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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Rheological Behavior of Thermotropic Liquid Crystalline Copolyester Vectra A950
An investigation of the transient, steady and dynamic flow properties of the thermotropic liquid crystalline polymer Vectra A950 (Ticona) is presented. The steady viscosity curve shows the typical three-region flow curve of LCPs. In the transient shear experiments, the shear stress grows during the start-up of constant shear rate flow and goes through a maximum at approximately ?=2. Dynamic mechanical experiments show the existence of a linear viscoelastic region at small strains, and that the onset of nonlinearity varies with frequency. In the linear viscoelastic region, the storage and loss modulus, G'(?) and G(?) do not display the typical dependence on ?2 and ? respectively. The results obtained for a frequency sweep using constant strain and constant stress instruments are qualitatively different."
Injection Molding Unfilled and Filled Polymers with Titanates and Zirconates - 2001
In addition to universal filler/pigment to polymer coupling, two parts of thermally stable neoalkoxy titanates and zirconates per thousand parts of polymer provide for in situ metallocene-like repolymerization catalysis of the filled or unfilled polymer during the plastication phase resulting in: significantly faster injection molding production cycles at lower temperatures while maintaining or increasing mechanical properties; the in situ regeneration of regrind polymer to virgin properties; the lowering of polymer recrystallization time; and the copolymerization of dissimilar polymers. Examples: both 40% CaCO3 filled and unfilled PP compounds experienced respective reductions of 35.5% and 42% in injection mold cycle time and 22% and 11% in process temperature; a 39.7% reduction in the recrystallization time of PPS; and a ten-fold increase in the elongation of a PET/PC alloy. The effect is shown to be permanent and recyclable.
Anisotropic Electrical Percolation Due to Chaotic Mixing of Short Carbon Fibers and Low Density Polyethylene
Three-dimensional batch chaotic mixing of short carbon fibers (SCF) and low-density polyethylene (LDPE) is investigated as a means to obtain thermoplastic composites with directional electrical properties. Previous studies investigated carbon black filled systems and revealed that anisotropic electrical properties can be obtained by chaotic mixing at various filler concentrations. The present study focuses on network formation among short carbon fibers used as the conducting filler. The directional electrical properties in terms of static dissipation times and volume resistivities are related to microstructures. These properties are compared to the properties of composites obtained by conventional mixing processes.
Study of Flow Marks during Thin-Wall Injection Molding
In this paper, the effect of polymer rheology, injection speed, mold geometry, melt temperature, mold temperature and lubricant on flow marks was studied. The results show that the most important factor affecting the flow marks is injection speed. It is found that the flow marks did not occur at high injection speeds. Mold geometry also has an effect on the flow marks. However, mold temperature and melt temperature were determined to have little effect on the flow marks. It is also found that the polymer with the highest dynamic viscosity, elastic modulus and first normal stress difference, and longest relaxation time exhibits flow marks over the widest range of processing conditions.
Effect of Layer Orientation on the Mechanical Properties of FDM Produced ABS Test Specimens
As with other forms of rapid prototyping, fused deposition modeling (FDM) creates parts by depositing a thermoplastic in layers. The mechanical properties of these parts are anisotropic due to this layering, with the part being weaker than the published material properties. Since FDM parts are sometimes used as working prototypes, it is important to understand the degree of these variations. This investigation studied the effect of six different build orientations on six mechanical properties for test parts built of ABS. While parts built on end were understandably the weakest in all tests, properties were the best for parts built on edge versus parts built flat. Also, specimens oriented parallel to the x-axis of the FDM had improved properties over specimens built with a 45° rotation, regardless of layer orientation.
Morphological Effects on the J-Integral Mode I Tear Resistance of HDPE Films
Mode I Tear resistance in high density polyethylene (HDPE) blown film has been characterized using a single specimen J-Integral approach. This method measures the load on the sample, crack initiation, and crack growth in a double-edge notch tensile specimen pulled at a constant extension rate. Tensile tests were performed to determine basic mechanical properties of the HDPE film. A systematic characterization of film morphology has also been performed. This work focuses on the use of a thorough morphological investigation to describe the fundamental aspects of deformation and tearing as they relate to different processing conditions.
Morphology-Property Relationship in Blown Films of LDPE, LLDPE and Their Blend
The morphologies of films blown from an LDPE, an LLDPE and their blend were characterized and compared using transmission electron microscopy, small-angle X-ray scattering, infrared dichroism, and thermal shrinkage techniques. Under similar processing conditions, the LLDPE film has a relatively random crystal orientation. The film made from the LDPE/LLDPE blend possesses the highest degree of crystal orientation. Nevertheless, the LDPE film has the greatest amorphous phase orientation. The physics that is responsible for the high degree of crystal orientation in LDPE/LLDPE blend film is proposed. The structure-property relationships of the films are also discussed.
