Biodegradation of PHB

Polymers exposed to the environment are degraded by their hydrolysis, mechanical, thermal, oxidative, and photochemical destruction, and biodegradation [7, 38, 55, 56]. One of the valuable properties of PHB is its biodegradability, which can be evaluated using various field and laboratory tests. Requirements for the biodegradability of PHB may vary in accordance with its applications. The most attractive property of PHB with... 

Biodegradability of PHB films under aerobic, microaerobic, and anaerobic conditions in the presence and absence of nitrate by microbial populations of soil, sludge from anaerobic and nitrifying/denitrifying reactors. 

Thus, the observed biodegradation of PHB showed coexistence of two different degradation mechanisms in hydrolysis in the polymer enzymatically or nonenzymatically catalyzed degradation. Although nonenzymati-cal catalysis occurred randomly in homopolymer, indicated by loss rate in PHB, at some point in a time, a critical molecular weight is reached whereupon enzyme-catalyzed hydrolysis accelerated degradation at the surface because easier enzyme/polymer interaction becomes possible. 

FIGURE 1.6 Biodegradation of PHB films in Vivo. Connective-tissue capsule with PHB thin films (outlined with broken line) 2 weeks (98% residual weight of the film) (left photograph) and 3 months (0% residual weight of the film) (left photograph) after subcutaneous implantation [18]. 

Some research works studied a biodegradation of PHB threads with a tendency of analysis of its mechanical properties in vivo [22, 23]. It was shown that at first load at break, index decreased rapidly from 440 to 390 g (12%) at 15th day and then gradually increased to the initial value at OO and remain almost unchanged up to 182nd day [22] or gradually decreased... 

Process of biodegradation of PHB phase influences on the structure of PIB. This is reflected in a sharp decrease of average molecular weight of PIB. 

Lotto et al. 2004 evaluated the effect of temperature in the biodegradation of PHB in soil compost at 24 and 46 °C. The higher temperature raised the biodegradation rate of PHB samples, probably due to a direct action on mechanism of the hydrolysis or an indirect action by enhancing the activity of thermophylic microorganisms, as stated by authors. It is well known that the decrease of temperature reduces and can inhibit the bacterial activity decreasing the biodegradation rate, as verified by Deroine et al. (2014). 

Figure 11.20 Effect of the addition of clay on the biodegradability of PHB/clay bionanocomposites as evidenced by a break down of their spherulitic crystalline structure [246].

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