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

Characterization of the Near-Surface Crystalline Structure and Morphology of Injection-Molded TPO

Houxiang Tang, David C. Martin, May 2000

Near-surface structure is expected to play an important role in determining the surface mechanical and adhesive properties of injection-molded Thermoplastic Polyolefins (TPOs). In this report we discuss the near-surface structure of injection-molded TPO based on isotactic polypropylene (iPP), with the intention to elucidate the influence of the TPO substrate structure on the adhesion of painted layers. Localized flat-film X-ray diffraction has been used to characterize the crystalline structure of the iPP component, while transmission electron microscopy (TEM) has been used to reveal the high resolution morphology of iPP crystals and secondary particles. The polymorphism and texturing of the near-surface iPP crystals is discussed, based on the generally accepted structures of iPP crystalline phases. There is evidence to support the presence of ?-phase PP crystals in the near surface area. Significant anisotropy in the secondary particle morphology was revealed by TEM imaging.

Mold Filling and Curing Analysis in Scrimp

Huan Yang, L. James Lee, May 2000

In recent years, vacuum-assisted resin transfer molding (e.g. Seemann Composite Resin Infusion Molding Process - SCRIMP) has been widely used for marine, civil infrastructure, transportation and defense applications. Unsaturated polyester and vinylester resins are two major resins used in these processes. Their kinetic and rheological behaviors were investigated experimentally. A model was developed to quantify the effects of different curing agents on the gel time and reaction rate. This model, in conjunction with fluid flow and heat transfer models, was used to determine the effects of resin type and composition, curing temperature, and part geometry on mold filling and curing. SCRIMP experiments were carried out to verify the simulation results.

Improving the Performance of Rotomolding Resins

Alvin Spence, May 2000

Rotational molding is one of the fastest growing processes in the plastics industry today. However, this growth has been somewhat restricted by the number of and types of resins available to the molder. Polyethylene has traditionally been the workhorse for the industry because of its ease of processing. Unfortunately polyethylene lacks stiffness, along with other mechanical properties, compared to the resins used in competitive processes. This paper outlines methods to improve the performance of rotomolding resins using processing techniques, modifying the design of the part and by the inclusion of strengthening additives in the polymer matrix.

High-Performance Poly Metal Composites Replace Lead in Many Applications

Larry Stover, Jeff Frankish, David Douglas, Robert Durkee, May 2000

A new injection moldable thermoplastic composite has been developed to eliminate problems associated with lead. This nontoxic polymer-metal composite can be formulated to meet the density, mass, and radiation-shielding properties of lead, while offering superior strength and design flexibility. The use of this material eliminates lead-toxicity issues encountered in handling, fabrication, and disposal. Target applications include: nontoxic projectile cores and shot, radiation shielding for medical and nuclear power, counterweights, sporting goods, ballast systems, vibration dampening, sound proofing, and many other applications where a nontoxic, high-density, high-strength material is required.

Ballistic Impact Resistance of Thermoplastic Composites

John W. Song, Nainesh Amin, Stephen Petrie, May 2000

The correlation between adhesive strength, stiffness, flexural properties and ballistic impact resistance of Kevlar-KM2 composites with polysulfone (PSU) resin matrix was studied through examination of the failure of the composites on different processing conditions. Processing temperature greatly changed resin molecular conformation. Resin molecular conformation directly influenced composite flexural properties as well as ballistic impact energy absorption. Composites processed at 260°C showed significantly higher ballistic impact resistance than composites processed at 350°C. Significantly different failure mechanisms of these composites that are induced by different processing conditions are considered to be responsible for this result. The former exhibited mainly tension mode of failure whereas the later failed mainly shear cut. Fiber straining accompanied with delamination due to the tension mode of failure is the preferred failure mechanism for better ballistic impact energy absorption.

New Thermally Conductive Thermoplastics Offer Freedom of Design in Heat-Management Applications

René Pastor, May 2000

A new thermally conductive compound available in a variety of crystalline thermoplastic matrices can be used to improve material management in a variety of industrial and consumer applications, including heat sinks, thermostats, heat exchangers, and as radiant heating coils. Replacing heavy metal shrouds and non-recyclable metallized plastics, the new compounds are non-corrosive, can be processed on all conventional thermoplastic equipment, and can even be melt reprocessed for in-plant recycling. A variant on the technology also produces compounds that are simultaneously thermally and electrically conductive.

Parameters Affecting the In-Line Measurement of Gas Solubility in Thermoplastic Melts during Foam Extrusion

Q. Zhang, M. Xanthos, S.K. Dey, May 2000

The knowledge of gas solubility at processing conditions is of paramount importance for the understanding and optimization of extrusion foaming by gas injection. A recently developed in-line optical method is used to generate data of the solubility of atmospheric gases in PS and PET in single or twin screw extruders with gas injection capabilities. Overall, the in-line data compare favorably with off-line data where Henry's law constants were obtained from the slope of solubility/equilibrium gas pressure plots. Results obtained with the twin-screw extruder configured for improved mixing indicate: a) better data consistency, presumably as a result of enhanced homogenization/dissolution and longer residence time, and, b) a higher degree of sensitivity in detecting differences in the solubility of different gases.

