Quantitative probing the interfacial structure of TPO/CPO blends by transmission electron microscopy via EDX

Abstract

High-resolution scanning transmission electron microscope (HR STEM) measurements were performed on a thermoplastic polyolefin (TPO) substrate coated with chlorinated polyolefin (CPO). This CPO was a maleated chlorinated polypropylene containing 21.8 wt% Cl. The TPO investigated was a blend of high-modulus isotactic polypropylene (iPP) with a crystalline ethylene–butene copolymer (EB9) containing 9 wt% butene. For these injection-molded samples, examined ca. 10 mm from the mold gate, a stratified morphology found at TPO surface consisting of thin fibers of EB9 trapped in a transcrystalline iPP matrix, with crystalline lamellae propagating from the matrix across the EB9 domains. This structure was unperturbed when the plaques were coated (from tetrahydrofuran solution) with a 5 μm layer of CPO, but underwent changes of increasing severity when subjected either to a dry bake at 120 °C or annealing at 120 °C in the presence of xylene vapor. The interfacial structure between the CPO and the TPO was probed by TEM with energy dispersive X-ray imaging (EDX). The elemental chlorine across the interface gave good fits to a tan h function, and the interface thickness increased from 23 ± 2 nm to 28 ± 1 nm upon annealing at 120 °C for 30 min. After annealing in the presence of xylene vapor, this value increased to 50 ± 4 nm. As reference points, we determined an interface thickness of 29 ± 3 nm for the CPO–EB interface and 15 ± 2 nm for the interface between CPO and iPP.