Epoxy-clay fabric film composites with unprecedented oxygen-barrier properties

A new barrier-film chemistry is described in which two materials, namely a clay fabric film and a polymer, are combined to form a composite with gas-barrier properties that are far superior to those of the parent end members. Homoionic inorganic smectite clay fabric films of sodium montmorillonite and synthetic lithium fluorohectorite were cast in self-supported film form, impregnated with liquid epoxy resin and amine curing agent, and then cured to form the final epoxy-clay fabric film composite. The oxygen permeabilities of the epoxy-clay fabric film composites were lower by 2-3 orders of magnitude in comparison to that of the pristine polymer and by 3-4 orders of magnitude in comparison to that of the pristine clay film. This unprecedented reduction in oxygen permeability was attributed in part to the high volume fraction (similar to 77%) of highly aligned and nonswellable clay nanolayers in the fabric film and to the polymer filling of voids formed between imperfectly tiled clay platelet edges in the film. Mixed organic-inorganic ion-exchange forms of clay fabric films made through ion-exchange reactions of inorganic clay films form a heterostructure in which the outer regions of the film contain a swellable organoclay phase and the interior regions retain the nonswellable inorganic clay barrier phase. The modulus and glass-transition temperature of the polymer phase is not compromised upon formation of the clay fabric film composites.