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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When Does Plastic Yield Occur?
The yield point of a ductile plastic material is commonly taken to be the maximum in the engineering stress-strain curve conducted in a constant cross-head rate experiment. With most plastic materials permanent strain actually occurs well before the maximum point is reached. In metals the point where permanent strain occurs can be determined by performing loading-unloading experiments. In plastics the determination of this point must also take into account the time under load because plastic deformation processes are time/rate dependent. There is a corresponding change in the microstructure when permanent deformation occurs. Uniaxial tensile deformation experiments on a polyacetal copolymer are used to illustrate these points. Scanning electron microscopy is used to show that permanent microstructural deformations develop over time. In polyacetal the deformation involves the formation of voids and fissures.
Designing Toughened Plastics through Control of Morphology and Properties of the Toughening Phase
The fracture resistance of homogeneous plastics can be increased by the incorporation of a second phase which may be an elastomer, a thermoplastic, or even an inorganic material. The choice of the second phase depends on the intrinsic deformation mechanisms of the host matrix. The microstructure of the toughening phase may have significant effects on the toughening efficiency. The inclusion of a third phase in the toughening phase is often desirable for facilitating cavitation. The desirable properties and morphologies of the toughening phase for triggering such mechanisms are discussed in this paper.
Design Tools for Rapid Thermal Cycling
Mold temperature control is very important in injection molding, influencing both the part quality and production rate. The solid freeform fabrication (SFF) processes such as 3D Printing have demonstrated the ability to construct complex internal channels inside the tool to improve the process temperature condition. By running the hot and the cold oil alternately through the conformal channels, the mold surface temperature is well controlled so that isothermal filling and rapid cooling are achieved for the high part quality and the short cycle time. A low thermal inertia tool and a rapid thermal cycling system are being developed at MIT. This paper discusses models and design rules involved in the design of tools for rapid thermal cycling.
Scratch Resistance and Material Property Relationship in Polymers
The scratch/mar damage in polymers is a complicated mechanical process and cannot be directly related to material properties of polymers. Scratch performance of materials is determined both by scratching stress field and by various material properties. Testing methods, which include two types of scratch tests and a depth sensing indentation test, are described. A scratch model is applied to simulate the scratch process under constant load. The roles of basic material properties, i.e. Young's modulus, yield stress, tensile strength, friction coefficient, hardness, elastic recovery on scratch resistance of polymers are addressed. Approaches for improving scratch resistance in relationship to material properties are discussed.
Preparation of Polypropylene/Acrylonitrile-Styrene Copolymer Alloys by One-Step Reactive Blending
The compatibilization of PP/AS blends through the addition of peroxide (DCP) was investigated. The in-situ formed grafting copolymers of PP-g-AS and AS-g-PP were then characterized by FTIR. The optimum blending condition was obtained. The maximum degree of grafting was found to be 6wt % for the 50/50 PP/AS/DCP blend. PP was more degradable than AS in the presence of peroxide at high temperature. SEM of PP/AS/DCP and PP/AAS/DCP showed a fine dispersion and a smaller domain size of the dispersed-phase particles implied that the in-situ formed grafting copolymer acts as a compatibilizer to reduce the interfacial tension between the PP and AS phases.
Unsaturated Polyester and Vinyl Ester Resins in Vacuum-Assisted Resin Transfer Molding - SCRIMP
Seemann Composite Resin Infusion Molding Process (SCRIMP) is a room temperature vacuum-assisted resin transfer molding technique developed in recent years for high strength composite fabrication. This process is being used for marine, civil infrastructure, transportation and defense applications. Unsaturated polyester and vinyl ester resins are the two major resins used in SCRIMP today. The objective of this study is to compare the resin moldability and properties of SCRIMP molded composites based on these two kinds of resins. Effects of resin type, initiator, promoter, inhibitor and retarder on the reaction kinetics, chemorheological changes and resin shrinkage were studied by using DSC, RDA and dilatometry respectively. The surface quality of the molded samples was measured by a profilometer. A kinetic model in conjunction with a heat transfer model was developed to simulate the SCRIMP process.
Simulation and Experimental Studies of a Non-Return Valve Performance during Injection Molding
This paper presents the results of the simulation of the dynamic behavior of a non-return valve during the recovery and injection stage of the injection molding cycle. A generalized Newtonian fluid model is used to simulate the flow with FLUENT software. The results of the analysis determine pressure drop, time taken for the valve to open during the recovery stage and time taken for the valve to close during the injection stage. The simulation results are compared with experimental data for three different thermoplastics including HDPE, PC and Nylon-66. Experimental data is obtained for several injection molding runs with pressure transducers installed in the barrel. In addition, the forces that occur on the ring during each molding stage and the relative rotational speeds between the valve and ring during the recovery stage were calculated.
