Highly efficient caffeine-based PVA composite film for UV shielding

A transparent film based on a composite of polyvinyl alcohol (PVA) and caffeine was prepared for UV light absorption. The caffeine was extracted from ground coffee without further purification; in parallel, a 5.00 wt$\text{\%}$ aqueous PVA solution was prepared and mixed at different concentrations from the extracted caffeine. Polymeric films were prepared by spin-coating the mixed solution of PVA/caffeine deposited onto a borosilicate glass substrate. UV–Vis spectroscopy was employed to test the transparency and efficiency of UV absorption from the film. Our results revealed that the film prepared from the 1.00 wt$\text{\%}$ precursor solution of extracted caffeine exhibited the best absorption at the UV-C region (200 – 275 nm). On the other hand, the film prepared at the highest concentration of 5.00 wt$\text{\%}$ showed the best absorption in both UV-A and UV-B regions, although it was quite brittle compared to the rest. Our FTIR analysis showed a significant decrease in the OH band from PVA after adding 1.00 wt$\text{\%}$ crude caffeine, implying that the hydroxide sites of PVA interact with the caffeine molecules, up to saturation. This result verifies the correct integration of crude caffeine filler within the polymeric matrix via hydrogen bonding. X-ray diffraction analysis suggests that the $\alpha$-phase of caffeine is crystallized in the composite film, however, the disappearance of the characteristic [11̄2] peak indicates the formation of caffeine clusters with preferred orientations along the [110] planes after saturation (1.00 wt$\text{\%}$). It is also confirmed that the most amorphous film was 1.00 wt$\text{\%}$ caffeine, with a crystalline degree of approximately 14.82%. Our XPS analysis confirmed a caffeine concentration of about 0.94%, impurity level of 13.57%, and humidity level of 32.74% for the composite film prepared at 1.00 wt$\text{\%}$ PVA/caffeine solution. These results are of high importance in the field of polymer engineering research. Countries like Ecuador must develop coating materials that can effectively block or absorb harmful UV radiation in UV-shielding applications, which would enhance durability, performance, and protection.