Mechanical Properties, Structure, and Morphology of Natural-Rubber/Low-Density Polyethylene Blends Prepared by Different Processing Methods

Abstract

Abstract Morphological studies with TEM and SEM showed that, in unvulcanized NR/LDPE blends, phase inversion occurred between NR/LDPE = 40/60 to 60/40; for dynamically vulcanized blends, LDPE remained as a continuous phase even at NR/LDPE = 70/30. Change in morphology of dynamically vulcanized blends of specified composition (NR/LDPE = 70/30) with vulcanization time as observed by SEM indicated that phase inversion occurred with the progress of vulcanization followed by fracture of the crosslinked phase into small particles. A model was proposed. For unvulcanized samples, the tensile strength steadily increased with increasing LDPE content, while their elongation at break first decreased and thereafter increased. Tensile strength and elongation at break of the statically vulcanized samples decreased to a minimum and thereafter increased with increasing LDPE content. However, an interesting trend appeared in the change in tensile strength and elongation at. break of the dynamically vulcanized system with increasing LDPE, where they first increased to a maximum and thereafter decreased. From the suggested model and the experimental results, it was shown that the mechanical properties of dynamically vulcanized blends were higher than those of unvulcanized blends but lower than those of statically vulcanized blends. The other physical properties of blends which are mainly dependent on the properties of the plastic phase, such as tear strength, 300% modulus, hardness and permanent set, all increased with increasing LDPE in different processing methods. In addition, changes in the mechanical properties of different compositions with the progress of dynamic vulcanization were also examined.