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The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.

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Conference Proceedings

PMMA Thermal Degradation and Modeling of Weight Loss Experiments
Alia M. Rdissi, Sindee L. Simon, May 2001

Residual polymerization catalyst can be detrimental to the thermal stability of polymers. We used thermogravimetric analysis (TGA) to demonstrate that the thermal stability of poly (methyl methacrylate) (PMMA) decreases upon doping with a transition metal catalyst. This effect could be reversed by adding a chelating agent to the doped PMMA. In addition, we modeled the TGA weight loss experiment. The modeling verified that weight loss for the experiments was not diffusion controlled and that weight loss linear with the square root of time does not necessarily indicate diffusion control.

Investigations into Rotational Moulding of Short Fibre Reinforced Thermoset Resins
Simon Bickerton, Roy J. Crawford, May 2001

The addition of reinforcing fibres, or fillers, to liquid thermosets significantly alters the rheological behaviour of such resins, drastically increasing viscosity. In order to successfully mould these materials a good understanding of their rheological behaviour is required. A simple numerical model is developed, predicting evolution of the resin cure reaction, and resulting in-mould rheological, and flow behaviour. Qualitative comparisons are made to initial moulding experiments completed with neat, and wood fibre filled polyester resins. Moderate additions of fibre were found to improve part quality due to the increase in initial viscosity, while a practical limit was reached above which excessive fibre clustering occurred.

Inventions in Polymers: It Takes Teamwork to Make a Successful Business
P.M. Subramanian, May 2001

The last five decades have seen the explosive growth of synthetic polymers. Innumerable types of polymers and their derivatives designed for specific properties and applications have been invented and developed. Fundamental to such growth are the creative discoveries of several scientists and innovators. Converting these brilliant discoveries into major business successes have taken the concerted efforts of a large number of a second set of inventors and innovators. While the primary inventors have been well recognized, often, the latter scientists and innovators, without whose contributions these products and processes would not have become large successful businesses, are relatively unknown. As examples, Teflon*, super-tough nylon, and sretch-blow-molding of PET bottles and the teamwork that made these into significant businesses, will be discussed here.

Experimental Investigation of Slip in Plug-Assisted Thermoforming
P. Collins, P. Martin, E. Harkin-Jones, Denis Laroche, May 2001

Surface friction is known to play a vital role in determining product wall thickness distribution during plug-assisted thermoforming. In this study this behavior has been investigated by carrying out experimental tests to measure both the static and dynamic coefficients of friction acting between typical plug materials (Delrin, syntactic foam and aluminum) and polypropylene (PP) sheet at elevated temperatures. Plug only tests were also conducted to investigate the effect of plug temperature on wall thickness distribution. Results showed that values of coefficient of friction varied from 0.13 up to 0.72 depending on sheet temperature and the combination of materials tested. Plug temperature was also shown to be very important, with a temperature of 90°C showing the greatest slip during plugging. It was concluded that friction at the plug-sheet interface was temperature dependant and further work is required to verify these initial observations.

Inventions, Patents and Innovations: A Beneficial Symbiosis - How I Learned to Stop Worrying and Love Patents"
Tai-Sam Choo, May 2001

Alter exploring the role of patents in encouraging disclosure of inventions as a significant stimulus to technological developments and innovations, this presentation will also probe how patents can protect commercial investments and provide a competitive advantage in global economy. Also presented will be certain practical considerations and tips on how to prepare and obtain patents others would envy." To this end the presentation will highlight major differences between the U.S. patent system and others will review important recent changes in legal requirements (with particular emphases on rule changes resulting from the enactment of the American Inventors Protection Act) and will examine common pitfalls to avoid. Where appropriate the patents relating to the innovations advanced by other speakers in Fundamentals Forum on Invention and Innovation will be featured as illustrations."

A Model and Parameter Formulation of Stress-Induced Crystallization Kinetics of Polymers
Jianxin Guo, Kwabena A. Narh, May 2001

A stress-induced crystallization model for semicrystalline plastics is proposed based on the theory that stress induced orientation of molecules and chains increase the melting point of the plastics, and hence, the supercooling which is the driving force for crystallization. By assuming that the effect of stress on crystallization is only by increasing the equilibrium melting point, the basic quiescent state crystallization equation can be directly applied to model stress-induced crystallization kinetics. The model predicts the most prominent features of stress-induced crystallization. The main advantage of the model is that the parameters in the quiescent state crystallization model do not change. Consequently, the parameters in the equilibrium melting temperature shift model are easy to determine, and the unknown constants are kept to a minimum.

Optimization in Process Control for Uniform Quality of the Optical Components
M. Rahman, N.R. Schott, May 2001

Part weight, dimensions, shrinkage and birefringence are a few important measurable parameters that are used to define the quality of plastic optical components. The quality of a plastic part can be assured by determining the proper and optimized set of injection molding process variables. Online cavity pressure data as a function of time for a dual cavity optical mold were analyzed with an equation of state for an Ising fluid for establishing the PVT relationship. The PVT data were then used in an empirical model to determine the optimized set of process variables for the expected quality of a part.

