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 Study on the Cell Size and Cell Density Distribution in Microcellular Injection Process with Dynamic Mold Temperature Control Assistance Technology
MuCell® (Microcellular injection molding) is a well-known green molding technology, but the surface defects are the common limitation for its application. Nowadays, the cosmetic drawback of MuCell® process could be resolved via high mold surface temperature and gas counter pressure control. The purpose of this study is to realize the correlation of cell size and density between microcellular injection molding in different mold temperature and composite mold inserts (M333, QC-10 and M333 combination, and QC-10). The numerical approach was also discussed with Moldex3D. In the experimental results of rapid cooling between three kinds of mold-insert design, the QC-10 insert has the best cooling efficiency to achieve 10 °C/sec. When the initial mold temperature was set at 120 °C, the average cell size can also be reduced from 192.92?m, 123.95?m, and 84.97?m, with the cooling rate 1.1°C/sec, 5.1°C/sec, and 10.9°C/sec individually. The DMTC (dynamic mold temperature control) was proved that it not only improves surface quality of product but controls the cell quality in microcellular injection molding effectively.
Investigation on the Powder Concentration Distribution and Surface Quality for Metal Injection Molding
Metal powder injection molding (MIM) is the combination of conventional injection molding and powder metallurgy process. Through de-binding and sintering after molded by high-precision mold, metal injection molding can allows complex parts to be shaped at once and in highly mass production. Most of the MIM studies focus on the binder they used for feedstock but the research of the processing and solving the defects such as shrinkage, warpage and black line was lacked. In this study, the objective is to discover the surface defects caused by powder-binder separation and verified by numerical approach. The results show that the optimum molding parameters when injection speed is 80mm/sec and mold temperature is 40°C has the best surface quality which powder and concentration difference of binder can be reduced from 45.33% to 2.73%.
Injection Molding of Ultra High Flow Elastomers
The injection molding process parameters and the elastomeric components play a major role on the final properties of the injection molded parts. In this paper, a Design of Experiment (DOE) was used to investigate the effect of injection molding process parameters and the molecular weight of the elastomer on the properties of the injection molded parts. It was observed that dry blending of a low molecular weight/low viscosity polyolefin elastomer with a polypropylene random copolymer (RCP) in an at-press injection molding process, significantly improved the dispersed morphology of the elastomer domains in the continuous matrix phase. Therefore, the parts made with a blend of 200 MI, 0.870 g/cc ethylene-octene copolymer and a 20 MFR polypropylene random copolymer had a finer dispersed morphology than the parts made with a 5MI, 0.870 g/cc ethylene-octene copolymer which is difficult to disperse into the RCP matrix. As a result, the fine dispersion of low molecular weight elastomer (200MI, 0.870 g/cc) in 20 MFR RCP resulted in good impact strength. Another improvement was observed in the weld-line strength due to the homogeneity of the elastomer domain in RCP matrix.
A Method to Characterize Blowing Agent Concentration Effects during Polymer Processing
During processing of foamed polymer products, variations in the mix of the polymer powder and blowing agent (BA) can lead to unpredictable thickness and porosity in the final product. Alterations can result from non-homogeneous mixing, due to broad ratios of particle size of polymer powder and BA. This paper evaluates methods of determining blowing agent composition in PVC powder mixtures. Quantifying small ranges of BA content (1-2%) in PVC compound yields higher costs and challenges in the characterization when tested through standard methods. Such methods include TGA and DSC. This is mostly because they are based on mass determination. A method for quantifying such small concentrations based on determining the volume of gas-released was developed; this volume is the gas that does not dissolve in the solid. It can be assumed that the solubility of the gas in the solid is constant, therefore the free gas volume would be constant for a specific concentration of blowing agent. From this point gas volume will refer only to free gas or undissolved gas. Volume changes in blowing agents are two orders of magnitude higher when compared to mass changes. In this method the volume of free gas released during foaming formation is quantified and related to the amount of BA. This technique can address quality control and process tuning in the field of foaming powder blends.
