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The Effect of Maleic Anhydride Coupling Agent on Melt Processed Semi-Crystalline PET Nanocomposite Films
Semi-crystalline PET/montmorillonite nanocomposite films were processed by melt-extrusion along with 0.5% maleic anhydride as a coupling agent. Mechanical, thermal, barrier and morphological properties of the nanocomposite films with and without the coupling agent were examined. The nanocomposites have demonstrated an intercalated/exfoliated morphology with the montmorillonite acting as a crystal-nucleating agent in all of the nanocomposite film samples. DSC experiments show this effect through faster nucleation rates and an increased overall degree of crystallization. A depressed glass transition temperature is observed in all nanocomposite samples along with an increased Young's modulus and decrease in film toughness.
The Influence of Molecular Weight on the Relaxation Behavior of Uniaxially Strethed PEN Films as Investigated by Real Time Spectral Birefringence Technique
The influence of molecular weight (Mw) on the structural evolution of as cast amorphous poly (ethylene naphthalene), PEN, during uniaxial stretching and further relaxation is investigated by real time measurement of the true mechanical and optical behavior of the material in the rubbery state. Uniaxial deformation behavior reveals that stress-optical behavior is composed of three regions: (I) traditional stress optical region where the polymer remains amorphous, (II) fast birefringence increase region that accompany rapid rise in crystallinity and (III) birefringence saturation region. Both materials follow the stress optical rule (SOR) at low deformation levels with a stress optical constant of 27.5 GPa-1. Stress-optical behavior deviates from linearity in both MW PEN's when crystallinity exceeds 7% and the material exhibit nematic order. The deviation from linearity occurs at lower stress levels for the low MW material, nevertheless. The mechanism of neck formation has a considerable influence on the crystallization of the material. After neck starts the crystallinity increases rapidly in both materials, reaching a saturation value of approx. 35% in crystallinity when strain hardening occurs. The preliminary studies revealed that the relaxation behavior of PEN involves a complete orientation recovery following the stress optical rule when the material is first stretched within the Region I and if stretched beyond the linear range the relaxation stage is found to accompany partial orientation relaxation followed by crystallization.
Haze Improvement with Addition of HP-LDPE or HDPE: Part I - Blown Film Property Comparison
Blends of a Metallocene Linear Low Density Polyethylene (mLLDPE) with a variety of high pressure Low Density Polyethylene (HP-LDPE) or High Density Polyethylene (HDPE) at different blend ratios were investigated. Effects of these additions on blown film haze and toughness are discussed.Dramatic improvement in haze is achievable either by HP-LDPE addition or by HDPE addition. The improvement in haze, however, is usually accompanied with losses in mechanical property. Careful choice of blending partner and level is crucial for the best balance of haze and mechanical properties.
The Influence of Draw Conditions on the Morphology and Physical Performance of POE Film
The influence of draw conditions on the morphology and physical performance of polyethylene-octene elastomer(POE) film were studied in this paper. The influence of draw conditions on the morphology of POE film was discussed via wide-angle X-ray diffraction (WAXD). The results showed that draw conditions caused POE film to produce a (110) plane crystalline peak in PE. When the draw ratio (DR) = 3, the interference intensity at draw temperature (DT) = 90? was greater than that at DT = 75?; and when DR = 6, the interference intensity at DT = 75? was greater than that at DT = 90 ? . Elastic recovery rate and stress-strain value were tested using an Instron multi-testing machine. The results were used to establish a dynamic deformation mechanism. The results showed that, after draw processing of POE, the stress value fell after approaching the saturation point with the increase in draw ratio. Furthermore, it was also shown that the elastic recovery rate and stress retention rate were better at DT = 75? than at DT = 90?.
Morphology Evolution in PTFE as a Function of Deformation and Melt Time and Temperature: Nano-Fibrils and Single- and Multi-Molecule Folded Chain Single Crystals
Evolution of the morphology of dispersed PTFE dispersion particles on glass and mica as a function of melt time and temperature indicates that individual molecules wander" on the substrate crystallizing (from a chain- folded "mesomorphic" state it is suggested) in single and multi-molecule chain folded single crystals when cooled. Shearing of the particles results in nano-fibril production; annealing results in shish-kebab formation through single molecule addition. Nascent dispersion particle structure will also be considered."
