RESISTANCE OF MATERIALS TO MARINE BIOLOGICAL ATTACK 1125 

 VII. SUMMARY 



A progress report has been presented on the results of a test program 

 designed to determine the relative resistance of materials to marine bio- 

 logical attack. Specific test i-esults have been reported wherever possible, 

 predominanth^ from the laboratory test procedures. In the case of the 

 natural exposure tests, which are intended to provide correlative data 

 for the laboratory program over longer periods of time, the information 

 which has been assembled thus far is of a more general nature. There 

 follows a summary of the more important information which has been 

 obtained : 



1 . In the biochemical 0x3' gen demand-type test it has been found that 

 polyethylene is not utilized by the aerobic bacteria or the anaerobic 

 suKate-reducing bacteria. Polyvinyl chloride plastics are attacked ac- 

 cording to the way in which they are plasticized. All of the samples tested 

 which had an added external plasticizer, mcluding the rigid plastic, were 

 attacked to some degree. In the latter case the attack was apparently 

 due to lubricants. The semi-flexible polyvinyl chloride copoljaiiers, and 

 the polj^vinyl chloride resin alone, were not utilized by the bacteria. The 

 five elastomers assayed were all attacked by aerobic bacteria, neo- 

 prene being the most resistant. The epoxide casting resin did not 

 serve as a source of carbon for the organisms, but further testing is re- 

 quired with a polyester casting resin. 



2. Coiled conductors insulated in one case with a rigid polyvinyl 

 chloride, and in the other with GR-S, have been exposed half in sea 

 water and half in marine sediment in the laboratory for thirteen months. 

 Capacitance measurements show that a considerable change has oc- 

 curred in the GR-S insulation apparently as a result of bacterial attack. 

 Although there has been a slight rise in the capacitance values for the 

 polyvinyl chloride-insulated conductors during the last five months, 

 further observations are necessary before attack can be considered defi- 

 nite. 



0. In three years of actual marine exposure of plastics, elastomers and 

 pasting resins, there have been definite penetrations by marine borers of 

 onl}^ three materials — a test rod of silicone rubber, a 0.0035-inch film 

 of poljanonochlor-trifluoroethylene wrapped on a Lucite rod, and on 

 Lucite rods themselves. The first two cases represent single instances of 

 penetration — both by pholads. The Lucite rods were penetrated at 

 many places bj^ pholads as a result of the organisms getting started in 

 an asphalt-impregnated jute wrapping and then progressing into the 

 Lucite. 



Secondary cellulose acetate yarn and tow have been deteriorated 

 badly, apparently by bacteria, in as short a time as six months. 



