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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The Influence of Rheological Properties of the Material Formulation on the Cell Size and Cell Density of Physically Foamed Polyethylene
In this study physical foaming of low density polyethylene (LDPE), high density polyethylene (HDPE) and different blends of the two polymers was examined. The rheological properties of formulations were characterized using a cone plate rheometer to compare the influence of the used polymers. The foaming behavior was investigated by using a grooved single screw extruder with a screw diameter of 45 mm. For the experiments three different die geometries were used to show the influence of the interaction of the deformations and the rheological properties of the polymer melts. For the study azodicarbonamide, normally used as a chemical blowing agent, was used as nucleating agent and supercritical CO2 as blowing agent. The aim of this study was to determine, how the rheological properties of the material formulations influence the cell size and the cell density of the polymer foams and to find out if there are correlations between the relaxation times of the material formulations and the foam morphology. The different dies were used to show the influence of the dwell time and the flow conditions in the dies. It was shown that there is a correlation between rheological properties and the foam morphology and that it is important to use proper die designs for polymer foaming, especially for formulations with high relaxation times.
Induction Heating Simulation for the Plastic Injection Molding Process
Injection molding technology now relies on in cycle variable mold heating and cooling in order to improve the surface finish and general part quality without increasing cycle time. Induction heating has the potential to be the most efficient method for heating specific areas of the mold quickly. Induction heating results in a non-uniform temperature distribution concentrated in the surface skin of the mold body touching the part. Simulation of induction heating offers the mold designer an insight into the mechanisms of induction heating before investing in this technology. This paper describes the development of a 3D finite element based electromagnetic solver that is used in the Autodesk Simulation Moldflow transient mold cooling solver. The derivations of the relevant equations are explained as well their effects on the mold during heating. Induction heating is then demonstrated on a real world model.
Non-Destructive Inspection of Plastic Components with Terahertz Time Domain Spectroscopy
The transparency of most plastics in the Terahertz (THz) range offers great potential for non-destructive testing (NDT) of plastic components. The demand for suitable NDT rises because of the increasing substitution of metals by plastics. We present the latest results of spatially-resolved inspection of plastic components with THz time domain spectroscopy (TDS).
In previous works it has already been demonstrated that THz waves are suitable for the detection of differences in wall thickness, moisture and filler content as well as for characterizing the structure of components, or differentiate various sorts of plastics . These measurements, however, were mostly made in transmission arrangement. Hence, an access from both sides of the part is necessary. In most cases of practical application, this cannot be realized.
The non-destructive THz imaging of component properties in reflection arrangement, as the next step towards practical applications, is presented in the following. For this purpose, a specific experimental setup for imaging and special data evaluation algorithms were developed. The detection of filler content and moisture fluctuations as well as the orientation of fibers are demonstrated based on examples of industrially relevant plastics.
Stress Relaxation Study of the Development of Microstructures in Blends of Isotactic Polypropylene, Sorbitol Nucleating Angent and Silsesquioxane
Stress relaxation experiments were carried on the blends of isotactic polypropylene (iPP), dibenzylidene sorbitol (DBS) and a polyhedral oligomeric silsesquioxane (POSS) - tetra-silanol-phenyl-POSS (Tetra-POSS) in order to study the development of physical gels. Relaxation plots were discretized as a series of Maxwell elements in parallel. In order to find the minimum number of relaxation modes, the Pad‚-Laplace technique was applied to the data. It was found that the decaying part of the relaxation plot could be described by four relaxation modes. However, the Pad‚-Laplace method was unable to identify the relaxation modulus of the gel. Stress relaxation demonstrated to be a more powerful technique to understand the structure development in iPP/DBS and iPP/DBS/Tetra-POSS blends than using oscillatory shear rheometry.
Advanced Visualization of Weld Lines, Pathlines and Sink Marks for Injection Molding
The way in which injection molding simulation results are displayed is a critical factor in determining how long an engineer will spend optimizing and analyzing a part?s design. Traditional static result displays such as contour or iso-surface plots, while informative, require significant interpretation and expertise on the part of the user to be interpreted effectively. Advanced injection molding simulation, when combined with sophisticated visualization techniques such as photorealistic rendering, time based visualization and pathlines, can provide users with an enhanced understanding of surface defects such as weld lines, sink marks and surface defects.
