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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Influence of Flame-Retardant Materials on the Weld Strength of Plastic Parts
Fire-safety requirements, especially in the transportation and the electronics industries, are becoming stricter and stricter, meaning that more and more plastic materials include flame retardants (FR) among their constituent elements. This FR process is an endothermic reaction combined with intumescence or foam formation. When welding plastics, the welding process involves high temperatures above the plastication temperature of the thermoplastics, which can inadvertently activate the FR-reaction. This reaction can result in a lower welding strength. In this study the activation of FR-reactions in thermoplastic materials and the strength of the resulting joint will be considered. Joints were welded using three of the most commonly used processes in the industry: ultrasonic welding, laser transmission welding and hot plate welding. The results show the influence of the material, the process parameters, the welding process, the temperature and the ratio of FR-material to non-FR-material on the strength of the welded joint. For example, higher temperatures in the hot plate welding process or higher laser energy in the laser transmission welding result in lower-strength connections because of a higher activation rate of the FR-material. However, the FR-material is not activated during ultrasonic welding. Here, the lower-strength connection results from the FR-material as a filler material and not because of FR activation.
Microcellular Injection Molding of Polypropylene and Glass Fiber Composites with Supercritical Nitrogen
Microcellular injection molding of polypropylene and glass fiber composites (PP-1684/GF-950) was performed using supercritical nitrogen as the physical blowing agent. Based on design of experiment (DOE) matrices, the influences of GF content and operating conditions on cell structure, GF orientation and mechanical properties of molded samples were studied systematically. The results showed the cell morphology and GF orientation of foaming parts were definitely influenced by the cooling and shear effects. The mechanical properties of foamed PP/GF composites could be effectively enhanced by improving the cell morphology, dispersion state and orientation of the GF at optimal weight percentage wGF/wPP=11.8%. And the optimal conditions for injection molding were obtained by analyzing the signal-to-noise (S/N) ratio analysis of the mechanical properties of the molded samples, which were a shot size of 36 mm, a supercritical N2 weight percentage of 0.4%, an injection speed of 52 mm/s, a melt temperature of 190 °C, and a mold temperature of 70 °C. The molded specimens of PP-GF composites, produced under those optimal conditions, exhibited very uniform fiber dispersion and microcellular structures with an average cell size less than 30 ?m. And the mechanical properties normalized by weight ratio of the microcellular samples were increased significantly, especially the impact strength.
Comparative Analysis of a Novel Clear Polypropylene Impact Copolymer for Use in Thin-Walled Injection Molding
A new technology from Braskem extends the use of clear polypropylene for thin-walled injection molding applications. Typical high melt-flow rate random copolymers have very poor impact resistance at low temperatures, and commercially available impact copolymers produce opaque containers. A new developmental grade from Braskem, PRISMA 1911, was developed to have high melt flow, relatively high stiffness, high impact, and excellent transparency. The goal of this paper is to compare this new grade with conventional impact copolymers, with random copolymers, and with blends of random copolymers and polyolefin elastomers.
Creep Rupture Failure under Conditions of Static Strain
The response of polymeric materials under long-term loading will vary due to several interrelated factors including time, temperature, and the magnitude of loading experienced by the material. A common failure mode encountered in plastic parts under long-term loading is creep rupture. Creep rupture describes a slow-crack growth failure in polymeric parts that is a consequence of molecular disentanglement over time as a result of exposure to continuous stress. This time-related phenomenon can lead to unexpected failures in plastic parts after days, months, or years in service. While creep rupture is more predictable and better understood under constant stress loading, creep rupture resulting from a constant strain condition is frequently encountered in several applications and is more complex to interpret. This complexity is due to the competing mechanisms of plastic creep and stress relaxation. This paper will provide insight into several long-term material behaviors in polymeric materials, with an emphasis on a scenario involving creep rupture as a result of constant strain over time.
