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

New Compositions of Matter from the Modular Disk Coextrusion Die

Henry G. Schirmer, Sherre Love, John Schelleng, Peter Loschialpo, May 2000

A new composition of matter never made before has been created from common thermoplastics. Coextruded blown films were made using two thermoplastic materials in sixteen alternating layers. Each of the sixteen layers was progressively varied in thickness in a controlled manner so that the thinner layers on outside of the bubble gradually progressed into thicker layers on the inside of the bubble. Refractive index differences between certain plastic materials can now be studied and the effect of films having progressively varied layer thickness can be compared to films having essentially uniform layer thickness.

Assessment of a New, Completely Controlled, IR Welding System Using Statistically Designed Experiments

Mike Troughton, Jörg Wermelinger, May 2000

Infrared welding has been used successfully for many years for joining plastics pipes in industrial applications. In order to increase the productivity of this technique, a new generation of machines has been developed that can reduce the weld cycle times by up to 45% compared with standard IR machines. This paper describes how a statistically designed experimental programme has been used to assess the performance of these new IR welding machine in the most cost-effective manner. Results have shown that low temperature welding factors achieved are within 4% of the values obtained on standard IR machines.

Continuous Anionic Polymerization of Polyamide-Based Thermoplastic Elastomer in a Counter-Rotating Twin Screw Extruder: Polyesteramide Triblock Copolymer

Byung Hwa Lee, James L. White, May 2000

Polyamide 6, polyesteramide triblock and polyetheresteramide pentablock copolymers were polymerized in a modular intermeshing counter-rotating twin screw extruder. Polyesteramide triblock and polyetheresteramide pentablock copolymers are polyamide-based thermoplastic elastomers (TPE) and had not been previously polymerized in a twin screw extruder. Characterization studies including thermal analysis, viscosity measurements, and solvent extraction clearly demonstrated that the new copolymers have two separated domains arising from the different block segments. These polymers were also melt-spun into oriented filaments from the die at the exit to the twin screw extruder.

The Modified Imbedded Disc Retraction Method for Measurement of Interfacial Tension in Polymer Melts

Milica Rodic, Andrew N. Hrymak, May 2000

The imbedded disc retraction method is used to estimate interfacial tension in LLDPE/PS system with PS as the imbedded disc. The Newtonian model of Rundqvist et al. [1] for the imbedded disc retraction is modified to include elastic effects and both are compared to experiments. The modified model is derived assuming uniaxial extension and the upper convected Maxwell model. The mean values of interfacial tension at 190, 200 and 210 °C are found to be 6.8±0.7, 3.9±0.3 and 3.7±0.2 mN/m respectively. A method of estimating whether elastic effects will significantly affect the estimated interfacial tension value during retraction for the given polymer pair is provided.

Development of Novel Applications of Crosslinked Elastomer Scrap in Thermoplastics

Helen S. Liu, Chris P. Richard, Joey L. Mead, Ross G. Stacer, May 2000

Materials ranging from impact-modified thermoplastics to thermoplastic elastomers (TPE) can be obtained from blends of recycled ethylene-propylene-diene rubber (EPDM) containing carbon black with poly(propylene) (PP) by varying the ratio of components in the blend. This study focused on developing TPE materials from PP and recycled ground rubber. The effect of rubber particle size, melt flow index (MFI) for the PP, and weight percent of the constituent fractions on the physical properties of the resultant blends was quantified. A design of experiments based on the processing conditions and variables was performed to determine the optimum processing conditions. Compatibilization techniques were used to improve the quality of the scrap rubber/plastic blends in response to the structural requirements of several potential applications. The cost factors for scale-up to manufacturing operations were also considered. It was found that the MFI of PP is a major factor controlling the mechanical properties of the blends. Through proper selection of the components and compatibilization techniques, blends were found to be tailorable to specific applications.

Real-Time Dielectric Measurements during Extrusion of Filled Polymers

Michael McBrearty, Anthony Bur, Stephen Roth, May 2000

Mineral fillers are added to polymers to extend and modify physical properties, and their concentrations should be carefully controlled to obtain the desired end-use properties. To achieve this control, real-time measurements are very useful. Previous work has shown that in-line dielectric sensors can measure the concentrations of fillers in non-polar polymers. This work extends the measurements to polar polymers.

