Multi-functional fluorescence cellulose composites based on a modified amphiphilic waterborne polyurethane by covalent suspension of the triazine groups

Abstract

Multi-functional fluorescent composites with maximal fluorescence emission are desirable in advanced materials and composites. We synthesized an amphiphilic fluorescent waterborne polyurethane (WPU) by covalent linking of a naphthalimide fluorophore (NF) containing a monochlorotriazine group. The synergy of the NF and triazine group improved absorption in the A- and B-range ultraviolet (UV). We obtained corresponding fluorescent cellulose composites by coating a cellulose matrix with modified amphiphilic WPU. We measured the fluorescence intensity and fluorescence quantum yield of modified WPU emulsions and films that contained various proportions of NF. In accordance with increasing proportion of NF in the WPU–NF, the emission peak exhibited a gradual bathochromic shift and the fluorescence intensity considerably increased. Compared with a physical blend of WPU and NF, covalent linking greatly enhanced the fluorescence intensity and fluorescence quantum yield of WPU–NF films. When the proportion of the fluorescent group was 0.200% and 0.400% (w/w), the fluorescence intensities of the covalently cross-linked polymer were 4.29× and 7.27× higher, respectively, than those of the physically mixed polymers. The cellulose composites exhibited excellent fluorescence and good UV protection. The monochlorotriazine formed covalent bonds with the cellulose matrix and in so doing improved the bonding stability. Our amphiphilic fluorescent polyurethane polymer and fluorescent cellulose composites have great potential for applications in advanced composites, biomaterials, and UV protection materials.