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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Real Time Development of Orientation in PP during Stretching as Detected by Spectral Birefringence Technique
The true stress- true strain and birefringence development in a series of PP films with varying levels of tacticity has been measured using a newly developed uniaxial stretching system. This system allows the real time study of the structural reorganization processes at industrially meaningful temperature and deformation rates. The system is fast enough to follow the deformation at high rates of strains and allows us see their deformation at temperatures well below the melting temperature of the samples provided that severe necking does not occur. It has been found that birefringence increases steadily with true strain. Certain stress is required to start to increase birefringence at lower temperature, meanwhile, the birefringence changes almost linearly with stress essentially following stress optical law behavior, as long as the temperatures are near melt temperature.
Recent Trends in Regulatory Activity by the Center for Biologics Evaluation and Research
The apparent trend in medical therapeutics is to move toward a biologically derived therapy stemming from human or xenobiology. The applications of this trend to the medical plastics industry are severe in the level of scrutiny and care necessary to meet the intent and letter of the legal regulations associated with biologic processing, control, and packaging. The Center for Biologics Evaluation and Research (CBER) is the responsible arm of the Food and Drug Administration charged with regulating the biologics industry. This paper will address some of the recent trends in regulatory activity by CBER.
Recommended Factors of Safety and Related Considerations
The only available mechanical design rules for plastics parts pertain to proportioning the sizes of ribs fillets, draft angles etc. Such rules help only to design the individual elements, but leaves a long way to go in settling questions in stress analysis. More specifically, such rules stop at ensuring success with the chosen process.Further, there is little formal guideline in the industry about dealing with creep strains, fatigue life, combined (thermal + molded-in + service) stresses etc., although enough technology is available to calculate them. Also, there is also little recognition of the fact that the long term presence of stress (or strain) depends on the cause of the stress.This paper addresses one of the resolutions to this situation by proposing minimum factors of safety for various service loading types, along with qualitative reasoning to back up. The proposal is motivated by (i) the arbitrariness in plastics of what stress levels are acceptable and what are not (ii) successful history of the use of factor of safety in bringing all structural performance to one common denominator (iii) coupled material behavior of plastic.Lastly, it is pointed out that all the factors are for products that are to survive loads, over certain period of time, and not for those which are designed to come apart at a specified force application.
Recyclability of Crosslinked Polyethylene Based on Creep
Crosslinking of polyethylene greatly improves the material's properties. The crosslinking process causes problems with the material's ability to be recycled. It prevents the material from remelting, making it nearly impossible to process in an injection molding machine.The crosslink density has an effect on both the material's ability to creep and on its ability to be recycled. Creep data was studied to determine the effects of increasing crosslink density on an injection molded polyethylene part. This data will be used as a baseline for how parts made from 25% recycled crosslinked regrind compares with the original crosslinked part. This paper will focus on recycling crosslinked polyethylene (PEX) determined by its creep data.
Reducing Curl in Multilayer Blown Film. Part I: Experimental Results, Model Development and Strategies
Multilayer films often curl or roll-up on themselves, making them difficult to be used in packaging equipment. Curl is particularly acute in asymmetric barrier blown films. Experimental results from simple two- and three-layer structures are described in an effort to understand the underlying mechanisms behind curl. A model from the literature based on beam theory" is adapted to film applications. In this model force and momentum balances are used to solve for curl as a function of each layer's thickness stiffness and shrinkage during fabrication. Of these inputs differential shrinkage is the most difficult to determine. Pressure-Volume-Temperature (PVT) curves are introduced to relate differences in volume change among polymers during quenching. PVT data alone are not sufficient for a predictive model. Qualitative agreement however between the experimental results and model predictions are obtained leading to several strategies for curl reduction. These include reducing crystallinity matching thermal expansion coefficients matching freezing points and increasing the rate of quenching. Another strategy is to change the thickness and distribution of layers in the film allowing the stiffness of one or more layers to counterbalance the curl. Such an approach can be greatly enhanced by a truly predictive model and is the subject of Part II."
Reducing Curl in Multilayer Blown Film. Part II: Application of Predictive Modeling to t Barrier Cereal Liner Film
Multilayer blown films often curl, particularly if the layers are not distributed symmetrically. A quantitative model is developed for predicting curl based on continuum mechanics: curl is the result of differential shrinkage between layers during quenching and is moderated by the stiffness and thickness of the layers. The difficulty in using such an approach is estimating differential shrinkage. Pressure-Volume-Temperature (PVT) data give good qualitative information on differential shrinkage, but they are generated under experimental conditions that differ greatly from commercial blown film processes. To correct the PVT data, a semiempirical approach is utilized. The model is run backwards" to compute the differential shrinkage in two-layer structures where the curl has been measured. From this PVT correction factors are obtained to predict the curl of multilayer structures.The model is applied to a (HDPE-tie-EVOH-tie-sealant) cereal liner structure. A sensitivity analysis shows that increasing the thickness of the HDPE layer reducing the shrinkage of the HDPE and reducing the thickness and stiffness of the EVOH layer can reduce curl. Experiments on a five-layer blown film line confirm the model predictions: a standard cereal liner structure had severe curl yet by using the model as a guide we were able to make essentially flat film."
