Poly(propylene)/organoclay nanocomposite formation: Influence of compatibilizer functionality and organoclay modification

Abstract

Poly(propylene) compounds containing organophilic layered nanosilicates were prepared by means of melt extrusion at 210°C in order to investigate the role of silicate modification and compatibilizer addition on morphology development and mechanical properties. Synthetic sodium fluoromica was used as water swellable layered silicate, which was rendered organophilic by means of cation exchange with various protonated alkyl amines such as butyl (C4), hexyl (C6), octyl (C8), dodecyl (C12), hexadecyl (C16), and octadecyl (C18) amine. Interlayer spacing of the organophilic silicates increased with increasing alkyl chain length of the amine. Only C12, C16, and C18 amine modifiers in conjunction with maleic-anhydride-grafted poly(propylene) (PP-g-MA) as compatibilizer promoted exfoliation and self-assembly of individual silicate layers within the poly(propylene) matrix. Interlayer distance increased with increasing content and increasing anhydride functionality of PP-g-MA. Only 10 wt.-% of fluoromica modified with C16 amine in conjunction with 20 wt.-% of PP-g-MA containing 4.2 wt.-% maleic anhydride grafts was sufficient to achieve effective poly(propylene) matrix reinforcement, as reflected by increase of Young's modulus from 1 490 to 3 460 MPa and increase of yield stress from 33 to 44 MPa with respect to bulk poly(propylene). Morphology, measured by means of transmission electron microscopy (TEM) and atomic force microscopy, and mechanical properties were examined as a function of the alkyl chain length of the amine modifiers, PP-g-MA compatibilizer addition and anhydride functionality of PP-g-MA.