CONICET | Buscador de Institutos y Recursos Humanos

Blends of P(HB-co-HV) with polypropylene glycols (PPG) and castor oil (CO) were prepared by casting from solution. Morphology, thermal properties, degradation and mechanical behavior of the films were investigated by 1 H NMR, FTIR, differential scanning calorimetry (DSC), thermogravimetry and tensile test. Formation of vinyl group confirms the mechanism of degradation, according to b-chain scission. Two temperature ranges were investigated. The range close to the melting point, from 100 to 200 ºC, where blend does not exhibited reduction in the weight. However a high loss of molecular weight and tensile stress in few minutes was found. The range of high mass loss or pyrolysis from 200 to 400ºC. In this range the kinetic of degradation was studied by means of two models: global kinetic model with order 1 and an autocatalytic model. In the first model, the apparent activation energy is close to the reported in the literature: Ea=310 kJ/mol, for copolymer P(HB-co-HV). The addition of polypropylene glycol enhances the degradation. The apparent activation energy decreases to 150 and 131 kJ/mol for PPG 400 and PPG1000, respectively. Except when castor oil was added to the P(HB-co-HV), in this case the blend thermal stability was higher (Ea=223 kJ/mol). The autocatalytic model was applied for the P(HB-co-HV) because the experimental results does not fit the model for all temperature and heating rate runs, an autocatalytic model with an apparent activation energy of 111 kJ/mol fitted the result. Mechanical properties of the blends before and after degradation were performed. Tensile modulus increases at the first step of degradation and after decrease with the degradation time. Castor oil blends show the more stable behavior in comparison with polyalcohols blends.

enviar mensaje