Minimization of Part Warpage in Injection Molding through Ideal Wall Thickness Distribution
In this study, a method to reduce the warpage of injection molded parts by optimizing the distribution of their wall thickness is proposed. The method is based on an optimization procedure consisting of mold flow analysis, a parameterization tool for geometry manipulation and an evolutionary optimization algorithm. Starting with the initial design for the mold cavity, the procedure modifies the wall thickness distribution at user-defined area-sections. The result is an STL-file of the optimized design. Application on a warpage demonstrator reveals the effectiveness and plausibility of the proposed optimization procedure.
Modeling of OBSH Decomposition Kinetics as Blowing Agent for Cellular EPDM Rubber
The decomposition kinetics of p’,p-oxybis benzene sulfonyl hydrazide (OBSH) and the change of its behavior when mixed with additives and rubber are determined by using thermal analysis. This study uses Differential Scanning Calorimetry (DSC) and Thermogravimetry (TGA) to understand the exothermic reaction. Different kinetic models were evaluated using the least-square method to determine activation energies and reaction variables. As a result, it was found that the Kamal-Sourour model is the most accurate reaction model, confirming the information found in literature.
Preliminary Results in Modeling in-Machine Fiber Breakage during Injection Molding
This work is concerned with the effect that the ratio of initial pellet length to screw channel width, or diameter, has on the percent of glass fiber breakage during processing in the screw. Experiments were carried out on a lab-scale single screw extruder. Data has been fit using an exponential decay model with a kinetic decay constant and a critical length value. This empirical model has been tested on glass fiber breakage in another size screw with a diameter 1.66 times larger than that of our single screw extruder and reasonable agreement with the empirical exponential decay model and experimental results are observed. For carbon fiber, similar breakage trends were observed.
Data Driven Decision Making for the Injection Mold Designer
The science of Tribology is generally known only to certain specialists who focus on its study and the effects on industrial materials. It can drive many decisions that are made daily by the injection mold designer. In many molds there are assemblies that benefit from optimizing a surface, to minimize the effect of wear, which can be the result of one surface coming in moving contact with another. The basics of Tribology are important for all designers to understand because it may improve the longevity, of the assembly, through design or to advise the end user of adequate, required maintenance. Component longevity is the goal, but ultimately cost savings is the outcome, when replacement components and lost man-hours make an assembly unaffordable to maintain and maintenance replacements are required too often. When Tribology knowledge can be used to extend the life of specific components so they will last longer and insure the assembly’s practical life, everyone benefits. This paper will review basic definitions, concepts the designer should have in mind, the effect on industrial materials and verification methods. At the very least, this information will lead to an understanding that additional testing and analysis may be required for verification of product life.
Investigation of the Influence of Color on Plastic Product Failure
The color of a polymeric compound must be engineered just like any other desired resin property such as mechanical or thermal. Reaching the desired color can be adversely affected by processing or the combination with modifiers and additives in the resin system. Even if colors can be achieved by increasing the amount of pigment used in the formulation, other performance attributes such as mechanical properties may be adversely affected as well. This paper discusses these color matching concerns.
Rebuilding Screws for Injection Molding Processes
Improper rebuilding of screws for injection molding plasticators can lead to screws with high wear rates and the formation of resin degradation products. Resin degradation can cause black specks and color streaks in injection molded parts, reducing the yield and profitability of an injection molding process. This paper presents two problems that occur when injection molding screws are not rebuilt properly.
Study on Interphase Transfer of the Liquid Tackifier between Immiscible Rubber Pair
The transfer phenomenon of a third component between immiscible rubber pair was studied using natural rubber (NR) and poly(isobutylene) (PIB). The coumarone-indene tackifier was employed as the third component. After the laminated rubber sheets were annealed at various temperatures, the tackifier distribution was characterized by the dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). It was found that the tackifier transfer between the rubbers occurs. Furthermore, the amount of the tackifier in each rubber depends on the ambient temperature.
