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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Solid State Properties of New Propylene-Ethylene (P/E) Copolymers
A series of ethylene-containing propylene copolymers (P/E) have been synthesized with up to 19 mol % ethylene. Tapping mode atomic force microscopy (AFM), wide angle X-ray diffraction (WAXD), optical microscopy (OM), differential thermal analysis (DSC) and stress-strain behavior were employed to characterize the solid state structure. Based on the combined experimental observations, a classification scheme with four distinct categories is proposed. Type IV copolymers (0-3 mol % ethylene and crystallinity greater than 48 wt. %) are comprised of space-filling ?-mixed spherulites that are primarily ?-phase crystals. Spherulites of Type III copolymers (3-7 mol % ethylene and 48-33 wt % crystallinity) are sheaf-like and non-space-filling. Unimpinged regions are comprised of an epitaxially crystallized cross-hatched network. Type III copolymers have both ? and ?-phase crystals. An increase in ?-to-? ratio suggests that spherulites are primarily ?-phase whereas the cross-hatched network is a mixture of ? and ?-phase. Type II copolymers (7-15 mol % ethylene and 33-18 wt % crystallinity) are characterized by axialites surrounded by a loosely woven cross-hatched network. Type I copolymers (more than 15 mole % ethylene and less than 18 wt % crystallinity) contain occasional assemblies of radial lamellae epitaxially grown off of a single lamella. Type IV materials exhibit thermoplastic behavior. With increasing ethylene content, the neck becomes more diffuse. Type I copolymers exhibit elastomeric behavior with uniform deformation and high recovery.
Elastomeric Properties of New Propylene-Ethylene Copolymers under Cyclic Loading
The elastic properties of new high comonomer propylene-ethylene copolymers are investigated. Although these materials show some degree of permanent set upon initial tensile deformation, the materials created as a result of a tensile “conditioning” process exhibit very high recovery during subsequent tensile testing. The stress-strain behavior of the conditioned materials is characterized by low modulus and reversible deformation to high strain. The data fit well with a two-parameter crosslink model. An increase in density is observed during the conditioning process suggesting melting and recrystallization. Wide angle x-ray scattering shows that the conditioning process increases orientation, and converts all ?-crystals into ?-crystals. Atomic force microscopy reveals that the conditioning process produces a fibrous network structure.
Effect of Unsaturated Compounds on Ethylene Polymerization with the Catalyst System Et(Flu)2ZrCl2/MAO
In this work several ethylene polymerizations were carried out with the metallocene system Et(Flu)2ZrCl2/MAO in the presence of different unsaturated substances. The reactions were performed at a temperature of 50°C and the concentration of the unsaturated substances, such as styrene, isoprene, indene, acrylonitrile and cyclopentene was varied. Some polymerizations with isoprene and indene showed, respectively, higher and lower activities compared to ethylene homopolymerization. The copolymerizations with styrene and cyclopentene at low comonomer concentration presented almost the same activity and with acrylonitrile did not show any activity. Another result was that the copolymers, especially with styrene, presented their melting temperature lower than that of polyethylene, which indicates that the substances did incorporate into the polymeric chain.
Metallocene Polyethylenes with Supported Catalyst
Linear low density polyethylenes were synthesized employing (nBu-Cp)2ZrCl2/methylaluminoxane catalyst in homogeneous and zeolite supported systems. The comonomer effect in homogeneous catalyst was observed as well as a slight negative comonomer effect in the supported system at higher comonomer content. The slight decrease in activity between 50°C and 80°C observed for the homogeneous system was attributed to the activation of the active centers at higher temperature and low MAO concentration. The increase on the comonomer content in the copolymer caused a reduction on the melting temperature and crystallinity and also multimodal melting endotherms. These multimodal Tm’s occurred due to the heterogeneous intrachain composition. The reactive ratio was calculated and according to r1 and r2 values we can expect long ethylene sequence lengths.
