O-08-617
SHEAR AND ELONGATIONAL FLOW BEHAVIORS OF LONG CHAIN
BRANCHED ETFE MELTS
Masataka Sugimotoa*, Eiichi Nishib, Takashi Satoub, Satoru Imaia, Kiyohito Koyamaa
a Yamagata University, Yonezawa 992-8510, Japan – sugimoto@yz.yamagata-u.ac.jp
b Asahi Glass Co., Ltd, Research and Development Div., Ichihara 290-8566, Japan
Abstract Rheological behavior of alternating ethylene-tetrafluoroethylene copolymer (ETFE) under shear andelongational flow was studied. Linear ETFE showed typical rheological behaviors as well as other linear polymer suchas polyethylen and polypropyrene. ETFE with long chain branch, however, showed outstanding behaviors. Thebranched ETFE indicated high G' at low frequencies, slow relaxation of relaxation modulus G(t), weak strain
dependency of damping function. Under elongational flow the branched ETFE showed strong deviation of elongational
viscosity from linear viscoelastic regime. This suggests enhanced processability of ETFE in film casting, film blowing,foaming, blow molding.
Keywords: ETFE, fluoropolymer, rheology, dynamic viscoelasticity, elongational viscosity
Introduction
Ethylene-tetrafluoroethylene copolymer (ETFE) iswidely used in many fields such as automobile, modernconstruction, airplane, solar battery panel areas due tothe high chemical and thermal resistant, flame
retardancy, weathering, an electric insulation
properties. Therefore ETFE is intensively explored on
the molecular parameters, microstructures,
crystallization behaviors, flow behaviors under steadyshear, flow instabilities. However, ETFE is one of
typical linear polymers and the improvement of therheological behavior by introducing the long chain
branch has not been reported.
Now more advanced control of rheologicalbehavior of ETFE is required for the wider applications
and precise processings in which ETFE has not beutilized owing to the limited rheological properties sofar. In this paper we try to introduce long chain branch
into ETFE and the shear and elongational flow
behaviors are reported.
Experimental
We used conventional ETFE (C88AX, Asahi GlassCo., LTD, Japan) and ETFE copolymerized with
divinyl compound, which is indicated as ETFE-B.
ETFE-B of weight percentages of 5, 10 and 30 wasblended with ETFE by twin-screw extruder, indicatedby notations of ETFE5, 10, 30, respectively.
Dynamic strain, frequency and temperature sweep
measurements were performed by Physica MCR-301(Anton Paar). Dynamic frequency tests were conductedfrom 0.1 to 100 rad/s at constant strain less than 0.05
and temperatures of 270 oC using parallel fixture.
Elongational viscosity was measured by rotationalrheometer (Ares, TA instruments) at constant rates andtemperature of 270 oC.
Mono-layer T-die cast film extrusion was carriedout by twin-screw extruder (φ=15mm, ULT-nano,Technovel Co., Japan). External gear pump was used
for constant volumetric flow rate.

Results and Discussion
Fig.1 shows storage (G’) and loss modulus (G”) ofETFE and ETFE-B at 270 oC. ETFE indicated terminal
flow behavior at low frequency range. On the other
hand, ETFE-B synthesized with divinyl compoundshowed much elastic viscoelastic behavior. Within themeasured frequency G’ was always higher than G”. G’
is parallel to G” at high frequency and the slope of G’leveled off with decreasing with frequency. This means
an existence of very long time relaxation component.

Fig.1 Storage and loss modulus of ETFE and ETFE-Bat 270 oC

Fig.2 Storage and loss modulus of ETFE blended withETFE-B (5, 10, 30 wt%) at 270 oC

Proceedings of the Polymer Processing Society 28th Annual Meeting ~ PPS-28 ~ December 11-15, 2012, Pattaya (Thailand)Fig.2 shows linear viscoelasticity of ETFE
blended with ETFE-B (5~30 wt%) at 270 oC. At highfrequency G’s of the blend samples were slightly
higher than ETFE. G’ of the blends at low frequency
increased with increasing the weight ratio of ETFE-B.
This is due to introduction of long relaxation timecomponent of ETFE-B which dispersed in ETFE.
Transient elongational viscosity of ETFE andETFE-B blends are illustrated in Fig.3. Linear ETFE
mere showed smooth increase of elongationalviscosity. The curves were independent of strain rate
and merged into one curve. The elongational viscosityof ETFE blended with EtFE-B exhibited steep increaseat a certain time, depended on the strain rate. ETFE30
showed the strong increase of elongational viscosity incomparison with ETFE10. This strong strain hardening
is nonlinear behavior and never expected to linear
ETFE. A small amount of the divinyl compound wasused to copolymerize with ETFE. The branch structure
can be expected for copolymerization of ethylene,
tetrafluoroethylene and divinyl compound. If the startype branching structure was formed for ETFE-B, thenonlinear viscoelastic behavior should not changed theway graft, pom-pom and random types branced
polymer do under elongational flow, while the linear
viscoelastic response was changed. Therefore we

consider that ETFE-B includes long chain branchedmolecules with two branching point at least.
We carried out T-die film casting extrusion ofETFE and ETFE-B blends. It was found that the neckin length was reduded according to the incorporated
ratio of ETFE-B, comparing with that of linear ETFE.
In the film casting uniaxial flow is dominant at edge
part of the film, while the rest is mainly subjected byplanar flow. We consider that the strain hardening
behavior of ETFE-B suppressed the neck-in length ofcasted film.
Conclusions
ETFE was modified by the incorporation of divinyl
compound in the copolymerization process. ETFE-B
copolymerized with divinyl compound and the blendswith ETFE showed very long relaxation time andpronounced strain hardening behavior underelongational flow which can never be expected forconventional fluorinated polymer. We confirmed thatthe enhanced rheological behavior provide thebeneficial effect on the T-die film casting extrusion
process.

Fig.3 Transient elongational viscosity of ETFE,ETFE10, ETFE30 at 270 oC

Proceedings of the Polymer Processing Society 28th Annual Meeting ~ PPS-28 ~ December 11-15, 2012, Pattaya (Thailand)