Influence of phenolic curative on crosslink density and other related properties of dynamically cured NR/HDPE blends

Abstract

Dynamically cured 60/40 NR/HDPE blends with various amounts of phenolic curative were prepared in an internal mixer at 160 C. A simple blend (i.e., the blend without curative) was also prepared using the same materials and blend proportion for comparison purposes. Mechanical, dynamic, and morphological properties; swelling resistance and crosslink density of the blends were investigated. It was found that the thermoplastic vulcanizates (TPVs) gave superior mechanical and dynamic properties than the simple blend. Furthermore, the mechanical properties in terms of elongation at break, modulus and tensile strength and elastic response in dynamic test in terms of storage modulus increased with increased loading amount of the curative. The complex viscosity also increased but the tan d and tension set decreased with increased loading level of the curative. The crosslink density of the TPVs was estimated based on the elastic shear modulus. It was found that the crosslink density of the blends increased with increased loading levels of the curative while the degree of swelling decreased. This correlated well with the trend of mechanical and dynamic properties. SEM micrographs were used to confirm the level of mechanical and dynamic properties. It was found that the simple blend at a given blend ratio exhibited co-continuous phase morphology. However, the TPVs showed micron scale of vulcanized rubber domains dispersed in a continuous HDPE matrix. The size of vulcanized rubber domains decreased with increasing amounts of the curative. This led to greater interfacial adhesion between the phase and hence superior mechanical and dynamic properties.

Influences of the phenolic curative content and blend proportions on the properties of dynamically vulcanized natural rubber/acrylonitrile–butadiene–styrene blends

“…Decreases in T S 1 with increasing curing loadings could also be explained by similar reasons. These results were in good agreement with results previously reported in literature . CRI is basically a measure of the rate of vulcanization.…”

“…The blended product is a valuable material in the polymer industry because it combines the excellent processing characteristics of thermoplastics and the outstanding elastic properties of rubbers. A number of reports have been published on rubber/thermoplastic blends made with either simple blending or dynamic vulcanization . It has been established that thermoplastic vulcanizates obtained by dynamic vulcanization can show improved mechanical and thermal properties; these are attributed to the unique morphology, in which small and uniform crosslinked rubber particles are finely dispersed in the thermoplastic matrix.…”

“…Among these, the curative content is one of the most important parameters. However, few articles have reported on the effects of the curative content on the mechanical and morphological properties of these blends …”

“…To overcome these disadvantages, a phenolic curing system has been used. It has been reported that the phenolic curing agent can overcome the degradation of thermoplastics and the unpleasant smell of the finished products …”

“…With growing environmental concerns, NR as a green polymer is therefore an interesting material to replace petroleum‐based polymers. Because of the excellent elasticity and mechanical properties of NR, it has been widely used for blending with various thermoplastics such as poly(methyl methacrylate), polypropylene (PP), high‐density polyethylene (HDPE), and nylon 12. 11 Acrylonitrile–butadiene–styrene (ABS) is one of the most important engineering thermoplastic materials.…”