Epoxy resin is a material commonly used for the encapsulation of light-emitting diodes (LED). Three epoxy resins were chosen in this study: D.E.R.-331 was a bisphenol A type epoxy resin, Eporite-5630 was a bisphenol A type epoxy resin modified with a UV stabilizer, and ERL-4221 was a cyclo-aliphatic epoxy resin. The curing agent was methyl hexahydrophthalic anhydride (MHHPA), and the catalyst was tetra-butyl ammonium bromide (TBAB). Thermal, environmental, and optical properties of the cured epoxy resins were studied. It was found that cured ERL-4221 had better UV resistance, but other properties of ERL-4221 were lower because of the internal stress generated during the curing process. D.E.R.-331 showed better thermal stability, but the aromatic groups in the main chains caused sensitivity to photodegradation. Eporite-5630 had the advantages of D.E.R.-331 and better UV resistance than D.E.R.-331 because of the addition of UV stabilizer. Among the three materials, Eporite-5630 was the best choice of the balance properties for LED applications. This finding may assist in the selection of epoxy resins used in LED technology. (C) 2004 Wiley Periodicals, Inc.
Dynamic mechanical analysis (DMA) was used to study the miscibility and various transitions (alpha, beta, and gamma) in binary blends of ethylene vinyl acetate copolymer (EVA) with low-density polyethylene (LDPE) and high-density polyethylene (HDPE). Addition of a rubbery phase, such as EVA, reduced all the transition temperatures. A peak broadening of tan 8 was observed with increasing EVA content in the blends. This can be explained by the observed reduction of the crystallinity of the systems. The presence of a single transition peak in the region of glass transition temperature (T-g) has indicated that the blends were miscible. However, morphological investigation by scanning electron microscopy (SEM) revealed the features of a two phase system in which the EVA domains would be dispersed in the polyethylene (PE) phase. The results have demonstrated that DMA is not sensitive enough to study the miscibility of polymeric blends with a similar backbone structures (such as PE and EVA) in view of the small difference in their T-g. For such blends, therefore, the use of direct observations, such as microscopic examinations is necessary. (C) 2004 Wiley Periodicals, Inc.
This paper presents an innovative design of a tandem extrusion system for fine-celled foaming of plastic/wood-fiber composites using a physical blowing agent (PBA). The plastic/wood-fiber composites utilize wood-fibers (WF) as a reinforcing filler in the plastic matrix and are known to be advantageous over the neat plastics in terms of the materials cost and some improved mechanical properties such as stiffness and strength. However, these improvements are usually accompanied by sacrifices in the ductility and impact resistance. These shortcomings can be reduced by inducing fine-celled or microcellular foaming in these composites, thereby creating a new class of materials with unique properties. An innovative tandem extrusion system with continuous on-line moisture removal and PBA injection was successfully developed. The foamed composites, produced on the tandem extrusion system, were compared with those produced on a single extruder system, and demonstrated significant improvement in cell morphology, resulting from uniform mixing and effective moisture removal. The effects of WF and coupling agent (CA) on the cell morphology were studied. An increase in the WF content had an adverse affect. The cell morphology and foam structures were improved when an appropriate CA was added. (C) 2004 Wiley Periodicals, Inc.
Born more out of necessity, the "awareness-attitude" of our society has caused the channeling of technological developments toward immediate economic and ecological benefits. The polymer industry has a newfound interest in fillers from industrial by-products and other waste materials having potential "recyclability" This new class of fillers includes fillers from natural sources (e.g., natural fibers), industrial by-products (e.g., saw dust, rice husks), and a recent entry in the form of rice husk ash-an industrial waste material-obtained by burning rice husks. Their recyclability and utilization has become a major driving factor in their acceptance and employability, as well as low cost and abundant availability. However, their performance in composites and processing requirements has hindered their applicability within the current economic framework. The present article reviews the performance of rice husk ash, or silica ash, in polymeric composites. Silica ash, composed mainly of silica, is obtained after burning rice husks and is a major industrial waste material in rice growing countries. Optimism surrounds the application of silica ash as a potential filler in a variety of polymeric composites, however, its performance has been limited by its inherent characteristics. This paper emphasizes the need for better characterization of silica ash to obtain an in-depth understanding of its behaviour with the view to identifying suitable modifications to improve its performance as a filler. It is emphasized that poor understanding of silica ash as a filler is linked to the lack of surface characterization, since its behaviour is significantly linked with its surface properties. Based on this analysis, a new approach to silica ash modification is proposed. (C) 2004 Wiley Periodicals, Inc.
