Estudo das propriedades de dosimetria e blindagem de compósitos preparados com PVDF/ZrO2-MWCNTs

Abstract

Polymer-based nanocomposites made of a poly(vinylidene fluoride) [PVDF] homopolymer matrix filled with multiwalled carbon nanotubes (MWCNT) and zirconia (ZrO2) were prepared, in order to investigate them for high gamma dose dosimetry and radiation shielding purposes. For dosimetry applications, the nanocomposites were exposed to gamma doses ranging from 1 kGy to 3 kGy. Samples were characterized by X-ray Diffraction (XRD), Fourier-transform infrared and ultraviolet spectrophotometry (FTIR and UV-Vis), Energy Dispersive X-ray Spectrometry (EDS), Field-emission electron microscopy (FE-SEM) and Differential Scanning Calorimetry. FTIR data revealed two distinct absorption peaks, centered at 1715 cm-1 and 1730 cm-1, whose absorption intensities have a linear behavior with gamma doses ranging from 400 kGy to 2750 kGy. These peaks were associated to the stretching vibrational modes of radio-induced C=C chemical bondsin =CF2-CH=CF-CH2 (1715 cm-1)and to the dimer stretching of C=O bonds in CF2-CH2-COOH (1730 cm-1). The linear fitting correlation coefficients were 0.99354 and 0.9945, respectively, suggesting that the PVDF/0.05% ZrO2/0.08% MWCNT nanocomposites are good candidates to be used as a high gamma dose dosimeter. The material post-irradiation analyses with DSC and SEM techniques revealed an increase in the nanocomposite crystalline stability, when compared to the pristine PVDF irradiated at the same conditions. This feature was inferred from a smaller decrease detected in the melting latent heat (LM).The radiation shielding characterization was performed by using the X-ray beam of a XRD equipment. The X-ray beams emitted from Co, Cu, Mo and Ag tubes provided monochromatic photons with energies of 6.5, 8.5, 17.5 and 22.1 keV, respectively. The better mass attenuation coefficient was measured for the samples with 1.0 mg and 1.5 mg of MWCNT, i.e. 76.2%, at 6.5 keV. The attenuation for the sample with 0.5 mg of nanotubes was 12.9% at the same energy. For comparison purposes with another graphitic materials, the radiation attenuation of composites produced without the presence of ZrO2 were also investigated for photons with energy of 8.5 keV.