Drying: A Closer Look

Thomas Schwab, John E. Perry, May 2000

This paper will discuss the adverse effect on viscosity when polymers are excessively dried. Many processors are concerned exclusively with excessive moisture and give little consideration to the permanent detrimental effects from over-drying. As part size gets smaller in many applications, dryer throughput is lower. The result is extended exposure to the drying process. Thus, the viscosity of the material is increased and permanent loss of material properties occurs. This effect was observed as an actual manufacturing problem.

Fluorescence Based Temperature Measurements and Applications to Real-Time Polymer Processing

Anthony J. Bur, Steven C. Roth, May 2000

Fluorescent dyes doped into polymer resins are used to monitor the true resin temperature during processing. Two examples of real-time process monitoring are presented: first, the effects of shear heating during extrusion are measured and second, the effects of poor temperature control during extrusion are observed.

Practical Guidelines for Predicting Steady State Cure Time during Sheet Molding Compound (SMC) Compression Molding

Lisa M. Abrams, Jose M. Castro, May 2000

The longest part of the molding cycle during SMC compression molding is the curing stage. Thus it is extremely important to be able to predict its duration to estimate the cost of manufacturing a part. To avoid blistering, the cure time must be increased with consecutive moldings until a steady state value is achieved (tcss). In this paper, we present a series of charts that can be used to estimate the steady state cure time for new parts. These values can then be used to estimate the manufacturing cost.

Use of Infrared Dyes for Transmission Laser Welding of Plastics

I.A. Jones, N.S. Taylor, R. Sallavanti, J. Griffiths, May 2000

A technique has been developed for transmission laser welding plastics with infrared dye, creating a joint almost invisible to the human eye. In typical applications for laser welding of plastics, carbon black would be used as the absorbing medium for the laser energy. This new approach enables two similar clear (or coloured) plastics to be joined with a minimal mark weld line. A number of dyes have been selected and assessed in terms of strength of light absorption at 1064nm wavelength with an Nd:YAG laser, as well as their visible light absorption. Lap welds have been made in clear PMMA using the infrared dye mixed into methyl methacrylate film as an absorbing medium at the interface between the plastic sheets. The selection of the dyes and processing methods is discussed for the new technique.

Color Stable, Glass Filled Thermoplastic Polyesters

Matthew R. Pixton, May 2000

Color stability is a general term which can be manifest in several ways, for example, color consistency over the course of a run, color stability on UV exposure, color stability on processing, chemical exposure or color stability of the final article at elevated temperature. Materials with enhanced capability of the latter type are positioned in applications where sustained high temperatures would rapidly discolor conventional thermoplastics or thermosets. This paper will discuss the variables that control heat aged color stability in ignition resistant and non-ignition resistant glass filled thermoplastic polyesters.

The Effect of Feed Particle Size on the Characteristic Size Scales for a Miscible SAN/PMMA Blend

Heidi E. Burch, Chris E. Scott, May 2000

Mixing in the model miscible blend poly(styrene-co-acrylonitrile)/ poly(methyl methacrylate) is examined. The effects of feed particle size upon the mixture characteristic size scales are investigated using Fourier transform infrared spectroscopy (FT-IR). FT-IR is used to measure the normalized sample variance as a function of sample size in an effort to elucidate the characteristic size scales, as well as to evaluate the overall level of mixedness in the model blend. An unexpected peak appears in the normalized sample variance versus sample size curve for nugget and pellet feeds, suggesting two radically different size scales of morphology are present in the blend at short mixing times.

The Effects of Comonomer Type on the Blown Film Performance of LLDPE Resins Made Using a Metallocene Single-Site Catalyst

Ashish M. Sukhadia, M. Bruce Welch, Raj K. Krishnaswamy, Syriac J. Palackal, May 2000

In this paper, we report on the effects of comonomer type viz. 1-butene, 1-hexene and 1-octene, on the blown film performance of linear low density polyethylene (LLDPE) resins made using a metallocene single-site catalyst. The effect of film thickness on blown film properties was also examined. The resins were characterized in detail with respect to their rheological, thermal and molecular characteristics. It was established that these three copolymers, despite the great similarities in their molecular, rheological and thermal properties, exhibited blown film performance that clearly increased with increasing length of the ?-olefin employed.

