Preparation of polypropylene-clay nanocomposites by the co-intercalation of modified polypropylene and short-chain amide molecules

The effect of short-chain amide (AM) molecules on the intercalation of montmorillonite clay has been investigated by the melt blending of polypropylene (PP) with clay in the presence of AM molecules such as 13-cis-docosenamide (erucamide). Polypropylene-clay nanocomposites (PPCNs) were prepared by the co-intercalation of maleic anhydride grafted polypropylene (PP-MA) and an AM compound. The resulting nanocomposite structures were characterized with X-ray diffraction (XRD) and transmission electron microscopy, whereas the thermal characterization of the PPCNs was conducted by thermogravimetric analysis. XRD results showed that the AM molecules intercalated into clay galleries and increased the interlayer spacing, a result confirmed by surface energy (contact angle) and melt flow index measurements. This additive allowed the formation of an intercalated nanocomposite structure, but an exfoliated PPCN structure was also formed with the use of AM with a PP-MA-based compatibilizer. A new preparation method for PPCNs was, therefore, developed by the co-intercalation of AM and PP-MA; this resulted in a significantly improved degree of intercalation and dispersion. The enhanced thermal stability of PPCN, relative to pure PP, further demonstrated the improved clay dispersion in the nanocomposite structures prepared by this method. A possible mechanism for the co-intercalation of AM and PP-MA into the clay galleries is proposed, based on hydrogen bonding between these additives and the silicate layers. Consideration is also given to possible chemical reactions and physical interactions in this rather complex system.