Rubber microbial degradation

Tsuchii, A., Suzuki, T., and Takeda, K., Microbial degradation of natural rubber vulcanizates, Appl. Bnviron. Microbiol., 50, 965, 1985. 

Natural rubber is a polymer of isoprene units. As a naturally occurring polymer, it is subject to microbial attack especially in hot humid conditions. The microbial degradation may be accentuated by chemical oxidation. 

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]. 

Microbial degradation of a relatively large amount of a surgery glove was demonstrated. 2.5 g of the rubber films was added into 3 1 of mineral... 

Figure 3. Microbial degradation of latex gloves. Tmi pieces of rubber (0.25 g each), cut from a commercial surgery glove, were added into 3 1 of culture medium every 5 days, and all pieces of degraded rubber films were recovered at day-131. I, incubated for 5 days II, incubated for 10 days m, incubated for 15 days. Any piece added 20 days before was not found. Small pieces of rubber (2 mm in diameter), at the upper-left in the figure, were edges of the glove.

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. 

Linos A and Steinbuchel A. (1998) Microbial degradation of natural and synthetic rubbers by novel bacteria belonging to the genus Gordon, Kauchuk Gummi Kunstsoffe, 51, 496-499. 

Tsuchii A, Tokiwa Y (1999a), Microbial degradation of natural rubber , in Steinbiichel A, Biochemical Principles and Mechanisms of Biosynthesis and Biodegradation of Polymers, Wiley-VCH, 258-264. 

Microbial attack of raw rubber was first reported early in 1914. Thin film of NR, floating on an aqueous medium, were shown to be disintegrated by some actinomycete strains to a certain extent, that could not be ascribed to the disappearance of impurities from the rubber [8]. Spence and van Niel [9] reported that NR, in the latex state, was degraded by some actinomycete strains, and ifrat a rubber weij t loss of up to 70% was observed after a 28-day cultivation period [9]. Thin films of NR on agar plates were also found to be d raded by strains of Streptomyces and Nocardia, and the weight loss reached 52% after the cultivation period of a month and a half [10]. It was reported that thin strips of NR and S3mthetic isoprene rubbm, with a diameter of 0.5 mm, were decomposed completely by a strain of Nocardia in 56 days [11]. 

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. 

Up till now, the purpose of most studies has been to protect rubber products from microbial deteriorations. Waste disposal of used rubber and estimation of the degradation rate in the natural environment will become more important subjects from now onward. 

Natural mbber, the other natural hydrocarbon polymer, consisting mainly of cfr-l,4-polyisoprene is relatively resistant to microbial attack in comparison to other natural polymers. A number of micro-organisms have been reported to degrade natural rubber. An enzyme which degrades the mbber was isolated from the extracellular culture medium of Xanthomonas sp., and the erude fractions which are capable of depolymerizing natural mbber in the latex state have been reported.The same authors " reported on a Nocardia strain that used natural mbber as its sole carbon source. 

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