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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Multi-Relaxation Test To Characterize Pe Pipe Performance
A new concept is proposed, which uses results from a multi-relaxation test to characterize transition of deformation mechanisms in polyethylene (PE) pipes, for plastic deformation from the amorphous phase only to the involvement of the crystalline phase. The former mechanism is believed to lead to brittle fracture, while the latter to ductile fracture. This phenomenon is believed to be related to the transition from ductile to brittle (DB) fracture that has been observed in creep tests of PE pipes by reducing the applied stress below a critical level. This paper presents results from 6 PE pipes of different density and molecular weight distribution. The results suggest that high-density PE pipes require a higher deformation level for the DB transition than the medium-density PE pipes. The results also suggest that the trend of change in the critical stress level for the DB transition is close to the trend of change in the hydrostatic design base, but the former takes less than two weeks to complete, while the latter more than 1 year. Therefore, the multi-relaxation test can be used as an alternative method to characterize PE pipe performance, as a means for preliminary screening or in-service monitoring of pipe performance.
Evaluating The Effect Of Stress Concentration On The Mechanical Properties Of Lfam Parts; Simulation And Verification
Large format additive manufacturing (LFAM) is gaining importance due to its ability to make large complex shape parts that are typically hard to make using traditional processing methods. Two of the critical mechanical properties required for any design process of brittle polymers or fiber-filled polymers are the modulus and the tensile strength. Tensile tests are typically used to characterize these properties of the material. Due to the larger size of the bead being deposited, regular ASTM/ISO standard specimens become difficult to produce. To the best of our knowledge, no standard procedure or test geometry is currently available. In this paper, various specimen types are evaluated to review the suitability for characterization of LFAM materials. From experiments, it was found that with a specimen with a straight gauge length and a transition radius between the wider fixation region and the gauge length, the failure region tended to be in the shoulder or the transition radius region. In addition, the variability in the tensile strength measurements was high. Attributing this to the stress concentrations in the shoulder region validated by finite element analysis, a specimen with a gauge length having an arc shape was evaluated. Experiments showed that the failure for such specimens consistently occur at the center due to the least width/cross section. In addition, the magnitudes of apparent tensile strength were much higher than those obtained for the specimens with a straight gauge length. Finite element simulations performed on both specimens validated the observations and the hypothesis on the cause of premature failure in the straight gauge length specimen.
Study On The Viscoelasticity Properties Of The Glass Mat Thermoplastics (Gmt) In Compression Molding System
Compression molding is one of the lightweight technologies able to provide efficient way to retain fiber length for better mechanical property comparing to injection molding. In compression molding development, materials such as glass fiber mat thermoplastics (GMT) are often applied. However, due to the complicated micro-structure of the reinforced material, and the interaction of fiber-resin matrix, it is still challenge to have uniform compressed GMT product. In this study, we have developed a method to measure the rheological properties of GMT material through a compression system. Specifically, we have utilized compression molding system to estimate the rheological parameters of GMT. Those rheological parameters are then integrated into CAE (Moldex3D) to evaluate the flow behavior under the compression operation. Results showed that the trend of the loading force is increased exponentially against displacement at various compression speeds. However, some significant differences between simulation and experiment are observed. Specifically, at the early compression stage, the volume of long fiber-resin matrix is expanded by 50% in real experiment. This causes the loading force difference at the beginning between simulation and experiment. On the other hand, at the middle to the end stage, due to the fiber-resin matrix separation, the more the resin left the matrix, the higher the resistance generated. This results in the jump up of the loading force in the real experiments comparing to the simulation prediction. This deviation can be validated through the measurement of fiber content through TGA.
Appearance Specifications For Plastic Parts: A Practical Method For Ensuring Consistent Appearance
The appearance of a molded plastic part is often an important design element. Appearance involves color, and also texture and gloss, lighting and viewing conditions, and the perspective of the viewer. While each of these can be defined and hopefully controlled, the methods can be expensive, and the terminology is often confusing. This paper presents a method for specifying and evaluating appearance in a simple and easy to understand manner. The method and can be used at any phase of the development process, from initial concept to the factory floor. Properly implemented, it provides a practical and cost effective means to ensure consistent appearance in molded plastic parts.
