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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In this work, 1.5D film casting membrane model proposed by Silagy et al. (Polym Eng Sci 36:2614-2625, 1996) was generalized considering single-mode modified Leonov model as the viscoelastic constitutive equation and energy equation coupled with crystallization kinetics taking temperature as well as stress induced crystallization into account. The model has been successfully validated for the linear isotactic polypropylene by using experimental data collected under extremely high cooling rate processing conditions (86°C/s), which were taken from the open literature. It has been found that utilization of flow induced crystallization significantly improves model predictions, especially for the film temperature and crystallinity. The model was consequently used to understand the role of heat transfer coefficient on the neck-in phenomenon as well as on the film velocity, temperature and crystallinity profiles.
Linear low density polyethylene (LLDPE) cast stretch films were produced to evaluate the effects of line speed, air gap, frost line and film thickness on the morphology of the prepared films. Surface morphology of the films were observed using scanning electron microscopy (SEM). It was found that the most effective parameter on the surface morphology of the films is line speed followed by air gap. In addition, relaxation behavior of LLDPE resins was investigated using rheological measurements. For the films with similar thicknesses but prepared at different line speeds the time scale for the melt to relax was correlated with the crystal phase development in the films, which affected the microstructure and crystalline morphology of the films.
The use of thermoplastic based fiber reinforced materials in demanding structural applications concerning long-term loading in combination with elevated temperatures and media influences requires comprehensive but experimentally practicable materials characterization. While for the long-term estimation of the time dependent deformation behavior a number of extrapolation methods for creep and creep rupture characterization is available, most of these methods are still rather time consuming. An useful approach for time-efficient creep characterization is the stepped isothermal method (SIM), which primarily was established for fiber and textile materials [1, 2]. The first goal of the present paper was to investigate the applicability of SIM for glass fiber reinforced PA6.6 and PPA materials in the saturated wet state. For this purpose, a specific media cell with an integrated deformation measuring system was built up for creep tests under water immersed test conditions for standard tensile test specimens. Based on the stepwise increased test temperature, the creep deformation was accelerated and subsequently used for the creation of creep modulus master-curve generation in accordance to SIM. Generally, plausible results for the time dependent creep modulus of the materials at 60 °C in wet state were obtained, also in good agreement with the corresponding short-term Young´s modulus values. Further on, a new methodical approach for the estimation of the long-term creep rupture behavior was developed. The established stress rate accelerated creep rupture test method (SRCR) allows for very time-efficient creep rupture estimation based on a series of stress rate dependent tests at various initial load levels. In the present study, this method was successfully implemented on glass fiber reinforced PPA materials. The time dependent creep rupture strength was obtained over a time range up to more than 5 years, also in good agreement with the results of additionally performed conventional creep rupture tests.
Barrier melting sections are extremely common and useful for single-screw extruders. Some common mistakes in their design and operation, however, can reduce their performance. A common mistake when attempting to decrease the discharge temperature for a single-screw extrusion process is to decrease all barrel temperature zones. This method, however, can cause the specific rate of the extruder to decrease for screws that use barrier melting sections. This paper will describe the problem, provide laboratory extrusions that demonstrate the problem, and then provide a case study.
