Rubber-degrading microorganisms

Spence and van Niel [9] noted that, when a sterile latex of NR was degraded by soil microorganisms, the relative viscosity of the dilute rubber solution became lower [9] it dropped from 20 sec (control) to 3 sec, showing that the residual rubber was thoroughly deteriorated, soft and dead. ... 

Microbial degradation of synthetic rubbers will be a subject of fiirther study. A rubber product is made from a number of complex ingredients, and smaller molecules in a synthetic polymer (e.g., stearate, process oils, and waxes in vulcanized synthetic rubber) may be decomposed by microorganisms. A clear distinction must be made between the superficial growth of microorganisms on non-rubber constituents in a synthetic polymmrs and the biodegradation of the rubber hydrocarbon [23]. 

Many conqionents in vulcanizates, sudb as accelerators, fillers, oils, and antioxidants, are known to affect microbial activities, and protection of rubber goods against microorganisms, by the addition of chemicals with microbiocidal activities, has been an important research area. However, the use of microbioddes is b ond the scope of this review, and extensive references have been given by Zyska [24,25]. The present review mainly covers the degradation of the polymer itself. 

Ecological study of microbial degradation of rubber is still at a primitive stage. The NR vulcanizate has been more or less degraded by microorganisms with both in vivo and in vitro conditions. However, the rate and the extent of microbial degradation nray be greatly influenced by the rubber formulations and by environmental circumstances. 

Natural rubber was one of the first important industrial polymers and it was recognised even before it reached the industrialised countries that that it very rapidly lost its initial useful properties in a process that, by analogy with human physical degradation, was given the name ageing . A particularly unique and desirable attribute of rubber was its rebound resilience and this was rapidly lost in a tropical environment. Furthermore, rubber latex products were attacked by microorganisms, which led to more general loss of mechanical properties and to eventual bioassimilation in the soil environment. 

FTIR studies of the surface of degrading PE shows the development of species identified as polysaccharides and protein by photo-acoustic FTIR [26]. These are both characteristic of the growth of microorganisms [26,29]. Ikram and co-workers [35] have shown that in normal soils at 25°C, NR gloves showed 54% loss of thickness after 4 weeks and 94% mass loss after 48 weeks. On the other hand nitrile and neoprene rubbers showed insignificant loss in this time and plasticised PVC showed a smaller mass loss (11.6%) due entirely to biodegradation of the plasticiser. Ikram went on to show (see Table 3) that the rate of mass loss is strongly dependant upon the nutritional quality of the soil [36]. 

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