TY - JOUR
T1 - Rheo-optical characterization of liquid crystalline acetoxypropylcellulose melt undergoing large shear flow and relaxation after flow cessation
AU - Teixeira, Paulo F.
AU - Fernandes, Susete Maria Brazão Nogueira
AU - Canejo, João Paulo Heitor Godinho
AU - Godinho, Maria Helena Figueiredo
AU - Covas, Jose A.
AU - Leal, Catarina
AU - Hilliou, Loic
N1 - Sem PDF.
This work was partially supported by the Portuguese Science and Technology Foundation through projects, PTDC/CTM/099595/2008, PTDC/CTM/101776/2008, PTDC/CTM-POL/1484/2012 and UID/CTM/500025/2013. S.N. Fernandes and J.P. Canejo acknowledge FCT for grants SFRH/BPD/78430/2011 and SFRH/BPD/101041/2014, respectively. Funding for project "Matepro e Optimizing Materials and Processes", with reference NORTE-07-0124-FEDER-000037 FEDER COMPETE, is also acknowledged.
PY - 2015/8/5
Y1 - 2015/8/5
N2 - The rheological and structural characteristics of acetoxypropylcellulose (APC) nematic melt are studied at shear rates ranging from 10 s(-1) to 1000 s(-1) which are relevant to extrusion based processes. APC shows a monotonic shear thinning behavior over the range of shear rates tested. The negative extrudate-swell shows a minimum when a critical shear rate (gamma) over dot(c) is reached. For shear rates smaller than (gamma) over dot(c), the flow-induced texture consists of two set of bands aligned parallel and normal to the flow direction. At shear rates larger than (gamma) over dot(c), the flow induced texture is reminiscent of a 2 fluids structure. Close to the shearing walls, domains elongated along the flow direction and stacked along the vorticity are imaged with POM, whereas SALS patterns indicate that the bulk of the sheared APC is made of elliptical domains oriented along the vorticity. No full nematic alignment is achieved at the largest shear rate tested. Below (gamma) over dot(c), the stress relaxation is described by a stretched exponential. Above (gamma) over dot(c), the stress relaxation is described by a fast and a slow process. The latter coincides with the growth of normal bands thicknesses, as the APC texture after flow cessation consists of two types of bands with parallel and normal orientations relative to the flow direction. Both bands thicknesses do not depend on the applied shear rate, in contrast to their orientation. (C) 2015 Elsevier Ltd. All rights reserved.
AB - The rheological and structural characteristics of acetoxypropylcellulose (APC) nematic melt are studied at shear rates ranging from 10 s(-1) to 1000 s(-1) which are relevant to extrusion based processes. APC shows a monotonic shear thinning behavior over the range of shear rates tested. The negative extrudate-swell shows a minimum when a critical shear rate (gamma) over dot(c) is reached. For shear rates smaller than (gamma) over dot(c), the flow-induced texture consists of two set of bands aligned parallel and normal to the flow direction. At shear rates larger than (gamma) over dot(c), the flow induced texture is reminiscent of a 2 fluids structure. Close to the shearing walls, domains elongated along the flow direction and stacked along the vorticity are imaged with POM, whereas SALS patterns indicate that the bulk of the sheared APC is made of elliptical domains oriented along the vorticity. No full nematic alignment is achieved at the largest shear rate tested. Below (gamma) over dot(c), the stress relaxation is described by a stretched exponential. Above (gamma) over dot(c), the stress relaxation is described by a fast and a slow process. The latter coincides with the growth of normal bands thicknesses, as the APC texture after flow cessation consists of two types of bands with parallel and normal orientations relative to the flow direction. Both bands thicknesses do not depend on the applied shear rate, in contrast to their orientation. (C) 2015 Elsevier Ltd. All rights reserved.
KW - Cellulose derivative
KW - Extrusion
KW - Liquid-crystal
KW - Rheo-optics
U2 - 10.1016/j.polymer.2015.06.056
DO - 10.1016/j.polymer.2015.06.056
M3 - Article
SN - 0032-3861
VL - 71
SP - 102
EP - 112
JO - Polymer
JF - Polymer
ER -