A Review on Dynamic Rheology for Polymers (original) (raw)
Related papers
Crystallinity and linear rheological properties of polymers
2007
The crystallization of a polymer melt, taking place during transformation processes, has a great impact on the process itself, mainly because it causes a large increase in the viscosity (hardening). Knowledge of the hardening kinetics is important for modeling and controlling the transformation processes. In this work, first an overview is given of the experimental and modeling work on the hardening of crystallizing polymers. Next, we present isothermal crystallization experiments using differential scanning calorimetry (DSC) and rotational rheometry to measure the dynamic viscosity. The evolution of the relative crystallinity and normalized complex viscosity are correlated by a novel technique which allows simultaneous analysis of several runs, even if they are not carried out at same temperatures; the main requirement with the traditional technique. The technique, described in detail in this paper, provides an experimental relationship between the crystallinity and the hardening, i. e. the increase in the viscosity. Moreover, by measuring the dynamic viscosity at different frequencies, surprisingly, a master curve is obtained which combines the effects of shear rate, temperature and the level of crystallinity.
The mechanical properties of solid polymeric materials quite generally depend on time, i.e., on whether they are deformed rapidly or slowly. The time dependence is often remarkably large. The complete description of the mechanical properties of a polymeric material commonly requires that they be traced through 10, 15, or even 20 decades of time. The class of polymeric materials referred to as thermorheologically and/or piezorheologically simple materials allows use of the superposition of the effects of time and temperature and/or time and pressure in such materials as a convenient means for extending the experimental time scale. This paper presents a critical review of models proposed to describe the effect of temperature and/or pressure on time-dependent thermorheologically and/or piezorheologically simple polymeric materials. The emphasis here is on the theoretical aspects, although experimental results are used as illustrations wherever appropriate.
Cornell University - arXiv, 2001
The time-dependent response of polystyrene and poly(methyl methacrylate) is studied in isothermal long-term shear creep tests at small strains and various temperatures in the vicinity of the glass transition point. A micromechanical model is derived to describe the experimental results. Constitutive equations are developed under the assumption that the behavior of amorphous polymers is governed by two micro-mechanisms: rearrangement of cooperatively relaxing regions (CRR) reflects the viscoelastic response, whereas displacement of CRRs with respect to each other is responsible for the anelastic response. It is demonstrated that some critical temperature exists slightly above the glass transition temperature, where the dependences of adjustable parameters on temperature are dramatically changed. The critical temperature is associated with transition from dynamic heterogeneity in amorphous polymers to static inhomogeneity.
The Role of Structure in Polymer Rheology: Review
Polymers, 2022
The review is devoted to the analysis of the current state of understanding relationships among the deformation-induced structure transformations, observed rheological properties, and the occurrence of non-linear effects for polymer liquids (melts, solutions, and composites). Three levels of non-linearity are the base for consideration. The first one concerns changes in the relaxation spectra of viscoelastic liquids, which are responsible for weak non-linear phenomena. The second one refers to the strong non-linearity corresponding to such changes in the structure of a medium that leads to the emergence of a new relaxation state of a matter. Finally, the third one describes the deformation-induced changes in the phase state and/or the occurring of bifurcations and instability in flow and reflects the thermodynamic non-linear behavior. From a structure point of view, a common cause of the non-linear effects is the orientation of macromolecules and changes in intermolecular interactio...
Viscoelastic Behavior of Amorphous Polymers near the Glass Temperature
Journal of Polymer Science Part B-polymer Physics, 1988
Lack of thermorheological simplicity and possible effects of the molecular weight distribution in the softening dispersion of linear amorphous polymers are demonstrated with viscoelastic data on polymethylacrylate PMA and polyvinylacetate PVAc. Superposition of the short time portion of the softening transitions of the retardation spectra of PMA, PVAc, polystyrene, and amorphous polypropylene APP indicates that the local molecular mobility is a constant at Tg within experimental uncertainty. The general features of the retardation spectra of linear amorphous polymers are discussed.
Effect of time and thermo-mechanical couplings on polymers
arXiv: Soft Condensed Matter, 2018
Analysis of the thermo-mechanical behaviour of polymers has been and still is the subject of many rheological studies both experimentally and theoretically. For small deformations, the modelling framework retained by rheologists is often of linear visco-elasticity, which led to the definition of complex modules and used to identify the glass transition temperature as the so called rule of time-temperature superposition. In this context, the effects of time are almost unanimously associated with viscous effects. It has also been observed that the dissipative effects associated with viscous effects are often very small compared to the coupling of sources indicating a high sensitivity of polymeric materials to temperature variations. This work is mainly focused on establishing the exact role of coupling effects, which also induce the effect of time. Using traditional experimental methods of visco-analysis (DMTA) and via an energy analysis of the behaviour, the goal of the thesis is to ...
Rheological Behavior Models of Polymers
Biointerface Research in Applied Chemistry, 2021
We studied and investigated the various viscosimetric and rheological polymers' behaviors during this comprehensive review. The viscosities relate to the investigation of the flux, the deformation, and the polymers' elasticity; we have employed the viscosity since this plays a primordial role in the phenomena flux and implementation of the polymer. The rheology behaviors were investigated for the determination of the physical properties of polymers. The rheological properties are mostly employed for improving polymers implementation. Further, three rheological behaviors models such as Newtonian, pseudo-plastic (Power Law, Law of Tile and Cross Law) and heat-dependent pseudo-plastic (Williams-Landel-Ferry Law (WLF), Law of Tile-Yasuda and Arrhenius law) were studied.
European Polymer Journal, 2013
Polytetrafluoroethylene (PTFE) has been used for many years in different application fields due to its outstanding chemical and physical properties. But, the value of its glass transition temperature is still today a matter of controversy and very different values are proposed in the literature. This paper proposes to answer to this scientific question using dynamic mechanical measurements. First, the viscoelastic properties of PTFE are described on a large temperature range and the influence of the shearing frequency is carefully investigated. Then, the effects produced by the polymer annealing on its thermomechanical behavior are detailed. This study comforts the idea that PTFE amorphous phase should be considered as comprised of two distinct regions. The first one named ''mobile amorphous fraction'' (MAF) is able to relax at low temperature (T = À103°C). The other one is specific of the macromolecular segments present at the boundaries between crystalline and amorphous domains. Due to the close vicinity of the crystallites, these macromolecular segments present a more restricted mobility. The corresponding phase is designated as the ''rigid amorphous fraction'' (RAF) and its mechanical relaxation produces itself at higher temperature (T = 116°C). Actually, this latter value is strongly dependent on the material crystallinity degree. In particular, it is shifted to higher temperature after occurrence of a recrystallization that is accompanied by a further reduction of the RAF's dynamic. Instead, the characteristics of the MAF relaxation are poorly affected. Tensile tests also support that the ''real'' T g of the polymer is located at low temperature. All these results have been compared to those of the literature to propose a real scientific discussion and to understand the origin of somewhat contradictory interpretations.