EFFECT OF PHYSICAL CROSSLINKING OF PVC/DOP GEL ON
SHEAR AND ELONGATIONAL FLOW: UNIVERSALITY OF
ELASTICITY
Masataka Sugimoto*, Yuji Aoki, Takuya Suzuki, Kentaro Hirayama, Sathish K. Sukumaranand Kiyohito Koyama
Graduate School of Science and Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa,Yamagata, 992-8510 Japan

E-mail of corresponding author: sugimoto@yz.yamagata-u.ac.jp
ABSTRACT
Shear and elongational behavior of mixtures of poly(vinyl chloride) (PVC) and dioctyl
phthalate (DOP) were studied using different molecular weights of PVC. PVC/DOP showedbehaviour typical of a gel below a critical temperature and the gel was thermoreversible. The shear
moduli and apparent start-up elongational viscosity of the PVC/DOP gels were examined at a fixed
relative distance to the gelation temperature, α. The moduli and the apparent viscosity exhibited
universality, i.e., the data for all three molecular weights could be superposed at a fixed α.

1. INTRODUCTION
PVC forms physical gels in various
solvents. Gelation can be induced either byvarying the concentration or the temperature [13]. At the critical gel point, the storage modulus(G′) and the loss modulus (G′′) exhibit powerlaw dependence on the angular frequency, ω,with identical power-law exponents [4]:G′(ω) = G′′(ω)/tan δ ∝ ωntan δ = tan(nπ/2).

(1)
(2)

The power-law exponent, n, is a characterstic
property of the network and is between 0 and 1.
For PVC, the relaxation exponent n ≈ 0.75 andhas been found to be independent of themolecular weight, the molecular weight
distribution, concentration of the polymer,
temperature, solubility of the plasticizer in thePVC, see [2,3] and the references therein. Thissuggests that, in general, PVC critical gelspossess roughly similar fractal network
structures.
In this study, we investigate the temperatureinduced gelation in PVC/DOP mixtures at a
fixed polymer concentration. In order to remove
the complications arising from the processing

and thermal history and various additives, weused the method introduced by Aoki [5] toprepare the PVC/DOP samples. The dynamic
modului and the elongational viscosities weremeasured and analyzed.
2. EXPERIMENTAL
PVC of weight-average molecular weights
61.9, 102 and 173 kg/mol (denoted as PVC6,
PVC10 and PVC17 respectively) andpolydispersity approximately were used. Thesuspension polymerized PVCs were supplied by
Mitsubishi Chemical Coorporation.
PVC/DOP mixtures with 20 wt% of polymer
were prepared by Aoki's method [5] mentionedabove. We confirmed that the method could
remove the processing history of the sample bynoting that no detectable change in therheological data was observed when themeasurements were repeated after 1 and 2months. The reproducibility of all of the datareported here was confirmed in this way.
The dynamic oscillation measurements anduniaxial elongational tests were carried out atdifferent temperatures using a rotationalrheometer (Ares, TA instruments).

3. RESULTS AND DISCUSSION
In order to probe the linear rheology, dynamic
viscoelastic measurements of three PVC/DOP
mixtures were carried out at varioustemperatures. For all of the samples, thebehaviour that was sol-like at high tempertures
became gel-like as the temperature was reduced.
At Tgel, the dynamic moduli obey Eqs. (1) and(2). Therefore, for each of the samples, weplotted tan δ versus ω at different temperatures,T. Using the plots, we determined the gelation
temperature, Tgel, as the temperature at which thetan δ became independent of ω. The determined
Tgel increased with an increase in the molecularweight of the PVC.
The dynamic modului of the gels were foundto be a function of both the molecular weight of
the PVC and the temperature. Using the value ofthe storage modulus at low frequencies andclassical rubber elasticity, we calculate theapproximate molecular weight of the networkstrands (see Fig. 1). Note that the calculated
molecularweight
between strands
issignificantly larger than the molecular weight of
the PVC chains. Further, the strand molecularweight depends only on the relative distancefrom Tgel, α = |T −Tgel|/Tgel, except for α = 0.05.
The reason for the lack of universality for α =0.05 is currently unclear.

using the same three PVC/DOP mixtures. The
samples displayed strong strain hardening below
their respective gel points. At a given
temperature, the higher molecular weightsample displayed stronger strain hardening.
However, similarly to the linear moduli, theapparent viscosity under start-up uniaxial
elongations for all of the samples could also besuperimposed at a fixed α, except for α = 0.05.

Fig. 2 Universality of noninear Viscoelasticity:
Apparent viscosity during start-up uniaxial
elongation for α = 0.25.
4. SUMMARY
We studied the rheological behavior ofPVC/DOP gels for three molecular weights ofPVC but at an identical polymer concentration.
For the three samples investigated, the dynamicmoduli and the apparent viscosity during startup uniaxial deformation could be superimposed
at equal α, except for α = 0.05. In addition, themolecular weight of the gel calculated usingclassical rubber elasticity is significantly larger
than the molecular weight of the PVC chains.

Fig. 1 Universality of Linear Viscoelasticity:“molecular weight of the network strand” as afunction of α.
We also performed start-up uniaxial
elongation experiments at various temperatures

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