In their early work with TEMPO oxidation of cellulose, Isogai and coworkers showed that aldehyde-reactive polymers increased the wet strength of paper when cellulose fibers were lightly oxidized with TEMPO. Their explanation involving covalent bond formation between cellulose and the water-soluble polymer has withstood the test of time. However, for conventional papermaking products, TEMPO oxidation has not been attractive because it is expensive, environmentally suspect and difficult to recycle. In addition, the use of bleach at high pH as the primary oxidant is a complication for paper mills. We have shown that these difficulties can be circumvented by covalently attaching TEMPO to polyvinylamine (PVAm-T), a strength-enhancing polymer, greatly reducing the total TEMPO concentration in dilute wood pulp suspensions. Furthermore the TEMPO remains with the fibers, reducing potential environmental impacts. Finally, we have shown that PVAm-T can be activated with laccase at neutral pH, instead of alkaline bleach. Although this technology is effective, the mechanisms are obscure – how can a colloidal complex of cationic PVAm-T and laccase increase wet cellulose adhesion? We have shown that TEMPO-to-TEMPO electron transfer in the PVAm-T/laccase complex is the critical feature.

Interactions of polyvinylamine-g-TEMPO with cellulose

251st National Meeting (2016)

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