Accelerated aging is used throughout the Medical Device sector and other sectors to evaluate materials and devices in an accelerated fashion. Accelerated aging has several typical modes, depending on the type of materials and functional mechanisms involved. One mode is related to stress relaxation and creep, which impacts the function of parts under sustained strain or stress as well as influencing time to develop cracks. This paper explores viscoelastic behavior of moderate melt flow medical grade polycarbonate as related to accelerated aging. The relationships between stress relaxation, creep, and complex modulus (as a function of time and temperature) are discussed. An example demonstrating the correlations between stress relaxation, creep, and Dynamic Mechanical Analysis (DMA) master curve data for a medical-grade polycarbonate is provided. Additionally, Q10 factors as intended for accelerated aging are estimated for stress relaxation of medical-grade polycarbonate using DMA master curve results. Accelerated aging is used throughout the Medical Device sector and other sectors to evaluate materials and devices in an accelerated fashion. Accelerated aging has several typical modes, depending on the type of materials and functional mechanisms involved. One mode is related to stress relaxation and creep, which impacts the function of parts under sustained strain or stress as well as influencing time to develop cracks. This paper explores viscoelastic behavior of moderate melt flow medical grade polycarbonate as related to accelerated aging. The relationships between stress relaxation, creep, and complex modulus (as a function of time and temperature) are discussed. An example demonstrating the correlations between stress relaxation, creep, and Dynamic Mechanical Analysis (DMA) master curve data for a medical-grade polycarbonate is provided. Additionally, Q10 factors as intended for accelerated aging are estimated for stress relaxation of medical-grade polycarbonate using DMA master curve results. Accelerated aging is used throughout the Medical Device sector and other sectors to evaluate materials and devices in an accelerated fashion. Accelerated aging has several typical modes, depending on the type of materials and functional mechanisms involved. One mode is related to stress relaxation and creep, which impacts the function of parts under sustained strain or stress as well as influencing time to develop cracks. This paper explores viscoelastic behavior of moderate melt flow medical grade polycarbonate as related to accelerated aging. The relationships between stress relaxation, creep, and complex modulus (as a function of time and temperature) are discussed. An example demonstrating the correlations between stress relaxation, creep, and Dynamic Mechanical Analysis (DMA) master curve data for a medical-grade polycarbonate is provided. Additionally, Q10 factors as intended for accelerated aging are estimated for stress relaxation of medical-grade polycarbonate using DMA master curve results.
In this work, the 3-D porous hydroxyapatite (HA)-modified polyurethane (PU) scaffold successfully fabricated by using simple ultrasonic assisted method. The hydrophilcity, water absorption and mechanical properties of HA-modified PU scaffold were significant higher than those of PU scaffolds. Compared with PU scaffold, the addition of HA nanoparticles could effectively improve the attachment and growth of human umbilical vein endothelial cells (HUVECs) cultured on the HA-modified PU scaffold. These results suggest that HA-modified PU scaffold possesses a great potential to be used as tissue engineering scaffold and the ultrasonic assisted technique could be a simple, effective and universal method to decorate the tissue engineering scaffold.
This paper presents a study about the effects of material properties on the modeling of the microcellular injection molding process. In particular, the effects of gas solubility and diffusivity data on the simulation results were examined. Often, actual measured data are not available for these properties. The effectiveness of using a generic equation to estimate these values has been evaluated by comparing the simulation results from this to a simulation that uses the actual measured data. The study indicates that by properly using these estimated material properties data, meaningful simulation results can be obtained.
Computer simulation to model the manufacturing as well as the performance of plastic part requires a good understanding of the material properties at the representative conditions. The same material behaves differently during different processes, e.g. extrusion is a shear dominated process, while thermoforming is elongation dominated. Additionally, viscoelastic effects may be relevant to capture since they control the amount of die swell depending on the geometry and process conditions. Additionally, plastics are also non-linear materials and exhibit non-linear stress-strain behavior that can possibly be rate dependent as well. This paper is a review highlighting the different processes that have been modeled before and the different material models that are required for a successful simulation will be discussed. The following case studies will be used to highlight the material models; catheter extrusion, tray thermoforming, and catheter kinking.
In this study, agricultural proteins were compounded into synthetic isoprene rubber (IR) and sulfur-cured. A constant filler loading of 8 parts per hundred rubber (phr) was used to evaluate the reinforcing capabilities of two full proteins, i.e., corn zein (Zein) and gliadin from wheat (Gd), a hydrolyzed protein, i.e., trypsin hydrolyzed gliadin (THGd), and a neat amino acid, i.e., arginine (Arg). Cure meter testing, tensile testing, and swelling experiments were performed to assess the curing kinetics, Young’s moduli (E), hysteresis, and crosslink densities of the vulcanizates. The filled vulcanizates exhibited comparable or higher E and [X] than an unfilled IR Control, but slower curing kinetics. The hysteresis, or unrecoverable mechanical energy, decreased with increasing elongation in the filled vulcanizates, which was opposite the behavior of the IR Control.
