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INDUSTRIAL SCALE-UP FEASIBILITY OF EXTRUDED PVC FOAMS USING BLENDS OF VIRGIN AND SUB-CRITICAL CO2 GAS-SATURATED PELLETS
Dustin Miller , Vipin Kumar, May 2010
The use of gas-saturated pellets as a means to deliver a controlled amount of blowing agent for foam extrusion was investigated. Various PVC blend ratios of unsaturated virgin and CO2 pre-saturated pellets were created before placing into the hopper. It was found that PVC profiles with a uniform microstructure can be produced. The blend ratio is a critical process parameter as it governs the amount of gas delivered to the process. Due to the high solubility of CO2 at room temperature sub-critical pressures can be used to saturate the PVC pellets. The process was successfully carried out in an industrial R&D lab and appears to be adaptable for large scale production. Due to manufactured parts having high surface area to volume ratios extremely high cooling rates are achieved. Thermal measurements using surface mounted thermocouples at comparable rates are impractical due to their relatively high response times. To address this issue an AGA 782 SW thermal imaging camera has been modified such that it runs in a linescan mode and data are collected using a high speed digitiser to allow capture rates of 2500 lines per second. The rapid cooling of a range of components and materials have been recorded and the superheating of air traps within the component have been observed.
HYDROXYAPATITE-COATED CARBON FIBER/POLYAMIDE 12 COMPOSITE FOR HIP REPLACEMENT WITH IMPROVED OSSEOINTEGRATION
S. Dimitrievska , J. Whitfield , S. A. Hacking , M. N. Bureau, May 2010
Bone loss around femoral implants used for total hip arthroplasty is a persistent clinical concern. In some cases, it may be caused by stress shielding, which is generally attributed to a mismatch in stiffness between the femoral implant and host bone. In this regard, a fatigue resistant, carbon fiber (CF) polyamide 12 (PA12) composite hip stem coated with hydroxyapatite (HA) for hip replacement has been developed to match bone stiffness and achievefixation by osseointegration. In vitro studies withosteoblast cells (MG63) showed no cytotoxicity of the composite components as seen by the cellular growth andcomposites interaction. In vivo studies comparing thecomposite and Ti-6Al-4V (Ti64) rods in the rabbit and rat femurs demonstrated significantly higher bone apposition to the composite than Ti64 rods. The results of this study indicate that the invasion of surrounding bone cells and thus osteointegration together with its bone-matching mechanical properties make the HA-coated CF/PA12 composite stem a promising hip replacement candidate.
NANOSCOPIC CHARACTERIZATION OF PLASTISOL GELATION AND FUSION PROCESS UTILIZING SCANNING ELECTRON MICROSCOPY AND ATOMIC FORCE MICROSCOPY
Jerome S. Jourdan , David P. Owen, May 2010
Understanding the physical properties associated with the gelation and fusion of a PVC plastisol will help to improve process efficiency. Plastisol gelation and fusion was characterized using both scanning electron microscopy (SEM) and atomic force microscopy (AFM) and compared to tensile properties developed at various temperatures. Both SEM and AFM show good agreement during the early stages of gelation. However AFM continues to show particle boundaries during latter stages of gelation and fusion that provide a more accurate comparison with resulting tensile properties.
ULTRASONIC MONITORING OF MICROMOULDING
EC Brown , BR Whiteside , R Spares , PD Coates, May 2010
An ultrasonic measurement system has been developed and operated in conjunction with a suite of process monitoring transducers on a Battenfeld Microsystem 50. Measurements are non-invasive; piezoelectric sol-gel sensors can be integrated with the mould and their low-profile nature is ideally suited to the constraints of the micromoulding environment allowing measurement of flow front position cooling dynamics shrinkage morphology changes during solidification and cycle repeatability. Ultrasonic measurements of mould filling and cooling dynamics have been validated using flow visualization techniques on the same machine.
ULTRASONIC MONITORING OF MICROMOULDING
EC Brown , BR Whiteside , R Spares , PD Coates, May 2010
An ultrasonic measurement system has been developed and operated in conjunction with a suite of process monitoring transducers on a Battenfeld Microsystem 50. Measurements are non-invasive; piezoelectric sol-gel sensors can be integrated with the mould and their low-profile nature is ideally suited to the constraints of the micromoulding environment, allowing measurement of flow front position, cooling dynamics, shrinkage, morphology changes during solidification and cycle repeatability. Ultrasonic measurements of mould filling and cooling dynamics have been validated using flow visualization techniques on the same machine.
