Further Studies on the Softening of Rigid PVC
by Aqueous Solutions of Organic Solvents
LOUISE V. PARKER AND THOMAS A. RANNEY
INTRODUCTION
Table 1. Literature values for the Flory-Huggins
interaction parameter, χ.
It has been known for some time that some
From
From
neat (undiluted) organic solvents can dissolve or
Organic chemical
Berens (1985)
Vonk (1985)
swell PVC well casings and screens. Products that
can dissolve PVC are referred to as PVC solvents,
acetone
0.61
--
and products that do not dissolve PVC but can
--
0.87
cause it to swell are referred to as swelling agents
benzene
0.83
0.83
of PVC. There has been concern that PVC casings
2-chloroaniline
--
0.58
3-chloroaniline
--
0.61
and screens might be degraded by well water
chlorobenzene
--
0.66
containing ppm and ppb levels of these chemi-
chloroform
0.64
--
cals. In the past few years, we have conducted a
1,2-chlorotoluene
--
0.74
series of studies (Taylor and Parker 1990, Parker
1,3-chlorotoluene
--
0.69
et al. 1992, Parker and Ranney 1994, 1995) to ad-
1,4-chlorotoluene
--
0.75
dress this issue.
1,2-dichlorobenzene
--
0.63
The solvent interaction parameter (χ) used in
1,3-dichlorobenzene
--
0.74
the Flory-Huggins equation* has been commonly
1,1-dichloroethane
< 0.68
--
used as a measure of the solvent or swelling power
1,2-dichloroethane
< 0.55
0.56
of a particular organic solvent (Berens 1985, Vonk
1,2-dichloropropane
0.68
0.65
1985, 1986, Jenkins et al. 1986). Table 1 gives χ
di-isopropylketone
--
0.56
values for a number of organic chemicals that
ethylbenzene
--
0.89
were derived experimentally† by Berens (1985) at
n-methylaniline
--
0.59
30C and by Vonk (1985) at 20C. PVC is reported
methylene chloride
< 0.53
0.55
to be softened only by solvents with a χ value less
methyl ethyl ketone
--
0.54
than 1 (Berens 1985) or 1.2 (Vonk 1985); the lower
nitrobenzene
--
0.54
propylbenzene
--
1.91
the number the greater the solvent or swelling
power. Also, a neat solvent with a χ value less
1,1,2,2-tetrachloroethane
--
0.59
tetrachloroethylene
1.17
1.58
toluene
0.80
0.82
1,2,4-trichlorobenzene
--
1.52
1,1,1-trichloroethane
0.85
0.92
* The Flory-Huggins equation relates activity (a) to the vol-
1,1,2-trichloroethane
< 0.56
0.58
ume fraction (V1) of the organic chemical in the polymer as
follows:
trichloroethylene
0.88
0.90
1,3,5 trimethylbenzene
--
2.52
ln (a) = ln V1 + (1 V1) + χ(1 V1) 2
vinyl chloride
0.98
--
where χ is the Flory-Huggins interaction parameter.
xylene
0.88
--
1,2-xylene
--
0.76
Berens (1985) and Vonk (1985) derived χ by exposing PVC
†
1,3-xylene
--
0.87
to different activities of organic chemicals in vapor and solu-
1,4-xylene
--
0.86
tion.
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