EFFECT OF PHYSICAL GELATION STRUCTURE ON
VISCO-ELASTICITY IN POLYPROPYLENE.
H. Uematsu, M. Sugimoto, T. Taniguchi, K. Koyama
Yamagata Univ. Jonan 4-3-16, Yonezawa, 992 JAPAN uematsu@ckpss.yz.yamagata-u.ac.jp
In this study we investigated effects of the network structure of sorbitol nucleator containing 0.5wt% on non-linear
visco-elasticity of the polypropylene (PP). We used (1,3:2,4-bis-O-(p-methylbenzylidene)-D-sorbitol) (PDTS) as ageleator in this study. From the data of linear visco-elasticity, it was found that the blend sample (PP/PDTS) exhibited aphysical gel behavior at 170 oC. On the other hand, PP/PDTS did not show a physical gel behavior at 210 oC. Theseresults mean that the network structure of PDTS depends on temperature. In order to clarify the role of the network
structure, we investigated a non-linear visco-elasticity at 170 oC. First, we carried out steady shear viscocity
measurements. In the measurements, we observed stress overshoots and found in the range of strain rate less than 0.1s-1
that the stress at the steady state does not depend on strain rate. Secondly, we performed measurments of uniaxial
elongational viscosity of PP/PDTS. The PP/PDTS showed a non-linearity of viscosity in lower strain rate less than 0.1s1. We concluded that the non-linearity of viscosity of start up shear and elongatinonal flow are caused by breakage ofPDTS network because network is fragile gel.
Introduction
Nucleator agent has been effectively used to enhance the crystallization of crystalline polymer. Sorbitol nucleator isusually used in polypropylene (PP) as a nucleation agent. It is reported that crystallization temperature (Tc) of PP andcrystallization rate are increased by addition of sorbitol nucleator1). However, the effect of sorbitol nucleator is not only
an enhancement of crystallization but also a change of linear visco-elasticity due to a network formed by sorbitol
nucleator in molten polymer.2) In polymer processing, polymer melt and polymer liquid go though a large deformation
and are molded into shape.We focus on network structures formed by sorbitol nucleators and study the effect of sorbitol
nucleator on non-linear visco-elasticity in PP.
Experimental-MaterialsAs a nucleator we selected (1,3:2,4-bis-O-(p-methylbenzylidene)-Dsorbitol) (PDTS) provided by New Japan Chemical co. LTD.. Figure1
shows the chemical structure of MDBS. The matrix polymer is isotactic
polypropylene provided by Chisso petrochemical Corporation.
-Coordination of sampleWe mixed PDTS (0.5wt%) and PP by a mixer (Toyo Seiki Seisakusho,LTD.). Mixing temperature is 210oC, screws revolution speed is
50rpm and mixing time is 5 minutes. Test specimens for dynamic viscoelasticity were molded by a hot press (Toyo Seiki Seisaku-sho,LTD.)at 230oC. Hereafter the blend sample is referred as PP/PDTS.
-AnalysisBoth dynamic visco-elasticity and uniaxial elongational viscosity
measurement were performed by ARES (TA instruments). Steadyshear viscosity measurements were performed by using Physica MCR(Anton-Paar). History of temperature is shown in Figure 2.

Figure 1 Chemical structure of sorbitol
nucleator used in this study

Figure 2 History of temperature usedin this study

Results and Discussion-Linear visco-elasticityDynamic visco-elasticity of PP and PP/PDTS were measured by frequency sweep mode at different 6 temperatures (170,180, 190, 200, 210, and 220 °C), which are substantially above their melting temperature, Tm. At high temperature, theslopes of G’ and G” for PP respectively approach to 2 and 1 in the low frequencies. The time-temperature superposition
could be applied over the entire temperature range.
In contrast, the PP/PDTS system expressed a gel behavior at low temperatures (T ≤ 190 °C). The slopes of G’ andG” in the PP/PDTS system showed almost the same values at each temperature. However, at high temperatures (T ≥200 °C), the PP/PDTS indicated same viscoelastic of PP. Figure 3 shows the tan δ at different ω vs. T plots for thePP/PDTS system. From the ω-independent tan δ point, the critical gel temperature (Tc) and n values could be
The Polymer Processing Society 23rd Annual Meeting5determined. It was found that Tc = 193 °C and n = 2/3. This n value
is in agreement with the value reported by Takenaka et al.3).
Therefor PDTS network depends on temperature, at low
temperature network forms in PP and at high tempearture networkdisappers in PP.

