Structural analysis of insulating polymer foams with terahertz spectroscopy and imaging

Structural analysis of polymer foams for insulation enables manufacturers and research facilities to optimise their products and production processes for applications such as building construction. Therefore, two- and three-dimensional investigation of the macro- and microstructure of these materials is important in order to characterize their physical and mechanical properties. In this paper, we present terahertz time-domain spectroscopy and pulsed imaging method to analyse the macroscopic structure of foamed polymers including analysis of voids, inclusions and bead distribution. By measuring the difference between the terahertz waveforms and by calculating the spectroscopic constants we analyse certain material characteristics such as foam density and infrared radiation absorption. Furthermore, we demonstrate that terahertz techniques have several advantages over other technologies, in particular as a non-ionizing alternative to X-ray tomography, and a complementary imaging method to optical or electron microscopy enabling chemical and structural characterization of foamed polymers.