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 Effect of Internal Cooling on Fingering in the Gas-Assisted Injection Molding
A new approach of liquid cooling of gas channel in the gas-assisted injection molding process was adapted in the development and investigation of a water injection system. The gas channel was used as an internal cooling by a liquid injection to increase the process efficiency.The major goal for this study is to minimize the fingering region by introducing the water in the conventional gas-assisted injection molding system. The gas penetration length and the gas fingering area were reduced with increase of the amount of water. The decrease of the penetration length is an undesirable effect and reduces the productivity. The gas injection pressure and the amount of water should be balanced to obtain the optimal part quality.
Effect of Mold Size on the Average Density and Density Gradients in a Polyurethane Foam System
Polyurethane foam is often molded directly in place as a thermal or vibration insulator, energy absorbing material, or core material for a sandwich structure. During the foaming process a smooth thin skin forms between the mold and the interior cellular structure of the foam. This thin skin is only part of a density variation within the cellular structure. This paper examines the effects of mold type on the density gradient. A general trend was found within three mold types; samples taken from the center were less dense than those taken near the mold side. From the center outward, all three molds exhibited a density increase in the form of a power curve. Another general trend was discovered within all three mold types; samples taken from the top section were less dense than those taken from the bottom section of the molds. It was also shown that as the mold size decreased, the vertical density gradient decreased.
The Effect of Molecular Structure on the Coalescence of Ethylene/?-Olefin Copolymers
An experimental study on the coalescence of polymer particles has been conducted on ethylene/?-olefin copolymers. Experimental evidence suggests that copolymers with a more homogeneous structure generally coalesce faster than their heterogeneous counterparts. In a few cases, however, the presence of some heterogeneities in the molecular structure seemed to be beneficial to the coalescence process. A controlled level of heterogeneities, while not significantly impacting the relative elasticity of the material, affected the thermal properties of the material in a favorable way.
The Effect of Molecular Weight and Polydispersity on the Rheological Properties of Pigmented Polypropylene
The rheological characteristics of a range of pigmented polypropylene (iPP) of different MFI values and molecular weight distributions, were investigated using dual capillary rheometry techniques, over the temperature range 190°C to 230°C and shear rate range of 10s-1 to 800s-1 . The various iPP resins were compounded with pigment masterbatch concentrations ranging from 0.2% to 3.0%, using a 38mm Killion compounding line. The pigment masterbatches investigated were iron oxide, titanium dioxide and phthalocyanine blue. The rheological data, showed that there were considerable increases in apparent viscosity of pigmented iPP even at relatively low pigment loadings. Calculation of the non-Newtonian index (n) from the rehological data, also showed the iPP with the narrower polydisperty were less shear thinning than the wider molecular weight distribution polymer resins, especially at the lower shear rates. Activation energies (Ea) calculated from the rheological data showed large increases in Ea especially for wide molecular weight distribution pigmented iPP resins, and compared favorably with crystallinity developed in the polypropylene during the low shear compounding process.
Effect of Molecular Weight on Mechanical and Morphological Properties of High Density Polyethylene Foams
Morphological and mechanical properties of linear polyethylene (HDPE) foams were investigated as function of polymer molecular weight and blowing agent concentration. The objective of this systematic study was to understanding the effect of polymer molecular weight via rheology on the final morphology of the foams. Shear and elongational properties of linear polyethylenes with a wide range of molecular weights were first measured using, respectively, a rotational rheometer (Bohlin CVO) and an elongational rheometer (RME). Azodicarbonamide (ACA) was used as the chemical blowing agent and concentrations between 1 and 3 wt% were used to produce HDPE foams. We present here the morphology of the foams and their tensile mechanical properties. The results are discussed in terms of the rheological properties of the polymer matrix which is related to their molecular weight.
Effect of Multiple Processing Cycles on Post-Consumer Plastics Recycled via Solid-State Shear Pulverization
It is well known that reprocessability of plastics is essential during both manufacturing and consequent recycling. Post-consumer materials, and in particular a five component blend of high- and low-density polyethylene, polypropylene, polystyrene, and polyvinyl chloride representing American film waste, have been successfully reprocessed multiple times by solid-state shear pulverization on a laboratory scale pulverizer. A processing cycle included pulverization, injection molding and conventional grinding. Physical properties such as notched Izod impact strength, elongation at break and flexural properties remained unchanged after four cycles. No change in color or surface appearance of the injection molded test specimens was observed.
The Effect of Natural Rubber Crosslink Density on Real Time Birefringence, True Stress and True Strain Behavior
The effect of crosslink density on the strain-induced crystallization behavior of uniaxially stretched sulfur-cured Natural Rubber vulcanizates was investigated. For this purpose, we measured the local strain and local birefringence in real time during deformation using the instrumented stretching machine developed in our group. In addition to the stress-strain-birefringence data, the evolution of the crystalline order at selected states of orientation as a result of strain is analyzed by WAXS measurements. The results show a continuous increase of molecular orientation as the rubber is stretched. The data also indicates a critical structural threshold beyond which crystallization suddenly takes place. After this threshold value, the relaxation stage also involves further crystallization. The crosslink density greatly affects the molecular orientation process and crystallization during stretching and will be discuss in detail in this paper.
