Recovery of Shear-Modified Polybutadiene Solutions

Roland, C. M.; Robertson, Christopher G.

doi:10.5254/1.3547937

Cited by 15 publications

(23 citation statements)

References 38 publications

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“…If the acceptance criterion for a steady state has been raised, then the direction of the frequency sweep is not very important. Rapid effects in polymer melts have not been measured due to limitations of measurement devices, but similar results have been found for polymer solutions, for which the timescale of transitions is longer [16].…”

Section: Simulations Of Transient Start-up and Cessation Viscositiessupporting

confidence: 66%

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Linear viscoelastic models

Borg¹,

Pääkkönen

2009

Journal of Non-Newtonian Fluid Mechanics

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Section: Simulations Of Transient Start-up and Cessation Viscositiessupporting

confidence: 66%

“…(16) and (17). We did not have dynamic data for the original IUPAC A LDPE, so we instead used the qualitatively similar rheological properties of 1840H LDPE in the simulations.…”

Section: Simulations Of Transient Start-up and Cessation Viscositiesmentioning

confidence: 98%

Linear viscoelastic models

Borg¹,

Pääkkönen

2009

Journal of Non-Newtonian Fluid Mechanics

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“…M 3.4 ) as the viscosity and linear relaxation time. 16 Herein we determine its dependences on temperature and shear rate for a polymer melt.…”

Section: 7mentioning

confidence: 99%

“…M 3.4 ) as the viscosity and linear relaxation time. 16 Herein we determine its dependences on temperature and shear rate for a polymer melt.Although the flow behaviors of concentrated polymer solutions and neat melts are similar, transient measurements can be problematic for the latter because their greater elasticity makes experiments at non-Newtonian rates more susceptible to artifacts, due inter alia to inhomogeneous flow (shear rate discontinuities within the flowing material) 17−20 or fracture and loss of material at the edge. 21 For this reason interrupted shear flow studies of entangled polymers to date have been carried out on solutions, 4,5,8−10,14−16 with the exception of two studies 11,12 on commercial, semicrystalline polyethylene resins.…”

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confidence: 99%

Reentanglement Kinetics in Polyisobutylene

Roy

Roland

2013

Macromolecules

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ABSTRACT:The rheological properties of a polyisobutylene (PIB) having a molecular weight five times its entanglement molecular weight were measured, along with interrupted shear flow experiments to quantify the time required for structural recovery following steady state shearing in the non-Newtonian regime. The reentanglement kinetics was substantially slower (by more than an order of magnitude) than expectations based on the linear relaxation time of the fully entangled material. This result is in accord with published interrupted shear flow results for concentrated polymer solutions. The retarded recovery of entanglements may underlie other anomalies, for example, the delayed development of autoadhesion (tack) in rubber, the behavior of freeze-dried dilute solutions and the limiting behavior of the molecular weight dependence of the viscosity. It also offers a route to more processable polymers and, being reversible, will not affect the ultimate physical properties. ■ INTRODUCTIONWhen a polymer melt or solution is sheared at rates sufficiently low that the perturbation of the chains is slow compared to the rate of Brownian motion, their equilibrium conformation is retained, and the viscosity is Newtonian. Shear rates exceeding the reciprocal of the linear relaxation time, however, induce chain stretching and a reduction of entanglements, causing a decrease of the steady-state viscosity, η ss ("shear-thinning"). 1−3During the initial phase of non-Newtonian flow, the stress and normal force both pass through a maximum versus time, as the chains disentangle prior to attaining steady state; 4 birefringence measurements reveal similar behavior.5 The magnitude of the overshoot peak increases with shear rate, occurring at strains around 2 to 3 2 with some increase at high rates. 4 Such behavior is characteristic of a viscoelastic material with time-dependent structure (entanglements in this case), although unentangled polymers can also exhibit stress overshoots and shear thinning, but the effects are weaker. 6,7Herein we study reentanglement kinetics using interrupted non-Newtonian shear flow experiments, in which after steady state is achieved, the flow is halted and the material held in a quiescent state for some time before resumption of the shearing. Since the flow-induced loss of entanglements is reversible, the magnitude of the stress overshoot during subsequent shearing has an amplitude governed by the time allowed for reentanglement. 4,8−15 The steady-state viscosity is unaffected by interruption of the flow, since it depends only on the shear rate. For rest times exceeding some characteristic time, the entanglements return to their equilibrium concentration, and the magnitude of the overshoot has its maximum (initial) value. For concentrated solutions, the time to recover the fully entangled state has been shown to have the same molecular weight dependence (ca. M 3.4 ) as the viscosity and linear relaxation time. 16 Herein we determine its dependences on temperature and shear rate for a polymer melt.Althou...

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“…4,5 The structural change in polymer caused by the complicated polymer melt flow as mentioned above will ultimately influence the final properties of the product. [6][7][8][9] Without a thorough understanding of what happens to the polymer melt flow in the mould cavity, the properties of polymer products are hard to predict, even so in the polymer industry where normally trial and error is being practiced to achieve a desirable product. It is understandable that with profit in mind, trial and error without much studying of the issue is quite favourable, but a good understanding of how the polymer melt behave is beneficial in a long run.…”

Section: Introductionmentioning

confidence: 99%