Polymers, soil degradation

Polymer samples were subjected to soil degradation in a laboratory at a temperature 22-25°C. Samples in the form of a film thickness of 50 microns was placed in the soil to a depth of 1.5-2 cm. Biodegradation rate was assessed by evaluating the mass loss of the samples. Mass losses were fixed by weighing the samples on an analytical balance. 

It is clearly difficult to give definitive rates of biodegradation but a few specific examples are given in Table 13 for PHB homopolymer. From this we can see that the polymer is degraded very rapidly in anaerobic sewage and progressively more slowly, in warm soils, aerobic sewage, estuarine sediments and sea water. 

Dharmalingam, S., et al. (2015). Soil degradation of polylactic acid/polyhydroxyalkanoate-based nonwoven mulches. Journal of Polymers the Environment, 25(3), 302—315. 

The biodegradable polymer when degraded and combined with other degradable plastics may be converted into useful soil improving materials. 

Other simple tests include the soil burial test used to demonstrate the biodegradabiUty of polycaprolactone (25), following its disappearance as a function of time, and the clear 2one method which indicates biodegradation by the formation of a clear 2one in an agar medium of the test polymer or plastic as it is consumed (26). The burial test is still used as a confirmatory test method in the real-world environment after quantitative laboratory methods indicate bio degradation. 

In nature, there are several sources of enzymes that are capable of catalysing the hydrolysis of PHB. The polymer itself is produced by bacteria and occurs in cells as discrete inclusion bodies. These bodies contain the necessary enzymes for degrading the polymer, preventing its build-up in the cell. As well as this, there are numerous bacteria and fungi, many of which are found in the soil, that are capable of secreting the necessary enzymes outside their cell walls, and thus of iiufiating degradation of PHB. 

SPME-IR has been applied to VOCs in soil samples [547], Industrial applications to in-process streams can well be envisaged. SPME has not yet extensively been explored for polymers, but the determination of residual volatiles, semi-volatiles and degradation products in polymers has been reported [548]. It is equally well possible to use SPME for plasticiser analysis in various matrices (water, milk, blood, processed food, etc.). 

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