LABORATORY LEACHING EXPERIMENT 



An experiment was conducted to determine the effect of leaching paint 

 films with rainwater on the resistance of resins to fungal growth. Four 

 resins were used in this experiment. One was the original Resin 1 with 1% 

 TBTO added to it, and the others were organotin Resins 1, 2, and 3. They 

 were pigmented as indicated in Table 5. The resin selections were made to 

 compare the lasting effect of TBTO added to a resin that has a slight nat- 

 ural resistance to growth to organotin resins of relatively high, medium, 

 and low tin contents. The pigmented resins were cast at a dry film thick- 

 ness of 0.003 inch (0.008 cm) onto sheets of mylar plastic. After complete 

 curing, the resin, films were subjected to continuous leaching with water 

 in a wind-driven rain machine of the type described in TT-C-555 [17]. 

 Samples were taken of each film after 0, 24, 48, and 72 hours of leaching 

 and tested for resistance to growth of A. 'pullulans by the method described 

 in the previous section. 



The results of the leaching experiment are summarized in Table 8. It 

 can be seen from this table that, after 72 hours, the average rating of 

 original Resin 1 with the added TBTO dropped to that of the original resin 

 alone (see Table 4), while organotin Resins 1 and 2 (which contained 9.2 

 and 4.8% tin,* respectively) had no loss and Resin 3 (which contained only 

 1.4% tin* and, thus, was much less resistant to growth) showed only a very 

 slight loss in growth resistance. 



Table 8. Resistance of Leached Resins fl 

 to Growth of A. pullulans 



Pigmented 

 Resin 



Leaching 

 Time 



Growth 

 Resistance 



Tested 



(hr) 



Rating 



Resin 1, 







3 b 1>;3 b 



Original 

 plus 1% 



24 

 48 



5;3; fc 3 b 

 3p 3p 36 



TBTO 



72 



2; 2; 3 b 









5; 5; 5 



Resin 1, 



24 



5;5;5 



Organotin 



48 

 72 



5; 5; 5 



5; 5;5 









5;5;3 fc 



Resin 2, 



24 



5;5;5 



Organotin 



48 



72 



5;5;3 fe 

 5; 5; 3 fe 



Resin 3, 







24 



3 b 3° 5 

 3 .b 3 .b 46 



Organotin 



48 

 72 



3 b 3 b 3 b 

 3 b 3 b 3 b 



a Pigmented as shown in Table 5. 



* Zone of inhibition around part of paint resin. 



* In the unpigmented resin. 



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