Reducing Shrinkage and Warpage for Printer Parts by Injection Molding Simulation Analysis
Injection molding simulation software was used for predicting shrinkage and warpage of a printer part. A paper tray, one of the larger injection-molded parts in a printer was warped and the simulation duplicated the part deformation. The part was modified by optimized runner system design and molding process conditions to improve the mold filling and reduce the part warpage. Simulations predicted the final warped shapes for the original and modified paper tray. The predicted shrinkage and warpage of the part were compared to the measurements of a production part. The part warp prediction was in good agreement with the actual part deformation.
Relationship between Optical Properties and Optimized Processing Parameters for Through-Transmission Laser Welding of Thermoplastics
Previously we reported to Antec our studies on optical characterization (laser energy transmission, absorption, etc.) at a wide range of infra-red wavelength for various nylon based plastics (un-filled and reinforced) with the influence of various colorants. Later we discussed our analysis on optimized mechanical performance of the laser welded joints. In this current paper, we will try to increase the understanding of the plastics engineering community regarding the relations between optical properties of thermoplastics and optimized processing parameters of through-transmission laser welding (simultaneous welding mode).
Reliability Assessment of New Polymer Products with Environmentally Driven Failures
A methodology is presented for the reliability assessment of new product offerings, where product failures are driven by environmental conditions. The methodology is valid for the case of limited related product field data and understanding of underlying environmentally driven failure mechanisms. The methodology uses reliability theory in concert with failure mechanistic models to provide high resolution models which can be used to forecast liability exposure of new product offerings. The methodology has been successfully demonstrated for evaluation of Vinyl based products. The quantitative results generated suggest environmental region risks, overall new product risk, and risk relative to existing related products.
Reliability-Based Method for Service Life Prediction of Materials
Standard test methods, such as ASTM C719, evaluate sealant performance though threshold test measurements. This method and its derivatives do not offer reliable predictions of in-service performance. This presentation will detail efforts to move away from the use of threshold tests towards a reliability-based method for predicting the service life of sealant materials. The central role of dose-damage based models in this approach is explained. The central role of accurate, rapid, prediction of in-service performance in developing models to communicate the economic consequences of the materials decisions will be presented.
Reliable Snap-Fit Connections
The reliability of snap-fit connections depends very much of the stiffness of the plastic parts to assemble. The higher the stiffness, the smaller the required assembly displacements will be. The displacement(s) are the difference between dimensions of plastic parts and the smaller the displacements the higher the relative tolerances of the displacements. In case of small displacements sharp bosses are designed to obtain maximal displacements. These sharp boss tips suffer from high contact stresses and are blunted during assembly.The design aspects will be illustrated of a problem of assembling a push-button on a rod and of mounting a semi-spherical shell on a glass bulb with snap-fits, using FEM calculations.
Resin-Gas Injection Technique for Bonding and Surface Modification of Polymer-Based Microfluidic Platforms
Polymeric materials have attracted a great deal of attention in microelectromechanical systems (MEMS) for biomedical applications (BioMEMS) over recent years, due to their low cost, good processibility, and broad range of physical and chemical properties. Polymer-based microfabrication has been developed and studied for years. However, bonding (i.e., sealing the platform with a lid) and surface modification are still challenging issues. In this paper, we present a new method recently developed in our lab: resin-gas injection-assisted bonding. This new approach can easily seal microfluidic devices with micron and sub-micron sized channels without blocking the flow path. It can also be used to modify the channel shape, size, and surface characteristics (e.g., hydrophilicity, degree of protein adsorption). By applying the masking technique, local modification of the channel surface can be achieved through cascade resin-gas injection. Experiments are carried out to demonstrate bonding efficiency and surface modification.
Review of Plastics Pipe Lifetime Evaluation Methods: Predictive Capability and Limitations
A reliable estimation of pipe lifetime (such as at least 50 years or 100 years of useful life) is a very important factor for business decision in selection of plastic pipes in specific applications. Various accelerated tests for lifetime evaluation and test results extrapolation techniques are discussed in this presentation. The acceleration is necessary to complete the evaluation process of the pipes within a reasonable time interval. However, an accelerated test implies the test condition different from that in service. Thus, the criteria of similarity (correspondence) between the service and an accelerated testing shall be clearly identified. At present the widely accepted by plastics pipe industry methodology for material ranking and pipe lifetime evaluation, is based on many years of PE pipes service experience. An analysis of the engineering background and the scientific foundation of the existing methodology are discussed. The limitations of the phenomenological approach to the pipe lifetime assessment is presented and illustrated by an example of failure of the lifetime predictions. The needs for fundamental understanding and theoretical modeling of the failure mechanisms for reliable piping lifetime prediction and a few steps in that direction are also addressed.
