Utilization of ionomers as compatibilizers in polymer-clay nanocomposites
The influence of clay on the flame retardant properties, mechanical properties of thermoset based clay nanocomposites was investigated. The incorporation of Cloisite® into the various thermoset vinyl ester matrices resulted in the greatest dispersions relative to the other organically-modified clays studied; however, only intercalated clay dispersions were produced. Minor improvements, relative to the pure resins, in the time to ignition and peak heat release rates were present in the cone calorimetry studies. Poly (ethylene terephthalate) and poly (ethylene terephthalate) ionomer clay nanocomposites were produced using both the solution and melt processing approaches. The incorporation of the ionomer as a compatibilizer or increasing the ionic content of the ionomer in the clay nanocomposite resulted in improved clay dispersions. Moreover, the solution processed dispersed clay was observed to nucleate bulk crystallization. The poor clay dispersions, larger clay aggregates of the sodium montmorillonite, were observed to act as more efficient nucleating agents than the finer clay dispersions (organically modified montmorillonite). Poly (butylene terephthalate) and poly (butylene terephthalate) ionomer clay nanocomposites were produced using the melt processing approach. The use of the low ionic content poly (butylene terephthalate) ionomer resulted in the production of exfoliated clay nanocomposites whereas the poly (butylene terephthalate)-based clay nanocomposites resulted in intercalated clay dispersions. Based on ionic interactions between the negatively-charged ionomer and the positively-charged edge surfaces of the montmorillonite clay platelets, a tentative model for the influence of ionic groups on exfoliation is rationalized. The PBT-ionomer-Claytone ® HY nanocomposites exhibited a significant decrease in nitrogen permeability, relative to the pure polymers, and is attributed to the exfoliated clay dispersion of the materials. Only intercalated clay nanocomposites were produced using poly (ethylene-co-vinyl alcohol) and poly (ethylene-co-vinyl alcohol) ionomer; however, the Cloisite ® 30A containing samples did have slightly larger final gallery spacing than the Cloisite® 15A samples. Only the twice extruded EVOHI(Na+)-Cloisite® 15A sample that was annealed for 24 h had a decreased nitrogen permeability relative to the pure poly (ethylene-co-vinyl alcohol). This was attributed to improved clay dispersion in the polymer matrix and increased degree of crystallinity of the polymer matrix during annealing.