Influence of Co-Monomer Distribution Profile on the Crystallization Characteristics and Physical Properties of High Density Polyethylene
Three sets of two-component blends from various narrow-MWD (molecular weight distribution), linear (no rheologically significant long branches) polyethylenes were prepared with multiple compositions in each set of blends. These blends were deliberately prepared such that the branching (from 1-hexene co-monomer) was present exclusively on either the high or the low molecular weight blend component. The average branching content in each blend component was verified to be uniform across its MWD. In this study, the influence exerted by such selective placing of the branching on the crystallization characteristics of the resulting blends will be discussed. Further, some new observations relating to the tensile stress-strain behavior of these blends will also be described.
The Effect of Blend Composition on the Deformation Behavior of PEN/PEI Blend Using Online Mechano-Optical Technique
The influence of blend composition on deformation as well as stress-optical behavior of cast amorphous PEN/PEI blends is investigated above their respected glass transition temperatures. To elucidate the structural changes occurring during stretching a real time birefringence technique coupled with true stress/strain measurement technique is used. These techniques are able to track fast changes in birefringence and stress levels as the film is being deformed. The results obtained by these two techniques permit determination of the stress optical coefficient and the limits of validity of Stress-Optical Rule (SOR). Further investigations by X-ray and DSC measurements help to understand and clarify the structure developed during the deformation process of the material. These studies indicate that the deformation of 95/5 and 90/10 PEN/PEI blends in rubbery state involves three main stages. In the first stage the material remains amorphous following the stress optical rule. In the second stage the birefringence rises rapidly and it is associated with the highly disordered nematic like structure formation. The final stage is attributed to finite chain extensibility resulting in little change in birefringence with significant stress increase. 80/20 PEN/PEI blend does not show up the final stage III in the deformation process and it seems it is delayed to higher stretch levels as the crystallization is highly suppressed due to dilution effect .
Structure-Property Relationships in Metallocene Based Ethylene-Octene Plastomers
Ethylene copolymers are extensively used in the automotive industry as preferred plastomers for impact modification of polypropylene. Performance of these plastomers is strongly effected by the molecular architecture determined by the type and amount of comonomer, and the distribution of the co-units along the polymer backbone. In this paper we describe the analysis of a series of commercial and developmental metallocene random ethylene-octene copolymers with low and ultra-low density in the range 0.860 g/cm3 to 0.906 g/cm3, and melt index between 0.5 to 27. Thermodynamic properties and crystallization behavior are evaluated using differential scanning calorimetry (DSC) to determine the effect of crystalline and amorphous phase on the density and mechanical performance. Peak melting temperature and crystallinity are almost linearly related to the density while MI does not appear to have any effect on the crystalline phase. A thermal segregation technique is used to determine the influence of octene branches on the sequence length of crystallizable methylene units. With an increase in octene content, glass transition broadens and decreases with density as crystallization mechanism changes. Longer sequences form lamellar structures while presence of shorter sequence lead to a mixed crystalline morphology consisting of predominantly fringed-micellar crystals. Results of modelling of properties and performance will be discussed and compared with the previous analysis of a series of ethylene-butene plastomers.
Controlled Epoxy Network Structure-Property Relationships: The Effect of Chain Termination
While epoxy thermosets are commonly used and are best known for their high glass transition temperature (Tg), creep resistance, environmental resistance and high stiffness, they are extremely complicated and intractable to thorough investigation. This is in part due to the fact that these are curing systems and gelation marks a turning point in the system’s performance as well as ability to be probed for effective structure-property relationships. In addition, practical formulations often contain multiple components that have subtle but important interactions to the final performance.In this presentation we will cover work that was performed recently to quantitatively probe the effect of one such practical yet important effect, namely chain termination. The effect of the size as well as flexibility of the chain termination group will be examined via a controlled host matrix chemistry that comprises of DER™ 332 as the epoxy, bisphenol A (BA) as extender and tris(4- hydroxyphenyl)ethane (THPE) as a crosslinker. Data and trends pertaining to Tg, stiffness, yield strength, fracture toughness and thermal expansion coefficient will be discussed.
Evaluation of Thermoset UV Curing Kinetics by Calorimetry, Rheology and FTIR Spectroscopy
UV curable polymer systems are commonly characterized for degree and time of cure by thermal methods such as scanning photocalorimetry. In this work, we modified existing thermal and rheological instruments in order to apply a controllable dosage of UV radiation and compare the curing kinetics of two commercial polyester and epoxy powder coating systems differing in rate of cure. In general, there is an optimal temperature range whereby the material is completely cured. The optimal conditions are generally set for material heated above its flow temperature to cure within 5 seconds of UV radiation. Our thermal and rheological results are in good agreement with each other and with manufacturer's published data employing photocalorimetry. The data were analyzed for temperature dependence and efforts were made to correlate thermal and rheological results with time dependent structural changes monitored by FTIR spectroscopy.
