The Synthesis And Characterization Of Waterborne Polyurethane Modified By Siloxane

Polyurethane has excellent comprehensive performance and it is widely used in many fields, such as coating, etc. The research of waterborne polyurethane(WPU) conforms to the current era theme of green, environmental protection and safety. The silane or siloxane component in WPU is able to improve water-resistance and heat-resistance, surface hydrophobicity and mechanical properties which is a promising research and development direction. In the work, the formulations and processes of waterborne polyurethane resin were optimized. On this basis, three following method were used to prepare WPU/silicon hybrid dispersions, a) PU perpolymer capped by amino silane coupling agent, b) The co-hydrolysis of silane coupling agent and PU perpolymer capped by silane, c) PU perpolymer capped by silane coupling agent and POSS. The influences of compositions and structures on the properties of hybrid films were systematically researched. The main work of this paper is as follows.(1) The determination of basic formulation and process to prepared WPU:The optimization of formulation and process was as purpose. The synthesis of thermoplastic WPU was as starting point. The stability of dispersions and the properties of films were as evaluation standard. A series of process and formulation were designed to prepare WPU. The key factors, namely the value of r/R, the degree of crosslinking, and the content of hydrophilic monomer were studied to obtain the optimal process parameters. The good dispersions could be obtained which could remain stable for more than half a year. The tensile strength was more than 40 MPa, the elastic modulus was 33.5 MPa, the elongation at break was 1000%, and the water uptake was 9.3%.(2) The preparation of WPU dispersions capped by amino silane coupling agent:On the basis of optimized process, a series of PU perpolymers wich NCO radical were prepared. Then the (3-aminopropyl)triethoxy silane (APTES) was introduced to block PU perpolymers. The products could be dispersed in water and a series of waterborne dispersions were obtained. The alkoxy at the end group would hydrolyze to form silanol which is good for the stability of aqueous dispersions. The structure of alkoxy silane and silicon would further hydrolyze and condense and form self-crosslinked structure. The influence of the content of crosslinking monomer and hydrophilic monomer, hard segments ratio, solid content, and pH on the main properties of films, such as mechanical properties, dynamic mechanical properties, water uptake, contact angle, and thermal stability. The surface morphology of films were investigated, as well. The result showed shat the hybrid dispersions could form fine hybrid films when the dispersions contained 10-15% APTES, lower than 40% hard segments, and lower than 40% solid content. The heat treatment to hybrid films through higher temperature and longer time was better for mechanical properties and water resistance. The synergistic effect of the crosslinkable structure introduced by APTES and the optimization of resin structure is an effective way to improve film performance forming at low temperature.(3) The preparation of hybrid dispersions by the co-hydrolysis of silane coupling agent and PU perpolymer capped with silane:By the co-hydrolysis of silane coupling agent and the perpolymer capped with APTES in the emulsifying process, a series of hybrid dispersions based on MTMS, PTMS, and PFTMS were prepared. In the process of film forming, by the process of co-condensation, it is realized that the preparation of silicone resin by condensation and the self-crosslink of polyurethane at the same time. Condensation/crosslink reaction in situ successfully suppress the phase separation in the system. The results showed that the dispersions could remain stable for more than six months. The heat-resistance of films could be improved at the same time. The introduce of perfluorinated alkyl chain segments to hybrid matrix could significantly improve the surface hydrophobicity. The results showed that the water contact angle get to 120° with 8wt% perfluorinated alkyl chain.(4) The preparation of hybrid dispersions by the co-capped with silane coupling agent and POSS:By the co-capped with silane coupling agent and POSS to PU perpolymers, a novel kind of POSS-modified self-curable WPU dispersions was prepared. The dispersions remain stable for more than six months. The introduce of POSS would increase the dispersion viscosity and showed the thixotropy. The hybrid PU dispersions were used as one-component waterborne resin and could form continuous and homogenous films under ambient conditions. The hybrid films were characterized by XRD and XPS. Many properties of hybrid films, such as mechanical properties, dynamic mechanical properties, water contact angle, water uptake and dielectric constant, were researched at different POSS levels. The results show that POSS would form microcrystalline during film forming which could show physical crosslinking effect. The synergy of physical crosslinking and chemical crosslinking could improve the mechanical properties of films. The enrichment of POSS component on the surface significantly increased water contact angle. Dielectric constant would also significantly decrease. After fluoride treatment, the water contact angle increased to 127°, by fluorine/silicon synergy effect. The dielectric constant and dielectric loss would further reduce at the same time.