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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Optimizing the High Speed Machining Process for Hardened Steel Molds
Constantly reduced product life cycles and increasing product variety compels the moldmaker to cut down on long production times especially in mold and die making. Electrical Discharge Machining (EDM) has been the conventional finishing technique for generating complex free form surfaces. However, the EDM process also generates a brittle, recast layer, which is often detrimental to mold performance. High speed machining technology of today offers an economical alternative to EDM, which does not significantly deteriorate mold surface properties. This paper will evaluate the benefits of a high-speed machined mold compared with conventional manufacturing techniques. It will also investigate the effects of different cutting parameters, in an attempt to optimize the high speed machining process.
Flow Behavior of Sparsely Branched Metallocene-Catalyzed Polyethylenes
The dramatic effect of chain architecture on the melt flow behavior of polyethylenes is well established. The advent of metallocene and other constrained-geometry catalysts now allows the precise control of molecular weight, branch content, and branch distribution. In the present study, the rheological responses of three different metallocene-catalyzed polyethylenes are analyzed. Despite similarities in their shear properties, the differences in transient extensional viscosities can be attributed to the presence of sparse long-chain branches and/or high molecular weight fractions. Melt fracture observations as well as full-field flow birefringence measurements are collected to further corroborate this idea.
Plastics Failure Due to Oxidative Degradation in Processing and Service
Aliphatic hydrocarbon polymers, such as PE, PP and copolymers thereof are particularly susceptible to oxidative degradation to lower molecular weight in processing and in service. The result is reduced strength, embrittlement, and shorter service life. High temperature required for melt processing is a major factor in oxidative degradation. Decrease in oxidative induction time or induction temperature measured by differential scanning calorimetry are practical methods of monitoring the effect. Formulations need sufficient antioxidant to be protected during processing and in service.
Nanocomposites: The Importance of Processing
Nanocomposites have been studied for nearly 50 years, but few references deal with the importance of how the organoclay was processed into the plastic of choice. Many articles focus on the importance of the chemistry used to modify the surface of the clay, usually montmorillonite, without including the role of processing. This paper demonstrates the importance of both the chemistry of the clay surface and how the clay was processed into the thermoplastic. Two different clay treatments were added to polyamide 6 using four different types of extruders with multiple screw designs.
Injection Molding and Physical Aging Properties of Amorphous Poly(ethylene terephthalate)
Physical aging characteristics of amorphous poly(ethylene terephthalate) have been evaluated in relationship to several important injection molding parameters. For these investigations; packing pressure, melt temperature, and mold temperature were each varied individually, with other conditions held constant. Aging studies were performed at three different storage temperatures, using the molded specimens. Changes in density, notched Izod impact strength, and enthalpy of relaxation were monitored as functions of aging times. Time temperature superposition analyses were performed using experimental data and master curves were constructed. Results give predictions of lower temperature long term enthalpies of relaxation and notched Izod impact strength properties.
3-D Simulation of Thin-Wall Injection Molded Part by CAE
This work reports the results of CAE simulation of thin-wall injection molded part by 3D TIMON. The model used in this simulation was a speaker grille that has thin wall and many tiny openings (net) for sound through them. These openings cause unfavorable weld lines. Effects on weld lines and effects of the number and location of gates were discussed.
An Investigation of the Rotomoldability of New Generation Polyethylene
Rotational molding is a fast growing process with a constant demand for new materials. As a result of the recent advances in the metallocene single site catalyst systems, a new generation of polyethylenes with unique molecular structure has been developed. The present study compares the rotomolding characteristics of polyethylenes made by metallocene and conventional catalysts.
Profile Extrusion of Highly Filled Recycled HDPE
Recycled high density polyethylene (HDPE) filled with up to 70 wt% rice hulls was compounded and tested for dynamic shear properties on a parallel plate rheometer. A 60 wt% formulation was extruded through two profile dies. Extrudate tearing occurred at all throughputs. The magnitude of the tearing increased with increasing throughput and decreasing land temperature. Observations, 2-dimensional finite element and fully 3- dimensional finite volume simulation suggest the tears are most severe where the wall shear stress is relatively lower.
