Infrared Spectroscopy - Analysis of Sealants

In perhaps the most straight forward cases infrared spectroscopy can be used to analyse sealants to identify generic type and possibly even a manufacturer. The generic types of sealant have very different and highly characteristic infrared spectra as can be seen in figure 1 showing infrared spectra of a silicone sealant, a polysulphide sealant and a polyurethane sealant. In cases where the project specification calls for a particular sealant type infrared spectroscopy can easily determine if the specified product has in fact been used.

Infrared spectroscopy can also be used to undertake condition surveys of sealants already in use. Because the sample size does not have to be very large sealant surfaces can be examined by an infrared method for degradation, and then compared with the body of the material to highlight potential sealant failures.

Figure 1: Infrared spectra of generic sealants.

Further uses of infrared spectroscopy in the examination of sealants is in the cases of two part sealants comprising a resin and a hardener. Infrared spectra can be obtained of both starting materials and of a range of reference laboratory mixes in different ratios. These can be compared with the spectra obtained from the site mixed sealant to ascertain that the correct materials had been used and in the correct mix ratios. Figure 2 shows the infrared spectra obtained for a two part modified polyurethane sealant mixed correctly and also overdosed and underdosed with hardener. The relative peak heights show whether the material has been correctly mixed and, whilst these differences may not appear great to the naked eye, the computer software can differentiate them.

Figure 2: Infrared spectra of different mix ratios of two part polyurethane sealants.