The electrical conductivity of resins can be increased by adding electrically conductive carbon fillers. A significant amount of work has been conducted varying the amount of single conductive fillers in a composite material. Limited work has been conducted concerning the effect of combinations of different conductive fillers. In this study, three different carbon fillers were used in nylon 6,6: carbon black, synthetic graphite particles, and a surface treated polyacrylonitrile (PAN) based carbon fiber. The goal of this project was to determine the effect of each filler and combinations of different fillers on the electrical conductivity of conductive resins. A 2(3) factorial design was analyzed to determine the effects of the three different carbon fillers in nylon 6,6. The results showed that carbon fiber caused the largest increase in composite electrical conductivity and that all the combinations of different fillers do have a statistically significant effect on composite electrical conductivity. (C) 2004 Wiley Periodicals, Inc.
The objective of this study was to investigate the relationships between starch melt transition characteristics, extrusion conditions, and final product properties. Cornstarch was extruded using a corotating twin-screw extruder at varying moisture content, medium/high screw configuration, and 300/400-rpm screw speeds. Extrudates were evaluated for bulk density, expansion ratio, cell structure, bending strength, thermal and pasting properties. Temperature change (DeltaT) was defined as the temperature difference between the native starch melting temperature and its melt temperature just behind the die during extrusion at a given moisture content. DeltaT was significantly affected by starch moisture content and mechanical shearing, which controlled the melting behavior of the starch in the barrel. Amylose-lipid complex formation during extrusion increased as DeltaT increased and leveled off at DeltaT of about 20degreesC. Pasting peak viscosity of the starch extrudates decreased as DeltaT increased and leveled off at DeltaT of about 15degreesC. Within the same range of mechanical shearing intensity, extrudate bulk density and bending strength decreased linearly as DeltaT increased. Extrudate expansion was negatively correlated to bulk density (C) 2004 Wiley Periodicals, Inc.
An understanding of flow behaviour of polymer melts through a slit die is extremely important for optimizing die design and, consequently, for die performance in processing polymer sheets and films. In view of the complex nature and the physical properties of polymer melts as well as of die geometries, such as coat-hanger dies, no simple mathematical formulae can be used to compute the flow regimes within dies. This paper illustrates the development of a three-dimensional (3-D) computer model of an example of a coat-hanger die design using the computational fluid dynamics package, FIDAP, based on the finite element method. A difference of only 3.7% was found when comparing the velocity distribution at the die exit obtained from the 3-D simulation with that calculated using a two-dimensional analytical design procedure, indicating that full 3-D analysis seems to be unnecessary. However it has been shown that unwanted flow phenomena and production problems can be ameliorated by means of visualization and the detailed information obtained from computer simulations. Comparative simulation results with polymers of different rheological properties in the same die are also described. The comprehensive analyses provide a means of interpretation for flow behavior, which allows modification of the die geometry for optimal design. (C) 2004 Wiley Periodicals, Inc.