Viscoelastic Stress Calculation in Multilayer Coextrusion Dies

C. Tzoganakis, M. Zatloukal, J. Perdikoulias, P. Saha, May 2000

Calculation of transient viscoelastic stresses in a coextrusion die is performed using the modified Leonov constitutive equation and the deformation rate field from finite element simulations. It is shown that a heuristic criterion based on the difference of normal stress differences across the layer interfaces may be used to potentially detect the onset of interfacial instabilities. Finally, it is shown how this criterion may be incorporated into current design practices to optimize resin selection and die design in order to eliminate interfacial instabilities.

An Overview on Polyvinyl Chloride (PVC) and Alternatives in Medical Applications

K.Z. Hong, May 2000

Numerous polymeric materials have emerged recently as potential alternatives to polyvinyl chloride (PVC) for medical device applications. The candidates include thermoplastic elastomers (TPE), metallocene-catalyzed polyethylenes and polypropylenes, co-extruded and laminated multi-layer structures, and multi-component polymer blends and alloys. Material performance requirements and manufacturability in medical applications will be discussed. Properties of alternative materials are compared with attributes of PVC and with functional requirements of medical devices to provide an overall perspective on potential opportunities of replacement.

Melt Rheological Properties of Natural Fiber-Reinforced Polypropylene

Jarrod J. Schemenauer, Tim A. Osswald, Anand R. Sanadi, Daniel F. Caulfield, May 2000

The melt viscosities and mechanical properties of 3 different natural fiber-polypropylene composites were investigated. Coir (coconut), jute, and kenaf fibers were compounded with polypropylene at 30% by weight content. A capillary rheometer was used to evaluate melt viscosity. The power-law model parameters are reported over a shear rate range between 100 to 1000 s-1. Effects on melt viscosity with the use of a coupling agent and different fiber types were also evaluated.

Injection Molding Tie Bar Extension Measurements via Strain Gauge Collars for Optimized Processing

Norbert Müller, Nick R. Schott, May 2000

The measurement of the clamping force in injection molding can give valuable insight for optimization of the process. Problems in production are often related to the level and the distribution of the clamping force. A novel measuring system that employs strain gauges that are clamped around the tie bars make a precise measuring method applicable in a rugged industrial environment. It was the objective of this work to evaluate the performance of the device in practical use.

Evaluating the Energetics of Heterogeneous Deformation in LLDPE Films under Biaxial Loading Conditions

Amiel B. Sabbagh, Alan J. Lesser, May 2000

Post-yield, heterogeneous deformation (dilatational bands) occurs in linear, low density polyethylene films under certain biaxial loading conditions. The dilatational band evolution occurs primarily by isotropic expansion and the energy release rate is therefore determined using the M integral. A thermodynamic model is used to determine a material property that describes the energy associated with the drawing process. The thermodynamic model and the M integral appear to be appropriate for modeling this process.

The Extrusion of Multi-Layer Barrier Tubing from Cross Linked Polyethylene (PEX)

John A. Colbert, May 2000

The use of multi-layer tubing, based upon PEX, is growing substantially especially in hot water plumbing applications. Improvements in Oxygen barrier, thermal stability and durability, are the major properties that are driving this growth. Whilst papers have been presented on the cross linking process, and long term durability of PEX, very little has been published on the process of producing five layer PEX tubing. This paper covers the process and methods used to achieve consistently high quality. It looks at extrusion conditions, screw design, die technology, control of layer thickness and centricity, and vacuum sizing techniques and how they can influence factors such as surface finish and ovality. It also looks at measurement of layer thickness and the overall tube dimensions. All aspects are illustrated with actual results from production scale work based upon a 90mm extruder line.

Incompressible Model of Solids Conveying in a Single-Screw Extruder

Shibo Zhang, Valentinas Sernas, May 2000

Experiments in corn meal extrusion [18] have shown that the flow of solids in the screw channel of a single-screw extruder has a helical pattern. This observation implies that there is a cross-channel velocity component in the solids conveying zone of the extruder. Existing solids conveying models [2,5,6,9] treat the solids moving in the channel as a plug flow without a cross-channel velocity component. The two-dimensional powder conveying model proposed in this paper contains both a down-channel component and a cross-channel component. The stress generating mechanism is much more complicated in a powder flow than in a fluid flow. The incompressible model incorporates a constitutive equation for the powder flow with slip boundary conditions. The energy equation with appropriate boundary conditions is also included in the model. The numerically solved model shows that the predicted down-channel pressure development, velocity and temperature distributions are all reasonable.