Influence of the flow history on stress growth and structure changes in the thermotropic liquid crystalline polymer Vectra B950

Beekmans, F.; Gotsis, A. D.; Norder, Ben

doi:10.1007/bf00366726

Cited by 21 publications

(19 citation statements)

References 33 publications

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“…Additionally, when the TLCP is super cooled below its melting point, it is interesting that the shapes of the stress growth curves in the super-cooled state are qualitatively similar to that at 310 o C. Previous work shows two physical phenomena are potentially responsible for the complicated stress behavior. One is the reorientation of the rod-like molecules [18] and the other is the rearrangement of the domain structure [27]. The similarity in the shapes of the curves suggests the transient rheological behavior is caused by the same type of structure change, both at 310 o C and in the super-cooled state.…”

Section: Startup Of Shear Flowmentioning

confidence: 90%

“…The shear rheology of commercial TLCPs has been well documented under conventional processing conditions above Tm [18][19][20][21][22][23][24][25][26][27][28][29]. Other than the 73/27 HBA/HNA, two other commercial TLCPs have been widely studied.…”

Section: Done and Bairdmentioning

confidence: 99%

“…The other is a polyesteramide containing 60 mol% HNA, 20 mol% terephthalic acid (TA) and 20 mol% 4-aminophenol (commercial name Vectra B950). TLCPs have demonstrated some unusual flow behavior, such as the three region flow curve [19,21,23,26], the debatable negative primary normal stress difference [24-26, 28, 30], the scaling of shear stress growth curves with strain at different shear rates [18][19]23], and the strong dependence of transient rheological behaviors on flow history [18,27].…”

Section: Done and Bairdmentioning

confidence: 99%

“…They concluded that instead of the shear induced orientation of the molecules, the domain structure change was responsible for the stress growth response in the startup of shear flow. On the other hand, Beekmans et al [18] studied the influence of mechanical history on the stress growth of 60/20/20 HNA/TA/ aminophenol. The startup and relaxation stress transients were at least partially attributed to the rotation and orientation of the molecules.…”

Section: Done and Bairdmentioning

confidence: 99%

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The transient shear rheology of a thermotropic liquid crystalline polymer in the super-cooled state

Qian

Baird

2016

Polymer

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To determine the processing temperature of a representative thermotropic liquid crystalline polymer (TLCP) in the super-cooled state, small amplitude oscillatory shear (SAOS), the startup of shear flow and differential scanning calorimetry (DSC) measurements were performed. Good agreement on the onset crystallization temperature was obtained from the SAOS and the startup of shear flow. Compared with DSC, the rheological measurements were more sensitive for detecting crystallization in the super-cooled state. The rheological study suggested that crystallization did not occur unless the TLCP was cooled 30 o C below its melting point, and its viscosity was significantly increased as the material was super cooled. Additionally, super cooling the TLCP did not significantly affect the relaxation of shear stress after preshearing. However, the recovery of transient shear stress in the interrupted shear measurements was suppressed to a great extent in the super-cooled state.

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Section: Startup Of Shear Flowmentioning

confidence: 90%

Section: Done and Bairdmentioning

confidence: 99%

Section: Done and Bairdmentioning

confidence: 99%

Section: Done and Bairdmentioning

confidence: 99%

See 2 more Smart Citations

The transient shear rheology of a thermotropic liquid crystalline polymer in the super-cooled state

Qian

Baird

2016

Polymer

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“…이때 주어진 속도는 항상 유한한 값을 가지기 때문에 단계 적 변형에 비하여 발생시키기가 용이하다 [5]. 단계적 속도를 부여하는 방법들 중의 하나인 정상전단 유동의 급개시(start-up)에 따른 점탄성 물질의 유동거동 해 석은 실제공정에서 공정가동시의 조건과 밀접한 관련이 있 으므로 공학적인 관점에서 볼 때 대단히 중요한 연구주제 로서 여러 연구자들에 의해 그 해석방법이 제안되었다 [6][7][8][9][10]. 이들 중에서 가장 일반적으로 채택되고 있는 고찰 방 법은 여러 가지 성장함수들(growth functions)과 긴 시간영 역에서 도달되는 정상상태에서의 함수들(steady state functions)과의 비로서 표기되는 환산함수로부터 과도적 상 태에서의 비선형 유동거동을 해석하는 것이라고 할 수 있 다 [11,12].…”

