Preparation and characterization of waterborne flame retardant polyurethane for microfiber synthetic leather
Objective In order to solve the problems of non-flame retardancy,low strength and lack of toughness of polyurethane coating on microfiber synthetic leather,type of phosphate-containing bialcohols as reactive flame retardants were prepared.It was copolymerized with methylene diphenyl diisocyanate(MDI),polytetramethylene ether glycol(PTMEG)and 2,2-dimethylol butyric acid(DMBA)to prepare water borne flame retardant polyurethane(WPU)with good dispersion,stability and performance,which is used for coating microfiber synthetic leather.Method A reactive flame retardant containing phosphorus was synthesized.It was characterized by Fourier transform infrared spectrometer(FT-IR)and nuclear magnetic resonance spectroscopy(1H NMR).Then,DHIMP was copolymerized with MDI,PTMEG and DMBA to obtain waterborne flame retardant polyurethane(P-WPU).P-WPU was prepared into coating slurry,and the soft and strong polyurethane coating was constructed on the surface of microfiber synthetic leather by double-side scraping,exchange curing and drying.Results The water dispersion of P-WPU was good.The particle size of the dispersion increased with the increase of DHIMP mass fraction.With the introduction of DHIMP,the Young's modulus of P-WPU film was gradually increased.When the mass fraction of DHIMP was 13.9%,the mechanical properties of P-WPU reached the best.The LOI of microfiber leather was continuously increasing with the gradual increase of DHIMP mass fraction.The results of vertical combustion test illustrated that the microfiber leather coated by P-WPU with different DHIMP mass fractions had a certain degree of flame retardancy.When the mass fraction of DHIMP was 16.1%,the vertical damage length was 2.3 cm,the continuous burning time was 0.6 s,the smoldering time was 0.3 s,the number of droplets was reduced to 0-1,and the absorbent cotton was not ignited,demonstrating a good flame-retardant effect.Conclusion 1)DHIMP was successfully prepared from p-hydroxybenzaldehyde,3-amino-propanol and DOPO.2)By introducing DHIMP as chain extender into waterborne polyurethane macromolecules,waterborne polyurethane with flame retardancy was successfully prepared.3)The flexible and flame-retardant microfiber synthetic leather was prepared with P-WPU coating.The maximum limiting oxygen index was 28.6%,the vertical damage length was 2.3 cm,the follow-fire time was 0.6 s,and the smoldering time was 0.3 s.