New Trends in Polymers - Progress in Organic and Physical Chemistry: Structures and Mechanisms - page 193

16.2.3 Biodegradation of PHB by Soil Microorganisms
Polymers exposed to the environment are degraded through their hydrolysis, mechani-
cal, thermal, oxidative, and photochemical destruction, and biodegradation [4, 32, 45,
46]. One of the valuable properties of PHB is its biodegradability, which can be evalu-
ated 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 respect to ecology is that it can be completely degraded by microorganisms
finally to CO 2 and H 2 O. This property of PHB allows to manufacture biodegradable
polymer objects for various applications (Figure 3) [2].
FIGURE 3 Moulded PHB objects for various applications. In soil burial or composting
experiments such objects biodegrade in about three months [2].
The degradation of PHB and its composites in natural ecosystems, such as soil,
compost, and bodies of water, was described [2, 32, 45, 46]. Maergaert et al. isolated
from soil more than 300 microbial strains capable of degrading PHB in vitro [45]. The
bacteria detected on the degraded PHB ¿ lms were dominated by the genera Pseudomonas ,
Bacillus, Azospirillum, Mycobacterium, and Streptomyces and so on . The samples of
PHB have been tested for fungicidity and resistance to fungi by estimating the growth
rate of test fungi from the genera Aspergillus, Aureobasidium, Chaetomium,
Paecilomyces, Penicillum, and Trichoderma under optimal growth conditions. The
PHB ¿ lm did not exhibit neither fungicide properties, nor the resistance to fungal dam-
age, and served as a good substrate for fungal growth [47].