MATERIAL SELECTIONS ROLE IN CHEMICAL RELATED FAILURES
Melissa L. Kurtz, May 2010
Failure of plastic products is the result of the materialƒ??s behavior in the application but is also influenced by human factors such as material selection design processing and use. Material selection is critical to the success of a product. One of the greatest challenges relates to understanding chemical exposure in the application and the materialƒ??s corresponding resistance.Unsuitable chemical resistance of a material accounts for a majority of failures with a significant number involving exposure to secondary fluids. This paper will explore case studies that focus on chemical related failures as the result of improper material selection and understanding of secondary exposure conditions.
HIGH STRAIN RATE RHEOMETRY OF POLYMER MELTS RELEVANT TO MICROMOLDING AND THIN-WALLED INJECTION MOLDING
A L Kelly , B R Whiteside , T Gough , P D Coates, May 2010
The rheology of polymer melts has been measured at strain rates up to 107 s-1, relevant to micromolding and thin walled molding processes, using an instrumented high speed injection moulding machine. Deviations from shear thinning behavior were observed for commercial grades of polyethylene, polypropylene, polystyrene and PMMA, and shear thickening behavior occurred for some of the polymers examined. Off line parallel plate rheometry and twin bore capillary rheometry were used to provide rheological data at low and medium shear strain rates respectively. Measured shear viscosity was found to follow Newtonian behavior at low rates and shear thinning power law behavior at intermediate strain rates. At shear strain rates approaching or above 106 s-1, shear viscosity reached a rate-independent plateau, and in some cases shear thickened with further increase in strain rate. A relationship between the measured high strain rate rheological behavior and molecular structure was found, with polymers containing larger side groups reaching the rate independent plateau at lower strain rates than those with simpler structures. These results have implications for micromolding of particular polymer architectures.
AN INVESTIGATION ON ANTIBACTERIAL PROPERTIES OF MEDICAL-GRADE PVC MODIFIED THROUGH A MULTISTEP PHYSICOCHEMICAL APPROACH
Tim Gough, Ben R. Whiteside, Phil D. Coates, May 2010
Medical-grade polyvinyl chloride (PVC) was modified through a multistep physicochemical approach to yield a novel anti-adherent surface against potentially pathogenic bacteria. This was fulfilled via surface activation by coplanar surface dielectric plasma, followed by radical graft copolymerization of a spacer to render a well-defined polymer brush finally coated by biologically active species. Various surface probes together with in vitro biological assay were performed. Up to 85 % and 50% reduction in adherence degrees of gram-negative and positive strains were attained, respectively. Along with bacteria structural characteristics, wettability and surface topography of substrate were established to be principal parameters in adhesion.
DETAILED CHARACTERISATION OF MICROMOULDED PRODUCTS
Tim Gough , Ben R. Whiteside , Phil D. Coates, May 2010
The Microscale Polymer Processing: Applying the Tools (MUPP2) research programme aims to understand how molecular architecture influences processability of polymers, and the structures obtained through processing. Part of this programme involves micromoulding of a range of products, including those made from very highly controlled molecular architecture polymers (e.g. controlled MWD polystyrenes, PMMAs with nanocomposites), at a range of processing conditions. These products have been characterised using stress birefringence and polarised Raman spectroscopy to assess residual molecular orientation in conjunction with Small Angle Neutron Scattering (SANS) techniques. Experimental results indicate the variation in properties along small bar specimens. These results will be discussed, along with associated very small scale shear and extensional flow characterisations at lower strain rates
BIODEGRADABLE POLYURETHANE/SOY PROTEIN SHAPE-MEMORY POLYMER BLENDS PREPARED VIA ENVIRONMENTALLY-FRIENDLY AQUEOUS DISPERSIONS
Atakan Altinkaynak, Mahesh Gupta, Mark A. Spalding, Sam L. Crabtree, May 2010
Biodegradable and biocompatible shape-memory polymer blends of soy protein (SP) and polyurethane (PU) based on poly(?æ-caprolactone) (PCL) has been synthesized using environmentally-friendly aqueous dispersion technique. High-pressure supercritical carbon dioxide (scCO2) foaming technique was applied to the blends to generate three-dimensional interconnected porous structures or scaffolds with special enhanced benefits for potential biomedical applications such as soft tissue engineering and/or drug release. Blending PU dispersion (PUD) with SP significantly increased the biocompatibility and biodegradability properties of the materials and improved their shape-memory capability. The PCL soft segment was found to be miscible with SP over the entire range of concentration as confirmed by DSC measurements, where a single Tg located between the Tg of the pure SP and PCL soft segment was observed for all blend concentrations. The shape-memory behavior of the blends was investigated for different concentrations under free-stress condition. The rate of strain recovery was found to be SP concentration dependent. The stress recovery of the blend reached a maximum value at wSP = 0.1 weight fraction. This finding was attributed to the maximum increase in the degree of crystallinity of PCLsoft segment at wSP = 0.1 as conformed by X-ray analysis.