Online measurements of the temperature and the diameter of fibers in the melt spinning process of thermoplastics are discussed. The temperature and the diameter of fibers can be applied in many fields such as fiber formation modelling, cooling rate behavior (Nusselt number), and rheological investigations (apparent extensional viscosity) of polymers. The online measurements along the spinline were carried out with an infrared camera during the melt spinning process. Two different experiments were designed and carried out to find the correction factor, i.e., the emissivity. The results show that the emissivity correction factor depends on the polymer type and the fiber diameter. Usually the diameter of the fibers is measured by an instrument or by direct velocity measurements invoking the continuity equation. In this new approach the diameter is found directly by the evaluation of the measured temperature. Therefore only one apparatus, namely an infrared camera taking snapshots, is required to find the fiber diameter. The key of this method can be seen in the temperature difference between the fiber and the environment. A mathematical procedure was developed to estimate the diameter of the fiber from the distribution curve. (C) 2004 Wiley Periodicals, Inc.
The effects of polyolefins composition, that is polyethylene (PE), polypropylene (PP) and a ethylene/propylene copolymer (EPM) of 45/55 monomer ratio, and of operating conditions (screw speed, throughput and screw configuration) on the grafting of maleic anhydride (MA) were investigated. Sampling devices located along the extruder barrel were used to collect samples of modified PE, EPM, and PP that were subsequently characterized in order to monitor the degree of grafting and of crosslinking/degradation. Although a similar trend of MA grafting evolution is observed along the extruder, the final MA graft content depends on the processing parameters, screw configuration, and particularly, throughput have a significant effect on the grafting yield. Taking PE as an example, and by means of a statistical experimental design, an optimal operating window in terms of screw speed, throughput, and geometry was identified, yielding MA graft contents of 2 wt% MA. (C) 2004 Wiley Periodicals, Inc.
Reactive extrusion of poly(urethane-isocyanurate) (PUIR) was studied in an intermeshing corotating twin-screw extruder. Toluene diisocyanate (TDI) and polypropylene glycol (PPG) were used as initial materials with dibutyltin dilaurate (DBTDL) as catalyst. The reaction was first examined in a batch reactor as well as in an internal mixer in order to obtain the kinetics and temperature/torque evolution trends during the formation of PUIR, respectively. For the specified screw speed and temperature profile of the extruder, a working domain can be recommended for the reactive extrusion, in terms of NCO/OH ratio (r) and catalyst concentration (C), to reach a sufficient extent of reaction. The effects of screw speed and temperature profile on the residence time parameters of the reaction mixture were investigated. It is found that the axial mixing and the RTD behavior of the reaction mixture in the extruder can be well represented by the axial dispersion model. For the reaction condition of r = 3, C = 2%, and barrel temperature profiles of 75-150degreesC or 90-165degreesC, the optimum screw rotation speed for complete NCO conversion is 20 rpm. The structures, thermal stabilities, morphologies, and physical and dynamic mechanical properties of reactively extruded PUIRs were investigated. (C) 2004 Wiley Periodicals, Inc.
The comparative tensile and impact properties and fracture morphologies between calcite and calcite/zeolite (hybrid) filled linear low-density polyethylene (LLDPE) and polypropylene (PP) composites have been studied. The incorporation of fillers into LLDPE, whether calcite or calcite/zeolite hybrid fillers, does not alter the T-m of LLDPE, but slightly reduces the T-m of PP. The melting peak area representing the heat of fusion of the crystal decreases with fillers; the effect of the calcite and the hybrid filler would be the same. The impact strength, Young's modulus, and yield stress of the calcite and the hybrid filled LLDPE increased, indicating a reinforcing effect of the fillers. In addition, the filled LLDPE decreases in elongation at break (EB) and ultimate tensile strength. However, the hybrid LLDPE composite exhibits slightly higher Young's modulus and ultimate tensile strength than the calcite one, while the same values of impact strength and yield stress were observed. In the PP system, the Young's modulus is enhanced, whereas the rest of the mechanical properties were reduced. From SEM photomicrographs of the hybrid filled composites, the tensile fractured surface of LLDPE dumbbell bar exhibits tearing surfaces while the composite shows formation of air holes and cracks in the LLDPE and PP system, respectively. Because of improved Young's modulus, yield strength, impact strength, and morphological observation along with substantial extension, the filled LLDPE composite with calcite/zeolite hybrid fillers is worth using for micro-porous film applications. (C) 2004 Wiley Periodicals, Inc.
