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 Injection Molding Parameters on the Surface Structure of Polyamide Parts
Injection molded and then electroplated plastic parts are mainly made of acrylonitrile butadiene styrene (ABS) or polycarbonate/acrylonitrile butadiene styrene (PC/ABS) blends. Nevertheless, compared to these materials, polyamide (PA) has superior physical properties. However, the coating quality is inferior to that of conventional polymers and the scrap rates of 25% to 30% are higher. The coating quality depends not only on the electroplating parameters but also on the surface of the injection molded part. The aim of this paper is to determine the influence of injection molding parameters on the surface structure of injection molded, mineral-filled polyamide parts. Therefore, mineral-filled polyamide parts are produced in a full-factorial design of experiments (DoE) and electroplated subsequently. Afterwards, surface parameters from DIN EN ISO25178 are determined by confocal microscopy for different pre-treatments of the electroplating process chain and at different positions.
Novel Foam Injection Molding of Polyamide/Glass Fiber (PA/GF) Composites Using Gas-Laden Pellets
A novel approach of producing foamed polyamide/ glass fiber (PA/GF) composite parts using gas-laden pellets was proposed. Gas-laden pellets loaded with nitrogen (N2) were produced by introducing sub-critical N2 into PA/GF during compounding using a twin-screw extruder equipped with a simple gas injection unit. Compared to the commercial microcellular injection molding (MIM) technologies, gas-laden pellets enable production of foamed parts with a standard injection molding machine, which is more cost-effective and easier to operate. The shelf life of N2-laden PA/GF pellets was examined. Results showed that the N2-laden pellets still possessed good foaming ability after one week of storage under the ambient atmospheric conditions. With this approach, the weight reduction of foamed PA/GF parts was able to reach 12.0 wt%. The tensile strength, cell morphology, and densities of foamed PA/GF parts were also investigated.
Study on the Quantification of the Advancement of Core Material in Co-Injection Molding Products
Co-injection molding has been developed for decades. However, due to too many factors which can affect its processing, it is very difficult to obtain good quality of co-injected products all the time. One of the major challenges is that the prediction and management of the advancement of core material is very difficult. In this study, both CAE simulation (Moldex3D) and experimental methods have been applied to investigate the advancement distance of core material in co-injection molding based on the standard tensile bar (ASTM D638 TYPE V) system. Specifically, the flow behavior of the core material has been predicted numerically and verified experimentally through short shot testing, and skin/core ratio effect testing. Moreover, based on the optimized skin core ratio, the major factors to influence of the advancement of core materials have been conducted. Finally, to quantify the advancement of the core material in co-injection molding, both simulation prediction and experimental observation were performed. Results showed that the advancement of the core material is strongly proportional to the core ratio in co-injection molding system. Moreover, the flow rate and the different skin/core material arrangement also can influence the advancement of the core material.
The Effect of Orotic Acid on the Crystallinity Development in Poly-Lactic Acid During Vibration Assisted Injection Molding
This research was focused on the synergistic effect of nucleating agents and an oscillatory motion on the crystallinity development of poly-lactic acid (PLA) during vibration assisted injection molding (VAIM). A differential scanning calorimetry (DSC) study was performed to understand the efficacy of orotic acid, a nucleating agent for 2500 HP PLA, under quiescent conditions. A new protocol for quantitative characterization of crystallization kinetics from DSC data was developed to gain insight on the crystallization kinetics. It was observed that the 1 wt.% orotic acid provided significant enhancement in crystallization kinetics. The isothermal crystallization, injection molded and VAIM data obtained from DSC were compared. The shear stresses introduced during traditional injection molding enhanced PLA crystallization at 90°C and 70° C mold temperature as compared to crystallization under quiescent conditions. The crystallization was enhanced by ~250% when VAIM was introduced at 70°C mold temperature as compared to traditional injection molding was observed. The effect of VAIM was nominal when the mold temperature was 90°C indicating that VAIM is more effective at lower mold temperatures.
Analysis of Injection Molding Simulation of Static Mixer Within the Runner System to Improve Melt Homogeneity, Filler Distribution, and Part Quality
A Kenics static mixer was introduced into the runner system of a convex-concave circular disc mold and simulated using Moldex3D. The set-up was tested with two mixers with the same diameter, length, and pitch but different mixer element thickness as well as various polymer resins with different rheological properties. The maximum sprue pressure rose with increasing mixer thickness but stayed within normal machine capabilities. Overall, simulations with the thin mixer exhibited improvements regarding melt homogeneity and part quality for polymers such as polyamide 6 (PA6), polycarbonate (PC), and poly-propylene (PP), while the thick mixer had a neutral or negative effect on the same properties. The fiber analysis showed a decrease in fiber alignment in runs including a mixer. Polymers with more extreme rheological properties, such as polybutylene terephthalate (PBT) and polymethyl methacrylate (PMMA), revealed unsatisfactory results.
