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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Development of High Quality Recycled Polyethylene Resins for the Replacement of Virgin Resins
Dairy and fruit juice bottles are a major source of post consumer recycled high density polyethylene (PCR HDPE). The recycled HDPE has limited post-consumer applications due to its poor stress crack resistance (SCR). This paper presents a review of a test method for SCR and some preliminary results of the development of recycled HDPE blends with improved SCR. The improvement has been achieved with the addition of a modifier, and results indicate that there is a potential to incorporate the use of recycled HDPE in non-pressure pipe applications. These customised blends have been tested for SCR according to the Notched Constant Ligament Stress (NCLS) test. The NCLS test is a new test method (ASTM F17.40) which is currently under development. The NCLS test will be used to determine the susceptibility of HDPE resins to slow crack growth (SCG) under a constant ligament stress in an accelerated environment. The results from the test will subsequently be correlated with field performance results.
The Development of Geometry and Polymer-Independent Product Quality Models Based on Injection Molding Cavity Pressure
Previous product quality models based on cavity pressure suffer from being geometry and polymer specific and requiring large amounts of data to develop. The present study focuses on the development of geometry/polymer independent models to predict part weight with a minimum of experimental data. Several product geometries were created using inserts in a standard ASTM tensile specimen cavity. Both amorphous and semi-crystalline polymers were utilized. Real-time cavity pressure data was collected, quantified via pressure curve attributes" and used to develop predictive models through multivariate linear regression. Future work will apply the model results to the molding of a typical commercial electrical connector."
Development of Rapid Heating and Cooling Mold Inserts Comprising a Heating Layer, an Insulation Layer and a Substrate
The injection molding process has several inherent problems associated with the constant temperature mold. A basic solution is the rapid thermal response molding process that facilitates rapid temperature change of the mold surface thereby improving quality of molded parts without compromising cycle time. Rapid heating and cooling systems consisting of one metallic heating layer and one oxide insulation layer were investigated in this paper. Design issues towards developing a mold capable of raising surface temperature from 25°C to 250°C in 2 seconds and cooling to 50°C within 10 seconds were discussed. To reduce thermal stresses in the layers during heating and cooling, materials with closely matched low thermal expansion coefficient were used for both layers. Effects of various design parameters, such as layer thickness and material properties, on the performance of the mold were studied in detail with the aid of heat transfer simulation and thermal stress simulation. Several rapid thermal response mold inserts were constructed on the basis of the simulation results. The experimental heating and cooling response agrees with the simulation and also satisfies the target heating and cooling requirement.
Using Truncated Relaxation Spectra in the Simulation of Viscoelastic Flows
The simulation of polymer viscoelastic flows is a complicated problem and until now it is not possible to perform simulations that are relevant from an industrial perspective. One of the limiting factors is the degree to which elasticity plays an important role in the flow. For a given constitutive equation and numerical technique, a higher material relaxation time, will result in a lower maximum deformation rate for which convergence is possible. Since industrial processes typically involve very large deformation rates, a practical way to allow their simulation might be to truncate the longest relaxation times. In this work the Leonov constitutive equation was used to simulate flow through an abrupt contraction. The possibility of truncating the relaxation spectrum was explored and the impact of using truncated spectra on simulations is described. Finally we propose a technique for obtaining a truncated relaxation spectrum that will be useful for flow simulations.
Effect of Compatibilization and Dynamic Vulcanization on the Microstructure and Performance of Polyethylene Terephthalate/Elastomer Blends
Blends of polyethylene terephthalate (PET) and ethylene-ethyl acrylate-maleic anhydride terpolymer (E-EA- MAH) were dynamically crosslinked in a one-step extrusion process. An amine-terminated glycol reacting with MAH moieties was used as the crosslinking agent. Systems were compatibilized by addition of ethylene-methyl acrylate-glycidyl methacrylate terpolymer (E-MA-GMA). The tensile properties and dynamic mechanical thermal analysis response of the unvulcanized and the dynamically vulcanized systems were studied. The effect of blend composition, compatibilization, dynamic crosslinking and processing conditions on the microstructure and tensile properties were investigated.
Deformation and Orientation of Polyamide 6 Nanocomposite
Mechanical deformation induced experimentally using a T. M. Long stretcher enabled an investigation of the effect nano size platelets can have on the clarity, barrier and mechanical properties of a polymerized nano polyamide 6. Clarity of cast film specimens did show a direct correlation between %Haze and nano platelet concentration. Non nano containing films biaxially stretched 2 times its original dimensions had a 1% - 3% haze reading. Nano containing films ranged from 5% -~ 20% over a nano concentration of 1.0% - 4%, respectively. The oxygen transmission rate, OTR , of 2% and 4% nano films had a 3X and 6X improvement in OTR compared to the unfilled polyamide 6 film, respectively. Biaxed nano polyamide 6 film did not significantly improve OTR, as is the case with non-nano containing polyamide 6 films. There was only a 6% improvement in OTR, which was due primarily to the minimal increase in molecular orientation or packing, which is shown by the small change in the degree of orientation ~77% to 83% for as cast nano films compared to biaxed nano containing films, respectively. The nano containing films do have improved modulus and yield strength and an expected reduction in elongation at break. By taking advantage of molecular orientation mechanical properties were modified via biaxially orientation.
Experimental and Numerical Analysis of Thin-Wall Injection Molding with Micro-Features
Injection molding of thermoplastics with small feature size is needed in many medical and bio-chemical applications, i.e., bioMEMS. Three types of mold inserts, CNC machined steel mold, photoresist molds, and photolithography produced nickel molds are tested in high speed and high pressure (i.e., thin-wall) injection molding. The feature size covers a range of 5 micrometers to several hundred micrometers. Two optically clear thermoplatics (PMMA, PC) were processed under different molding conditions including mold temperature, injection speed, shot size, and holding pressure. The replication accuracy, molded-in stress, and mold wear were measured. Numerical simulation was carried out to calculate flow front profile and stress distribution. The simulation and experimental data were compared and the results can be used to design the process window for micro-injection molding.
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.
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