This paper presents the design and development of a chassis mounted pick-up truck front bumper for the 2018 Ranger Raptor which meets pedestrian safety performance. Truck bumpers are traditionally made of steel to meet customer expectations of a durable vehicle capable of suitable crash protection performance, firmness of feel and rugged styling. Pedestrian safety performance is increasingly becoming a regulation for the sale of vehicles in selected markets around the world.A traditionally mounted steel bumper does not have suitable energy absorption to meet this regulatory requirement. The bumper developed by Ford of Australia uses sandwich plastic bumper fascia with a steel support structure to meet the conflicting requirements of a soft front for pedestrian protection and a solid substructure to meet low speed crash requirements including static and dynamic stiffness for durability.
In this work, neat polypropylene (PP) foam boards was produced under different saturation pressure and foaming temperature by using supercritical CO2 as a blowing agent in an industrial-scale batch foaming system. In addition, the effort was made to prepare for flame-retardant PP foam samples by introducing a basic magnesium sulfate whisker (MSW). The preliminary results showed that with addition of MSW, PP composite samples have increased Limiting Oxygen Index (LOI) and increased tensile property. As the increase of amount of MSW, the average cell sizes of PP foams have little change but the cell densities were decreased thus the volume expansion ratios were decreased as result. To obtain low-density flame-retardant PP foam products, systemic study on the foaming condition on cell morphology need be conducted.
In this work, polypropylene (PP) reinforced with cellulose filaments (CF) nanocomposites were studied. Nanocomposites with CF loadings ranging from 0 to 30 wt% were produced by melt extrusion and characterized. Rheology using Carreau-Yasuda with yield stress model was used to estimate the dispersion state of CFs and showed that a suitable dispersion was achieved. Tensile tests were conducted to study the mechanical behavior of the materials. Results showed that nanocomposites with a higher rigidity can be obtained when a suitable dispersion is achieved, however, those nanocomposites are consequently more brittle.
In recent years, injection molding has become a common polymer molding process in the plastics industry. Injection molding can produce products which have complicated shapes, and offers high efficiency and productivity with low cost. However, uneven volume shrinkage during the injection molding process will cause deformation after demolding and poor product roundness. To find the best approach, this study focused on round products under different molding conditions, including melt temperature, mold temperature, and injection speed. CAE simulation was used to identify the effect of different fiber content and molding conditions on product roundness. Results showed that the roundness of PC material products without fibers was better than those with fibers. Moreover, those which contained more fibers exhibited lower dimensional stability. The uneven shrinkage and variations in roundness were caused by the different fiber orientations in the product. Changing the position of the gate improved the uneven shrinkage caused by fiber orientation. Furthermore, raising the mold temperature also improved the roundness of the product.
Discontinuous fiber reinforced thermoplastics materials combine the process related advantages of injection molding with the enhanced mechanical properties of fiber-reinforced plastics. Since the mechanical properties of FRPs are dependent on the fiber length, long fiber reinforced thermoplastics (LFT) offer a huge potential for lightweight design. In order to analyze the influence of the fiber length and orientation on the stiffness and strength of LFT under high strain rate loading, the authors conducted tensile impact tests as well as part impact tests. Thereby, polypropylene (PP) specimens with different fiber length were analyzed. It can be shown that the influence of the fiber length on the strain rate behavior can be neglected compared to the influence of the fiber orientation. Furthermore, a first implementation to describe the strain rate-dependent material behavior of LFT is presented.
