Comparison of the Supercooled Uniaxial Elongational Behavior andFlow-induced Crystal Stracture of PE/UHMW-PE Blends
Ryohei Komuroa, Yuji Jinboa, Takashi Taniguchib, Masataka Sugimotoa, Kiyohito Koyamaa,
aGraduate School of Science and Engineering, Yamagata University, Yonezawa, Yamagata, Japanb
Department of Chemical Engineering, Kyoto University, Kyoto, Japane-mail; komuro@yz.yamagata-u.ac.jp

1. Introduction:
It is known that when semi-crystalline polymers in melts are crystallized under flows theso-called shish-kebab structure is often formed. It is believed that the long chain plays an importantrole to form the shish-kebab structure. Recently, many researchers report about the effect ofultra-high molecular weight (UHMW) component on the shish-kebab formation process under shear
flow [ref. 1-3]. They reported that entanglements of UHMW chain have a significant influence on
the shish-kebab structural formation. Generally, the strain-hardening under an elongational flow isoften observed for polymer melts with a long relaxation time component. In homopolymer system,
the strain-hardening is believed to be arisen from the stretching of the polymer chain to thedirection of flow. Minegishi et al. [ref. 4] reported that the enhancement of strain-hardening was
greatly affected by entanglements among a small amount of UHMW chains which were added tostandard molecular weight distribution analogue.
Generally, the uniaxial elongational flow behavior has conspicuous difference to the shear flow
behavior. It is thought that this difference will affect the flow-induced crystallization behavior.
However, the most of study about the flow-induced crystallization were investigated under shear
flow. Therefore, the aim of this study is to evaluate the effect of UHMW component on the uniaxial
elongational behavior under supercooled condition and the crystal structure.
2. Experimental:
We used two types of linear polyethylene that themolecular weights are      and     , respectively. We prepared the blend samples
in which UHMW-PE of 0, 0.5, 1, 3, 5, and 10wt% isadded, respectively (e.g. CUHMW-PE =3wt% is labeled as
PE3). The uniaxial elongational measurement wasmeasured by Meissner-type rheometer (Toyo Seiki
Seisaku-sho Co, Melten Rheometer). The temperature Fig. 1 Temperature protocol for the supercooled
protocol for the uniaxial elongational viscosity uniaxial elongational measurements
measurements is shown in Fig. 1. We obtained the crystal structure of the extended samples after
the supercooled elongational measurements for SAXS measurements (Rigaku, Micro Max-007HF).
3. Results and discussions:Fig. 2(a) depicts the uniaxial elongational viscosity     of PE0, PE3, and PE10 at various
elongational strain rates  and 130 oC. The strain-rate-independent linear elongational viscosity
increases with increase of CUHMW-PE. The strain-hardening starts to appear above a critical strain( ). The critical strain was found to be independent of the strain rates. To compare thestrain-hardening behavior among PE0-10, we defined the strain-hardening parameter  ) and T=130 oC.
 !"# $  !"# . Fig. 2(b) depicts %& as function of  for PE0-10 at  ' (As seen from Fig. 2(b),  is found to be almost independent of CUHMW-PE. The slope of %& versus
 are enhanced with increase of CUHMW-PE because of the increase of long relaxation time component.
To analyze quantitatively, we defined the strain-hardening intensity * (the slope of %& versus ).
* as function of CUHMW-PE is shown in Fig. 2(c). * starts to increase between CUHMW-PE + ,-. Thesevalues which start to show stronger
strain-hardening
hardening may be related to theentanglement number of UHMW-PE
chains 34. PE01 and PE05 give 34 valueof 1.4 and 6.8, respectively. From theseresults,
itisfoundthat
thestrain-hardening
hardening is enhanced by theentanglements among UHMW-PE
UHMW
chains,and the enhancement of strain-hardening
strainare almost zero above the entanglement
number of UHMW--PE chains 34 7 8.34
is estimated as follows;
follows
34  CUHMW-PE(MUHMW-PE(1)
PE/ Me)where MUHMW-PE and Me are the molecularweight of UHMW-PE
PE and the molecularweight between entanglement  8 9:
Fig. 2 (a)Uniaxial
Uniaxial elongational viscosity of PE0,3,10 at 130o)C under various  . (b) as function of  at  ' ( at56% [ref. 5], respectively.
respectively
130 oC. (c)*as function of CUHMW-PE at various  .
Fig. 3(a) shows the 2D SAXS patterns ofthe stretched PE10 up to  ' 1 at 2() .
This
his 2D SAXS pattern clearly showedshish-kebabkebabstructure.
Toanalyze
quantitatively, the degree of orientation oflamellar in the stretched sample of PE0,
PE3, and PE10 around  () and  ()at various  was determined by using theFig. 3(a) 2D SAXS patterns of the stretched PE10 up toHerman’s method [ref. 6] in Fig. 3(b)(c). .
 ' 1 at 2( ) .. as function of PE0, PE3, and PE10
starts to increase above critical-orientation
critical))around (a)  ( and (b)  ( at various .
# strain (   ),, and . enhanced withincrease of  and CUHMW-PE. Fromrom the comparison between the strain-hardening
hardening and orientation
function . , the critical strain of strainstrain-hardening (   ) and thehe critical-orientation
criticalstrain
# ( ) exhibited almost same tendency. These results suggest that the forming of shish-kebabshish
structure is necessary to stretch the polymer chain to the flow direction, since the strain-hardening
strainisarose from the stretching of the long polymer chain to the direction of flow
flow. AtA higher strain region( / 0), the polymer chain is not able to stretch any further,, since the polymer chain are sufficientlystretched already. In case of PE0 around  (), since * is very weak, the polymer chain are notsufficiently stretched to the flow direction. From these results, we found that it is necessary tostretch the polymer chain above #  in order to form of shish-kebabkebab structure.
4. Summary:
We found that the reason for the enhancement of the forming of shish-kebab structure wasdominated by the stretching of UHMW
UHMW-PE chain. In our presentation, we explain more detail.
5. References:[1] Ogino, Y. Fukushima, H. Takahashi, N. Matsuba, G.. Nishida, K. and Kanaya, T.
Macromolecules. 39,, 7617, (2006)[2]] Seki, M. Thurman, D. W. Oberhauser, J. P. and Kornfield, J. A. Macromolecules. 35, 2583,(2002)[3]] Somani, R. H. Yang, L. Zhu, L. and Hsiao, B. S. Polymer 46, 8587, (2005)[4] Minegishi, A. Nishioka,ishioka, A. Takahashi, T. Masubuchi, Y. Takimoto, J. and Koyama, K. Rheol.
Acta. 40, 329, (2001)[5] Ferry, J. D. Viscoelastic properties of polymers, John Wiley & Sons, New York, (1980)[6] Alexander, L. E. X-ray
ray diffraction in polymer sciencescience, New York, Wiley, (1969)