Effects of Nano-ZrO₂ Additions to Color Properties of Weathered Polysiloxanes

Objectives: The effects of nano-ZrO₂ additions on facial silicone weatherability are largely unknown. This study's purpose was to assess weathering effects on color properties of PDMS loaded with 2-3 nm, 20-30 nm and 200-300 nm ZrO₂, and compare to standard silica-reinforced PDMS.
Methods: 1 wt% nanoparticles or 13% silica and 0.2% functional intrinsic yellow pigment were mixed into vinyl-terminated PDMS, then polymerized into discs 34 mm diameter x 6 mm thick (n=5). Samples were weathered for 600 hours in UVB (0.72 J/cm²/h), heat (65C), humidity (80%r.h.) or control (C) (darkness, 25C, 30%r.h.). CIELab color was measured at baseline (B) and 600 hours. Color changes were compared according to nanoparticle size and test condition (ANOVA/Tukey, p<0.01) and evaluated according to minimum and maximum values for acceptability and perceptibility (1.1<ΔE*<3.0).
Results: After 600 hours UVB: -1.7<ΔL*<-3.2, 0.8<Δa*<2.5,-3.7<Δb*<-4.9; Heat: -0.5<ΔL*<-4.3, 0.4<Δa*<1.2,-0.7<Δb*<-6.9; Humidity: 0.0<ΔL*<-0.4, 0.1<Δa*<0.85, 0.0<Δb*<-0.4; Control 0.0<ΔL*<3.7, 0.2<Δa*<0.4, 0.0<Δb*<8.4. Mean (s.d.) ΔE* values for the different particle sizes are shown in the Table 1; superscript comparisons are both horizontal and vertical (p<0.01).
Conclusions: 20-30 nm and 200-300 nm ZrO₂ additions reduced inherent color changes occurring under control conditions, but increased color changes in response to heat. Humidity imposed the least weathering challenge to color change, whereas UVB induced fading in all formulations that exceeded the maximum value for 50:50 acceptability (ΔE*>3.0).