Properties of Siloxane-Modified Epoxy Resins
A diglycidyl ether of bisphenol A (DGEBA) epoxy resin was chemically modified using a silanolterminated polymethylphenylsiloxane (PMPS) and two methoxy-terminated PMPS intermediates with high (3.3/1) and low (0.5/1) phenyl/methyl ratios. At room temperature, the methoxy-terminated PMPS with the high phenyl/methyl ratio was miscible with the epoxy resin and formed a one-phase system; however, both the silanolterminated PMPS and the methoxy-terminated PMPS with low phenyl/methyl ratio were incompatible with the epoxy resin and phase separation occurred. While, at 120?, resins modified with all three PMPS intermediates formed homogeneous solutions. A range of the tensile and the fracture properties of unmodified and modified epoxy systems was obtained by changing the modification method, the concentration and the type of PMPS modifiers, the type of curing agent, and the cure cycle. The modified epoxy systems have slightly decreased tensile moduli. The chemical modification method is more efficient in the improvement of the fracture toughness than the physical blending method. The fracture toughness increases with an increase in PMPS concentration. The silanol-terminated PMPS has a better toughening effect than the two methoxyl-terminated PMPS modifiers. The polyoxypropylene diamine (POPDA) cured epoxy systems have much higher fracture toughness values than the 1,3- phenylenediamine (MPDA) cured epoxy systems.
The Effect of Absorbed Moisture on the Elevated Temperature Properties of Polyetherimide
The effects of moisture absorption on products molded from polyamides are well documented. However, other high-performance materials such as polyetherimide and polyethersulfone also absorb significant amounts of moisture from the atmosphere. Early tests suggest that this moisture absorption influences the glass transition temperature of these polymers. This has implications for short-term elevated temperature service as well as creep resistance and fatigue resistance at lower temperatures. This paper quantifies the effects of absorbed moisture on the elevated temperature properties of polyetherimide and characterizes rates of moisture gain and loss at different environmental conditions.
Measurement and Prediction of Fibre Orientation within a Three-Dimensional Flow
In this paper we describe a comparison of the fibre orientation structures developed in a transverse ribbed plate during injection moulding, with those predicted using the Moldflow commercial software, for a model transverse ribbed component. Fibre orientation measurements were carried out using a large area image analysis system developed at the University of Leeds. Moldflow analyses of the ribbed plate were conducted and compared to measured fibre orientation distributions. Adjustments of the fibre interaction coefficient within Moldflow analyses have yielded significant improvements in model accuracy.
Effect of Freeze-Drying on the Glass Temperature of Cyclic Polystrenes
The calorimetric glass temperature was measured for three cyclic polystyrenes with apparent molecular weights ranging from 4.0 x 103 to 195.5 x 103 g/mol for both bulk material and for samples freeze-dried from dilute solution. Freeze-drying from dilute solution was found to reduce the glass temperature by 7 to 14 K depending on the sample. These Tg depressions are 5 to 12 K greater than those found previously for freeze-dried linear polystyrene. Annealing at 403.2 K and 443.2 K (130 °C and 170 °C) resulted in recovery of the Tg back to the bulk value with the time scales depending on both temperature and the magnitude of the Tg reduction; the low apparent activation energy dependence of the recovery of Tg precludes its being due to viscous flow.
Modeling the Yield Behavior of Glassy Networks using Molecular-Based Parameters
Recent findings suggest that the yield behavior of glassy networks is governed primarily by two molecular based parameters. The first of these parameters is the glass transition temperature, Tg, and reflects the network stiffness including backbone stiffness, crosslink density, crosslink functionality, and other inter and intra-molecular interactions. The second of these parameters is the cohesive energy density, Ecoh, reflects the cohesive strength of the network. In this paper, we present a framework to incorporate these parameters in a molecular-based yield model. We extend the framework to include alterations in temperature, strain rate, stress state, and molecular composition (through these parameters). We also outline current experiments to evaluate the limits and capabilities of the hypothetical model presented and summarize recent findings.
