Porous polymethacrylimide (PMI) is a polymerized foamed […]
Porous polymethacrylimide (PMI) is a polymerized foamed material with an isotropic, completely closed cell structure, uniform pore size distribution, low density, excellent dimensional stability and mechanical properties, and at the same time Has a high heat distortion temperature. At the same time, PMI foam is easy to process, fireproof, non-toxic, and resistant to low concentrations of inorganic acid solutions. These excellent properties make PMI foam commonly used in sandwich structures of composite materials, commonly found in aerospace, radar, high-speed vehicles, sports equipment and other fields. Although it has been proposed as early as 1961, there are still few studies on the thermal conductivity of PMI foam. On the one hand, because the foam preparation is complicated, there is no mature and perfect preparation method in China. On the other hand, most of the current measurement methods of thermal conductivity, such as laser flash method, hot wire method, etc., are not suitable for porous materials, and also limit the research on the thermal conductivity of PMI foam. A suitable method for testing the thermal conductivity of porous polymethacrylimide is the heat flow meter method, HFM 436 thermal conductivity meter.
According to the measurement results, the thermal conductivity of the dense PMI foam is higher in the range of room temperature to 100 ° C, and the thermal conductivity of the same density PMI foam increases linearly with the increase of temperature. Due to the large pore diameter of the sample, the solid phase, gas phase and radiation heat transfer in the material increase with temperature, which leads to the linear increase of the effective thermal conductivity of the PMI foam with increasing temperature. Also, due to the large pore size, the gas phase heat transfer and the radiation heat transfer are independent of the density. Therefore, the effective thermal conductivity of the material is proportional to the solid phase content, which leads to the increase of the effective thermal conductivity of the sample with the increase of the density.