Revealing Adsorption Behaviors of Amphoteric Polyacrylamide on Cellulose Fibers and Impact on Dry Strength of Fiber Networks

Strong and ductile cellulose film improved by the in situ incorporation of a genetically engineered protein conjugated synthetic polymer during bacterial cellulose growth

Bacterial cellulose (BC) has been extensively applied to fabricate advanced biomaterials, although it remains challenging due to its poor toughness and water stability. Herein a genetically engineered protein-conjugated synthetic polymer is designed to improve BC film's strength and flexibility. Initially, the hybrid polymer is constructed by grafting Family 3 carbohydrate-binding modules (CBM3) to amphoteric polyacrylamide polymer (AmPAM), one of the paper industry's most widely used dry-strength agents. Then, the conjugated polymer is added to the culture medium of BC growth, enabling it to incorporate into the matrix of cellulose chains. The results show that the BC film modified by CBM3-AmPAM exhibits superior mechanical properties, registering 9.94 % in strain and 13.8 MJ/m3 in toughness, 12.1 and 8.0 folds over the sample with AmPAM addition only. Additionally, the BC film improved by CBM3-AmPAM has excellent gas resistance, thermal stability, and environmental endurance. The adsorption of CBM3-AmPAM on BC film revealed by quartz crystal microbalance with dissipation monitoring indicates that the adsorbed layer is thin and rigid, suggesting the strong interaction between the conjugated polymer and BC substrate. As a result of this reinforcing strategy, BC composites can be used in a wider range of applications.

Surprising Nanomechanical and Conformational Transition of Neutral Polyacrylamide in Monovalent Saline Solutions

Polyacrylamide (PAM) is one of the most important water-soluble polymers that has been extensively applied in water treatment, drug delivery, and flexible electronic devices. The basic properties, e.g., microstructure, nanomechanics, and solubility, are deeply involved in the performance of PAM materials. Current research has paid more attention to the development and expansion of the macroscopic properties of PAM materials, and the study of the mechanism involved with the roles of water and ions on the properties of PAM is insufficient, especially for the behaviors of neutral amide side groups. In this study, single molecule force spectroscopy was combined with molecular dynamic (MD) simulations, atomic force microscope imaging, and dynamic light scattering to investigate the effects of monovalent ions on the nanomechanics and molecular conformations of neutral PAM (NPAM). These results show that the single-molecule elasticity and conformation of NPAM exhibit huge variation in different monovalent salt solutions. NPAM adopts an extended conformation in aqueous solutions of strong hydrated ion (acetate), while transforms into a collapse globule in the existence of weakly hydrated ion (SCN-). It is believed that the competition between intramolecular and intermolecular weak interactions plays a key role to adjust the molecular conformation and elasticity of NPAM. The competition can be largely influenced by the type of monovalent ions through hydration or a chaotropic effect. Methods utilized in this study provide a means to better understand the Hofmeister effect of ions on other macromolecules containing amide groups at the single-molecule level.

Morphology-induced differences in adsorption behaviors and strength enhancement performance for fiber networks between quaternized amylose and amylopectin

Cationic starch is the most widely used paper strength additive for papermaking wet end applications. However, it remains unclear how differently quaternized amylose (QAM) and amylopectin (QAP) are adsorbed on the fiber surface and their relative contribution to the inter-fiber bonding of papers. Herein, separated amylose and amylopectin were quaternized with different degrees of substitution (DS). After that, the adsorption behaviors of QAM and QAP on the fiber surface, the viscoelastic properties of the adlayers and their strength enhancement to fiber networks were comparatively characterized. Based on the results, the morphology visualizations of the starch structure displayed a strong impact on the adsorbed structural distributions of QAM and QAP. QAM adlayer with a helical linear or slightly branched structure was thin and rigid, while the QAP adlayer with a highly branched structure was thick and soft. In addition, the DS, pH and ionic strength had some impacts on the adsorption layer as well. Regarding the paper strength enhancement, the DS of QAM correlated positively to the paper strength, whereas the DS of QAP correlated inversely. The results provide a deep understanding of the impacts of starch morphology on performance and offer us some practical guidelines in starch selection.

Interplay of electrolyte concentration and molecular weight of polyDADMAC on cellulose surface adsorption

Cationic polyelectrolytes (PEs) are commonly used additives in manufacturing of cellulose based products such as regenerated fibers and paper to tailor their product properties. Here we are studying the adsorption of poly(diallyldimethylammonium chloride), PD, on cellulose, using in situ surface plasmon resonance spectroscopy (SPR) measurements. We employ model surfaces from regenerated cellulose xanthate (CX) and trimethylsilyl cellulose (TMSC), mimicking industrially relevant regenerated cellulose substrates. The effects of the PDs molecular weight were strongly depending on the ionic strength and type of electrolyte (NaCl vs CaCl₂). Without electrolytes, the adsorption was monolayer-type, i.e. independent of molecular weight. At moderate ionic strength, adsorption increased due to more pronounced PE coiling, while at high ionic strength electrostatic shielding strongly reduced adsorption of PDs. Results exhibited pronounced differences for the chosen substrates (cellulose regenerated from xanthate (CX_reg) vs. regenerated from trimethylsilyl cellulose, TMSC_reg). Consistently higher adsorbed amounts of the PD were determined on CX_reg surfaces compared TMSC. This can be attributed to a more negative zeta potential, a higher AFM roughness and a higher degree of swelling (investigated by QCM-D) of the CX_reg substrates.