The Temperature Dependent Viscoelastic and Viscoplastic Properties of Nylon 12
We report the viscoelastic and viscoplastic properties of Nylon 12 by treating the polymer as an equivalent network of chains bridged by temporary junctions (entanglements, physical cross-links and lamellar blocks). The network is thought of as an ensemble of meso-regions linked with each other. Tensile tests were carried out with constant crosshead speeds (ranging from 5 to 200 mm/min) from 35 to 140°C using a tensile test machine with an oven attachment. Stress strain relations for uniaxial deformation were developed by using thermodynamic principles. These governing equations involve two material constants that were derived by fitting the experimental observations. Good agreement was obtained between the numerical simulation and experimental data. These results will be used as a basis for characterizing the bending prior to thermoforming of Nylon 12 automotive tubing.
Finite Element Analysis of Hyperelastic Materials: Elastomeric Seal
Seals are critical components in virtually all mechanical devices, which are used for closing the gap and/or to separate two liquids or gasses in static or dynamic applications. But the complexity of seals and the difficulties associated with resolving essential parameters, both material and geometric, have hindered the effectiveness of experimental and theoretical understanding of seal design. The present paper describes the axisymmetric analysis of elastomeric seals at medium strain (strain less than 100%) under static and dynamic conditions using Abaqus software. The stress strain behavior of a black filled ethylene propylene (EPDM) rubber are studied in extension over a range of temperature to examine the validity of Arruda-Boyce, Mooney-Rivlin, Neo-Hooke, Ogden, Polynomial, Reduced polynomial, Van der Waals and Yeoh models. The analytical form for strain energy density function of Arruda-Boyce model gives a very good fit to the experimental data for strains less than 100%, which cover the range of interest for most engineering applications.
Review of the Ultrasensitive Oxygen Consumption Method for Making More Reliable Extrapolated Predictions of Polymer Lifetimes
Predicting polymer lifetimes in air is often based on unconfirmed extrapolations of elevated-temperature Arrhenius behavior. To improve confidence in such extrapolations, we describe an ultrasensitive oxygen consumption approach. Measurements are made at elevated temperatures to confirm correlation between activation energies (Ea) for consumption and conventionally measured properties (e.g., mechanical). In addition, the sensitivity of the consumption approach allows measurements to be made in the lower-temperature extrapolation region, thereby testing whether the hightemperature Ea remains constant.
Real-Time Synchrotron X-Ray Techniques for Polymer Processing Research
The Advanced Polymers Beamline (X27C) at the National Synchrotron Light Source (NSLS), Brookhaven National Laboratory (BNL) was commissioned in January 1997 by Ben Hsiao and Ben Chu from the State University of New York at Stony Brook (SUNY-Stony Brook). This facility is the first synchrotron facility in the United States dedicated to chemistry/materials research (with emphasis on polymers) using combined small-angle x-ray scattering (SAXS) and wide-angle x-ray diffraction (WAXD) techniques. Today, X27C has become a major workhorse serving the U.S. polymer community for time-resolved and in-situ x-ray scattering and diffraction studies. The primary focus of the X27C beamline is to investigate polymer structures, morphologies and dynamics from atomic, nanoscopic, and microscopic to mesoscopic scales in real-time and/or in-situ using SAXS and WAXD techniques. Selected examples of studies carried out in X27C include characterizations of nanocomposites, crystallization, melting and phase transition of polymers, polymer melts and solutions during shear, fiber formation and deformation, high pressure study under supercritical conditions, biopolymers, organic/inorganic hybrid nanocomposites and supramolecular structured biological molecules. In this presentation, we will focus on the current research opportunities of using real-time synchrotron techniques to assist varying polymer processing research.
Some Recent Developments in Melt Rheometry
The linear viscoelastic behavior of the melt provides a wealth of information concerning the structure of a highly-entangled polymer and is widely used to characterize polyolefins. Long-time relaxation processes are most sensitive to molecular structure but are difficult to probe in the case of polymers with broad molecular weight distributions or long-chain branching. By combining complex modulus data with creep/creep recovery data using a continuous relaxation spectrum one can often reach the terminal zone even when this zone is inaccessible using standard techniques. Nonlinear viscoelascitity plays an important role in many melt processing operations, but the characterization of nonlinear behavior poses major challenges for the rheologist. The sliding plate rheometer has proven valuable for establishing nonlinear behavior in shear and for the study of wall slip and melt rupture. A new extensional rheometer designed as an accessory for a standared rotational rheometer has also been evaluated.
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