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Conference Proceedings

Crosslinking Kinetics during Continuous Polymerization
Kal R. Sharma, May 2000

The kinetics of crosslinking polymerizations entail a complex combination of behaviors such as diffusion-controlled propagation, reaction diffusion controlled termination, volume relaxation, heterogeneous network formation, and non-constant initiator efficiency, chain depropagation and precipitation. One would like to be able to predict the mechanical properties of a material from the conditions used during the polymerization, or alternatively one would like to be able to create materials with specific properties purely through an understanding of the kinetics. A more complete understanding of the polymerization process is required before this can be achieved. We use Monte Carlo simulations to understand the characteristics such as a predisposition to hydrogen abstraction, chain length, and the ability of the system to exhibit some level of microscopic ordering, as in urethaneacrylate networks. Specifically, the effect of initiation rate on the rate of polymerization and correspondingly, the propagation and termination kinetics has been studied and aspects of the termination kinetics such as when, if ever, reaction diffusion controlled termination becomes the dominant termination mechanism have also been explored. The reaction time and yield curve generated by Monte Carlo simulations was com pared with the experimental values reported in the literature for the continuous mass polymerization of HIPS and ABS. The crosslinked polybutadiene is influential in the determination of the impact strength gloss balance.

Processing Methodology for Transparent Armor Nanocomposites
Kal R. Sharma, May 2000

The design of a single processing method to produce transparent nanocomposite is presented. This will enable the weight of the transparent armor systems to be reduced by at least 35 % against armor piercing threats relative to present systems. Transparent armors currently in use consist of soda-lime glass or borosilicate glass laminated to polycarbonate. Fabrication of large sized materials is a new feature of the new design. The chosen fabrication route is by using a twin screw non intermeshing co-rotating extruder. The cost analysis to determine production costs for 100 panels per annum is presented. The processing parameters and their effect on the strength, thermal conductivity, thermal expansion, as well as transmittance in the visual and Infra-red spectrums. The transmit wavelengths to the ratio of the particle size is used to evaluate the haze formation in the material.

Reclamation of Rubber Crumb from Army's Discarded Tires
Kal R. Sharma, May 2000

Polybutadiene is obtained by acid washing the rubber tires followed by thermal treatment of the devulcanized component of the pulverized rubber powder. The process consists of tire grinding and pulverizing steps, a devulcanizing step to reduce the cross-link density, followed by thermal polymerization of the aromatic vinyl mononers and grafting of the polybutadiene followed by melt filtration of the carbon black and the steps of finishing and packaging. The devulcanizing yield can be improved by providing a cocuurent leaching step. This is compared with the yield by the in situ thermal grafting concept.

Mesoscopic Simulation of Ballistic Impact Resistance of Nanocomposites
Kal R. Sharma, May 2000

The ration of areal density to level of ballistic protection is a critical factor in evaluating the ballistic impact resistance performance of silicate nanocomposites. The current goal of Army is 3.5 lb/ft2 areal density able to defeat all types of 7.62 mm bullets. Mesoscopic simulations were performed on the dynamics of the nanoparticle system. The energies absorbed by the interface, the particles, is quantitated. Comparisons are drawn between polymer polymer nanocomposites and micro composites. The polycarbonate matrix systems and exfoliated polybutadiene as the elastomeric phase was compared with the ceramic nanocomposites. The low temperature multi-axial impact strength as a function of the volume fraction of dispersion is predicted. The shift in the glass transition temperature of the polymer matrix is evaluated.

Mesoscopic Devolatilization Efficiency in Diskpack Device
Kal R. Sharma, May 2000

The design considerations of a diskpack devolatilizer cum discharger is discussed. The mixing times are compared with the time for discoloration of polymer. The mesoscopic devolatilization efficiency in diskpack device is compared with the single screw extruder devolatilizer, twin screw extruder devolatilizer, twin screw corotating non intermeshing, twin screw counter rotating intermeshing and multiple screw configurations, flash falling strand devolatilizer systems, thin filmtruder, thin film evaporator, forced circulation evaporator, falling film evaporator. The mixedness in the melt in continuous polymerization process is modeled using stochastic differential equations. The solution is obtained and a new procedure to estimate the mass transfer from the QC data is presented.

