Studying the pulverization mechanisms of low-cross-link-density natural rubber with and without carbon black

The effects of the temperature in the different heating zones and the rotating speed of the screw in the Solid State Shear Extrusion (SSSE) process were studied to obtain a better understanding of the pulverization mechanisms of the low-cross-link-density natural rubber. Results showed that providing a range of both temperature and normal stress was required to pulverize cross-linked natural rubber, but shear stress plays the most important role to produce fine particles. Two rubber samples were provided with the same composition, but one with carbon black (CB) and the other one without, and were pulverized at the same process conditions to show the effect of the material mechanical properties on the produced particles' average size. The average produced particle size of the sample without CB was considerably smaller than the one with, and they were electrostatically charged. Based on this result, under combination of the shear and normal stresses, adding hard particles (in this case CB) to the cross-linked rubber increases its dissipation energy, therefore less energy is restored for the material fracture.