Hierarchically Porous Polymeric Materials from Ternary Polymer Blends
Hierarchically porous polymeric materials with controllable pore size were successfully generated through a ternary polymer blending strategy. Polylactide/highdensity polyethylene/styrene-ethylene/butylene-styrene copolymer (PLA/HDPE/SEBS) was used as a model system to demonstrate this technique. After melt blending, the SEBS was driven into the HDPE phase owing to the presence of the PE block in the copolymer. With proper volume fractions of HDPE/PLA/SEBS (e.g., 25/50/25), a bi-modal, dual co-continuous morphology was obtained and hierarchically porous polymeric materials were further generated by selectively removing the PLA and SEBS phases. Annealing and composition variation were further employed to control the pore size and it is shown that the length scales, for each of the two co-continuous morphologies, can be controlled independently.
Radiopaque Filler Enhances Nanocomposite Catheter Shaft Performance
Nylon 12 and polyether block amide nanocomposites are being used to stiffen catheter shafts. Montmorillonite clay is the filler of choice to make the nanocomposite. Typically the construction is a dual layer where one layer is the nanocomposite and the second layer is a radiopaque layer. We are evaluating the possibility of combining radiopaque properties along with the nano fillers to enhance strength as well be visible under fluoroscopy. Our study is also aimed at looking at the effect of particle shape of the radiopaque filler on the final properties of the material. We want to evaluate if synergy exists between the nano particles and radiopaque fillers to further enhance the physical properties of the material.
Strain-Induced Crystallization, Structure, Orientation and Thermal Property of Polypropylene Film during BOPP Process with Sequential Stretching
Biaxially Oriented Polypropylene (BOPP) films prepared with a laboratory film stretcher KARO IV were studied by Small-Angle X-ray Scattering (SAXS) and Differential Scanning Calorimetry (DSC) in order to understand the crystal orientation, structure and crystallinity at processing temperatures, and to differentiate crystals induced by stretching and cooling processes, respectively. The present study shows that stretching in partially melt state can promote Shish-Kebab structure due to significantly less chain relaxation. Annealing at a higher temperature before stretching in Transverse Direction (TD) can lead to appreciably higher crystal orientation, presumably due to the melting of smaller crystals which were less oriented initially. Orientation of BOPP films at room temperature can be very different from its orientation in partially melt state which is more related to shrinkage property. The crystallinity of the partially melt polypropylene (PP) can be evaluated by DSC together with SAXS. Stretching induced crystals are larger in size and have significantly higher melting point than crystals formed during a cooling process.
Importance of Processing and Converting Conditions on the Use of Carbon Nanotubes in Thermoplastic Applications
In recent years, multiwall carbon nanotubes (CNTs) have progressively captured wider industrial acceptance as an alternative to deliver electrically conductive materials. Currently, CNT-containing polycarbonate (PC) is widely used in the manufacture of integrated circuitand hard disk-trays. In this work, the influence of the extrusion parameters in an industrial environment on the dispersion of CNTs in PC was investigated in details. In addition, the effect of injection molding parameters on electrical conductivity, surface quality and mechanical properties is investigated. Under optimized extrusion conditions, the PC-CNT compounds displayed remarkable electrical conductivities (0.5 x 10-3 Siemens.cm-1) at only 1 wt% loading.
Effect of Different Coupling Agents and Chemical Treatments on the Mechanical Properties of Polypropylene-Rice Husk Composite
In this study, rice husks and polypropylene were applied as the fibers and matrix polymer to make natural fiber composites (NFCs). Polypropylene grafted maleic anhydride (PP-g-MA) and styrene ethylene butadiene styrene graft maleic anhydride (SEBS-g-MA) were used as coupling agents. In addition to coupling agents, rice husks were treated with NaOH, silane and NaOH+HCl+silane.alkaline or silane to enhance the effect of coupling agents. The results showed that adding both PP-g-MA and SEBS-g-MA improved the mechanical properties of composite significantly. In addition, an optimized ratio of coupling agents was found. On using a combination of 2 wt % PP-g-MA and 1 wt % SEBS-g-MA, the impact strength of the composite increased significantly, but the tensile strength and modulus were not reduced to any appreciable extent relative to the use of PP-g-MA alone. Finally, all of the three treatments improved impact strength of the composites.
Internal and Free-Surface Viscoelastic Flow Simulations Using the Corotational Maxwell Constitutive Model
Understanding and modeling of viscoelastic fluid flows is essential for several industrial applications. Simulations of internal viscoelastic flows as well as of viscoelastic free-surface flows are quite complex and it is necessary to utilize advanced material models. This work focuses on the study of the Corotational Maxwell constitutive model which is implemented in the viscoelasticInterFoam solver developed with the OpenFOAM computational fluid dynamics package. Simulations of viscoelastic secondary flows in a square channel are presented and validated with experimental results. This is followed by a viscoelastic free-surface flow application to simulate a process developed within the Polymer Engineering Center that uses a microcapillary die for the production of micropellets.