INFLUENCE OF THE COMPRESSION MOLDING PROCESS ON IMPACT BEHAVIOR
Alex G. Zestos, Cole L. Grinnell, Long J. Vinh, Robert D. Pike, William H. Starnes, Jr., May 2010
Self-reinforced polypropylene composites are particularly appropriate for process-induced property gradation during the compression molding process. They react especially sensitive to temperature and pressure and can therefore cover a large gradation spectrum. With the help of a newly developed, differentially tempered compression mold, area-dependent thermal gradation is possible. The locally varying material properties yielded by compression molding can be optimally verified by instrumentalized impact experiments. The equivalents for stiffness (modulus of resilience) and strength (maximal force) can be determined, alongside energetic characteristic values like dissipative and storage work.
SMOKE SUPPRESSION OF PVC BY METAL-EXCHANGED CLAY AND ZEOLITE ADDITIVES
Alex G. Zestos , Cole L. Grinnell , Long J. Vinh , Robert D. Pike , William H. Starnes Jr., May 2010
Cone calorimetry studies showed that various metalexchanged clays and zeolites containing only 3–4% of Cu(II) Cu(I) Zn(II) or Al(III) were effective smoke suppressants and fire retardants for plasticized PVC. Copper(II)-Zn(II) and Cu(II)-Al(III) synergism for smoke and heat reduction was observed with binary blends of the clays and the effectiveness of the additives was usually improved considerably by heating plasticizer-additive mixtures under very high shear before combining them with the polymer. Possible mechanisms of action of the additives are discussed.
SMOKE SUPPRESSION OF PVC BY METAL-EXCHANGED CLAY AND ZEOLITE ADDITIVES
Alex G. Zestos , Cole L. Grinnell , Long J. Vinh , Robert D. Pike , William H. Starnes Jr., May 2010
Cone calorimetry studies showed that various metalexchanged clays and zeolites containing only 3'4% of Cu(II), Cu(I), Zn(II), or Al(III) were effective smoke suppressants and fire retardants for plasticized PVC. Copper(II)-Zn(II) and Cu(II)-Al(III) synergism for smoke and heat reduction was observed with binary blends of the clays, and the effectiveness of the additives was usually improved considerably by heating plasticizer-additive mixtures under very high shear before combining them with the polymer. Possible mechanisms of action of the additives are discussed
THE EFFECTS OF ROTOR INCORPORATED MOLD FOR THE ELIMINATION OF THE WELDING LINE IN INJECTION MOLDING
Y.P. Tsai , J.C. Wang , T.Y. Huang , R.Q Hsu, May 2010
A built-in rotor inside the mold was designed. The rotorƒ??s surface was constructed with the purpose of disturbing the skin layer and core layer of the molten material and hopefully destroy the fountain flow structure of plastic flow. Several specimens were made by changing the rotorƒ??s surface profiles. Angular velocity four polymers were chosen as the parameters. Numerical software was used to simulation the filling process.Experimental results showed that the equipment did twist the weld line and in some cases even made the weld line disappear the effects were more apparent in ABS and ASA. Numerical analysis showed the similar results as the experiments.
MORPHOLOGY DEVELOPMENT BY CHAOTIC ADVECTION IN PA-EVOH BLENDS WITH POLYMER COMPONENT INTERACTIONS
X. Jin , D. A. Zumbrunnen, May 2010
To take advantage of the superior oxygen gas barrier property of ethylene-vinyl alcohol random copolymer (EVOH) and the balanced mechanical properties of polyamide (PA) blend morphologies with high interfacial areas at constant compositions were produced with a laboratory chaotic advection blender. This new processing technology intrinsically develops blends having very high interfacial area so it has special applicability to barrier films. Even with influences from component interactions multi-layer films with submicron layer thicknesses were formed. The layers became finer for more extensive chaotic advection as has been documented earlier in immiscible nonreacting polymer blends. Influences of structure on impact toughnesses are specifically reported.
