Korea-Australia Rheology Journal最新文献

Characterized by high strength to unit weight, poly(ethylene terephthalate) (PET) remains one of the most widely used engineering plastics, hence the attention to its associated waste and recycling technology development has been paid from academic and industrial perspectives. Herein, we investigate the mechanical degradation of PET through degradative compounding process cycles and the effect of chain extender (Joncryl^® ADR 4468) to prevent molecular degradation of PET during melt processing. They are characterized based on rheological and mechanical measurements. Characterization of the bottle-grade PET samples reveals low viscosity and crystallinity owing to isophthalic acid units within the PET copolymer structure over PET homopolymer. Mechanical shear and thermal impact by virtue of the increase in rotor speed and temperature are employed to study the degradation of the PET samples. Both samples respond to degradation in successive processing cycles with as much as 70% decrease in their complex viscosity and moduli. The molecular weight of PET copolymer accordingly decreases from 23,400 to 8010 g/mol. Chain scission arising from thermo-mechanical degradation results in high crystallinity by more than five folds in the processed PETs. Attributed to recoupling of the degraded short chains, the chain extender compensates with the increase in viscosity and moduli up to 20% whilst serving to increase crystallinity but almost ineffective in appreciating mechanical performance with barely any significant variation in tensile strength and elongation at break. This study shows that mechanical shear is verified to impact a pronounced degradation on PET more than thermal action on the samples.

Since the discovery of MXene, which has been attracting attention as an alluring two-dimensional material with a distinct structure and mechanical and electrical capabilities, numerous attempts have been made to combine MXene with polymer additives to enhance and compensate for MXene’s inherent weakness. In this work, the rheological properties of MXene (Ti₃C₂T_x)-polymer composite inks of three different polymers with various interaction with MXene particles are examined. Polyethylene glycol (PEG), which is known to physically adsorb on the surface of MXene, improved MXene dispersion while enhancing the viscoelastic property of ink. MXene ink containing polyethylenimine (PEI) was destabilized forming a viscoelastic network structure as PEI of strong positive charge adsorbed on the MXene surface to neutralize negative charge and diminish electrostatic repulsion. In the case of MXene-polyacrylic acid (PAA) composite ink, the formation of hydrogen bonds between MXene and PAA resulted in a dense network structure with high viscoelasticity. In terms of rheological property sensitivity to concentration, MXene ink without polymer additives exhibited power-law behavior with the largest exponent, whereas MXene-polymer composite inks indicated moderate sensitivity. Our findings will aid in the design of MXene-based composites with optimum rheological properties for specific processes such as 3D printing and coating.

Influence of cationic polymer (KN) on the floccule size of cement pastes containing plycarboxylate superplasticizer (PCE) and Na-bentonite was studied. The proportion of floccule size and grain size ({d}_{f}/{d}_{g}) was obtained from a rheological analysis with the application of Herschel–Bulkley model and modified Krieger–Dougherty model. Herschel–Bulkley model was used to gain the yield stress according to our previous study. Cement pastes were investigated both at the beginning and after one hour. The results showed that a high value of ({d}_{f}/{d}_{g}) was noticed under low shear rate range and then the proportion decreased with the increase of shear rate. For cement paste containing PCE and Na-bentonite in the absence of KN, larger floccule was formed due to the intercalation of polyethylene glycol branch chain of PCE into the interlayer space of Na-bentonite. However, the floccule size of cement pastes obviously decreased with the increasing addition amount of KN. Thus, KN will restrain the formation of floccules in cement pastes containing PCE and Na-bentonite to a certain extent.

In this study, conductive polyindole (PIn) was coated onto initially fabricated magnetic iron oxide (Fe₃O₄) particles via chemical oxidative polymerization, and the synthesized core–shell structured hybrid smart particles were used as smart electrorheological/magnetorheological (EMR) materials. The synthesized Fe₃O₄/PIn particles were characterized using scanning electron microscopy and transmission electron microscopy. In addition, the chemical composition of the synthesized particles was confirmed using Fourier-transform infrared spectroscopy. Their magnetic properties were further analyzed using VSM. Consequently, the Fe₃O₄/PIn particle-based suspension, which was both magnetic and conductive, was found to exhibit interesting dual stimuli under both external electric and magnetic fields. Various rheological measurements, including shear simple steady shear and dynamic tests, were employed to evaluate the behavior of typical EMR suspensions. Furthermore, the dielectric properties of the particles were analyzed using an LCR meter. Based on the dielectric spectrum data, the relaxation time (λ) was estimated to be 1.5 × 10^–8 s at the maximum frequency (λ = 1/2πfmax). Measurements conducted using a Turbiscan indicated enhanced sedimentation stability of the particles owing to a decrease in the particle density from 4.34 to 2.93 g/cm³.