Improvement of Thermal Stability of PVC Plastisol Dip Molding Products
Electrical insulator products used in the automotive and electronic industries are made from polyvinyl chloride (PVC) plastic using dip molding process. The thermal stability of the insulators is less than 90 °C which limits the application. The addition of additives to increases the thermal stability of polymers but the softness of the products decreased. This research aimed to study the additives which will increase the thermal stability of the PVC products but maintains the softness of polymers. The PVC plastisol type PG-740 with organic plasticizer, TOTM and AC-256 as stabilizer showed standard physical properties and good thermal stability at 180 °C for 45 min.
Friction Riveting of Pultruded Thermoset Glass Fiber Reinforced Polyester Composite and Ti6Al4V Hybrid Joints
The challenge of the present work is to apply the innovative joining technology Friction Riveting for pultruded glass fiber reinforced thermoset composites for emergency bridges. Pultruded glass fiber reinforced polyester plates and Ti6Al4V rivets were used in this work. Adequate levels of deformation at the tip of the rivet inserted into the composite plate led to good anchoring of the rivet. The correlation between joining parameters, energy input, process temperature and rivet deformation was studied. Two affected zones could be observed in the composite: the polymer heat affected zone and the polymer thermal mechanically affected zone which consists of two distinct parts, the partially and highly degraded. The maximum average ultimate lap shear force achieved for the selected conditions was 6.7 ± 1.6 kN,indicating the potential of Friction Riveting as an effective joining technique for thermosetting composites.
Friction Staking: A Novel Staking-Based Joining Method for Hybrid Structures
One of the most used methods for assembling simple structures of plastics and metals is staking. FricStaking is an alternative joining technology based on principles of staking, intended to overcome the limitations of current technologies. Sound joints can be produced in cycles of 10-20 seconds, with efficient use of material, creating a strong and aesthetically pleasing joint. This paper presents a preliminary study of FricStaking, investigating the joint microstructure, local and global mechanical properties, as a function of different levels of tool rotational speed. Local effects on the polymer can be seen through microscopic analysis and microhardness testing. The investigated joints achieved up to 1590 ± 95 N in lap shear tensile testing, and 463 ± 38 N for stake head strength in cross tensile loading.
Applications of Electrospinning to Develop New Biocomposites
Electrospinning has emerged as a versatile method to produce submicron fiber mats from natural or synthetic polymers. Electrospinning is a physical process used for the formation of ultrathin fibers by subjecting a polymer solution to high electric fields. At a critical high voltage (5-35 kV), the polymer solution droplets distort and forms the so-called cone of Taylor that erupts from the solution to form a charged polymer jet. This stretches and is accelerated by the electrical field towards a grounded and oppositely-charged collector. As the electrospun jet travels through the electrical field, the solvent completely evaporates while the entanglements of the polymer chains prevent it from breaking up. This results in the generation of highly functional and flexible ultrathin polymer fibers in the form of non-woven mats. Core-shell structures, produced by coaxial electrospinning, are of great interest for use in food packaging applications. In this area, our group has recently developed high throughput equipment based in a multinozzle coaxial technology that allows high productivity of fibers.
Experimental Investigation of Combined Electrical and Mechanical Joints for Thermoplastic Composites
Textile-reinforced thermoplastics including embedded sensor networks allow for the production of competitive lightweight structures with integrated functionalities. With regard to assembly processes, material- and function-adapted techniques are needed to join such components efficiently. A combined joining technique based on blind riveting is investigated in the present paper, which enables both the transmission of mechanical loads and electrical signals. Therefor, specimen plates made of glass-fiber-reinforced polypropylene (GF/PP) with embedded conductors were joined by blind riveting. Different joint configurations were analyzed regarding their electrical performance. Also, the characteristics of the rivet joint under mechanical loading were investigated revealing a stable electric connection until the ultimate failure of the joint.