The Effects of Compatibilizers, Polyamide-6 Grade, and Filler Type on the Properties of TPO/Polyamide-6 Blends
This study examined the effect of compatibilizers, polyamide-6 grade, fillers, and injection rate on the properties of polyamide-6/TPO blends. The addition of polyamide-6 to TPO raised tensile and flexural moduli, and consequently, DTUL and scratch resistance; however, it adversely affected Izod impact strength. While a di-terminated polyamide-6 (NH2 capped) exhibited better properties than a non-terminated material (COOH end), wollastonite fillers had a greater influence on the blend properties. Compatibilizers primarily impacted elongation, impact strength, and scratch resistance whereas high injection velocities increased impact strength and scratch resistance.
Recycled Fiberglass Composite as a Reinforcing Filler in Post-Consumer Recycled HDPE Plastic Lumber
Post-consumer high-density polyethylene is commonly used to make lumber products, but such products are substantially less stiff than wood lumber. Using a two factor full factorial experimental design, the effects on tensile, flexural and impact properties of adding ground recycled fiberglass composite in combination with wood flour to high density polyethylene were investigated. The addition of ground fiberglass composite was found to significantly increase tensile and flexural modulus, while decreasing impact strength. Ground fiberglass was found to have a greater stiffening effect than wood flour, but wood flour had no significant effect on impact strength.
Polymer Near-Surface Behavior Characterized by Reflectometry and Complementary Techniques
Engineering the near-surface structure and properties of materials requires characterization tools that are sensitive to that structure and those properties. X-ray and neutron reflectometry provide exquisite depth resolution for near surface structure. These tools are most powerful, however, when combined with lower resolution complementary techniques that give the depth profile directly or with techniques which resolve the structure laterally. Reflectometry's capabilities are demonstrated by a study of the interfacial segregation of star-branched polymers in a blend of linear and star chains. Dynamic secondary ion mass spectroscopy and nuclear reaction analysis are used as complementary probes.
Compatibilization of PP/HDPE Blends: Morphology and Interfacial Tension
In this paper the compatibilization of polypropylene (PP)/high-density polyethylene (HDPE) blend was studied through morphological and interfacial tension analysis. Three types of compatibilizers were tested: ethylene-propylene-diene copolymer (EPDM), ethylene-vinylacetate copolymer (EVA) and styrene-ethylene/ butylene-styrene triblock copolymer (SEBS). The morphology of the blends was studied by Scanning Electron Microscopy. The interfacial tension between the components of the blends was evaluated using small amplitude oscillatory shear analysis. Emulsion curves relating the average radius of the dispersed phase and the interfacial tension to the concentration of compatibilizer added to the blend were obtained. It was shown that EPDM was more efficient as an emulsifier for PP/HDPE blend than EVA and SEBS.
New Thermoplastic Resin Compounds Utilizing Highly Efficient Conductive Filler System
During the last few years, there has been a rapid growth of electronic equipments within industrial, commercial and domestic environments. This has led to a need to control the problem of static build-up and discharge during the manufacture, distribution and usage of products containing microprocessors. In addition, often it is necessary to contain electromagnetic radiation (EMI), which can inhibit normal operation of microprocessor containing devices. The issue of static control and discharge is also important in areas such as prevention of ignition of flammable fluids and handling of powder (to prevent dust explosion). Commercial plastic materials are insulators and hence, are often modified using conductive materials like carbon fibers to provide static dissipation and EMI shielding. This paper describes highly efficient ESD / inherently shielding engineering thermoplastic resins which can be used in a broad variety of applications. A binder was identified in this study that enhanced shielding effectiveness and reduced resisitivty of resin systems with which it was incompatible.
Failure Analysis Case Studies, Part II: Effect of Material and End-Use
Some case studies are presented in this paper to show the effect of material choice and end-use on product failure. Microscopic analysis was used in these investigations to identify the fracture features. Additionally, mechanical analysis was utilized occasionally. The first case shows the importance of material choice and processing conditions on the failure of plastic products. The second case illustrates the negative effect of adverse end-use conditions on the failure of plastic parts. The third case describes the combined contribution of material choice and end-use to the plastic product failure.
