| Waterborne polyurethane(WPU)has been widely used in many fields such as textiles,leather,and coatings due to its advantages of no pollution,good compatibility,and easy operation and processing.But most of its molecular chains are linear structures,resulting in its mechanical properties and thermal stability insufficient.The comprehensive performance of WPU can be effectively improved by modifying it with the excellent properties of nano-silica(SiO2).However,the excellent properties of WPU/SiO2 nanocomposites depend not only on the properties of the two components,but also on the interface structure and interfacial action between the two phases.Therefore,it is of great scientific significance to study the interface interaction of composite materials for the optimization design of its properties.In this dissertation,WPU and various modified SiO2 were synthesized respectively,which resulted in electrostatic interaction,hydrogen bond,ionic bond and covalent bond between nano-SiO2 and WPU.The microstructure and mechanical properties of the composites were analyzed using modern instrumental analysis methods,and the interface parameters of the composites were calculated by molecular dynamics simulations.The structure-activity relationship between the microstructure and properties of WPU/SiO2 nanocomposites with different interactions was studied.Finally,WPU/SiO2 nanocomposite emulsions with different interactions were applied in leather finishing.Based on the above research,the following results were obtained:(1)The nano-SiO2 with particle size of 90?110 nm was successfully prepared by sol-gel method using cetyltrimethylammonium bromide(CTAB)as surfactant template,ethyl orthosilicate(TEOS)as silicon source,and sodium hydroxide(NaOH)as alkaline catalyst.The optimal preparation process was explored and the formation mechanism of nano-SiO2 was proposed.The WPU emulsion was successfully prepared by the prepolymer dispersion method using isophorone diisocyanate(IPDI)as isocyanate monomer,polypropylene glycol(PPG 1000)as oligomer glycol,and 2,2-dimethylolbutyric acid(DMBA)as hydrophilic chain extender,respectively.The emulsion showed translucent blue light appearance,small particle size,uniform distribution and good stability.(2)The WPU/SiO2 nanocomposite films with electrostatic interactions were prepared by physically blending methods to introduce negatively charged SiO2(SiO2(-))and positively charged SiO2(SiO2(+))into WPU emulsion,respectively.When there was electrostatic repulsion between WPU and SiO2(-),the interface between the two phases was weak,and a "hole" structure would appear in the section of the composite film,which:ffected the continuity between the two phases,and leaded to a decrease in the mechanical properties of the composite film.When there was electrostatic attraction between WPU and Si02(+),the interface between the two phases was stronger,and the continuity between the two phases was better,which enhanced the mechanical properties of the composite film.(3)The modified nano SiO2(-)and modified nano SiO2(+)with different contents of-OH and-SH on the surface after hydrochloric acid acidification and 3-mercaptopropyl trimethoxysilane(TMMPS)were introduced into WPU emulsion,respectively.The WPU/SiO2 nanocomposite films with both hydrogen bond and electrostatic repulsion,hydrogen bond and electrostatic attraction were prepared.When the hydrogen bond and electrostatic interaction existed simultaneously between WPU and SiO2,the microstructure and tensile strength of the composite film were mainly affected by electrostatic interaction,while the elongation at break was mainly affected by hydrogen bond.(4)The WPU/SiO2 nanocomposite films with ionic bond were obtained by introducing y-aminopropyl triethoxysilane(APTES)modified nano-SiO2 during the neutralization reaction of preparing WPU.APTES modification could effectively improve the water dispersion stability of nano-SiO2 and the mechanical properties of the composite films.(5)The WPU/SiO2 nanocomposite films with covalent bond were obtained by introducing hydrochloric acid acidification and APTES modified nano-SiO2 in the prepolymerization reaction of preparing WPU.The characterization results of microstructure and mechanical properties of composite films showed that the mechanical properties of composite films could be effectively enhanced even if the nanoparticles were severely agglomerated in the polymer matrix,and the enhancement trend was consistent with the change of the interface strength of the composite materials.(6)The mechanical properties and interfacial bonding strength of WPU/SiO2 nanocomposites with different interactions were compared.It was found that the effect of the four kinds of interactions on the mechanical properties and interfacial bonding strength were in order,covalent bond>ionic bond>electrostatic attraction>hydrogen bond.This indicated that the results of molecular dynamics simulation and instrumental analysis were in good agreement,and the mechanical properties of composite materials were closely related to the interfacial bonding strength.Finally,the WPU/SiO2 nanocomposite emulsions with different interactions were applied to leather finishing.Compared to pure WPU emulsions finished leather,the leather samples after finishing with WPU/SiO2 nanocomposite emulsions showed higher strength and less deformation,which effectively improved the application performance of leather products. |
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