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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Toughness Enhancement through Conversion of Cyclic Polybutylene Terephthalate to Linear PBT
The fracture toughness of macrocyclic polybutylene terephthalate (simple ring molecules) and linear PBT is correlated with the size of the plastic zone at the crack tip, which is inversely related to the yield stress. Macrocyclic PBT (c-PBT) molecules have a lower melt viscosity than linear molecules of comparable molecular weight, making them easier to process. However, the cyclic molecules are highly crystalline, with a high yield stress, and consequently a lower toughness. A ten-minute heat treatment in the melt opens the rings, and allows molecular entanglement, causing lower crystallinity of the solid polymer, and increased toughness. Therefore, control of the molecular structure of PBT provides a polymer with low viscosity that can be toughened by an easy heat treatment.
Effects of PP-MMA Alloy and Impact Modification on Weathering Performance of Polypropylene
The weathering performance of polypropylene and a novel polypropylene/acrylic alloy with and without impact modifier was investigated. Accelerated weathering testing was completed using Xenon Arc Weather-ometer. Surface cosmetics (gloss and color change), microscopy, and FTIR were used to characterize the surface and bulk properties after exposure to accelerated weathering. Dramatic improvements in weathering performance were observed through the addition of propylene/acrylic alloys and a proprietary impact modifier to the base polypropylene homopolymer. The individual significance of the propylene/acrylic and the impact modifier on weathering performance were similar. The benefit observed with weathering when combining the propylene/acrylic alloy and proprietary impact modifier was additive with respect to weathering performance.
Prediction of the Weld Lines in Injection Molding Process Using Neural Networks
A model is developed for the prediction of the weld lines in injection molding process. The position of the weld lines in a multigate cavity system, with holes and/or inserts in the part, are predicted using a neural network-based back propagation algorithm. The neural network was trained with data obtained from simulation and actual molding experimentation. For a number of test cases, the performance of the method is investigated on comparing predicted weld lines with those obtained using a complete mold filling simulation. It was found that the proposed method can predict the position of the weld lines with a good accuracy as compared to the filling simulation. Applying the neural networks reduced the amount of computational time and eliminated the pre/post processing time as compared to simulation methods.
The Effects of Mold Filling on Living Hinge Performance
Filling characteristics of polypropylene living hinges and their performance were compared in order to create a model that will predict the quality of living hinges. In this study, three filling characteristics correlated to hinge quality: melt front advancement, skin orientation, and hinge fill time percentage. First, the melt front advancement; should be parallel to the axis of hinge rotation and free from discontinuities. Then, the skin orientation must be perpendicular to the hinge's axis of rotation. Finally, the most critical parameter was the hinge fill time as a percentage of the fill time for the part.
Applications of Gas-Assisted Injection Molding and Injection/Compression Molding in Thinwall Molding
Gas-assisted injection molding (GAIM) and injection/compression molding (ICM) processes are studied and compared with the injection molding (IM) process for thinwall applications (also called thinwall molding). In this paper, analysts for these three processes arc carried out. A cellular phone part will be used as an example. Analysis results will be reported and comparisons of these three processes will be made. Injection pressure, clamp force and deformation will be used to evaluate these processes. Injection pressure and clamp force reduction in the GAIM and ICM processes and their effectiveness in packing will be emphasized.
Measuring Frosted Glass Effects for Plastics: A Closer Look at One Frosting Agent
To produce consistent frosted plastic effects it is necessary to measure basic performance characteristics of the frosting agents. Frosted plastic, like frosted glass, serves a variety of aesthetic and functional needs. In testing, the most crucial characteristics are transmittance, haze, clarity and yellowness This paper examines two sets of data: 1. Comparative results of testing a series of frosting agents at differing loads 2. Specific, in-depth results of testing a single frosting agent at differing particle sizes.
Super Phosphorescent Additives for High-Quality Illumination at Low Additive-Loading Levels
A new super-phosphorescent additive represents a breakthrough in the use of phosphorescence for plastic products. The new additive provides a substantially longer glow time than conventional zinc sulfide phosphorescent additives. Additionally, it, can be compounded at far lower loading levels, which facilitates compounding and processing, and makes the new additive more compatible with other fillers than zinc sulfide. This paper discusses attributes, applications, and performance characteristics of this novel product, and compares it to commonly used phosphorescent compounds.
