Handbook of Solvents - George Wypych - ChemTech - Ventech!

400 Seung Su Kim, Jae Chun Hyun
Figure 7.3.15. Comparison between gravimetric and FT-IR data.
[Adapted, by permission, from Saure, R. and V. Gnielinski, Drying
Technol., 12, 1427 (1994)].
ment to analyze organic materials.
Development of powerful methods
for the quantitative analysis
made it possible to use the FT-IR
technique for the drying studies.
Moreover, with the aid of rapid
scanning FT-IR the concentration
of coating is measured with high
resolution and sensitivity. The
FT-IR spectrometer was modified
for the drying experiment as
shown in Figure 7.3.13. 47 A typical
spectra of a coated film, which
contains methanol and polyvinyl
acetate (PVAc), is shown in Figure
7.3.14. The typical absorption
bands of PVAc and methanol can
be identified from the literature
and is shown in the Figure 7.3.14
for a reference. 47 Basically the plot of FT-IR spectra and the ratio of band heights between
the solvent and nonvolatile material give the information of concentration. The calculated
methanol contents along with methanol bands are also seen in the Figure 7.3.14. The comparison
between FT-IR and gravimetric data shows a good agreement as shown in Figure
7.3.15. 47 The calibration method affects the qualitative analysis result, so care should be
given in selecting the spectra to evaluate, baseline correction of the spectra and selection of
the wavenumber ranges to evaluate. 47
Besides the usefulness of FT-IR method to measure the solvent content at the high airflow
ranges, it gives the concentration of each solvent in a multi-solvent system. Suzuki et
al. applied the rapid scanning FT-IR technique to obtain the individual solvent concentration
of binary solvent containing coating. 50 The process path and phase diagram can be
drawn from the FT-IR data. Figure 7.3.16 shows the phase diagram of MEK-toluene-polyvinylchloride
and polyvinylacrylate copolymer (VGAH) system. The initial and final
coating composition are given as an initial condition and a measured residual solvent
content of a coating respectively. With the aid of FT-IR technique the drying process path
between the two points can be found, and it enables us to investigate the phase separation
phenomena during drying and the mechanism of structure formation of coating. Figure
7.3.16 shows how the coating of various initial solvent compositions is dried. The drying
process path of toluene rich coating, sample 1, go through inside region of spinodal line in
the early drying stages, but the drying process path of MEK rich coating do not go through
the inside of binodal or spinodal region until the most of the solvent is evaporated. While the
appearance of sample 3 and 4 kept clear after dried up, sample 1 whose drying process path
was number 1, looked like a frosted glass due to the phase separation. 50
Though the FT-IR technique is useful to study the various kinds of drying phenomena,
the application of FT-IR spectrometer is restricted to a certain solvent system because the
bands of spectrometer of each component of a solution must be separated. While the above