Warpage of a large‐sized orthogonal stiffened plate produced by injection molding and injection compression molding

Rectangular plates of the size of 1800 × 600 × 12 mm³ and 1200 × 600 × 12 mm³ were selected for injection molding and injection compression molding, respectively, in order to investigate warpage characteristics of the large‐sized polymer plates with orthogonal stiffener. To determine the mold system and to reduce warpage of the specimen, numerical analyses for injection molding and injection compression molding were performed by using a commercial simulation code. Experiments were performed to verify the suggested mold system and warpage of the specimen. Relatively large warpage of the injection molded product was observed and small warpage of the injection compression molded product was generated. Compression force of the injection compression molding was only 6% of the clamp force of the injection molding. Warpage of the product was reduced significantly by using the injection compression molding. The injection compression molding will be used to substitute expensive and disused wood forms with inexpensive and recyclable polymer plates for concrete casting. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Kinetic rate equation combining ultraviolet‐induced curing and thermal curing. I. Bismaleimide system

A novel and general kinetic rate equation combining ultraviolet‐induced (UV‐induced) curing and thermal curing was successfully derived from the conventional thermal‐kinetic rate equation. This proposed novel kinetic rate equation can be applicable to the curing system either simultaneously or individually by UV‐induced and thermal cure methods. This general kinetic rate equation is composed of the reaction order n, activation energy E_a, curing temperature T, energy barrier of photoinitiation E_Q, intensity of UV radiation Q, concentration of photoinitiator [I], and a few other parameters. The proposed equation was supported by experimental data based on the curing systems of 4,4′‐bismaleimidodiphenylmethane (BMI) and 2,2‐bis(4‐(4 maleimido phenoxy) phenyl propane (BMIP). The BMI and BMIP systems were isothermally cured at various temperatures, or simultaneously cured with varying intensity of UV radiation (wavelength 365 nm). Conversion levels for the various cured samples were subsequently measured with a FTIR spectrometer. The reaction order n = 1.2, activation energy E_a = 40,800 J/mol, and E_Q = 7.5 mW/cm² were obtained for curing BMI system. The reaction order n = 1.3, activation energy E_a = 53,000 J/mol, and E_Q = 9.1 mW/cm² were obtained for curing BMIP system. The values of n and E_a in the same curing system (BMI or BMIP) are irrespective of the curing method (either simultaneously or individually by UV‐induced and thermal cure methods). The salient results of this study show that UV radiation only enhances the initiation rate and UV ration do not influence the activation energy E_a. The experimental results are reasonably well represented by these semi‐empirical expressions.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A new ionic liquids‐based monolithic column for determination of caffeine and theophylline

The present study has concentrated on finding a new stationary phase in liquid chromatography. To improve the selectivity of monolithic column, a new ionic liquids–based (ILs‐based) monolithic column (150 × 4.6 mm i.d.) is synthesized. Characteristic and evaluation of monolithic column are investigated by field emission‐scanning electron microscopy (FE‐SEM) and determination of caffeine and theophylline in high performance liquid chromatography (HPLC). FE‐SEM images show that this monolithic column has a porosity structure. At the condition of mobile phase was 0.06 mol L^?1 Na₂HPO₄ (pH 9.0) and flow rate was 0.7 mL min^?1, a good linear relationship was demonstrated when the concentrations of caffeine and theophylline were in the range of 0.1–60.0 μg mL^?1. These two compounds can obtain better resolution on the ILs‐based monolithic column than non‐ILs monolithic column, and the recoveries ranged from 97.40% to 108.00% and the interday and intraday relative standard deviations were less than 5%. The HPLC method, developed in this study, was proved to be acceptable for drugs assay, and this ILs‐based monolithic column as the stationary phase was a potential tool for future HPLC separation. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Crystallization of poly(l-lactide-dimethyl siloxane-l-lactide) triblock copolymers and its effect on morphology of microphase separation

This investigation characterizes the molten morphologies following isothermal crystallization of poly(l-lactide-block-dimethyl siloxane-block-l-lactide) triblock copolymers, which were synthesized by ring-opening polymerization of l-lactide using hydroxyl-telechelic PDMS as macroinitiators, via small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The break-out and preservation of the nanostructure of the triblock copolymer depended on the segregation strength, which was manipulated by varying the degree of polymerization. The crystallization kinetics of these semicrystalline copolymers and the effect of isothermal crystallization on their melting behaviors were also studied using DSC, FT-IR and WAXS. The exclusive presence of α-phase PLLA crystallite was verified by identifying the absence of the WAXS diffraction signal at 2θ = 24.5° and the presence of IR absorption at 1749 cm⁻¹ when the PLLA segment of the block copolymers was present as a minor component. The dependence of the crystallization rate (Rc) on the chemical composition of the triblock copolymers reveals that the Rc of the triblock copolymers was lower than that of PLLA homopolymer and the Rc were substantially reduced when the minor component of the crystallizable PLLA domains was dispersed in the PDMS matrix.     