FAILURE CHARACTERIZATION OF VIBRATION WELDED POLYPROPYLENE JOINTS
Valeria Pettarin , Laura A. Fasce , Patricia M. Frontini, May 2010
The failure behavior of vibration welded polypropylene T-peel joints was investigated. The quality of welded joints was assessed using several mechanical tests including: smooth tensile notched tensile DENT and DART. The depreciation of properties was evaluated as the ratio between the properties of the pristine material and the joint. The morphological features of deformed and fractured materials were examined using polarized light optical microscopy and scanning electron microscopy.From our investigations it emerges that the vibration welding process resulted in low weld efficiencies for all mechanical testing techniques. SEM inspection of the fracture surfaces also revealed the presence of unwelded points and scarce material inter-diffusion consistent with the low weld efficiencies achieved. The investigations also revealed the drawing capability of the pristine material was negatively affected by the thermal history involved during the welding process. Contrary to pristine material behavior welded samples developed a small outer plastic zone before fracture.
MODELING OF FLOW AND HEAT TRANSFER WITHIN HOT RUNNER SYSTEMS USING THE RADIAL FUNCTION METHOD (RFM).
Martin N. Bureau, , Tan-Minh Ton-That, Kenneth Cole, May 2010
The radial functions method (RFM) was used to model the flow and heat transfer within hot runner systems. The technique is a meshless method that deals well with highly non-linear problems. The technique was implemented to simulate the coupled flow and heat transfer effects, as well as the interaction with the metal surroundings of hot runner systems. Practical problems were simulated, and the results clearly show various effects that control the flow in injection molding runner systems, such as the thermal imbalance generated by the runner bifurcations, that may lead to flow imbalances during the filling process.
MODE I AND II INTERLAMINAR FRACTURE TOUGHNESS OF NANOCLAY-REINFORCED EPOXY/GF COMPOSITES
Martin N. Bureau , Tan-Minh Ton-That , Kenneth Cole, May 2010
Of prime importance in fiber reinforced composites is the interfacial strength between glass fiber reinforcement and matrix. A potential benefit of nanoclays (NC) is to improve the matrix-reinforcement stress transfer due to their positive interactions with glass. Double cantilever beam (DCB) and end-notch flexural (ENF) tests were performed to evaluate the interfacial fracture toughness (Gc) in mode I and II, respectively, of GF composites with a NC/epoxy matrix. Results show no benefit of NC on mode I toughness while a significant 20%+ improvement on mode II was obtained. Given the non-optimal chemistry of the epoxy/GF laminate used, this result is encouraging.
EFFECTS OF HANNEBACHITE ADDITIVE ON THE MECHANICAL BEHAVIOR OF PHENOLIC-NATURAL FIBER COMPOSITES
Stephen Hofer , Gediminas Markevicius , Vivak M. Malhotra , Charles Miller , Francois Botha, May 2010
The issue of global warming demands more effective management of our forested lands thus requiring the reduction in the consumption of natural wood products. Therefore for the last few years we have been attempting to develop structural composite materials from natural fibers derived from annual crops and phenolic polymer. Recently we systematically incorporated plate-like hannebachite (calcium sulfite) crystallites as an additive into the composites derived from phenolic and miscanthus. The concentration of hannebachite crystallites in the compressive molded composites varied between 30 to 80 wt%. The SEM measurements indicated that the hannebachite crystallites maintained their plate-like structure in the composites and the flexural strength of the materials inversely scaled with the concentration of the inorganic phase i.e. it ranged from 60 MPa to 3 MPa. The addition of jute mesh fibers in our composites further significantly improved the ductile behavior of the fabricated materials. The thermal and thermomechanical behaviors of the composites were ascertained by DSC and DMA measurements.
EFFECTS OF HANNEBACHITE ADDITIVE ON THE MECHANICAL BEHAVIOR OF PHENOLIC-NATURAL FIBER COMPOSITES
Stephen Hofer , Gediminas Markevicius , Vivak M. Malhotra , Charles Miller , Francois Botha, May 2010
The issue of global warming demands more effective management of our forested lands, thus, requiring the reduction in the consumption of natural wood products. Therefore, for the last few years, we have been attempting to develop structural composite materials from natural fibers derived from annual crops and phenolic polymer. Recently, we systematically incorporated plate-like hannebachite (calcium sulfite) crystallites as an additive into the composites derived from phenolic and miscanthus. The concentration of hannebachite crystallites in the compressive molded composites varied between 30 to 80 wt%. The SEM measurements indicated that the hannebachite crystallites maintained their plate-like structure in the composites, and the flexural strength of the materials inversely scaled with the concentration of the inorganic phase, i.e., it ranged from 60 MPa to 3 MPa. The addition of jute mesh fibers in our composites further significantly improved the ductile behavior of the fabricated materials. The thermal and thermomechanical behaviors of the composites were ascertained by DSC and DMA measurements.


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