PREFERENTIAL MIGRATION OF CARBON BLACK IN NR/EPDM BLENDS INVESTIGATED THROUGH MICROSCOPIC APPROACHES

ABSTRACT The segregation of carbon black within a blend of NR/EPDM rubber at different mixing proportions (especially 70/30 and 30/70) was investigated via various microscopic techniques—transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM)-mapping, field emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM)—to analyze the characteristics of the rubber matrix in pristine rubber to final filled rubber blends. The investigation spans from the unfilled rubber to ultimate filled blends with low (25 phr) and high (50 phr) carbon black content. The use of OsO 4 for selective chemical staining, in conjunction with microscopy, made it possible to distinctly understand each rubber phase within the blend, greatly aiding in the identification of filler migration to the preferred rubber phase. In addition, STEM-mapping confirmed the phase distribution by identifying the continuous and dispersed phases through precise detection and validation of the stained areas. The combined outcome of the microscopic studies (TEM, FESEM, and AFM) revealed that the carbon black filler is more inclined to move toward the unsaturated NR phase due to its active graphitic edges, making it more compatible with the NR phase, which has a higher degree of unsaturation than EPDM.