Enhanced flocculation of aluminum oxide particles by lignin-based flocculants in dual polymer systems

Lignin is an abundant phenolic polymer produced vastly in pulping processes that could be further valorized. In this work, anionic (AKLs) and cationic (CKLs) lignin-based polymers were made by polymerizing kraft lignin (KL) with acrylic acid (AA) or [2-(methacryloyloxy) ethyl] trimethyl-ammonium chloride (METAC), respectively. In the polymerization reactions, various molar ratios of AA or METAC to KL were applied to produce AKLs and CKLs with different characteristics. The produced AKLs and CKLs were used in single and dual systems to flocculate aluminum oxide in suspension. To assess the interaction of these lignin-based polymers with the aluminum oxide particles; the zeta potential, adsorption, and flocculation of the colloidal systems were evaluated comprehensively. The flocculation performance of the lignin-derived polymers was compared with that of the homopolymers of AA and METAC (PAA and PMETAC) and commercially used flocculants. In single polymer systems, among the anionic synthesized polymers and homopolymers, KL-A4 (an AKL) was the best flocculant for the aluminum oxide suspensions owing to its largest molecular weight (330 × 10³ g/mol) and highest charge density (-4.2 mmol/g). Remarkably, when KL-A4 and KL-C4 (the CKL with the highest molecular weight and charge density) were used subsequently in a dual polymer system, a larger adsorbed mass and a more viscous adlayer were formed than those of single polymer systems on the surface of aluminum oxide particles. The synergy between KL-A4 and KL-C4 was even stronger than that between homopolymers, which led to more significant adsorption on the aluminum oxide surface and, consequently, more efficient flocculation, producing larger (22 μm) and stronger flocs, regardless of the agitation intensity used in the systems.

Carbohydrate-Binding Modules of Potential Resources: Occurrence in Nature, Function, and Application in Fiber Recognition and Treatment

Great interests have recently been aroused in the independent associative domain of glycoside hydrolases that utilize insoluble polysaccharides-carbohydrate-binding module (CBM), which responds to binding while the catalytic domain reacts with the substrate. In this mini-review, we first provide a brief introduction on CBM and its subtypes including the classifications, potential sources, structures, and functions. Afterward, the applications of CBMs in substrate recognition based on different types of CBMs have been reviewed. Additionally, the progress of CBMs in paper industry as a new type of environmentally friendly auxiliary agent for fiber treatment is summarized. At last, other applications of CBMs and the future outlook have prospected. Due to the specificity in substrate recognition and diversity in structures, CBM can be a prosperous and promising 'tool' for wood and fiber processing in the future.

Adsorption Mechanism of Chloropropanol by Crystalline Nanocellulose

Paper packaging materials are widely used as sustainable green materials in food packaging. The production or processing of paper materials is conducted in an environment that contains organic chlorides; therefore, potential food safety issues exist. In this study, the adsorption behavior of organic chlorides on paper materials was investigated. Chloropropanol, which has been extensively studied in the field of food safety, was employed as the research object. We studied the adsorption mechanism of chloropropanol on a crystalline nanocellulose (CNC) model. The results demonstrated that physical adsorption was the prevailing process, and the intermolecular hydrogen bonds acted as the driving force for adsorption. The adsorption effect assumed greatest significance under neutral and weakly alkaline conditions. A good linear relationship between the amount of chloropropanol adsorbed and the amount of CNC used was discovered. Thus, the findings of this study are crucial in monitoring the safety of products in systems containing chloropropanol and other chlorinated organic substances. This is particularly critical in the production of food-grade paper packaging materials.

Impacts of degree of substitution of quaternary cellulose on the strength improvement of fiber networks

The degree of substitution (DS) of cellulose derivative is significantly associated with its properties. In this paper, a series of quaternary cellulose (QC) samples with different DS (ranging from 0.16 to 0.51) were synthesized with assistance of microwave and their relationship with strength improvement of fiber networks was investigated systematically. QCs were characterized by elemental analysis, FT-IR, ¹H NMR, and TGA, etc. The results showed that the cationic quaternary ammonium salt group was successfully grafted onto the backbones of cellulose chains and the thermal stability was associated inversely with the DS of QCs. However, the results of strength test for the fiber networks from secondary fiber of old corrugated containers showed that the tensile and burst strength was enhanced by addition of QCs, and their performance was positively correlated their DS. The best result achieved in this investigation was in the case of QC with DS of 0.51, with increments of tensile and burst strength 6.17% and 11.68%, respectively, at a dosage of 1.0 wt% based on oven-dry pulp. This investigation highlights the importance of DS of QC to its application in strength improvement for fiber networks.