Andrew N. Hrymak

Crystal Morphology of Hydrogenated Castor Oil in the Crystallization of Oil-in-Water Emulsions: Part II. Effect of Shear

Crystallization of hydrogenated castor oil-in-water emulsions has been studied by polarized light microscopy, scanning electron microscopy, X-ray powder diffraction, and differential scanning calorimetry. Three types of crystal morphologies have been observed: rosettes, fibers, and irregular crystals. The energy barrier to nucleation for fibers is suggested to be higher than that of rosettes. Irregular crystals are thermodynamically less stable and tend to transform into stable polymorphs. Under isothermal crystallization at a temperature of 70 °C, mainly rosettes are observed. With an increase of supercooling, by decreasing the temperature to 55 °C, more fibers form due to a lower energy barrier to nucleation. If the crystallization temperature is set to 45 °C, irregular crystals form first and then transform into rosettes. A nonisothermal crystallization study shows that at a cooling rate of 1 °C/min, more rosettes and fibers are produced compared to a higher cooling rate of 5 °C/min, which produces more irregular crystals.

Recent developments in the production and applications of bacterial cellulose fibers and nanocrystals.

Abstract Cellulosic nanomaterials provide a novel and sustainable platform for the production of high performance materials enabled by nanotechnology. Bacterial cellulose (BC) is a highly crystalline material and contains pure cellulose without lignin and hemicellulose. BC offers an opportunity to provide control of the products’ properties in-situ, via specific BC production methods and culture conditions. The BC potential in advanced material applications are hindered by a limited knowledge of optimal BC production conditions, efficient process scale-up, separation methods, and purification methods. There is a growing body of work on the production of bacterial cellulose nanocrystals (BCNs) from BC fibers. However, there is limited information regarding the effect of BC fibers’ characteristics on the production of nanocrystals. This review describes developments in BC and BCNs production methods and factors affecting their yield and physical characteristics.

Coupled CFD–DEM of particle-laden flows in a turning flow with a moving wall

Abstract The nature of the particle–solid interactions and particle–fluid interactions in rectangular duct bend geometry with/without a moving wall is studied, taking into account particle collision, colloidal, and hydrodynamic forces, and four way coupling between the fluid flow and particles. The focus is on systems where particles and fluid phase have similar length scales, fluid Reynolds number ( Re f )xa0∼xa01, and particles Stokes number ( St )xa0∼xa01. Particles move toward the walls of the channel near the bend, and have long residence times in these regions. Buoyancy force has negligible effect on particle motion, where adhesion and drag forces lead to particle motion and agglomeration patterns. The effect of a free surface on agglomeration sites in the turning flow is elucidated.

Characterization of Extruded Thermoplastic Starch Reinforced by Montmorillonite Nanoclay

The purpose of this study was to understand how the montmorillonite (MMT) nanoclay influences physical and mechanical properties of thermoplastic starch (TPS), which was produced by a conventional extrusion procedure. MMT nanoclay was added at 0, 4, and 8xa0% (w/w) concentrations. Transmission electron microscopy (TEM) showed most MMT platelets existed in tactoid structure in the starch matrix. In addition, FTIR spectra indicated TPS/MMT nanocomposites kept chemically stable after the extrusion. Tensile strength (TS) was about 7.0xa0MPa, while elongation-at-break (E) and elastic modulus (EM) were about 52xa0% and 32–41xa0MPa, respectively. Moisture sorption behaviour of the samples was well described by GAB and BET models. Thermal property tests exhibited the glass transition temperature (Tg) of the nanocomposites decreased with increasing MMT from 0 to 8xa0%, indicating MMT nanoclay had a plasticization effect.

Investigation on dip coating process by mathematical modeling of non-Newtonian fluid coating on cylindrical substrate

A mathematical model for the dip coating process has been developed for cylindrical geometries with non-Newtonian fluids. This investigation explores the effects of the substrate radius and hydrodynamic behavior of the non-Newtonian viscous fluid on the resulting thin film on the substrate. The coating fluid studied, Dymax 1186-MT, is a resin for fiber optics and used as a matrix to suspend 1 vol. % titanium dioxide particles. The coating substrate is a 100 μm diameter fiber optic diffuser. Ellis viscosity model is applied as a non-Newtonian viscous model for coating thickness prediction, including the influence of viscosity in low shear rates that occurs near the surface of the withdrawal film. In addition, the results of the Newtonian and power law models are compared with the Ellis model outcomes. The rheological properties and surface tension of fluids were analyzed and applied in the models and a good agreement between experimental and analytical solutions was obtained for Ellis model.

Coupling of Mold Flow Simulations with Two-Scale Structural Mechanical Simulations for Long Fiber Reinforced Thermoplastics

The entire simulation process for long fiber reinforced thermoplastics is examined to determine the effective mechanical properties which are influenced by the microstructural fiber orientation state. Therefore, flow and fiber orientation simulations are conducted and the obtained fiber orientation tensors are used in two-scale structural simulations. The fiber orientation distributions as well as the mechanical properties are compared with micro-computed tomography data and results from threepoint bending tests performed by dynamical mechanical analysis (DMA), respectively. The validated results show that prediction of the essential mechanical properties is possible with the applied combinated methods and that the knowledge of the fiber orientation and its gradients is of crucial importance for the entire simulation process.

