Influence of iron content on thermal stability of magnetic polyurethane foams

Magnetorheological (MR) materials are a group of smart materials which have the controllable magnetic properties with an external magnetic field. Magnetic foams, a specific type of MR solids, were synthesized from flexible polyurethane (PU) foams and carbonyl iron particles. Effects of the carbonyl iron particles on the thermal stability of the magnetic foams have been studied. Thermogravimetric analysis (TGA) was applied to characterize the thermal degradation process of the magnetic foams and then the apparent activation energy of degradation was calculated by using Ozawa's method [Ozawa T. A new method of analyzing thermogravimetric data. Bulletin of the Chemical Society of Japan 1965; 38: 1881-1886.]. The carbonyl iron particles were found to improve the thermal stability of magnetic foams in nitrogen by showing higher 10 wt% loss temperature, slower weight loss rate and higher apparent activation energy than pure PU foams. But the magnetic foams were observed to have slightly worse thermal stability in air than pure PU foams at the earlier degradation stage. At the later degradation stage, the magnetic foams exhibited the higher activation energy than pure PU foams in air.