Theoretical Validation of Long Chain Branching Quantification Technique for Polyethylene
Chunxia He, Stéphane Costeux, Paula Wood-Adams, May 2001

An empirical technique for determining long chain branching level in well-defined polyethylene (PE) was recently proposed by Wood-Adams and Dealy. This technique consists of comparing the molecular weight distribution measured by GPC with an apparent molecular weight distribution derived from the complex viscosity. The method was proved to be robust for PE synthesized using constrained geometry catalysts. Nonetheless the theoretical basis underlying this technique remains not fully understood. This paper clarifies and widens the validity of the method by making use of the molecular dynamics theory based model of Milner et al. for blends of linear chains and three-arm stars.

Model Based Prediction of Permeability in Preform Materials
Frederick R. Phelan Jr., May 2001

Knowledge of the permeability tensor in liquid composite molding is important for process modeling and optimization. However, experimental determination of the permeability is difficult and time consuming. In this work, a lattice Boltzmann simulation which has been modified for flow in porous media is used to predict permeability as a function of yarn location, orientation, and fiber fraction. Calculated permeabilities are compared with experimental measurements for a variety of systems. Good agreement is achieved as long as the mesh size is greater than the size of the smallest throats in the porous medium.

The Effects of Varying Peroxides Concentration in Moisture-Crosslinking of LLDPE
Jenn-Fong Kuan, Liang-Chi Tu, Kuo-Hsiung Wang, Jaine-Ming Huang, May 2001

The effects of linear low density polyethylene (LLDPE) grafting with vinyltrimethoxysilane by different types and contents of peroxide were studied. When grafting silane onto LLDPE, 0.10 phr content of Dicumyl peroxide (DCP) or 0.05 phr content of 2,5-Dimethyl-2,5-di (tert-butyl- peroxy)-hexane (DHBP) was found to improve the grafting effect; however, as Di (2-tert-butylperoxypropyl -( 2))-benzene (F40) or excess DHBP was used, LLDPE was supposed to cause self-crosslinking which deducted the grafting percentage of silane and invalided the processing of extrusion.

Linear Viscoelasticity of Binary and Ternary Immiscible Blends
Daniel Ercoli, Graciela Goizueta, Numa Capiati, May 2001

The linear viscoelastic behavior of binary and ternary immiscible Polypropylene (PP) based blends with linear low density polyethylene (LLDPE) and different ethylene-propylene copolymers (EPR) is studied in this work. The effect of changing the composition and concentration of the dispersed phase under the small amplitude oscillatory shear flow is analyzed. It was found that the influence of the type of elastomer used is more important in the low frequency range. The predictions of a simplified constitutive equation for emulsions of viscoelastic fluids are only in good qualitative agreement with experimental results when an elastomer of lower Mw is used and in the high frequency range.

Compatibilized PP/PHAE Blends by Reactive Blending
Ruth Zacur, Graciela Goizueta, Numa Capiati, May 2001

Blending of immiscible polymers is a powerful method to create materials with enhanced properties at competitive costs. Reactive compatibilization additionally gives a more stable morphology and improved adhesion between phases. Blends of polypropylene (PP) and materials of very low oxygen permeability are very promising in this area. In this work we study polypropylene and polyhydroxyaminoethers (PHAE) blends of different compositions prepared in a batch mixer. The reaction of maleic anhydride graft polypropylene (MA-g-PP) with PHAE is analyzed. The reaction products were analyzed by FTIR, DSC and SEM. MA-g-PP is found to be an effective compatibilizer of PP and PAHE.

Reactive PP/Elastomer Blends Using Coupling Agents
Gustavo Silbestri, Ruth Zacur, Graciela Goizueta, Numa Capiati, May 2001

Reactive blending is an attractive way to produce block or graft copolymers in situ to compatibilize immiscible polymer. Location of the copolymer at the interface decreases the interfacial tension and at the same time a steric stabilization occurs that reduces particle coalescence. In this work we explore the efficiency of 1,4- Phenylenediamine (PDA) as a coupling agent for polypropylene (PP) and ethylene-propylene diene (EPDM) funcionalized with maleic anhydride to produce PP-co-EPDM. Different concentrations of the coupling agent were used at fixed mixing conditions and reaction products were characterized by FTIR, DSC and SEM.

The Effect of Layer Stretching on the Onset of ‘Wave’ Interfacial Instabilities in Coextrusion Flows
M. Zatloukal, J. Vlcek, C. Tzoganakis, P. Saha, May 2001

The effect of layer stretching on the onset of 'wave' interfacial instabilities in coextrusion flows is evaluated through transient viscoelastic stress calculation by modified Leonov model and the velocity field determination through FEM with the help of newly proposed criterion based on the difference of normal stress differences across the layer interface. The study shows how this criterion can be used to investigate the role of the die design and elongational viscosities of coextruded materials from the interfacial instability point of view. It is shown that both the die geometry and the elongational strain hardening have a crucial effect on the interfacial wave instability.

