Preparation And Properties Of Solvent-free Polyurethane/hollow TiO₂ Microsphere Composites

With the increasing awareness of environmental protection,solvent-free polyurethane（SFPU）has excellent environmental performance and has become one of the research hotspots in the polyurethane coating industry.However,SFPU requires a relatively high temperature during film formation process,which causes the reaction system to cure too fast,and the foam layer and the coating layer of the polyurethane film are relatively dense,so the polyurethane film exhibits poor hygienic properties and mechanical properties.Based on this,this research proposes to introduce hollow TiO₂ microspheres with large specific surface area and special internal cavity structure into SFPU film,increase the free volume of the film and the water vapor transmission channel,and improve the hygienic and mechanical properties of the film.The specific research contents are as follows:Different types of commercially available inorganic nanoparticles were introduced as nano-fillers into SFPU prepolymers to prepare SFPU/nanomaterial composite film.The composite films were characterized by FT-IR,SEM and TGA.The results show that the nanomaterials are successfully introduced into the prepolymer and have good dispersibility in the composite film,and the thermal stability of the composite film is improved.The elongation at break,tensile strength and water vapor permeability of the composite film were taken as indicators to optimize the types of nanoparticles,introduction methods and introduction amount of the nanoparticles.The results show that when 0.5%nano-TiO₂ is introduced into polyether polyol to prepare SFPU composite film,the composite film has the best performance,and the tensile strength of the film increases by 162.76%,the elongation at break increases by 73.25%,and the water vapor permeability increases by 46.22%.The SFPU film and the microfiber base cloth were bonded together under high temperature conditions to prepare a SFPU synthetic leather.The results showed that the water vapor permeability of the solventless polyurethane/nano-TiO₂ synthetic leather increased by 14.86%.The gas permeability increased by 56.46%,the tensile strength increased by 26.84%,the tear strength increased by 18.29%,and elongation increased by 4.32%compared with the synthetic leather without the addition of nano-TiO₂.Hollow TiO₂ microspheres（HTSs-1）were successfully prepared by hard template method using TBOT and glucose(C₆H₁₂O₆)as titanium source and C source,respectively.The preparation process of HTSs-1 was optimized by SEM,TEM and FT-IR.The results showed that when the reaction time was 4 h,the reaction temperature was 180°C,the reaction pH was 7,the glucose concentration was 0.78 mol/L,and the TBOT dosage was 4%,the hollow nano-TiO₂ microspheres（HTSs-1）with the particle size of 150nm were obtained.The hollow TiO₂ microspheres were introduced into the polyurethane prepolymer emulsion to prepare a solventless polyurethane/hollow TiO₂composite film,and the composite film was characterized by FT-IR,SEM and TGA.The results show that the hollow TiO₂ microspheres were successfully introduced into the prepolymer and had good dispersibility in the composite film,and the thermal stability of the composite film was improved.When the introduction amount of HTSs-1 is 0.3%,the mechanical properties and hygienic properties of the composite film and synthetic leather are greatly improved.The water vapor permeability of the composite film is increased by 90%,the tensile strength is increased by 107%,and the elongation at break is increased by25.54%.The SFPU film and the microfiber base cloth were bonded together under high temperature conditions to prepare a SFPU synthetic leather.The tensile strength of synthetic leather increased by 48.17%,the elongation at break increased by 2.24%,the tear strength increased by 7.28%,the water vapor permeability improved by 93.78%,and the gas permeability increased by83.64%.Hollow TiO₂ microspheres（HTSs-2）were successfully prepared by using TBOT as the titanium source and ammonium fluoride（NH₄F）as the foaming agent.The characterization of hollow TiO₂ microspheres by one-step template-free method was optimized by SEM,TEM and FT-IR characterization of hollow TiO₂ microspheres.The results show that when the reaction time is12h,the reaction temperature is 180°C,the pH value of the system is 7,the ratio of NH₄F and titanium source is 1:1,the HTSs-2 with the particle size of 450nm are obtained with good dispersion,and the regularity is higher without obvious breakage.The hollow TiO₂ microspheres were introduced into the polyurethane prepolymer emulsion to prepare SFPU/hollow TiO₂ composite film,and the composite film was characterized by FT-IR,SEM and TGA.The results show that the hollow TiO₂ is successfully introduced into the prepolymer and has good dispersibility in the composite film,which has a certain improvement on the thermal stability,hygienic properties and mechanical properties of the composite film.The water vapor permeability,the tensile strength,and the elongation at break of composite film were increased by 137.22%,41.11%and 55.81%,respectively.The SFPU film and the microfiber base cloth were bonded together under high temperature conditions to prepare a SFPU synthetic leather.The tensile strength of synthetic leather increased by 36.37%,the elongation at break increased by 70.37%,the tear strength increased by 58.26%,the water vapor permeability improved by 23.01%,and the gas permeability increased by50.00%.The double-shell hollow nano-TiO₂ microspheres（S@S-TiO₂）were prepared by hard template method with titanium tetrafluoride（（NH₄）₂TiF₆）as the titanium source,glucose as the carbon source.The SEM,TEM and FT-IR characterization of double-shell hollow TiO₂ microspheres were carried out to optimize the process conditions of S@S-TiO₂ prepared by hard template method.The results showed that when the reaction temperature was 180°C,the pH of the system was 7,and the ratio of glucose to（NH₄）₂TiF₆ was 10:1,the S@S-TiO₂had a regular morphology and good dispersion.It was introduced into the polyurethane prepolymer emulsion to form a film,and then the synthetic leather was prepared.The results show that the introduction of S@S-TiO₂ has greatly improved the mechanical properties and hygienic properties of composite film and synthetic leather.The water vapor permeability of the composite film increased by 73.10%,the tensile strength increased by 117.77%,the elongation at break increased by 76.59%,and the antibacterial rate increased by 173.70%.The tensile strength of synthetic leather increased by 34.63%,the elongation at break increased by 74.11%,the tear strength increased by 55.65%,the water vapor permeability improved by 33.69%,and the gas permeability increased by85.28%.The HTSs-1,HTSs-2 and S@S-TiO₂ prepared by the above different methods were introduced into the solventless polyurethane emulsion to form the film.The tensile strength,elongation at break and water vapor permeability of the composite film were investigated.The results show that the mechanical and hygienic properties of the composite film are better than those of the SFPU film.The mechanical and hygienic properties are as follows:SFPU/S@S-TiO₂composite film>SFPU/HTSs-2 composite film>SFPU/HTSs-1 composite film>SFPU film.Finally,different composite films will be separately coated on the super-fiber base fabric to prepare a synthetic leather.The application results show that the mechanical and hygienic properties of synthetic leather are as follows:SFPU/S@S-TiO₂syntheticleather>SFPU/HTSs-2synthetic leather>SFPU/HTSs-1 synthetic leather>SFPU synthetic leather.