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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Processing Fine-Celled Recyclable CBA-Based Polyolefin Foams in Compression Foam Molding
This paper focuses on understanding the technological potentials for producing recyclable polyolefin foams by using a modified technique of the conventional compression molding process, referred to as compression foam molding. A two-step compression foam molding method is being developed. The main processing feature of this method is that it allows for complete sintering of the non-foamable resin prior the activation of the CBA. First, completely sintered intermediate foamable products that have no pre-decomposed CBA particles and entrapped air bubbles are manufactured. Second, these intermediate products are used in the actual foaming process. The principal advantage of this compression foam molding method is that it produces high quality recyclable foamed structures with high volume expansion ratios by avoiding the need for cross linking.
Study of Residual Birefringence in Injection Molded Lenses
Injection-molded lenses have been widely employed for 3C products more recently. In this paper, 3D CAE flow analysis embedded with DOE methods have been adopted for studying lenses molded with cyclic-olefin-copolymers together with residual birefringence measurements. In addition, thermal annealing experiments have been performed on the relaxation effects on thermal history for further studies. Results have shown that shear stresses as birefringence are contributed by melt temperature and injection speed during filling; while, dimensional errors on optical surfaces of lenses have been influenced by melt temperature and holding pressure during the packing and cooling.
Screw Element Characterization in an In-Line LFT-D Process
Studies have been done on three different elements (mixing element and kneading blocks) to determine their influence on fibre length and wetting properties during an in-line direct compounding process using glass fibre with PP at a nearly constant specific output. Effects of individual elements could be ascertained by using only 6D length of the barrel. At 30wt% loading, the screw element geometry plays a dominant role in fibre length distribution. At 50wt% loading, fibre length is influenced mainly by the screw speed. SEM analysis results of the samples are provided. Characterization of the individual type of elements can be used as guidelines in future application.
A Compressible Model for Three-Dimensional Melt Filling and Gas Penetration in Gas-Assisted Injection Molding Processes
The numerical prediction of three-dimensional melt filling and primary gas penetration in a clip-shaped square tube is conducted using compressible models in this paper. Similar to other fully three-dimensional methods, the full Navier-Stokes equations are solved together with the front transport equation using a front capturing approach. Different from previous studies assuming incompressible fluids in the filling process, the gas compressibility is considered in the proposed compressible model. For the case of a clip-shaped square tube, the gas penetration length and gas core size are compared among numerical predictions and experimental measurements, where a 3D Hele-Shaw model is also presented. The proposed compressible model has much better prediction accuracy than the 3D Hele-Shaw model. The proposed compressible model in the present study is proven to be accurate in the three-dimensional simulations of melt filling and primary gas penetration problems.
Three-Dimesional Simulation of Injection-Compression Molding Process
A numerical model for the fully three-dimensional simulation of melt filling in an injection-compression process is proposed in this paper, where a moving grid strategy is employed. Similar to other fully threedimensional methods, the fully three-dimensional Navier-Stokes equations are solved together with the front transport equation using a front capturing approach. To avoid the difficulty in specifying gas outlet required by SIMPLE-type algorithms with incoming melt, the escape of air is modeled through source terms described by a compressible model. Filling predictions of a lens part are conducted to demonstrate the advantages of proposed scheme in simulating injection-compression processes. After conducting several computations under different processing conditions, the proposed numerical model in the present study is proven to be promising in the three-dimensional melt filling simulations of injection-compression problems.
Study on the Mixing Ability of Different Mixing Elements in Co-Rotating Twin Screw Extruder
The mixing abilities of the normal screw element, kneading disc element and rotor element were studied. Based on the molding of the 3-D isothermal non-Newtonian flow field, the speed field, shear rate field and pressure field were obtained. The residence time distribution, average shear rate and shear rate distribution of certain percent particles vs. time were acquired. The results show that the kneading disc element provide more dispersive mixing behavior, the rotor element achieves both good dispersive and distribute mixing effects and the normal screw element has the better conveying ability. And the results of experiments correspond well with the numerical analyses.