A Parametric Study of the Crack Growth Behavior of High Density Polyethylene Based on Crack Layer Theory
Due to unique characteristics of the crack growth behavior of polymers, conventional fracture mechanics approaches on the crack growth have not been very successful. Crack Layer theory (CL) can be a good theoretical approach to model the sophisticated crack growth behavior of polymers. According to CL theory, polymers have different size and shape of process zone (PZ), and, especially, in the case of high density polyethylene (HDPE), a crack commonly propagates in a discontinuous manner under fatigue and creep loading conditions. In this paper, a parametric study was performed by a computer program based on CL theory for HDPE with two general types of test specimens, i.e. single edge notched tension (SENT) specimen and compact tension (CT) specimen. The effects of key parameters, i.e. the stress ratio (R-ratio) which is defined as the ratio of minimum and maximum stress of loading, specific fracture energy, and draw stress, on the crack growth behavior of HDPE were studied.
Electrospun Protein and Polysaccharide Nanostructures to Improve Barrier Properties of Multilayer Systems Based on Polyhydroxyalcanoates and Biopolyesters
This work studies de effect of incorporating high barrier se lf-adhesive nanostructured interlayers of zein, pullulan and whey protein isolate between of polyhydroxyalkanoate (PHA) materials. Oxygen and water vapour barrier properties were greatly influenced by the morphology, thickness and inherent barrier of the electrospun interlayer materials. Thus, zein (in agreement with previous works) and pullulan formed fibrillar structures which significantly contributed to improve barrier properties of the multilayer systems. On the other hand, electrospun WPI formed bead microstructures and did not improve oxygen and water barrier properties of these multilayer systems. While the oxygen barrier properties was significantly improved by the presence of a zein nanostructured interlayer, the water vapour permeability of this multilayer system was seem to vary among materials since the zein interlayer was only efficient as a barrier element in the PHA materials as compared to polylactic acid (PLA).
The Influence of Process Parameters on the Mechanical Properties of Textile-Reinforced Thermoplastic Composite Structures and the Functional Capability of Integrated Sensor Elements
Within the Collaborative Research Centre 639 “Textile-reinforced composite components for function-integrating multi-material design in complex lightweight applications” novel processes for the manufacturing of structures are developed. In this context the process chain from the filament to the part is considered [1, 2]. One focus is on the production of biaxial reinforced multi-layer fabrics (MKF) out of hybrid yarn textile thermoplastics (HYTT) and their processing to complex structures using novel mold- and manufacturing technologies. Based on preliminary tests it is known that process parameters like temperature, applied pressure and holding time have an influence on the mechanical properties of the analyzed material combination glass fiber and polypropylene (PP). Hence, the correlation of these parameters was analyzed using a statistical design of experiments method to set and achieve high mechanical properties of the samples. Furthermore, to exploit possible application and function integration, the capability of this applied material combination can be utilized by embedding sensor elements. In this context, the integration of sensors was investigated in some random tests. Here, different exemplary chosen production processes were compared concerning the functional capability of the sensors.
Influence of Interfaces/ Weld Lines on Fracture Behavior of Polypropylene Specimens Related to Material Properties
In this study the correlations between inner properties and fracture behavior were investigated on the “cold” interface that occurs during a multi-shot injection molding process and “hot” interface or well known as weld line, which represents two melt streams meeting. By using Nanoindentation, inner properties, like Young’s modulus, were measured through the cross section and had shown similarities to break surfaces. With reference to in-situ SEM tensile test the fracture behavior becomes clearer. Imbalances of mold design, caused by core mechanisms, which are required for multi-shot injections, are reasons for deviation of properties. As basis for complex components, these results provide fundamental approaches.
On the Microstructure and Mechanical Performance of Friction Spot Joining with Additional Film Interlayer
Friction Spot Joining (FSpJ) is a new technology for joining polymer-metal hybrid structures. The technique is environment-friendly and involves very short joining cycles. The feasibility of FSpJ to produce composite to metal structures has already been demonstrated. The intention of the current work is to investigate the FSpJ of aluminum AA2024-T3 / CF-PPS with additional polymer film interlayer. The joints showed similar bonding mechanisms to other composite-metal FSp joints, i.e. mechanical interlocking and adhesion forces. Sound joints with promising mechanical strength (up to about 2000 N) were produced. The temperatures involved during the joining process were also studied (peak temperatures between 350 to about 400°C). The strength of the FSp joints with interlayer proved to be affected largely by the tool plunge depth in the selected range.
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