Improvements On The Hydrolysis Resistance Of MDI-type Waterborne Polyurethane

Waterborne Polyurethane(WPU) is widely used in coatings, adhesives and other fields because of excellent performance and environmental friendliness. IPDI and TDI are in common use for waterborne polyurethane, which give the WPU excellent performance and high cost. MDI isocyanate is low-cost and slightly poisonous to humans, but possess high activity which contributes it difficulty to emulsion synthesis. Mixing 2,4’-MDI and 4,4’-MDI can get MDI-50 which is a liquid at room temperature. Using MDI-50 for WPU could take advantage of high performance and low cost.This thesis uses MDI-50 isocyanate to prepare WPU, and studies factors how to effect the WPU emulsion and films. Optimized factors to get best synthesis formula and best WPU film. The factors include-NCO/-OH molar ratio r1 in prepolymer stage,-NCO/-OH molar ratio r2 in chain extension stage, polyols species,-COOH content, TMP content. It was found that when r1 is 1.4, r2 is 1.1,-COOH content is 1.8~2.0wt%, with some TMP modified, the H7104-type WPU possesses best comprehensive performance. The WPU’s particle size is nearly 60 nm and emulsion is stable. The tensile strength of the film is more than 10 MPa, elongation at break is over than 500%, but water absorption beyond 15%, tensile retention after hydrolysis is about 20% which shows bad performance in hydrolysis-resistance.Via crosslinking modification to improve hydrolysis resistance of WPU film. Introduced crystalline polyol and trifunctional chain extender TMP, WPU showed better mechanical properties. However, there is not much improvement on hydrolysis resistance. Using siloxane KH560 or aziridine crosslinking agent Sa C100 to modify waterborne polyurethane emulsion. We found when KH560 content is 8~12wt% or Sa C100 content is 8wt%, WPU film gain at least 85% tensile retention rate which demonstrated positive impact about crosslinking for hydrolysis resistance. Because KH560 is easy to hydrolysis and Sa C100 has a strong tendency to self-polymerization, the modified emulsion has short shelf life.