ception, there was also no significant change in
Hardness readings of samples that were ex-
the weight change data. These results support
posed to aqueous solutions with a relative solu-
our hypothesis that softening will not be detected
bility of 0.1 were significantly lower than the con-
at activities where diffusion is reported to be slow-
trols after one year. Samples exposed to solutions
est (Fickian), i.e., for PVC solvents and better swell-
with higher relative solubilities (0.2, 0.4) softened
ing agents less than 0.1 (Vonk 1985, 1986).
earlier in the study. However, none of these
samples were pliable. Presumably
these materials become slightly soft-
Table 4b. Percent weight gain of PVC exposed to methylene chlor-
ened but never become pliable or
ide solutions.
rubbery. This conclusion is sup-
ported by the fact that there does
Relative
Contact time, months
not appear to be much additional
solubility
3
6
9
12
15
18
weight gain after the first three to
0.00
0.13
0.24
0.26
0.20
0.33
0.17
six months for any of the samples
0.00
0.26
0.28
0.17
0.09
0.00
0.32
exposed to the solutions with rela-
0.00
0.15
0.35
0.35
0.28
0.25
0.19
tive solubilities of 0.10 and 0.20 and
0.00
0.17
0.35
0.26
0.16
0.27
0.16
0.00
0.25
0.35
0.27
0.14
0.20
0.26
after 12 months in samples exposed
0.19a
0.31a,b
0.26a
0.17a
0.21a
0.22a
to solutions with a relative solubil-
X
S.D.
0.06
0.05
0.07
0.07
0.13
0.07
ity of 0.40. This may mean that the
test pieces have reached equilibrium
0.01
0.35
0.18
0.26
0.26
0.35
0.17
with the test solution, and thus we
0.01
0.17
0.26
0.35
0.34
0.17
0.24
0.01
0.25
0.27
0.41
0.36
0.16
0.21
do not expect any further changes.
0.01
0.34
0.36
0.35
0.27
0.08
0.18
We also observed that softening
0.01
0.41
0.42
0.42
0.35
0.34
0.08
occurred more slowly for the sam-
0.30a
0.30a
0.36a
0.32a,b
0.22a
0.18a
X
ples exposed to solutions with rela-
S.D.
0.09
0.09
0.06
0.05
0.12
0.06
tive solubilities of 0.10 and 0.20 than
0.05
0.44
0.25
0.40
0.34
0.27
0.35
what we observed previously (Park-
0.05
0.34
0.33
0.40
0.34
0.33
0.50
er and Ranney 1994). This is most
0.05
0.34
0.44
0.36
0.31
0.24
0.17
likely a result of the pieces being ap-
0.05
0.34
0.44
0.33
0.61
0.33
0.41
proximately 20% thicker in this
0.05
0.24
0.25
0.34
0.34
0.25
0.28
study.
0.34a
0.34a,b
0.37a
0.39b,c
0.28a
0.34a,b
X
S.D.
0.07
0.09
0.03
0.12
0.04
0.13
Long-term TCE studies
0.10
0.33
0.41
0.62
0.53
0.72
0.43
Table 5 gives the results of expo-
0.10
0.37
0.41
0.55
0.42
0.52
0.64
sure to aqueous solutions of TCE
0.10
0.43
0.62
0.53
0.50
0.59
0.52
0.10
0.26
0.69
0.64
0.54
0.60
0.58
with relative solubilities of 0.05, 0.1,
0.10
0.32
0.37
0.69
0.69
0.51
0.44
0.2, 0.4, and 0.6. The samples exposed
0.34a
0.50b
0.60b
0.54c,d
0.59b
0.52b,c
X
to the solutions with relative solu-
S.D.
0.06
0.14
0.06
0.10
0.08
0.09
bilities of 0.6 and 0.4 had significant
changes in their hardness readings;
0.20
0.75
1.01
0.74
0.74
0.82
0.60
0.20
0.72
0.64
1.11
0.59
0.87
0.67
however, they did not become pli-
0.20
0.87
0.76
0.66
0.61
0.92
0.58
able. It should be noted that TCE
0.20
0.61
0.60
1.00
0.81
1.05
0.61
has never before been shown to be
0.20
0.65
0.75
0.83
0.85
0.84
0.59
active at such a low relative solubil-
0.72b
0.75c
0.87c
0.72d
0.90c
0.61c
X
ity, and that it took more than a year
S.D.
0.10
0.16
0.19
0.12
0.09
0.03
before significant changes in hard-
0.40
1.33
1.39
1.69
2.38
2.37
2.18
ness were detected in those samples.
0.40
1.51
0.79
1.91
2.15
2.13
2.01
There were also significant changes
0.40
1.65
1.01
1.66
1.94
1.67
2.20
in the weights of the samples ex-
0.40
1.99
1.25
1.36
2.26
2.50
1.41
0.40
1.43
1.39
1.66
1.67
2.01
1.97
posed to the solutions with relative
1.58c
1.17d
1.66d
2.08e
2.14d
1.95d
solubilities of 0.4 and 0.6.
X
S.D.
0.26
0.26
0.19
0.28
0.32
0.32
It is clear from this and the pre-
vious study that small but measur-
S.D. = standard deviation
able changes occur in the weight
Values with different letters, taken at the same time, are significantly different.
9
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