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Processing of concentrated lignocellulosic biomass suspensions typically involves the conversion of the cellulose into sugars and sugars into ethanol. Biomass is usually pretreated via methods like comminution or steam explosion to form fine cellulosic fibers to be dispersed into an aqueous phase for further treatment. The resulting cellulose suspensions need to be pressurized and pumped into and out of various processing vessels without allowing the development of flow instabilities that are typically associated with 'demixing', that is, the segregation of the cellulosic biomass from the aqueous phase via the formation of mats of cellulosic fibers and the filtration of the aqueous phase. Such demixing can prevent continuous processing at high rates. Here, the development of flow instabilities via the demixing effect for cellulose suspensions is demonstrated using capillary and compressive squeeze flows. It is shown that the use of a gelation agent, hydroxypropyl guar gum, at the critical concentration of 0.5 wt% or higher significantly affects the viscoelastic material functions of cellulosic suspensions, improves the dispersive mixing of the fibers within the aqueous phase, and results in the elimination of the flow instabilities and associated demixing effects that are ubiquitously observed during the pressurization and processing of cellulosic suspensions. KEYWORDS cellulose, suspension, biomass, gels, demixing, extrusion, gelation, mixing, phase separation, processing, squeeze, 1 | INTRODUCTION Lignocellulosic biomass has played a key role in daily life for centuries for heating, cooking, clothing, and paper manufacture. It also serves as an energy source that [...]

Here we present a solution-based method of growing three-dimensional flower-shaped metal halide perovskite crystals by drop casting solutions of FAxMA1−xPbyI1+2y precursors (FA = formamidinium, MA = methylammonium) on close-packed monolayers of titanium dioxide (TiO2) colloidal particles. The colloidal films directed perovskite crystallization during solvent evaporation, with crystals first nucleating within the confining interstitial sites between colloidal particles and growing perpendicular to the substrate surface. When growth proceeded above the colloidal film, the crystals blossomed outwards to form flower-shaped hopper crystals with a hierarchical 3D structure. The crystal shapes ranging from circular discs to pointed snowflakes were achieved by varying the solution pH and precursor composition. Structural complexity in these crystals was observed across multiple length scales – X-ray diffraction patterns and spatially-resolved photoluminescence mapping revealed three polymorphs present for all compositions tested: two bulk phases and one surface phase. These structures exhibit broad areas for light absorption but small contact areas with the underlying substrate for charge transport, which may be useful for optoelectronic devices, such as 2D photodetectors. [ABSTRACT FROM AUTHOR]

Foams of an engineering plastic, poly(ether imide), were extruded using a single screw extruder employing pressurized C[O.sub.2] as the blowing agent. The porosity, pore size distributions, and the density of the foams were especially affected by the pressure drop, the pressure loss rate, and temperature at the die. Significant increases in porosity and pore size and corresponding decreases in density were observed when the pressure imposed on C[O.sub.2] became greater than the critical pressure values of C[O.sub.2] (i.e., the temperature was always greater than the critical temperature of the C[O.sub.2] in the extruder and the die). The viscoelastic material functions of the extruded foams depended especially on the density of the foam, with the elastic modulus increasing with density. The incorporation of nanosilica particles in the 0.08-0.6% by weight range increased only the density of the foam and did not provide any benefits in controlling of the nucleation rate and the pore size distribution, presumably due to their poor dispersibility and agglomerated state in the single screw extruder. POLYM. ENG. SCI., 54:2064-2074, 2014., INTRODUCTION The need for polymeric foams with advanced functionalities is increasing especially for applications in aerospace, electronics, construction, automotive and energy [1-3]. Important foam properties include low foam density, adequate [...]