There is an often ignored correlation between mechanical and chemical stress in plastics parts, which is very time- and cost-intensive to test. The model that was developed in this research allows the prediction of the mechanical properties of fiber-reinforced amorphous thermoplastics under media influence. The media influence is taken into account by the modulus of elasticity of the matrix, which is determined by a molecular dynamics simulation. The results correspond well with the tests for polycarbonate after storage in distilled water. An acoustic emission analysis shows an influence of the medium on the damage behavior of the fiber-reinforced samples during the test. The media storage results in significantly more acoustic emissions during the test. This indicates damage already during the test and not just shortly before the break.
The characteristics and the quality of a blown film are strongly influenced by the stretching and simultaneous cooling of the molten polymer within the bubble formation zone. Moreover, the output rate of the process is generally limited by the cooling rates and the stability of the bubble. As a consequence, the design of cooling systems is highly relevant in terms of process optimization. Beside intensifying the heat removal, the concept of secondary air cooling aims at eliminating unsteady ambient influences during bubble formation and increasing bubble stability. Different concepts for cooling systems with integrated secondary air cooling are presented and experimentally tested. The results confirm that the implementation of secondary air cooling is feasible and generally supports bubble cooling regarding the aforementioned intention. Furthermore, the study reveals that an accurate design of such cooling systems is required.
In this study, adhesive metal-polymer composites were investigated using pretreated aluminum substrates, each with an adhesion-promoting powder coat, a thermoplastic urethane elastomer (TPU) stress-compensation layer and a polyamide 6 top coat to allow further functionalization. One of the composite’s key features is the powder coating, which acts as a reactive adhesive agent and possesses a high-quality surface finish and very good formability. The composites were examined in terms of shaping and assembly behavior. The interfacial bonding was investigated using a peel test. Finally, a demonstrative part was manufactured for the automotive-interior sector.
Poly(methyl methacrylate- co- trimethoxysilyl)propyl methacrylate)(P(MMA-co-TMSPMA), and a chain extender, Joncryl ADR 4368 were used in this study. P(MMA-co- TMSPMA) copolymers were prepared by dispersion polymerization using a azo initiator with different TMSPMA content. The effect of the chain extender and/or P(MMA-co-TMSPMA) blends on the properties were investigated. The thermal and mechanical properties were analyzed with a differential scanning calorimeter, rheometer, and universal tensile machine. The crystallinity of the blends was found to be decreased while the complex viscosity increased. The results of the mechanical properties revealed that the addition of chain extender have an effect on increasing the tensile strength. Joncryl system increased molecular weight by forming a long chain branching structure for PLA blends. Also, it was found that the incorporation of the chain extender could enhance the degree of P(MMA-co-TMSPMA) dispersion.
Although modern injection molding machines allow operating processes resulting in high part quality and low reject rates, there are still external influences such as fluctuations in the material properties that may cause the production of reject parts. These are often detected with a time delay, which entails high costs. Hence, quality forecasting or control based on process data would be desirable. However, existing approaches did not yet prevail in industrial applications for several reasons. Therefore, supervised machine learning approaches may not always be applicable. Based on previous, univariate approaches aiming to overcome the limitations of the standard process monitoring with its fixed tolerance limits, this paper presents a procedure for multivariate anomaly detection in injection molding process data using cluster analysis as a means of unsupervised machine learning. The procedure allows detecting critical process states in real time and thus lays the foundation for root cause analysis and holistic process optimization.
In industry wear-prone components of injection molding machines are usually replaced by specified maintenance intervals. On the one hand, often these components are replaced too early, so the component service life is not utilized to full capacity. On the other hand a failure causes time-consuming and costly production downtimes. Thus, applications for predictive maintenance of wear-prone components are highly desired by injection molding machine manufacturers and users. Based on this, the present paper describes a procedure to use production planning data available in injection molding production to predict the service life of machine components, resulting in increased machine uptime while reducing storage and maintenance costs.
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