Preparation And Performance Of Titanium Dioxide/Polyurethane-Urea Composites

Polyurethane elastomer is a kind of polymeric material formed by the blocks of hard and soft segments.It has been widely used in transportation,petrochemical,aerospace,military,automobile manufacturing and other fields because of its excellent comprehensive properties,and has become one of the indispensable important materials.However,due to its poor heat resistance,weather resistance,solvent resistance,antistatic and other properties,its application is limited.In order to further expand its application field,the preparation of polyurethane-urea nanocomposites by adding nanoparticles into polyurethane-urea system has become a research hotspot.Nano-titanium dioxide not only has four major effects common to ordinary nanoparticles,such as surface effect,quantum size effect,small size effect and macro quantum tunnel effect,but also has the characteristics of good chemical stability,high ultraviolet absorption and photocatalysis,which have attracted wide attention in improving the comprehensive properties of polyurethane.However,titanium dioxide nanoparticles are easy to form large size aggregates and have poor compatibility with polyurethane matrixIn order to obtain higher dispersibility in polyurethane matrix,surface modification of titanium dioxide nanoparticles has become a commen way.In thiswork,a series of titanium dioxide nano/micron particles were modified by using 12-hydroxyl stearic acid as modifier and "water only method" established in our group.Then,titanium dioxide with different particle sizes was added to polyurethane urea system,and a series of titanium dioxide/polyurethane urea composites were prepared by in-situ polymerization,and their properties were characterized.The specific research contents are as follows.(1)Using water as dispersing medium and 12-hydroxyl stearic acid as modifier,a series of modified titanium dioxide particles with different particle sizes,5-10nm,25nm,40nm,60nm,100nm and 2-3?m,were synthesized.The results showed that the effect of 12-hydroxyl stearic acid on the modification of titanium dioxide with different particle sizes was different under the same conditions.Thermogravimetric analysis(TGA)showed that the grafting ratio of titanium dioxide particles with the diameter of 5-10nm was 25%,and that of 2-3?m was 8%.Then,the optimum modification conditions of 2-3?m titanium dioxide particles were obtained by orthogonal design,i.e.reaction temperature 120?,reaction time 16h.and the amount of dodecyl stearic acid 60%to the mass of titanium dioxide.Transmission electron microscopy(TEM)test showed that the modification of 12hydroxyl stearic acid was beneficial to improve the dispersion of titanium dioxide particles in the polyurethane urea matrix.X-ray diffraction results indicated that the crystal structure of titanium dioxide particles has no change before and after modification,indicating that the modification of dodecyl stearic acid has no effect on the crystal structure of titanium dioxide.Infrared spectra suggested that the content of 12-hydroxyl stearic acid on the surface of modified nano-titanium dioxide(25nm)decreased gradually with the increase of ultraviolet irradiation time.(2)A series of titanium dioxide/polyurethane-urea nanocomposites were prepared by in-situ polymerization or simple blending by adding 12-hydroxyl stearic acid-modified titanium dioxide into polyurethane urea system.The properties of titanium dioxide/polyurethane-urea nanocomposites were analyzed by infrared spectroscopy,dynamic mechanics(DMA),thermogravimetric analysis(TGA),scanning electron microscopy(SEM)and mechanical properties.The results showed that the mechanical properties of the titanium dioxide/polyurethane-urea nanocomposites synthesized by in-situ polymerization with particle size of 25nm were the best,i.e.,the tensile strength was 59MPa and the elongation at break was 633%.Compared with pure polyurethane-urea,the tensile strength and the elongation at break of titanium dioxide/polyurethane-urea nano composites were improved by 2.9 times and 1.1 times,respectively.Compared with the simple blending method,the mechanical properties of polyurethane-urea nanocomposites synthesized by in-situ polymerization were better,because the distribution of nano-titanium dioxide in polyurethane urea matrix is more uniform.The results of DMA showed that the glass transition temperature of polyurethane urea nanocomposites increased and the elastic plateau increased with the addition of titanium dioxide nanoparticles.TGA results showed that the thermal decomposition temperature of titanium dioxide/polyurethane urea nanocomposites was increased.In addition,due to the ultraviolet shielding effect of titanium dioxide,titanium dioxide/polyurethane urea composites exhibited less degradation compared to pure polyurethane urea.