# UV-Induced Aging in Thermochromic Pigment-Integrated Food-Grade Polymers: A Performance Assessment
## 3 Results
### Impact Strength After UV Exposure  
Using notched and unnotched samples, the impact strength of different polymer blends was assessed with exposure to various UV food contact conditions (Table 5). The corresponding results are visualized in Figure 8, which illustrates the degradative trends across both UV devices and exposure durations. The impact strength data presented in Table 5 demonstrate the effect of UVA radiation on the fracture resistance of thermochromic polypropylene blends (PP98/TP2 and PP92/TP8), assessed under both unnotched and notched conditions after exposure to RS 559-934 (360 nm) and QUV/Solar Eye (340 nm) for 500 and 1000 h. Control specimens exhibited high unnotched impact strength (99.94 kJ/m\({}^{2}\)) and moderate notched strength (23.52 kJ/m\({}^{2}\)), consistent with ductile fracture behavior and high energy absorption capacity [91]. A progressive decline in both impact values was observed upon UVA exposure, with more significant reductions under the QUV/Solar Eye conditions. For PP98/TP2, the RS 559-934 exposure led to a 14.30% and 29.42% decrease in unnotched impact strength after 500 and 1000 h, respectively, while notched strength declined by 13.61% and 23.69%. Under the QUV conditions, losses were more pronounced, with unnotched values dropping to 60.22 kJ/m\({}^{2}\) (\(-\)39.8%) after 1000 h, notched--to 15.23 kJ/m\({}^{2}\) (\(-\)35.2%). Figure 8: (a) Unnotched and (b) notched impact strength of thermochromic polypropylene blends PP98/TP2 and PP92/TP8 following UVA exposure at 0, 500, and 1000 h under the RS 559-934 (360 nm) and QUV/Solar Eye (340 nm) devices. Error bars indicate standard deviation (\(n=10\)). \begin{table}
\begin{tabular}{c c c c c} \hline
**Specimen** & **UV Device** & **Exposure Hours** & **Unnotched Impact Strength** & **Notched Impact Strength** \\
**ID** & **UV Device** & **(h)** & **(k/m\({}^{2}\))** & **(k/m\({}^{2}\))** \\ \hline \multirow{4}{*}{PP98/TP2} & None (control) & 0 & 99.94 (\(\pm\)2.12) a & 23.52 (\(\pm\)1.21) a \\  & RS 559-934 (360 nm) & 500 & 85.65 (\(\pm\)2.87) b & 20.32 (\(\pm\)1.44) b \\  & RS 559-934 (360 nm) & 1000 & 70.54 (\(\pm\)3.23) c & 17.95 (\(\pm\)1.58) c \\  & QUV/Solar Eye (340 nm) & 500 & 78.41 (\(\pm\)2.51) d & 18.61 (\(\pm\)1.33) d \\  & QUV/Solar Eye (340 nm) & 1000 & 60.22 (\(\pm\)3.13) e & 15.23 (\(\pm\)1.67) e \\ \hline \multirow{4}{*}{PP92/TP8} & None (control) & 0 & 99.86 (\(\pm\)2.07) a & 23.44 (\(\pm\)1.13) a \\  & RS 559-934 (360 nm) & 500 & 81.19 (\(\pm\)2.72) b & 18.87 (\(\pm\)1.56) b \\ \cline{1-1}  & RS 559-934 (360 nm) & 1000 & 66.37 (\(\pm\)3.08) c & 16.05 (\(\pm\)1.49) c \\ \cline{1-1}  & QUV/Solar Eye (340 nm) & 500 & 75.04 (\(\pm\)2.95) d & 17.22 (\(\pm\)1.32) d \\ \cline{1-1}  & QUV/Solar Eye (340 nm) & 1000 & 52.37 (\(\pm\)3.43) e & 13.09 (\(\pm\)1.58) e \\ \hline \end{tabular}
\end{table} 
Table 5: The effect of UV exposure on the impact strength of PP98/TP2 and PP92/TP8 with and without notches after UV exposure post 0, 500, and 1000 h.  
PP92/TP8 followed a similar but more severe trend. Unnotched impact strength declined by 18.70% and 33.54% after 500 and 1000 h in the RS chamber, while the QUV exposure caused a drop to 52.37 kJ/m\({}^{2}\) (\(-\)47.56%). Notiched strength decreased by 19.50% and 31.52% under the RS exposure and by 44.15% under the QUV, suggesting that higher pigment loading in PP92/TP8 accelerates UV-induced embrittlement. UVA radiation significantly deteriorates unnotched and notched impact resistance, indicating increased material sensitivity to crack initiation and propagation. The more aggressive degradation observed under the QUV/Solar Eye exposure compared to RS 559-934 underscores the critical role of the UV source and spectral intensity in accelerating mechanical failure.