Improved Organotin Stabilizers: Continuing Health and Environmental Research

Sandra R. Murphy, C. Bertelo, R. Ringwood, M. Cochran, May 2000

Years of experience and significant research support using organotin mercaptides as PVC stabilizers. Safe use of organotin stabilizers involves following Material Safety Data Sheet instructions and using adequate engineering controls and/or personal protective equipment. Modifications of stabilizers to develop more efficient formulations continue. Product stewardship includes continued development of data to improve our understanding of the effects of materials. An overview of stabilizer trends in the industry, existing data, and planned health/ environmental research is presented.

Preparation of Microporous Films from Immiscible Blends via Melt Processing

C. Chandavasu, M. Xanthos, K.K. Sirkar, C.G. Gogos, May 2000

Microporous films from immiscible blends were produced via melt processing and post-step treatments. Polystyrene (PS)/polypropylene (PP) and poly(ethylene terephthalate) (PET)/polypropylene (PP) blend systems with different viscosity ratios were studied. The blends were first compounded in a corotating twin-screw extruder and subsequently extruded through a sheet die to obtain the precursor films. These were uniaxially or biaxially drawn (100-400%) with respect to the original dimension to induce microporous structure and post treated at elevated temperature to maintain the porous structure which consisted of uniform microcracks in the order of a few hundred nanometers. The fabrication process here is shown to be a promising technique for producing microporous films that can be used for liquid and gas separations, as suggested from permeability measurements.

High Molecular Weight Film Resins with Increased Stiffness

Leonard Cribbs, Dale Vedder, May 2000

High Molecular Weight High Density Polyethylene resins for film markets typically fall into a relatively narrow range of densities to provide the desired product functionality. For example, resins targeted for the tee shirt bag market require tear and puncture properties that require melt indices of around 0.05 and densities around 0.950. Development of these resins and their respective bags has allowed for substitution of HMW-HDPE for paper in many markets. Additional substitution appears available, but require resins with both high strength and higher modulus. Using technology to produce bi-modal molecular weight distributions, film resins meeting these requirements have been produced. The resins and their end-use applications will be discussed.

Properties and Applications of Sandwich Panels Based on PET Foams

M. Xanthos, R. Dhavalikar, V. Tan, S.K. Dey, U. Yilmazer, May 2000

PET foams of variable densities, (1 g/cc to 0.2 g/cc), based on virgin and recycled material were produced by extrusion with physical or chemical blowing agents and evaluated as low density core in sandwich panels having M/F impregnated paper or flame retardant mineral reinforced PET as skin faces. Flexural and shear stiffness of the laminates were determined by variable span three point bending. Panels were also tested for thermal and moisture stability and compared with competitive sandwich constructions based on PVC foam, flake board, particleboard and plywood. Potential applications of the PET based laminates in building and construction are presented.

On the Experimental Investigation of High-Frequency Dielectric Sealing of PVC

Brahim Brahimi, Ulku Yilmazer, May 2000

This feasibility study deals with the investigation of welding Polyvinyl Chloride (PVC) sheets of different formulations, using high dielectric frequency technique. The experimental work consisted of PVC formulation (rigid sheet), mold design (new products), experimental design to quantify the effect of process parameters, mechanical characterization (tensile, peel testing) of the weld area, and process optimization. Rigid PVC formulation was selected based on two primary mechanical properties, tear resistance and shear modulus. The weld was well achieved within the studied range of parameters, while the processing conditions were experimentally optimized. Finally, new office items were successfully produced as a result of the design of new molds combined with new process layout (sheets).

Comprehensive Study of a New Extensional Flow Mixer

Weining Song, May 2000

A patented Extensional Flow Mixer (EFM) (1) has been developed in which plastics is hydrodynamically mixed by flowing through a series of convergent and divergent regions so that very efficient dispersive and distributive mixing can be achieved. The EFM can be attached to any plastics pumping machine, such as single-screw and twin-screw extruders, for injection molding, blow molding, extrusion, and compounding. Comprehensive laboratory and industrial tests have been conducted especially for film applications, which indicate the mixing of a single-screw extruder (SSE) with an EFM can outperform that of a twin-screw extruder (TSE) in certain aspects. Results of gel elimination, strength enhancement and morphology changes are presented.

