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Polymer Testing Methods for Conventional and Technical Textiles
Published in Sheraz Ahmad, Abher Rasheed, Ali Afzal, Faheem Ahmad, Advanced Textile Testing Techniques, 2017
Usman Zubair, Sheraz Ahmad, Abher Rasheed, Ali Afzal, Faheem Ahmad
Rheological testing provides information in three tiers, which helps researchers to establish structural characteristics (configuration, molecular mass, molecular mass distribution), to predict process parameters (shear rate, extrusion, process temperature), and to understand end user performance (strength, use temperature, dimension stability). The model depicted in Figure 2.17 shows that material structure directly dictates the rheology of the material that in turn is determinant of material process behavior and material performances and properties. Making measurements of the rheological properties of materials is termed “rheometry.” For rheological characterization, knowledge of capillary rheometers and steady/dynamic shear rotational rheometers is requisite. Rotational rheometry works very well at a low shear rate, so it is helpful for understanding polymer structure, dynamic properties, and possible phase transitions occurring due to shearing and thermal treatment. Capillary rheometry is performed to provide the best simulation of high shear rate extrusion processes over a specific temperature range, as reported in Figure 2.18. In this way, rheological characterization helps to determine both dynamic properties and process parameters that regulate product end properties. In the case of thermoset samples, such as epoxy resins and adhesives, it is important not only to analyze the material properties prior to curing, but also to analyze the change in mechanical properties during and after the curing process.
Shear rheometry with concentrated suspensions
Published in Philippe Coussot, Mudflow Rheology and Dynamics, 2017
Rheometry aims to determine the rheological properties of materials when they are in such conditions that, during flow, they can be considered at each instant as homogeneous systems undergoing continuous deformations at a macroscopic scale. This means that discontinuity in strain field and material heterogeneities should be avoided. One can therefore study the suspension in the field of continuum mechanics. Furthermore, the rheological behaviour of the material is deduced from rheometrical measurements assuming a theoretical (viscometric) flow within the rheometer. The experimenter’s task will be to check that these hypotheses are respected or even, ideally, to control them. Under these conditions the stress-strain rate couple deduced from measurements will effectively corresponds to the true behaviour of the homogeneous suspension. In practice shear rheometry with concentrated suspensions requires specific attention to various phenomena such as: observable strain field, changes of free surface form with time, evaporation rate, wall slip, particle migration and any slow or rapid changes of recorded shear stress or shear rate. These precautions are crucial since they will avoid interpreting some disturbing effects as real material properties and should make it possible to obtain relevant measurements of some peculiar properties of these suspensions. However this is not so easy because the different phenomena which may occur are hardly quantifiable and a great number of tests are often necessary before it is possible to distinguish them. The developments and quantifications of disturbing phenomena and their relation with suspension properties remains widely unexplored. Here we shall only review techniques and precautions for shear rheometry of concentrated suspensions to obtain data reflecting intrinsic fluid behaviour.
Carbon nanotubes for improving rheological and chemical properties of styrene–butadiene–styrene modified asphalt binder
Published in International Journal of Pavement Engineering, 2023
Yujie Tang, Zhen Fu, Feng Ma, Jun Liu, Qiyu Sun, Chen Li
The objective of this paper is to evaluate the effects of CNTs on the rheological and chemical properties of the SBS-modified asphalt (SBSMA) binder. In this paper, six modified asphalt binders with different amounts of carbon nanotubes and SBS (CSMA) were prepared. Based on previous studies (Ren et al. 2019, Wei et al. 2022, Li et al. 2022b), it is reasonable for composite modified asphalt binder to be 4% SBS content, and the CNTs content of 0.3%, 0.6%, 0.9%, 1.2% and 1.5%, respectively. The modified asphalt binder samples were aged by thin-film oven test (TFOT), pressure aging vessel (PAV) and ultraviolet (UV) aging test. The stability and motion state of modified asphalt molecules was captured by molecular dynamics simulation, involving binding energy, mean square displacement (MSD), radial distribution function (RDF) and relative concentration distribution (RCD). The rheological properties were characterised through bending beam rheometer (BBR) and dynamic shear rheometry (DSR), including frequency sweep, temperature sweep, viscosity–temperature susceptibility (VTS) and multiple stress creep recovery (MSCR) tests. The chemical component was analysed by Fourier transforms infra-red (FTIR) spectroscopy. The experimental design flowchart is shown in Figure 1.
Cure-induced stress build-up in adhesives: model building and parameter studies
Published in The Journal of Adhesion, 2023
Jonas Wirries, Till Vallée, Martin Rütters
In further experiments, shrinkage that did not contribute to stress development was separated from stress-relevant shrinkage using the extended rheometry (ExRheo). The line-scanning laser of the ExRheo was used to observe the adhesives meniscus, laterally. Simultaneously, axial forces induced by chemical shrinkage were measured by the rheometer’s force rebalance transducer (FRT), while keeping the rheometer plates locked at a constant gap. Exemplary results of an isothermally cured two-component epoxy (2C-EPC) that was analysed using ExRheo are depicted in Figure 3. The shrinkage was showing steep increase at the beginning of the reaction, thus confirming literature. The increase in axial force was sigmoidal and increased even though shrinkage was not observed anymore. One assumption that was made in this experiment was constant gap height. According to the scope of this paper (refer to section 1.4), this assumption will be addressed in this manuscript. The modelling procedure presented in this publication is based on the aforementioned experiment.
Rheo-NMR velocimetry characterisation of PBLG/m-cresol
Published in Liquid Crystals, 2023
Catarina R. Leal, Gabriel M. Feio, Pedro L. Almeida
Previously [10], the time evolution of the director field distortion of PBLG/m-cresol during the inhomogeneous reorientation following a 90° of the initially homogeneous sample in a strong magnetic field, was observed through a deuterium NMR experiment using benzene-d6 as probe. The numerical simulation of the reorientation process has provided the four Leslie’s viscosities γ1, α1, α2 and hbend, as well as the elastic constants ratio K11/K33. Data from classical rheometry provided the fifth independent Leslie’s viscosity. The full set of viscoelastic parameters was determined for the 17% PBLG/m-cresol using benzene-d6 as probe, as described in the literature [8,10] and presented in Table 1.