Preparation And Properties Of Polysiloxane-based Waterborne Polyurethane

Waterborne polyurethane(WPU)is favored by scientific researchers because of its environmentally friendly characteristics,but due to introducing of hydrophilic groups during the synthesis process,its water resistance is poor.Polysiloxane has the advantages of low surface tension,good hydrophobicity,etc.and was used to improve the water resistance of WPU films.But at present,more attention is paid to the modification effect of polysiloxane on the water resistance of film,while its effect on the performance of WPU emulsion stability is ignored.Three polysiloxanes with different structures were designed and synthesized,which were used to modify the WPU,respectively,and by adjusting the structure and position of the hydrophilic groups,WPU with good emulsion stability and water resistance of film were obtained,and to study the comprehensive performance of WPU emulsion and film.The following is the research contents.Firstly,trimethylchlorosilane(TMCS)partially blocked hydroxysilicone oil(HSO)to obtain single-ended hydroxysilicone oil(SHSO),then using isophorone diisocyanate(IPDI),polyadipate 1,4-butyrate(PBA2000),2,2-dimethylolpropionic acid(DMPA)as raw materials to synthesize polyurethane prepolymer(PPU),finally,SHSO and lactic acid(LA)were used as hydrophobic and hydrophilic agent to modify PPU to prepare the waterborne polyurethane(ATPU)with hydrophilic/hydrophobic chain ends.The single factor experiment preferred optimal reaction conditions were n(IPDI):n(PBA2000)was 2.5,DMPA dosage was 3.0 wt.%and SHSO dosage was 10.0 wt.%.The results of Fourier transform infrared spectroscopy(FTIR)and Nuclear magnetic resonance hydrogen spectroscopy(1H-NMR)indicated that the reaction proceeded as expected;the X-ray diffraction(XRD)test results showed that ATPU crystallinity decreased;the thermogravimetric analysis(TGA)results show that:the initial decomposition temperature of ATPU is reduced,but its high temperature resistance is improved;atomic force microscopy(AFM)and scanning electron microscopy(SEM)observations results showed that the degree of phase separation of ATPU increased;scanning electron spectroscopy(EDS)test results showed that the Si element on the surface of the ATPU was significantly enriched 24%higher than that of the longitudinal section.Contrast unmodified WPU,the average particle size of ATPU emulsion was reduced by 46.52 nm and it was more stable.The water absorption of ATPU declined 4.7%,the water contact angle increased 19.9°,the tensile strength reduced 2.8 MPa,the elongation at break increased 78%.It showed that this modification method simultaneously improved the water resistance and emulsion stability of WPU.In order to avoid the influence of the blocking agent on the molecular weight and thus affect the comprehensive performance of the film,the modification effect of hydrophilic and hydrophobic modifiers simultaneously grafted to WPU molecular side chains was studied.Specifically:the methoxypolyethylene glycol acrylate(mPEG-AC)is modified by diethanolamine(DEOA)to obtain methoxypolyethylene glycol N,N-dihydroxyethylaminopropionate(SDPG);SHSO two steps of reaction with acryloyl chloride(AC)and DEOA to obtain N,N-dihydroxyethylaminopropionic polydimethylsiloxane ester(SDPSi);finally,SDPG and SDPSi were used as hydrophilic and hydrophobic agents to modify the PPU to prepare amphiphilic comb-like waterborne polyurethane(SSPU).The experiment of single-factor preferred the best reaction conditions were:n(IPDI):n(PBA2000)was 2.5,DMPA dosage was 3.0 wt.%,SDPG and SDPSi dosage were 10.0 wt.%.The results of FTIR and 1H-NMR analysis showed that the reaction proceeded as expected;XRD test showed the crystallinity of SSPU decreased;TGA showed that the initial decomposition temperature of SSPU reduced,but its high temperature resistance is improved;AFM and SEM observation results showed that the phase separation degree of SSPU film increases;EDS test results showed that the concentration of Si element on the surface of the SSPU film is obviously 3 times of that in the longitudinal section.Compared with unmodified WPU,the emulsion average particle size of SSPU reduced 20.22 nm,proving it had better emulsion stability,the water absorption of SSPU film reduced by 5.3%,the water contact angle increased by 11.5°,the hardness decreased to 2H from 3H,the tensile strength increased by 4.6 MPa and the elongation at break increased by 126%.These mean that this modification method not only improved the water resistance of film and the stability of the emulsion,but also improves the mechanical property.The above two modification methods reduced the hardness of the film,increased the degree of phase separation simultaneously,and less improved the mechanical properties of the film,therefore,using the structural properties of hyperbranched polymer further improves these defects.Firstly,amino-terminated hyperbranched polysiloxane(HPSi-NH2)was synthesized by y-aminopropyltriethoxysilane(KH550),dimethyl diethoxysilane(DMDES)and trimethylchlorosilane(TMCS),then,used it as a post-chain extender for the modification of PPU to prepare amino-terminated hyperbranched polysiloxane modified waterborne polyurethane(HSiPU).The preferred synthesis conditions by single factor experiment were:n(IPDI):n(PBA2000)was 3.5,the amount of DMPA was 5.0 wt.%and the amount of HPSi-NH2 was 2.0 wt.%.HSiPU emulsion prepared under these conditions was stable and translucent.The results of FTIR and 1H-NMR analysis proved that HSiPU had been successfully synthesized.XRD showed that its crystallinity reduced;TGA analysis showed that the thermal stability of HSiPU is improved;AFM and SEM observation results showed that the degree of phase separation of HSiPU reduced;EDS test results showed that the Si element on the surface and longitudinal section of the HSiPU film is evenly distributed.Compared with unmodified WPU,the emulsion average particle size of HSiPU increased to 73.85 nm from 56.76 nm,the film hardness changed from 3H to 4H,the water absorption rate decreased 10.9%,the water contact angle,the tensile strength and the elongation at break increased by 26.3°,10.1 MPa and 183%respectively.It showed that HPSi-NH2 modification improved the water resistance,mechanical properties,thermal stability and hardness of WPU film,as well as the degree of phase separation of the film is reduced.