PVA-degrading microorganisms

PVA is the only C-C backbone polymer that is biodegradable imder both aerobic and anaerobic conditions. However, the degradation rate under natural environmental conditions, if in the absence of PVA degrading microorganisms is too slow. The PVA with sugar pendants might be a new approach to improve the biodegradability of PVA. 

Figure 5. Biodegradation curves of atactic PHB and PVA samples and their graft copolymers and blends in an aqueous medium in the presence of PVA-degrading microorganisms.

The limited bioassimilation observed in the case of the aPHB2 sample can be explained by considering that very likely PVA-degrading microorganisms are able to use only the low molecular weight finctions of atactic PHB. 

The inhibitory effects of PVA can also be found in degradation studies of polycaprolactones (PCLs). These polyesters can be readily split by lipase enzymes binding to hydrophobic domains of that linear substrate. PVA/PCL films in contrast are not biodegradable by PCL-degrading microorganisms. It can be assumed that the surface properties of PCL change upon interaction with PVA in a manner that enzymatic accessibility of the hydrolysable PCL backbone motifs is decreased. 

As an industrial and commercial product, PVA is valued for its solubility and biodegradability, which contributes to its very low environmental impact. Several microorganisms ubiquitous in artificial and natural environments — such as septic systems, landfills, compost and soil — have been identified and they are able to degrade PVA through enzymatic processes. 

PVA films buried in soil were tested after 120 days and showed only very limited signs of biodegradation, and even field tests with PVA sheets buried for 2 years in different natural soil sites showed only limited (10%) weight loss. No traces of colonising microorganisms were detected on the incubated material. Degradable polymers like poly(hydroxy butyrate), PCL or starch are usually extensively... 

Poly(vmyl alcohol) is one of the few truly biodegradable synthetic polymers the degradation products are watei and carbon dioxide. At least 55 species or varieties of microorganisms have been shown to degrade or participate in the degradation of PVA. 

Varieties of microorganism (at least 55 known) degrade PVA (e.g., Acinetobacter, E. coli, Pseudomonas (19 species), Saccharomyces, Lipomyces etc.)... 

Three different films obtained by a hot pressing procedure of powder mixtures containing plasticized PVA, PVAc with and without bactmal PHB were submitted to the biological degradation of soil microorganisms in a respirometric test aimed at simulating soil burial conditions. The compositions of the blend films are summarized in Table 1. 

Synthetic biodegradable polymers are generally made by polycondensation methods from petroleum-based feedstocks. However, different from other petrochemical-based resins that may take centuries to degrade, these synthetic polyesters decompose rapidly into carbon dioxide, water, and humus under appropriate conditions where they are exposed to the combined attack of water and microorganisms [109, 116, 117). Petroleum-based biodegradable polymers that have been used in bionanocomposites are PCL, polyesteramides (PEAs), PBS, aliphatic polyesters (APES), and poly(vinyl alcohol) (PVA) [116]. 

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