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 Zn2+ 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/m2. SEM & EDS, FT-IR, GPC confirmed that the crosslinking copolymerization was enhanced by dopamine and Zn2+, 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.