Retrospective Evaluation of Cured-in-Place Pipe - (NEPIS)(EPA ...

4.2.15 Raman Spectroscopy. Raman spectroscopy was used to assess the liner material’s degree of
aging. The specimens used were ½ in. × ½ in. as only a very small surface area of the sample is required
for collecting Raman spectra. The specimens were polished using a mechanical polisher and cleaned with
distilled water.
Raman spectroscopy is a technique based on inelastic scattering of monochromatic light, usually from a
laser source. Inelastic scattering refers to change in the frequency of photons in the monochromatic light
upon interaction with a sample. Photons of the laser light are absorbed by the sample and then reemitted.
The frequency of the reemitted photons is shifted in comparison with the original monochromatic
frequency, a phenomenon called the “Raman Effect”. This shift provides information about vibrational,
rotational, and other low frequency transitions in the molecules, which are indicators of degradation and
breakdown of the resin at its most fundamental (molecular) level.
Spectra from 200 to 2100 cm -1 were collected using an R-3000 HR Raman spectrometer utilizing a 785
nm diode laser operating at 290 mW via a fiber optic probe. Integration time was 30 seconds. As shown
in Figure 4-25, the measured intensity of the Raman signal in arbitrary units (a.u.) is plotted on the y-axis,
while the wave length in cm 1 is plotted on the x-axis.
The plots are nearly identical for the base resin and liner used for 25 years, with no significant change in
the intensity of the peaks or region shift, indicating high chemical stability. Additional tests were carried
out on the exterior surface of the liner, but no significant changes from the spectra shown in Figure 4-25
were detected.
Figure 4-25. Raman Spectra (Denver 8-in. Liner)
4.2.16 Differential Scanning Calorimetry (DSC). DSC is used to perform thermal
characterization studies on thermosetting resins. As the components in a resin system cure, heat is
evolved which is measured by the DSC. When no significant heat of cure is observed, then it is assumed
that the resin sample is completely or 100% cured. DSC can also be used to measure the glass transition
temperature (Tg) or softening temperature of a thermoset resin. Tg represents the region in which the
resin transforms from a hard, glassy solid to a viscous liquid. As a thermosetting resin cures, the Tg
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