Impact Modification of Nylon 6,6 Resins with Functional Polyolefin Modifiers Based on Conventional and Metallocene Backbone Resins
N.R. Dharmarajan, T.C. Yu, J.R. Schauder, L.G. Kaufman, May 2000

This paper examines the impact toughening of nylon-6,6 resins of varying molecular weight with maleic anhydride grafted polyolefin modifiers. The modifier backbones are comprised of either conventional catalyzed ethylene propylene copolymers or metallocene catalyst based ethylene higher alpha olefin copolymers. The modifiers have maleic anhydride contents ranging from 0.5 to 1.2 wt. %; crystallinity, as measured by heat of fusion ranging from 0.7 to 6.2 J/gm; and melt flow rates ranging from 9 to 24 gm/10min. Results from the study show that modifier crystallinity has a dominant effect on impact toughening, with the amorphous modifier providing excellent low temperature toughness over a wide range of nylon-6,6 molecular weights. Higher grafting levels of maleic anhydride demonstrates no added benefit in impact toughening. A, morphological analysis using Atomic Force Microscopy, reveals the presence of nyon-6,6 sub inclusion within the modifier particles. The volume fraction of the occluded nylon, depends on the grafting level and the viscosity differences between the nylon-6,6 matrix and the functionalized modifier.

Laser Transmission Welding of Semi-Crystalline Thermoplastics-Part II: Analysis of Mechanical Performance of Welded Nylon
V.A. Kagan, G.P. Pinho, May 2000

Selecting thermoplastics for a wide industrial application (automotive, appliances, lawn & garden, power tools, etc.) strongly depends on the plastic material composition, part design, processing (molding and welding) conditions. The structure of used thermoplastics, mechanical properties and composition (reinforcements, fillers, additives, pigments, etc.) may have the greater influence and need to be characterized for optimum material selection for the laser transmission welding (LTW) application. To provide a guide to nylon based thermoplastics selection for laser transmission welding (LTW) applications we have evaluated the influence of specific material composition factors and properties, such as fiber-glass, mineral filler, impact modifier content, and color / pigment version on the Near InfraRed (NIR) transmission characteristics, including the laser wavelength (1.06 ?m). The results of an optical characterization of nylon 6 based thermoplastics are discussed in the Part I of this report to ANTEC'20001. The mechanical performance (tensile strength at room temperature conditions) of nylon welded joints was evaluated in terms of the influence of transmission laser welding technology parameters (laser power, welding speed, laser beam spot sizes, clamp pressure, etc.) and thermoplastic composition (reinforcements, fillers, additives, pigments, etc.). Technical results of this comprehensive evaluation (optical properties of nylon 6 based plastics and mechanical performance of welded joints) will assist plastic parts designers and technologists in selecting nylon based thermoplastics and developing new products using laser transmission welding (LTW) technology. The purpose of Part II of this report is to increase understanding within the plastics engineering community regarding the usefulness and possible applicability of laser transmission welding (LTW) technology for nylon made components.

Gate Land and its Effects on Gate/Cavity Pressure Loss
Bill Fierens, Sean Mertes, May 2000

In injection molded tool design, an optimum gate land has been specified as ~1.2 mm in length. This is typically given in order to optimize gate aesthetics and/or follow-up injection times. The thought process being that if the gate land is too long; gate aesthetics and part dimensions will suffer. Too short, and gate solidification will not be attainable in an efficient time frame. The data that is generated will be intended for real-world" applications and an aid to those manufacturers interested in optimization of tool design. Our goal will be to further develop the degree at which the alteration of this dimension impacts the efficiency of the process."

Hot Runner Molding: Products, Systems and Applications
Douglas Hugo, May 2000

Injection molding of thermoplastics has matured from cold sprue bushings to internally heated systems and more recently to externally heated systems. By far, the largest requirement at this time is for externally heated systems because greater benefits are derived with this approach. Hot Runner tools of 128 cavities with 128 nozzles are now common. In addition, the Hot Runner Systems of today have to be properly suited for each application with the ability to process commodity resins, such as polypropylene, or engineering resins, such as glass-filled Ultem. Some Hot Runner Systems are required to operate above 370°C (700°F) processing temperature. Also, in many applications, wear-resistant components are absolutely necessary to satisfy customer demands for longevity, maximum uptime and increased productivity. The development of new products driven by diverse customer requirements w ill continue to enhance hot runner technology.