A Practical Approach to Polymer Rheology for Quality Control
Rheological data obtained under the conditions of temperature and shear existing in conversion processes are required for the prediction of the performance of polymer resins in those processes. The capillary rheometer simulates the conditions seen in conversion processes and can be used to produce pertinent data. The ± 3 ? variation of the viscosity verses shear rate curves (over the range of shear rates seen in a process) for a resin or compound, can be used as a tool for monitoring consistency and predicting processability. When the measured viscosities for a material fall within the tube" formed by the upper and lower limits of the variation the product is consistent. If not the way the curve moves out of the "tube" will provide information on the root causes of the product variation. This talk discusses the application of the "tube" concept to a range of filled and unfilled resins using an automated capillary rheometer system that makes the "tube" concept practical for application in quality assurance and process control."
A Practical Approach to Polymer Rheology for Quality Control
Rheological data obtained under the conditions of temperature and shear existing in conversion processes are required for the prediction of the performance of polymer resins in those processes. The capillary rheometer simulates the conditions seen in conversion processes and can be used to produce pertinent data. The ± 3 ? variation of the viscosity verses shear rate curves (over the range of shear rates seen in a process) for a resin or compound, can be used as a tool for monitoring consistency and predicting processability. When the measured viscosities for a material fall within the tube" formed by the upper and lower limits of the variation the product is consistent. If not the way the curve moves out of the "tube" will provide information on the root causes of the product variation. This talk discusses the application of the "tube" concept to a range of filled and unfilled resinsusing an automated capillary rheometer system that makes the "tube" concept practical for application in quality assurance and process control."
Blends of Ethylene/Styrene Interpolymers and Other Polymers: Benefits in Applications
Ethylene Styrene Interpolymers (ESI) exhibit compatibility with a wide range of polymers due to their inherent combination of olefinic and styrenic functionality. In particular, blends of ESI with atactic polystyrene, and polyolefins including polypropylene, have been found to offer interesting and unique combinations of performance properties. Fundamental blend morphology, structure/property relationships, and processability of ESI blends are discussed. Examples and benefits of such blends in applications such as molded articles, films, and foams are discussed.
Effect of Kneading Block Tip Clearance on Performance of Co-Rotating Twin-Screw Extruders
Over the years the design of the co-rotating intermeshing twin-screw extruder has evolved to meet the processor's never ending need for improved performance and processing efficiency. The most significant change in recent years has been the introduction of the high speed high torque machines. These high speed extruders, while producing increased throughput and reduced average residence time, also generate significantly higher shear rates and exit melt temperatures. This paper examined the effect of kneading block tip clearance on machine performance as a function of screw speed and specific rate. Machine performance will be defined in terms of power consumption, extrudate melt temperature, residence time distribution, melt index, and mix quality.
Modification of Cement Using Post Industrial Recycled Acrylonitril Butadiene Styrene (ABS) Latex Powder
Polymer latex modification of cement has increased the ductility of the resultant concrete. However, practical application of the concrete is limited since latex is used in a liquid form. In contrast, we have examined use of post industrial Recycled Acrylonitrile Butadiene Styrene powder (r-ABS). Pullout tests indicate an increase in adhesive bond strength between the polymer-modified mortar and steel re-bar. Thermogravimetric analysis is carried out to examine the influence of the latex on the kinetics of degradation. The results indicate a novel approach of using r-ABS in cement modification.
Thermal Aging Effects on Transport Properties of Polymeric Membranes for Fuel Cell Applications
Although solid polymer electrolyte fuel cells have been considered as environmentally attractive power sources, to date little work has been done on the durability of eletrolyte membranes. It is conceivable that time and prolonged exposure of membranes to elevated temperatures will significantly diminish the effectiveness of electrolyte cells. The goal of this study is to investigate and compare thermal aging and morphology effects on transport properties, such as ion diffusion coefficients and permeability parameters of the membranes for hydrogen ion transfer, of commercially available Nafion® and Dias® membranes and experimental phosphorus containing polyimide membranes. The emphasis of this paper is placed on the design and properties of a diffusion cell necessary for hydrogen ion measurements.
Thermoporometric Characterization of PHPMA Hydrogels
Differential Scanning Calorimetry (DSC) has been used to determine the pore size and pore size distribution of a surgical poly(N-2-hydroxypropyl) methacrylamide (PHPMA) hydrogel. The dry PHPMA (xerogel) was swollen in H2O and the pores size of the gel was determined from the solidification thermogram of H2O obtained at very slow cooling rate. The shift in the solidification equilibrium temperature of a known condensate held inside a porous material is pore size-dependent and enables the deduction of pore radii distribution of the material. The results obtained from this technique were compared with those obtained by B.E.T (Brunauer, Emmett and Teller).
