Soil burial

Another variation on a theme includes AATCC 30 Soil Burial Test (a. 11). A temperature of 28 °C, relative humidity of 85% and water content of 20-30% for incubation over 16 weeks is the change in essential criteria. 

However, some of these types of test introduee a high level of nutrient that may not neeessarily be found in practice. 

This test method assumes weight loss is due to metabolism of the plasticiser and also loss of other components sueh as lubrieants, stabilisers, stearates or PU. It is possible that the measured loss is lower than the aetual loss sinee metabolie by-products may remain in the plastie. 

One of the disadvantages of these test methods is that they monitor differences in the migration of the plasticiser and components of biostabilisers rather than 

Typical soil burial test, here on a PVC ground sheet 

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Resistance to Microorganisms and Insects. Resistance of triacetate to microorganisms, based on soil-burial tests, is high, approaching that of polyester, acryUc, and nylon fibers. Sod-burial test results on acetate, triacetate, and cotton are shown in Figure 8. Neither acetate nor triacetate fiber is readdy attacked by moths or carpet beedes. 

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. 

Soil burial tests are popular despite the precautions that are needed. It is also important that a sufficient number of specimens are exposed so that statistical treatment of the results may be applied to compensate for some of the inevitable variations in the exposure conditions. Certain precautions originally set out in 1937 are still valid, and are as follows ... 

Soil burial is widely used as the method of testing susceptibility to degradation. It closely mimics the conditions of waste disposal used for plastics but it is often difficult to reproduce results obtained because of absence of control over either the climate at the test site or the variety of micro-organisms involved in the degradation. Soil burial is thus used to provide qualitative indications of biodegradability, with more controlled laboratory work with cultured micro-organisms being used to obtain more quantitative detail. 

It is effectively impossible to accelerate biological attack substantially. ISO 846 [44] defines laboratory methods for determining the resistance of plastics to fungi and bacteria, while BS 6085 Section 2 [45] and EN 12225 [46] are soil burial methods for... 

While these relatively simple soil burial tests are directly relevant to the underground environment, the conditions of testing have deliberately been optimised to ensure a maximum rate of degradation. The relation between this rate and the predicted rate of attack in service can only be deduced by comparison. 

EN 12225, Geotextiles and geotextile-related products. Method for determining the microbiological resistance by a soil burial test, 2000. 

Testing of decay resistance can be performed in a laboratory environment or in outdoor field trials, and there are many standards defined for these tests. The first objective of a laboratory-based test is to provide a methodology for the rapid screening of a candidate wood preservative, treatment or modification in order to assess which ones exhibit decay resistance. Broadly speaking, laboratory-based tests can be divided into sterile (pure culture) tests and unsterile tests (such as fungal cellar, soil burial etc.). 

Figure 1. Scanning electron micrograph of cryofractured film containing 40% starch, 60% LDPE + EAA 5ter 64 days of soil burial. Top of photo shows film surface bottom shows film interior. Bar = 20 jum.

Figure 2. Carbon dioxide evolution from films containing cornstarch, LDPE, and EAA during soil burial. Circles 13% (v/v) starch squares 20% starch trianges 28% starch. values were obtained by linear regression of time versus cumulative CO2 evolved.

Hesistance lo Microorganisms and Insects. Resistance of triacetate to microorganisms, based on soil-burial tests, is high, approaching that of polyester, acrylic, and nylon fibers. 

ASTMD1413 fungal enriched soil burial weight loss, decay... 

The two most common natural textile fibers encountered in modern fabrics have contrasting responses to soil burial. Under most soil burial conditions cellulose will degrade rapidly whereas wool will decay at a slower rate. These phenomena are demonstrated by the degradation of textile fibers from the Experimental Earthworks Project (Janaway 1996a). Figures 7.9 and 7.10 compare wool and linen buried in the chalk environments at Overton Down for 32 years. The linen is denatured to the point that there is little surviving morphology, whereas the wool retained some fiber structure. 

Synthetic fibers have been characterized by a resistance to degradation over forensically relevant timescales (Table 7.4). Nylon (polyamide), polyester, and acrylic fibers show considerable resistance to soil burial. Regenerated cellulose fibers (rayon viscose), however, share the vulnerability of natural cellulose to decomposition (Rowe 1997). However, they do show a higher degree of resistance to biodegradation compared with natural fibers or regenerated cellulose, with the exception of triacetate. 

McGrath, C. (1999). Biodeterioration of cotton denim in soil burial environments. Unpublished M.Sc. Dissertation, University of Bradford, Bradford, UK. 

Fungal inoculation. This can be a Petri dish test, a tropical humidity test, or sometimes a soil burial test, which can be considered a type of superinoculation. 

Biocides. The attack of fungi on the several components of a vinyl formulation may manifest itself as an unsightly growth looking much like dirt or may result in the formation of discolored areas (yellow, pink, blue, clear) on the finished goods. Outdoor exposure, indoor exposure in humid atmosphere, soil burial or contact, and electrical insulation compounds are typical areas where biocide addition is indicated. Since most commercial biocides are heavy metal derivatives, care must be taken to assess their effect on heat and light stability and compatibility with the vinyl system in which they are used. 

Table 4.24 Soil burial tests of 5 yr duration with aluminum alloy specimensa,b...

The chemical and physical properties of nylons have been extensively described (76). Nylon will not support mildew or bacteria. Moth larvae may bite their way through nylon if imprisoned. In soil burial tests, it was found that nylon 6 retained more than 95% of its strength after six months. By contrast, wool and cotton were rotten after one month (3). Nylon may be affected by chlorine bleach, and strong oxidizing bleaches can damage it (31). 

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