The influence of dispersion and distribution of ultrafine kaolinite in polyamide-6 on the mechanical properties and fire retardancy

• Elastic properties of composites are not sensitive to the kaolinite surface treatment.
• The yield stress decreases with the increase of median diameter.
• The resilience decreases with the increase of interparticle distance.
• The pHRR increases with the increase of interparticle distance.

The aim of this paper is to demonstrate that morphological particle properties inside the polymer matrix are responsible for the variability of mechanical properties (elasticity, strength, resilience) and fire retardancy properties. Ultrafine kaolinites were modified and employed to obtain composites of polyamide. These composites were characterized by means of mechanical (tensile static and dynamic tests) and fire retardancy properties (cone calorimeter). Their morphological properties differed significantly according to the aspect ratio and surface treatment of the kaolinites. These morphologies, characterized by the particle dispersion (interparticle distance ID) and size distribution (median diameter MD) in the polymer matrix, were directly related to the mechanical properties. The experimental results demonstrate the sensitivity of strength, resilience and flammability to particle dispersion and distribution. The yield stress decreases with the increase of MD, the resilience decreases with the increase of ID with a critical ID value from which the composite became brittle, and the pHRR increases with the increase of ID.