Phenolic resin‐crosslinked natural rubber/clay nanocomposites: Influence of clay loading and interfacial adhesion on strain‐induced crystallization behavior

Abstract

Nanocomposites of natural rubber (NR) and pristine clay (clay) were prepared by latex mixing, then crosslinked with phenolic resin (PhOH). For comparative study, the PhOH‐crosslinked neat NR was also prepared. Influence of clay loading (i.e., 1, 3, 5, and 10 phr) on mechanical properties and structural change of PhOH‐crosslinked NR/clay nanocomposites was studied through X‐ray diffraction (XRD), transmission electron microscopic (TEM), wide‐angle X‐ray diffraction (WAXD), tensile property measurement, and Fourier transform infrared spectroscopy (FTIR). XRD and TEM showed that the clay was partly intercalated and aggregated, and that the dispersion state of clay was non‐uniform at higher clay loading (>5 phr). From tensile test measurement, it was found that the pronounced upturn of tensile stress was observed when the clay loading was increased and a maximum tensile strength of the PhOH‐crosslinked NR/clay nanocomposites was obtained at 5 phr clay. WAXD observations showed that an increased addition of clay induced more orientation and alignment of NR chains, thereby lowering onset strain of strain‐induced crystallization and promoting crystallinity of the NR matrix during tensile deformation. FTIR investigation indicated a strong interfacial adhesion between NR matrix and clay filler through a phenolic resin bridge. This suggested that the PhOH did not only act as curative agent for crosslinking of NR, but it also worked as coupling agent for promoting interfacial reaction between NR and clay. The presence of strong interfacial adhesion was found to play an important role in the crystallization process, leading to promotion of mechanical properties of the PhOH‐crosslinked NR/clay nanocomposites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43214.

Morphological evolution and mechanical property enhancement of natural rubber/polypropylene blend through compatibilization by nanoclay

“…In our previous study on the chemical structure of PhOH‐crosslinked NR/clay nanocomposite, the FTIR spectrum revealed that the clay was chemically bound onto NR molecules through phenolic bridge during high temperature molding (at 180 °C), forming NR‐PhOH‐clay [product (A) in Scheme ]. So, in the NRPPNCs, the clay locally existed at the NR/PP interface could be reacted with the NR assisted by PhOH (dispersed at interface boundary as mentioned previously) in the NRPPNC blends, yielding intermediate NR‐PhOH‐clay.…”

“…The NR and PP was blended at 80/20 wt %. Based on previous study, the recommended dosage of clay into NR was at 5 phr. This concentration was then chosen for the preparation of NR/PP blend nanocomposites.…”

“…For the masterbatch mixing method, the NR latex was firstly mixed with clay suspension in water (2 wt %) under vigorous stirring (600 rpm) at room temperature for 30 min. The NR/clay mixture was dried at 50 °C for 3 days . The dried NR/clay masterbatch was later added to the molten PP.…”

“…In past few decades, an addition of inorganic solid nano‐filler such as silicate layer or sodium montmorillonite (clay) into the NR for reinforcement purpose has been reported by several authors . Interestingly, when the blends of NR and polyolefin were combined with pristine clay, the NR/polyolefin blends showed improvement in phase morphology.…”

Presence of vacuoles in natural rubber–Cloisite 15A nanocomposites

“…During the last decade, since Arroyo et al . showed that organically modified clay causes an increment of more than 350% in the strength compared to unfilled NR (and > 300% compared to the same amount of CB), organoclays have been studied as a substitute for CB . A significant reduction in weight, preserved elasticity, and an enhancement in the strain‐induced crystallization (SIC) are additional advantages.…”