# UV-Induced Aging in Thermochromic Pigment-Integrated Food-Grade Polymers: A Performance Assessment
## 3 Results
### Color Stability
The trends in the \(\Delta E^{\star}\)ab values were also reflected in the RGB values, with PP92/TP8 showing more pronounced shifts toward lighter and redder tones. The higher pigment loading in PP92/TP8 may have increased its vulnerability to UV-induced matrix disruption or pigment fading, supporting the conclusion that pigment concentration influences long-term color stability in thermochromic systems. To support the interpretation of statistical variability, 95% confidence intervals (CIs) were calculated for all \(\Delta E^{\star}\)ab values. For example, the PP98/TP2 blend exposed to RS 559-934 UVA for 500 h exhibited a \(\Delta E^{\star}\)ab of 19.29 \(\pm\) 0.81 (95% CI), while the same blend under \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Specimen** & **UV** & **Exposure** & & & & & \\
**ID** & **Device** & **Hours (h)** & \(\Delta L^{\star}\) & \(\Delta a^{\star}\) & \(\Delta b^{\star}\) & **(\(\Delta E^{\star}\)ab)** & **RGB** \\ \hline \multirow{4}{*}{PP98/TP2} & — & 0 & 0.00 & 0.00 & 0.00 & 0.00 & 155, 112, 125 \\  & RS 559-934 & 500 & 14.22 (\(\pm\)0.82) & 8.16 (\(\pm\)1.03) & 11.38 (\(\pm\)0.92) & 19.29 (\(\pm\)1.13) d  & 213, 142, 142 \\  & RS 559-934 & 1000 & 19.58 (\(\pm\)0.91) & 6.03 (\(\pm\)0.75) & 13.53 (\(\pm\)0.61) & 23.50 (\(\pm\)1.02) b  & 227, 158, 152 \\  & QUV/SE & 500 & 19.21 (\(\pm\)1.00) & 10.78 (\(\pm\)1.26) & 14.46 (\(\pm\)0.45) & 26.36 (\(\pm\)1.97) c  & 233, 153, 150 \\  & QUV/SE & 1000 & 24.62 (\(\pm\)1.06) & 8.07 (\(\pm\)1.01) & 15.65 (\(\pm\)0.48) & 30.29 (\(\pm\)1.08) a  & 246, 170, 162 \\ \hline \multirow{4}{*}{PP92/TP8} & — & 0 & 0.00 & 0.00 & 0.00 & 0.00 & 148, 109, 121 \\  & RS 559-934 & 500 & 13.14 (\(\pm\)0.53) & 7.51 (\(\pm\)0.86) & 10.81 (\(\pm\)0.15) & 17.82 (\(\pm\)0.91) c  & 206, 140, 141 \\  & RS 559-934 & 1000 & 24.78 (\(\pm\)0.45) & 3.27 (\(\pm\)0.62) & 12.98 (\(\pm\)0.49) & 27.57 (\(\pm\)0.62) a  & 234, 174, 167 \\  & QUV/SE & 500 & 17.57 (\(\pm\)0.62) & 10.13 (\(\pm\)0.96) & 13.43 (\(\pm\)0.58) & 24.34 (\(\pm\)1.10) d  & 224, 149, 148 \\  & QUV/SE & 1000 & 30.34 (\(\pm\)0.43) & 4.09 (\(\pm\)0.66) & 14.96 (\(\pm\)0.30) & 34.07 (\(\pm\)0.21) b  & 252, 188, 179 \\ \hline \end{tabular}  
* Superscript letters indicate statistically significant differences between groups (Tukey HSD, \(p<0.05\)). Values sharing the same letter are not significantly different.  
\end{table} 
Table 3: \(\Delta L^{\star}\), \(\Delta a^{\star}\), \(\Delta b^{\star}\) color parameters, total color difference (\(\Delta E^{\star}\)ab), and RGB values across UVA radiation (internal). QUV/Solar Eye UVA for 1000 h reached 30.29 \(\pm\) 0.76. The PP92/TP8 formulation showed the highest variability under the QUV exposure, with a \(\Delta E^{*}\)ab of 24.34 \(\pm\) 0.76 at 500 h and \(34.07\pm 0.15\) at 1000 h. These confidence intervals confirm that the observed differences between materials and exposure conditions are both statistically and practically significant. The comparative data underscore that outdoor UVA exposure (QUV/Solar Eye) induces more aggressive color degradation than indoor-equivalent UVA exposure (RS 559-934). Additionally, PP92/TP8 continuously displayed larger \(\Delta E^{*}\)ab values than PP98/TP2 under the same exposure settings, indicating it is more susceptible to discoloration. For long-term esthetic performance in outdoor packaging and display applications, the study emphasizes the significance of implementing UV stabilization procedures and preserving a balance in thermochromic pigment concentration [81]. Time-dependent color instability was confirmed by the overall increase in \(\Delta E^{*}\)ab with exposure duration for both interior and exterior UVA settings. Discoloration was more likely to occur in the higher pigment-loaded formulation, PP92/TP8, underscoring the need to maximize pigment concentration and add potent UV stabilizers in applications needing resilience to prolonged exposure [82].