Effects of film and substrate dimensions on warpage of film insert molded parts

Three‐dimensional flow and structural analyses were carried out for film insert injection molding to investigate warpage of film insert molded (FIM) parts with respect to variation of film and substrate thickness. Asymmetry of temperature distribution in the thickness direction was increased with increasing film thickness but decreased with increasing substrate thickness. Asymmetry of the in‐mold residual stress distribution in the FIM specimen was generated by the nonuniform temperature distribution, and it was increased with increasing film thickness but reduced with increasing substrate thickness. Warpage of the ejected FIM specimen was determined by relaxation of the asymmetric in‐mold residual stress distribution, and it was increased with increasing film thickness but reduced with increasing substrate thickness. Warpage of FIM specimens annealed at 80°C for 30 min showed complex behavior, and the behavior was understood by using factors such as degree of warpage of the ejected part, thermal shrinkage of the inserted film, and retardation of heat transfer. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Multiple effects of operating variables on heat transfer in three-phase slurry bubble columns

Characteristics of heat transfer were investigated in pressurized slurry bubble column reactors whose diameter was either 0.051, 0.076, 0.102 or 0.152 m (ID) and 1.5 m in height, respectively. Effects of gas velocity (U _G ), solid contents (S _C ), pressure (P), liquid viscosity (μ _L ) and column diameter (D) on the heat transfer coefficient (h) between the immersed vertical heater and the column were determined. Multiple effects such as UG and D, P and D, μ _L and D, and S _C and D on the value of heat transfer coefficient were discussed. Temperature fluctuations were also measured and analyzed by adapting chaos theory, which was used to explain the effects of operating variables on the heat transfer in the column. The heat transfer coefficient increased with increasing gas velocity, pressure or solid content in the slurry phase, but decreased with increasing liquid viscosity or column diameter. The decrease trend of h with increasing column diameter was somewhat sensitive when the gas velocity was relatively high (U _G ⩾12 cm/s). The effects of column diameter on the h value became almost linear when the operating pressure (P=4−10 kg _f /cm²), liquid viscosity (μ _L =20−38 mPa·s) or solid content in the slurry phase (S _C =10−20 wt%) was relatively high and gas velocity was relatively low, within these experimental conditions. The heat transfer coefficient was well correlated in terms of dimensionless groups as well as operating variables.     

Physical and thermal properties of acid-graphite/styrene-butadiene-rubber nanocomposites

In general, carbon-based materials play a major role in today’s science and technology and are required to advance with better properties to meet new requirements or to replace existing materials. We fabricated rubber composites reinforced with 5-weight% acid-graphite. The structural, mechanical and thermal properties of these composites were studied and compared. XRD studies indicated that the structure of the acid treated pristine-graphite (acid-graphite) did not change that of pristine graphite. Tensile properties of the composites indicated higher modulus, tensile strength and elongation in comparison with composites of pristine graphite, carbon black. Also, the composites were found to be in improving tendency with thermal properties and fatigue properties. The acid-graphite was investigated for surface morphology by scanning electron microscopy (SEM) and defects or purity by Raman spectroscopy. In this article, we discuss the influence of acid-graphite on rubber with high mechanical and thermal properties.     

Characteristics of Y3Al5O12:Ce phosphor powders prepared by spray pyrolysis from ethylenediaminetetraacetic acid solution

Nanometer and submicron-sized YAG:Ce phosphor powders were prepared by spray pyrolysis from the spray solutions with ethylenediaminetetraacetic acid (EDTA). The precursor powders with hollow and thin wall structure turned to the fine-sized YAG:Ce phosphor powders after post-treatment at high temperatures of 1400 and 1500 °C. The mean size of the phosphor powders post-treated at a temperature of 1500 °C was 0.72 μm. The white LEDs formed from the YAG:Ce phosphor powders post-treated at 1400 and 1500 °C showed (0.2781, 0.2871) and (0.2731, 0.2795) on the CIE chromaticity diagram, and about 78.20 and 79.04 of Ra. The luminous efficiency of the white LED formed from the commercial YAG:Ce phosphor powders was 84.36 lm/W. However, the luminous efficiencies of the white LEDs formed from the YAG:Ce phosphor powders post-treated at 1400 and 1500 °C were 47.74 and 76.64 lm/W.     

Synthesis and characterization of multiferroic BiFeO3 powders fabricated by hydrothermal method

The influence of processing parameters on phase formation and particle size of hydrothermally synthesized BiFeO₃ powders was investigated. BiFeO₃ powder was synthesized by dissolving bismuth nitrate and iron nitrate in KOH solution at temperatures ranging from 150 to 225 °C. X-ray diffraction patterns and scanning electron microscopy observation indicated that rod-like α-Bi₂O₃ phase was formed at initial stage of reaction and dissolved into ions to form thermodynamically stable BiFeO₃ phase. Single-phase perovskite BiFeO₃ has been formed using a KOH concentration of 8 M at a temperature of ≥175 °C in a 6 h reaction period. BiFeO₃ particle growth was promoted by lowering the KOH concentration, or increasing the duration time or reaction temperature. The effects of processing conditions on the formation of crystalline BiFeO₃ powders were discussed in terms of a dissolution–precipitation mechanism. The magnetization of the BiFeO₃ powders at room temperature showed a weak a ferromagnetic nature.     

橡胶品种对白炭黑填充胶料硫化特性和物理性能的影响

自从20世纪初炭黑对橡胶具有优异的补强性能被阐明后,炭黑一直作为主要补强剂与一些辅助补强剂,如粘土、碳酸钙和硅酸盐等共同用于改善硫化胶的物理性能。