Synthesis of Water-Soluble Polyurethane Using Lignin, Dopamine and Zn²⁺ and Its Effects on Paper Properties

A novel water-soluble polyurethane copolymer (i.e., LnBPU-[Zn(DOPA) 2 ]) was synthesized through a route mainly using a prepolymer (i.e., BPU), lignin, dopamine and Zn 2+ as the raw materials by cross-linking copolymerization. The optimal reaction conditions are as follows: m ( Lignin ) :m ( BPU ) is 1:4, time is 4 h and temperature is 70 °C. The prepared LnBPU-[Zn(DOPA) 2 ] was turned out to improve the strength, resistance to water, oil and Escherichia coli of fibre when it was evenly coated on the paper with a dose of 15 g/m 2 . SEM & EDS, FT-IR, GPC confirmed that the crosslinking copolymerization was enhanced by dopamine and Zn 2+ , which can give the polyurethane copolymer better strength and water and oil resistance. This study provided an efficient and green approach for preparing lignin-based polyurethane, and contributes to the application of paper in more fields such as food or medical packaging.