Chemical Crosslinking of Flexible PVC Foam Formulations
Rigoberto Ibarra-Gómez, Isaura G. Yáñez-Flores, Oliverio S. Rodríguez-Fernández, Marianne Gilbert, May 2000

Infrared, thermal and elemental analysis were carried out to study the development of crosslinking, to characterize the gel and to evaluate the presence of residual unsaturation of a flexible foam formulation of PVC crosslinked by a peroxide/co-agent system. The crosslink density of some samples was measured and compared with a sample crosslinked by triazine/MgO system in order to learn more about the structure of the crosslinked network. Thermal stability of crosslinked samples was evaluated to compare the two crosslinking systems. The use of the Peroxide/TMPTMA appears to be a reliable method of producing foamed and crosslinked plasticized PVC formulations; it allows the formation of a very dense network, due to the trifunctional nature of the co-agent compared with the network formed with the Triazine/MgO. The samples crosslinked by the Peroxide/TMPTMA system did not show residual unsaturation after the optimum curing time.

Direct Numerical Simulations of Drops and Bubbles in Viscoelastic Shear and Pressure Driven Flows
P. Singh, S.B. Pillapakkam, A. Narh, May 2000

A finite element code based on the level set method is developed for simulating the motion of viscoelastic drops and bubbles in two- and three-dimensions. The viscoelastic fluid is modeled via the Oldroyd-B and FENE dumbbell constitutive models. The Marchuk-Yanenko operator splitting scheme is used to decouple the main difficulties of the governing equations, i.e., incompressibility constraint, nonlinear convection, viscoelasticity. The code is used to study deformation of drops in simple shear and Poisuelle flows over a wide range of dimensionless capillary and Deborah numbers. Simulations show that there are limiting values of these two parameters above which the drops become unstable and a cusp shaped training edge develops. The numerical results show that the viscoelastic stresses near the trailing edge are extensional and act in the direction normal to the drop surface. The front of the bubble however remains round as the local viscoelastic and viscous stresses act to round the bubble. These numerical results are important as they imply that during the extrusion processes the drops and bubbles may develop cusp-like trailing edges which may effect the mechanical properties of molded parts.

Stability of Blends of Polyethersulfone with Thermotropic Liquid Crystalline Polymers
Gang Qiao, Kalman Migler, Charles C. Han, May 2000

The formation and stability of various liquid crystalline polymers in an amorphous polymer matrix, Polyether sulfone (PES) over the melting temperature has been studied by in-line optical video microscopy and light scattering. The fiber breakup morphology profiles after shear cessation was examined to study the stability of the thermotropic liquid crystalline polymers (TLCP) fibers in the PES matrix. The TLCP are aromatic copolyesters with different chain structures, Ln 001 and LC-5000. Shear induces a droplet-fiber transition along the flow direction, but the TLCP fibers are highly unstable and can break up in a few seconds upon cessation of shear. The TLCP fibers break up into droplets by the combination of Rayleigh distortions, end pinching and retraction. The apparent values for the interfacial tension was calculated with Tomotika's theory and compared with the individual fiber experiment in literatures. The results suggest that the viscosity ratio and the interfacial tension between the materials components control both the shear-induced fiber formation and fiber stability.

Developing Animations and Simulators for Plastics Education
Kirk Cantor, May 2000

Instructional technology, computer-based training, and multimedia are a few of the modern words associated with the wave of technological advancement in educational methods. The plastics industry is not only riding this wave, but has been a contributor in leading these advancements. This paper describes the development of several projects that expand the body of technology-based plastics education. These projects include animations used to describe machinery or present difficult polymeric concepts and simulators used to teach operational techniques. Hardware, software, and methods used in these projects are discussed.

Understanding the Interrelationship between Blown Film Process Variables and Bubble Geometry Using a Blown Film Extrusion Simulator
Kirk Cantor, May 2000

Blown film extrusion is a process requiring a high level of operator skill. Producing film to geometric specification requires a good understanding of the dependence of bubble dimensions on the interrelationship of process variables. Dimensions include film thickness, bubble diameter, and frost line height. Process variables for controlling these dimensions include screw speed, nip speed, cooling air speed, and bubble air volume. An experienced operator understands that changing any one variable will affect all three dimensions, and understands the change that will result. A highly realistic blown film extrusion simulator is used to elucidate these interrelationships for all personnel.

