Synthesis of an exfoliated kaolinite–poly(urea–formaldehyde) nanocomposite

Abstract

In this study, kaolinite–poly(urea–formaldehyde) was successfully prepared through the polymerization of urea intercalated within the kaolinite structure. Polymerization was carried out under ambient conditions by immersing kaolinite–urea in formaldehyde. Evidence of urea intercalation and polymerization was obtained from FTIR, XRD, and thermal analysis (TG–DSC). The XRD pattern of the kaolinite–poly(urea–formaldehyde) composite shows that polymerization induces exfoliation of the kaolinite layers, leading to the formation of a nanocomposite. Textural analysis through nitrogen adsorption on raw kaolinite and kaolinite–urea demonstrates that polymerization mainly occurs within the interlayer. Water resistance tests show that poly(urea–formaldehyde) within the nanocomposite is less sensitive to decomposition when immersed in water compared to pristine poly(urea–formaldehyde). Additionally, a self-healing effect was observed for poly(urea–formaldehyde) in the nanocomposite, indicating that fragments from the decomposition of the intercalated polymer when immersed in water remain trapped within the composite matrix owing to interactions with kaolinite mineral layers. Modeling of kaolinite–poly(urea–formaldehyde) interactions allows for the proposal of a mechanism for the interlayer polymerization of intercalated urea.