Effect of Strain Rate and Thermal History on the Mechanical Properties of Polycarbonate
This paper compares the strain-rate behavior of injection and compression molded Polycarbonate plates in compression through Split Hopkinson Pressure Bar (SHPB) experiments. The samples are tested under strain rates ranging from 0.01 to 6,000 /s and at a temperature ranging from - 25°C to 75°C. The difference in mechanical response of specimens fabricated using the two different processes is relatively well understood when tested in plane and is influenced by the different molecular orientation distributions resulting from processing [1-4]. However, there has not been a systematic study of out-of-plane response of such materials, particularly for higher strain rates relevant to impact performance of Polycarbonate. The results of this study suggest that an orientation distribution difference between the samples fabricated via the two paths may not fully account for the observed differences, which become more pronounced at the higher ranges of strain rate based on SHPB testing.
Extrusion Foaming of Newly Developed High-Melt-Strength Polypropylene
We report systematic studies on the foamability of our novel high-melt-strength long-chain branched polypropylene under supercritical CO2. Continuous foaming experiments were conducted using a tandem extrusion system and a set of filamentary dies with similar pressure drops but different pressure drop rates. The foam expansion was controlled by varying the temperature at the die exit. Under identical CO2 loadings, the expansion ratio plotted as a function of die temperature exhibited similar shapes across multiple pressure drop rates. However, the shape of the curve varied across different amounts of CO2, under which the highest achievable expansion ratio occurred at a lower die temperature with increasing CO2 content. The cell density displayed strong dependence on both the pressure drop rate and the amount of dissolved CO2. The effect of the latter became more apparent at lower pressure drop rates. The average cell size decreased with increasing CO2 loading but generally showed weak dependence on pressure drop rate except at the highest value.
Design and Engineering of Insoluble, High Performance Starch Foams Via Extrusion Technology
Insoluble, high performance starch foams with high resistance to moisture were prepared by ZSK-30 twin screw extruder using additives such as chitosan, polyvinyl butyral (PVB) and sodium trimetaphosphate (STMP). Under the optimized extrusion conditions, water acted as a plasticizer and a blowing agent breaking up the hydrogen bonds within the starch granules and releasing the starch polymer chains without significantly reducing their molecular weight. The pressure drop at the die led to expansion and formation of closed cell foams. A screw configuration made up of 3 kneading sections was found to be the most effective for better mixing and foaming. The use of PVB was extremely effective in minimizing moisture sensitivity and made the foams hydrophobic and insoluble in water. Crosslinking of starch with STMP gave anionic mono and di-starch phosphates which formed an insoluble polyelectrolyte complex with cationic chitosan due to electrostatic attraction. This also increased the compressive strength of the foams by 3 times compared to the control foams. STMP also reduced the cell size and gave more uniform cell size distribution. It was found that properties like density, expansion ratio, compressive strength, resiliency, and cell size distribution of foams can be controlled by adjusting feed rates of starch, chitosan, and the crosslinking agent. These insoluble composite foams absorbed over 600% by weight water and formed a gel kind structure; a property which could be useful in hemostatic applications. Densities of foams were found to vary from 21 to 51 kg/m3 for different compositions studied. A maximum expansion ratio of 74.5 was obtained for the formulation containing 10% PVB and 4% chitosan.
Separation of Multi-Component Parts for Mechanical Recycling
The recyclability of plastic components has become an important objective in the product development process of packaging and technical products. In this study an approach is taken to produce hard-soft combinations with a better recyclability by using an adhesion and, at the same time, recycling layer. This additional layer is placed between the hard and the soft component. The intermediate layer shows good adhesion to both components for the use phase of the product. At end-of-life-stage of the products, the two components can be separated by melting the intermediate layer and shearing of the parts in recycling machines. Polypropylene (PP) as the hard component and thermoplastic polyurethane (TPU) as the soft component are combined with an EBA (Polyethylene-n-butylacrylate) functioning as the intermediate layer by an overmolding injection molding process. The peel strength is investigated for the combination hard component/ intermediate layer, intermediate layer/ soft component and for the combination of all three materials. The combination without the intermediate layer shows no adhesion of the two components. For simulating a separation process the peel tests are carried out at higher temperatures. The results show a lower bond strength at temperatures around 80 °C and the failure location between the TPU part and the EBA-layer. Furthermore, the results show that with the functional intermediate layer two materials can be joined for the use phase and also separated by heating at the end-of-life-stage.
