Determination of additive content in polymeric compounds with terahertz time-domain spectroscopy

We present terahertz transmission time-domain spectroscopy measurements on a variety of additive-polymer combinations with differing additive contents. At lower terahertz frequencies, standard polymers are transparent. When processed into compounds, their terahertz properties are distinctively affected by additives in most cases. The materials under investigation are magnesium hydroxide in linear low-density polyethylene, glass-fibres in polyamide, and calcium carbonate, silicon or silicon dioxide in polypropylene. The extracted indices of refraction provide a reliable determination of the additive content of the material combination. Hence, terahertz time-domain spectroscopy is capable of characterising additive-polymer systems and it seems to be a promising non-destructive technique for quality control in compounding processes.