Adhesives with Controllable Degradability for Wet Cellulosic Materials

Abstract

Cellulose wet adhesives are applied to enhance the wet strength of paper products by binding individual paper fibers together. However, the recycling of the wet strength paper is a challenge as the fibers are hard to re-disperse in water. This project demonstrates new strategies for developing cellulose wet adhesives with controllable degradability, facilitating the recycling of wet strength papers. In this project, regenerated cellulose membranes were used to simulate paper fibers. In adhesion measurements, two wet cellulose membranes were laminated with a thin layer of adhesive (1–30 mg/m2), and the 90-degree wet-peel was used as a measure of cellulose wet adhesion. It was shown that the wet-peel was a simple and reliable method to evaluate the wet adhesives for paper products. Cellulose wet adhesives, in the form of microgels or linear polymers, were synthesized by incorporation of hydrazide, amine or azetidinium functional groups that can form covalent bonds to cellulose surfaces. Two strategies to design degradable adhesives were demonstrated in this project. 1) Reductant-responsive microgel adhesives were created by introducing cleavable disulfide linkages, either in the polymer chains tethering adhesive groups or as the microgel crosslinks. More than 70% reduction in wet adhesion was achieved after exposure to a reductant. 2) Degradable polymer cohesive bonds were used to “switch off” the cellulose wet adhesion. This adhesive was created by introducing labile boronate-dextran complexes to the PVAm adhesive layer between cellulose surfaces. The introduction of this new interaction between PVAm chains enhanced the cellulose wet adhesion. In response to subtle pH changes or the presence of monosaccharides, the wet adhesion decreased by 60%.