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

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 At higher temperatures, this model was no longer applicable.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.

An Experimental Design Approach: Effect of Slip and Antiblocking Agents on the Performance of a LLDPE Polymer

Kasinath Nayak, Norris M. Tollefson, May 1999

Most low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) films (cast or blown) exhibit blocking during processing and end use applications. Antiblocking agents such as amorphous or crystalline silicas reduce blocking, film-to-film adhesion and thus render these films usable. We have undertaken a systematic approach in evaluating both synthetic amorphous and crystalline silicas as antiblocking agents in presence of a slip additive on the performance of an octene based linear low density polyethylene copolymer. A series of formulations were prepared with three different antiblocking agents along with a slip additive. The slip agent erucamide" was added to the formulations at five different concentrations resulting in a total of 35 formulations. The film properties including %haze yellowness index coefficient of friction and blocking force were measured. An experimental design approach was employed to determine the effect of slip and antiblock on the blocking force using selected formulations."

An Experimental Design Approach: Effect of Slip and Antiblocking Agents on the Performance of a LLDPE Polymer

Kasinath Nayak, Norris M. Tollefson, May 1999

Creation of Plastic Prototypes and Molded Plastic Parts via Selective Laser Sintering

Christian Nelson, May 1999

The SLS® Selective Laser Sintering process is a rapid prototyping (RP) process with the unique advantage of processing a broad range of materials in a single RP platform. Prototype parts for functional testing are produced with polyamide, glass-filled polyamide, or TPE. For small quantities of molded parts, the SLS process is used to produce composite, short run mold inserts for molding several hundred parts with common plastics. For large quantities of molded parts, the SLS process is used to produce metal mold inserts for molding over 100,000 plastic parts with most plastics. This paper will provide background information on the SLS process, describe how the process is used to manufacture metal mold inserts, and provide application examples showing time and cost savings for designers and manufacturers.

Prediction of Stiffness from Orientation Data of Glass Reinforced Injection Moldings

N.M. Neves, A.S. Pouzada, May 1999

The complex thermo-mechanical process developing in injection molding leads to through-thickness and point to point variation of fiber orientation. It is not economically viable to characterize experimentally the variation of fiber orientation. Thus, efforts have been put into modeling the fiber orientation in injection molding. Some commercially available programs already allow the prediction of fiber orientation distribution in moldings. If the fiber orientation field is known it is possible to calculate the major elastic properties, which can be input into finite-element structural analysis codes to predict product performance. That approach was followed in this work to compare the experimental flexure behavior of glass fiber reinforced polycarbonate injection molded discs with predictions obtained from FEM simulations. The data used in the FEM code was calculated from the fiber orientation data predicted using the software C-Mold.