Improvement of the Molded Part Quality-Optimization of the Plastification Unit
The three-zone plastification screws traditionally used in the injection molding process are nowadays limited in their efficiency. Reasons are increasing demands on the quality of the molded part and on the machine technology which is more and more adapted to the different process groups like packaging or optical parts. Therefore different types of screw geometry, e.g. barrier screws or multi-threaded screws, are used to investigate the influence of the dosing parameters and the screw geometry on the melting capacity and the homogeneity of the melt .
Shrinkage and Warpage Analysis of Injection-Molded Parts
Hot polymer melt shrinks when it is injected into the cold mold cavity. In the injection molding process, pressure is high near the polymer entrance and low at the last-fill location. The polymer temperature is low near the mold wall surface and high at the core region. Because of these two types of non-uniformity, the part will shrink differently at different planar and thickness locations. This causes warpage. Different process conditions will result in different non-uniformity. In this study, the effects of packing time, packing pressure, fill time and mold wall temperature will be discussed. Computer-aided engineering (CAE) and design of experiment (DOE) will be carried out first. The process window will be investigated. Experimental results will also be reported.
Quantitative Relationships between the Parameters of Thermal Degradation of Polyvinyl Chloride and the Loss of Mechanical Properties
Thermal degradation of polyvinyl chloride (PVC) was studied to obtain quantitative relationships between temperature and duration of polymer degradation and the corresponding loss of tensile strength, flexural modulus, and impact strength. Test specimens of rigid PVC containing different concentrations of dibutyltin bis(isooctylthioglycolate) and barium-cadmium stearate were subjected to five different temperatures for five different durations. The selected test properties were determined before and after degradation. Percentage property retention was plotted against logarithm of heating time. Values of log heating time corresponding to acceptable levels of property retention obtained from these plots were then plotted against temperature to obtain Arrhenius-type relationships between the parameters of thermal degradation and the deterioration of properties.
Injection Molding Process Simulation: A Productivity Tool for the Processor
To be productive as an injection molder you have to be innovative in using new technologies. To produce a high quality molded part you need a well designed part and mold, a molding cell which is able to mold the part within it’s specification, a plastic material which is produced to tight specifications and employees who are well trained. Would it be nice to train employees on how to run, optimize and troubleshoot a molding machine in a classroom environment and not on the production floor. On the production floor in order to make money the machines have to run and produce. A process simulator can fill the gap between learning theoretical knowledge and hands-on molding.
Enzymatic Template Synthesis of Processable Polyphenol
Phenolic polymers and phenol formaldehyde resins are of great interest for a number of electronic and industrial applications. Unfortunately, the toxic nature of the starting materials (formaldehyde) and extreme reaction conditions required for the synthesis of these polymers have severely limited their use in today's markets. We present here an alternative, biocatalytic approach where the enzyme horseradish peroxidase is used to polymerize phenol in the presence of an ionic template. Here the template serves as a surfactant that can both emulsify the phenol and polyphenol chains during polymerization and maintain water solubility of the final polyphenol/template complex. The reactants and conditions of this approach are mild and results in high molecular weight, electrically and optically active, water-soluble complexes of polyphenol and the template used. Polystyrene sulfonate, lignin sulfonate and dodecyl benzene sulfonate (micelles) were the templates investigated in this study. In each case, soluble polyphenol complexes were formed with molecular weights ranging in the millions. Thermal analysis and UV-Vis spectroscopy shows that these complexes have exceptional thermal stability and a high degree of backbone conjugation. Conductivities on the order of 10-5 S/cm and a?(3) of 10-12 esu are also observed. In the case of the SPS template under certain conditions, a sol gel complex may be formed. This enzymatic approach offers exciting opportunities in the synthesis and functionalization of a new class of processable polyphenolic materials.
Sharksin Melt Fracture in High-Performance Hexene-LLDPEs
Several types of High-Performance Hexene (HPH)-LLDPE have been introduced in recent years for high-strength blown film applications, with substantial enhancement of film properties over conventional Ziegler-Natta LLDPEs. The present work is a study of the comparative behavior of the various types of LLDPEs under processing conditions designed to induce sharkskin melt fracture (SSMF). Both capillary rheology and blown film studies were conducted. The ability of capillary rheology to capture the difference between resins in terms of their relative tendency to sharkskin melt fracture was investigated in parallel with blown film studies at different shear rates and die gaps. Film blowing is more effective in discriminating between resins and identifying melt fracture tendency. The influence of sharkskin melt fracture on the film properties was also quantified, showing the film impact strength to be affected most sensitively, and negatively, by the presence and severity of sharkskin melt fracture (SSMF).