PVDF Injection Molding — Standard Guidelines And New Technologies
Polyvinylidene fluoride (PVDF) has long been used as a fluoropolymer for injection molding. With its robust chemical and temperature resistance, PVDF components such as valves, pumps, fittings, and other molded parts offer high performance properties. Having the lowest melting point of any fluoropolymer, PVDF can be processed on equipment used to mold polyolefin components. Common practices for molding PVDF resins will be outlined in the paper, with recommendations for optimal processing conditions. Furthermore, common issues and troubleshooting for defects such as splay, voids, warpage, and discoloration will be discussed. The paper will also highlight new PVDF low-shrink technologies that allow for fluoropolymer resin properties as a “drop in” replacement using the same molds as polyolefins. Advancements in technology by adding glass or carbon fillers to PVDF resins have greatly reduced the shrinkage values to as low as 0.5%.
Tie-Bar Elongation Based Prediction Of Injection Molding Quality
Filling-to-packing switchover (also called as V/P switchover) is critical for assuring injection molding quality. An improper filling-to-packing switchover setting may result in various defects of injection-molded parts, such as excessive residual stress, flash, short shot, and warpage, etc. To enhance consistent molding quality, recent V/P switchover approach applies cavity pressure profiles requiring sensors embedded in mold cavities, which is invasive to mold cavities and even expensive. Instead of using cavity pressure sensors, this study thereby proposes a novel approach of identifying ideal V/P switchover timing using a tie-bar elongation profile. In this investigation, a dumbbell testing specimen mold is applied to experimentally verify the feasibility of the proposed method. The results show that the mold filling and packing stages can be observed along the tie-bar elongation profile detected by mounting strain gauges on tie bars. Moreover, the varying process parameter settings including injection speed, filling-to-packing switchover point, and holding pressure, can be reflected in these profiles. By extracting their characteristics, the decision of filling-to-packing switchover is proved to be realistic.
A New Flow-Orientation Coupling Analysis In Injection Molding Simulation Of Fiber Composites
In the past, the Dihn-Armstrong flow-fiber coupling model has been demonstrated to only be relevant in semi-concentrated fiber suspensions. However, the broader core of fiber orientation distribution induced by the plug flow velocity profile for high fiber concentrations cannot be predicted by the flow-fiber coupling approach. In addition, some peculiar, irregular filling patterns for short/long fiber-reinforced melts at high fiber concentrations are known to occur, with the free surface advancing faster along the side walls of the cavity. However, state-of-the-art predictive engineering tools cannot provide satisfactory flow behavior of fiber-reinforced melts. More recently, a new fiber-suspension constitutive equation of the Informed-Isotropic (IISO) viscosity model was developed by Favaloro, Tseng, and Pipes [Composites A, 115 112-122 (2018)]. Therefore, the IISO model is used to simulate the plug flow in reality and predict the broader core in good agreement with experimental data.
Nanoparticle Production By Solvent-Free Extrusion Emulsification
This study examines the effect surfactants have on the mechanisms of solvent-free extrusion emulsification method featuring a twin-screw extruder. Two sets of surfactants were studied in this work, three anionic surfactants: SDBS, Unicid 350, Calfax, and three nonionic surfactants: Igepal CO-890, Brij 58, Synperonic F-108. Comparing the anionic surfactants, it was found that both SDBS and Calfax exhibited great particle stabilization characteristics and resulted in 100-200 nm sized particle emulsions, while Unicid 350 was seen to result in coarse particle generation in the 100-200 μm size range. Comparing the non-ionic surfactants, it was found that Synperonic F-108 was the least successful of the three, and did not pass initial bench testing. Igepal CO-890 and Brij 58 both produced nano-sized emulsions, but with Brij 58 only a fraction of extrudate was true emulsified material, with the majority of the polymer exiting the process without emulsification. Overall it was found that a higher molar concentration of non-ionic surfactants was required to achieve results similar to those found with SDBS and Calfax.
