Strain‐induced crystallization behavior of phenolic resin crosslinked natural rubber/clay nanocomposites

Abstract

Nanocomposites of natural rubber (NR) and unmodified clay were prepared by latex compounding method. Phenolic resin (PhOH) was used to crosslink NR. Crosslinked neat NR was also prepared for comparison. The structure–property relationship of uncrosslinked and crosslinked NR/clay nanocomposites was examined to verify the reinforcement mechanism. Microstructure of NR/clay nanocomposites was studied by using transmission electron microscopic (TEM), X‐ray diffraction (XRD), wide angle X‐ray diffraction (WAXD), and small angle X‐ray scattering (SAXS) analyses. The results showed the evidence of intercalated clay together with clay tactoids for the nanocomposite samples. The highest tensile strength was achieved for the crosslinked NR/clay nanocomposite. The onset strain of deformation induced the crystallization of NR for nanocomposites was found at almost the same strain, and furthermore their crystallization was developed at lower strain than that of the crosslinked neat NR because of the clay orientation and alignment. However, at high strain region, the collaborative crystallization process related to the clay dispersion and conventional crosslink points in the NR was responsible to considerably high tensile strength of the crosslinked NR/clay nanocomposite. Based on these analyses, a mechanistic model for the strain‐induced crystallization and orientational evolution of a network structure of PhOH‐crosslinked NR/clay nanocomposite was proposed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42580.

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

“…On the other hand, the WAXD images of the PhOH‐NR and PhOH‐NRNCs containing 1 and 3 phr clay did not show the reflection spots and their WAXD patterns still showed an amorphous halo at strain of 200%. For the neat NR crosslinked with 10 phr PhOH, it was found that the crystallization occurred at the strain level approximately about 300%, while the crystallization was developed at much lower strain of about 100% in the NR nanocomposite with 5 phr clay crosslinked with the same amount of PhOH because of faster NR chain alignment in the presence of clay . It is also interesting to see that the intensities of crystalline peaks at the strain of 200% [Figure (B)] appeared to increase with increasing clay loading from 5 to 10 phr, indicating an increased NR chain alignment.…”

“…According to WAXD patterns of the PhOH‐NR and PhOH‐NRNCs at different levels of strain, the degree of crystallinity (X c ) could be determined from the intensities of the (200) and (120) plane diffraction peaks . Figure shows the change of X c as a function of strain.…”

“…As a consequence, the onset of strain‐induced crystallization of NR/clay nanocomposites started at lower strain, and the rate of crystallization was greater upon stretching when compared with the neat crosslinked NR. Recently, Masa et al . have developed the NR/pristine clay nanocomposites with a much higher level of mechanical property improvement when compared with the neat NR through the use of phenolic resin (PhOH) as curative agent and fixed clay loading (5 phr).…”

“…The role of interfacial adhesion on the crystallization process was discussed. Further, the reinforcement mechanism proposed by Masa et al . was refined to better understand the strain‐induced crystallization of NR/clay nanocomposites.…”

The Effect of Surface Modification on the Properties of Palygorskite Filled Natural Rubber Nanocomposite

“…Natural rubber (NR) is an elastomer with a basic monomer of cis‐1,4‐polyisporene and its stereoregularity contributes to the strain‐induced crystallization when stretching due to the ability of molecular chain arrangement along the stretching direction . NR can provide high tensile strength and resistance to cutting, tearing and abrasion, owing to the strain‐induced crystallization.…”