A study on morphology and physical properties of natural–acrylic rubber blends

Abstract Morphology and physical properties of natural–acrylic rubber blends were investigated as a function of blend compositions and mixing methods. In the first method, the masticated natural rubber was cross‐blended with the acrylic rubber for 15 min, followed by a sequential addition of vulcanizing chemicals (ZnO, stearic acid, MBT, sodium stearate, and sulfur), and the mixing was terminated within 15 min. In the second method, the masticated natural rubber was premixed with its relevant vulcanizing chemicals (excepting the sulfur) for 7 min, followed by blending it with the acrylic rubber and sodium stearate for 20 min. Finally, the sulfur was added and the mixing was continued for further 3 min before termination. The resulting blends were vulcanized to their optimum cure time in a compression mold. The rubber sheet was cut into a dumbbell‐shaped specimen, and tensile properties were determined at a cross‐head speed of 500 mm/min. The morphology of the blends was examined with scanning electron microscopy (SEM). The SEM specimen was prepared by cryo‐fracturing, followed by staining with OsO 4 . It was found that all of the rubber blends were immiscible, as shown by there being two separated phases in the SEM micrographs. The result was in a good agreement with that from a thermal analysis (using a differential scanning calorimeter), which showed two glass transition temperatures. Morphology of the rubber blends changed from a cocontinuous morphology to a dispersed particle morphology as the natural rubber content was increased from 20% to 80% by weight. Increasing the natural rubber content enhanced tensile properties of the rubber blends at the expense of their oil and heat resistance. Most of these properties being examined seemed to be unaffected by the mixing method, with the exception of the retention of tensile strain after aging. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1532–1539, 2002