tan δ

3PP/PDTS

2-Start-up shear flowFigure 4 shows time dependence of steady shear viscosity (ηS) at
various strain rate for PP/PDTS at 170 °C. We observed stressovershoots in this system although PP did not show non-linear
viscosites. It seems that decrease of viscosities followed by the stressovershoot are caused by breakeage of PDTS network in shear flow
process.

1Tgel0443 453 463 473 483 493
T/K

Figure 3 Tanδ plotted against temperature
T for the PP/PDTS at various frequency.
105

T =170 oC0.005ηs / Pa s

0.0075

Acknowledgements
We would like to thank New Japan Chemical co. LTD. for supplied
the sorbitol nucleator (PDTS) and thank Dr. Aoki for having avaluable discussion with about a sol-gel transition.
References
1) R-D. Mair, C. Wang, R. Yhomann, C. Friedrich, R. Mulhaupt
Proceedings of Aannual Meeting Polymer Processing Society
PPS 16 in Netherlands, 2000
2) S. Yamasaki, Y. Ohashi, H. Tsutsumi, and K. Tsujii Bull. Chem.
Soc. Jpn., 68, 146-151 (1995)
3) Takenaka M, Kobayashi T, Saijo K, Tanaka H, Iwase N,Hashimoto T, Takahashi M J Chem Phys 121, (7), 3323-3328 (2004)

0.05

0.1
104
10010

1102341010t/ s
Figure 4 Time dependence of shear viscosity
at various strain rates for PP/PDTS at 170 °C.
10

7-1

10

6

0.5s

-1

0.02s

1.0s

0.05s

-1

2.0s

-1

3.0s

510

4T = 170 C
PP/PDTS-1-1
-1

0.1s

10o-1

0.01s

ηE / Pa sConclusion
We have investigated the linear and non-linear viscoelastic
measurements of a PP/PDTS system. It was found that the PP/PDTSsystem exhibited a sol-gel transition (Tc) at 193 °C. In large
deformation flow, non-linear properties were caused by breakege ofnetwork because PDTS network is fragile gel.

0.01
0.025

3η+(t):PP/PDTS
3η+(t):PP

3

10-2
1010-1

10010

1102t/sFigure 5 Time dependence of uniaxial
elongational viscosity at various strain rates
for PP/PDTS at 170 °C.
106o

T=170 C
105

σMax/Pa-Start-up uniaxial elongational flowFigure 5 shows time dependence of uniaxial elongational viscosity(ηE(t)) at various strain rates for PP/PDTS at 170 °C. Solid line anddotted-line stand for 3η+(t) that are evaluated by using data ofdynamic visco-elasticity of PP/PDTS and PP, respectively. It isfound that the ηE(t) exhibited strong strain-softening. ηE(t) decreased
with increasing ε& at ε& ≤ 0.1s-1. Above 0.5 s -1, ηE(t) is in goodagreement with 3η+(t) of PP. These results imply that the network
structure of PDTS was destroyed at higher strain rates. Figure 6
shows the maximum elongational stress σMax plotted against ε& for
the PP/PDTS system at 170 °C. σMax is the ruputure stress of thestrand sample under the elongational process. Closed and opensymbols respectively denote σMax of iPP and PP/PDTS. The σMaxvalues of PP/PDTS at high ε& (≧0.5s-1) agree with those of iPP.
However, they deviate from those of iPP at low ε& (≦0.1s-1) andindicate a constant value of 104 Pa. This result implies that thenetwork structure of PDTS was broken above critical stress about 104
Pa.

0.158
0.1
0.03980.01584

opened symbol : PP/PDTS10410

3

closed symbol : PP10-2

10-1

0.
10ε / s-1101Figure 6 Maximun stress plotted against
strain rate for PP/PDTS and PP at 170 oC.
The Polymer Processing Society 23rd Annual Meeting