more time that softening might have occurred, or
nificant change in the Barcol readings after only
it might have been due to the heterogeneous na-
one day, and after 14 days several of the test
ture of PVC. We noted that at the lower relative
pieces were noticeably softened when tested
solubilities, the test pieces continued to gain
manually, although none actually became pliable.
weight, and therefore equilibrium was not
It is clear from these studies that there is a cumu-
reached. We concluded that a longer-term study
lative or possibly synergistic effect when several
should resolve the lowest relative solubility that
PVC solvents and/or swelling agents are present
can soften PVC.
in an aqueous solution.
We thought that the sum of the relative solu-
bilities (or activities) of the organic solutes in the
Studies on aqueous solutions that
test solution might prove to be useful in estimat-
contain several organic solutes
One question that has not been addressed in
ing the ability of a solution to soften PVC. In this
the literature is what effect does an aqueous solu-
study (Parker and Ranney 1995), the sum of the
tion that contains several different PVC solvents
relative solubilities of the organic solutes was 0.9.
or swelling agents have on PVC. This is an impor-
This solution was more aggressive than a solu-
tant question for the groundwater monitoring in-
tion containing a PVC swelling agent (the TCE
dustry since most contaminated groundwater con-
solution) with a relative solubility of 1.0, but less
tains several organic contaminants, each at ppb
aggressive than a solution containing a PVC sol-
or ppm levels. In cases where there is only one
vent (the methylene chloride solution) with a rela-
organic solute in a solution, there can be interac-
tive solubility of 0.8 (Parker and Ranney 1994).
tions between the organic and the polymer, the
Although it does not explain how the organic
organic and water, and among the organic mol-
solutes interact with the polymer, water, or each
ecules. In cases where there is more than one
other, the sum of the relative solubilities does
organic solute, there can be all those interactions
give some measure of the ability of an aqueous
as well as interactions among the various organic
solution containing two or more organic solutes
solutes (i.e., a and b, b and c, a and c, etc.). We
to degrade PVC.
have conducted several studies that have looked
We concluded that there were a number of
at softening by solutions containing multiple or-
unanswered questions, such as 1) whether a mix-
ganic solutes.
ture of organic solutes that are at even lower rela-
In the first study, we (Parker and Ranney 1994)
tive solubilities could soften PVC, 2) whether PVC
found that after two days' contact, the hardness
solvents and swelling agents have any synergistic
readings of samples exposed to an aqueous solu-
effect on other, poorer swelling agents, and 3)
tion that contained three PVC solvents or swell-
what happens in solutions that contain a number
ing agents were significantly lower than those of
of solutes with varying but very low relative
the controls, and these samples were rubbery. The
solubilities?
test solution contained methylene chloride, 1,1,2-
trichloroethane, and 1,2-dichloroethane, each with
Aqueous solutions containing
a relative solubility of 0.3. The χ values for these
organics that are miscible in water
three compounds are reported to be less than 0.6
Another issue that had not been addressed in
(Table 1). At this relative solubility, Berens would
the literature prior to our studies was whether
predict that none of these organic solutes should
aqueous solutions of PVC solvents and swelling
be able to soften PVC by themselves. Our own
agents, which are also completely miscible in wa-
studies (Parker and Ranney 1994) have shown
ter, can soften PVC. It is impossible to calculate
that methylene chloride was able to cause soften-
the relative solubility of these solutions, because
ing at a similar relative solubility (0.4), but it took
this involves dividing the analyte's concentration
eight weeks. The test solution in this study be-
by an infinitely large number. We have conducted
haved more like a test solution containing meth-
several studies that look at this issue.
ylene chloride at a relative solubility of 0.8, which
In our most recent paper (Parker and Ranney
softened the PVC pieces almost immediately
1995), PVC test pieces were exposed to varying
(Parker and Ranney 1994).
concentrations of aqueous solutions containing
In a follow-up study (Parker and Ranney 1995),
one of four organic chemicals that were totally
an aqueous solution that contained 18 PVC sol-
miscible in water: acetone, tetrahydrofuran,
vents and swelling agents, each with a relative
dimethylformamide, and pyridine. Acetone is a
good swelling agent of PVC (χ = 0.61 [Berens
solubility of 0.05, softened PVC. There was a sig-
4
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