The Effect of Oil Type and Content on the Rheological, Mechanical and Thermal Properties of a Polyolefinic Based Thermoplastic Elastomer
Thermoplastic elastomers (TPEs) based on 65 wt. % ethylene-octene copolymer (EOC)/ 35 wt.% polypropylene (PP) plasticised with two paraffinic oils of different viscosities and a naphthenic oil, were prepared using a twin screw compounder. The oil content of the thermoplastic elastomers ranged between 10 and 20 wt.%. Rheological characterisation of these blends was studied over the shear rate range of 30 to 1000 sec-1. The apparent viscosity at temperatures 197 to 237 °C was shown to be dependent on the quantity rather than type of oil. The tensile modulus, impact strength decreased and elongation at break increased with increase in oil content. The compatibility of each plasticiser was studied by measuring the change in glass transition temperature, melting point of PP phase, and enthalpy of melting of each polymer component.
The Effect of Orientation on Mechanichal Properties of Recycled PET
The use of plastic products is becoming more prevalent in society. Scrap from plastics processing is reground and reused by plastics manufacturers. When the percentage of reground plastic becomes higher than 30% a decrease in mechanical properties is seen. No research has currently been found to encourage runner, vent, or gate modifications to enable manufactures to use a higher percentage of recycled material. The objective of this investigation determine if pin point, standard, or fan gates have an effect on the molecular orientation of virgin, 30%, and 80% recycled PET. Molecular orientation can be evaluated by performing mechanical property testing such as yield strength, tensile modulus, percent elongation, and hardness testing. Tensile bar inserts will be machined with pin point, standard, and fan gate styles. The resulting bars will be subjected to the mechanical tests of yield strength, tensile modulus, percent elongation, and hardness. By using a 2k factorial designed experiment, the results will be analyzed to determine which, if any, gate causes the mechanical properties of the recycled plastic to be similar, within 10%, of the virgin material.
Effect of Part Parameters on Vibration Welding
Much previous work has been done to assess the effect of material, geometric and vibration welding parameters on weld strength. This study examines a series of part parameters and their effect on the joint strength and meltdown-time profiles. These parameters include the plate temperature before welding, edge conditions (cut or molded), initial glass fiber orientation, thickness and injection molding conditions. 33% glass reinforced nylon 66 was used in this study. Plates were molded and then butt-welded on a laboratory linear vibration welding machine. The meltdown-time profiles and the tensile strength of the butt weld were measured for each sample.
The Effect of Phyllite as a Filler for PVC Plastisols
Phyllites are abundant methamorphic rocks composed by fine particles of clay minerals and quartz. This paper investigates the use of a Phyllite from Itapeva, SP, Brazil, as a filler for PVC plastisols and compared the properties of the obtained plastisols with the ones obtained for plastisols containing calcium carbonate, the usual industrial filler. Four different formulations were prepared. The pastes were tested for their Brookfield viscosities, gellation and melting temperature and plate-plate rheology. Films were laminated at 180ºC and tested under tensile stress and for heat stability. PVC plastisols containing phyllite exhibited better mechanical properties and acceptable viscoelastic properties.
The Effect of Pigment Type and Concentration on the Mechanical and Thermal Properties of Injection Moulded Polypropylene
Polypropylene (iPP) is increasingly being used in products for elevated temperature applications. The morphological development during processing of this semi-crystalline polymer is known to be dependent on processing conditions and the presence of nucleating agents such as pigments, influencing both mechanical and thermal properties. A range of injection moulded samples was manufactured from iPP containing 0.1 - 2.0% pigment loadings of different pigment types, using different mould cooling conditions. DSC, tensile and thermal analysis of the various samples showed significant increase in both crystallinity and tensile modulus with a decrease in impact strength for both increased pigment loadings and mould temperatures.
The Effect of Polypropylene MFI on the Rheological, Morphological and Mechanical Properties of Polypropylene/Polyethylene-Octene Copolymer Blends
Blends of polypropylene (PP) of MFIs 4 and 25 g/10 min with up to 30 wt. % ethylene-octene copolymer (EOC) were prepared using a Killion compounding extruder fitted with a barrier design screw. Rheological characterisation of these blends was studied over the shear rate range of 300 to 2000 sec-1. The apparent viscosity at temperatures 197 to 237 °C was shown to be dependent primarily on the MFI of the PP rather than the EOC concentration of the blend. The MFI had a significant effect on the mechanical and phase morphology properties of the various blends. Dynamic mechanical thermal analysis (DMTA), and differential scanning calorimetry analysis (DSC) would tend to indicate some degree of polymer miscibility especially at the higher EOC concentrations, with slight decreases in crystallinity and the phase transition temperature of EOC.
