Shear Mixing Process Research Articles

Effect of interfacial bonding on impact properties of chopped glass fiber polymer nanocomposites

This paper aims to presents the investigations made on the effect of impact response of chopped glass fiber–epoxy nanocomposite laminates subjected to low velocity impact using instrumented falling weight impact tests. The laminates were prepared using six layers of chopped strand mat with density of 610 gsm with epoxy resin and nanoclay content varied from 1, 3, and 5 wt%, by hand lay-up method. The nanoclay was dispersed into the epoxy by high shear mixing process in order to obtained uniform distribution of individual nanoclay. Laminates were impacted at constant mass with different impact energies. During these low velocity impact tests, the maximum load, absorbed energy, and deflection at peak load were recorded. It was observed that by dispersion of nanoclay as reinforcement, there was significant improvement in load carrying capacity and energy absorption. When a small amount of nanoclay (1 wt%) was added into the epoxy, the maximum load was enhanced by 20%. The presence of stiffer nanoclay significantly reduced the surface cracks propagation and controlled delamination area. Scanning electron microscopy was performed to characterize the damage progression.

Mechanical and Tribological Behaviour of Epoxy Reinforced with Nano Al<sub>2</sub>O<sub>3</sub> Particles

In the present work systematic study has been conducted to investigate the matrix properties by introducing nanosize Al2O3 (particle size 100 nm, 0.5–10 wt %) fillers into an epoxy resin. High shear mixing process was employed to disperse the particles into the resin. The experimental results indicated that frictional coefficient and wear rate of epoxy can be reduced at rather low concentration of nanoAl2O3. The lowest specific wear rate 0.7 x 10-4 mm3/Nm is observed for the composites with 1 wt.% which is decreased by 65% as compared to unfilled epoxy. The reinforcement of Al2O3 particles leads to improved mechanical properties of the epoxy composites. The results have been supplemented with scanning electron micrographs to help understand the possible wear mechanisms.

Low shear compounding process for thermoplastic fabrication of ferroelectric lead-free fibres

The thermoplastic ceramic extrusion process involves the shaping of a polymer highly filled with inorganic powder, the so-called ceramic–thermoplastic feedstock. The limitation faced with the process is the amount of raw material required to produce the feedstock. Depending on the density and desired volume of the materials used, the typical amount of ceramic powder required is a minimum of ∼100 g. The validation of a low shear feedstock preparation method against a standard high shear mixing method occurred. Microstructure investigation and single electromechanical fibre characterization of low shear produced KNN ( d 33 – 49 pC/N; P r – 3.7 μC/cm 3 ) and PZT ( d 33 – 392 pC/N; P r – 32.4 μC/cm 3 ) fibres, in terms of PE, SE loops and d 33 measurements, demonstrating the reproducibility of the results when compared to a standard ceramic–thermoplastic high shear mixing process. The repeatability of the measurements showed the proposed procedure to be robust, validating the new compounding method for wide-scale use.

Dry Sliding Wear Behaviour of Epoxyreinforced with nanoZrO2 Particles

A systematic study has been conducted to investigate the matrix properties by introducing nanosize ZrO2 (60-100 nm, 0.5–10 wt.%) fillers into an epoxy resin. High shear mixing process was employed to disperse the particles into the resin. The experimental results indicated that the frictional coefficient and wear rate of epoxy can be reduced at rather low concentration of nano-ZrO2. The lowest specific wear rate 0.1 x 10-4 mm3/Nm is observed for the composites with 0.5 wt.% which is decreased by 95% as compared to the value of unfilled epoxy. Although the incorporation of nano-ZrO2 particles leads to increased flexural modulus and flexural strength of epoxy, the wear performance of the composites does not correlate with these static mechanical properties. In contrast, there is a positive correlation between wear resistance and impact strength (i.e. increase in impact strength correlates with a decrease in specific wear rate).

