PREFERENTIAL MIGRATION OF CARBON BLACK IN NR/EPDM BLENDS INVESTIGATED THROUGH MICROSCOPIC APPROACHES
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 OsO4 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.ABSTRACT
TEM images of NR 100 and EPDM 100 gum compound unstained and stained. (a and b) NR unstained and (c and d) NR stained in 8600× and 17 500× magnifications, respectively. (e and f) EPDM unstained and (g and h) EPDM stained at 8600× and 17 500× magnifications.
TEM images of NE73 and NE37 pristine compound unstained and stained. (a and b) NE73 unstained and (c and d) NE73 stained in low and high magnifications, respectively. (e and f) NE37 unstained and (g and h) NE37stained at two different magnifications.
FESEM image of NE73 and NE37 pristine compound unstained and stained. (a and b) NE73 unstained and (c and d) NE73 stained in low and high magnifications, respectively. (e and f) NE37 unstained and (g and h) NE37stained at two different magnifications.
(a) STEM-HAADF image of NE37; (b and c) are the images with selective elemental mapping on HAADF image and excluding HAADF image, respectively. (d–h) Mapping for C, O, Os, Zn, and S, respectively, as individual elements.
(a) TEM image of NE7325 at 28 500× and (b) 46 000× magnification. TEM image of NE7325 after 1-h exposure to OsO4 at (c) low and (d) high magnification. Similarly, TEM image of (e) unstained NE3725 at low and (f) high magnification. TEM images of stained NE3725 at (g) low and (h) high magnification.
STEM-HAADF image of (a) NE7325 and (d) NE3725. Selective mapping image of Os and C on HAADF to understand the stained phase: (b) for NE7325 and (e) for NE3725. Selective mapping image with only C and Os without HAADF to ensure clarity for (c) NE7325 and (f) for NE3725.
FESEM images of unstained (a) NE7325 and (b) NE3725. (c and d) FESEM images of stained NE7325 and NE3725, respectively.
(a) TEM image of NE7350 at 28 500× and (b) 46 000× magnification. TEM image of NE7350 after 1-h exposure to OsO4 at low (c) and (d) high magnification. Similarly, TEM image of (e) unstained NE3750 at low and (f) high magnification. TEM image of stained NE3750 at (g) low and (h) high magnification.
FESEM images of unstained specimens: (a) NE7350 and (b) NE3750; corresponding stained specimens: (c) NE7350 and (d) NE3750.
STEM-HAADF image of (a) NE7350 and (d) NE3750. Selective mapping image of Os and C on HAADF to understand the stained phase: (b) for NE7350 and (e) for NE3750. Selective mapping image with only C and Os without HAADF to ensure clarity for (c) NE7350 and for (f) NE3750.
(a and d) AFM images in 5 μm × 5 μm and (b) and (e) in 2 μm × 2 μm for NE7350 and NE3750, respectively. (c and f) Three-dimensional image profile for NE7350 and NE3750, respectively.
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