Photodegradation of poly(3-hydroxybutyrate)

Photodegradation and Photostabilization of Poly(3-Hydroxybutyrate)

“…The exposed surfaces, previously brown and caramel, turned into caramel and whitish, respectively, after 12 weeks under UV exposure. According to previous works done by one of the current authors 17,18 , this whitening does not result from the formation of chromophoric groups, but it is probably originated from a topological feature of the UV exposed samples, where cracks are formed on PHB 1 and PHB 2 surfaces. The occurrence of surface cracking was previously associated with polypropylene whitening during UV exposure 17 , in which the cracks increase the roughness of the surface, raising the diffuse reflectance of the visible light.…”

“…After 12 weeks of severe weathering conditions of UV, temperature and condensed water, the tensile strength of PHB 1 and PHB 2 decreased 32% and 34%, the strain at break decreased 30% and 42%, respectively. According to work reported elsewhere 17 when PHB is under UV radiation, two mechanisms might occur in parallel, i.e., macromolecular crosslinking and chain scission; one of them will be dominant and may be visualized by the change in number-average molecular weight (M n ). Concerning the results showed in Table 1, M n values of PHB 1 and PHB 2 decreased upon UV exposure, hence it can be deduced that the macromolecular scission is the preponderant mechanism observed here and that this is the main reason for the reduction in tensile properties.…”

“…Since the HV unit is bulkier than the HB unit (see Figure 1), we have an expectation that the copolymer with a higher HV content (PHB 2 ) would be more susceptible to the degradation effects due to a higher free volume and hence a higher diffusion of oxygen and moisture. Commonly, PHB suffer degradation also by hydrolysis mechanisms [17][18][19][20][21] , i.e., under humidity environment and temperature, chain scission occurs and, together with the photodegradation effects, will contribute to the deterioration in the polymer properties. If the specimen has a more open structure as it is in PHB 2 the effects of UV radiation, humidity and temperature may be more severe -as was observed for PHB 2 specimens in Figure 2, and serious damage are usually observed in the mechanical properties, as shown in Table 1.…”

“…Under this situation, the product can be exposed to ultraviolet radiation and, like the other types of polymers, suffer from this weathering condition. The photodegradation behavior of PHB, and the stabilization strategies, is scarcely reported in the literature 17 . The main objective of this work is to investigate the effects of ultraviolet radiation on PHB with different contents of hydroxyvalerate (HV) comonomers.…”

SÍNTESE, CARACTERIZAÇÃO E DEGRADAÇÃO DE P(3HB) POR Cupriavidus necator UTILIZANDO GLICEROL COMO SUBSTRATO

“…A biodegradação e a degradação térmica de P(3HB) são amplamente estudadas, porém, segundo Sadi et al (2010), a fotodegradação não é objeto de muitos estudos. Os estudos existentes na literatura são, na sua maioria, estudos de fotodegradação de copolímeros.…”