Study On The Effect Of Red Pigments And Nanometer TiO₂ On The Color Stability Of Silicone Rubber Under Ultraviolet Aging

Objective:The purpose of this study was to evaluate the color stability of silicone rubber caused by ultraviolet-A aging when mixed with different red pigments,different surface treatment of nanometer TiO₂ and different concentrations of nanometer TiO₂ at different UV aging time.Materials and Methods:Experiment 1:1.0wt%oil painting cadmium red,propylene red, gouache red,oil painting rose red,oil soil red were separately added to the silicone rubber, without red paint silicone rubber for the control group.The specimens were made of 6 groups, each 10,a total of 60.The specimens were exposed to ultraviolet-A for 600h.CIE L^*,a^*,b^* values were measured before and after ultraviolet aging.The color differences(â–³E) were calculated.Experiment 2:2.0wt%Si-Al-coated nanometer TiO₂(inorganic treatment),silane coupling agent treated nanometer TiO₂(organic treatment) and Si-Al-coated - silane coupling agent treated nanometer TiO₂(inorganic - organic treatment) were separately added to the cadmium red paint silicone rubber,without surface treated nanometer TiO₂ specimens for the control group.The specimens were made of 4 groups,each 10,a total of 40.CIE L^*,a^*,b^* values were measured before and after 720h of ultraviolet aging.The color differences(â–³E) were calculated.Experiment 3:The concentration of 0.00%,0.50%,1.00%,1.50%,2.00%, 2.50%(total amount of colored silicone rubber) of the Si-Al- silane coupling agent treated nanometer TiO₂ were separately added to the cadmium red paint silicone rubber.They were made into six groups of specimens,each 5,a total of 30.CIE L^*,a^*,b^* values were separately measured before and after 240h,480h and 720h of ultraviolet aging.The color differences(â–³E) were seperately calculated.Results:Experiment 1:After 600h of UV aging,the control group specimens had the least color change.Theâ–³E was 12.84±1.09.Among the five red pigments,oil painting cadmium red had the smallest color change,followed by,in order,oil painting rose red,oil soil red, propylene red and gouache red.Theirâ–³E were 15.96±0.88,16.84±1.39,18.09±0.65, 18.27±1.59,18.30±0.61.After UV aging,the L^* value of all specimens increased.The a ^*and b^* values of all specimens decreased.This shows that the brightness of the specimens after aging increased,while the red and yellow tone decreased.Experiment 2:After 720h of UV aging,Si-Al-coated - silane coupling agent treated nanometer TiO₂ specimens had the least color change,followed by,in order,silane coupling agent treatment specimens, Si-Al-coated specimens and the control group specimens.Theirâ–³E were 6.06±1.02,7.11±1.10,7.81±1.09,9.42±0.96.Experiment 3:After UV aging,the different concentrations of Si-Al- silane coupling nanometer TiO₂ specimens had the different color changes at different aging time.When the UV aging time is a certain value,with the concentration of nanometer TiO₂ increased,theâ–³E of the specimens gradually decreased.When the concentration is 2.00%,the specimens had the smallest color change;when the concentration of nanometer TiO₂ is a certain value,with the UV aging time increased,theâ–³E of the specimens gradually increased.After 240h and 480h of UV aging,theâ–³E of specimens increased large.After 720h of UV aging,theâ–³E of specimens changed little,which is compared with 480h.Conclusion:1.After UV aging,the red pigment decreased the color stability of silicone rubber.Among the five red pigments,oil painting cadmium red and oil painting rose red had more color stablility than the other red pigments.2.After UV aging,Si-Al- silane coupling agent(inorganic -organic) treated nanometer TiO₂ specimens had more color stability than the other surface treated nanometer TiO₂ specimens.The control group specimens had the worst color stability.3.The different concentrations of Si-Al-coated-silane coupling agent treated nanometer TiO₂ were added to protect the cadmium red paint silicone rubber from color degradation after UV aging.When the UV aging time is a certain value,with the concentration of nanometer TiO₂ increased,theâ–³E of the specimens gradually decreased.When the concentration is 2.00%,the specimens had the strongest UV shield.When the concentration is more than 2.0%,theâ–³E of the specimens began to increase.Because nanometer TiO₂ appeared saturation in the colored silicone rubber,the UV-shielding ability of the specimen began to decrease.4.when the concentration of nanometer TiO₂ is a certain value,with the UV aging time increased,the specimens appeared color degradation.The color degradation of specimens occured mainly within the 480h of UV aging.Theâ–³E of 720h,compared with 480h,was not statistically significant.The colored silicone rubber occurred color degradation mainly in the early stage after fabricated.