Application of Terahertz Spectroscopy to Rubber Products: Evaluation of Vulcanization and Silica Macro Dispersion

Abstract

Industrial applications of terahertz (THz) technology are becoming more widespread. In particular, novel evaluation methods for essential rubber products are being developed. THz absorbance spectra of various rubber polymers and reagents enable visualization of filler dispersions and vulcanization reactions. Here, improved visualization of the vulcanization reaction in thick rubber samples is discussed. Silica macro-dispersion is also analyzed because it is a general filler in automobile tires and has been difficult to evaluate with conventional techniques.

A Novel Approach to Non-Destructive Rubber Vulcanization Monitoring by the Transient Radar Method

“…Having the complex permittivity of each sample, we calculated the speed of light through each rubber sample. The speed of light in every medium (once the illumination is perpendicular) can be calculated using the following equation [15]. Although the calculation of speed of light once the illumination is oblique is more complex, using Equation ( 3) is a good approximation in determining the speed of light in the rubber samples.…”

“…For instance, mass swelling analysis needs approximately 72 h for its measurement procedure, which is relatively longer compared to other measurement methods. Although some analysis techniques like terahertz wave and ATR-FTIR spectroscopy are promising to be used for vulcanization monitoring, they are not able to deal with thick samples, as their penetration depth is limited (a few µm of penetration depth) [14,15]. In other words, rubber characterization on the basis of terahertz wave and ATR-FTIR spectroscopy might have high error, since the tests are done according to the surface and sub-surface characteristics, and no information from deeper regions can be obtained.…”

Terahertz Technologies and Its Applications

“…Further applications for non-destructive testing using THz radiation are presented in Reference [14], where an optimal scanning technique for honeycomb sandwich composite panels is proposed. THz spectroscopy is applied in Reference [15] to evaluate the vulcanization and macrodispersion of silica for rubber products using THz absorption measurements.…”