SPE Library
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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Conference Proceedings
Formulation Issues: Predicting Polymer Miscibility
Fiona Case, May 1999
A number of different techniques have been applied to the study of miscibility and phase separation. Properties of individual components (solubility parameters) have been predicted from first principles and used to estimate the free energy of mixing, ?Gmix, which is the driving force for miscibility. Specific interactions between molecules, which may cause dissimilar materials to combine, have been studied using molecular mechanics models. Atomistic scale models of bulk mixtures are generated and used to study the first stages of phase separation of oil and water. These models are also used to obtain more accurate predictions of ?Gmix. A modified version of the Flory Huggins ? parameter, with both temperature and concentration dependence is then introduced. The parameters in this semi-empirical function are obtained by fitting to data from the other modeling techniques, or from experiment. ?eff is used to predict a wide range of different phase behaviors. The last set of modeling approaches introduced is used to model the phase behavior of materials that show mesoscale structure. A more coarse-grained model is used to predict microphase separation and the formation of micelles. By appropriate use of the range of available techniques, an informed scientist can gain considerable insight into the behavior of mixtures.
Comparison of the Large Deformation and Recovery Behavior of Semicrystalline Ethylene-Styrene Interpolymers and Ethylene-Octene Copolymers
A. Chang, E.V. Stepanov, S.P. Chum, A. Hiltner, E. Baer, May 1999
The tensile deformation and recovery behavior of semicrystalline ethylene-styrene interpolymers (ESI) and ethylene-octene copolymers (EO) were compared as a function of temperature, comonomer content, and crystallinity. At high temperatures, ESI and EO exhibited almost no strain rate dependence during loading and complete recovery upon unloading, characteristics of elastomeric behavior. At low temperatures, the materials were elasto-plastic with high amounts of permanent set after unloading. This transition from low to high temperature behavior originated from a difference in deformation mechanisms. Under conditions where the behavior was elastomeric, the slip-link model was applied to describe the entire stress-strain curve.
Effect of Molecular Weight and its Distribution Related to Melt Processing Parameters of Polyphenylene Sulphide
Sujeev K. Kommana, Kyung-Ju Choi, May 1999
Poly Phenylene Sulfide (PPS) is a relatively new Polymer, which is now finding an increasing number of applications in industry. It couples good chemical and impact resistance with high temperatures. This material has been the focus of intensive research over the past few years. However, not much Rheological or Processing data has been published for PPS. This research provides an insight into the effect of molecular weight and its distribution by the rheological properties of PPS, as well as processing parameters like extruder output, die pressure and torque. It is found that a sample with a narrow molecular weight distribution and low molecular weights when compared to other samples is relatively easier to process with wider operating windows.
Orientation Analysis of Cast and Blown Polyethylene Films
F. Chambon, S. Srinivas, May 1999
Orientation and chain architecture play a dominant role in determining the mechanical properties of semi-crystalline polymers. Morphological features of linear low density polyethylene (LLDPE) films obtained from carefully controlled processing conditions are studied using a combination of WAXS, SAXS, TEM, AFM and birefringence. Analysis of crystalline orientation is studied in detail and differences found between polyethylenes produced with distinct catalyst types are pointed out. Orientation of the non-crystalline phase is then extracted by subtraction of the in-plane and out-of-plane birefringence from WAXS data. This integrative approach provides us with a deep insight of structure-property relationships in LLDPE films and is a prerequisite for development of a consistent model for the solid-state.
Large Strain Stress Relaxation and Recovery Behavior of Ethylene-Styrene Interpolymers
H. Chen, E.V. Stepanov, S.P. Chum, A. Hiltner, E. Baer, May 1999
The large strain, nonlinear stress relaxation and recovery behavior of amorphous ethylene-styrene interpolymers (ESIs) was studied at temperatures above the glass transition temperature (Tg). At longer times, the nonlinear stress relaxation curves could be superposed by vertical shifting. The damping function determined from these shift factors was well described by the Doi-Edwards tube model. The instantaneous recovery after stress relaxation was also investigated. For lower temperatures and shorter times, the data were described by Gent's two network model. At higher temperatures, this model was no longer applicable. A modified two network model using the damping function from stress relaxation was developed to successfully describe the instantaneous recovery.
Technology of Filled Ethylene/Styrene Interpolymers
M.J. Guest, Y.W. Cheung, S.R. Betso, T.P. Karjala, May 1999
INSITE™ Technology has enabled the production of ethylene/styrene interpolymers (ESI), typically containing up to about 50 mole % styrene. These ESI show good filler acceptance, and this technology allows the engineering of novel materials. Materials have been produced by melt compounding based on a range of fillers, including calcium carbonate and aluminum trihydrate (ATH). The properties of filled ESI are presented and discussed, including solid state dynamic mechanical spectroscopy and ignition resistance. The toughness of highly filled materials, such as indicated by elongation at rupture from tensile stress/strain behavior is described. Melt rheological properties of filled ESI are related to processing operations. Some potential applications for filled ESI are introduced.