Optimizing Process Condition Of Pu Chemical Foaming: Validation Of Material Properties For Numerical Simulation
Herein, we present the recent development in PU chemical foaming simulation by simultaneously considering the two competing major reactions governing PU chemical foaming, namely, the foaming reaction between isocyanate and water, and curing reaction between isocyanate and polyol. It has been demonstrated that these two reactions possess different reaction kinetics. For a realistic PU chemical simulation, it’s crucial to have separate rate equations describing foaming and curing reactions. In the first part of this study, we demonstrated an accurate measurement of PU reaction properties by employing a universal foam qualification system to measure physical parameters during foam formation such as foam rise height, reaction temperature, rise pressure, curing and viscosity. Foaming simulation is validated with the experimental results, and good agreements were obtained. Subsequently, the validated material parameters are used in real part simulation to yield optimal process conditions during foam formation. The study demonstrates promising results, and is of great relevance to light weighting application. We anticipate that in turn, this should reduce the product-to-market cycle time by eliminating the need for the traditional-trail-error method.
Computer-Aided Engineering Approach To Composite Manufacturing Solutions Of Resin Transfer Molding Process
Fiber reinforced plastic composites provide improved part performance in a wide variety of applications. One of the most promising manufacturing processes nowadays is resin transfer molding (RTM). Latest advancements in simulation technology make the advanced manufacturing processes to be simulated accurately. A computer-aided engineering (CAE) simulation tool enables manufacturers to well predict material behaviors and to optimize part performance in the molding process, such that expensive and time-consuming trial-and-error procedures can be greatly reduced. In this work, a closed-loop integrated workflow using CAE analysis tools is established to simulate draping and filling behaviors in RTM process. The influences of fabric shearing and fiber orientation on the filling and warpage stages in the process are studied. A cost-effective simulation approach for the advanced composites’ manufacturing is demonstrated.
Investigation On The Microstructures Of Long Fiber And Their Influences On Warpage And Mechanical Property In Injection Reinforced Thermoplastics (Frt) Parts
In recent years, due to its excellent properties, the fiber-reinforced thermoplastics (FRT) material has been applied into industry as one of the major lightweight technologies, especially for automotive or aerospace products. However, due to the microstructures of fiber inside plastic matrix are very complex, they are not easy to be visualized. The connection from microstructures to the final shrinkage/warpage is far from our understanding. In this study, we have proposed a benchmark with three standard specimens based on ASTM D638 where those specimens have different gate designs. Due to the geometrical effect, the local warpage behaviors are quite different for those three specimens. Specifically, it causes one specimen warped downward and bended inward, another warped upward, and the other slightly upward at the same time. The local warpage behaviors are validated by experimental study with excellent agreement. Moreover, the fiber length effect on the full warpage behavior was also conducted. When the longer fiber length is introduced, the full model warpage behavior can be reduced. The detailed of the full model warpage behavior has been analyzed side-by-side using both of numerical simulation and experiment. The trend is in a reasonable agreement for both simulation and experiment. Furthermore, the mechanical property variation of the finished parts due to the different fiber length was also investigated. Results showed that when the fiber is reinforced the tensile strength is increased linearly for all Models. However, the tensile strength of the Model I is always better than that of Model II, while Model III is much worse than others due to its double gate effect. The reason why the tensile strength of the Model I is always better than that of Model II could be due to the side-gate structure to provide strong fiber orientation and also more uniform fiber distribution at NGR.
Effect Of Polyethylene Structure On Silane Grafting And Properties Of Associated Moisture-Crosslinked Compositions And Cable Constructions
Different types of alkoxysilane functionalized ethylenic polymers are discussed herein, with reactor ethylene silane copolymer being preferred to silane grafted technologies from the perspective of shelf life at ambient conditions as well as extrusion characteristics during cable manufacturing. The properties of wire and cable constructions (in which the sheaths around the conductors were made of moisture-crosslinked alkoxysilane functionalized ethylenic polymers) have been found to be satisfactory. Crosslinking of the silane functionalized polymerwas induced through the use of a silanol condensation catalyst. The polymer characteristics that were observed to influence the properties of the crosslinked polymeric formulations (and cable constructions) included melt indexand molecular weight distribution.
