PSI - Issue 82

Lenka Markovičová et al. / Procedia Structural Integrity 82 (2026) 274 – 280 L. Markovičová et al./ Structural Integrity Procedia 00 (2026) 000–000

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For the composite with 30% glass fiber content (Fig. 6), a decrease in viscosity was observed in the first analyzed layer (250 µm). In the second (500 µm) and third layers (750 µm), the viscosity values were almost the same as those of the sample not exposed to UV radiation. Similar to the previous samples, the composite with 30% glass fibers also exhibited a reduction in molecular weight due to UV exposure. UV radiation had the greatest effect on the first layer (250 µm), where the measured values differed most from those of the UV-unexposed sample. The deeper the layer (500 µm and 750 µm), the weaker the influence of UV radiation.

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Fig. 6. Comparison of the rheological characteristics of individual layers of the composite with 30% glass fiber content affected by UV radiation with the unaffected layer. 4. Conclusions Based on the obtained results and analyses, the following conclusions can be drawn: l Shore D hardness measurements did not show a significant effect of UV radiation on the degradation of polymer composites. For samples exposed to UV radiation, composites with 10% and 20% glass fiber content exhibited lower values, while for samples with 30% filler, the hardness values were even higher than those of the UV-unexposed samples. This was likely due to a large scatter in the measurements—the measured value depended primarily on the location of the test. l Impact strength measurements using the Dynstat method also did not reveal a significant negative effect of UV radiation. The results for UV-exposed and unexposed samples were very similar. For composite samples with 30% glass fiber content, higher values were recorded for UV-exposed samples, similar to the hardness measurements. l Both of the aforementioned measurements (Shore D hardness and Dynstat impact strength) demonstrated the influence of filler content on the properties of the composites. The higher the glass fiber content, the higher the measured hardness and impact strength values. l Rheological parameter measurements confirmed the degradative effect of UV radiation. In all UV-exposed samples, a decrease in molecular weight and a shift toward a broader molecular weight distribution were observed, indicating the formation of shorter chains. The first layers (250 µm) of all composite types were the most affected, which was in line with expectations. In the final layer (750 µm), the monitored parameters had values almost identical to those of the layer not exposed to UV radiation.