Optimal process conditions of shrinkage and warpage of thin‐wall parts

Optimal process conditions of thin‐wall injection molding of a cellular phone cover were investigated with the consideration of interaction effects between process parameters. L₂₇ experimental tests based on Taguchi's method were performed, and then Cyclone Scanner, PolyCAD and PolyWorks were used to measure the shrinkage and warpage of the thin‐wall injected parts to determine the optimal process conditions. Based on the results of the analysis of variables and the F‐test, interaction effects for each observed factor were determined. The results indicated that the packing pressure was the most important process parameter affecting the shrinkage and warpage of the thin‐wall part. The optimal process conditions were different for the shrinkage and the warpage. This was because during the injection process, the mechanisms affecting shrinkage or warpage were different. Compared with the results obtained with simplified thin‐wall parts in the literature, it was found that the geometry of a real commercial part did affect the optimal process conditions and the order of influence of process parameters. The optimal process conditions determined by Taguchi's method for reducing the shrinkage and warpage were verified experimentally in this work. Polym. Eng. Sci. 44:917–928, 2004. © 2004 Society of Plastics Engineers.     

Stormer-numerov approximation for numerical solutions of ordinary and partial differential equations

Stormer-Numerov approximations of high accuracy were developed for solutions of non-linear boundary value problems and nonlinear elliptic partial differential equations. The approximations can be easily adopted also for parabolic partial differential equations in one and more space dimensions and feature fourth-order accuracy. For boundary value problems only three nodes are necessary to obtain the desired fourth order accuracy. The finite difference formula for parabolic partial differential equations can be readily generalized to a nonequidistant mesh so that automatic regridding in space may be used. The Stomer-Numerov approximations are important for solution of problems where storage limitations and computer time expenditure preclude standard second order methods. Because of the fourth order approximations a low number of mesh points can be used for a majority of chemical engineering problems. The application of Stormer-Numerov approximations is illustrated on a number of examples.     

The effect of various anti-setting systems in wool dyeing. Part 4; Sodium tetrathionate based systems

The tetrathionate anion has the potential to oxidise thiols specifically to disulphides; this property has been investigated in this paper from the point of view of using tetrathionate as an anti-setting agent in wool dyebaths. It was found that at pH 3 the addition of tetrathionate actually made the degree of permanent set greater than in its absence; however at pH 5 and pH 7 significant anti-setting benefits were achieved. The reason for the apparently contradictory result at pH 3 was found to be the substantivity and subsequent reactivity of thiosulphate anion for wool – this anion is a product of the reduction of tetrathionate by wool cysteinyl thiol residues.     

Effect of Co2+, Ni2+, Cu2+, or Zn2+ on properties of polyaniline nanoparticles

Uniform polyaniline (PANI) nanoparticles with typical sizes of about 50 nm were electropolymerized on indium tin oxide surfaces in the presence of Co²⁺, Ni²⁺, Cu²⁺, or Zn²⁺. According to shaping theory, we first suggest the reason forming PANI spherical particles. Their conductivity, UV‐vis spectra, FTIR spectra, X‐ray diffraction, and thermogravimetric analysis were investigated. The conductivities and crystallinity of PANI doped with these ions are higher than those of PANI doped with HCl (PANI/HCl). Both UV‐vis absorption spectra and FTIR spectra indicate the interactions between Co²⁺, Ni²⁺, Cu²⁺, or Zn²⁺ and PANI chains. TG analysis also shows that the thermal stability of PANI doped by Co²⁺, Ni²⁺, Cu²⁺, or Zn²⁺ is lower than that of PANI/HCl. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effects of the Addition of Different Types of Fillers on the Properties of BaO–ZnO–B2O3–SiO2 Glass Composites for Application to Barrier Ribs of Plasma Display Panels

Various types of crystalline ceramic fillers (TiO₂, ZrO₂, Al₂O₃, MgO, and cordierite) were added to BaO–ZnO–B₂O₃–SiO₂ (BZBS) glass (5–20 wt%), and the resultant dielectric constant, coefficient of thermal expansion (CTE), and optical reflectance were investigated for the application of the composites to the barrier ribs in plasma display panels. All the investigated fillers were partially dissolved into the glass at the fabrication temperature (575°C), and the residual fillers were aligned along the boundaries of sintered glass frits. By considering all aspects of the properties, the addition of TiO₂ fillers of about 10 wt% to BZBS glass was the most desirable of the types of fillers investigated. The addition of TiO₂ filler (10 wt%) yielded 61% in optical reflectance, 8.3 × 10⁻⁶ K^–1 in coefficient of thermal expansion, and 15.5 in dielectric constant, which were properties comparable with the currently used Pb-based barrier ribs.     

