Creep and physical ageing of polypropylene: a comparison of models

Tomlins, P E; Read, B. E.

doi:10.1016/s0032-3861(97)00258-9

Cited by 46 publications

(38 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…When relaxation time is independent of real time ( ( ) t  =constant), equation (4) For the glassy materials in general and the polymer glasses in particular relaxation time is observed to show power law dependence of on real time given by (Cloitre et al 2000, Derec et al 2003, Fielding et al 2000, McKenna et al 2009, O'Connell and McKenna 1997, Struik 1978, Tomlins and Read 1998:…”

Section: A Effective Time Domain Approachmentioning

confidence: 99%

Long time response of aging glassy polymers

Joshi

2014

Rheol Acta

View full text Add to dashboard Cite

Abstract:Aging amorphous polymeric materials undergo free volume relaxation, which causes slowing down of the relaxation dynamics as a function of time.The resulting time dependency poses difficulties in predicting their long time physical behavior. In this work, we apply effective time domain approach to the experimental data on aging amorphous polymers and demonstrate that it enables prediction of long time behavior over the extraordinary time scales. We demonstrate that, unlike the conventional methods, the proposed effective time domain approach can account for physical aging that occurs over the duration of the experiments. Furthermore, this procedure successfully describes timetemperature superposition and time -stress superposition. It can also allow incorporation of varying dependences of relaxation time on aging time as well as complicated but known deformation history in the same experiments. This work strongly suggests that the effective time domain approach can act as an important tool to analyze the long time physical behavior of aging amorphous polymeric materials. | P a g e I Introduction:Glassy materials such as amorphous polymers (Hodge 1995), colloidal glasses and gels (Fielding et al. 2000), spin glasses (Rodriguez et al. 2003) are usually time dependent materials owing to thermodynamically out of equilibrium state they are arrested in. Typically specific volume (and specific entropy/enthalpy) associated with an amorphous polymer is in excess compared to its equilibrium value (Donth 2001, Larson 1999, Struik 1978.Inherent tendency of any material to achieve equilibrium initiates structural rearrangement in the amorphous polymeric compounds so as to cause relaxation of specific volume (accompanied by decrease in specific entropy/enthalpy) as a function of time (Callen 1985, Struik 1978. This phenomenon is addressed in the literature as physical aging (Hodge 1995). In polymeric glasses, while taking the material closer to the equilibrium state, physical aging manifests itself by causing enhancement in relaxation time and stiffness as a function of time (Struik 1978). This time dependency continuously changes the material response to the external stimuli such as application of deformation field (stress field or strain field), electric field, etc.Consequently, a priory prediction of the long time behavior of the response function becomes a challenging task. In this work we employ the so called effective time domain approach, which allows direct prediction of long time material response of amorphous polymers by carrying out tests over the practical timescales. | P a g eThe amorphous polymeric materials when quenched rapidly from the molten state undergo glass transition (McKenna 1994). Physical aging initiates in the material subsequent thermal quench (Hodge 1995). The time elapsed since thermal quench is typically known as the aging time or the waiting time.If the material is deformed during this annealing period, response functions (such as creep compliance and relaxation modulus, depending upon ...

show abstract

Section: A Effective Time Domain Approachmentioning

confidence: 99%

Long time response of aging glassy polymers

Joshi

2014

Rheol Acta

View full text Add to dashboard Cite

show abstract

“…Because the attempt rate ⌫ a and the average potential energy ⍀ are mutually dependent [eq. (40) implies that the growth of ⍀ results in an increase in ⌫ a ], we set ⌫ a ϭ 1 s and approximate the relaxation curve at 1 by using three experimental constants: ⍀, ⌺, and a . To find these parameters, we employ a procedure similar to that used in fitting the stressstrain curve.…”

Section: ϫ4mentioning

confidence: 99%

“…39,40 In the past couple of years, the linear viscoelastic behavior of isotactic polypropylene was analyzed by Fricova et al, 41 Andreassen, 42 LopezManchado and Arroyo, 43 Gallego Ferrer et al, 44 and Souza and Demarquette, 45 to mention a few. Two pronounced maxima were found on the graph of the loss tangent of isotactic polypropylene versus temperature: the first maximum (␤-transition in the interval between T ϭ Ϫ20 and T ϭ 10°C) is associated with the glass transition in the most mobile part of the amorphous phase, whereas the other maximum (␣-transition in the interval between T ϭ 50 and T ϭ 80°C) is attributed to the glass transition in the remaining part of the amorphous phase (the so-called rigid amorphous fraction 46 ).…”

Section: Introductionmentioning

confidence: 99%

Model for the viscoelastic and viscoplastic responses of semicrystalline polymers

Drozdov

Christiansen

2003

J of Applied Polymer Sci

View full text Add to dashboard Cite

Constitutive equations are derived for the time-dependent behavior of semicrystalline polymers at isothermal loading with small strains. A semicrystalline polymer at temperatures above the glass-transition point for its amorphous phase is thought of as a network of macromolecules bridged by junctions (physical crosslinks, entanglements, and crystalline lamellae) that can slide with respect to their reference positions in the bulk material under straining. The network is assumed to be highly inhomogeneous, and it is modeled as an ensemble of mesoregions (MRs) with various strengths of interchain interaction. Two types of MRs are distinguished: passive, where these interactions prevent detachment of strands from junctions; and active, where active strands separate from junctions and dangling strands merge with the network at random times as they are thermally agitated. The viscoelastic response of a semicrystalline polymer reflects reformation of strands in active MRs, whereas its viscoplastic behavior is associated with sliding of junctions. Stress-strain relations for uniaxial deformation are developed by using the laws of thermodynamics. Adjustable parameters in the constitutive equations are found by fitting experimental data for isotactic polypropylene in a tensile test with a constant strain rate and in tensile relaxation tests at various strains. Fair agreement is demonstrated between the observations and the results of numerical simulation. It is revealed that the viscoplastic flow of junctions strongly affects the rearrangement process in active MRs, whose rate reaches a threshold value in the vicinity of the apparent yield point.

show abstract

“…This number is noticeably lower than the number of experimental constants in any conventional phenomenological equation. For example, the classical Zener model, [49] the two-component model with a log-normal distribution function, [20] the Maxwell model with an anharmonic spring, [11] the KWW (Kolhrausch-Williams-Watt) model, [50] and the power-law model [50] contain at least three adjustable parameters.…”

Section: Substitution Of This Expression and Equationmentioning

confidence: 99%