Reducing gas-loss in rigid polyisocyanurate foams using metal-organic frameworks

Polyisocyanurate (PIR) foams are widely used to insulate buildings, but their performance reduces over time leading to wasted energy and higher heating costs. High molecular weight gases used to blow the foams gradually diffuse out and are replaced by air leading to an increase in thermal conductivity. A wide variety of additives have been tested to improve the barrier properties of polymers including metal–organic frameworks (MOFs) which have proved promising candidates thanks to their tunable surface chemistry. In this work, a new and robust method for determining gas loss from rigid PIR foams has been developed, and utilised to determine the effect of different MOF additives on gas loss. An accelerated ageing method was developed, in which the mass of a fixed volume of foam was kept in an oven at 70 °C and weighed at 24 hour time intervals. This was found to provide reproducible measurements of gas loss over a period of 28 days with a variation of 1.1% by mass for typical samples. Five different MOFs were added to polyisocyanurates, and their effects on cell size, closed cell content, and gas loss over time were measured. Cu(ABDC)(DMF) was found to enhance the gas retention of PIR foams with minimal change to cell size or closed cell content. A modulated (flower-like) NH2-MIL-53 MOF increased the closed cell fraction whilst reducing cell size, with no effect on gas loss, whilst an unmodulated (cube like) NH2-MIL-53 MOF increased the gas loss without affecting cell size or closed cell percentage. Two further MOFs, Cu(BTetC)(DMF) and Cu(BDC)(DMF), were found to have no effect. This work therefore identifies Cu(ABDC)(DMF) as a promising additive for reducing gas-loss and maintaining the long-term performance in PIR foams, with its effectiveness demonstrated via an accelerated ageing technique developed for this study.