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.
Injection molding with bio-based and/or bio-filled resins is becoming more commonplace as the plastics industry responds to the environmental and sustainable desires of the economy. This paper presents some intricacies of part design and processing developments when injection molding with bio-based and bio-filled resins.
Value added cost effective and sustainable polyamide 6 and 66 compounds were prepared by incorporating 10 to 30% recycle content without significantly sacrificing physical properties. This was achieved by reactive extrusion with chain extending additives to couple low molecular weight chains in recycled feed streams. Three types of chain extending additives with different functionalities were evaluated in this study. Based on the performance and cost, one of the chain extending additive was identified as the best option.
Transient uniaxial elongational viscosity for binary blends composed of conventional isotactic polypropylene with linear structure (PP) and low-density polyethylene produced in an autoclave reactor (LDPE) was evaluated. The blends were prepared by melt-mixing to make PP as the continuous phase. Although LDPE exists as dispersed droplets, it was found that the LDPE addition provides the strain-hardening in transient elongational viscosity for PP. During elongational flow, LDPE droplets dispersed in the PP matrix were deformed in the flow direction because the viscosity of LDPE used is lower than that of PP. As increasing the strain, however, the deformed LDPE droplets act as rigid fibers due to its strain-hardening behavior. Consequently, the PP matrix located between the fibrous LDPE droplets is deformed greatly during elongational flow. This excess localized deformation is responsible for the strain-hardening in the transient elongational viscosity for the blends.
Safety for patient and user is an essential requirement for medical products. Subsequently, plastics grades used in medical have to fulfil particular requirements, i.e. constant properties, formulation lock or biocompatibility. Surprisingly, no standard has existed to define the requirements for medical grades so far. This gap has been filled recently by the new guideline VDI 2017 developed and launched by a work group of the German Engineer’s Society (VDI). This article addresses the development of the new guideline and presents the essential requirements to be covered by a medical grade.
Although not fully understood it is well recognized that optimal working of glass fiber sizings is necessary to maximize the performance of glass fiber reinforced polymer composites. However, test results indicate that the performance of polypropylene compatible glass fiber sizing can be significantly compromised by thermooxidative degradation at normal composite processing temperatures. Results obtained using TGA, DSC, microbond adhesion measurement and composite mechanical testing indicate that a significant reduction in composite performance is directly related to a loss of fiber-matrix adhesion caused by thermal degradation of some of the principal sizing components.
An advanced Finite Element Method (FEM) based transient pellet heat transfer model with crystallization kinetics is developed to better understand the cooling requirements for a clean pellet cut during polyethylene manufacturing. This model considers conduction/convective heat transfer in and around a polymer pellet with enthalpy changes, considering a pellet of spheroid shape surrounded by a cooling water off constant temperature. The model further accounts for the changes in stiffness or elastic modulus obtained from rheological measurements using multi-wave oscillatory test during cooling/crystallization stages of the polymer. A series of simulations were performed to understand the effects of several parameters such as resin architecture/formulation, crystallization kinetics, initial molten pellet temperature, water inlet temperature, water to pellet ratio (i.e., water flow rate) and pellet dimensions. It was found that for resins of similar Melt Index (MI) and density, the differences in structural characteristics can significantly affect the pelletization process and pellet cut. This model may serve as a strong tool for efficient design, operation and troubleshooting of downstream equipment (e.g. pelletizer, cutter, Pellet Conveying Water (PCW) system, stripper etc.) through understanding of the effects of molecular architecture of the resins and/or optimization of various processing and operating conditions.
To understand transient cell size patterns in extruded foams, computational fluid dynamics (CFD) modeling was used to map temperature, velocity, and pressure in a foamable mixture traveling through a simplified heat exchanger geometry. A comparison was made between cases of clean and partially plugged heat exchanger device. The analysis revealed that the predicted inhomogeneities of temperature, pressure, and velocity do not correlate with the observed cell size pattern. However, residence time maps showed clear similitude with the observed pattern, in particular for geometries simulating partial plugging of the individual heat exchanger channels.
