Thermal Conductivity of Low Density Polyethylene Foams Part I: Comprehensive Study of Theoretical Models

Polymeric foams are one of the most applicable thermal-insulation materials due to their low thermal conductivity, high mechanical properties, and low cost. Optimization of thermal-insulation performance of polymeric foams needs a theoretical model in order to predict the overall thermal conductivity. So far, several theoretical approaches are presented in this regard but to the best knowledge of the authors, there is no comprehensive investigation on comparing the proposed models. Therefore, the study of validity of the theoretical models in comparison with the experimental results is one of the main goals of the present study. Low density polyethylene (LDPE) foams are selected as the case study due to the wide application range. Different models to predict the overall conductivity of the foam based on conduction through the combined gas and solid phases (lambda(gs)) as well as radiation thermal conductivity (lambda(r)) are presented. The results indicate that the best model is a model in which lambda(gs) is calculated using Gibson and Ashby model and lambda(r) is obtained using Williams and Aldao model based on the root mean square (RMS) parameter. The results show that the theoretical error of this model is smaller than 10%.