Effects of Additives on Scratch Resistance of Polypropylene Materials
J. Chu, May 1999
Pigmented mineral-filled polypropylene (PP-PMF) is marketed as a potential alternative to ABS (acrylonitril-butyldiene-styrene) and ABS/ PC (acrylonitril-butyldiene-styrene/ polycarbonate) for interior automotive components. PP-PMF is more easily damaged by surface scratch & mar, thus limiting its acceptance for interior applications. This study investigates the scratch and mar mechanisms of talc-filled PP and the effects of various additives on the scratch and mar resistance of PP-PMF. Talc filler provides higher modulus for PP. The addition of nucleation agent and lubricant showed beneficial effects.
True Stress-Strain-Temperature Diagrams for Polypropylenes
J. Liu, A. Chudnovsky, C.P. Bosnyak, K. Sehanobish, May 1999
The relationship between the stress - strain characteristics and material morphology has been well studied for many types of polymers. Large morphological variations that occur during the cold drawing process determine the basic parameters of necking. Recently, true stress - strain - temperature (TSST) diagrams have been proposed as a tool of an invariant characterization of thermo-mechanical properties of polymers. In the present work we illustrate an application of this technique for comparing TSST diagrams of two polypropylenes from a structure - properties relationship viewpoint. The implications of TSST diagrams for strain localization and fracture of polypropylene are also addressed.
On Modeling of Slow Crack Growth in Polyethylene
J. Fan, Y. Shulkin, A. Chudnovsky, May 1999
A crack and a domain of crazed material ahead of the crack (process zone), commonly observed in polyethylene, are considered as a thermodynamic system called the crack layer. According to the crack layer theory, slow crack growth in polyethylene is largely a result of degradation of the process zone material. In the present work, a simplified version of the theory is employed to model discontinuous slow crack growth often observed in polyethylene. The proposed model predicts the relation between the rate of crack growth and the stress intensity factor consistent with that obtained experimentally for the steady stage of fracture process. Lifetime evaluation is discussed.
Observation and Characterization of Slow Crack Growth in Water Pipe Grade Polybutylene
X. Niu, W. Zhou, A. Chudnovsky, S.S. Stivala, May 1999
Polybutylene (PB) piping has been widely used in portable water distribution systems. Premature brittle fracture constitutes the major limitation for PB in its application. The fracture process of PB consists the well recognized three stages: crack initiation, slow growth and fast propagation. In present work, the observations of crack initiation in service, fatigue slow crack growth (SCG) at elevated temperature, strain localization in front of the crack constituting the process zone (PZ) as well as variability of the strength of PB are reported.
Structural Characterization and Thermomechanical Behavior of Ziegler-Natta Polypropylenes of Varying Crystallinity
J. Liu, A. Chudnovsky, C.P. Bosnyak, M.T. Bishop, B. Landes, J. Zryd, May 1999
In this study three isotactic polypropylenes, PP, made via a Ziegler-Natta catalyst are employed with similar molecular weights, but of varying levels of crystallinity. The lowest crystallinity sample studied here is a random copolymer, RCP, with ethylene as the comonomer. The three polypropylenes are characterized by calorimetry, X-ray and tensile tests. A specific feature of this report is the development of true stress-true strain behavior maps as a function of the strain rate and temperature and analysis of the yielding behavior.
A Comparison between Forced Air Convection Heating and Direct Electrical Heating of Moulds in Rotational Moulding
Michael J. Wright, Roy J. Crawford, May 1999
The rotational moulding process is unique in that the mould and the plastic must be heated from room temperature to over 200 °C (400 °F). This stage in the process is slow using conventional convection heating because the polymer is a poor conductor. This is particularly evident when a large mass of polymer has to be heated. In recent times other methods of heating have been proposed to improve the heat transfer and give the moulder better control over what is going on inside the mould. This paper compares an electrical heating method with forced air convection heating to identify any advantages that may accrue from direct electrical heating of the mould.
Structure and Dynamics of Polymers in Confined Geometrics: Neutron Studies of Intercalated Clay-Polymer Nanocomposites
Robert Ivkov, Peter M. Gehring, Nick C. Maliszewskyj, Ramanan Krishnamoorti, May 1999
Clay-polymer nanocomposites are a relatively new class of materials that have already proven useful in several applications. These materials make possible studies into the structure and dynamics of polymers in severely confined geometries. We present neutron time-of- flight spectroscopy results on the dynamics of polyethylene oxide (PEO) intercalated into fluorohectorite (FH) clay. We compare the spectra obtained from two samples of intercalated materials, with PEO mass fractions of 0.18 and 0.30, with those obtained from bulk PEO and pure FH clay. We also report conclusions regarding the structure of the polymer chains in the intercalated materials that can be obtained from the spectroscopic data.
