Nanoparticle filled polymeric systems for gas barrier and flame retardant properties

Yingji Wu, University of Southern Mississippi


Polymer composite gas barrier and fire retardant properties were studied in this investigation. An increase in the gas barrier property was observed by adding silicate nanotubes or clay nanoparticles into polymeric systems. Oxygen permeability, diffusivity, solubility and water vapor permeability were determined for polyimide/silicate nanocomposites with 0 to 9.99% (vol/vol) filler loading. Both oxygen and water vapor permeability for the system gradually decreased when adding increasing amounts of nanofiller up to 4.50% (vol/vol) and increase again after that. The permeability decrease was caused by both the diffusivity and solubility coefficient changes, although diffusivity (the tortuous factor) is the main reason of permeability deduction. Other than polyimide systems, high aspect ratio mica filled LLDPE/LDPE multilayer materials were used for gas barrier property improvement. Multilayer coextrusion is an attractive approach for creating designed particulate-filled nanocomposite polymer film structures with enhanced gas barrier properties. Multilayered materials were annealed above the melting temperature of the polymers to activate interdiffusion and to concentrate the mica platelets in the filled LLDPE layers. SEM, TEM and WAXS analysis were employed to probe the films' layer morphology and the platelet orientation/dispersion in the nanocomposite blends and nanoparticulate filled multilayer systems. The oxygen barrier of the blends and multilayer composites were measured and related to their morphologies. It was shown particle concentrated multilayering leads to an enhancement in oxygen barrier properties as compared to the as-received multilayer materials and nanocomposite blends with the same mineral compositions. Mica LLDPE/LDPE multilayers were tested for flammability. The multilayer technique and moving boundary effect causes further improvement of the flame retardant properties due to the particle concentration in the LLDPE layers. Although clay and various other types of nanoparticles have been reported and used as flame retardant materials, this study marks the first time nanoparticles were used as flame retardant materials in co-extruded multilayer systems. Flame retardant properties of the blends and multilayer composites were measured and related to the morphological observations. It was shown that multilayer materials have decreased peak heat release rate and enhanced char formation as compared to nanocomposite blends with the same mineral compositions. Flame retardant materials, zinc acetate (ZnAc), zinc undecylenate (ZnUnd) and Zinc stearate (ZnSt), were studied for thermal degradation and flame retardant properties on standard epoxy/amine systems. The zinc salts had improved flame retardant properties (decreased peak heat release rate (PHRR), smoke emission and improved char formation) on epoxy/amine systems and the flame retardant efficiency order was ZnAc, ZnUnd and ZnSt. The char of ZnUnd epoxy/amine composites, with surface protecting zinc oxide layers, formed a better physical barrier for the flame. SEM and X-ray were used to further understand the mechanism of zinc salts on flame retardant properties.