Impacts of Degraded Surface Removal on Mechanically Recycled Marine Debris
This study was conducted to show the effects of inclusion of highly degraded surface material in recycled ocean plastic HDPE. Two primary materials were studied, one (HDPE-SD) contains high surface degradation while the other (HDPE-MP) had the surface removed for comparison. Each material was mechanically recycled (granulated, compounded, granulated) and then injection molded to create test specimens. Optical microscopy was performed before processing to observe and measure the surface degradation. After molding, FTIR, DSC, rheology, and mechanical characterizations were done to draw conclusions about the impacts of the degraded surface on the recycled properties. Inclusion of the degraded surface was found to increase fracture elongation, zero shear viscosity and lower the melt temperature. These findings were related to the chemical structures observed via FTIR. Additionally, comparisons and insights on the challenges and benefits of recycling ocean plastics are described.
Dimensional and Mechanical Comparison of the Conventional Injection Molding Process to Imflux's Constant Pressure Process Featuring AVA Technology
One of the major issues the plastics industry is trying to solve today is the lack of a circular economy. Plastics do not biodegrade fast enough to keep up with the waste being generated, and therefore present ecological and environmental problems. To take discarded plastics and continuously give them new life in a variety of applications is the goal of many plastics industries. However, to reprocess recycled plastics has shown many challenges. iMFLUX’s Auto-Viscosity Adjust (AVA) technology has made doing so easier with their low, constant pressure injection molding process. This technology enables the injection molding process the ability to independently adjust parameters in real time. This research focuses on comparing the dimensional and mechanical integrity of virgin ABS and PCR ABS in the conventional and iMFLUX processes. It was determined that the conventional process had better mechanical integrity with the virgin ABS than iMFLUX, and the iMFLUX process had less deviation overall between dimensions and material transition.
Injection Moldable 5G Plastic Antenna Dipole
In the past decade, the wireless communication technology has expanded rapidly over the globe, thus stipulating higher data rates and lower latency communication. The advancement in wireless technology has led to drastic increase in number of end users, demanding higher efficiency. To fulfil the requirement of data traffic, the unexplored millimeter wave frequency region is being studied which is recognized as the 5th generation of wireless communication system. This range of frequencies of millimeter waves can facilitate larger bandwidth, higher data rates, lower latency and can connect large number of devices. New technologies emerging for the foundation of 5G include massive MIMO, small cells, beamforming that plays an important role in revolutionizing the cellular network technology. Miniaturization, lightweight trends lead for utilization of thermoplastic materials being used for the antennas. The dielectric properties of thermoplastic materials are measured & used in building simulation models for antennas. A broadband dual polarized, injection moldable base station antenna with crossed dipoles, balun, feeding connectors and reflectors is designed to operate in the 5G spectrum at frequencies up to 10GHz. Sensitivity analysis is performed to examine the antenna performance and most efficient antenna design is chosen.
In situ Visualization of Microstructure of Polypropylene under Shear and CO2 Pressure
Crystallization and foaming behaviors of a semi-crystalline polymer in conditions comparable to those found in polymer processing, where the polymer melt experiences shear under elevated pressures, are key for modeling polymer processes and predicting the final structure and mechanical properties of polymer products. We investigate the crystallization behaviors of a newly developed high-melt strength polypropylene (PP) resin using a novel high-pressure visualization system. Overall crystallization kinetics can be easily controlled through the effect of induced-shear stress and the presence of pressurized CO2.
Increasing the Efficiency of the Continous Depolymerisation of Polystyrene
Unlike other thermoplastics, polystyrene can be thermally recycled into its monomer form. During the continuous depolymerization of polystyrene in the twin screw extruder, low-molecular volatile substances are gradually split off at temperatures above 400 °C. Depolymerization in a twin screw extruder offers a number of advantages for the recycling of polystyrene. The heating time in a twin screw extruder is short and high material throughputs can be achieved. The reaction products are removed directly by a vacuum system. To make the depolymerization of polystyrene more efficient and to increase process stability, the vacuum system has been optimized with regard to the vacuum dome geometry. As a result, the reaction products are removed faster and the migration of the low-viscosity melt into the vacuum dome is avoided. In addition, the constructive adaptation of the vacuum dome geometry made it possible to increase the realizable vacuum pressures during depolymerization from 400 mbar to 50 mbar and the maximum condensate yield from approx. 30 % to over 60 %. Depolymerization in a twin-screw extruder thus represents a promising process for recycling polystyrene on an industrial scale.