Rheological Probing of Structure in Polypropylene / Clay Nanocomposites
D. Marchant, K. Jayaraman, May 2001

Polypropylene/clay nanocomposites have been prepared with a variety of hybrid structures by melt mixing a fixed amount of organically modified clay, different levels of a maleated polypropylene and polypropylene. The structure has been investigated with X-Ray diffraction and transmission electron microscopy. An optimum level of maleated polypropylene is found to yield the greatest degree of exfoliation in polypropylene. The relative viscosity curves reveal a systematic trend with the extent of exfoliation and show promise for quantifying the hybrid structure of the nanocomposites.

The Effect of Cavity Pressure Transducers on the Overall Performance of a Multi-Cavity Hot Runner Injection Mold
Christopher N. Guimond, Robert Simas Jr., May 2001

Multi-cavity hot runner injection molds have historically had problems with unbalanced and/or unrepeatable filling patterns sometimes related to thermal variations in the manifold which can typically result in a number of processing issues. Typically, if a scientific approach to identifying optimal filling patterns is utilized, the overall performance of a multi-cavity hot runner tool can be improved. Scientific processing techniques in addition to cavity pressure transducers can be an advantageous approach to identifying optimal filling patterns and any variations that may exist in these types of injection molds. The purpose of this study is to identify the effect of cavity pressure transducers on the overall performance of a 32- cavity hot runner injection mold. Typical scientific processing techniques such as short shot studies and on-machine rheology curves were used as the foundation of the study. Once the preliminary molding conditions were identified and the cavity pressure transducers strategically placed, a design of experiments (DOE) was conducted to determine the effects of varying process conditions (injection velocity, hold pressure, and hold time) on specific cavity pressures in the 32-cavity hot runner injection mold. The short shot study provided an idea of the mold filling imbalances and allowed for the cavity pressure transducers to be strategically placed, an end of fill transducer in each quadrant of the mold. The results showed that an injection velocity ranging from 35 to 95% resulted in adequate material viscosities during the fill stage. The DOE indicated that injection velocity and hold pressure had the most significant effect on the cycle integrals. Also, the hold time tended to have a significant effect on the cycle integral when increased from 1 to 3 seconds. Additionally, increased injection velocity tended to increase flash and decrease warpage.

Criteria for Flow Instabilities in End-Gated Injection Molds
Neelesh S. Jain, Carol M.F. Barry, May 2001

Jetting depends on material properties, the gate and cavity design in a mold, and injection molding parameters. Although various criteria define the limits between jetting and fountain flow, these rules are often contradictory. In this study, jetting flow instabilities were examined with a broad range of materials, molds, and processing conditions. The jetting depended on materials and gate and cavity dimensions, but was not eliminated or induced with increasing injection rates to ~200 cm3/s. Prediction of flow instabilities using extrudate swell-based criterion failed with some materials, particularly at high shear rates. Gate dimension design criteria also failed to predict jetting. Although not yet verified, a criterion incorporating melt elasticity and melt friction seems promising.

Composite Droplet Viscosity Ratio Effect on the Morphology of HDPE/PS/PMMA Ternary Blends
Joël Reignier, Basil D. Favis, May 2001

The influence of the sub-inclusion component viscosity on the composite droplet morphology was investigated in the melt state, using scanning electron microscopy. Based on previous work, a blend of high density polyethylene (HDPE), polystyrene (PS) and a low molecular weight poly(methyl methacrylate) (L-PMMA) is chosen as a model system. While it might be expected that a high engulfing-to-engulfed viscosity ratio could delay or even hinder the composite droplet formation, it is clearly demonstrated that the tendency for the dispersed components to combine to form PS-PMMA core-shell structures is only dependent on the spreading coefficients analysis.

Topological Characterization of Pultruded Rods Reinforced with Continuous Carbon Fibers
S.C. Barwick, T.D. Papathanasiou, May 2001

We describe the use of Large Area Automated Microscopy (LAAM) for the topological characterization of entire cross-sections of pultruded carbon fiber reinforced rods. This characterization is an essential step in developing currently unavailable quantitative correlations between processing conditions and component properties. Usage of LAAM involves the automated scanning of samples of relatively large area O(cm2), capturing of thousands of image frames, montaging of these frames, and extracting topological information for all inclusions in the sample. In this work we describe the use LAAM to obtain such data from large (~1cm2) cross-sections of unidirectional carbon fiber-reinforced rods, containing over 106 individual fibers. Analysis of this data for industrial-scale pultruded rods has revealed several mesostructural features (fiber clustering and fiber misalignment) that can be of assistance in identifying processing or sample preparation defects.

Optimization of Process Conditions in Gas Assisted Injection Molding
Ming Chen, Donggang Yao, Byung Kim, May 2001

Gas-assisted injection molding has been widely used to provide promising solutions to problems in conventional molding. With additional process parametcrs introduced, optimization in gas-assisted injection molding is much more complex than that in conventional injection molding. This paper proposes an automated design methodology for gas-assisted injection molding with robustness in consideration. By introducing a definition of gas penetration cost, the optimization problems dealing with multiple quality issues can be modeled as constrained optimization problems, with the gas penetration cost as main objective function and other quality quantities as constraints. A direct search-based optimization procedure, the Complex method, is used to optimize the bounded single-criterion problem. To illustrate the methodology, a case study is carried out on simulation results.







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