Non Woven Textiles from Melt Spun Recycled PET
This study examines the effect of nucleating agents on the physical properties of melt drawn fibres made from post consumer Recycled Polyethylene Terephthalate (RPET). Clear and coloured RPET derived from carbonated soft drink bottles have been used in this study. Titanium dioxide (TiO2) and carbon black (CB) have been added at varied addition rates in a linear low density (LLDPE) and PET carrier. The effect these additives have on the physical properties of the finished textile were evaluated. Evaluations show that reprocessed bottle grade PET is suitable for fibre applications if the intrinsic viscosity and the final fibre properties are carefully controlled. LLDPE masterbatch containing TiO2 and CB at addition rates in the order of one percent were able to improve processing, physical properties and the rate of crystallisation.
Recycling of Multilayer and Barrier Coated PET Containers
This paper describes the process for removing barrier layers and coatings (oxygen and carbon dioxide) from polyethylene terephthalate (PET) substrates through a conventional mechanical bottle recycling system. Varied wash chemistry and barrier medium have been examined and the effect on residual multilayer material or coating has been evaluated. Wash chemistry was found to be the controlling factor in improving the external coating removal efficiency. Delamination through mechanical working was found to be the controlling mechanism for separating multilayer materials. The conclusion drawn from our experiments is that the PPG Bairocade coatings were removed most efficiently. Internal deposition techniques may contribute fewer residues to the RPET, however substantiating this is difficult.
Three-Dimensional Non-Isothermal Numerical Analysis of Multi-Layer Coextrusion
This paper presents a three-dimensional finite volume algorithm together with the Lagragian mesh technique for simulating the non-isothermal non-Newtonian stratified flow of two or more polymers in a square channel. From the benchmark calculations, the simulated interface shape shows good agreements with numerical results of previous researchers. Moreover, the effects of temperature, viscosity, flow rate ratios and the contact angle on the encapsulation phenomena are also examined. Flow system up to five-layer is also reported in this study. The efficiency of the proposed approach makes it possible to simulate even more complex system on a regular PC.
Injection Molding Unfilled and Filled Polymers with Titanates and Zirconates - 2001
In addition to pigment/reinforcement/filler to polymer coupling, two parts of thermally stable neopositioned quaternary carbon based neoalkoxy [neopentyl(diallyl)oxy] type titanates and zirconates per thousand parts of polymer provide for in situ metallocene-like Repolymerization" catalysis of the filled or unfilled polymer during the plastication phase resulting in: faster injection molding production cycles at lower process temperatures; maintenance or increase in mechanical properties; the in situ regeneration of regrind polymer to virgin properties; the lowering of polymer recrystallization time; and the copolymerization of dissimilar polymers. For example using a neoalkoxy tridodecyl-benzene sulfonyl titanate both 40% CaCO3 filled and unfilled "Repolymerized" PP compounds experienced respective reductions of 35.5% and 42% in injection mold cycle time and 22% and 11% in process temperature; and a 39.7% reduction in the recrystallization time of PPS. Two parts of a neoalkoxy tridioctyl phosphato titanate regenerated and copolymerized one thousand parts of a PET regrind/PC regrind providing a nine-fold increase in the elongation of the alloy. The effect is shown to be permanent and recyclable."
Three-Dimensional Numerical Analysis of the Single Screw Plasticating Extrusion Process
This paper presents a 3D numerical model to investigate the plasticating phenomena in the single screw extruder. The FVM is adopted to solve the governing equations to obtain the velocity and pressure profiles. The enthalpy formulation for the energy equation and the liquid fraction method are introduced to model the melting mechanism between the melts and the solid bed. The 3D simulation can predict both the melting length in the down channel and the local solid fraction in the cross channel. The predicted pressure drop, temperature distribution and melting behavior are in reasonably good agreement with the experimental results.
Thermal Analysis of Blends of Recycled HDPE and Virgin Polyolefins
This paper investigates the melting point and crystallinity behaviour of blends of recycled milk bottle HDPE with injection moulding and film blowing grade high density polyethylene (HDPE), linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) as part of a larger investigation into blends of recycled HDPE and virgin polyolefins. The variation in melting points and crystallinity levels for blends of recycled HDPE with either HDPE or LLDPE were linear with composition, and displayed only one melting point, while recycled HDPE with LDPE displayed separate melting points for each compositional component.
The Effect of Inertia on Fill Pattern in Injection Molding
By numerical simulation of the full three dimensional Navier-Stokes flow equations, it is possible to observe the influence of inertia effects on the filling pattern of an injection molded part. Traditional shell-based Hele-Shaw flow simulations have assumed that the momentum (inertia) contribution to the fluid flow is negligible. However, thick walled parts and complex parts are poorly represented by shell models. Under certain processing conditions for these thick geometries, inertia effects will influence the flow pattern. Simulation studies are presented in this paper which compare flow solutions with and without inertia effects.
