Handbook of Solvents - George Wypych - ChemTech - Ventech!

7.3 Drying of coated film 399
Figure 7.3.13. Schematic diagram of FT-IR spectrometer for the
measurement of solvent content. [Adapted, by permission, from
Saure, R. and V. Gnielinski, Drying Technol., 12, 1427 (1994)].
tion is originally prepared for the
anode cell of the lithium ion battery.
The solvent content represents
the percent of remained
solvent to the weight of non-volatile
component, (W-W o)/W o,
where W and W o represent the wet
weight during drying and dry
weight, respectively. NMP has
very high boiling temperature
(about 202 o C) and low volatility,
thus the drying of coating shows
long period of constant rate. Figure
7.3.12 shows the comparison
of drying rate between pure sol-
vent and coating solution. The drying rate of coating solution is nearly equal to that of pure
solvent during the CDRP. But the drying rate of coating gradually decreases as the solvent
concentration falls, while the evaporation rate of pure solvent is constant throughout the
evaporation.
7.3.3.2 Rapid scanning FT-IR spectrometer analysis
Recently Fourier-Transform-Infrared (FT-IR) spectrometer is applied to drying studies to
obtain the drying rate at a higher air velocities. 47,50 FT-IR is a widely used analytical instru-
Figure 7.3.14. An example of FT-IR spectra of drying film. The methanol bands disappear slowly while the polymer
bands remain constant. The ratio of the band height contains information on concentration. Methanol contents
spectrum1 54 g/m 2 , spectrum2 19 g/m 2 , spectrum3 3.7 g/m 2 , spectrum4 1.5 g/m 2 , and spectrum5 0 g/m 2 , PVAc
content 57 g/m 2 . [Adapted by permission, from Saure, R. and V. Gnielinski, Drying Technol., 12, 1427 (1994)].