Biodegradation of PVAs with Various Stereoregularities

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Biodegradation of poly(vinyl alcohol) with high syndiotacticity (s-PVA) was studied under the presence of Pseudomonas sp. as a bacterium. The effects of stereoregularity of s-PVA on its biodegradability were evaluated compared to PVA homologs, i.e. atactic PVA (a-PVA) and isotactic PVA (i-PVA). Changes in total organic carbon concentration (TOC) in PVA cultures with incubation time were checked, and pentad tacticity was estimated by ¹³C NMR analysis for tacticity contents of degraded PVA. TOC in i-PVA culture decreased rapidly in early stage of the incubation. Sixty-two percent of initial amounts of i-PVA was assimilated in 12 days of incubation. On the contrary, only 13% of the initial amounts of s-PVA was assimilated even after 20 days of incubation. Little changes were observed in ¹H NMR spectrum of s-PVA compared with that of a-PVA or i-PVA after the incubations. It was obviously confirmed in the present work that mmmm sequence is especially subject to degradation in meso sequences on the basis of ¹³C NMR analysis and the enzyme engaged in this degradation should have a sequence selectivity at pentad level. Experimental results supports the view that i-PVA having a number of long meso sequences should be susceptible to biodegradation, and s-PVA should not so.