LAOS and uniaxial elongational flow behavior ofPoly(vinyl chloride)/bis(2-ethylhexyl) phthalate blend
Koji KIKUCHI, Kentarou HIRAYAMA, Masataka SUGIMOTO, Takashi TANIGUCHI*,
Yuji AOKI and Kiyohito KOYAMA
Graduate School of Science and Engineering, Yamagata University,
Graduate School of Engineering, Kyoto University*
kikuchi@ckpss.yz.yamagata-u.ac.jp
1. Introduction:
Poly(vinyl chloride) (PVC) is widely used due to the ease with which its properties can betuned by the addition of plasticizers. In fact, plasticized PVC remains elastic even upon addition oflarge quantities of plasticizer. This is because the PVC molecules undergo gelation into a threedimensional molecular network. In addition, the crosslinks leading to the gel state aremicrocrystallites of PVC. Consequently, the gel that is formed is a physical gel and isthermoreversible.
A significant amount of research has been devoted to the elucidation of the variation of thephysical properties of PVC gels with temperature [1], concentration [2], etc. The structure of thePVC gel is generally thought to be adequately described by the fringed-micelle model [3]. Themodel describes the gel as being composed of microcrystalline domains, which act as crosslinks
with flexible chains connecting the microcrystalline domains. In spite of this, the mechanism ofgelation in PVC and also the structure of PVC gels are hitherto only poorly understood. In order toshed further light on these topics here we study the variation of the gel properties with temperature,especially focusing on the connection between gel structure and rheological properties.
2. Material:
We used three different molecular weights of commercial poly(vinyl chloride) (labeled asPVC06, PVC10 and PVC17). The PVC was made using suspension polymerization by Mitsubishi
Chemical Co. Three gelling systems of the PVC in bis(2-ehylhexyl)phthalate (DOP) were preparedat room temperature from THF solutions (about 80 wt% of THF). No stabilizers were added to thesolutions. After the THF evaporated completely, the solid film obtained was used for further testing.
3. Experiment:
Linear viscoelastic measurements were carried out at various temperatures between 60ºC and175ºC with a strain controlled rheometer (ARES, TA Instruments) using parallel plate geometry(diameter is 25 mm). Elongational viscosity measurements were performed with ARES using theelongational viscosity mode at several temperatures between 30ºC and 150ºC. The strain rates usedwere between 0.1 to 1.0 s-1. Large amplitude oscillatory shear (LAOS) measurements were carriedout with ARES using the parallel plate fixture at several temperatures between 30ºC and 172ºC. The
strain amplitude ranged from 10 to 400% with the angular frequency fixed at 1 rad/s.
4. Result and Discussion:
Fig.1 shows G’ versus ! curves for PVC06 at 6 different temperatures: 60, 80, 100, 120, 130
and 140ºC. The curves indicate that the behavior changes from that of a sol at high temperatures tothat of a crosslinked gel at low temperatures. At the intermediate temperature of 130ºC, we foundthat105

G '(! ) " G"(! ) " !

nPVC06104oG' [Pa]60 C
with n=0.75 [4]. This behavior is the well known
80oC
rheological signature for the occurrence of a critical gel
103
100oC
and was used to deduce the critical gel temperature of102
PVC10 and PVC17 also.
120oC
Fig.2 shows the start-up elongational viscosity of101
130oC
PVC06 at several strain rates at 60ºC. It is clear that the140oC
010material exhibits strain hardening and similar behavior
10-2
10-1
100
101102was found for the other two PVC samples. Further, if! [rad/s]
we consider the start-up elongational viscosity of the Fig.1 Strage modulus G’ of PVC06 plotted against
different samples at the same fractional undercooling, angular frequency ! for various temperature.
",
7106

Tgel

!E+(t,") [Pa s]!"10

T # Tgel.

PVC0660ºC

510
where T is the measurement temperature and Tgel is the.
critical gel temperature, we find that the different curves
104
could essentially be superimposed. This behavior is0.1(1/s)
103
showen in Fig.3 and suggests that the network structure
0.3
1.0
in the PVC/plasticizer system is determined only by the102 -2
1010-1100
101
102
value of ".
t [s]Moreover, we carried out LAOS measurements, Fig.2 Time dependence of uniaxial elongational
and we examined the relation with gel structure. viscosity at various strain rates for PVC06 at 60ºC
Details will be provided during the presentation.
108!E+(t,") [Pa s]

5. Conclusion:
We carried out three kinds of measurements.
.
Using the linear viscoelasticity measurement wedetermined the critical gel point of the samples. .
During theuniaxial elongational viscosity
measurement, all of the blend systems showed strain
hardening and the elongational curves could besuperimposed by considering the relative distancefrom the critical temperature.

107#=0.15

106
105
104
10

PVC06 60ºC

3102 -2
10

PVC10 84ºC
PVC17 105ºC
10-1

t [s]

100

101

Fig.3 Time dependence of uniaxial elongational
6. Reference:!
[1] Lopes, D. Mijangos, C. Munoz, M. E. viscosity. strain rates: 1.0, for PVC06, PVC10 and
PVC17 at same ".
Santamaria, A. Macromolecules, 29, 7108, 1996#
[2] A. T. Walter, J. Polym. Sci., 13, 207, 1954#
[3] A. Keller, Faraday Discuss. 1, 101, 1995#
[4] L. Li, Y. Aoki, Macromolecules, 30, 7835, 1997