Strength from Within: Reversible Reinforcement of Paper through In-Sheet Formation of Thiol-Catechol Polymers

Mechanical integrity of paper materials is crucial for many applications, yet reinforcement strategies with polymer strengthening agents that interact strongly often result in inhomogeneous coatings. In-sheet polymerization and adhesion (InSPA) methodology enables the in situ generation of reinforcing polymers, facilitating their uniform deposition on the cellulose fibers despite high interaction capabilities, and significantly increasing the dry and wet strength of commercial filter papers. A set of polymers containing highly adhesive thiol-catechol-connectivities (TCC) is prepared from <i>o</i>/<i>m</i>/<i>p</i>-isomers of benzenedithiol and bisquinone A by the InSPA thiol-quinone Michael-type polyaddition route. During polymerization, the interaction capabilities of the TCC-polymers are built up gradually, enabling effective cellulose fiber penetration and homogeneous fiber coating. Polymer loadings of up to 48 wt.-% are reached, transferring rigidity and hydrophobicity to the paper fibers without jeopardizing paper porosity. The noncovalently modified papers show a doubling in tensile index in the dry and a 7-fold increase in the wet state, paving the way for effective oil/water separation membranes, where end-of-life recyclability by removal of the polymer coating in a water-based process is demonstrated.