Amelioration of mechanical brittleness in hyperbranched polymer. 1. Macroscopic evaluation by dynamic viscoelastic relaxation

Hyperbranched poly(ether ketone)-b-linear poly(ether ketone)-b-hyperbranched poly(ether ketone) (HLHPEK) triblock copolymers with two different block compositions were prepared as an approach to improve the mechanical brittleness of hyperbranched poly(ether ketone) (HPEK). From the time-temperature superposition of dynamic shear moduli, G′(ω) and G″(ω), of HPEK and two HLHPEKs, it was investigated that the junction points between G′(ω) and G″(ω) shifted to the higher frequencies and the rubbery plateau region spread wider over the reduced frequency axis as the linear blocks were introduced and their compositions were increased. Such changes in viscoelastic response were consequences of increase in the amount of chain entanglements additionally formed by the linear blocks. In order to verify the effect of the linear block incorporation on amelioration of the mechanical brittleness, the degree of brittleness and its improvement were evaluated from the temperature dependence of the shift factors, a_Ts, experimentally obtained during the superposition of the dynamic moduli and of the average viscoelastic relaxation times, τ_HNs, determined with empirical Havriliak-Negami distribution function. From the nonlinear curve fittings of the a_Ts and the τ_HNs by the Vogel-Tamman-Fulcher equation, the degree of brittleness for HPEK and HLHPEK triblock copolymers were quantified as values of the material parameter D, an indicative of deviation from the linear Arrhenius behavior and a measure of fragility of the given material. The tendency of increasing D values with the linear block compositions confirmed substantial improvement of the mechanical brittleness in the HLHPEK triblock copolymers compared to HPEK. Therefore, the approach to copolymerize HPEK with its chemically analogous linear counterpart was verified to be an effective strategy to impart molecular entanglements and hence ameliorate the mechanical brittleness on the basis of macroscopic rheological evaluation.     

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.     

The permeation resistance of interface and the directional dependence of permeation in plasma-grafted composite membranes

Composite membranes were prepared by grafting plasma-polymerized films onto the surface of nonporous poly (dimethylsiloxane) films. Gas permeabilities of the composite membranes were measured at 35°C, 1 atm for N₂, 0₂, CO₂ and CH₄. The permeation properties of the composite membrane was analyzed using the series resistance model. There was a great interfacial resistance to CH₄ permeation through the composite membrane. The interfacial resistance was negligible for the other gases. The interfacial resistance seems to be a result of an interfacial layer caused by the interaction between the bulk two layers. For CH₄ gas, the permeation rate through the composite membrane was affected by the direction of flow. The directional dependence was negligible for the other gases.     

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.     

Compositional analysis of biodegradable polyphosphoester copolymers using nmr spectroscopic methods

The chemical composition and quantitative molar ratios among all components of biodegradable polyphosphoester copolymers of DL ‐lactide and ethylphosphate were determined by a comprehensive set of NMR spectroscopic methods. The polyphosphoester copolymers studied were synthesized using condensation polymerization of oligomeric DL ‐lactide prepolymers and ethyl dichlorophosphate. Conclusive identification of the chemical shift patterns of all functional groups in the copolymers required additional NMR methods such as ³¹P‐NMR and two‐dimensional ¹H–¹H COSY NMR, in addition to the synthesis and comparative NMR analysis of model compounds possessing identical phosphoester linkages in the polyphosphoester copolymers. For the polymers synthesized using the bulk polycondensation process, ¹H–¹H COSY NMR analysis revealed the presence of a small amount of side products that were undetected by ¹H‐NMR alone. These side reactions most likely occurred between the pendant ethoxy group of the phosphoesters and the hydrogen chloride gas generated in the bulk polycondensation process. ³¹P‐NMR spectra of the copolymers revealed a consistent triple‐peak pattern characteristic of phosphoesters linked to a racemic mixture of D,L ‐lactides. These results offered new insight into the side reactions occurring in bulk polymerization of polyphosphoesters and provided a powerful tool of characterizing complex biodegradable polymers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 4021–4031, 2003