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A two dimensional axisymmetric simulation for predicting the flow-induced orientation of glass fibers in injection molded composite parts is presented. The mass and momentum balance equations are discretized using Galerkin finite element method and the constitutive equation for fiber orientation is discretized using discontinuous Galerkin finite element method. Material parameters used in the model are determined using rheology and experimental fiber orientation is used for initial conditions. Simulation results are in close agreement with the trend seen in experimental data with still need for improving the simulation to capture the orientation in regions close to frontal flow and the walls.
The curing reaction of an aliphatic epoxy resin and EPDM rubber is modeled from differential scanning calorimetry, generalizing a methodology proposed by Hernandez-Ortiz and Osswald. The kinetics is represented by Kamal-Sourour model with and without diffusion reaction control and was extracted using a non-linear regression method coupled with the heat and mass balance equations. The kinetic fitting methodology uses dynamic and isothermal differential scanning calorimetries allowing the differentiation of high and small peaks during the curing and diffusion reaction control regimens.
Fiber orientation within long glass fiber polypropylene composites in center-gated injection molded discs was determined at various percentages of flow. The results were compared directly to short fiber results for the same geometry. In addition, end-gated plaques were molded using the same short and long fiber materials for additional comparison. Results suggest that an area of high radial flow occurs for long fibers at low fill percentages during the filling process for end-gated plaques. Due to the increased length, long fibers have a large increase in flexibility and curvature within the injection molded system, complicating flow and prediction of orientation.
Two renewable copolymers, poly(trimethylene malonate) (PTM) and poly(trimethylene itaconate) (PTI), have been produced with ester bonds incorporated into the polymer backbone to facilitate hydrolytic and/or enzymatic degradation. A hydrolytic degradation study of these renewable polymers in aqueous solutions adjusted to pH values is described. Final weight loss varied from 20 to 37 wt% for PTM and from 7 to 21 wt% for PTI as a function of aging time and initial solution pH. Degraded samples were characterized by FTIR, GPC, DSC, and TGA. PTI showed a slower degradation rate than PTM.
In this paper, a novel electromagnetic dynamic foaming simulator was designed to investigate the combinational effects of shear and vibration on the morphology of microcellular polymethyl metacrylate (PMMA) samples by using supercritical carbon dioxide (ScCO2) as a blowing agent. Mechanical vibration induced by electromagnetic field was introduced into the foam process. Furthermore, in order to strengthen the shear effect, the rotor of the special designed simulator was machined to be whorled. It was shown that at a certain amplitude and frequency of vibration, the cell diameter of samples decreased and cell density increased.
Novel polyimide/poly(N-ethyl-aniline-co-aniline-2-sulfonic acid-clay(SPNEAC-PI) nanocomposite films containing water soluble poly(N-ethyl-aniline-co-aniline-2-sulfonic acid-modified-clay (SPNEAC) have been successfully synthesized. The Dynamic Mechanical Spectrometry (DMS) results show decreasing Tg of the nanocomposite films with increasing SPNEAC loading. The area under the ñ-transition curve which is correlated with damping and impact energy increases with increasing SPNEAC loading. A 5wt% addition of SPNEAC improved damping of neat-PI films by 137%. SEM micrographs of the nanocomposite films showed an open cross-sectional morphology.
To produce electrically conductive or electrostatic dissipative polymer composites containing carbon nanotubes (CNT) melt processing is the favored route. As electrical properties are desired at low filler fractions, a high degree of dispersion is required in order to benefit from the intrinsic CNT properties. This study discusses the influence of screw configuration, rotation speed, and throughput on the residence time and specific mechanical energy (SME) and the resulting macroscopic CNT dispersion in polycaprolactone (PCL) based masterbatches containing 7.5 wt.% multi-walled carbon nanotubes (MWNT) using an intermeshing co-rotating twin-screw extruder Berstorff ZE25. From the best masterbatch a dilution set was performed.
Medical applications in healthcare market most often require multiple use or reuse of the instrument. Autoclave sterilization is one of the most common methods to effectively clean the instrument before reuse. To understand the capability of newly developed high heat Lexan* XHT resins in autoclave applications, mechanical property retention including tensile, flexural and practical impact properties were evaluated after multiple autoclave cycles at both 120?øC and 134?øC. These new class of high heat Polycarbonates offer better performance in comparison to conventional polycarbonates at high sterilization temperatures.
The unique morphology and strong inter-tube attraction among CNTs and CNFs makes the dispersion of CNTs and CNFs a big challenge and hence limits their effective use. The comparison of reinforcement efficiency of CNFs and MWNTs in PEI was studied. Ultrasound assisted single and twin screw extruder was used to prepare PEI/CNFs and PEI/MWNTs nanocomposites respectively. The effect of ultrasound on electrical, rheological, morphological and mechanical properties of polyetherimide filled with 1-10wt% of MWNTs and 2-20wt% of CNFs was studied. Ultrasonic treatment caused a reduction in electrical percolation threshold value with a permanent increase of viscosity of treated samples.
The Phelps-Tucker fiber breakage model has been implemented along with fiber orientation models in Autodesk Moldflow Insight to predict fiber length attrition during injection-molding process. The fiber length breakage model is based on the buckling criterion for hydrodynamic force determined by Dinh-Armstrong model, and probability distribution of the length breakage which parameters can be adjusted to match fiber length measurement. A set of measurement data has been used to validate the fiber breakage model implementation, and it has been extended to 3D simulation for more complicated geometries to predict the fiber length distribution in practical applications.
