Organo-montmorillonite barrier layers formed by combustion: Nanostructure and permeability

Self-assembly of nanoparticles into barrier layers has been the most cited theoretical explanation for the significant reduction in flammability often noted for polymer/montmorillonite nanocomposites. Both mass and heat transport reductions have been credited for such improvements, and in most cases a coupled mechanism is expected. To provide validation for early transport models, the structure of model barrier layers was investigated, these being produced by combustion of a homologous series of organo-montmorillonites. One model barrier layer was subjected to novel permeability analysis to obtain a flux, which will be useful in the evaluation of transport models. The effects of compatibilizer structure, temperature and pressure on barrier layer structure were examined. XRD versus TGA results suggest that the onset of chemical degradation and the onset of physical collapse on heating are correlated. Addition of pressure as low as 7kPa affected the onset of structural collapse; for the case of a "two-tailed" dimethyl dialkyl quaternary ammonium ion compatibilized organo-montmorillonite this meant expansion of the basal spacing rather than the expected densification. Permeability of Ar through the ash was found to be a sensitive measure of structural change of high aspect ratio MMT nanoparticles. Actual fluxes ranged from 0.139 to 0.151mol (m²s)^-1 for 0.5mm thick samples.