We present an experimental investigation of the linear viscoelasticity for a series of covalent adaptable network (CAN) polymers of β-amino esters possessing tertiary amines at the β position of ester linkages. CAN polymers were synthesized by aza-Michael addition from di-acrylate monomers with or without β-hydroxyl groups using a tri-amine cross-linker. The prepared CAN polymers exhibited dissociative-type bond exchanges by aza-Michael reaction. The additional inclusion of β-hydroxyl group endowed them with associative-type bond exchanges by transesterification. Time–temperature superposition (TTS) was used to construct pseudo-master curves of storage, loss, and stress-relaxation moduli over wide timescales. The results showed that without transesterification, the slow kinetics of aza-Michael reaction considerably retarded terminal relaxation. The introduction of transesterification accelerated terminal relaxation rates but did not modify the overall broadness of terminal relaxation modes. Horizontal shift factors displayed Williams–Landel–Ferry (WLF) dependence below 120 °C but Arrhenius dependence above 120 °C. The former was due to slow segmental dynamics, whereas the latter reflected the characteristic of exchange reaction kinetics. In addition, we also compared and discussed two definitions of topology freezing transition temperature, an important concept for associative-type CANs. Conclusively, the topology freezing transition temperature obtained from the transition of shift factors (WLF → Arrhenius) was a more practical definition for the potential processing and applications of CAN polymers.

The occurrence of barite sag in drilling fluids has relatively often been the cause for gas kicks in oilwell drilling. The subsequent absorption of gas into drilling fluid could lower the density and reduce the viscosity of the drilling fluid, thereby aggravating both pressure control and hole cleaning. In this paper, we present experimental measurements of rheological properties and barite sag in a typical North Sea oil-based drilling fluid at downhole pressure and temperature conditions. A new experimental apparatus was setup for barite sag measurements at static condition with operational temperature and pressure capabilities up to 200 °C (392°F) and 1000 bar (14,503.8 psi), respectively. Rheometry measurements were conducted on fluid samples with and without barite particles at operating conditions up to 90 °C and 100 bar. We observed that at a typical shear rate of 250 s⁻¹, which is experienced in 8.5″ hole annulus, the viscosity of fluid sample with barite increased nearly three times as that of the fluid sample without barite as the temperature and pressure increased. However, temperature effect on viscosity dominates at high shear rates compared to pressure effect. Furthermore, the fluid samples showed more shear-thinning effect with increasing yield stress as the temperature increased. On the other hand, barite sag measurements revealed that whereas fluid samples under high pressure are less prone to sag, high temperature fluid samples, however, promote sag significantly. The data from this study are useful to validate extrapolations used in computational models and to improve understanding and operational safety of sag phenomena at downhole conditions. We also discuss the importance of this study in optimizing drilling operations.

Optimisation design of composite structures requires an accurate predictive model for forming behaviour. The simulation process contains a number of model parameters which include transverse and longitudinal viscosities of continuous fibre-reinforced viscous composites, fundamental to predicting the shear rheology. Shearing the unidirectional composite along the fibre direction gives a measure of the longitudinal viscosity (LV), whilst shearing across or transverse to the fibre direction gives a measure of the transverse viscosity (TV). Numerous experimental work was conducted in the past to measure these two viscosities for various materials. However, conflicting measurements by different test methods were obtained and these apparent discrepancies had not yet been systematically investigated in any single study. This paper reviews previous work on characterisation techniques to further understand the cause of such discrepancy, and hence to improve measurement accuracy, which would benefit future work on theoretical modelling of the composite viscosities and optimisation simulation of composites forming. Some important findings, such as effects of resin-rich areas, contributory factors of elastic effects, non-Newtonian behaviour for composites with Newtonian matrix, aspect ratio and end effects of test samples, geometry effects of fibres and fibre rearrangement during shearing, existence of a mathematical relationship between LV and TV and necessary benchmarking exercise using Newtonian matrix composites, were summarised.

We study the flow behavior of a Newtonian fluid in a planar 4:1 contraction channel using two numerical methodologies: the two-relaxation time lattice Boltzmann method (TRT-LBM) and the finite element method (FEM). To confirm the validity of the TRT-LBM, hydrodynamic quantities such that velocity, pressure, and vortex are carefully investigated at the wide ranges of Reynolds numbers (Re = 0.1–100). At first, we analyze the velocity along the channel. The results of TRT-LBM look reasonable and also coincide with the analytical solution and FEM results. Richer features are observed in the pressure profile along the flow direction. At low Reynolds numbers, the one-step change of the slope in the pressure profile is observed near the contraction region. The slope gradually grows up with the increase of Reynolds numbers, and eventually, this evolves the two-step change. Non-monotonic behavior is observed in the characteristics of the vortex. The size of the vortex non-linearly decreases as the Reynolds number increases. Also, the center of the vortex gradually moved toward the corner of the channel as an increase of Reynolds numbers with non-linearity. Not only the velocity and the pressure profiles but also the characteristics of the vortex quantitatively coincide in TRT-LBM and FEM results. Through this study, we confirm the robustness of the TRT-LBM as a simulation tool to investigate inertial flow in a planar contraction geometry.

Thermoplastic resin transfer molding (T-RTM) of polyamide 6-based composite is one of the promising process to mass-produce an environmentally friendly textile composite with recyclable thermoplastic resin, in which ε-caprolactam monomer with low viscosity is injected and in situ polymerized into the fabric. The side reactions caused by water in the anionic polymerization process of the monomer is a crucial problem for fabricating the composite with a high quality. In this study, we introduced zeolite, a porous ceramic water-absorbing particle, into the ε-caprolactam to improve the moisture sensitivity during the anionic polymerization. The selective water-absorbing effect of zeolite particle was verified by measuring the monomer conversion, viscosity-average molecular weight, and viscosity change during polymerization, and mechanical properties of the resultant carbon fiber reinforced polyamide composite were investigated. It is expected that processability of the T-RTM is remarkably improved by reducing both the drying time during process and quality deviation of the composite by variation of humidity, which can make T-RTM process a viable technology for mass-production of thermoplastic composites.