Intercalation process in the preparation of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-montmorillonite nanocompounds and their application in epoxy resins

To enhance the flame retardancy of epoxy resins (EPs), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and montmorillonite (MMT) nanocompounds were prepared. In their preparation, anhydrous, pristine and watery calcium-based montmorillonite (CaMMT) and sodium-based montmorillonite (NaMMT) were used through molten DOPO, a DOPO solution in ethanol, and ball milling. The intercalation processes of DOPO into MMT were studied. It was found that water and ethanol molecules were disadvantageous to the intercalation. In the anhydrous state, DOPO could intercalate faster into NaMMT than CaMMT. It was observed that the DOPO-CaMMT nanocompounds could induce good intercalated and exfoliated dispersion in EPs by transmission and scanning electron microscopy. The flame retardancy, glass transition and mechanical properties of the EPs were investigated by limiting oxygen index (LOI), UL-94 vertical burning test, cone calorimetry, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and three-point bend testing. The DOPO-CaMMT nanocompounds ensured that the EP composites exhibited good performance due to the good dispersion of the CaMMT layers in the matrix.