Non-Destructive Testing of Polymer Components Using All-Electronic Terahertz Systems
This paper presents a terahertz (THz)-based measurement system that offers great potential in non-destructive testing (NDT) of plastic components. The system is all-electronic and based on radio frequency technology working similar to frequency modulated continuous wave (FMCW) radar. The measurement results show the ability of measuring material properties such as filler content or fiber orientation as well as detecting different kinds of contaminants or defects such as metal pieces or air pockets. Even time-dependent processes such as the curing of a resin are observed with the THz measurement system.
Tuning 3D Topography on Biomimetic Surfaces Produced by Microinjection Compression Molding
At present, the micro/nano topography on polymeric replica is generally limited to 2D when using a mechanical demolding approach. One-step replication of bio-inspired 3D topography is achieved using microinjection compression molding (?-ICM) with novel dual-layer molds in this work. Using a proposed flexible template, polypropylene replica topography and wettability are highly tunable. Moreover, dual-scale topography on the mold is developed by coating the micropatterned insert with submicron silica particles. Contact angle and roll-off angle measurements demonstrate that the lotus leaf, rose petal, and rice leaf effects are achieved on biomimetic surfaces using the ?-ICM process. Among the three kinds of surfaces, the petal inspired surface possesses the superior performance in self-cleaning submicron contaminants and mechanical robustness, which are highly related to the low roughness-induced adhesive superhydrophobicity and the absence of fragile submicron-/nano-structure, respectively.
Alkylation of Nanocellulose for the Improvement of Dispersion in the Polymer Matrix
Nanocellulose tends to be aggregated due to the hydrogen bonding between three of the hydroxyl groups in each repeating unit, resulting in poor dispersion in the non-polar polymer matrix. In this research, to improve the dispersion of nanocellulose particles in the polymer matrix, a long hydrophobic alkyl chain was substituted for hydrogen in the hydroxyl group of nanocellulose via a bimolecular nucleophilic substitution (SN2) reaction with alkyl bromide. The octyl (-C8H17) and dodecyl (-C12H25) groups were applied to this reaction, which is faster and simpler compared to other substitution reactions. The chemical structure of octyl and dodecyl nanocellulose was identified by the Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) analysis. The contact angle with water and methylene iodide was measured to calculate the surface energy of alkyl nanocellulose. The surface energy was decreased by the substituted alkyl chain. The thermal properties, morphology and crystal structure of octyl and dodecyl nanocellulose were also investigated to qualify the probability as a reinforcement. This research is supported by Korea Ministry of Environment. (Project No. 2013001470001).
Process Optimization ? A New Model for Calculation of the Axial Temperature Curve for Twin-Screw Extruders
When conceptualizing and setting parameters for processes on co-rotating twin-screw extruders, the axial temperature development is one of the most important factors. As determing this factor experimentally is, however, extremely time- and cost-intensive, there are many analytical and numerical models with which the temperature gradients can be calculated and/or simulated. These models reduce the experimental effort needed for parameter determination, but they can also deviate strongly from the real process.
The following article will introduce a new model for calculating the axial temperature curve. In addition to the average melt mass temperature, this model can be used to determine the radial temperature development, i.e. the change in temperature in the direction of channel depth. The model is based on an analytical equation, providing significantly faster calculation results than comparable 3D simulations. After introducing the model, the high degree of exactness in the results obtained from it, in general as well as in direct comparison to established models, will be shown by comparison with experimental investigations.
Evaluation of Long-Term Performance of GFRTP for Hot Water Supply
Glass fiber reinforced thermoplastics (GFRTP) are generally used for valves, pumps, and connecters in water heaters. GFRTP, however, are degraded in hot water with the immersion time. In this research, the tensile test and SEM observation were conducted to investigate the degradation mechanism of GFRTP. As a result, it was clarified that reduction of adhesive performance between matrix and glass fiber could be the cause of GFRTP degradation even if the high-performance engineering plastic was used as a matrix. Therefore, it is important to improve the adhesive performance. That is the reason why we are going to make the glass fiber reinforced polypropylene, which has the better adhesive performance between matrix and glass fiber.
