Analysis of rubber particles produced by the solid state shear extrusion pulverization process

Vulcanized natural rubber was pulverized using a single screw extruder in a non-cryogenic Solid State Shear Extrusion (SSSE) process where rubber granulates were subjected to high compressive and shear stresses. The produced particles had diameters ranging from 40 to 1700 mu m Reprocessing of the produced powder resulted in a narrower particle size distribution. Considerable heat generated in the extruder due to friction caused surface oxidation of the fine rubber particles and. in turn, initiation of agglomeration of a portion of the produced particles. Physical, chemical, and thermal analyses were performed on the produced rubber particles and the rubber granulates to determine the effects of the pulverization process. The produced particles had irregular shapes with rough surfaces. The external surfaces of the particles were porous, but no microporosity was detected by nitrogen BET analysis. Swelling and extraction experiments showed that both the crosslink density and gel fraction of the particles were lower than those of the rubber granulates. The reprocessing of the produced particles caused further reduction in the crosslink density and the eel fraction A correlation was established between the crosslink density and the gel fraction. Thermal analysis revealed similar behavior of all particles and the granulates in a nitrogen environment, but there was considerable thermo-oxidative degradation of the fine panicles in air. The chemical analysis indicated that some of the bonds were broken during the pulverization process, and partial devulcanization had taken place.