Effect of layered silicate nanoclay on the properties of silane crosslinked linear low-density polyethylene (LLDPE)

In the present work, the effect of pristine layered silicate montmorillonite (MMT) nanoclay on the properties of silane-crosslinked LLDPE prepared by melt compounding is investigated. The effect of the sequence of feeding additives (nanoclay and grafting agent) into the mixer on gel content, thermal and mechanical properties were studied. Results demonstrate that the sequence of feeding additives influences the final properties of nanocomposites. For samples prepared by first grafting of silane on LLDPE followed by incorporation of nanoclay into the polymer matrix, the gel content and the rate of crosslinking increased, while the elongation at break decreased. For samples prepared by first mixing nanoclay into the LLDPE matrix followed by the grafting reaction, the rate of crosslinking and the tensile properties did not change significantly. The gel content increased with increasing content of nanoclay for both process routes due to an enhanced permeation of water molecules into the polymer matrix in the presence of polar montmorillonite particles. Wide angle X-ray scattering (WAXS) results proved the intercalation/partial exfoliation morphology of nanoclay in the silane-grafted LLDPE matrix. Differential scanning calorimetry (DSC) data showed multiple melting behaviour for crosslinked samples which is indicative for different crystalline structures of the sol and gel part of the LLDPE matrix.