Numerical simulation of the dip-coating process with wall effects on the coating film thickness

The dip-coating process for liquid film deposition on cylindrical substrates is numerically simulated, and the effects of the coating bath walls proximity to the substrate are investigated for the deposited film thickness. In the present work, the hydrodynamics of non-Newtonian liquid films are studied, applying Carreau and power law models. The free surface position is determined by the volume of fluid technique in a three-dimensional system, while the impacts of density, viscosity, and surface tension are taken into account. The momentum and mass balance, alongside the constitutive equations, were solved for dip-coating process using numerical simulations in an open source CFD software package of OpenFOAM. Numerical outcomes are validated with experimental data over a large range of withdrawal velocities up to 6xa0m/s. Also good agreement is obtained for numerical simulation results with experimental data for coating thickness, considering the proximity effects of bath walls to the cylindrical substrate being withdrawn from a coating bath.

Effect of Hybrid Carbon Fillers on the Electrical and Morphological Properties of Polystyrene Nanocomposites in Microinjection Molding

The effect of hybrid carbon fillers of multi-walled carbon nanotubes (CNT) and carbon black (CB) on the electrical and morphological properties of polystyrene (PS) nanocomposites were systematically investigated in microinjection molding (μIM). The polymer nanocomposites with three different filler concentrations (i.e., 3, 5 and 10 wt %) at various weight ratios of CNT/CB (100/0, 30/70, 50/50, 70/30, 0/100) were prepared by melt blending, then followed by μIM under a defined set of processing conditions. A rectangular mold insert which has three consecutive zones with decreasing thickness along the flow direction was adopted to study abrupt changes in mold geometry on the properties of resultant microparts. The distribution of carbon fillers within microparts was observed by scanning electron microscopy, which was correlated with electrical conductivity measurements. Results indicated that there is a flow-induced orientation of incorporated carbon fillers and this orientation increased with increasing shearing effect along the flow direction. High structure CB is found to be more effective than CNT in terms of enhancing the electrical conductivity, which was attributed to the good dispersion of CB in PS and their ability to form conductive networks via self-assembly. Morphology observations indicated that there is a shear-induced depletion of CB particles in the shear layer, which is due to the marked difference of shear rates between the shear and core layers of the molded microparts. Moreover, an annealing treatment is beneficial to enhance the electrical conductivity of CNT-containing microparts.

Properties of microinjection-molded multi-walled carbon nanotubes-filled poly(lactic acid)/poly[(butylene succinate)-co-adipate] blend nanocomposites

In this study, the morphological, thermal and electrical properties of microinjection-molded multi-walled carbon nanotubes (CNT)-filled poly(lactic acid) (PLA) and PLA/poly[(butylene succinate)-co-adipate] (PLA/PBSA) immiscible blends were studied systematically. The PLA/PBSA/CNT immiscible blends were prepared by melt blending of PLA, PBSA and CNT in a batch mixer. Four different types of compounding procedure were employed to investigate the influence of compounding sequence of various components on the electrical conductivity of subsequent micromoldings. Results revealed that despite the compounding sequence, the electrical conductivity of PLA/PBSA/CNT microparts is invariably higher than that of CNT-filled mono-PLA counterparts and the selective localization of CNT in PBSA is thought to be the contributing factor. Furthermore, the prevailing high shearing conditions in microinjection molding (µIM) could lead to the coalescence of CNT-enriched PBSA domains, favoring the formation of conductive pathways in the melt flow direction, as confirmed by morphology observations. The crystallinity of PLA/PBSA immiscible blends is higher than that of mono-PLA system and a further increase in crystallinity after µIM suggested flow-induced crystallization. Moreover, thermal stability analysis indicated that the prevailing high shear rates in µIM might have a chain scission effect on PLA and PBSA.

Electrical, Morphological and Thermal Properties of Microinjection Molded Polypropylene/Multi-Walled Carbon Nanotubes Nanocomposites

Abstract A series of polypropylene/multi-walled carbon nanotubes (PP/CNT) nanocomposites were prepared by masterbatch dilution, then followed by microinjection molding under a defined set of processing conditions. A micropart (μ-part) which has a three-step decrease in thickness along the flow direction was fabricated to study the effect of abrupt geometrical changes in mold cavities on the distribution of CNT in PP. To facilitate characterization, the μ-parts were divided into three sections based on thickness. The distribution of CNT within each section of subsequent μ-parts was evaluated by morphological observations and electrical resistivity measurements. In addition, the thermal properties of pure PP and PP/CNT nanocomposites as well as each section of subsequent μ-parts, were assessed by differential scanning calorimetry and thermogravimetric analysis.