Impact Test with Flat-Ended Impactor for Protective Materials: Specimen Thickness Effect
Thickness effect on impact parameters is studied and a model is developed for flat-ended drop weight impact testing of visco-elastic materials. The model represents a relationship of specimen thickness with impact force/stress and impact energy. A polymeric material, ethylene-vinyl-acetate (EVA), was used for experimental verification. Experimental results for a thickness range of 1 to 9 mm at impact energy levels of 0.42, 0.96 and 1.54 Joules have been found to be in good agreement with predictions based on the model.
Multi-Component Injection Molding-Part 1: Interface and Microstructure Development
The purpose of this paper is the physical modeling and numerical simulation of the interface and microstructure development during the multi-component injection molding process. A software has been developed based on the control volume finite element method to calculate the transient non-isothermal multi-phase flow of viscoelastic polymer melts and to predict the stress-induced crystallization within the semi-crystalline polymers. Based on the developed simulation software material selection and process optimization becomes possible.
Gas Barrier Behavior of Syndiotactic Polystyrene
The effect of crystallinity on barrier properties of syndiotactic polystyrene (s-PS) was studied. The crystallinity was induced in s-PS by cold crystallization and crystallization from the melt. Two thermally induced crystalline forms ? and ? were observed in all crystallized samples as well as the presence of ?-mesomorphic phase in the samples cold crystallized at lower temperatures. The oxygen permeability and diffusion occurred at finite rates in the loose a hexagonal crystalline phase while it was negligible in better-packed ? orthorhombic phase. The permeability and diffusion of oxygen increased with an increase of the amount of a ordered phase while the solubility decreased, remaining, however, still soluble for oxygen even at 100%.
A Study of the Tensile Creep Behavior of Recycled High Density Polyethylene in Aqueous Mediums
Recycled polymers are currently being used in the design of commercial products for the maritime structure industry. Marine pilings, pier fenders, and pier support elements are just some of the products being designed with recycled polymers. Understanding the effect of submersion in salt and fresh water on the mechanical properties of the material used in these products is important. This study will examine the tensile creep behavior of recycled HDPE in ocean water, fresh water from Lake Erie, distilled water, and air. A specially designed apparatus for aqueous creep testing was utilized to obtain the data for this study.
A Comparison between Open Flame and Hot Air Heating Methods for the Rotational Moulding of Plastics
In the 1940's when rotational moulding of plastics was first developed, open flames were used to heat the mould. In the 1950's there was a switch to hot air ovens as a cleaner method to heat biaxially rotating moulds. Today hot air ovens dominate the market due to the convenience that they offer the user, although it is widely recognised that they are relatively inefficient as a means of heating. This paper presents results from an experimental investigation to assess the relative merits of open flame and hot air oven rotational moulding machines. Polyethylene mouldings of varying thickness were produced on both types of machine and cycle times were compared by using ROTOLOG to record mould internal air temperatures. It is shown that significant cost savings are possible using the open flame heating method. These savings arise from both lower energy consumption and reduced cycle times.
Evidence for a Master Curve Behavior for Polypropylene (PP) Degradation and Durability
We have studied material degradation and durability in a broad based program in selecting medical materials. In addition, the specific requirement that medical devices and packaging must have specified shelf-lives supported by real time data also prompted for quantitative evaluation. A large number of PP types and samples were studied under diverse conditions. These included high temperature oxidative stability by oxidation induction time (OIT), high oxygen pressure OIT, oven aging, aging and oxidative stability after ionizing radiation and real time ambient storage. The activation energies from the surface embrittlement processes were also found to have a striking similarity to the thermal processes. To overcome the difficulties in generating long term ( greater than 10 years) data, well characterized historic samples of up to 23 years in age were included in this study. When all data were combined, a striking feature was apparen very few data points at higher temperatures could allow a reasonable determination of the shift factor and quite accurate estimates for lower temperature durability. This methodologyt: that for PP, a self-similarity existed among all systems examined. This allows a simple vertical shift of data to construct a master curve" similar to rheological master curves. The implication being if the master curve can be constructed when supported by further studies could lead to broader applications and deeper understandings on polymer degradation"
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