Síntese e caracterização óptica de filmes de poli(fluoreto de vinilideno) dopados com urucum (Bixa orellana L.)

Abstract

In this work, pure poly(vinylidene fluoride) (PVDF) films and PVDF films doped with 1, 2, 3, 4, and 5% annatto (Bixa orellana L.), designated PVDF/URU, were prepared using N,N-dimethylformamide (DMF) solution processing. The films were characterized by Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible absorption spectroscopy (UV Vis) to evaluate the incorporation of the natural material into the polymer matrix and its influence on the vibrational and optical characteristics of PVDF. The FTIR spectra showed the preservation of the main characteristic bands of the polymer and the presence of contributions compatible with organic constituents of annatto, including carbonyl groups, oxygen-containing groups, and conjugated systems. The relative β-phase fraction was 71.79% for pure PVDF and remained between 72.77 and 74.77% for the doped films, indicating that annatto incorporation did not produce a significant change in this parameter. In contrast, the optical response was markedly modified. The absorption edge shifted from approximately 251 nm to as high as 645 nm, while the full width at half maximum of the absorption band increased from about 30 to 355 nm. Annatto incorporation also reduced transmittance and modified the absorption coefficient, extinction coefficient, and penetration depth. The indirect and direct optical bandgap values decreased from 4.93 and 5.48 eV, respectively, to approximately 1.85 and 2.15 eV for the PVDF/URU 5% film. The Urbach energy decreased from approximately 0.598 to 0.147 eV, indicating a narrowing of the localized-state tail near the absorption edge. Taken together, the results show that annatto produces pronounced changes in the optical response of PVDF films while the relative β phase fraction remains approximately constant, highlighting the potential of these materials for further studies involving optical, photonic, and ultraviolet-radiation-protection applications.