Benefits of High Speed Machining Technology to Plastic Injection Mold Builders
This paper will show significant time and cost savings to plastic injection mold builders by using high speed machining (HSM) technologies. It addresses overall productivity and production process improvement in the manufacture of sophisticated three dimensional core and cavity mold components using hardened steel machining processes compared to conventional mold production processes. A case study will compare the HSM process to conventional processes in the production of a complex mold cavity. The case study results will demonstrate real benefits of HSM to reduce overall manufacturing operations, man hours, capital resources and delivery time.
The Effects of PE/PA/PVA Blends' Compositions upon the Barrier Properties of Blow-Molded Containers
This research investigates how compositions of PE/PA/PVA (Polyethylene/Polyamide/ Polyvinylalcohol) blends influence the barrier properties of blow-molded containers for methanol/gasoline fuel. The objectives of this research is to improve the barrier properties of PE/MPAPVA blend for methanol /gasoline fuel. We found that the content of PVA and CP (Compatibilizer Precusor) affect methanol/gasoline fuel permeation rate. Furthermore, the compositions of MPAPVA exhibit a significant influence on the barrier properties of blow-molded PE/MPAPVA containers. The composition of PE/MPAPVA blends for the best permeation resistance is 20% of CP blended with MPAPVA. This formula exhibits the best barrier properties for methanol/Gasoline fuel with weight lost less than 1g/24Hr.
The Kinetics of Shear-Induced Crystallizatio in Poly(Ethylene Terephthalate)
The kinetics of shear-induced crystallization in PET was studied. The shear-treated samples were obtained from controlled shear rate apparatus (CSR, Fig. 1) and the capillary viscometer. The samples of use were observed the differences of crystallization behavior by DSC. The kinetic model suggested by Hoffman-Lauritzen, Nakamura were used to analyze experimental results. The crystallization behavior of shear-treated samples depended also on temperature and shear stress. On the lower shear rate region, the rate of crystallization depended on shear stress. And the growth rate induced by fluid flow reached the critical point on the region of a certain high shear rate. The empirical data were simulated by the suggested model
Processing Characteristics of PSU/PC Blend Associated with Degradation in Injection Molding
This study investigates the effect of degradation of the PSU/PC blend on quality characteristics of the molded parts. Experiments were conducted at two sets of melt temperatures - 'normal' temperature, where no severe degradation is expected (T-zone 1); and 'elevated' temperature, where significant degradation should occur (T-zone 2). ASTM D638 tensile bars were used for molding and measured for quality parameters of part weight, warpage, and tensile strength. Small fluctuations in the process variables were purposely introduced for T-zone 1 and T-zone 2. As the results, T-zone 1 provided more consistent shot-to-shot part properties and less process disturbances for all the parameters than T-zone 2. The subsequent baking of the molded parts rendered most of the parts excessively warped for T-zone 2. Back pressure was an important variable regarding shot-to-shot variations in all the parameters.
Correlation Study for Minimizing Shrinkage of PFA Molded Parts
This study deals with investigating the relationship between part weight and shrinkage of PFA molded parts against process variations. The extensive experiments were conducted using DOE techniques in the ranges of process variables. Resulting part weight is also compared to the predictions. This study extends further to determine the influences of varying hold time and back pressure, respectively, on part weight and shrinkage. An optimum hold time is obtained comparatively from the results of the experiment, prediction, and theoretical formula. As the results, there existed good correlation between part weight and shrinkage, and between actual part weight and predictions against process variations. As the hold time varied, both the experiment and the predictions of the part weight matched well in trend, and indicated a distinctive gate freezing time.
Study of Moisture Diffusion Behavior in Hybrid IM7/BMI Composites
Moisture diffusion behavior in IM7 carbon fiber-reinforced bismaleimide composites (IM7/BMI) is investigated under two different temperatures at 100% relative humidity. Three-ply uni-weave, crossply-weave and hybrid of uni-weave and crossply-weave composites are utilized for the present study. Diffusion behaviors in those IM7/BMI composites are found to be significantly influenced by laminate architecture. A finite element model based on Fick's second law is used to predict the moisture diffusion behavior in hybrid composites. It is found that both the neat resin and composites follow the Fickian diffusion behavior only at short times. At longer times, moisture diffusion begins to deviate from Fickian behavior and suggests that addition moisture absorption mechanisms take place.
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