Efeitos da radiaÃÃo Gama no polÃmero biodegradÃvel Poli(HIDROXIBUTIRATO) e no copolÃmero Poli(Hidroxibutirato-co-Hidroxivalerato)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

Poly(hydroxybutyrate), PHB, is a biodegradable commercial polyester manufactured in Brazil and biosynthesized by Alcaligenes eutrophus bacteria from sugar cane biosynthesis. The great number of petrochemical plastics has brought about attention to biodegradable polymers. PHB is a thermoplastic with good properties and an excellent option as commodity. On the other hand, this biopolymer has great potential in medical and pharmacological applications. For this reason, it is important to know the chemical and physical effects caused by the sterilization process, in particular, by gamma irradiation. In this work, the effects of gamma irradiation in the national PHB and in its copolymer, poly(hydroxybutyrate-co-hydroxyvalerate), P(HB-co-HV), with 6.3 mol% of valerate were investigated. This study was divided in: samples 1, i.e, PHB-1 and P(HB-co-HV)-1; and samples 2, PHB-2 and P(HB-co-HV)-2, that correspond to two different batches from the same maker. PHB-1 and P(HB-co-HV)-1 presented G values (scissions/100 eV) very high, however PHB-2 and P(HB-co-HV)-2 presented greater radiolytic resistance, with G values ten or more times lower than the samples 1. The value found for PHB-1 film was 26.8 (scissions/100 eV) in sterilization dose range (0 â 25 kGy), and to PHB-2 this value was 7.0 (scissions/100 eV), both as received. Gas chromatography associated with mass spectroscopy (GC-MS) revealed residual organic acids in PHB-1, which are considered as being responsible for the high degradation parameters. These acids were not found in PHB-2. Spectroscopy analyses, Fourier Transform Infrared (FT-IR), UV-visible and mainly Nuclear Magnetic Resonance (1H-NMR) spectra showed arise in saturated end-groups induced by gamma irradiation, due to the scissions of ester groups in the radiolysis of the macromolecules. Better results were presented in PHB-2 than in PHB-1, for this reason, the physical properties of the PHB-2 were studied Thermal analyses showed that the crystalline fusion temperature, Tm, decrease with the dose, and that PHB presented double endothermic peaks. The increase in the crystalline fraction was observed by thermal analysis(differential scanning calorimetry - DSC) and by x-ray diffraction. The x-ray diffraction also showed changes in the lattice parameters of the irradiated samples. PHB-2 mechanical properties are dramatically affected by the irradiation dose, mainly, tensile strength, impact strength and elongation at break, on the other hand, YoungÂs modulus is altered in doses above of 100 kGy

ASSUNTO(S)

polÃmeros biodegradÃveis engenharia nuclear radiaÃÃo gama difraÃÃo de raios-x

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