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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Injection Molded Asymmetric Spur Gear Tooth Deflection: Numerical and Experimental Investigation
In the recent years, asymmetric gear tooth profiles are being considered for the unidirectional power transmission applications due to the advancement in gear manufacturing techniques. Additionally, the advancement in material development makes polymer and polymer composite gears to replace the metallic gears for the motion as well as power transmission applications. Number of researches has been carried on asymmetric steel gear as well as symmetric polymer gears using numerical techniques. This work attempts to understand the structural behavior of asymmetric polymer spur gears with the aid of experimental and numerical investigation. Four tooth 3mm module, 4mm face width, 18 number of teeth of asymmetric (34°-20°) and symmetric (20°-20°) polypropylene gears were considered for this work. An experimental test rig was developed to simulate gear mesh and torque was applied through dead weights and gear tooth deflection was measured with the aid of rotary encoder. The effect of pressure angle at drive side matches well with the experimental values. Asymmetric gear tooth profile having larger pressure angle (34°) at drive side exhibited least deflection and symmetric gear with 20° pressure angle at both drive and coast side exhibited maximum deflection.
Improving Adhesion between Kevlar®129 Fibers and Natural Rubber Matrix Using Morphological Treatments and Coupling Agents
Kevlar fibers are known for their exceptionally high tensile strength, and hence used in a wide variety of high performance applications ranging from military to aerospace and civil applications. However, the expected strength of composites fabricated using Kevlar fibers has not been reached due to poor interfacial adhesion between the fiber and matrix of the composite. This poor interfacial adhesion has been attributed to the highly crystalline and oriented molecular structure of the fiber.
Herein, we present new methods to improve the adhesion between Kevlar fibers and natural rubber matrix. Pre-treatments were used to create new surface morphologies on the fiber. The pre-treated fibers were then subject to treatments with coupling agents. The coupling agents were soaked also in the presence of supercritical carbon dioxide (scCO2). Treated fibers were embedded in rubber matrix and adhesion was measured by fiber bundle pull-out adhesion test. Adhesion was found to improve by around a 100%. Comparative results are reported for both untreated fibers and a range of pre-treatments. Failure analysis of fiber surface revealed a suppression of interfacial failure. The effect of pre-treatments on fiber properties are also characterized, and the optimization between fiber properties, fiber-matrix interface properties, and overall composite properties are discussed.
Use of Core Retraction to Achieve Low Density Foams in Microcellular Injection Molded Polypropylene Parts
Core retraction was used with the conventional microcellular injection molding (MIM) process to foam thick polypropylene (PP) parts with high density reductions of 30% and 55%. The cavity volume was changed by changing the retraction distance, which resulted in varying density reductions. The lowest densities were achieved with a core retraction-aided microcellular injection molding (CRMIM) process, the results of which could not have been achieved by the conventional MIM process alone. The effects of delay time and weight reduction on the microstructure of the core and skin layer were investigated. It was shown that the CR-MIM process yielded a better microstructure and a higher tensile modulus than the conventional MIM process. Use of core retraction also yielded more consistent densities and tensile properties at different distances from the gate location.
Simulation of Long Semi-flexible Fiber Orientation during Injection Molding
This work is concerned with the effect of fiber length on the performance of the Bead-Rod fiber orientation model which takes into account the flexibility of semi-flexible fibers. Different averaging techniques are used to represent the average fiber length for the population, which give different fiber length parameters for the Bead-Rod model. The sensitivity of the Bead-Rod model is evaluated with regard to the fiber flexibility parameter k and length parameter ????. Fiber orientation simulation is conducted for the Center-Gated-Disk (CGD) geometry and compared with experimental data.