A Kinetic Study of the Polymerization of Methyl Methacrylate under Supercritical Fluid CO2
The kinetics of the in situ polymerization of methyl methacrylate (MMA) in the presence of benzoyl peroxide (BPO) initiator under supercritical fluid CO2 (sCO2) was studied by high pressure DSC. The influences of the reaction medium, initiator content, and reaction temperature on the polymerization rate were studied. The results indicated that the formation of PMMA follows a first order reaction mechanism. The polymerization rate in the presence and absence of sCO2 were found to be similar but the exothermic profiles were different, with the polymerization under sCO2 having a lower profile. Increasing the amount of BPO initiator accelerated the rate of PMMA formation and reduced the induction time. The molecular weight of PMMA produced under sCO2 was 34% higher than that obtained in air.
Effect of TSE Screw Configuration on Dissolution and Melt Sealing of HFC 134a Blowing Agent in Polystyrene
The effect of screw design on dynamic dissolution and melt sealing of HFC-134a in PS during foam twin-screw extrusion has been investigated. Ultrasound velocity and viscosity monitoring in the polymer/blowing agent solution showed that HFC-134a dissolution is sensitive to screw design. The screw configuration also played an important role in the creation of an efficient melt seal. Correlation between blowing agent pressure and concentration in the extruder were shown to obey Henry’s law and were similar to pressure – solubility data obtained off-line in the quiescent state.
Effect of Montmorillonite on Formation of Polystyrene Foams Using Supecritical CO2
Polystyrene was in-situ polymerized with a range of montmorillonite layered silicate (MLS) concentrations, and subsequently compression molded into thin laminates. The laminates were foamed in a batch supercritical CO2 chamber at various temperatures and pressures from 60°- 85°C and 7.6-12MPa. The resulting foams were analyzed by scanning electron microscopy to determine effect of MLS on cellular morphology. Differential Scanning Calorimetry was used to determine the impact of nanocomposite microstructure on glass transition of the foamed polymer.
Effect of Talc Content on the Volume Expansion Behavior of Extruded PP Foams
This paper elucidates the effects of cell density on the volume expansion behavior of polypropylene (PP) foams blown with butane in extrusion. The cell density was controlled by varying the talc content, and foam expansion was observed at a fixed blowing-agent content while varying the melt and die temperatures. As observed in our previous studies, the curve of the final expansion ratio of PP foam versus temperature showed a typical mountain shape for each talc content, indicating the two governing expansion mechanisms which are gas loss and stiffening of melt. As the talc content increased, the expansion curve skewed towards the lower temperature, which showed that the expanded foams of high talc content were more susceptible to gas loss. In order to analyze this change, the early-stage expansion behavior of extruded PP foams was investigated using a CCD camera. The expansion-profile images captured at the die exit show that the expansion rate of extruded foams was observed to be faster at a high talc content because of the reduced diffusion distance of gas molecules to the nearest stabilized cell. The higher growth rate promoted the formation of an initial hump in the expansion profile which is known to be detrimental to large expansion. In order to decrease the expansion rate and thereby to remove the initial hump, the temperature had to be further decreased, and consequently, the optimum temperature to maximize expansion decreased at a higher talc content. On the other hand, the increased cell density at a high talc content increased the number of cell layers in the cross section of the extruded foam, and thereby the gas loss was localized to the cells on the surface which acted favorable for the final expansion ratio to a certain degree.
Lightweight Performance of Load Bearing Plastic Components with an Integral Foam Structure
Employing a modified injection-molding technology, where the mold is opened a short stroke after injection of the polymer melt, it is possible to manufacture plastic parts with low overall density and an integral foam structure. For this processing approach, thermoplastic materials together with chemical foaming agents are used. The resulting plates are a real lightweight design with compact skin layers and a foamed core fraction. A significant gain in stiffness can be observed. The lightweight potential of the design was investigated using mechanical testing methods and the stiffness enhancement was modeled using several models for multi-layer arrangements.
