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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Effect of DCP Crosslinking on the Mechanical and Electrical Properties of LDPE
The good electrical and mechanical properties of low density polyethylene (LDPE) make it an ideal insulation for the electric cables. The main draw back of polyethylene is its softening temperature. Crosslinking of polyethylene improves its properties.The effect of dicumyl peroxide (DCP) on mechanical, thermal and electrical properties of crosslinked polyethylene (XLPE) have been investigated. Crosslinking of LDPE improves its mechanical properties and, to some extent, improves its thermal degradation. DCP increases dielectric breakdown voltage, elongation at break, tensile strength and gel-content of XLPE, but decreases young modulus, crystallinity, heat of fusion and melting point of XLPE.According to the results, an optimized amount of DCP is determined. In this study, the LDPE (POLIRAN LF0200) was used to produce insulators for medium and high-voltage electrical cables.
The Effect of Extrusion Processing Conditions and Polyisobutylene Concentration on the Properties of Polyethylene for Stretch and Cling Film Applications
A range of LLDPE films with polyisobutylene (PIB) content from 2%-8% was manufactured using a Killion blown film extrusion system and a cast film extrusion system. The films were aged at 25, 35 and 45°C for up 28 days, to enable tack (cling) development. The results show that tack, in both blown and cast films, improved significantly with ageing, at increased storage temperatures and at higher film blow up ratios. DSC analysis showed only a slight decrease in film crystallinity with increasing PIB concentration. The film tensile modulus, elongation and tear properties in both MD and TD were not significantly affected by increase in PIB concentration.
The Effect of Extrusion Processing Conditions on the Thermal and Mechanical Performance of Extrusion Cast Metallocene Polyethylene Films
Cast extruded films were prepared from a range of mPE resins with various co-monomer types (hexene, octene), using different chill roll temperatures from 30 to 60°C. Mechanical analysis showed that the tensile modulus of the films increased with progressive increase in chill roll temperature. DSC analysis showed increases in crystallinity with increasing quench temperature and decreasing MFI. Rheological and molecular weight distribution analysis showed that activation energies of flow for mPE (18-28kJ/mol) were low, this is attributable to the narrower polydispersity of mPE (2.1-3.1) compared to the wider distribution of conventional polyethylenes (4.0-5.0).
Effect of Fluoropolymer Processing Aids on the Processibility of an Octene LLDPE
Polymer processing additives (PPA) have found their niche in the extrusion and processing of polyolefins, especially to improve their processing characteristics. It has been known that PPA can be used in the range of 100 – 1000 ppm to eliminate surface defects including melt fracture and gels, as well as to reduce die build up. The main focus of this paper is to determine the effect of various fluoropolymer processing aids in the elimination of melt fracture of an octene linear low density polyethylene. Also the influences of both antiblocking agent and slip additive on the performance of PPA are assessed.
Effect of Functionalized Polyolefin Coupling Agent Types on the Mechanical Properties of HDPE/Wood-Flour Composites
The performance of fiber reinforced thermoplastic composites strongly depends on solid fiber-matrix adhesion to allow stress transfer between the phases. Fiber surface modification with coupling agents is generally needed to induce bond formation between the fiber and the polymer. This study investigated the effects of coupling agent's functional monomer (acrylic acid vs. maleic anhydride) and base resin (polyethylene vs. polypropylene) types on the on the tensile and flexural properties of high-density polyethylene (HDPE)/wood-flour composites. The experimental results indicate that the types of functional monomer and base resin are important factors determining the effectiveness of functionalized coupling agents for HDPE/wood-flour composites. Maleic anhydride-functionalized polyolefins perform better than acrylic acid counterparts whereas polyethylene-based maleated coupling agents are more effective than polypropylene-base counterparts in improving the mechanical properties of HDPE/wood-flour composites.
Effect of Gamma-Irradiation on the Mechanical Behavior of PS/PP Blends
The effect of Gamma-irradiation on the tensile behavior of PS/PP blends (80/20) and its mathematical analysis indicates that the blend presents a high radiation resistance to low doses (80-70 kGy), since mechanical properties present no significant changes; this is due to the presence of the aromatic ring in the PS structure, factor which was confirmed by the lineal mathematical adjustment. On the other hand, at high doses of irradiation (70-1300 kGy), a dramatic change on the mechanical properties was observed and the mathematical adjustment showed a third order polynomial behavior, which indicates a competition between crosslinking and degradation mechanisms, being the latter predominant.
The Effect of High Barrier Emulsion Polymers on the Reduction in Water Vapour Transmission Rates of Laminated Carton
The water vapour transmission rate (WVTR), or moisture vapour transmission rate, of carton boards can often be critical, especially in high performance packaging applications. A range of laminated two-ply carton boards were prepared using litho-lamination techniques. These boards were manufactured using a range of polymer based emulsions and adhesives. Different carton board materials and polymer/adhesive layer thicknesses were used during this investigation.The WVTR of these carton boards were measured using a MOCON Permatran automatic water vapour permeability analyser at 60% relative humidities (RH) and at 20°C temperature. The results show significantly lower WVTR with the EVOH based emulsion than with the other polymer based emulsions and the adhesives.
Effect of High Density Polyethylene Concentration and Melt Temperature on Crystalization Dynamics during Film Blowing of Linear Low Density Polyethylene
The crystallization of low density Polyethylene is investigated relative to the influence of small, up to 4 wt.%, of high density PE at different melt temperatures. The process was evaluated by the use of simultaneous on-line SALS (Small Angle Light Scattering) and IR (Infrared) temperature measurements to study structure development as influenced by nucleation during tubular blown film extrusion of LLDPE. As the concentration of the nucleation aid, HDPE, was increased, the observed scattering intensity was decreased probably due to impingement and truncation of spherulites. The effect of melt temperature was also investigated and the scattering intensity increased as the temperature increased as a result of lower internal disorder.
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.
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