The Effect of Processing Conditions on the Appearance of Flow Lines in Injection Molded Articles Incorporating Pearlescent Pigments
The purpose of this study was to evaluate the effects of injection molding conditions on the appearance of a weld line/flow line in injection molded parts incorporating pearlescent pigments. In this study, a general-purpose grade polypropylene was the carrier resin used. Three different pearlescent pigments were mixed into the polypropylene at concentrations by weight of 0.5%, 1.0% and 2.0% and injection molded. The appearance of a flow line for each of the concentrations was characterized by a transmitted light intensity method for various settings of the main molding parameters, melt temperature, mold temperature, holding pressure and injection speed.Overall, the experimental results indicated that melt temperature and injection speed most significantly affected flow line appearance. The mold temperature had a less significant effect, and the holding pressure did not have significant effect on the appearance on the flow line.
Effect of Processing Conditions on the Development of Morphology in Clay Nanoparticle Filled Nylon 6 Fibers
Nylon 6/montmorillonite nanocomposites were melt-spun at extrusion temperatures of 230º, 240º and 250ºC. The resulting fibers display interesting features in differential scanning calorimetry scans: an exothermic peak just below the melting region and at least three melting peaks depending on the spinning temperature. The presence of nanoparticles was found to limit spinning speeds due to premature fiber breakup. Increasing melting temperature from 230º to 250ºC alleviated this problem. The spun fibers were found to possess ? crystal form. At higher take-up speeds ?-crystals begin to appear in the mixture. The orientation levels in crystalline regions were found to be quite substantial due to the presence of nanoparticles that increases the overall viscosity and the spinline tension.
Effect of Pulsed Tool Cooling on the Injection Moulding Process
Experimental studies have been carried out to assess the effect of using an advanced tool temperature management system for injection moulding, compared to conventional tool heating and cooling techniques. A highly instrumented 75 tonne servo-hydraulic moulding machine was used, moulding tensile test specimens from HDPE. Tool temperature was monitored at high frequency (50 Hz) during each cycle, as was nozzle melt pressure, temperature and screw position. Conventional tool temperature control was employed using a water heater/chiller to control temperature in both halves of the tool by controlling water temperature. The effect of tool temperature control on start-up times, process and part repeatability has been examined.
The Effect of Sealing Parameters on the Fracture Mechanism and Peel Properties of Medical Packaging Materials
This paper assesses the effect of sealing parameters, (time, temperature and pressure) on the peel properties and fracture mechanism of medical packaging materials. A design of experiment (DOE) methodology was adopted to conduct the trials and analyze the results; the materials studied were a heat-sealable coated Tyvek® bonded to film (of the types used to manufacture pouches).The properties of the peelable seal were characterized in terms of peel strength parameters and fracture mechanism. A novel method to quantify fracture mechanism, by measuring the amount of adhesive transfer with predictive capability is presented. A window of seal time, temperature and pressure exists which results in the optimum peel properties and fracture mode.
Effect of Surface Treatment on the Interfacial Interactions and Impact Properties of Calcium Carbonate Filled Polypropylene Composites
The present study investigated the effects of surface treatment on the surface properties of calcium carbonate and on the interfacial interaction between filler and matrix. An extensive comparison was made on the efficacy of the surface treatment between stearic acid, a non-reactive surfactant, and LICA 12, a reactive coupling agent. The change in surface properties due to surface treatment was characterized through inverse gas chromatography (IGC) at infinite dilution. The stearic acid treated filler showed lower dispersive and polar components of the surface energy than LICA 12 treated system for completely coated CaCO3 fillers. Infrared analysis demonstrated that stearic acid reacted extensively with the filler surface to produce organic salt compound. Izod impact strength was measured on sharp-notched samples. It was found that stearic acid treated composites exhibited greater impact strength than LICA 12 treated systems.
Effect of Thermoplastic Elastomer Material Properties on Mold Filling Imbalances
Significant shear induced filling differences are commonly seen between cavities in multi-cavity injection molds. These filling variations can be particularly important when over-molding TPEs on delicate plastic inserts. This paper compares the amount of imbalance detected when molding different grades of TPEs. It then evaluates the relationship of the materials shear, temperature, and viscosity indexes on the magnitude of shear-induced mold filling imbalances to determine which factors most directly influence this imbalance. This understanding will help a molder more readily predict and address the problem. Furthermore, the study evaluates the use of melt rotation technology (1) to minimize the imbalances.
Effect of Viscosity on Low Density Foaming of Poly(Ethylene-Co-Octene) Resins
Foaming of low density poly(ethylene-co-octene) resins by injection molding is the result of various reactions occurring during the process. This includes simultaneous decomposition of the chemical blowing agent and cross-linking of the polymer matrix during curing in the mold, followed by foaming after mold opening. Dynamic rheology as well as elongational viscosity were investigated for compounds prepared from resins with different MFIs and various cross-linking agent levels, and these results were linked to the morphology and density of the corresponding foams. Rheological requirements were finally defined quantitatively for this set of conditions.
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