High Temperature Polymeric Microspheres and Foams: Liquid Phase Models
The present paper focuses on the understanding of processes and property changes during formation of precursor forms of polyimides for high temperature foam applications. This understanding is to be used in the development of models for the void formation in the liquid state. The relationship of these voids to the initiation and formation of microspheres from the solid phase polymer particles will be discussed. Three sources of inflation pressure will be examined: organic compounds within the chemical structure of the polymer, volatiles released in the imidization process and residual solvents. The influence of reaction kinetics and molecular weight development on diffusion transport and viscosity within the polymer in both the liquid and solid phases will be examined to describe a major source of rate dependence of these phenomena. Void topology within solid phase polymeric particles will be studied as a cause of the multiple microstructures realized in the foaming process.
Glass Filled Polycarbonate Ester-Polyetherimide Blends
Polymer blending is an attractive and convenient way to obtain new polymeric materials with flexible combination of desired properties. Polyetherimide-polycarbonate blends provide attractive heat, flow and impact balance with high strength and dimensional stability. These blends find various applications for small appliances, microwave trays and automobile lighting bezels.Glass fiber filled PEI/PCE blends have been recently developed to further improve the dimensional strength and stability of these blends. It was found that fiberglass used in these blends compatibilizes the resins giving good control of viscosity and easy compounding. These reinforced resins are suitable for variety of applications in the area of automotive, telecommunication and electronics.This paper will discuss the work has been done on the fiber glass reinforced PEI/PCE blends, the influence of level of glass loading on blend performance.
Injection Molding of Polyetherimide Using Water Cooled Molds
Many injection molders when processing high temperature amorphous resins like Polyetherimide (PEI) use oil cooled molds to enhance the mold filling process and achieve the best mechanical properties attainable. The practice of molding with high mold temperatures is generally recommended by material suppliers in order to reduce molded-in stress, which can have a negative effect on final molded part performance. While it is still good molding practice to use oil cooled molds, there are many instances in which PEI can be molded into acceptable parts using water as the heat transfer fluid. Water cooled molds offer several advantages over oil and includes reducing environmental and personnel safety concerns in addition to lower capital cost and ease of operation.
Mold Release Agents for Polyetherimides
Thermoplastic resins with mold release agents are currently used as a means to improve the ejection of molded parts during the injection molding process. Their use can be found in many different grades and types of thermoplastics including amorphous and semicrystalline materials. However, as processing temperatures increase in excess of 300°C (572°F) for resins such as Polyetherimide (PEI), the choice and availability of releases agents are limited due to their volatility and inherent thermal instability. New mold release formulations have been developed for Polyetherimide for use in opaque and transparent applications. These formulations have reduced incidence of part sticking and improved overall material processability. Process improvements of cycle time reduction, increased productivity, and wider process windows have been reported in the molding of automotive reflectors and food service cookware.
Polyetherimide Films for High Temperature and Electronics Applications
Polyetherimide films are often used in applications requiring high temperature capability, good dimensional stability, and excellent mechanical and electrical performance. One example of such an application is flexible circuitry for airbag sensors. In order to extrude films to meet demanding electrical requirements, the films must be virtually defect free to avoid arcing and other electrical anomalies. To avoid these problems and enable, generation of defect-free films, there is a need for resins with excellent thermo-oxidative stability and processing that optimizes melting and residence time.
Branched Polyethylene Terephthalate Foaming Using HFC-134a: On-Line Process Monitoring
PET chain extension and branching was made through reactive extrusion. A terpolymer of ethylene, ethyl acrylate and glycidyl methacrylate selected for its ability to react with PET end-groups was extruded with PET. The effect of various processing parameters on the extent of reaction was monitored using a commercial on-line process control rheometer mounted on the twin-screw extruder.The reactively modified PET was foamed using 1,1,1,2-tetrafluoroethane (HFC-134a). On-line solubility measurements were made using an ultrasonic technique. The relationship between HFC-134a solubility and PET branching level was established. The opportunities to develop low density extruded PET foams were then identified.
Characterization of Epoxy Curing Using High Heating Rate DSC
A limitation in the characterization of epoxy cure with DSC is the overlap between the glass transition and the curing exotherm. Since the glass transition is independent of rate, whereas the curing reaction is dependent, scanning rate can be used to shift the exotherm while not affecting the glass transition temperature. At 100°C/min, the two overlapping events are separated, whereas at 200°C/min, the curing doesn’t occur in the temperature range studied. The glass transition temperature can be measured without affecting the degree of cure, the exotherm can be shifted to separate it from the glass transition for accurate measurement of enthalpy and the complete glass transition can be measured.
