Estudo dos efeitos da radiação gama na estrutura do homopolímero PVDF e seus copolímeros fluorados para aplicação em dosimetria gama de altas doses e na preparação de nanocompósitos com nanotubos de carbono e óxido de grafeno

Abstract

Poli(vinilidene fluoride) [PVDF] is a linear semi-crystalline homopolymer well known by its good chemical, mechanical and electromechanical properties. Its polymeric chain is composed by the repetition of CH2-CF2 monomers. In this work, PVDF and its fluorinated copolymers P(VDF-TrFE), with 28%, 35% and 50% of TrFE contents, and P(VDF-HFP),were systematically investigated for gamma dosimetry purposes, for doses ranging from 1 to 3,000 kGy. We studied the use of P(VDF-TrFE)50/50 copolymers applied to high dose gamma dosimetry, with the UV-Vis spectrometry technique. We have demonstrated that it is a good candidate to be used as a dosimeter, measuring the optical absorbance at 274 nm, for doses ranging from 1 to 750 kGy. On the other hand, using FTIR spectrometry, we have identified two absorption peaks, at 1715 cm-1 and 1754 cm-1 wavenumbers, respectively, with potentialfor dosimetric applications. We have also studied this copolymer using differential scanning calorimetry (DSC). We have observed an exponential relationship between the melting latent heat and gamma doses ranging from 1 to 1,000 kGy. As for the PVDF homopolymer investigation, we have demonstrated its potential to be used as a dosimeter, for doses rangingfrom100 to 1,000 kGy. We have also used the optical absorbance at 274 nm, with the UV-Vis technique, and at the wavenumbers 1715 and 1730 cm-1 with the FTIR spectrometry, for dose evaluation. DSC data revealed that PVDF could be an excellent candidate for gamma dosimetry, for doses between 100 and 3,000 kGy, also presenting an exponential relationship between the melting latent heat and absorbed dose. As a second approach, we have investigated the possibility of preparing nanocomposites of PVDF and its copolymers with carbon nanotubes (CNT) and graphene oxide (GO), through the radio-induction of molecularbonds between the polymeric material and the carbon nanostructures. This investigation aimed to produce nanocomposites with new properties such as high capacitance and high electrical conductivity. We have got some results that indicate good interaction between the polymeric matrix and the carbon nanostructures. The most promising results were obtained for PVDF/GO nanocomposites where, apparently, the GO nanosheets promote a gradual transformation from the initial PVDF gamma-phase into a beta-phase in the composite material.