TY - JOUR
T1 - Kinematics of the stick-slip capillary flow of high-density polyethylene
AU - Rodríguez-González, Francisco
AU - Pérez-González, José
AU - Marín-Santibáñez, Benjamín M.
AU - de Vargas, Lourdes
N1 - Funding Information:
This research was supported by CONACYT (CIAM 51837K) and SIP-IPN (20082313, 20080302). F.R.-G. and B.M.M.-S. had CONACYT and PIFI-IPN scholarships to carry out this work. J.P.-G. and L. de V. are COFFA-EDI fellows.
PY - 2009/11/16
Y1 - 2009/11/16
N2 - A study of the kinematics of the stick-slip capillary flow of high-density polyethylene has been carried out in this work by using particle image velocimetry (PIV). The experiments covered a wide range of shear rates and the velocity maps and profiles across the die were obtained for the different regimes of the discontinuous flow curve. In the low shear rate region, the melt exhibited shear thinning without slip. In the unstable stick-slip regime, an alternating behavior between full adhesion and slip was observed, whereas both, the maximum velocity and the slip velocity of the melt, changed continuously during pressure oscillations. In addition, non-homogenous slip, characterized by regions with and without slip at the die wall, was occasionally observed during the oscillations. In contrast to the general assumption, the flow in the high shear rate region was found to be unstable, and characterized by high frequency pressure oscillations. A steep rise of the slip velocity took place from the onset of the stick-slip regime and reached values higher than 70% of the maximum velocity for the profiles in the high shear rate branch. However, a true plug flow was never observed due to shear thinning of the melt. Finally, a direct proof of the Mooney hypothesis to account for slip in polymer melts is given on the basis of the comparison of velocity profiles measured in the low and high shear branch.
AB - A study of the kinematics of the stick-slip capillary flow of high-density polyethylene has been carried out in this work by using particle image velocimetry (PIV). The experiments covered a wide range of shear rates and the velocity maps and profiles across the die were obtained for the different regimes of the discontinuous flow curve. In the low shear rate region, the melt exhibited shear thinning without slip. In the unstable stick-slip regime, an alternating behavior between full adhesion and slip was observed, whereas both, the maximum velocity and the slip velocity of the melt, changed continuously during pressure oscillations. In addition, non-homogenous slip, characterized by regions with and without slip at the die wall, was occasionally observed during the oscillations. In contrast to the general assumption, the flow in the high shear rate region was found to be unstable, and characterized by high frequency pressure oscillations. A steep rise of the slip velocity took place from the onset of the stick-slip regime and reached values higher than 70% of the maximum velocity for the profiles in the high shear rate branch. However, a true plug flow was never observed due to shear thinning of the melt. Finally, a direct proof of the Mooney hypothesis to account for slip in polymer melts is given on the basis of the comparison of velocity profiles measured in the low and high shear branch.
KW - Extrusion
KW - High-density polyethylene
KW - Particle image velocimetry
KW - Polymer processing
KW - Rheology
KW - Stick-slip
UR - http://www.scopus.com/inward/record.url?scp=70349496369&partnerID=8YFLogxK
U2 - 10.1016/j.ces.2009.02.033
DO - 10.1016/j.ces.2009.02.033
M3 - Artículo
SN - 0009-2509
VL - 64
SP - 4675
EP - 4683
JO - Chemical Engineering Science
JF - Chemical Engineering Science
IS - 22
ER -