On the viscosity-temperature behavior of polymer melts

Wang, Jeou-shyong; Porter, Roger S.

doi:10.1007/bf00396562

Cited by 108 publications

(91 citation statements)

References 27 publications

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“…A comparison of our data on the activation energy with that from the literature on activation energy for shear flow shows good agreement;10–18 activation energies between 4.5 and 17 kcal/mol for PE and 8.5 and 21 kcal/mol for PP are reported. As our data show, the activation energy is higher for LDPE compared to HDPE8, 10, 14, 16–18 and higher for PP compared to PE 8, 11, 15. Long chain branching increases the activation energy of PE 19.…”

Section: Resultssupporting

confidence: 74%

Temperature shifting of convergent flow measured effective elongational viscosity

Collier

Petrovan

Patil

2002

J of Applied Polymer Sci

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ABSTRACT:The effective elongational viscosity data on a series of polyolefins as a function of temperature are shifted to a reference temperature using the approach for shifting shearing viscosity data. The temperature shift factors are obtained from complex and capillary shear rheology, and these are the same factors used for shifting the shear rheology. A Carreau rheological model was used to determine the zero shear rate viscosity at different temperatures, and an Arrhenius expression was used to determine the temperature shift factors. The same shift factors are shown to produce separate master curves for shear and elongational rheology at reference temperatures. The commercial grades of polyolefins studied include an extrusion grade of polypropylene and metallocene and conventionally catalyzed low and high density polyethylene materials.

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Section: Resultssupporting

confidence: 74%

Temperature shifting of convergent flow measured effective elongational viscosity

Collier

Petrovan

Patil

2002

J of Applied Polymer Sci

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“…The apparent activation energy, E a = 69 kJ/mol, is equivalent to that reported by Wang and Porter. 23 Included in the figure are literature viscosity data 22 for a higher molecular weight PIB, which show some deviation from Arrhenius behavior.…”

Section: ■ Resultsmentioning

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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“…mainly because slip velocity increases with temperature. One can also confirm that the effect of viscous heating is more significant for the case of PP compared to those of HDPE and LLDPE by examining the flow-activation energies, E * , using an Arrhenius type of equation to model the temperature dependence of viscosity 7 = A exp(E*/RT) (Van Krevelen, 1992;Wang and Porter, 1995). For PP it is about 10 kcal/mole, for LLDPE, about 6.3 kcal/mole, and much less for HDPE.…”

Section: Combined Slip and Viscous Heating Effects In The Capillary Fmentioning

confidence: 90%