Exploration of novel heat and flame-resistant poly(urethane–imide)/functional layered silicate-based foams

Poly(urethane–imide) (PUI)/hydroxyl functional montmorillonite (MMT; H-MMT) nanocomposites and foams have been prepared with modified layered silicates (hydroxyl-modified H-MMT) via in situ polymerization. The physical properties of PUI/H-MMT nanocomposites and foams were investigated and were found to be dependent on the structure of polyurethane, functional groups of the modifiers, and chemical reaction between the hydroxyl of H-MMT and matrix. Field-emission scanning electron microscopy revealed imprecise honeycomb cellular structure with increased cell density and reduced cell size compared with pure PUI foam. Compression strength and modulus of PUI/H-MMT 1 foam (1 wt% nanofiller) were 26.5 MPa and 4 GPa, respectively, which were augmented to 31 MPa and 7 GPa in PUI/H-MMT 5 foam (5 wt% nanofiller). Thermogravimetric results for 10% thermal decomposition temperature of PUI/H-MMT 1–5 foams were in the range of 476–511°C. Dynamic mechanical thermal analysis showed that PUI/H-MMT 1 foam had glass transition temperature of 155°C which was enhanced to 161°C in PUI/H-MMT 5 foam. Limiting oxygen index and UL 94 results showed that PUI/H-MMT 1–5 foams exhibited enhanced nonflammability (V-0 rating) with the clay loading.