Carbon Dioxide Extrusion Foaming of Engineering Thermoplastics
Many engineering thermoplastics require extrusion temperatures which are too high for foaming with chemical blowing agents. Carbon dioxide foaming by direct super critical fluid injection has no such restrictions as well as offering economic benefits. This study describes preliminary work on a laboratory scale extrusion line using retrofitted parts to produce foams from a number of engineering polymers. Results of an evaluation of a very simple low cost method for measuring melt strength (an important polymer property with regard to foaming) is also included.
Effect of Nanosilica on Properties of Segmented Polyurethanes
Thermoplastic polyurethane elastomers having soft segment concentration (SSC) of 50% and 70% were synthesized in the presence of 12 nm silica nanoparticles. The concentration of nanosilica was varied from 0% to 30% in both series. Nanosilica had not significant effect on glass transition of the soft segment but it increased tensile strength and particularly elongation at break. Tear strength of the series with 70% SSC was not affected by the presence of nanosilica while initial decrease was observed in the series with 50% SSC.
Structure-Property Characteristics of Ethylene/1-Hexene Copolymers with Tailored Short Chain Branching Distributions
Recently, we have developed a metallocene catalyst system that can produce polyethylene and ethylene/a-olefin copolymers with tailored molecular weight and short chain branching distributions. Ethylene/?-hexene copolymers produced with this system have narrow molecular weight distributions as expected from metallocene catalysts. However, these copolymers are quite unique in that their short chain branching distributions are broad and sometimes bimodal, similar to Ziegler-Natta LLDPE. To examine the effect of these broad short chain branching distributions on the polymer properties, tensile and viscosity characteristics were measured. It was found that the tensile properties of these broad distributions could be controlled by the relative amounts of each species. In this study, the best tensile properties were achieved with a distribution that contained a large proportion of crystalline material and a small fraction of lower crystalline material. It was also found that the distribution of short chain branches can have an effect on the viscosity behaviour of these copolymers.
Superstructures in Polyamide Elastomers-The Key for Super Performance?
Polyether block amides are known as thermoplastic elastomers with excellent chemical resistance, outstanding physical properties, and easy processing. This is closely related to the type of chosen polyamide blocks and the morphology of crystalline and amorphous phases. In contrast to other multiblock thermoplastic elastomers which are forming only net points of crystallized polyamide blocks polyether block amides exhibit a spherolithic superstructure of crystallized lamellae. As a consequence there is an intrinsically reinforcing effect in the material depending on block composition which is reflected by a unique mechanical behavior which will be discussed in the paper.
HDPE Blending Technology for Enhanced LDPE Film Properties
Numerous blown film applications involve the blending of high density polyethylene (HDPE) with low density polyethylene (LDPE) to achieve desired physical properties. For example, HDPE blended with LDPE provides greater stiffness and holding power for product retention in shrink films. HDPE/LDPE blends are also used in sanitary paper packaging applications, with the HDPE component providing needed stiffness for high speed machinability. Likewise, a variety of other packaging applications utilize HDPE/LDPE blends for improved machinability, especially as downgauging opportunities are pursued. This paper documents the effect of HDPE resin choice and content on the strength, optical and shrink properties of LDPE/HDPE blown films.
The Hydraulic Permeability of Dual Porosity Fibrous Preforms
We present a computational analysis of viscous flow through arrays of fiber bundles using the Boundary Element Method (BEM) implemented on a multi-processor computer. Up to 700 individual fibers are included in each simulation. These are simple but not trivial models for fibrous preforms used in composites manufacturing - dual porosity systems characterized by different inter- and intra-tow porosities. The way these porosities affect the hydraulic permeability of a preform is currently unknown and is elucidated through our simulations. Numerical results are compared to analytical models. Through a large number of simulations we construct a master curve for the permeability of arrays of fiber bundles for various packing arrangements.
Minimizing Sandwich-Panel Warpage
Honeycomb-cored composite sandwich panels are widely used in commercial airplane interiors. Sandwich-panel warpage can cause assembly difficulties and has been a deterrent to implementation of determinant assembly techniques. A series of statistical experiments were used to minimize sandwich-panel warpage on an airplane stowage-bin shell. Warpage was broken down into three components to facilitate analysis. Twist was shown to be influenced by prepreg orientation. Spring-in was affected by the presence of a decorative poly(vinyl fluoride) film; this effect was counteracted primarily by the addition of a ply of style-120 prepreg on the opposite side of the panel. The additional ply of 120 prepreg also helped to minimize bow.
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