Handbook of Solvents - George Wypych - ChemTech - Ventech!

7.1 Introduction to diffusion, swelling, and drying 349
Mass uptake, %
250
200
150
100
50
0
0 20 40 60 80 100 120
Time, min
Figure 7.1.15. The mass uptake of TCE by PEEK vs.
time. [Adapted, by permission, from B H Stuart,
D R Williams, Polymer, 35, No.6, 1326-8 (1994).]
Carbonyl frequency, cm -1
1654
1652
1650
1648
1646
1644
0 50 100 150 200 250 300 350
Temperature, o C
Figure 7.1.16. The frequency of carbonyl stretching
mode of PEEK vs. temperature. [Adapted, by
permission, from B H Stuart, D R Williams, Polymer, 36,
No.22, 4209-13 (1995).]
Figure 7.1.1 can be discussed from a
different perspective of results given in Figure
7.1.17. There are also three regions here:
region 1 which has a low concentration of
solid in which solvent evaporation is controlled
by the energy supplied to the system,
region 2 in which both the energy supplied
to the system and the ability of polymer to
take up the free volume vacated by solvent
are important, and region 3 where the process
is free volume controlled. Regions 2
and 3 are divided by the glass transition
temperature. Drying processes in region 3
and to some extent in region 2 determine the
physical properties of dried material and the
amount of residual solvent remaining in the
product. A sharp transition between region
2 and 3 (at glass transition temperature)
might indicate that drying process is totally homogeneous but it is not and this oversimplifies
the real conditions at the end of drying process. The most realistic course of events occurring
close to the dryness point is presented by these four stages: 27,28
100
solution rubbery glassy
80
60
40
20
0
0 0.2 0.4 0.6 0.8
Time, arbitrary units
1
Figure 7.1.17. Solvent concentration vs. drying time.
• elimination of the volatile molecules not immobilized by the adsorption onto the
polymer
• elimination of adsorbed molecules from the polymer in its rubbery state
Solvent concentration, %