Three-dimensional modelling of Non-Newtonian fluid flow in a coat-hanger die

The three-dimensional model of isothermal flow of power-law fluid in a coat-hanger die has been developed using finite element method. The shape of coat-hanger die used in the present model was determined according to the previous analytical design equation which is based on one-dimensional flow model in the manifold and the slot. Because uniform flow rate across the die outlet is most important to achieve uniform thickness of extruded polymer sheet or film, flow rate distribution is mainly examined to determine the valid process condition for the design equation as the design parameters are changed. The effects of fluid property in terms of power-law index and process parameters not considered in one-dimensional design equation such as die inlet size and the presence of land were analyzed. Results show that the manifold angle is the most influencing design parameter on flow rate distribution. When the material of different power-law index from design value is processed, the change of power-law index affects the uniformity of flow rate appreciably.     

Preparation of Monodisperse ZrO2 by the Microwave Heating of Zirconyl Chloride Solutions

Based on the principle that the solubility of a salt decreases as the dielectric constant of the solvent decreases, zirconia powders were prepared by heating a zirconyl chloride solution with a 2-PrOH-water mixture as the solvent. The morphology, size, and size distribution of the resulting particles were highly sensitive to the heating method used on the starting solution. Particles formed under conventional heating methods were polydisperse, agglomerated spherical, or irregularly shaped because of inhomogeneous precipitation through the temperature gradient, the shear force induced by stirring, compositional nonuniformity, and the low heating rate. The present study demonstrated that microwaves provide an excellent means of heating uniformly and rapidly without stirring. The particles resulting from microwave treatment were monodisperse and spherical, with a mean diameter of 0.28 μm.     

Kinetics of cellobiose decomposition under subcritical and supercritical water in continuous flow system

The effects of reaction temperature, pressure and residence time were investigated with a flow apparatus. Cellobiose decomposition kinetics and products in suband supercritical water were examined at temperatures from 320 to 420 °C at pressures from 25 to 40 MPa, and at residence times within 3 sec. Cellobiose was found to decompose via hydrolysis and pyrolysis. The yield of desired hydrolysis product, glucose, was the maximum value of 36.8% at 320 °C, 35 MPa, but the amount of 5-(hydroxymethyl)furfural (HMF), fermentation inhibitor increased too because residence time increased in the subcritical region owing to decrease of reaction rate. Meanwhile, though the yield of glucose is low in the supercritical region, the yield of HMF decreased compared with the subcritical region; and at the minimum yield of HMF (380 °C, 25 MPa), the yield of glucose was 21.4%. The decomposition of cellobiose followed first-order kinetics and the activation energy for the decomposition of cellobiose was 51.05 kJ/mol at 40MPa.     

Monodisperse polymer/metal composite particles by electroless chemical deposition: Effect of surface functionality of polymer particles

Micron‐sized polymer particles were coated with layers of nickel compounds by plating electrolessly in the presence of aqueous solutions of nickel chloride, sodium hypophosphite, sodium citrate, and ammonium chloride at elevated temperature. The uniform functional polymer particle could be obtained by seeded polymerization. To investigate the effect of surface functionality on the conditions for nickel deposition, the polymer particle was functionalized with the thiol group. From morphological observation, it was found that the mode of nickel deposition was greatly dependent on the surface functionality of the polymer particle. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 420–424, 2003     

Binary blends of nylons with ethylene vinyl alcohol copolymers: Morphological,thermal, rheological,and mechanical behavior

Binary blends of ethylene vinyl alcohol copolymers, containing 62 (EVOH-62) and 71 (EVOH-71) mole percent vinyl alcohols, with nylons (nylon-6, nylon-6/12, and nylon-12) have been prepared from melt mixing in a twin screw compounding machine. Morphological, thermal, rheological, and mechanical properties were determined. EVOH-62/nylon-6 and EVOH-71/nylon-6 blends showed homogeneous phase morphologies in the nylon-6-rich region, and fine phase separations (c.a. 2 × 10^?7 m) in the EVOH-rich region. Melting point depression, positive deviations in viscosity and flexural modulus, and negative deviation in impact strength from the simple additive rule were generally observed. And the results were possibly interpreted in terms of compatibility and increased nylon/EVOH interactions over the nylon/nylon interactions. On the contrary, clean phase separations in large domains were observed from EVOH-71/nylon-6/12 and EVOH-71 /nylon-12 blends. Fibrillation was also obtained from EVOH rich blends. Probably due to the incompatible nature of these blends, yield at low rate of shear and a mechanical property drop were also observed.     

Electrochemical behavior of Sn8Hg (gamma-2) and dental amalgam in a phosphate buffer solution

The gamma-2 phase (Sn₈Hg) and a dental amalgam in phosphate buffer have been studied by means of potentiostatic and galvanostatic techniques, along with a rotating ring-disc electrode (RRDE). The analysis of results has shown that phosphate ions play an important role in the corrosion of amalgam. The anodic reaction leads to the formation of soluble species and a passivating film, which is probably composed of tin hydroxide and tin phosphate.     

