Adsorption of paper strength additives to hardwood fibres with different surface charges and their effect on paper strength

Abstract

Light-weight paper products that contain less fibres, but with a maintained bulk and improved strength properties, are highly desirable due to the low cost of raw materials and improved logistics of packaged goods. In this respect, the adsorption capacity of dry strength additives onto fibres, which is affected by the surface charge of said fibres, is very important for the development of these mechanically robust paper products. The influence of the surface charge on the adsorption of strength additives was investigated for, dissolving grade fibres, kraft fibres and kraft fibres modified with carboxymethyl cellulose (CMC) with different surface charge densities, but the same fibre dimensions. The strength additives investigated were cationic starch (CS), anionic polyacrylamide (APAM) and polyelectrolyte complexes (PECs), containing CS and APAM. A linear relationship was found between the surface charge of the fibres and the saturated adsorbed amount of CS. However, when either APAM or PECs adsorbed as secondary layers onto the CS, no correlation between cellulose charge and the saturation adsorption could be observed. The adsorption of APAM was dramatically affected by the pre-adsorbed amount of CS, whereas PECs were less influenced. Moreover, the additives improved the tensile strength (60%) and strain at break (> 100%) of handsheets formed with the kraft fibres and adsorbed APAM. It was also found that CS/APAM increased the sheet density while CS/PECs lowered it. In conclusion, the gained fundamental understanding of these adsorption of additives is of significant importance to facilitate the industrial development of sustainable low-cost high-end packaging products. Graphical abstract

Chemical Gradients in Polymer-Modified Paper Sheets—Towards Single-Layer Biomimetic Soft Robots

“…The observations furthermore indicate that the copolymer in solution does not appear to have interacted (electrostatically) with the molecular structure of the cellulose fibers in an attractive fashion (i.e., without having measured, we suspect a rather low enthalpy of adsorption), which would have affected the migration inside the paper sample. As shown by Wågberg and coworkers [ 29 , 40 ] electrostatic interactions between cellulose fibers and polymer molecules affect the spatial adsorption on the surface or throughout the fiber wall to a large extent. Attractive forces between the polymer and the cellulose fibers would have led to the adsorption of the macromolecules on/in the fibers, where they first came into sufficient contact.…”

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

“…The electrostatic interaction of cationic starch and cellulose fiber can be affected by ionic strength, pH, and temperature [48]. More stable interactions can be achieved by adsorbing alternating layers of cationic and anionic starch where multilayers can be formed [49,50].…”

Cationized dialdehyde cellulose synthesized with deep eutectic-like solvents: Effects on sheet dewatering and mechanical properties when used as wet-end additive

“…A possible explanation for the reduction in charge density is that DES solvent efficiency decreases after each recycling cycle, but it still demonstrates its effectiveness and sustainability. Using CDAC Recycle or Twice Recycle in paper making may require a higher amount of these additives due to the fact that using a lower charge density additive in pulp results in a low saturation, requiring a higher amount of additives for compensation (Zhao et al 2022). The CDAC-Fresh DES additive would also be more appealing since the high charge density additive competes with other ions for attachment to fibers/fines in the pulp (Taheri et al 2022).…”

“…This is evident from the figure that when 2% of CDAC-Fresh DES was added to the pulp, the mechanical properties of the handsheets were similar to those obtained with 5% of CDAC-recycle DES. It is also important to consider that the additives' cationic demand affects saturation adsorption, but not always tensile index (Zhao et al 2022). The dewatering study of pulp containing CDAC-Recycle DES and CDAC-Twice Recycle DES showed that the cationized additive caused no significant differences in moisture ratio and water retention value of the pulps when compared with pulp containing CDAC-fresh DES (Fig.…”