Development of Ring Tensile Creep Test Method for Composite Pipes
The composite pipe based with polyolefin resin has recently been developed in order to obtain the higher performance for gas and water distribution. Although the stress rupture test is major test method to evaluate the long-term durability of the composite pipe, it is required to develop the new convenient and easy test method which makes it possible to evaluate the properties of the composite pipe. Therefore, in this study, the tensile creep test with a ring specimen as a new simple test method instead of the stress rupture test was suggested as a method of evaluation of the long-term performance. The results of the tensile creep test with a ring specimen were compared with them of the conventional the stress rupture test. As the results of the new test method indicated the similar tendency as compared with the conventional method, it is suggested that the new test method will have a possibility of replacing the conventional tests.
Application of Taguchi Method on Weldline Strength of Nylon6 Nanocomposites Thin Wall in Mold Decoration Molded Parts
Nylon6 nanocomposites (addition 4.0 wt% Montmorillonite) were used as molding material for thin-wall in mold decoration (IMD) injection molded part (tensile specimen with thickness of 0.6mm). The Taguchi method with L18 orthogonal array was used to determine important factors affecting weld line strength in Nylon6 nanocomposites thin-wall IMD molded parts. It was found that the significant contributing factors in descending order were melt temperature (31.66%), packing pressure (24.76%), mold temperature (13.51%), vent depth (8.43%) and injection speed (6.61%); moreover, higher melt temperature, higher packing pressure, lower mold temperature, lower injection speed and vent depth of 0.1 mm increased weld line strength for Nylon6 nanocomposites thin-wall parts when combined with 0.125 mm thick polycarbonate (PC) film.
The Effect of PBAT on the Physical Properties of PLLA Multilayer Structure Film
Poly(L-lactic acid) (PLLA)/poly(butylene adipate-co-terephthalate) (PBAT) blend films (BF) and five layers co-extruded films (MF) at a variety of compositions were manufactured from the co-extrusion process to evaluate the general physical and equivalent sound level (ESL) properties of both BF and MF. Both films were well produced with the uniform thickness. It was found that the addition of PBAT enhanced the thermal stability, and Tm of PLLA decreased. The mechanical properties such as the tensile strength and modulus revealed the decrease tendency with addition of PBAT due to immiscibility of two polymers, and the elongation at break of PLLA/PBAT BF was significantly increased as compared to that of MF. The energy transfer at interfacial area of multi-layers films under the tensile stress was found to be not efficient as compared to blend samples having matrix-domain internal structure. The addition of PBAT on PLLA had a great effect on the reduction of ESL, and it was suggested that the sound measurement technique used in this study could be utilized as a test tool for assessing the ESL.
Influence of a Substrate Bias on the Adhesion of Silicon Organic PECVD-Films on Polypropylene
Plasma enhanced chemical vapor deposition processes can be used to deposit thin films on plastics. Enhancing gas barrier performance of packages, improving scratch resistance of polymer surfaces or adhesion of subsequently applied coatings or materials are just a few fields of application of these coatings. The properties of the deposited coatings depend on the material to be coated as well as on the deposition process. During the process, a low pressure plasma is excited in front of the polymer material using monomers as a precursor. As a result, a cross-linked thin film forms on the surface. The properties of the interphase and the coating can be varied by changing the process parameters. Regarding the interphase between polymer surface and coating, an interesting parameter is the bias between plasma and substrate. In this study, polypropylene substrates are coated in pulsed microwave-excited low pressure plasmas with hexamethyldisiloxane as monomer. The bias is controlled using a second generator connected to the substrate holder which functions also as an electrode. The adhesion of the coatings is evaluated using pull-off tests in a centrifuge. Furthermore, the growth of the different coatings is analyzed microscopically. The results show that silicon organic coatings applied with a bias of -100 V have a significantly higher adhesion on the PP-substrate compared to coatings applied without an additional bias.
Improvement of Mechanical Behavior of Polypropylene Nanocomposites Varying Nanoclays and Compatibilizers
There is a significant interest in the potential for layered silicates to increase strength, toughness, thermal stability, thermal conductivity, and flame retardancy of polymers. Montmorillonite and hectorite are the most commonly used smectite-type layered silicates for the preparation of polymer nanocomposites (PNCs). The objective of this study is to evaluate the enhancement of mechanical and thermal properties of polypropylene matrices by adding various smectite based nanoclays with various compatibilizers. These PNCs were produced using the Polymer NanoComposite Injection Molding Compounder (PNC-IMC).Tensile strength and Young?s modulus were measured to evaluate the influence of different nanoclays in the PP matrices. In order to study the nanoclay dispersion and the degree of intercalation/exfoliation of the materials obtained, small angle X-ray scattering (SAXS) measurements were carried out.