Rigid polyurethanes were synthesized using hydroxy alkylated cardanol formaldehyde and hydroxy alkylated dimerized-cardanol formaldehyde resins and dicyclo hexyl methane diisocyanate. The studies on the aging (hydrolytic stability, absorption of water/toluene, chemical resistance, dimensional stability, and thermal stability) of these polyurethanes reveal appreciable stability. The performance of these polyurethanes was compared with elastoplastic polyurethanes synthesized with the addition of commercially available poly(ethylene glycol). The rigid polyurethanes are distinctly stable than elastoplastic polyurethanes under various aging conditions. (C) 2004 Wiley Periodicals, Inc.
Poly(O-anisidine) coating was successfully electrodeposited onto Al-2024. Cyclic voltammetry and reflection absorption infrared spectroscopy (RAIR) analysis were carried out in order to fully understand the formation and structure of the resulting polymer coating. RAIR spectrum showed the characteristics peaks of poly(O-anisidine). As the reaction time was varied, the CV peak shifted from 0.75 to 0.81 V vs. SCE suggesting that a change in structure of the polymer from a reduced state to a partially oxidized form has occurred. UV spectrum showed two peaks at 320 and 620 nm suggesting the presence of conjugation on the polymer backbone. The deposition of the poly(O-anisidine) onto the substrate was controlled by nucleation and growth mechanism. DC polarization technique was used to evaluate the corrosion protection offered by poly(O-anisidine) coatings. Preliminarily data shows that these coatings help to ennoble the surface of the substrate. (C) 2004 Wiley Periodicals, Inc.
This paper presents a newly developed experimental apparatus, based on an extrusion system, which can economically and accurately measure the pressure-volume-temperature (PVT) properties of polymeric fluids. The density or specific volume of a polymer melt is determined by measuring the mass and volume flow rates of the melt. A positive displacement gear pump mounted on an extruder is used to measure the volume flow rate of the melt. In order to reduce the leakage across the gear pump, the difference between the upstream and downstream pressures is minimized by using a variable resistance die attached to the downstream outlet of the gear pump. The positive displacement volume of a gear pump was determined in calibration experiments with water and oil with the aid of a syringe pump. Two critical sets of experiments were carried out to measure the specific volumes of polystyrene and polypropylene as case examples. The measured results were compatible with the known PVT data, confirming the validity of the system. (C) 2004 Wiley Periodicals, Inc.
Poly(maleic anhydride-alt-acrylic acid) and its transition-metal complexes with Ni(II), Cu(II), and Cd(II) were synthesized. Poly(maleic anhydride-alt-acrylic acid) was characterized using Fourier transform infrared (FTIR), titration, viscometry, differential scanning calorimetry (DSC), and thermogravimetric (TGA) analysis. The temperature dependence of the conductivity of the copolymer and polychelates of transition metals was investigated between 300 and 453 K. The polychelates and copolymers were also analyzed by using FTIR spectroscopy before and after transition point. The observed conductivity followed by a semiconductor behavior with increasing temperature is discussed in relation to the presence of transition-metal ions. (C) 2004 Wiley Periodicals, Inc.
Styrene/ethyl acrylate (Sty/EA) free-radical copolymerizations have been conducted in bulk with and without initiator and in solution using p-xylene and m-xylene (30 wt% and 60 wt% solvent level) at 100degreesC and 130degreesC. The monomer reactivity ratio values and their temperature dependence have been determined from low conversion copolymer composition data using the computer software package RREVM, which is based on the error in variables model (EVM) method. Copolymer composition data at low conversion confirmed the Mayo-Lewis model at both temperatures. The reactivity ratio values of the Sty/EA system do not seem to change with dilution by nonpolar solvents at low concentration from the reactivity ratio values obtained in bulk with and without initiator. However, xylene isomers were found to have a slight effect on the reactivity ratio value of ethyl acrylate when high solvent concentration was utilized. (C) 2004 Wiley Periodicals, Inc.