New Cost-Efficient Process for the Production of Large-Volume High-Voltage-Insulators Made of Liquid Silicone Rubber (LSR)
The unique combination of chemical and physical properties predestines LSR for applications in the field of electrical insulation. Due to high investment for mold and machine technology an economical production can be reached for medium or large series only. In this thesis a new technology is developed for casting large volume parts at a low level of cavity pressure. Separate heating of the material components to a temperature level just below mold temperature leads to a controlled decrease in cavity pressure. Simultaneously, a considerable reduction in cycle time is reached due to a faster curing process. Since the new technology developed enables the use of simple mold designs without clamping units, a significant reduction in investment is achieved.
Recycling of Crosslinked Multi-Layer Thermoplastic Films - Miscibility Studies
This study was part of a program of work undertaken to develop recycling technology for multi-layer films which are not currently recycled. These multi-layer films comprise barrier layers with surface layers for mechanical strength, and tie layers between. Crosslinking is used to enhance various mechanical properties. The crosslinked layers have a high viscosity which creates processing problems, eg. if the film is recycled, high processing pressures are required. Furthermore, material blend component incompatibilty can result in inferior mechanical properties. Monolayer films of the virgin materials were produced. Multi-layer film with crosslinked EVA/LLDPE and a barrier layer was produced on a blown film line. This multi-layer film was agglomerated" then reprocessed in a twin screw extruder with virgin LDPE and LLDPE and blown into film. The blend miscibility was then determined using a TA Instruments TMDSC. It was found that LDPE blends were initially miscible with the containing scrap whereas LLDPE blends were immiscible. The LDPE miscibility was partly reversible as the blend components phase separated after the second heat treatment during testing in the TMDSC instrument. The initial miscibility was attributed to being induced by high shear during processing."
Thermal and Mechanical Properties of Silane-Grafted Moisture-Crosslinked Polyethylene
The vinyl trimethoxysilane VTMS" was grafted onto various polyethylenes ( HDPE LLDPE and LDPE) using DCP as an initiator in a twin screw extruder. The grafted polyethylenes were able to cross-link utilizing water as the crosslinking agent. The effects of varied crosslinking time on the mechanical properties of the crosslinked polyethylenes were studied. It was found that the HDPE and LLDPE were apt to cross-link during the grafting process and thus decreased the grafting ratio. Multiple melting behavior was observed for cross-linked LDPE and LLDPE. The mechanical and thermal properties of the crosslinked PE are better than uncrosslinked PE." LLDPE and LDPE) using DCP as an initiator in a twin screw extruder. The grafted polyethylenes were able to cross-link utilizing water as the crosslinking agent. The effects of varied crosslinking time on the mechanical properties of the crosslinked polyethylenes were studied. It was found that the HDPE and LLDPE were apt to cross-link during the grafting process and thus decreased the grafting ratio. Multiple melting behavior was observed for cross-linked LDPE and LLDPE. The mechanical and thermal properties of the crosslinked PE are better than uncrosslinked PE."
Application of Liquid Gas-Assisted Injection Molding to the X-Arm of a Chair
Application of gas-assisted injection molding (GAIM) has been expanded within last 15 years because of many advantages such as design flexibility, dimensional stability, reduction of machine tonnages, and so on. But, for thick parts, it is observed the surface defects including hesitation mark and gloss difference. Difficulties in lay-out of the gas channel and processing condition are another disadvantages. Liquid gas-assisted injection molding (LGAIM) is a good alternative of conventional gas-assisted injection molding especially in manufacturing simple and very thick parts. The heat-activated liquid vaporizes and pushes the melt downstream and creates hollow channels within parts[2,3]. We developed the total system that includes control unit (control of volume, pressure, and time of the liquid), liquid-injection nozzle, recipe of liquid system, and part/mold design (CAE analysis). As an applicable part, X-arm of a chair was selected. From experiments, it was observed stable hollow formation without hesitation mark and sink mark. And we was able to reduce the cycle time and weight
Polymer/clay nanocomposites prepared from intercalated montmorillonite and PVC were compounded in KO-kneader with dioctylphtalate (DOP) as a plasticizer. An influence of the type of used organoclay on thermal stability was observed. Problems with the composition thermal stability during compounding can be eliminated by pretreatment of the organoclay with plasticizer which creates a barrier between polymer and quaternary amine. Simultaneously co intercalation of plasticizer facilitates exfoliation and dimension clay platelets in the polymer matrix. A positive influence of nanoclay on dimensional stability and permeability was observed.
Influence of Temperature and Initiator Type on the Functionalization of High Density and Lineal Low Density Polyethylenes
The obtaining of compatibilizers for blends by functionalization has led the study of this modification in the polyethylene. Three initiators were used in the grafting of High-Density Polyethylene (HDPE) with diethylmaleate. Also was investigated the dependence of the functionalization degree on the temperature of Linear-Low Density polyethylene (LLDPE). The compared initiators were 2,2'- Azobisisobutyronitrile (AIBN), benzoyl peroxide (BP) and 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane (DBPH). It was found that under the same experimental conditions the grafting degree in the HDPE decrease follows the order of the initiators: DBPH > BP > AIBN.
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