Differences And Similarities In Fatigue Failure Mechanisms Of Pa12 Pipe Grades Compared To Modern Pe Pipe Grades
Polyamide 12 (PA12) has been successfully introduced as material for SDR 11 gas piping systems up to 18 bar, representing itself as an attractive alternative to steel pipes for high-pressure applications. Practical experience and studies have confirmed excellent resistance against relevant pipe failure mechanisms such as slow crack growth (SCG) as well as any third-party attack or external surface damages (i.e. indentation effects of stones in the soil). Four different PA12 materials with varying macromolecular structure were investigated within the current paper. On the one hand, a major focus was put on the general applicability of the Cyclic Cracked Round Bar (CRB) Test as fracture mechanical approach to provoke quasi-brittle failure. On the other hand, the influence of the molecular weight MW, expressed by the relative viscosity number VNrel for PA12 grades, on the fracture mechanical failure behavior of PA12 grades and three different PE100 grades of increasing molecular weights was examined. Additionally, a fundamental comparison between PA12 and typical PE80, PE100 and PE100RC pipe grades in terms of long-term properties and relevant failure mechanisms was undertaken. The results demonstrate that the Cyclic CRB Test is a suitable method to provoke real SCG, and that the average molecular mass has a considerable influence on the SCG resistance of PA12 as it is the case for PE. Furthermore, findings of this paper outline an extraordinary SCG resistance for high-viscous PA12 pipe grades, which is exceeding typical toughness values of PE100RC by at least a magnitude at comparable stress levels and further confirm a high suitability for pipe installation techniques without sand beddings.
Performance Analysis Of Five Plasticating Screws
Three multi-channel “fractal” screws are compared with general-purpose and barrier screws using an instrumented single screw extruder for HIPS and LDPE at varying screw speeds. Cold screw freezing experiments were performed for all five screws with 5% black, blue, and violet colorants serially added to neat HIPS. The cold screw pulls showed that the general-purpose and barrier screws exhibited significant racing of the materials within their screw channels and, thus, broad residence time distributions. Examination of the material cross-sections indicated persistent coiled sheet morphologies which were best dispersed with the third fractal screw.
Online Film Casting Of Pc/Mwnt Composites Using Ultrasound Assisted Twin Screw Extruder
The online ultrasonic film casting process to manufacture nanocomposite films was developed. In this process, polycarbonate (PC) of two different molecular weights was mixed with carbon nanotubes (CNT) and cast into films. Due to the relatively lower viscosity of low molecular weight PC (LPC) than that of high molecular weight PC (HPC), the torque of extruder and the die pressure of LPC was lower than those of HPC. The necking phenomenon during film casting of composites was investigated. It was found that at the same processing conditions, the film width of HPC was larger than that of LPC. The necking along film line decreased with increasing CNT concentration and imposition of ultrasound. This indicated that incorporation of the rigid CNT and imposition of ultrasound restrained the elongational flow behavior of melt, resulting in film of a larger width. The stress-strain behavior of composite films indicated that the incorporation of CNT improved the yield stress and decreased the elongation at break of the composite films. The light transmittance of the films continuously decreased with increasing CNT concentration.
Effects Of Post-Mixing Time And Dispensing Methods On The Dual Curability Of A Two-Part Acrylate-Epoxy Hybrid Adhesive System
The dual UV and ultimate thermal curability of a model, two-part acrylate-epoxy hybrid adhesive system and relevant governing factors are investigated by using dynamic rheometric and calorimetric techniques. Raw adhesive mixture samples were prepared with using the same static mixer, but via two different sampling methods (i.e. sequential and concurrent). The UV curability and ultimate thermal curability of mixture samples were measured in terms of heat of photo-induced cure reactions and ultimate glass transition temperature by using a differential scanning colorimeter (DSC) with and without the inclusion of a photocalorimeter accessory (PCA), respectively. In addition, the time-evolving viscosity of a fresh adhesive mixture sample was probed as a function of post-mixing time in small-amplitude oscillatory shear (SAOS) mode under ambient condition by using a dynamic rheometer, and is then correlated with the measured results of dual curability. Accordingly, the proper UV cure condition and pot life relevant to each of two different dispensing methods are determined based on practical optimization of UV curability and ultimate thermal curability of the hybrid adhesive system. The findings from the present study would provide some practical knowledge for advanced process development of similar acrylate-epoxy hybrid adhesive systems.