Pressure-Volume-Temperature Dependence in Polyvinylidene Fluoride and Polyvinylidene Fluoride-Hexafluoropropylene Copolymers

Nafaa Mekhilef, May 2000

The relationship between pressure, volume and temperature (PVT) of polyvinylidene fluoride homopolymers (PVDF) and polyvinylidene fluoride hexafluoropropylene (PVDF-HFP) copolymers was determined in the pressure range of 200 to 1200 bars and in the temperature range of 40°C to 230°C. Differential scanning calorimetry (DSC) analysis was performed on each resin to simulate the cooling process during the PVT experiments and to determine the crystallization and melting temperatures at atmospheric pressures. The TAIT state equation describing the dependence of specific volume on the zero-pressure volume (V0,T), pressure and temperature has been used to predict the specific volume of PVDF and PVDF-HFP copolymers.

On the Prediction of Crystallinity Distribution in Injection Molded Semi-Crystalline Thermoplastics

Jianxin Guo, Kwabena A. Narh, May 2000

Injection molded semi-crystalline thermoplastic parts show variable morphologies across their thickness. Process parameters such as injection speed, mold temperature, and melt temperature, play important role in forming these morphologies. The heat and shear history has great effect on the crystallization process of the semi-crystalline plastics. In this study, different available crystallization models were used to predict the crystallinity distribution, and capabilities of the models compared. Based on the results from these models, a more realistic model, which considers stress relaxation during the crystallization process, is proposed.

Factors Affecting Adhesion of Tie Layers between Polypropylene and Polyamides

Gregory W. Kamykowski, May 2000

Adhesion properties were determined on five-layer coextruded cast films. With a few exceptions, the cap layers consisted of polypropylene, the tie layers consisted of blends of polypropylene and maleic anhydride-grafted polypropylene, and the center layer consisted of various polyamides. Up to a point, the adhesion increased as the overall film thickness and the level of maleic anhydride-grafted polypropylene were increased. The molecular weight of the grafted resin had a small effect on adhesion. Homopolymer diluent outperformed random copolymer diluents. Adhesion did not vary much when different types of polyamides were used as the center layer, but each exhibited much greater adhesion than an ethylene-vinyl alcohol center layer.

Investigations on Stretched Block Copolymers of Poly(butylene terephthalate) and Poly(tetramethylene oxide)

Angelika Schmidt, Carmen Alves, Maria Soliman, Wiebren S. Veeman, May 2000

The changes in phase structure under uniaxial deformation of block copolymers of Poly(butylene terephthalate) (PBT) and Poly(tetramethylene oxide) (PTMO) have been investigated using 13C solid state NMR spectroscopy and infrared spectroscopy on in-situ stretched samples. The study was focused on the strain-induced crystallization of the PTMO. It became obvious that a minimum stress level in the material is necessary for the strain-induced PTMO crystals to form and to be stable at room temperature. The amount of crystalline PTMO is dependent on the stress level and on the temperature. We also found, that the PTMO crystallization is favored by a large PTMO block length and a large PTMO content.

Microfibrillar Composites with Ultimate Properties

Marianna Sarkissova, Maria Soliman, Gabriel Groeninckx, May 2000

In the past decade, numerous novel polymeric products were introduced, including polymer blends, for various applications in the automotive and electronic industry. Up to now a homopolymer as such has to be reinforced to meet the high demands on stiffness and strength in engineering applications and glass fibres were the major reinforcing element used in these materials. Microfibrillar reinforced composites based on polycondensates are new polymeric construction materials with ultimate properties. Such a composite has specific economical and ecological advantages since, upon recycling, a polymer blend is obtained which can be re-used to make again polymeric materials with specific properties.

Residence Distribution Models for Twin Screw Extruder

Jun Gao, Gregory C. Walsh, David Bigio, Robert M. Briber, Mark D. Wetzel, May 2000

Transformation of the residence time distribution (RTD) to give both the residence volume distribution (RVD) and the residence revolution distribution (RRD) yields new physical insights into the extrusion process. These new tools motivate the development of a simple residence distribution model which characterizes the partially filled and fully filled screw sections and is capable of distinguishing between screw configurations and operating conditions. A least square error fit method is used to identify the parameters of the RTD model and it is indicated that the model function is appropriate to describe the RTD experimental data. The model for the RTD is validated on the analysis of data collected from the extrusion of polyethylene on a 30 mm Krupp Werner and Pfleiderer (W&P) Co-rotating twin screw extruder.

Mean Residence Time Characterization in Co-Rotating Twin Screw Extruder: Screw Configuration Comparison

Paul Elkouss, David Bigio, Gregory Walsh, Paul Andersen, May 2000

Many industrial processes are described by residence time distribution functions (RTD). Experiments were carried out on a 30mm Krupp Werner and Pfleiderer co-rotating twin-screw extruder (CoTSE) equipped with reflectance optical probes to study the residence functions of different screw geometries to distinguish them. Theory described by Gao, Bigio, et al, shows that the mean number of screw rotations can be found from these RTD functions from the product of the screw speed and mean residence time. This equipment was used to show that the mean number of screw rotations is proportional to the inverse of the specific throughput. In addition, different geometries exhibit different functional relationships between the mean number of screw rotations and the inverse of the specific throughput.