Cure Characterization of an Epoxy Resin System by Thermal Analysis
Walter X. Zukas, Linda L. Ghiorse, E. Jason Robinette, May 2000

Torsional braid analysis (TBA) and differential scanning calorimetry (DSC) were used to characterize the cure of an epoxy resin used in the fabrication of Army composite structures. The work was carried out as part of a Cooperative Research and Development Agreement (CRDA) between the U.S. Army Research Laboratory and Foster-Miller, Inc. Understanding the cure behavior of a thermosetting system is essential in the development and optimization of composite fabrication processes. This understanding is based on the ability to characterize the relationships between the degree of cure, temperature, time, and material processes of the curing resin.

Non-Isothermal Crystallization of Syndiotactic Polystyrene-Pre-Melting Temperature Effects
Fang-Chyou Chiu, Chi-Gong Peng, Qiang Fu, May 2000

Differential scanning calorimetry (DSC) was used to study the influences of pre-melting temperature (Tmax) and cooling rate (C) on the non-isothermal melt crystallization kinetics of syndiotactic polystyrene (sPS). It was found that as Tmax or C was raised, the crystallization peak temperature (Tp) and crystallization initiating temperature (Ti) were both decreased. The Ozawa exponent n and parameter K were determined for Tmax=340°C and 315°C specimens, but for the Tmax=290°C specimens Ozawa equation was not valid. Activation energies for the non-isothermal crystallization processes were estimated to be around 415 kJ/mol.

The Determination of PET Crystallinity by Different Analytical Techniques
Vladimir Gruver, Don Showers, Ming-yuan Kao, Lena Klebanov, May 2000

The degree of crystallinity in industrial Polyethylene Terephthalate (PET) has major effects on the physical and mechanical properties of the polymer when used in films, fibers, and molded parts. Crystallinity of injection molded and heat treated PET bars was investigated using x-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), differential scanning calorimetry (DSC), and the material density technique. The data showed that amorphous PET starts to crystallize at ~105°C and, while both XRD and FTIR are consistent and reliable techniques in quantifying crystallinity, the FTIR method is more efficient in terms of instrument operation and data analysis.

Estimating Fully Developed Melt Temperature in Extrusion
Chris Rauwendaal, May 2000

It is very useful to be able to predict melt temperature in extrusion, particularly in the extrusion of temperature sensitive polymers. Examples are extrusion of crosslinkable polymers, foamed polymers, and polymers that are susceptible to degradation. Unfortunately, the proper calculation of melt temperature is rather involved and requires the use of numerical techniques, the most popular one being finite element analysis. This paper describes a method to predict the fully developed melt temperature in screw extruders based on simple analytical expressions. The method is easy to use and leads to quantitative results with a minimum of time expenditure.

On-Line Product Quality Measurements for Continuous Sheet Processes
Bill Embleton, Steve Axelrod, May 2000

Continuous sheet processes include film/ sheet flat sheet extrusion lines, PVC Calendering lines, Blown film lines, and a variety of Coating processes. Manufacturers who own one or more of these processes, are interested in knowing the thickness or weight per area of the product that they are making and whether it is being made within specification. Knowing this while the product is made can lead to a reduction in the amount of out of tolerance material and scrap. There are several measurement technologies that can be used to provide this information while the product is being made. Several of these are introduced and discussed. The pros and cons of their application are presented along with a description of the technology.

Brownian Dynamics Simulation of Non-Dilute Fibre Suspension Flows in a Centre-Gated Disk
R. Zheng, P. Kennedy, X-J. Fan, N. Phan-Thien, R.I. Tanner, May 2000

We present a Brownian dynamics simulation method for predicting the flow-induced fibre orientation of non-dilute suspensions in the filling of a centre-gated disk cavity. The evolution of fibres is modelled by the combination of the Jeffery equation and a stochastic process to describe the deviation of the fibre motion from Jeffery's orbits due to the interaction among fibres. The present method does not require any type of closure approximations and enables us to obtain accurate solutions for a wide range of volume fractions of fibres. Results showing the fibre orientation evolution along the radial distance and through the thickness are reported.

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