Understanding Scratch And Mar Behaviors Of Textured Polymer Surfaces Through Fem Modeling
Surface damages, such as scratch and mar, can significantly affect the aesthetics of polymer surfaces. Understanding the scratch and mar behaviors of polymer is more challenging if the surface is textured. Scratch and mar can be easily detected when the surface is smooth, whereas surface texture may hide the scratches. Introduction of texture to polymer surfaces has been shown to improve scratch visibility resistance; however, it also exposes polymers to new form of surface damages. In this study, a method of transferring actual surface texture characteristics into a finite element method (FEM) model is presented for realistic simulation of polymer scratch and mar behaviors. Influence of texture on scratch and mar behaviors is investigated through analysis of stress and strain field development. Implications of the numerical findings on scratch and mar visibility resistance are discussed.
Influence Of Meltspinning Conditions On The Morphology And Crystallization Of Polyester Fibers
Polyester, as a highly versatile polymer with desired physical and mechanical properties, conforms a major share in the synthetic fibers market. This article investigates the effect of meltspinning conditions on the morphology and thermophysical properties of a commercial bottle-grade amorphous copolyester in comparison with a semi-crystalline homopolymer polyester. After being molten in an extruder and exiting the die, polyester extrudates were drawn using a custom-made rotating drum at high speeds up to 1000m/min to form thin meltspun filaments. Microscopic images show the decrease in the diameter of fibers with increase in the drawing speed and temperature. Between two polyesters the homopolymer shows a more significant attenuation with the average fiber diameter down to 25.2 µm (equivalent to the diameter decrease of about 140 times or the drawing ratio of above 19,000 times) for the drawing speed of 1000m/min and at 260°C. Cohesively, differential scanning calorimetry shows a lower cold crystallization temperature for the homopolymer polyester, pointing to its higher crystallization kinetic, which can be attributed to a higher degree of chain orientation in this polymer. In a similar way, increase in the drawing speed and decrease in meltspinning temperature for both polyesters results in their decreased cold crystallization temperature, as a sign of their increased molecular chain orientation. Upon annealing the meltspun fibers at 200°C for 20min the cold crystallization peak vanishes to confirm their significant increase in the crystallization degrees. Both polyesters, particularly upon being annealed, show increase in the degree of crystallinity with increase in the drawing speed and decrease in the meltspinning temperature.
Fracture Properties Of Polyolefin Recyclate Formulations
A high utilization of polymeric recyclates must be considered to achieve current and future policy goals for a circular economy. Therefore, recyclate formulations will have to meet the application specific performance requirements in order to substitute virgin materials. In this research, four commercially available polyolefin recyclate grades were characterized with analytical and mechanical methods. Furthermore, as a highly accelerated technique to characterize long-term mechanical performance, fatigue crack growth experiments were conducted. In all recyclates, contaminations of foreign particles were found and impair the mechanical properties as well as fatigue crack growth behavior. Nevertheless, the experiments point out clear differences and allow for a distinct ranking of the recylates in terms of fatigue crack growth resistance.
Flow Behavior And Polymer-Particle-Interaction In Highly Filled Polylactides
Adding fillers to polymers allows highly functional materials and thereby properties like electrical conductivity that are not achievable by polymers themselves. But higher amounts of fillers cause an increase in viscosity and thus a change in flow behavior which in turn induces difficulties in plastic processing. Above a certain value (percolation threshold) there is a flow restriction which has to be overcome by a higher pressure in plastic processing. Besides the amount of filler the flow behavior of highly filled polymers depends on the filler itself and its particle shape. Especially the aspect ratio plays an important role. Another important factor is the combination of the polymer and the filler and whether there are any interactions between each other. By differing the amorphous phase of polymers into a rigid amorphous and a mobile amorphous fraction, predictions about interactions are possible. The objective is the generation of such a flow restriction and the combined investigation of a polymer-particle-interaction. Polylactide (PLA) was used as matrix whereas minerals were used as filler material in different amounts up to 50 vol.-%. SiO2 was chosen because it is available in different spherical sizes and clay because of its platelet geometry. Rheological investigations were done on a plate-plate rheometer while the interactions were investigated using differential scanning calorimetry. The results show that a higher aspect ratio leads to a faster increase in viscosity achieving the rheological threshold. As a result of the caloric investigations the highly filled plastics show only a minor interaction between polymer chains and filler surface. This leads to the conclusion that the change in flow behavior is mainly caused by a direct interaction between the particles.
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