Conventional electrospinning is a simple process, suitable for the processing of solvated polymers at relatively low rates. It lacks the capabilities of conveying of solids, mixing of polymeric resins and devolatilization and has limited capabilities in melting and incorporation of fillers, including nanoparticles. The use of a twin screw extruder as the front end of the electrospinning process provides these capabilities but only becomes feasible at relatively high throughput rates. Such high rates of electrospinning can only be achieved by using multi-nozzle spinnerets. However, the dynamics of electrospinning processes using multi-nozzle spinnerets has not been well studied. Here a multi-nozzle spinneret attached to a hybrid twin screw extrusion and electrospinning apparatus was employed for the characterization of the dynamics in terms of the electrospun mesh thickness distributions of poly(caprolactone), PCL, as a function of the principal parameters of the electrospinning process, i.e., applied voltage, distance of separation between the spinneret die, and the collector, i.e., a conductive mandrel, and its rotational speed. PCL fiber diameter and orientation distributions, as well as the thickness, crystallinity, and mechanical properties of the non-woven meshes, were characterized to gain a basic understanding of how the electro-spun mesh properties develop as a function of process parameters in the multi-nozzle configuration. POLYM. ENG. SCI., 53:1463-1474, 2013. © 2012 Society of Plastics Engineers, INTRODUCTION Electrospinning of polymeric resins is a simple process that is widely used to generate experimental quantities of polymeric fibers and nanofibers. The conventional electrospinning process, practiced with little change [...]

The complex micro-/nanostructure of native cartilage-to-bone insertion exhibits gradations in extracellular matrix components, leading to variations in the viscoelastic and biomechanical properties along its thickness to allow for smooth transition of loads under physiological movements. Engineering a realistic tissue for osteochondral interface would, therefore, depend on the ability to develop scaffolds with properly graded physical and chemical properties to facilitate the mimicry, of the complex elegance of native tissue. In this study, polycaprolactone nanofiber scaffolds with spatially controlled concentrations of [beta]-tricalcium phosphate nanoparticles were fabricated using twin-screw extrusion-electrospinning process and seeded with MC3T3-E1 cells to form osteochondral tissue constructs. The objective of the study was to evaluate the linear viscoelastic and compressive properties of the native bovine osteochondral tissue and the tissue constructs formed in terms of their small-amplitude oscillatory shear, unconfined compression, and stress relaxation behavior. The native tissue, engineered tissue constructs, and unseeded scaffolds exhibited linear viscoelastic behavior for strain amplitudes less than 0.1%. Both native tissue and engineered tissue constructs demonstrated qualitatively similar gel-like behavior as determined using linear viscoelastic material functions. The normal stresses in compression determined at 10% strain for the unseeded scaffold, the tissue constructs cultured f or four weeks, and the native tissue were 0.87 [+ or -] 0.08 kPa, 3.59 [+ or -] 0.34 kPa, and 210.80 [+ or -] 8.93 kPa, respectively. Viscoelastic and biomechanical properties of the engineered tissue constructs were observed to increase with culture time reflecting the development of a tissuelike structure. These experimental findings suggest that viscoelastic material functions of the tissue constructs can provide valuable inputs for the stages of in vitro tissue development. [DOI: 10.1115/1.4001884] Keywords: functionally graded, interface, osteochondral, scaffold, tissue engineering, electrospinning

Coextrusion is widely used to fabricate multilayered products with each layer providing a separate functionality, including barrier resistance to gases, strength, and printability. Here an analytical model of the coextrusion die flow of two incompressible, viscoplastic fluids in a slit die, subject to nonlinear wall slip and under fully developed and isothermal conditions, is developed to allow the prediction of the steady-state velocity and shear stress distributions and the flow rate versus pressure gradient relationship. The resulting model is applied to the coextrusion of two layers of viscoplastic fluids in a thin rectangular slit die (slit gap, h ≪ slit width, W). The analytical solution recognizes a number of distinct flow conditions (eleven cases) that need to be treated separately. The solutions for all eleven cases are provided along with an apriori identification methodology for the determination of the applicable case, given the shear viscosity and wall slip parameters of the two viscoplastic fluids, the slit geometry and the flow conditions. Simplifications of the model would provide the solutions for the fully developed and isothermal coextrusion flows of any combination of Hershel-Bulkley, Bingham, power-law and Newtonian fluids with or without wall slip at one or both walls of the slit die. POLYM. ENG. SCI., 50:652-664, 2010. [C] 2009 Society of Plastics Engineers, INTRODUCTION Multilayered coextrusion involves the bringing together of two or more fluids (1) to generate layered products with structural distributions and ultimate properties that depend on the properties of the [...]