Structure and Acoustical Property of Polyolefin Film/Foam Alternating Multilayer Composites
A novel alternating film/foam multilayer sheet was prepared through multilayer co-extrusion. The film layer was a blend of LLDPE with poly(ethylene-octene) elastomer (POE) and the foam layer was cross-linked and foamed POE. The multilayer film/foam sheet exhibited advantaged acoustical properties. In select wavelength regions, the sound absorption coefficient of the multilayer film/foam structure improved 2-3 times compared with conventional single-layer materials.
Effects of Barrel and Screw Heating in Rubber Extrusion
This paper deals with the effects of barrel and screw heating in rubber extrusion particularly with regard to the throughput and the melt temperature. To determine exactly the impact of heating on throughput behavior during extrusion, experimental investigations were conducted on two rubber extruders of different sizes. In addition, numerical flow simulations were carried out for non-isothermal shear thinning melt flows, under consideration of dissipative heating in the screw channel.
Novel Poly (Lactic Acid) Foams: Micro to Sub-Micron Size Transition
Chemical modification of poly(lactic acid) (PLA) through a reactive extrusion process was performed in the presence of a free-radical initiator and multi-functional chain extenders. Batch foaming, using nitrogen as the blowing agent, was done at various temperatures to differentiate the effect of chain branching and nucleation on the cell size of reactively modified foams. Depending on the conditions very fine, sub-micron size foams were obtained in reactively modified PLA.
Process Optimization of Single-Screw Extrusion Systems for Polyolefin Resins
Many existing extruders running polyethylene (PE) resins can be optimized to operate at higher production rates and also with higher qualities by the mitigation of gels. This paper provides an assessment process where the extruder is studied for potential rate increases and quality improvements. It is recommended that such an assessment be made prior to purchasing new screws or when a line is close to becoming sold out and more product is required.
Testing Fused PVC Water Pipe with the ISO 13477 S4 Method for Critcal Pressure
While a test method for thermoplastic pipe to determine resistance to rapid crack propagation has been standardized for nearly 20 years, very little testing of PVC for water use has been done. Test methodology and results are presented in this paper for the S4 testing for water for fused PVC manufactured to the AWWA C900 PVC pipe standard, Critical pressure, crack speed, and decompression wave speed are discussed..
Characterizing an Extrusion Process Using Design of Experiment (DOE)
Including an explanation of design of experiment (DOE) principles, this paper describes the procedures and results of a designed extrusion experiment. The goals were to understand and model the influence of key process variables (barrel zone temperatures and screw speed) on several performance indicators, such as output, pressure variation, and temperature variation. One important finding was a quadratic model of melt temperature variation, primarily as a function of screw speed and barrel zone 1 temperature.
Reduced Adhesion Strippable Insulation Shields Using Nano-Scale Mineral Fillers for TRXLPE Insulated Medium Voltage Power Cables
Semiconducting insulation shield compounds with reduced adhesion to tree retardant cross-linked polyethylene (TRXLPE) are presented. Through a combination of additives comprising 5% by weight of the formulation or less, adhesion force can be reduced by 40% or more without compromising other critical properties such as volume resistivity, cure kinetics, and physical characteristics including tear strength.
Estimate of Astm Melt Flow Rates from Oscillatory Shear Rheology
ASTM Melt Flow Rate is one of the most common product specifications and is widely used by resin manufacturers and users. Small Amplitude Oscillatory Shear (SAOS), on the other hand, is the preferred rheology data for researchers. A one-to-one correlation between these two kinds of rheology data has not been observed or reported in the past. With a new approach of applying the Cox-Merz Rule, excellent estimates of ASTM melt flow rates were obtained from the SAOS data for a wide range of linear polyethylene resins.
Improvements in Processing Semi-Crystalline Polymers for Thermoforming Sheet in Multiple Nip Systems
Covering higher output rates in the production of thermoforming sheet motivated the development of a new roll-stack design. While amorphous materials like HIPS and A-PET are not sensitive to cooling parameters, the quality of sheet made of semi-crystalline polymers like PP and PE is showing a great dependency on their cooling history. In the daily production environment not only higher outputs were achieved, but improvements in quality and performance were obtained.
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