Table 5. Means of relative hardness (Barcol) values of PVC exposed to
miscible solvent solutions for various contact times.
Solution (%)
2
4
8
12
16
20 days
Acetone
0.0 control
77.0
79.4
80.0
79.2
78.6
79.6
2.5
76.6
78.8
79.8
79.0
75.0*
77.6
5.0
76.6
78.4
79.2
79.0
77.0
76.4
10.0
76.4
78.2
79.4
79.2
72.4*
73.8*
20.0
76.2
76.4
77.6
75.4
72.8*
70.2*
40.0
37.2*
26.0*
30.6*
21.6*
29.4*
23.2*
Dimethylformamide
0.0 control
79.8
79.5
79.3
79.5
79.5
79.3
20.0
79.3
78.3
79.3
76.5
76.3
76.8
40.0
79.0
78.5
78.3
76.5
75.8
76.8
60.0
78.3
75.8
78.3
76.0*
73.5*
71.3*
80.0
33.0*
29.3*
10.0*
14.8*
12.5*
16.5*
Pyridene
0.0 control
79.8
79.5
79.3
79.5
79.5
79.3
20.0
77.8
77.5
78.0
78.8
76.8*
73.3*
40.0
77.0
76.8
76.5*
74.0*
74.5*
71.5*
60.0
76.3*
75.8
75.3*
72.8*
72.5*
66.0*
80.0
28.0*
17.8*
22.0*
10.8*
10.8*
7.0*
Tetrahydrofuran
0.0 control
79.8
79.5
79.3
79.5
79.5
79.3
0.01
79.0
77.8
79.5
79.5
78.0
74.8*
0.10
78.5
77.8
77.0*
78.8
78.5
73.5*
1.00
78.5
78.0
76.8*
76.8*
78.3
73.0*
10.00
76.8*
77.0
75.5*
70.8*
74.8*
67.8*
* Value significantly different from controls (95% level).
to the 60% (8.2 M) and 80% (10.9 M) solutions
but not for the samples exposed to the 2.5% (0.43
had Barcol readings that were significantly lower
M) and 5% (0.86 M) solutions. Again, only the
than the controls. The samples that were exposed
samples exposed to the 40% solution were no-
to the 80% solution were also pliable (i.e., easily
ticeably softened when tested manually. It may
bent in half). The weight change data indicate that
be that given more time the other solutions (10
all these samples may have reached equilibrium,
and 20%) would also have caused pronounced
as there was no additional weight gain during
softening. Although the weight gain data were
the last four weeks of the study.
highly variable, it did appear that the samples
It is clear from this study that several organic
exposed to the 40, 10 and 5% solutions had reached
solvents that are totally miscible in water can soften
equilibrium (Table B2). A longer-term study would
PVC when dissolved in aqueous solutions and
show whether equilibrium had been reached or
that the ability of an organic solvent to soften PVC
whether further change occurs.
when dissolved in aqueous solution is correlated
There was a significant change in the hardness
with the neat organic solvent's ability to dissolve
readings for the samples exposed to the lowest
or soften PVC.
concentration (20%, or 2.5 M) of pyridine. Samples
exposed to the highest concentration tested, the
80% (10 M) solutions, were actually pliable (i.e.,
Mixed-solvent study
This study was conducted to determine if a
easily bent in half).
combined solution of 18 PVC solvents and swell-
Dimethylformamide again was the least ag-
ing agents, each at an activity of 0.05, can soften
gressive solvent, and only the test pieces exposed
8
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