Effect of processing variables on mechanical properties of montmorillonite clay/unsaturated polyester nanocomposite using Taguchi based grey relational analysis

Abstract The present investigation addresses the influence of process variables on the mechanical properties of montmorillonite (MMT) nanoclay with unsaturated polyester, using the mechanical shear mixing process. The rotational speed, mixing time, rotor blade design and clay content were chosen as process variables. The influence of these process variables on mechanical properties were studied with the help of grey relational analysis. Organically modified MMT nanoclay was used as the reinforcing filler, in order to increase the swelling of the clay with the polyester resin. Nanocomposites were fabricated based on the experimental design using the L9 orthogonal array. Among the parameters studied, blade design was identified as the parameter with the most influence, due to the presence of a varying shear force, which peeled off the clay platelets from the stacked arrangement of clay tactoids. Grey relational analysis was used to obtain the optimum process parameters for multiple quality characteristics such as tensile, flexural and impact strength. It was observed that the Shore D hardness values for all nine experiments possess higher values than virgin polyester. Morphological studies have been carried out for the specimen with optimum process parameters using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Tensile, flexural and impact fractured specimens were studied using scanning electron microscopy (SEM) for optimum conditions.

Electrical resistance of CNT-PEEK composites under compression at different temperatures

Electrically conductive polymers reinforced with carbon nanotubes (CNTs) have generated a great deal of scientific and industrial interest in the last few years. Advanced thermoplastic composites made of three different weight percentages (8%, 9%, and 10%) of multiwalled CNTs and polyether ether ketone (PEEK) were prepared by shear mixing process. The temperature- and pressure-dependent electrical resistance of these CNT-PEEK composites have been studied and presented in this paper. It has been found that electrical resistance decreases significantly with the application of heat and pressure.

Fabrication and fracture toughness properties of carbon nanotube-reinforced cement composite

Multi-walled carbon nanotube (MWNT) reinforced cement composites (MWFRCs) were prepared with surfactant dispersion, ultrasonic treatment, and subsequently high-speed shear mixing processes. These MWFRCs were characterized in the fracture toughness property with single edge notch bend method. As found, the addition of nanotubes improves the stress-intensity factor (KIC), critical crack mouth opening displacement (δC) and flexural strength (σs) of the cured nanocomposite, significantly. The maximal enhancement arrives up to 56.4%, 119.4%, and 54.8%, compared to the baseline, respectively. These achievements are mainly attributed to the superior pulling-out effect of dispersed and tough MWNT fiber upon the notched cracks. Incorporation of acid-treated MWNT balances the σs, KIC, and δC values. Additional nanophase carbon black mixed into the above MWFRC further increases the corresponding fracture toughness, while additional short carbon fiber shows a negative effect.

Fluid dynamics simulation of the high shear mixing process

The Eulerian–Eulerian two-fluid approach for modelling multiphase flows is used to simulate the flow in a high shear mixer. The results are compared with experimental velocity profiles for the solids phase at the wall in the mixer obtained using a high speed camera (Darelius et al. Chem. Eng. Sci. 62 (2007) 2366). The governing equations are closed using relations from the Kinetic Theory of Granular Flow (KTGF) combined with a frictional stress model due to Johnson and Jackson and Schaeffer and inter-phase drag due to Wen and Yu. In addition, calculations are presented for a model with a constant particle phase viscosity (CPV). Free slip and partial slip boundary conditions for the solid phase velocity at the vessel wall and the impeller have been utilized. The results show that the bed height could be well predicted by the partial slip model, whereas the free slip model could not capture the experimentally found bed height satisfactorily. For the KTGF model, the swirling motion of the rotating torus that is formed by the moving powder bed was over-predicted and the tangential wall velocity was under-predicted, probably due to the fact that the frictional stress model needs to be further developed, e.g. to tackle cohesive particles in dense flow. The CPV model gave predictions in good agreement with the experiments for a solids viscosity of 0.1 Pa s and a wall slip parameter of 0.005 m/Pa s. However, for a very low or very high value of the particle phase viscosity and for a high value of the wall slip parameter the agreement with experiments was poor. Interestingly, values of the viscosity that are commonly employed for fluidized beds seem applicable also in the present case.