Comparative Analysis of Low-Smoke, Zero-Halogen Compounds for Wire and Cable Applications
The choice to use low-smoke, zero-halogen cable jackets is becoming increasing popular in certain applications, allowed by advances in materials expertise that overcame many of the historical difficulties of this class of cable jacket. Test method optimization has occurred in order to better predict how the jacket will perform in the field, and these tests have been used to understand how certain filler and polymer choices affect the jacket performance. These same sets of tests are also used to compare commercially available low-smoke, zero-halogen jackets, in order to evaluate how well the different jackets balance the potentially conflicting property requirements. Analyzing various jackets highlights the variation in properties and quality that can be seen.
Backflow Compensation for Thermoplastic Injection Molding
Minimization of fail parts save companies time and money. Therefore, the injection molding process has to be optimized regarding part quality, cycle time and fault frequency. Machine and process capability are a measurable property of a process to the specification and compare the output of an in-control process to the specification limits. Through process control on different levels of machine control, a high part- and process-quality is achieved. It involves both machine operation and the behavior of plastic. To accomplish these goals and to improve existing machine technology, an alternative injection concept is developed and examined to improve the process and machine capability using a reciprocating screw without moving, locking elements at the screw tip (Figure 1).
Nonwoven Microfilters Produced by a Novel Melt Coextrusion Process
Fibrous filters were fabricated using a novel melt co-extrusion and two-dimensional multiplication technology combined with a high pressure water jet delamination technique. The filters made from polypropylene (PP) / polyamide 6 (PA6) system exhibited micro to nano scale fibers having uniform fiber distribution and superior mechanical properties. Effects of film draw ratio upon co-extrusion on the final filter characteristics were investigated. It was found that increasing the film draw ratio significantly improves the filter’s surface area and porosity, and decreases the mean pore size. This melt-based, versatile technology is applicable to any melt-processable polymers to produce fibrous filters having tunable properties for various filtration applications.
Impact of Pigments on the Dimensional Stability of Plastics
Shrinkage and Warpage phenomenon are common issues faced by injection molders in the plastics industry. These dimensional stability issues are more prevalent in semi-crystalline polymers such as HDPE. Formulation of organic pigments into semi-crystalline polymers impact the nucleation rates and can lead to further shrinkage and warpage. Dimensional instability with the organic pigments can be can be minimized or eliminated through processing steps as well as through surface treatment of the pigments. This paper will describe the shrinkage and warpage distortions, test methods for determining warpage, and recommend solutions.
Case Studies of PP Based OBC for Multilayer Packaging
Dow has developed a new family of polypropylene (PP) based olefin block copolymers (OBCs). This novel family of block copolymers enables high performing multilayer structures when used as a component in multilayer films for combining PP and polyethylene (PE), or combining PP with polar polymers. These multilayer systems offer customers unique combinations of properties such as exceptional adhesion, temperature resistance, durability and film design flexibility. The current paper discusses film structures and property enhancement when the PP OBC is used for retort tie layer application and as a versatile sealant film.
Heat Activated Dry Granulation within the Twin Screw Granulator
This paper highlights preliminary results related to a new dry granulation process that is run in a twin-screw extruder. This heat-activated dry granulation method can produce suitable dry granules representing an exciting new area for continuous granulation. However, the current method makes starting granulation difficult. It is believed that high compaction produces sufficient friction at the barrel wall to cause the binder to soften. Once a plug of dense granular matter is built up in the kneading section of the screws, it appears that any flow condition will produce granules but establishing this plug initially represents a major challenge and is where further studies are needed to simplify the approach.
Studying Polymer Particle Sintering with an Automated Imaging System
The formation of hollow plastic parts during rotational molding requires sintering, which involves the melting, coalescence and densification of polymer thermoplastic powder. Monitoring, visualizing and measuring the densification, which includes bubble formation and bubble dissolution, yields valuable information and is a useful technique to assess the rotomold-ability of different resins. An image visualization technique had been developed referred to as the automated Polymer Analyses Vision System (PAVS) to perform the quantification of a granular assembly rather than just a few particles.
