PARAGUTTA, A NEW INSULATING MATERIAL 



141 



represent a substantial improvement over those of the classical insula- 

 tion compounds and its cost is lower. 



The final steps in processing paragutta are very similar to those 

 used for gutta percha and involve blending and washing the depro- 

 teinized rubber and deresinated balata or gutta together, masticating 

 to remove excessive water and at the same time incorporating such 

 waxes as are found necessary. The material is then strained through 

 fine sieves under hydraulic pressure to remove adventitious impurities, 

 kneaded to remove air and finally placed on the covering machine rolls 

 to be forced around the conductor. The machinery in use for pro- 



I 140 



5 



- 120 



^ 



o 



8 100 



O 40 



2 3 



TIME IN WEEKS 



Fig. 4 — Effect of washing and removal of proteins on conductivity of crude rubber 

 when immersed in 3.5 per cent NaCl solution at room temperature. 



cessing gutta percha is suitable for handling paragutta in these 

 operations. 



Comparative Properties of Paragutta and Gutta Percha 



Tensile Properties: Although submarine insulation is not subjected 

 to tensile deformation in practice, tensile properties indicate to some 

 degree the relative mechanical suitability of a given material for the 

 purpose. Figure 5 shows the stress-strain characteristics of paragutta 

 and gutta percha submarine cable insulation. These results show 



