Thermal, mechanical and flame retardant behavior of poly(urethane-ester) nanocomposite foams reinforced with hydroxyl modified montmorillonite

Abstract

Presently, poly(urethane-ester) (PUE)/modified montmorillonite (MMT) nanocomposites and the respective foams have been prepared with organically tailored layered silicates (hydroxyl modified MMT-OH). In-situ polymerization was used to react the poly(urethane-ester) and modified montmorillonite. According to morphology analysis, the modified clay consequence in increased cell density and reduced cell size compared with pure PUE foam. The silicate layers of MMT-OH were well exfoliated in the PUE matrix due to chemical reaction between the hydroxyl groups of MMT-OH and functional groups of PUE. During foaming, the montmorillonite clay nanoparticles played a multifunctional role. The nanoplatelets acted as nucleating agents (improving the cellular structure) and also in increasing the thermal and mechanical properties of the resulting material. The tensile strength and modulus of PUE/MMT-OH 1 Foam (1 wt.% nanofiller) was 49.5 MPa and 17 GPa respectively, which was increased to 51.1 MPa and 20 GPa in PUE/MMT-OH 5 Foam (5 wt.% nanofiller). 10 % decomposition temperature of PUE/MMT-OH 1-5 Foams was in the range 461–487 °C. In PUE/MMT-OH 5 Foam Tg was higher 134 °C relative to PUE/MMT-OH 1 (Tg 121 °C). The dispersion of clay layers in the polymeric matrix determined the thermal and mechanical stability of the nanocomposites. Evaluation of the non-flammability properties was also important for structural applications of new materials. Limiting oxygen index and UL 94 results depicted that PUE/MMT-OH 1-5 Foam showed increased non-flammability (V-0 rating) with the clay loading. Novel polyurethane/clay foams may act as energy saving materials in construction, heat insulation systems and aerospace structural parts.