Section: 서 론unclassified

Stress Growth Behavior of Aqueous Poly(ethylene oxide) Solutions at Start-up of Steady Shear Flow

Bae¹,

Lee²,

Song³

2013

Textile Science and Engineering

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The objective of this study is to systematically elucidate the transient rheological behavior of viscoelastic polymer solutions at start-up of steady shear flow. Using a strain-controlled rheometer [Advanced Rheometric Expansion System (ARES)], the stress overshoot behavior of concentrated aqueous poly(ethylene oxide) [PEO] solutions has been thoroughly investigated with applying a number of shear rates to these polymer solutions. In this article, the typical stress growth behavior of aqueous PEO solutions was firstly presented on the basis of experimentally obtained data and nextly the effects of shear rate, molecular weight, and concentration on this behavior were discussed in depth. In order to theoretically predict the stress growth behavior, the Wagner constitutive equation (a time-strain separable constitutive equation) and the Bird-Leider model were employed and the applicability of these models was examined in detail. The main findings obtained from this study can be summarized as follows: (1) At the inception of low shear rates, the stress overshoot behavior is not observed but the shear stress progressively increases with time until the steady state stress value is reached. As the shear rate is increased, however, aqueous PEO solutions exhibit a pronounced stress overshoot followed by a stress decay to reach the steady state flow condition. (2) The maximum shear stress increases linearly with an increase in shear rate in a double logarithmic scale and becomes larger with an increase in concentration. (3) The time at which the maximum shear stress occurs, t max , shows a linear relationship with the inverse of shear rate in a double logarithmic scale, regardless of molecular weight and concentration. (4) When the Wagner constitutive equation is used, the Wagner damping function exhibits superior performance to the Soskey-Winter damping function in predicting the transient stress growth behavior of aqueous PEO solutions. (5) The Bird-Leider empirical model can be successfully used for predicting the transient stress growth behavior of aqueous PEO solutions. This model is especially effective for expressing the maximum shear stress as well as the time at which this maximum stress is observed.

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Transient shear flow properties of carbon fiber-filled liquid crystalline polymer

et al. 2005

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Unsteady flow of filled polymer systems can cause some difficulties in their processing, such as injection or extrusion molding, in which flow in the molten state is involved. In order to determine the optimum conditions and thus improve the performance of the end products, it is necessary to understand the transient/unsteady flow behavior of these systems. In a previous work, we found remarkable non‐Newtonian properties and shear thickening flow behavior of liquid crystalline polymers (LCP) and their filled systems. This article deals with the dependence of transient flow properties, including shear thickening, of pure and carbon fiber‐filled LCP upon the shear rate and shear strain history; the effect of the filler content is also discussed. The results indicate that the abnormal flow behavior of the tested materials may be caused by gradual disintegration of the domain structure formed in LCP (materials exhibit apparent yield stress) and then continual orientation of molecules under shear flow. The shear thickening behavior of the materials seems to disappear with increasing fiber content. This behavior suggests that it is necessary to measure the flow properties under a sufficient ramp point delay time and equilibration time in order to obtain reliable data under stable conditions. POLYM. COMPOS., 26:470–476, 2005. © 2005 Society of Plastics Engineers.

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Influence of the flow history on stress growth and structure changes in the thermotropic liquid crystalline polymer Vectra B950

Cited by 21 publications

References 33 publications

The transient shear rheology of a thermotropic liquid crystalline polymer in the super-cooled state

The transient shear rheology of a thermotropic liquid crystalline polymer in the super-cooled state

Stress Growth Behavior of Aqueous Poly(ethylene oxide) Solutions at Start-up of Steady Shear Flow

Transient shear flow properties of carbon fiber-filled liquid crystalline polymer

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