Synthesis and Characterization of Segmented Block Copolymers Based on Hydroxyl‐Terminated Liquid Natural Rubber and α,ω‐Diisocyanato Telechelics

Summary: Segmented block copolymers, consisting of non‐polar soft segments from hydroxyl‐terminated liquid natural rubber (HTNR) and polar hard segments from α,ω‐diisocyanato telechelics obtained by “criss‐cross”‐cycloaddition, have been synthesized. The block copolymer formation took place under relatively mild reaction conditions at 80 °C in dichloroethane in the presence of dibutyltin dilaurate as a catalyst. The resulting block copolymers were characterized by spectroscopic techniques (¹H NMR, FTIR, UV‐vis spectroscopy) as well as GPC for molar mass determination. The block copolymers were compression molded in a hot stage press, and the resulting samples were characterized by DSC and stress‐strain measurement. The solubility and phase morphology of the materials have also been studied.

Segmented block copolymer from HTNR and α,ω‐diisocyanato telechelics     

Synthesis of syndiotacticity‐rich high molecular weight poly(vinyl alcohol) by suspension polymerization of vinyl pivalate and saponification

Vinyl pivalate (VPi) was suspension‐polymerized to synthesize high molecular weight (HMW) poly(vinyl pivalate) (PVPi) with a high conversion above 95% for a precursor of syndiotacticity‐rich HMW poly(vinyl alcohol) (PVA). Also, the effects of the polymerization conditions on the conversion, molecular weight, and degree of branching (DB) of PVPi and PVA prepared by the saponification of PVPi were investigated. Bulk polymerization was slightly superior to suspension polymerization in increasing the molecular weight of PVA. On the other hand, the latter was absolutely superior to the former in increasing the conversion of the polymer, indicating that the suspension polymerization rate of VPi was faster than that of the bulk one. These effects could be explained by a kinetic order of a 2,2′‐azobis(2,4‐dimethylvaleronitrile) concentration calculated by the initial rate method. Suspension polymerization of VPi at 55°C by controlling various polymerization factors proved to be successful in preparing PVA of HMW [number‐average degree of polymerization (P_n): 8200–10,500], high syndiotactic diad content (58%), and very high yield (ultimate conversion of VPi into PVPi: 94–98%). In the case of the bulk polymerization of VPi at the same conditions, the maximum P_n and conversion of 10,700–11,800 and 32–43% were obtained, respectively. The DB was lower and the P_n was higher with PVA prepared from PVPi polymerized at lower initiator concentrations. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 832–839, 2003     

Preparation of water‐soluble syndiotacticity‐rich high molecular weight poly(vinyl alcohol) microfibrillar fibers using copolymerization of vinyl pivalate and vinyl acetate and saponification

Water‐soluble high molecular weight (HMW) syndiotactic poly(vinyl alcohol) (s‐PVA) microfibrillar fibers were prepared by the saponification with various conditions such as amount of alkali solution, saponification temperature, and saponification concentration from copoly(vinyl pivalate (VPi)/vinyl acetate (VAc)) copolymerized using various VPi/VAc feed ratios. To produce s‐PVA microbrillar fibers having various water‐soluble temperatures for many industrial applications, the intrinsic viscosities, syndiotactic diad (S‐diad) contents, and degrees of saponification (DS)s of PVAs were finely controlled to 1.2–3.6 dL/g, 56.3–58.3%, and 91.4–98.3%, respectively. Through a series of experiments, it was found that the amount of alkali may alter the structure of the saponified polymers, primarily the DS, and the structural variation changes viscosity. That is, intrinsic viscosity was sharply decreased as the amount of alkali solution was increased. DS was increased with an increase in the amount of alkali solution. S‐diad content was increased with an increase in the VPi content. HMW s‐PVA microfibrillar fibers having S‐diad content of 56.3–58.3% prepared by the saponification of copoly(VPi/VAc) were completely soluble in water at 100°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1482–1487, 2003     

PSA performances and viscoelastic properties of SIS‐based PSA blends with H‐DCPD tackifiers

Hotmelt pressure sensitive adhesives (PSAs) usually contain styrenic block copolymers like styrene–isoprene–styrene (SIS), SBS, SEBS, tackifier, oil, and additives. These block copolymers individually reveal no tack. Therefore, a tackifier is a low molecular weight material with high glass transition temperature (T_g), and imparts the tacky property to PSA. The SIS block copolymer with different diblocks was blended with hydrogenated dicyclopentadiene (H‐DCPD tackifier), which has three kinds of T_g. PSA performance was evaluated by probe tack, peel strength, and shear adhesion failure temperature. PSA is a viscoelastic material, so that its performance is significantly related to the viscoelastic properties of PSAs. We tested the viscoelastic properties by dynamic mechanical analysis and the thermal properties by differential scanning calorimeter to investigate the relation between viscoelastic properties and PSA performance. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 2839–2846, 2006