Mechanical Properties and Morphology of PMMA Grafted Silica/PMMA Injection Molded Composites
Micro- and nano-scale silica particles filled poly (methyl methacrylate) (PMMA) composites were prepared using high shear compounding and thin-wall micromolding. Mechanical performances of the composites were elucidated through tensile tests and internal structures of fractured surfaces were obtained from microscopic observations. The incorporation of silica particle has raised the tensile modulus of all specimens irrespective of processing conditions. Distribution of micro-fillers in the molded specimens was preferential towards the end side than the gate and center sides. Nano-filler particles were dispersed uniformly in most parts of the specimen while boundary separations between filler and matrix could be observed at the skin layer in micro silica filled PMMA. This led to an assumption that there was better filler-matrix adhesion in nano-filler composites than in micro-filler composites.
Numerical Simulation on Intermeshing Counter-Rotating Twin Screw Extruder with Pin-Barrel
The 3-D isothermal non-Newtonian flow field of intermeshing counter-rotating twin screw extruder with pin-barrel was researched. The pressure field, viscosity field and shear rate field were attained and analyzed. Statistic analysis are applied on the dynamic flow field simulation of intermeshing counter-rotating twin screw extruder with pin-barrel and without pin. Based on the above simulation, statistic methods have been introduced to calculate the RTD and max shear rate distribution. The results have showed intermeshing counter-rotating twin screw extruder with pin-barrel provides better distributive mixing than intermeshing counter-rotating twin screw extruder without pin.
True 3D Simulation of Flow-Induced Residual Stress in Injection Molding
Flow-induced residual stress has been one of the essential issues in plastics injection molding. It affects many physical properties of the finished parts, such as warpage behavior and optical properties. Flow-induced residual stress is caused by the high shear rate of plastics flow during filling, and can be relaxed or frozen during the post-filling process and after ejection. Furthermore, flow-induced stress of non-transparent or complicated parts can't be easily measured by experiment. In this paper, we incorporate viscoelastic models in an integrated three-dimensional numerical approach to predict flow-induced residual stress in injection molding.
A Novel Approach for Predicting Birefringence of Optical Parts
Plastic optical parts or components have been used in many industrial applications, such as optical disks, lenses, and waveguides. For the development of optical products, the control of birefringence is crucial. Basically, it is dependent on optical characteristics of material and global features given by polymer processing. However, the prediction and control of birefringence is difficult. In this study, a novel approach for the prediction of birefringence distribution of injection-molded parts is developed by the 3D simulation technology, which incorporates photoelastic analysis and viscoelastic mechanics.
High Molecular Weight (MW) Nano Sized Polyethylene (PE): Effect of Particle Size, Macro-Micro-Nano
The high MW PE with average particle size of 60 nm was synthesized using Ziegler-Natta catalyst. The AFM, SEM and TEM studies showed that PE nanoparticles were spherical in shape. Structure and crystallinity were concomitantly studied through FTIR and XRD. It shows nanospherical PE particles are more crystalline (~75%) compared to macrosized PE (~59%). The mechanical properties and surface roughness were also evaluated through AFM. At last the properties of nano sized PE were compared with micron and macro sized particles.AFM studies show the Young's modulus of nanosized PE particle varies from 1 to 1.4 GPa whereas for macro sized PE its varies from 0.6-0.7 GPa.
An Investigation on the Temperature Behavior in Mold Embedded with Heater
Conventionally, a mold is to be cooled by cooling channels in an injection molding process. However, the demand for the high quality plastics has popularized the varied-thermo control of mold system. An electrical heater system is one of the popular heating methods used in varied-thermo type methods for its low cost and ease of use. To achieve good efficiency, the system layout and the switchover between heating and cooling have to be properly designed and optimized. In this study, a true 3D fully transient approach is proposed to simulate the temperature behavior of mold embedded with heater. Furthermore an experimental apparatus is also set up to measure and verify this transient behavior.
Apatite-Poly(Ether Etherketone) Nano Composites: Prosthesis Materials: SBF-Conditioned Study
A prosthesis material using calcium phosphatespoly( ether etherketone)thermoplastic nano composite was developed. The nanosized calcium phosphates were synthesized by sol-gel technique. The biocompatibility test was carried out by SBF-conditioned study using freshly prepared simulated body fluid (SBF) at a temperature of 25-40°C and pH of 6.5-7.7. XRD was used to see the crystallinity and composition. The morphology and component distribution were performed by OM, SEM, AFM, etc. The functional groups present in composite materials were evaluated by FTIR. The growth study of SBF crystal was carried out by OM and XRD. The porous microsphere of HAp-PEEK composite was observed in SEM.
