was shown that the dry, wet strength and hydrophobicity of cellulosic paper sheets were obviously improved. When the m (PEI):m(KH560) is 1:2, the strength of papers after sizing by Mw of PEI at 600 and 1800 is the most obvious, with the dry strength increased by 227.9 % and 187.5 %, and the wet strength increased by 183.8 % and 207.8 %, respectively. The maximum hydrophobicity was found at the PEI1800-KH560 with the contact angle value of 130.6°. The resultant environmental-friendly agent (PEI-KH560) obtained in this work provides valuable significance for the preparation of household and food packaging paper.

Enhancing Cross-Linking Network for Superior Wet Strength of Paper by Sustainable Hyperbranched Polyimines

The paper industry has long been a crucial part of our lives, providing printing materials, tissue paper, and packaging products. However, the low wet strength of commercially available paper limits its application in packaging, particularly when it comes into contact with liquids. To address this issue, researchers have explored various strategies, including the use of wet strength agents. The most widely used agent, polyamide-epichlorohydrin resin (PAE), has limitations, such as poor dimensional stability and limited recyclability. Additionally, PAE can release harmful chlorinated organics. To overcome these challenges, we report a novel approach using a hyperbranched wet strength agent (referred to as "OA-PI") based on the cross-linking of oxidized amylopectin from waxy corn and polyamines through the Schiff base reaction. The hyperbranched structure of OA-PI provides multiple binding sites, enhancing the cross-linking strength of cellulosic paper under wet conditions. The paper treated with OA-PI exhibited exceptional wet strength, significantly higher than that of PAE-treated paper and paper with traditional starch-based additives. Moreover, the biomass-based OA-PI showed improved recyclability and reduced harm from chlorinated organic compounds. This study not only enhances the wet strength of paper but also opens sustainable avenues for the design of functional adhesives.

Dilemma of Low-Cost Filter Paper as Separator: Toughen Its Wet Strength for Robust Aqueous Zinc-Ion Batteries

The industrialization of aqueous zinc-ion batteries (AZIBs) is hampered by poor-performance separators. Filter paper (FP), with mature production processes and low prices, has potential as a separator. However, its swelling and decline of mechanical durability in aqueous environments make it easily punctured by dendrites. In response, wet strength promotion is proposed to toughen FP for robust AZIBs, termed wet-strengthened FP (WSFP). Due to the self-cross-linking network formed on cellulose fibers, water molecules are prevented from easily permeating and disrupting the hydrogen bonds between cellulose molecules. Moreover, the positively charged network can anchor SO42-, thus increasing the Zn2+ transference number and facilitating uniform zinc deposition. Surprisingly, the half and full cells with the WSFP separator present much more stable cycling than untreated FP and glass fiber (GF) separators. These results suggest that robust and low-cost WSFP separators provide a new avenue for the development of high-performance AZIBs with potential for commercialization.

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.

Starch/PVOH aqueous solutions: a chemical-physical characterization

This work investigates the relationship between the structure and physicochemical properties of three different starches in starch/polyvinyl alcohol aqueous solutions. For this purpose, accurate nuclear magnetic resonance (NMR) analyses were performed to determine the role that the starch structure plays in the formation of binder solutions. Moreover, a dynamic shear rheometer (DSR) was used to investigate the mechanical properties of the solutions and correlate them with the structure of each starch. Complete characterization of the analysed starches and the starch/PVOH solutions was also carried out through light scattering measurements. Furthermore, by crossing the data coming from NMR and light scattering with those coming from rheology, the best solution was identified. Finally, to confirm the interaction mechanism between starch and PVOH, thermogravimetric analysis and an NMR study, using 1H and 13C NMR spectra, were carried out on the film obtained from the best solution. The analyses carried out showed that PVOH has a stabilizing effect on starch/PVOH solutions, and the starch with the greatest branching degree is the one that forms a more structured network.