Synthesis and Characterization of Epoxidized Natural Rubber/Clay Nanocomposites

Sodium montmorillonite (Na-MMT) was modified by alkyl ammonium ions by cation exchange process. The influence of long chain primary (octadecylammonium ion) and quaternary alkylammonium ions (cetyltrimethylammonium ions) on the clay structure was studied. X-ray diffraction (XRD) analyses show that the basal spacings of cetyltrimethylammonium-montmorillonite (CTA-MMT) and octadecylammonium-montmorillonite (ODA-MMT) increase from 12.78 Å for Na-MMT to 19.76Å and 29.83 Å, respectively, after the organo-modification. The infrared spectra of CTA-MMT show the presence of the peaks at 2920 and 2850 cm-1 while ODA-MMT at 2928 cm-1 and 2854 cm-1, which correspond to the C-H asymmetric and symmetric stretching vibrations, respectively. This suggests that both cetyltrimethylammonium (CTA+) and octadecylammonium ions (ODA+) are sorbed into the silicate layers of Na-MMT. CHNS elemental analysis and density analysis showed that more ODA+ are intercalated in the Na-MMT layer when the initial concentration of the octadecylamine is increased. However the effect is not significant when the CTAB concentration is varied. ENR50/clay nanocomposites were prepared by melt and solution blendings by introducing various amounts of CTA-MMT and ODA-MMT. XRD analyses of the nanocomposites show that there are increments of basal spacing for ENR50/clay nanocomposites prepared by both methods. This indicates that ENR50 is successfully intercalated into the interlayer galleries of the organoclays. Transmission electron microscopy (TEM) showed that the nanocomposites are of intercalated type. The effect of CTA-MMT and ODA-MMT in the rubber matrix on the curing, crosslink density, mechanical properties and thermal stability were also studied. Vulcametric curves show that both ENR50/ODA-MMT and ENR50/CTA-MMT nanocomposites had shorter times than that of the ENR50/Na-MMT microcomposite. An increment of more than 2.5 times in the tensile strength and a highest crosslink density were observed in ENR50/ODA-MMT nanocomposite with 5 phr ODA-MMT content. High moduli were also observed in the compounds incorporated with CTA-MMT and ODA-MMT. ENR50/ODA-MMT nanocomposite with 15 phr of ODA-MMT content has the highest modulus and the lowest elongation at break. TGA studies reveal that ENR50/ODA-MMT nanocomposites with 10 and 15 phr ODA-MMT contents have the highest Tmax, which occurs at 415oC.

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