TABLE 224.— PROPERTIES OF NATURAL RUBBER (HEVEA) 



235 



Vulcanizate 

 containing 

 Pure-gum about 33% Ebonite 



Unit Unvulcanized vulcanizate carbon black (hard rubber) 



Density gem- 3 .906-.916 .92-1.0 



Expansivity 

 (l/V)(dV/dT) (degC)" 1 67X10" 6 66X10- 5 



Thermal 



Thermal conductivity cal sec" 1 cm -1 32X10" 5 34X10" 5 



(deg C)- 1 

 Specific heat cal g * .45 .44— .51 



(deg C)- 1 



Heat of combustion cal g" 1 10.82x10 s 10.63X10 3 



Second-order transition 

 temperature deg C —69 to —74 —72 



Optical 



Refractiveindex.no 1.5191 1.5264 



dn D /dT (degC)" 1 -37X10- 6 -37X10" 8 



Electrical 

 Dielectric constant 



(1000 cps) 2.37-2.45 2.7 



Loss factor, tan (90' -0) 



(1000 cps) .002 .002 



Conductivity (1 min) mho cm" 1 2-40X10" 17 10"" 



Mechanical 



Compressibility 

 (l/V)(dV/dP) bar 1 54X10-* 51X10" 9 



Shear modulus dynes cm -2 4X10" 



Initial slope of stress-strain 

 curve dynes cm" 2 10-20X10 9 



Ultimate elongation percent 750-850 



Tensile strength kg cm" 2 170-250 



Complex dynamic shear mod- 

 ulus (60 cps), ... 



Real part G', - dynes cm" 2 3-10X10 6 



Imaginary part G", — dynes cm -2 .3-.6X10" 



Resilience (ball rebound)., percent 75 75 



1.12-1.15 1.13-1.18 

 53X10" 5 19X10" 5 



39-45X10-" 39-42X10" 

 .36 .34 



9.61X10" 7.92X10 3 

 +80 



1.6 



2.8-2.9 



.005 

 10"" 



37X10' 9 

 20X10" 



24X10- 



30-60X10" 55X10° 

 550-650 3-8 



250-350 600-800 



25X10" 



3X10" 

 45-55 



SMITHSONIAN PHYSICAL TABLES 