Characterization of Polycarbonate/Polyethylene Terephthalate Blends Undergoing Transesterification
In this work, transesterification in polycarbonate/ polyethylene terephthalate blends annealed in the melt at 300°C is discussed. The reaction initially proceeds by formation of a high molecular weight block copolymer. Degradation of PET, or PET-segments, appears to be an important contributor to transesterification. Randomization of PC and PET structures during annealing was also observed in our NMR spectra. SEM showed phase coarsening occurred during annealing and FTIRmicroscopy confirmed that 2 distinct phases, namely “PCrich” and “PET-rich”, still persisted after 60 minutes at 300°C.
Helibar® – a Powerful Single Screw Plasticizing System
A single-screw-extruder is presented, consisting of a barrel with grooved feed zone (helical grooves), a grooved melting zone (axial or helical grooves) and a barrier-screw with mixing and shearing elements. Compared with extruders with a smooth melting zone, significant process improvements are achieved regarding mass throughput, pressure build up, melt temperature, melt homogeneity, feed-zone cooling, processing wall-slipping polymers, abrasive wear, residence time, total degree of efficiency and economy. The processing principles of the new extruder are explained. Experimental results confirm the theoretical predictions. The system has proven to be very worth wile in more than 500 extrusion blow molding machines and other extrusion and injection molding applications since the year 1999.
Environmental Stress Crazing in Polystyrene: The Roles of Chain Length and Architecture in Craze Initiation
This work aims to assist in optimising the solid state performance of polymer products, by developing an understanding of the molecular factors involved in initiation of environmental stress crazing. Experiments measuring craze initiation stress in miniature rectangular beam samples saturated in diethylene glycol were performed on 26 isotropic atactic polystyrenes with molar mass from 66 kD to 1148 kD, including a wide range of monodisperse linear and branched materials. Results indicate that both solid-state molecular disentanglement and chain scission play roles, depending on the chain architecture and length of the polymer. A simple rule is suggested for predicting ESC raze initiation in polydisperse polymers.
The Influence of Fibre Length and Concentration on the Properties of Sisal Fibre Reinforced Polypropylene Composites
In this work we investigated the influence of length and concentration of sisal fibres in PP for injection moulded composites. The fibres were incorporated into the matrix with a co-rotating twin screw extruder, in order to get the different compounds, which were injection moulded subsequently. The actual fibre length was determined after an extraction with xylene. Tensile strength and modulus and Charpy impact properties were measured and the flow curves were recorded with a capillary rheometer. The results show good correlations with the fibre length of the composites, and the tensile strength as well as the notched Charpy impact strength can be evaluated using rule-of-mixture like models.
Sandwich Injection Molding of Polypropylene and Biodegrable Polymer
Polypropylene (PP)-based sandwich injection moldings with biodegradable polymers in the core were carried out. A compatibilizing agent and high flow PP were used as modifiers to improve interfacial adhesion between the skin and the core. In order to investigate the interfacial strength between the skin and the core, 180o peel test was conducted whereby the skin was peeled from the core. It was found that the interfacial strength between skin and core was improved by incorporation of modifiers, whose functions were understood by the morphological observation. From the combination of sandwich molding and polymer alloying technologies of this study, the possibility was derived to make products composed of PP and biodegradable polymer.
Generating Alternative Time and Energy Saving Processing Concepts for Rotational Foam Molding
The nature of the rotational molding process is cyclic. It requires the temperature of the rotating mold and the plastic it is charged with to be elevated from room temperature to beyond its melting temperature and then cooled back to room temperature. Consequently, rotational molding cycle times are lengthy, which is often considered as the fundamental drawback of this plastic fabrication process. The motivation and objectives of this paper are twofold. First, the presently proposed research focuses on developing an innovative processing technology for the manufacture of integral-skin cellular composite moldings having adjacent, but clearly distinct, layers of non-cellular and cellular structures, consisting of identical or compatible polyolefin grades. Its primary goal is to significantly reduce the processing cycle time in comparison with respective currently implemented technologies.
Analysis and Validation of Mold Design Guidelines for Cooling Time and Runner Sizing
Injection molds have been designed over the years using rules of thumb" which have become almost standard guidelines in industry practice. This paper analyzes and validates two common guidelines for 1) estimation of cooling time and 2) determination of runner sizing. The common guideline for cooling time estimation is compared to the analytical solution of the heat equation and found to have a small average error but significance variance across material properties and processing conditions and validated against industry data. A common guideline for runner system design was found to provide very good results compared with optimal designs produced with the Hagen-Pouiselle flow equations."
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