Fluoroelastomer‐MWNT nanocomposites‐1: Dispersion, morphology, physico‐mechanical, and thermal properties

AbstractThe present article reports the preparation and characterization of fluoroelastomer/multi‐walled nanotube hybrid nanocomposites prepared by conventional rubber mixing using a two‐roll mill. The morphology of the resulting hybrid nanocomposites were characterized by X‐ray diffraction (XRD), scanning (SEM) and transmission electron microscopies (TEM). SEM photographs showed the formation of completely exfoliated and uniformly dispersed nanotubes in the polymer matrix during the high shear mixing process. Magnetic force microscopy (MFM) has been used to further study the topography of the composites which also showed complete exfoliation. The effect of increasing MWNT loadings on the mechanical properties like tensile strength, modulus, elongation at break, hardness, and tear resistance has also been studied. The fracture surface of the composite has been studied by SEM. A “cross hatched pattern” has been observed. The thermal stability of the composites has been studied by TGA and increase in decomposition temperature with increase in MWNT loadings has been observed which was attributed to the antioxidant nature of nanotubes. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers.

CFD simulation of the high shear mixing process using kinetic theory of granular flow and frictional stress models

In order to enhance process understanding and to develop predictive process models in high shear granulation, there is an ongoing search for simulation tools and experimental methods to model and measure the velocity and shear fields in the mixer. In this study, the Eulerian–Eulerian approach to model multiphase flows has been used to simulate the mixer flow. Experimental velocity profiles for the solid phase at the wall in the mixer have been obtained using a high speed camera following the experimental procedure as described by Darelius et al. [2007a. Measurement of the velocity field and frictional properties of wet masses in a high shear mixer. Chemical Engineering Science, 62, 2366–2374]. The governing equations for modelling the dense mixer flow have been closed by using closure relations from the kinetic theory of granular flow (KTGF) combined with frictional stress models. The free slip and partial slip boundary conditions for the solid phase velocity at the vessel wall have been utilized. The partial slip model originally developed for dilute flows by Tu and Fletcher [1995. Numerical computation of turbulent gas–solid particle flow in a 90 ∘ bend. A.I.Ch.E. Journal, 41, 2187–2197] has been employed. It was found that the bed height could be well predicted by implementing the partial slip model, whereas the free slip model could not capture the experimentally found bed height satisfactorily. In the simulation, the swirling motion of the rotating torus formed was over-predicted and the tangential wall velocity was under-predicted, probably due to the fact that the frictional stress model needs to be further developed, e.g. to tackle cohesive particles in dense flow. The advantage of using the Eulerian–Eulerian approach compared to discrete element methods is that there is no computational limitation on the number of particles being modelled, and thus manufacturing scale granulators can be modelled as well.

Experimental constraints on shear mixing rates and processes: implications for the dilution of submarine debris flows