Extrusion Foaming of LLDPE/Wood Fiber Composites
Foamed wood fiber/plastic composites (WPCs) with a fine-cell structure offer many benefits compared with the un-foamed WPCs, such as the reduced material cost, the decreased density, the improved mechanical properties, the enhanced processability, and their increased nailing-ability and screwing-ability. It is known that the gaseous emissions released from the wood fiber (WF) during processing should be suppressed to ensure a fine-cell structure. Linear low density polyethylene (LLDPE) is less shear sensitive due to its narrower molecular weight distribution and shorter chain branching, compared with conventional polyethylene. This paper investigates the feasibility of LLDPE as a matrix for making WPC foams with a fine-cell structure. The foaming behaviors of LLDPE/WF composites with both a chemical blowing agent (CBA) and a physical blowing agent (PBA) were investigated, to provide some guidance to WPC manufacturers.
Optimization of the FDM™ Additive Manufacturing Process
One of the most common Additive Manufacturing (AM) technologies is Fused Filament Fabrication (FFF), more commonly known by the trademarked name “Fused Deposition Modeling™” (FDM™). As FFF continues to gain popularity as a method of manufacturing, an understanding of all factors involved in the FFF process becomes essential. This study is an attempt to understand four primary printing parameters and the effects they have on part quality, solidity, and strength. These printing parameters are extrusion rate, nozzle travel speed, layer height, and path width.
A recommendation for the determination of optimal extrusion temperature and feed rate was found. A theoretical relationship between the four print parameterswas developed. The resulting solidity was found to vary throughout a printed part, which has effects on the predictability of part strength. Micro computed tomography was proven valuable in this analysis as well as being an effective tool for investigating the bead structure.
Injection Molding and Mechanical Characterizion of Carbon Fiber-Woodfiber/Polyproplene Hybrid Composites
Hybrid composites are made by incorporating two or more different types of fillers in a single matrix, which is highly tailorable. Carbon fiber (CF) reinforced composites have been well developed for certain industries such as aerospace and sporting goods. However, the high cost of carbon fiber, as well as lack of cost effective processing technologies for mass production, prevents its penetration to many different markets. Wood fiber (WF), an environmentally sustainable bio-fiber, has been used widely in making wood/plastic composites (WPCs) for building products and automotive applications, due to its low cost and lightweight. Nevertheless, WPCs have very limited structural applications where strong mechanical properties are required. Incorporating CF and WF into a polymer matrix to make hybrid composites through injection molding, would be a path to expanded applications for both. This paper investigated the injection molding of CF-WF/polypropylene hybrid composites and their mechanical properties. The effects of fiber content and hybridization on the mechanical properties were studied.
Stochastic Modeling and Quantification of Uncertainties of the Injection Molding Process
Uncertainties of the injection molding process are stochastically modeled. A system is considered showing the interaction of the clamping unit and the mold. Therefore, a deterministic equation is obtained modeling the system simplified as a set-up of springs in order to easily determine the resulting forces in the load path of the system. As an example for uncertain process parameters the mold temperature and the pressure force of the injected polymer are chosen. The Monte Carlo method is used to receive the stochastic results for the mean and the probability interval. Furthermore, an optimization algorithm is applied to improve the system in terms of the stiffness of the clamping unit and the temperature variation of the mold. This procedure is well suited to predict possible failures which appear only very seldom and therefore would not be revealed by commonly used set-up procedures.
Effect of Void Fraction on Dielectric Properties of Injection-Molded Polypropylene/MWCNT Foams
Polypropylene-multiwalled carbon nanotube (PP-MWCNT) nanocomposite foams with various void fractions ranging from 0 to 40% were prepared using injection molding. Their microstructure, cellular morphology and dielectric properties were studied. The results indicated that overall the real permittivity increases with void fraction. However, the void fraction effect was more pronounced at higher MWCNT contents. It was found that by a proper combination of void fraction and MWCNT content, real permittivity can be increased while the dielectric loss is decreased. For instance, 20% void fraction in PP-1.95vol.%MWCNT nanocomposites resulted in ~7 times increase in permittivity (reaching to 73.1) and ~3 times decrease in dielectric loss (reaching to 0.03). Such enhancements were explained in terms of the interfacial polarization and the rearrangement of MWCNTs caused by cell growth during foaming.
