With increasing needs of recycling composite materials in the context of circular economy and re-use of the fiber and matrix material as new resources, composite materials often pose problems as they are complex materials. The user properties of high strength and long lifetime require development of strong interfaces between the matrix and reinforcing fibers, while recycling would benefit from easy separation of both phases. Therefore, the design of an interface with reversible bonding upon thermal or chemical activation may offer a good balance. In addition, the request for bio-based composites incorporating cellulose fibers should be combined with bio-inspired interface modification avoiding traditional chemical surface modification. An impressive example of reversible bonding in nature is observed in the mussels and regulated by so-called mussel-foot proteins. The latter main component includes dopamine that presents reversible bonding upon change in pH. In present work, the cellulose fibers were modified with a catechol coating that was polymerized in contact with the cellulose surface. The chemical compatibility and covalent bonding of the coating through reaction with the cellulose hydroxyl groups was demonstrated. The adhesive properties of modified cellulose fibers were investigated by local adhesive measurements through AFM mapping, and the interface strength of fibers embedded into a PMMA matrix was evaluated through single fiber pull-out testing. The adhesion strength of the modified fibers dropped after submersion in solutions with pH above 10. The pull-out strength of the modified fibers similarly decreased after diffusion of a solution with pH above 10 through the interface. A proof of concept for recycling the cellulose/PMMA composites was demonstrated by shredding and chemical treatment in solutions at different pH, where cellulose fibers were successfully recovered at high pH.
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Opportunities for reversible bonding at the cellulose/matrix interface of composites by novel interface design
Published: 27 October 2023 by MDPI in 4th International Electronic Conference on Applied Sciences session Nanosciences, Chemistry and Materials Science
Keywords: composite, fiber, coating, debonding