Cleavable Comonomers Enable Degradable, Recyclable Thermoset Plastics
Thermosets play a key role in the modern plastics industry. Their high density of chemical crosslinks result in excellent mechanical properties for high-performance applications, but also prevent them from being readily reprocessed once formed. We have recently developed degradable, recyclable versions of existing high-performance thermosets by incorporating small quantities of a cleavable co-monomer additive. This approach maintains the performance profiles of the parent materials while seamlessly integrating with existing manufacturing workflows.
3D Numerical Simulation and Experimental Observation of Bubble Growth and Collapse in Nitrogen-Gas Saturated Molten Polymer for the Core-Back Foam Injection Molding
We have demonstrated the dynamics of bubble growth and collapse in the visual observation experimental and foam injection simulator in physical foaming of molten plastics. The modified Han and Yoo model can predict the bubble size for both the situation of bubble growth and collapsed. Our modified model is promising for the application of core-back foam injection molding.
Cell Dissolution in High-Pressure Foam Injection Molding: Towards a More Efficient Packing
Packing/holding stage as one of the most important stages during foam injection molding is often overlooked in the industry. It not only influences the part’s geometrical accuracy and stability, and the residual stress distribution but also has a significant impact on the production time, machine tonnage, etc. In this work, we attempted to predict the evolution of the cell size during packing using a previously developed model. The model predicted dissolution profile was then compared with measured cell size obtained from visualized high-pressure foam injection molding. Moreover, the use of the visualization mold granted us access to characterize the dissolution time for gate nucleated cells, thereby systematically study the efficiency of each individual packing parameters (i.e. gas concentration, packing pressure, and injection speed).
Inline Cross-Linking Degree Measurement in Continuous Vulcanization of Rubber
In the production of rubber profiles, there is a risk for the processor because measured values for the actual degree of cross-linking of the extrudates are only available with a time delay due to offline measuring methods. Therefore, the aim of this work is to develop an online method which provides the degree of crosslinking in a continuous extrusion and vulcanization process. Therefore, this paper shows how the degree of crosslinking can be determined by measuring the surface temperature drop and the eigenfrequency of the profile. On the one hand, the cooling rate on the surface of a heated extrudate is used to determine the core temperature. With the help of this core temperature, the degree of cross-linking in the core of a profile can be calculated. For this purpose, temperature measurements were carried out by varying the type of heating so that a homogeneous and inhomogeneous temperature distribution was present before the cooling process. On the other hand, the eigenfrequency of differently long vulcanized test specimens was determined with a laser vibrometer and compared with the cross-linking isotherms. Since the stiffness and thus the resonance frequency of the elastomer increases with the degree of crosslinking, a correlation was found. The investigations show a basic applicability of the presented methods for an inline measurement. Further investigations are necessary to prove the evidence of the presented correlations, so that a control loop for process optimization can be established.
Comparative Creep Evaluation of Polyacetal and Polyketone Resins
Failures occurred within threaded fasteners used in an outdoor industrial application. Specifically, cracking was observed within fasteners used to terminate a pipe conveying a gaseous chemical product. The parts had been installed leak free as verified through leak testing. However, failures occurred within some of the installations between four and five years, as identified by leakage of the gaseous project. A failure analysis identified that some of the fasteners had cracked through a mechanical short-term overload mechanism in which the stresses applied during installation exceeded the short-term strength of the material. Other parts, however, cracked through creep rupture, whereby the applied service stress exceeded the long-term strength of the material. In both cases, crack propagation and ultimate rupture was associated with the creep properties of the material. A material conversion was considered to increase the creep performance of the fasteners. This paper will review the testing performed to characterize and compare the creep performance of the incumbent and proposed materials.
Investigation of Influences on The Melting of Polyethylene and Polystyrene in a Co-Kneader
The co-kneader is well known for its superior mixing performance and its exact temperature control capabilities. Therefore, it is widely used in the polymer industry for the compounding of shear- and temperature-sensitive materials. In contrast to the considerable amount of scientific work that deals with investigation, modeling or simulation of the process behavior of single and twin screw extruders there are only few studies about the co-kneader. Due to increased quality requirements and the trend for cost reduction by process optimization, this is increasingly becoming a problem for plant construction and processing companies. To address this problem, experimental investigations of the melting behavior of polymer materials in the co-kneader were conducted. In order to determine the melting degree along the extruder length a special barrel was used which can be opened in axial direction. Based on the experimental results, a theoretical consideration for co-kneaders that are operated as plastification extruders is proposed. Therefore a disperse solid melting model is used. A comparison between simulated results and experimental data shows a descent agreement, when the point of melting initiation is estimated accurately.
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