Abstract Submarine debris flows show highly variable mixing behaviour. Glacigenic debris flows travel hundreds of kilometres along the sea floor without undergoing significant dilution. However, in other locations, submarine slope failures may transform into turbidity currents before exiting the continental slope. Rates and processes of mixing have not been measured directly in submarine flow events. Our present understanding of these rates and processes is based on experimental and theoretical constraints. Significant experimental and theoretical work has been completed in recent years to constrain rates of shear mixing between static layers of sediment and overlying turbulent flows of water. This work was driven by a need to predict transport of fluid mud and the erosion of cohesive mud beds in shallow water settings such as estuaries, docks and shipping channels. These experimental measurements show that the critical shear stress necessary to initiate shear mixing (around 0.1 to 2 Pa) is typically several orders of magnitude lower than the yield strength of the debris. Shear mixing should initiate at relatively low velocities (about 10–200 cm s −1 ) on the upper surface of a submarine debris flow, at even lower velocities at its head (about 1–10 cm s −1 ), and play an important role in mixing over-ridden water into the debris flow. Addition of small amounts of mud (approximately 3% kaolin) to a sand bed dramatically reduces the rate of mixing at its boundary, and changes the processes by which sediment is removed. Estimates are presented for rates of shear mixing at a given flow velocity, and for the critical velocity necessary for hydroplaning or a transition from laminar to turbulent flow. Although these estimates are crude, and highlight the need for further experimental work, they illustrate the potential for highly variable mixing behaviour in submarine flow events.

Effects of an Organotitanate Cross-linking Additive on the Processing and Properties of Macro-Defect-Free Cement

We have investigated the effects of an organotitanate cross-linking additive on the processing and moisture sensitivity of macro-defect-free (MDF) cements. The modified samples were formed by a two-part process: first, the as-received calcium aluminate cement powder was coated with the organotitanate compound, followed by the standard MDF cement fabrication procedure. It was estimated that 6 wt% (by weight of the cement powder) of the additive was adsorbed. Rheological measurements showed that cross-linking reactions between the organotitanate additive and the polymer (polyvinyl alcohol-acetate) used to form MDF cement occurred during the high shear mixing process. This led to a 65% reduction in the processing window for the modified pastes as compared to the standard MDF cement pastes. However, the organotitanate-modified MDF cement samples exhibited improved moisture resistance as compared to the standard samples when exposed to 100% relative humidity at 22°C. The most significant result was that the modified samples retained nearly 100% of their initial strength after 200 days of exposure to these conditions, whereas the strength of the standard MDF samples was decreased by approximately 45%.

Effects of an organotitanate cross-linking additive on the processing and properties of macro-defect-free cement

Abstract We have investigated the effects of an organotitanate cross-linking additive on the processing and moisture sensitivity of macro-defect-free (MDF) cements. The modified samples were formed by a two-part process: first, the as-received calcium aluminate cement powder was coated with the organotitanate compound, followed by the standard MDF cement fabrication procedure. It was estimated that 6 wt% (by weight of the cement powder) of the additive was adsorbed. Rheological measurements showed that cross-linking reactions between the organotitanate additive and the polymer (polyvinyl alcohol-acetate) used to form MDF cement occurred during the high shear mixing process. This led to a 65% reduction in the processing window for the modified pastes as compared to the standard MDF cement pastes. However, the organotitanate-modified MDF cement samples exhibited improved moisture resistance as compared to the standard samples when exposed to 100% relative humidity at 22°C. The most significant result was that the modified samples retained nearly 100% of their initial strength after 200 days of exposure to these conditions, whereas the strength of the standard MDF samples was decreased by approximately 45%.

Microstructure of Melt Blended Polymer Systems

Two thermodynamically incompatible polymers were melt blended. The resulting microstructure and, consequently, the physical properties were dependent on the blending conditions and the rheological properties of the components. In this study the blending conditions were held constant while the rheological properties were varied and correlated with dispersion characteristics of the phases and the physical properties of the composite. A series of five atactic polystyrenes (weight average molecular weight from 75,000 to 400,000) and five linear polyethylenes (weight average molecular weight from 43,000 to 347,000) were used. The blending was done over a range of composition ratios in a normal stress extruder. Viscosity and normal stress of each pure component were measured in torsional flow. The mixed extrudates were examined by light interference microscopy, scanning electron microscopy, and solvent leaching. The nature and the fineness of the microstructure were interpreted in terms of the composition ratios, mixing history, and the melt rheological properties of the components. It was concluded that the fineness of the minor phase in a shear mixing process is a function of the difference between both the viscous and elastic behavior of the components.