Carbon Monoxide Reduced Low-Defect Graphene Nanocomposites with Poly(styrene-b-butadiene-b-styrene)
The aim was to prepare poly(styrene-b-butadiene-b-styrene) (SBS) graphene nano-composites with effective dispersion to enhance physical and mechanical properties and investigate the effect of increasing low defect graphene from 1?20 %úw/w. Graphene was produced by rapid thermal expansion using expandable graphite oxide and compared to a commercial graphene. The graphene was further reduced and repaired with carbon monoxide (CO). The matrix phase was SBS. SBS was dissolved in benzene and the graphene was ultrasonically suspended in the benzene solution. A range of analyses: Raman spectroscopy and characterisation techniques: stress-strain tensile mechanical analysis (TMA), thermogravimetry (TGA), and transmission electron microscopy (TEM) were used. CO reduction of graphene removed 84 % of oxide groups and produced the least defects (0.41 D/G ratio). Ultrasonication improved the exfoliation and dispersion of graphene. Dispersion of graphenes in SBS utilised ã-interactions. SBS physical properties improved by the addition of GT-CO: the tangent modulus increased 100 % and strain decreased 94 % as graphene loading increased to 20 %úw/w.
Prediction of Part Dimensions Using Sensed Melt Pressure and Melt Temperature and Estimated Specific Volume
A sensor stack strategy was implemented to acquire melt temperature from infrared detectors replacing ejector pins and melt pressure from a load cell located behind the pin in the ejector plate. Data from the sensor stack was used to predict the part dimensions according to a pressure-volume-temperature (PVT) model. The results indicated that the shrinkage predictions follow the same trends as the observed shrinkage, and could be used to remove issues associated with the delay and accuracy of acquiring equilibrated part dimensions in tight tolerance molding applications.
Flow Analysis of Injection Molding with Inserts or Cores Supported by Retractable Pins
Some injection molds utilize retractable pin supports of inserts. In this process the inserts are initially supported by the pins that are retracted before the melt touches them. This method is commonly used for manufacturing golf balls and similar moldings. Retractable pins can also be used for injection molds with slender cores to minimize the core shift effect.
The article presents algorithms and results of mold filling simulations that take into account movement of the inserts and cores supported by those retractable pins. The simulation is implemented as a new feature of the core shift analysis for mold filling simulation.
Model-Based Temperature Measurement for Thermoforming Applications
Thermoforming generally describes the shaping of three dimensional parts by heating a flat part (sheet) above its softening temperature and subsequently stretching it by means of a mold. The stage of heating is the crucial process step, since the sheet temperature significantly influences process stability and part quality.
In many applications, the sheet is heated in a radiation furnace  and the sheet temperature is controlled simultaneously using infrared sensors. Infrared sensors measure electromagnetic radiation and convert the measured signal into corresponding temperature values. When installed inside of a radiation furnace, the amount of measured electromagnetic radiation that is not attributed to the sheet can be significant, especially in the case when the sheet is heated from both sides and partially transparent for the heater radiation. This, in turn, causes wrong in most cases considerably inflated temperature values given by the sensors.
The aim of this paper is to present a model-based approach, which separates the electromagnetic radiation from the totally measured radiation in order to determine the sheet temperature more precisely. At first, a mathematical description of this approach with made assumptions will be given. Secondly, an experimental setup for the case of unidirectional radiation heating will be presented. This setup is used to verify the mathematical approach. Experimental results will be discussed using a polypropylene as sheet material.
Influence of Material Batch and Moisture Content on the Processing Behavior and Dimensional Stability of Phenolic Molding Compounds
Rising temperature requirements in automotive applications as well as lower target costs require materials with low production costs on the one hand and excellent thermal properties on the other. Due to their specific properties moldable thermoset materials like phenolic molding compounds appear to be an interesting alternative to cast aluminum or expensive high temperature thermoplastics such as PPA, PPS or PEEK. The scope of this paper is to investigate the suitability of such compounds for the large scale production of high-performance parts with special requirements on the dimensional stability.
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