Abstract
Low thermal conductivity and adequate mechanical strength are desired for extruded polystyrene foams when they are applied as insulation materials. In this study, we improved the thermal insulation behavior and mechanical properties of extruded polystyrene foams through morphology control with the foam nucleating agent 1,3,5-benzene-trisamide. Furthermore, the structure–property relationships of extruded polystyrene foams were established. Extruded polystyrene foams with selected concentrations of benzene-trisamide were used to evaluate the influence of cell size and foam density on the thermal conductivity. It was shown that the addition of benzene-trisamide reduces the thermal conductivity by up to 17%. An increase in foam density led to a higher compression modulus of the foams. With 0.2 wt % benzene-trisamide, the compression modulus increased by a factor of 4 from 11.7 ± 2.7 MPa for the neat polystyrene (PS) to 46.3 ± 4.3 MPa with 0.2 wt % benzene-trisamide. The increase in modulus was found to follow a power law relationship with respect to the foam density. Furthermore, the compression moduli were normalized by the foam density in order to evaluate the effect of benzene-trisamide alone. A 0.2 wt % benzene-trisamide increased the normalized compression modulus by about 23%, which could be attributed to the additional stress contribution of nanofibers, and might also retard the face stretching and edge bending of the foams.
Highlights
With the development of technology and society worldwide, the energy demand is increasing constantly, while fossil energy resources are becoming increasingly short
It is assumed that the total thermal conductivity can be described by four different contributions, as expressed in Equation (2): λ t = λ c + λ s + λ g + λr where λc represents the thermal convection between neighbouring foam cells, which can be neglected as all extruded foam samples had closed cells and cell sizes smaller than 4 mm [23]; λs is the thermal conduction along the solid phase, namely cell walls and cell struts; λ g is contributed by the thermal conduction across the cells by the impulse transfer of gas molecules to the cell walls and struts; and λr is the thermal radiation term, which is caused by electromagnetic radiation emitted by all surfaces [12]
XPS foams with 0.1 wt % and 0.2 wt % BTA had similar thermal conductivity due to their similar foam densities and foam cell sizes
Summary
With the development of technology and society worldwide, the energy demand is increasing constantly, while fossil energy resources are becoming increasingly short. In the European Union, the total energy consumption of buildings accounts for more than 40%. The CO2 emitted by buildings and constructions corresponds to almost a quarter of the global CO2 emissions [1]. Over 60% of the energy is wasted by heat loss through building elements such as walls, roofs, floors, and windows [2,3,4,5]. The thermal insulation of buildings is of high environmental importance. Among the commonly used thermal insulation materials for building applications such as glass, stone wool, and polymer foams, polymer foams accounted for a share of 41% in 2015 and Polymers 2019, 11, 268; doi:10.3390/polym11020268 www.mdpi.com/journal/polymers
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