Modification Mechanisms, Curing Kinetics and Properties of Polymethylphenyl Siloxane-Modified Epoxy Resins
The mechanisms of chemical modification of diglycidyl ether of a bisphenol A (DGEBA) epoxy resin modified with a methoxyl-terminated polymethylphenyl siloxane oligomer were characterized by Fourier Transform Infrared Spectroscopy, Thin Layer Chromatography, and Epoxy Equivalent Weight measurements. The curing behavior, the thermal and mechanical properties of the modified epoxy resins cured with meta-phenylenediamine were investigated as a function of the weight concentration of siloxane modifier. The activation energy and frequency factors were dependent on the siloxane content. For modified epoxy resins, an enhancement in thermal stability and the flexural and the tensile strength were observed, and the overall toughness was increased by three to four fold. The glass transition temperature and the flexural moduli of cured samples showed a decrease with an increase in the siloxane content.
Dynamic Mechanical Analysis of UV-Curable Coatings While Curing
A method has been developed for following the dynamic mechanical properties of a UV-curable coating while the sample is curing. The resulting data and plots can be used to measure the material’s cure speed. The precision is sufficiently high to allow small differences in cure speed between different formulations to be reliably estimated.The sample is contained in parallel plate stress rheometer in which the usual metal bottom plate has been replaced by a UV-transparent quartz plate, allowing UV light to illuminate the sample from below. A nitrogen atmosphere is established before every run.The instrument is set up to measure G’, G”, and phase angle vs. time at a frequency of 10 Hz, taking 72 data points per second. Two seconds after a run starts, the software puts out a signal for input to a relay that opens the UV shutterTwo arbitrary criteria for cure times are: 1) The time for G’ to reach 2X104 Pa; 2) The time for the phase angle to decrease to 45°. Typical cure times for fiber optic coatings range from 0.2 to 0.6 seconds
Thermal and Mechanical Properties of Epoxy/Monofunctional and Epoxy/Multifunctional POSS Nanocomposites
The thermal and mechanical properties of diglycidyl ether of bisphenol-A (DGEBA) copolymerized with two types of polyhedral oligomeric silsesquioxane (POSS) nanophases, namely, monofunctional POSS-epoxide macromer (MoPOSS) and multifunctional POSS-epoxide macromer (MuPOSS) cured with polyoxypropylene diamine were investigated. The glass transition temperature, Tg, measured by DSC increased with an increasing weight fraction of the MoPOSS. For the MuPOSS series, the Tg of the composite containing 3.0 wt.% MuPOSS increased; however, the Tg’s of the composites containing equal to or greater than 5.0 wt.% MuPOSS decreased because of a reduced cross-linking density and a plasticization effect from the excess curing agent. The curing of the MoPOSS systems followed firstorder kinetics with lower activation energies and frequency factors. TGA experiments indicated that both types of the POSS provided enhancement in the thermal stabilities compared to the epoxy network. Fracture analysis showed that the POSS-incorporated epoxy network glasses had higher fracture toughness values than the neat epoxy resin.
A Mathematical Model for the Increase of G’ with Time during the Irradiation of UV Curable Coatings
Another paper in this session describes a method for following the development of rheological properties of a UV-curable coating while it is being cured. An equation has been found that models the development of G’ as a function of time from that method. It is an empirical model, not one derived from theory, e.g. reaction kinetics. The model curve conforms to the data points on a plot, all the way from start to finish of curing. Standard non-linear curve fitting algorithms such as Marquardt-Levenberg and Quasi- Newton work satisfactorily. Since the G’ values cover 2 to 3 orders of magnitude, a weighted fit emphasizing lower G’ values gives better results than an unweighted fit. The model is useful for comparing and classifying cure behavior of coatings used for fiber optic waveguides.
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