The rheological and processing behavior of BaS[O.sub.4]-filled medical-grade (additivefree) thermoplastic polyurethanes (TPUs) was investigated. The rheology and the singlescrew and twin-screw extrusion processing of filled TPU were found to be complicated by the moisture and the air entrained into the suspension upon the incorporation of the filler BaS[O.sub.4]. It was observed that the 20 vol% BaS[O.sub.4]-filled TPU exhibits decreased, rather than increased, shear viscosity and elasticity (as manifested through smaller storage modulus values in small-amplitude oscillatory shear flow) in comparison to unfilled TPU in the temperature range of 190[degrees]C to 200[degrees]C at which these materials are usually processed. The moisture remaining in the BaS[O.sub.4] will hydrolyze the polymer, leading to a decrease in the molecular weight of the TPU. However, the moisture contained in the filler itself is not sufficient to explain the significant reductions in viscosity and elasticity of the suspension upon the compounding of the BaS[O.sub.4]. It is shown that the major factor giving rise to the reductions in elasticity and the viscosity of the suspension of TPU and BaS[O.sub.4] is the air (and the moisture air contains) entrained into the extruder during the feeding of the BaS[O.sub.4]. Air, carried with the filler into the extruder, is entrained into the suspension to hydrolyze the TPU and to further impart a foamy structure under typical processing conditions to significantly reduce the shear viscosity and the elasticity of the suspension in comparison to unfilled TPU. Polym. Eng. Sci. 44:1941-1948, 2004. [c] 2004 Society of Plastics Engineers., INTRODUCTION Barium sulfate (BaS[O.sub.4])-filled thermoplastic polyurethane is widely used in the medical device industry. Barium sulfate is radiopaque and is usually given to patients in a 'barium meal' as a [...]

The selection of operating conditions and geometry for the processing of thermoplastic polyurethane, TPU, is a complicated task. This complication arises from the relatively high melting temperature of the crystalline hard blocks and the oxidative and thermal degradation and crosslinking that occur at temperatures that are relatively close to the melting temperature of the TPU. This article documents the rheology, extrusion, and structure development of a medical-grade TPU. The medical application requires that the additives commonly utilized in the development of polymeric resins, i.e., stabilizers, antioxidants, and lubricants, should be minimized; the TPU of this study contains no additives. At temperatures 10-20°C lower than the melting temperature of the TPU, the morphology of the hard blocks continues to evolve to generate a reversible increase in elasticity and shear viscosity of the TPU with increasing time. At temperatures greater than the melting temperature, the TPU undergoes degradation and crosslinking reactions, which give rise to a permanent increase in the elasticity and the shear viscosity of the TPU. The ramifications of the degradation and crosslinking at temperatures greater than 200°C and morphology modification upon the continuing evolution of the hard blocks at temperatures less than 200°C on the rheology and processing were investigated., INTRODUCTION Thermoplastic polyurethanes (TPU), which are composed of alternating soft and hard segments along a high molecular weight polymeric backbone, are very versatile polymers with a wide range of applications. [...]

The development of the electrical properties of composites as a function of the degree of mixedness of a conductive filler distributed into an insulating polymer is investigated. A wide-angle X-ray diffraction (WAXD)-based quantitative phase analysis method was used to characterize the variations of the concentrations of the insulating binder and the conductive particles around their mean values as a function of mixing time in an intensive batch mixer. Increasing the time and hence, the specific energy input, during the mixing process results in a more homogeneous spatial distribution of the conductive filler in the polymeric matrix, which in turn results in a decrease of the volume conductivity of the composite. The decreasing conductivity of the composite is attributed to the better coating and hence the isolation of the conductive particles from each other, thus hindering the formation of a conductive network 'percolation.' Overall, these results suggest that the control of the electrical properties of con ductive composites could benefit from a good understanding and adequate control of the dynamics of the mixing process and the resulting degree of mixedness of the conductive particles in the polymer matrix., INTRODUCTION AND BACKGROUND OF THE STUDY Electrically conductive nonmetallic materials are used in various applications including electromagnetic interference (EMI) shielding, adhesives, devices and sensors (1-6). Doping of the polymer, vacuum [...]