Morphology and curing behaviors of phenolic resin-layered silicate nanocomposites prepared by melt intercalation

The melt intercalation and curing behavior of phenolic resin (P1) were investigated by use of layered silicates, such as pristine montmorillonite (PM), dodecylammonium-modified montmorillonite (C12M), octadecylammonium-modified montmorillonite (C18M), benzyldi-methyloctadecylammonium-modified fluorohectorite (C18BH), and hexamethylenetetramine (HMTA), as curing agents. It was found by X-ray diffraction that the uncured phenolic resin was intercalated into PM, C18M, and C18BH. Cured phenolic resin-layered silicate nanocomposites were prepared by two methods: one was the sequential process of intercalation and curing (IC, the suffix of sample code), and the other was the simultaneous process of mixing and curing (MC). The intercalated structures were preserved in cured P1C18BH but not in cured P1C18M, i.e., the phenolic resin intercalated in C18M was deintercalated when it was cured. It was suggested that the intercalated structure of P1C18BH was more stable in the curing process than that of P1C18M due to chemical affinity derived from the favorable interaction between the phenolic resin and intercalant-containing benzene ring. Transmission electron micrographs showed that a splitted-stacked structure was formed in the samples of P1PMMC and P1PMIC, indicating the phenolic resin did not intercalate the PM. Conclusively, the modification of layered silicate and the resulting interaction between organic modifier and phenolic resin played an important role in determining the stable nanostructure and the final morphology of phenolic resin-layered silicate nanocomposite.