Slip effects in HDPE flows

Entry flows of polylactides with slip

“…6 plots the ends correction (pressure drop for capillary extrusion with die length L/D = 0) for the four PLAs at 180°C, for an extended range of the apparent shear rate from 11 s À1 to 650 s À1 . The highest results are obtained for the PLA 7001D, but even for this melt the results hardly exceed 1 MPa, which is far less than the results obtained for the LDPE [32] and HDPE [25] Table 1 as a function of the wall shear stress at 180°C. It is noted that the slip velocity increases with a decrease in molecular weight.…”

“…We observe that the average relaxation times are in the order of 1 s. These values indicate elastic melts with moderate average relaxation times, but certainly less elastic than typical low-density polyethylene (LDPE) and high-density polyethylene (HDPE) melts studied before [25,32]. It is to be noted that these average relaxation times are not used anywhere, but are given as an indication of the elasticity level of the melts.…”

“…The results for L/D = 0 were obtained as in our previous works [25,32] by subtracting from the longest dies results obtained for the same dies without the reservoir. Thus, it was found again necessary to use long dies to fully unravel the viscoelastic stresses of the PLA melts.…”

“…This might be expected due to their linear structure and similarities with other linear molecules that exhibit slip and melt fracture [17][18][19][20][21][22][23][24]. In flow simulations, such effects (slip) should be taken into account in order to model/describe experimental results accurately [25].…”

Rheology of organoclay assisted extrusion of HDPE using Particle Image Velocimetry

“…This type of measurement was used in planar couette (Hatzikiriakos and Dealy, 1991;Reimers and Dealy, 1996;Dhori et al, 1997), torsional (Mackay and Henson, 1998;Yoshimura and Prud'homme, 1988;Hay et al, 2000) and pressure driven (Kalika and Denn, 1987;Hay et al, 1999;Yang et al, 1998) shear flows. Direct methods have been employed more recently due to their higher sensitivity to wall slip than the other methods (Archer, 2005;Ansari et al, 2012;Kaoullas and Georgiou, 2013), and they provide 'direct' quantitative measurement of the relative motion of the polymer melt and solid at the interface. These methods include fringe pattern fluorescence recovery after photo bleaching (Migler et al, 1993), hot film (Kraynik and Schowalter, 1981;Lim and Schowalter, 1989), and local velocimetry (Mhetar and Archer, 1998;Rodríguez-González et al, 2010;Münstedt et al, 2000;Robert et al, 2004;Mitsoulis et al, 2003;Fournier et al, 2009;Mackley and Moore, 1986;Nigen et al, 2003) methods.…”