This work investigates the effect of extrusion parameters and formulation on the properties of polypropylene / short flax fiber composites. The parameters that were varied during the twin-screw extrusion process were screw configuration, screw rate, extrusion temperature and flow rate. The effect of the location of the feeding zone of flax fibers is also considered. Concerning the composite formulation, the effect of flax content, presence of coupling agent and of a reactive additive on composite properties are analyzed. The materials were characterized in terms of morphological characteristics, rheological, thermal and mechanical properties.
Melt extrusion has been gaining interest in the pharmaceutical industry due to the continuous nature and ability to provide unique dosage form characteristics. Enhancement of oral bioavailability to enable drug products has been exploited extensively using melt extrusion. In this study melt extrusion was used for the preparation of griseofulvin extrudates. Using this technology amorphous formulations using non-ionic polymers were prepared. Compositions were evaluated for physical characteristics, chemical performance and dissolution rate. Results showed that all formulations could be prepared below the melting temperature of the drug substance and the resulting formulations provided significant levels of supersaturation during dissolution testing.
This paper presents the design of a lab-scale bead foaming system for investigating the mechanism of the formation of cellular morphology and evolution of the crystal melting peaks of the expanded beads. A propeller-guided-cylinder design was incorporated to enhance the circulation during the heating, saturation and downward force during the depressurization of the polymer pellets/water/blowing agent mixture. EPP beads of an average 16-time expansion ratio were fabricated and an extensive study will be conducted to examine the effects of processing parameters on the foaming and crystallization behavior of the beads.
Epoxy based composites containing multi-walled carbon nanotubes (MWCNTs) have been successfully prepared. The effects of the addition of eight different block copolymers on the dispersion stability of MWCNTs have been systematically analyzed. The suspension of CNTs in different components of the epoxy, i.e epoxy resin and hardener, have been evaluated by preparing suspensions using a tip sonicator and different amounts of block copolymers relative to the concentration of CNTs. The stability of MWCNTs in various media was investigated by using a centrifugation technique. Dispersing agents suitable for the acquisition of long-term stable dispersions of MWCNTs have been identified.
Previously, it had been demonstrated that extensional stresses has strong effects in cell nucleation and growth within plastic foaming processes. In particular, our previous work investigated the foaming behavior of polystyrene, an amorphous polymer, under extensional stress via in situ observation of the foaming processes. On the other hand, the effects of extensional stress on semi-crystalline polymers are still not well-understood. This study aims to fill this gap by investigating the foaming behaviors of three different types of polypropylene (PP): linear PP, branched PP, and a PP-PE copolymer, via in situ observation.
Analytical methods have been widely used to predict mechanical properties of polymer composites. The theories assume perfect filler-matrix interfacial contact and homogenous dispersion of individual fillers into the matrix, which however is not what is observed experimentally especially in nanocomposites. The reason is that in nano-size reinforced polymers the dominant effects of interfacial interaction and presence of fillersƒ?? agglomeration have to be considered. This study investigates the effects of these two factors on the tensile modulus of nanocomposites by combining experimental observations and micromechanical models.
This study focuses on understanding the deviation between experimentally obtained and numerically predicted tensile modulus of carbon nanotube /polypropylene (CNT/PP) composites. The tensile modulus is measured according to ASTM D638 testing method. Characteristics such as presence and size of CNT agglomerates, voids at the CNT-PP interface and width and modulus of the CNT-PP contact area are studied using atomic force microscope (AFM) and scanning electron microscope (SEM). Finite element analysis is performed to determine the effective Youngƒ??s modulus considering i) ideal case (no CNT agglomeration, perfect CNT-PP contact) and ii) non-ideal case where the experimentally observed characteristics are accounted for.
Thermogravimetric (TGA) monitoring of poly(vinyl chloride) PVC degradation kinetics by loss of HCl is complicated by plasticizer evaporation, unlike monitoring by color change due to conjugated polyenes formation. Thermal degradation of PVC films plasticized with diethylhexyl phthalate and tri-isooctyl trimelitate was monitored by color change, by optical density at 350nm, and by TGA at 160C to200C. Plasticizer-free PVC powder degradation kinetics was obtained by TGA at temperatures from 160C to 220C. Apparent activation energies of plasticizer-free PVC powder degradation was 152kJ/mol (by TGA); for plasticized PVC-ranged from 165kJ/mol to 180kJ/mol (color change) and 147kJ/mol (by optical density at 350nm).
POM or polyoxymethylene is an engineering resin used for the past 50 years primarily in injection molding. Parts thusly formed typically replace metal. POM's usefulness is derived from its strength, stiffness, toughness, creep resistance and natural lubricity. Both POM copolymer and homopolymer producers compete in this market space. POM homopolymer grades exhibit a small but significant advantage in mechanical properties, while the copolymer grades exhibit advantages in thermal stability and chemical resistance. This paper presents a new POM copolymer grade with mechanical properties essentially equivalent to homopolymer while maintaining the thermal stability and chemical resistance of POM copolymers.
In this study, we investigate injection molding of 5 wt% CNT with polystyrene polymer matrix into a mold equipped with three different cavities. Electrical conductivity testing was applied in the thickness and in-flow directions of the molded samples. The injection molding conditions of mold temperature, melt temperature, injection/holding pressure and injection velocity were varied to investigate the effect of process parameters on the electrical conductivity of each sample. Among the process parameters, the injection velocity and melt temperature showed the largest influence on alignment and, consequently, the electrical conductivity of the samples.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
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