Structural Characterization of Commercial Impact Resistant Polypropylene
Ruth Zacur, Graciela Goizueta, Numa Capiati, May 1999
Commercial impact resistant polypropylene copolymers (IPC) are produced by a sequential gas phase polymerization process. The final product is a complex blend of polypropylene (PP) and ethylene- propylene copolymer (EPC) of different ethylene contents. In the present work, the composition of two different impact copolymers was estimated performing a separation by Analytical Temperature Raising Elution Fractionation (TREF) using the step elution method. Recovered fractions were analyzed by DSC and SEC. The morphology of the whole material was examined by SEM. The differences in the disperse phase particle sizes are interpreted taking into acount the molecular weights of both EPC and PP, and the EPC content.
Low Density Polyethylene/Thermoplastic Starch Blends: Effect of Glycerol Content and LDPE Concentration on Morphology and Tensile Properties in the Dual Phase Continuity Region
Francisco J. Rodriguez Gonzalez, Bruce A. Ramsay, Basil D. Favis, May 1999
Starch was gelatinized, plasticized and melt blended with LDPE in a one step process with three different glycerol/water ratios. In LDPE/thermoplastic starch (TPS) blends, the percentage by weight of LDPE was varied from 40 to 70 in order to study the region of dual-phase continuity. Extruded sheets were characterized for composition, tensile properties and morphology. Hydrolytic degradation was carried out in order to determine the degree of connectivity of TPS domains. TPS domains presented a fiber-like-structure when glycerol content was higher than 27.5%. Co-continuous morphologies were found close to 45 wt. % of TPS produced by fiber coalescence. Those results were confirmed by the degree of connectivity of TPS domains. Elongation at break of blends having high TPS loading, and compounded with 27.5% glycerol or more, maintain in excess of 80% of the original elongation of LDPE.
Bubble Removal in Rotational Molding
George Gogos, May 1999
Simple closed form solutions have been obtained for bubble dissolution in typical polymer melts encountered in rotational molding. The solutions are in excellent agreement with experimental data available in the literature. Using these closed form solutions it is shown that under typical rotational molding conditions the polymer melts may be almost saturated. As a result, bubble shrinkage occurs over long periods. Depending on the degree of saturation, surface tension may contribute substantially to the concentration gradient that drives bubble shrinkage. A pressure increase imposed on such an almost saturated polymer melt leads to a steep concentration gradient in the vicinity of the bubble/melt interface that can lead to extremely fast bubble shrinkage. The effect of surface tension on the rate of bubble shrinkage is negligible under such undersaturated conditions.
An Application Comparison of Orbital and Linear Vibration Welding of Thermoplastics
David A. Grewell, Avraham Benatar, May 1999
This paper compares the differences in weld quality between orbital vibration and linear vibration welding of thermoplastics. Generally, orbital welding was found to weld parts faster with no loss in tensile or impact strength. For parts with thin unsupported walls, orbital welding was found to produce more uniform welds with higher tensile strength than linear vibration welding. In cases where low vibration amplitudes are required, orbital welding was able to join parts with slightly lower vibration amplitude and slightly lower collapse than linear vibration welding without sacrificing joint quality.
Applications with Infrared Welding of Thermoplastics
David A. Grewell, May 1999
This paper reviews the development of IRAM™ welding (Infrared Assembly Method). In particular one mode of IRAM welding which is based on the concept of passing light (?=800 to 950 nm) through one component being welded and having the second component absorb the light at the interface. This absorption results in heating and melting of the interface and allows the parts to be welded. The major breakthrough in this technology is the ability to illuminate the entire welding surface simultaneously. There are many advantages to this technology compared to heating a single spot and translating the laser spot across the welding zone including: faster (3-10 seconds/weld), no problems with run-on" / "run-off" less residual stresses able to weld to large collapses no moving parts and easily automated."
High Thermal Conductivity Rapid Dies: Backfilled and Coated Dies
Richard Gnegy, Amod Ogale, May 1999
Rapid polymer tooling uses stereolithography to make injection molding dies in a matter of hours. These dies can be used to mold a small number of prototypes for evaluation. However, the poor thermal properties of these dies cause them to deform or fail during molding. Two methods were investigated to improve the thermal properties of such dies. The first technique consisted of creating thin polymer shells, which were backfilled with high thermal conductivity, low-melt alloys. The second technique involved the deposition of a thin layer of nickel onto the working surface of the die. This created a pathway for heat to escape to the sides of the die. The electroless coatings did not cover the entire surface of the die uniformly. Temperature data was obtained from the backfilled, nickel-coated, and solid polymer molds using embedded thermocouples. The temperature data indicated that the backfilled die cooled much faster than the other two types, and displayed enhanced thermal conductivity.
Effect of Temperature Dependent Thermal Properties on the Accuracy of Simulation of Injection Molding Process
L. Sridhar, K.A. Narh, May 1999
The effect of using temperature dependent thermal conductivity and specific heat data on the simulation of injection molding process is examined. Results of the simulation based on temperature dependent thermal conductivity and specific heat data are compared with those based on constant thermal conductivity and specific heat. These results are presented for a representative selection of crystalline and amorphous thermoplastics. The results show that the prediction of cooling time and the frozen layer fraction of the part thickness in injection molding is strongly influenced by the type of temperature dependent thermal data used.
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