Revisiting an Old Tool for Plastics Manufacturing Education
The small pneumatic ram injection molding machine is a common sight in undergraduate plastics manufacturing laboratories. Although useful for demonstrating basic concepts they are limited in pressure and temperature control, repeatability, and can only use a limited range of materials. They have the advantages however, of inexpensive tooling, a simple easily understood process, and low cost.This paper describes modifications to this basic machine to extend their usefulness in the teaching environment and the development of course materials to accompany them. The modified injection molder supports a broad range of subject matter, including control schemes for temperature (PID, Off-On, etc), design of tooling, design of experiments, and process optimization.
The Rheological and Mechanical Performance of Ethyl-Vinyl Acetate/Polyvinyl Chloride Formulations
A range of powdered ethyl vinyl acetate (EVA) copolymers and polyvinyl chloride (PVC) formulations were compounded at PVC:EVA ratios 100:0, 60:40, 50:50, 40:60 and 0:100 respectively. Two grades of EVA with 20% and 27% vinyl acetate (VAc) (EVA I and EVA II) and two grades of PVC with K-values 56 and 71 (PVC I and PVC II) were used in the investigation. Mechanical analysis was performed on injection moulded samples of these blends and the results showed that the tensile and flexural modulus decreased significantly with increasing EVA concentration. Rheological analysis was performed using dual capillary rheometry and the results showed only slight changes in shear viscosity with increasing EVA content even at lower shear rates. Dynamic mechanical thermal analysis showed partial miscibility of the PVC and EVA over the range of concentrations studied.
Rheological Characterization of Polyesters Based in Terephtalates
The objective of this work is to measure the rheological properties of some engineering polyesters based in terephthalates. These polyesters were poly(ethylene terephthalate)(PET), poly(trimethyl terephthalate)(PTT) and poly(butylene terephthalate)(PBT). Materials behaviors in steady, oscillatory and transient flows were studied at different temperatures from 250 to 310°C. Cone-plate and capillary rheometry were used to measure the rheological properties. No significant variation of the power law index was observed when the temperature was increased for the PET and PBT. The relaxation spectrum of the polymers did not show any significant variation for the PET and PBT, but for the PTT a small variation was observed. PET had the highest elasticity in all the experiments, as shown by the normal force (shear), the storage moduli (oscillatory), the elastic recovering (creep) and the stress overshot. PBT was the most sensitive to degradation at the tests conditions, due its longer aliphatic sequence in the chain. This sensibility was the main experimental obstacle to perform reliable measurements.
Rheological Characterization of Pressure Sensitive Adhesives
The rheological behavior of a material is important when mixing, melting, extruding, pumping, pressing, etc... Rheology is used to predict a material's response to differing modes of flow and deformation at any point from the processing step through its final end use. In the pressure sensitive adhesive (PSA) field, three terms are generally used to describe its performance: Shear Resistance, Tack and Peel Strength. These properties are directly related to the PSA's response to the application of stress and therefore its rheological behavior.The property of tack describes the ability of a PSA to spontaneously form a bond to another material under light pressures within a short application time. As the contact time increases, higher shear resistance and peel strength properties are found, related to a materials long time flow behavior. It is found that a single rheological test is able to directly determine the response of a PSA to varying deformation times, related directly to its shear resistance, tack and peel strength behavior.
Rheological Cure Monitoring in Blends of PMMA and Epoxy
The rheological behavior of blends of PMMA and epoxy is investigated. Time-temperature and time-concentration superposition is found to be valid in all cases as long as a homogenous solution is present. During curing of these blends phase separation occurs so that superposability is lost. As soon as the thermoset-rich phase gelates it dominates the mechanical behavior because of the co-continuous morphology, which is obtained with a 50/50 blend composition. The incorporation of reactive solvents in thermoplastic polymers leads to a dramatic reduction of viscosity until phase separation sets in. This makes such blends interesting systems for low-pressure processing for electronic applications.
Rheological Properties and Their Influence on Extrusion Characteristics of HDPE-Wood Composite Resins
The rheological properties of HDPE-maple wood composite resins were studied. The blends studied ranged from 0% (pure HDPE) - 50% 40-mesh size maple wood flour. Shear viscosity measurements and Bagley entrance corrections were performed in a capillary rheometer. It was found that the wood composite resins displayed yield stress behaviour especially at high percentages of wood content. Attempts were made to measure the yield stress using steady shear experiments in a rotational rheometer. Preliminary studies were also done on the extrusion parameters such as melting profiles, pressure profiles and outputs for the virgin HDPE and 50% HDPE-wood resins. Two Brampton Engineering single-stage compression screws with two compression ratios, 2 and 3.8, were used.
Rheology and Extrusion of CO2 Plasticized Acrylic Copolymers
The effects of plasticizing acrylic copolymers, in particular a 90% (molar) polyacrylonitrile/ 10% (molar) methyl acrylate (PAN/MA) copolymer, with carbon dioxide (CO2) are studied. Differential scanning calorimetry (DSC) is used to evaluate the resulting shift in the glass transition temperature (Tg) following plasticization. Pressurized capillary rheometry is used to evaluate the melt rheology prior to and after plasticization. Dynamic and steady shear rheology data are used to evaluate the thermal stability of the copolymer. An estimated 20°C decrease in processing temperature can be obtained upon CO2 plasticization, which slows the kinetics of the copolymer degradation (crosslinking).
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