Investigation on the melting and crystallization behaviors, mechanical properties and morphologies of polypropylene/sericite composites

Sericite was treated with pimelic acid (PA) and PA/Ca(OH)(2) by wet grinding, separately. The particle size of the sericite decreased after ball milling. The carboxylates were produced after the treatments. Polypropylene (PP)/sericite composites were prepared by using a twin-screw extruder. The melting and crystallization behaviors, mechanical properties, morphologies, heat resistances and processing properties of the composites were investigated. It is found that potassium pimelate (PA-K) and calcium pimelate (PA-Ca) are effective nucleating agents for PP, while PA and aluminum pimelate (PA-Al) are nucleating agents. PA-treated sericite increases the crystal content of the composites at 1wt% content due to the presence of PA-K. PA/Ca(OH)(2)-treated sericite greatly enhances the crystal contents of the composites because of the best -nucleating agent, PA-Ca. The addition of untreated and treated sericites increases crystallization temperature, reflecting the heterogeneous nucleation effects, especially for PA/Ca(OH)(2)-treated sericite. The tensile strengths of treated sericite composites are improved when the filler contents are less than 5wt%. The tensile yield strength and flexural modulus of untreated sericite composites are higher than those of treated sericite composites. Higher crystal contents in PA/Ca(OH)(2)-treated sericite composites lead to increased tensile strain at break and Izod notched impact strength. The morphologies of the impact-fractured surfaces show that the treated sericites improve the interface adhesion, and the orientation of sericite flakes facilitates the impact resistance. The heat deflection temperatures, shrinkages and densities of treated sericite composites are greater than those of untreated sericite composites.