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 gran ulates were subjected to high compressive and shear stresses. The produced particles had diameters ranging from 40 to 1700 mu m Reprocessing of the pr oduced powder resulted in a narrower particle size distribution. Considerab le 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 rub ber particles and the rubber granulates to determine the effects of the pul verization process. The produced particles had irregular shapes with rough surfaces. The external surfaces of the particles were porous, but no microp orosity was detected by nitrogen BET analysis. Swelling and extraction expe riments showed that both the crosslink density and gel fraction of the part icles were lower than those of the rubber granulates. The reprocessing of t he produced particles caused further reduction in the crosslink density and the eel fraction A correlation was established between the crosslink densi ty and the gel fraction. Thermal analysis revealed similar behavior of all particles and the granulates in a nitrogen environment, but there was consi derable thermo-oxidative degradation of the fine panicles in air. The chemi cal analysis indicated that some of the bonds were broken during the pulver ization process, and partial devulcanization had taken place.