Study On The Synthesis And Properties Of Waterborne Polyurethane Fabric Coating Agent

Waterborne polyurethane is dispersible in water medium, which has hydrophilic groups in the molecular chain, with strong affinity for water. Not only it has the excellent properties of solvent-borne polyurethane with good low temperature resistance, great adhesion, as well as outstanding toughness combined with good flexibility, but also advantages of innocuity, incombustibility, low odor, environmental friendliness, energy conservation, security, convenient operation processing, and good film-forming breathability. Recently, the rising price of organic solvent and the strict limitation of using organic solvent and discharging waste from environmental protection department are leading to the replacement of solvent-borne polyurethane.At present, most materials used in local research of waterborne polyurethane are in the type of toluene diisocyanate, which has bad weatherability, easy yellowing, and can't meet special requests of market. With the development of the living standard of people and the increasingly urgent demand for environmental protection, health and high performance products, the green chemicals gradually become the future development's main current. Therefore, aliphatic waterborne polyurethane will become the main direction.A series of aliphatic waterborne polyurethane emulsions were prepared from hexamethylene diisocyanate (HDI), polypropylene oxide glycol (PPG), dimethylolpropionic acid (DMPA) and small molecular dihydric alcohol. And then cross linked with cross-linking agent, coating on cotton fabrics. The property of the WPU emulsion, the mechanical property of the WPU film, the thermodynamic analysis of the WPU film and the water permeation resistance of coating fabrics were investigated. The experimental data showed that: As the molecular weight of polyhydric alcohol increased, the WPU emulsion changed from transparent to translucent then to milk-white, the viscosity increased gradually, and the stability of the WPU emulsion decreased slightly; As the molecular weight and the rigidity of the chain-extender increased, the transparency and stability of the emulsion decreased; As the amount of cross-linking agent HM increased, the stress at specified strain of the WPU film increased while the strain at specified stress decreased; Regarding the linear chain hydrocarbon chain-extending WPU film, both the breaking stress and the breaking strain reduced along with the polyhydric alcohol molecular weight increased; Regarding the aromatic ring and the ether chain-extending WPU film, the stress at specified strain increased along with the polyhydric alcohol molecular weight increased, while the strain at specified stress reduced along with the polyhydric alcohol molecular weight increased; As the number of carbon atoms in the linear hydrocarbon chain-extender increased, the WPU film mechanical property dropped; The breaking stress and the breaking strain of the ether chain-extending WPU film were lower but the stress at specified strain was higher, regarding chain-extender with same number of carbon atoms; If the molecular structure of aromatic ring chain-extender located in the same plane, the stress at specified strain of WPU film would be higher while the breaking stress and the breaking strain would be lower; The WPU film chain-extended by BPA had the best mechanical property; The elasticity and toughness of HDI-WPU film had an advantage over TDI-WPU and IPDI-WPU films, and the HDI-WPU film wouldn't turn yellow during application; After baking, the stress at specified strain of the WPU film increased slightly, but the strain at specified stress reduced a little; The hydrostatic pressure of coating fabric increased along with the coating quantity increased, but reduced as the molecular weight of polyhydric alcohol increased; The fabric coated by TDI-WPU bore higher hydrostatic pressure; After cross- linking, the hydrostatic pressure of coating fabrics increased.