Study on Orientation and Distribution of Metal Fiber in Epoxy Substrate by Using Electromagnetic Control
Controlling fiber orientation and distribution in flow field is one of the important issues in composite materials. In this study, induction electromagnetic is used to control fiber orientation and distribution in flow field so as to investigate effect of distribution of fiber orientation angle and penetrating conductivity. The result of this study demonstrates that the ratio of static electromagnet controlling, dynamic electromagnet controlling and nonelectromagnet controlling is 12.2:9.6:1. Besides, the smaller viscosity of base can cause the fiber to be more easily arranged according to the magnetic field. Key Words: stainless steel fiber, fiber orientation, electromagnet.
Impact of Foaming on Fiber Breakage, Conductivity, and EMI Shielding of Injection-Molded Polypropylene/Stainless Steel Fiber Composites
Lightweight polypropylene/stainless-steel fiber (PP-SSF) composites with 15-35% density reduction were fabricated using foam injection molding and supercritical carbon dioxide (CO2). The electrical percolation threshold, electrical conductivity, and electromagnetic interference (EMI) shielding effectiveness (SE) of the PP-SSF composite foams were characterized and compared against the solid samples. The effects of physical foaming on fiber breakage were investigated. The results showed that the presence of dissolved CO2 decreased the fiber breakage by about 30%, which contributed significantly to the enhancement of electrical and EMI shielding properties. Consequently, the percolation threshold decreased up to four folds from 0.85 to 0.21 vol.% as the void fraction increased from 0 to 35%. The specific EMI SE was also significantly enhanced. A maximum specific EMI SE of 75 dB.g-1cm3 was achieved in PP-1.1vol.% SSF composite foams, which was highly superior to 38 dB.g-1cm3 of the solid PP-1.0vol.% SSF composites. The results reveal that light and efficient products with a lower fiber content can be developed by foaming technologies for EMI shielding applications.
Open Cell Microcellular Foams of Poly(Lactic Acid) Blend with Poly(Butylenes Succinate)
Biodegradable poly(lactic acid) (PLA)-based PLA/Poly(butylenes succinate) (PBS) foams with open cell structure were prepared via batch foaming method using supercritical carbon dioxide as blowing agent. It was found that PLA was immiscible with PBS, and PBS phase was dispersed as tiny spheres or large domains at various concentrations. The addition of PBS reduced the viscosity of the blends. During foaming process, the PLA/PBS interfaces acted as cell nucleation sites and the low melt strength PBS contributed to the formation of cell connection channels, which resulted in open cell structure. The investigation of PBS content found that PLA/PBS (80/20) foamed at 100 °C obtained the highest cell opening rate (96.2%).
Effects of Thermoplastic Elastomers on Mechanical Properties of Glass Fiber Reinforced Poly(3-Hydroxybutyrate-Co-3- Hydroxyhexanoate)
This study investigates the effects of thermoplastic elastomers on the mechanical properties of glass fiber reinforced bacterial polyester, poly(3-hydroxybutyrate-co- 3-hydroxyhexanoate) (PHBH), composites. The thermoplastic elastomers used were styrene-ethylenebutylene- styrene copolymer (SEBS) and maleated styrene-ethylene-butylene-styrene copolymer (SEBSMA). Composites were prepared by melt-compounding and injection molding. Mechanical test results suggested that SEBS-MA was more effective than SEBS in improving ductility, fracture energy, and notched Izod impact strength of glass fiber reinforced PHBH composites. Scanning electron microscopy results suggested that SEBS-MA encapsulated fibers as well as dispersed in the PHBH matrix, whereas SEBS dispersed in the PHBH matrix without fiber encapsulation.
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