Temperature is an important criterion, on which many process variables depend. Therefore, temperature measurement plays a major role in various technical areas, from system monitoring to process improvement. It is often of particular interest to detect temperatures on components and tools during the production process in order to react as quickly as possible to undesired temperature changes. Otherwise, these temperature differences result in uneven melt viscosity and cause defects, component distortion and surface degradation. Also, measuring the temperature within tools via conventional sensors is often not possible due to the risk of causing defects within the product and the negative temperature influence of the tool walls. In order to determine an appropriate inline temperature of the actual melt temperature without interrupting the melt flow, this paper shows various steps of a thin-film thermocouple development. Different custom-made thin-film thermocouples are evaluated based on their long-term stability, thermal insulation capability and response time.
Recently, many Internet of Things (IoT) have been proposed and developing to industry and markets. They drive people to design and create an automatic production environment. Before executing automatic production, how to retain good quality for injection products is one of the crucial factors. To retain good quality, it is commonly using CAE to assist from original design to revision and to fabrication. However, even using CAE, it doesn’t guarantee the quality factors obtained from CAE can be applied to real experiments. In this study, first we have focused on what the major factors were to cause the difference between CAE simulation and real testing on the warpage quality. We further applied numerical simulation to decouple what the main driving forces are to make the difference. Results showed that in the original process setting, the warpage difference between simulation prediction and experiment is 0.34 mm. We further found out the major difference came from the injection filling response is too slow (delayed about 29%) and packing pressure is insufficient (23% lower) in real experiment comparing to simulation prediction. Moreover, after calibrate the machine response the warpage difference between simulation prediction and experiment is reduced to 0.12 mm. We also studies viscoelastic (VE) effect and found the VE has a great impact on the warpage in this case study. However, the influence of VE is great or not for other cases that should be further investigated.
The coatings of tools and moulds used in plastics processing, especially in extrusion and injection molding, are of importance in various respects. In most cases, coatings serve to reduce wear and increase the service life and maintenance intervals of the molds during production. Such anti-adhesive and corrosion-protective coatings can be used to produce high-quality products that stand out from those of other competitors. Conventional surface coating techniques have so far led to very good coating properties, such as the reduction of wear, and guarantee anti-adhesive behaviour between the plastic melt and the metallic mold surface. However, in addition to their limited applicability for micro- or nanostructured surfaces, such processes are often a significant cost factor due to their complex application processes. Moreover, it is difficult to remove damaged inorganic coatings. This paper presents an investigations method that enables a study of the long-term stability and wear resistance of coatings.
Monitoring physiological parameters of crew on spaceflight missions is of upmost importance for long term microgravity expeditions. Body temperature is one particularly important parameter, as changes in thermoregulation or circadian rhythms may be connected to decreased mental and physical performance if it deviates significantly from 37° C. In this paper, the effects of temperature and frequency on the dielectric properties of 3D printed polyvinylidene fluoride (PVDF) discs were studied. The objective is to incorporate the polymer into an electromagnetic resonating sensor to measure skin temperature. The temperature dependent dielectric permittivity of the polymer interacting with the electromagnetic field of the sensor will result in a resonant frequency shift that can be correlated to report body temperature in a noninvasive, lightweight, and wirelessfashion.
The direct and converse piezoelectric effects are useful for stress/strain monitoring and actuation, respectively. We report these effects in 3D-printed (bottom-up stereolithography, 26-46 μm layer thickness) polymer without filler or poling, using a polymer (unmodified photopolymerizable resin) that is not known to be piezoelectric. This means that the piezoelectric behavior is inherent to the printed material. The inherent behavior is due to the process-induced 2D in-plane shear stress encountered by the resin during printing and the consequent 2D in-plane molecular alignment. The smaller is the layer thickness, the greater is the shear stress, the more is the molecular alignment, and the stronger is the piezoelectric effect. The out-of-plane piezoelectric coupling coefficient is up to 0.43 pC/N - higher than values previously reported for 3D-printed polyvinylidene fluoride, which is known to be piezoelectric.
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.
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.
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.
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.
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%.
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.
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.
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.
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