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

The Effects of Stress Hardening on the Crystallization and Density of Polypropylene
Desiree A. Nichols, May 2000

When polymers undergo stress hardening, their crystallinities and densities are affected. Polypropylene was the material tested in this experiment. It was put under various levels of strain by using a tensile tester. Each sample was pulled to a predetermined strain, allowed to relax for a period of time, and measured for crystallinity using the Differential Scanning Calorimeter (DSC). Stress-hardened and original samples were used to compare the change in crystallinity. The density of each sample was also determined using the Density Gradient Column.

Comparison of Aluminum, Wood, and Epoxy as Thermoforming Mold Materials
Danell Oliver, May 2000

There are many different types of materials used in the thermoforming industry for the molds used to form plastic products. The most commonly used are aluminum-alloys, soft and hard woods, and epoxy. Each of these materials has distinct characteristics that make them useful under certain design conditions and manufacturing production processes. The following addresses the qualifying factors for each of the commonly used materials based on their characteristics and manufacturing requirements.

Rheological Characteristics of Polymer Blends
Roberto Guimarães Pereira, Alexandre Alves Costa Oliveira, May 2000

This work presents an experimental observation of the rheological characteristics of the TPE/SB blend (Thermoplastic Elastomer / Styrene-Butadiene) used in the plastic transformation industry for medical applications. The flow curves (shear viscosity x shear rate) of the blend were investigated at different temperatures and in a wide range of shear rates. During the extrusion, the instability phenomenon (melt fracture) and its relation with the shear rate and temperature parameters was also investigated. All the experiments, the flow curves and melt fracture observation, were performed in a Capillary Rheometer ( a Rosand Rh-2100 capillary rheometer) working with a 1 x 16 mm rod capillary die.

Evaluation of Liquid Gas-Assisted Injection Molding
Doyoung Moon, Seungwook Lee, Donghak Kim, May 2000

Gas-Assisted injection molding has been applied successfully in plastic industry within last 10 years. Liquid gas-assisted injection molding (LGAI) is a good alternative of conventional gas-assisted injection molding process. In LGAI process, a liquid is injected under low pressure into the melt stream. The liquid vaporizes and pushes the melt downstream and creates hollow channels within part. HELGA® patents this process originally. We had evaluated this process with different-type molds and liquid nozzles that we develope. Finally, we compared the LGAI process to the conventional gas-assisted injection molding process.

Surface Enrichment in Polymer Blends Involving Hydrogen Bonding
Yuzhi Duan, Eli M. Pearce, May 2000

Poly(4'-hydroxyl-4-ethylphenylsiloxane)(PHEPS) has been synthesized via hydrosilylation followed by hydrolysis. This polymer, hydrogen bonding donor, was blended with three kinds of hydrogen bonding acceptors that include poly(4-vinylpyridine) (PVPy), poly(acrylonitrile) (PAN) and poly(ethylmethyacylate) (PEMA). The surface enrichment with PHEPS, which has lower surface energy, was characterized by X-ray Photoelectron Spectroscopy (XPS). The effect of the strength of hydrogen bonding interaction on the surface compositions of the blends was studied. The results showed that surface enrichment in miscible polymer blends was responded to the balance between the differential in the surface energy of the constituents and the bulk enthalpic interactions.

The Effect of Chemical Blowing Agent Dosage on the Properties of Extruded Expanded Polypropylene
Dorian Dixon, P.J. Martin, E. Harkin-Jones, May 2000

This paper investigates the influence of CBA (chemical blowing agent) concentration on the properties of extruded EPP (expanded polypropylene) rod samples. A design of experiment methodology was adopted to quantify the effect of CBA (endothermic type) dosage on EPP properties. Foam characteristics measured, were density, cell structure, tensile properties, premature foaming, and extrusion parameters (melt temperature and pressure). The research revealed that an optimal blowing agent concentration of 0.5% exists in terms of obtaining the finest cell morphology and most efficient material savings/density reduction.

Reactive Extrusion of Polyolefin Blends
Claudia M.C. Bonelli, John M. Pochan, T.H. Mourey, Eloisa B. Mano, Charles L. Beatty, May 2000

The incompatibility of polypropylene (PP) and high density polyethylene (HDPE) is a source of industrial problems for recycling post-consumer polyolefins. Blends of PP and HDPE with peroxide and 3 vector fluid additives have been prepared in a co-rotating reactive twin-screw extruder. Compatibilization has been examined by stress-strain tests, impact tests and scanning electron microscopy (SEM). Molecular weight of the blends has been evaluated by gel permeation chromatography (GPC). An increase in elongation at break and impact resistance of some reactive blends compared to the mechanical blend was observed, with some links between the phases, as revealed by SEM.

Crushed Recycled Glass as a Stiffening Agent for HDPE Compared to Traditional Plastic Lumber Fillers
N.L.H oekstra, B.P. Duffey, S.H. Dillman, May 2000

bstract The objective of this study was to determine the flexural, impact, and tensile properties of a compound of crushed recycled glass, HDPE, and coupling agent using a two-level, three-factor designed experiment. This study determined that glass content, sieve size, and coupling agent all have a significant effect on the mechanical properties. The use of recycled crushed glass was found to increase the flexural modulus, but not as efficiently as calcium carbonate, wood flour, and fiberglass. Additionally, crushed glass improved the impact strength but decreased the tensile strength. It was found that smaller glass particle size performed better and the use of coupling agent decreased all mechanical properties.

Effects of Processing Parameter on Pinch-Off Designs
Chad Weller, Matt Marlowe, May 2000

This study examines the effects of process changes on weld line strength using different pinch-off designs. Mold closing speed and melt temperature were varied with four different pinch-offs. To determine the effect of these process changes on weld line strength, 4 D.O.E.'s were used. Five specimens were taken from each D.O.E. run and tested for tensile strength at the weld.

Shearing of Plastic in Runners Causes Property Differences in Parts
Richard H. Bishop, May 2000

This paper presents a study of the effect of shear variations, developed in a runner of a multi-cavity mold, on the impact properties of molded parts. The study has found that impact strength can vary by as much as 2:1. The effect of runner designs are also presented.

The Effects of Pulse Cooling on The Molding Cycle and Part Variation
Andrew S. Lamont, Corey J. Linden, May 2000

A design of experiments study was performed that analyzed the effect of pulsed heating and cooling on warpage of an injection molded part. The study involved the following factors: inlet water temperature, melt temperature, mold temperature, and cooling time. The critical dimension was measured by an optical coordinate measuring scope with a repeatable process determined by an R&R study. The gathered data determined that, within the range of the factors study, the inlet water temperature was the only one that did not effect warpage.

An in Vitro Study of the Mechanical Property Loss of Poly(L-Lactic Acid), PLLA, Fibers during the Hydrolysis in Tissue Engineering Applications
Stacey L. Russell, Stephen P. McCarthy, Aldo M. Crugnola, May 2000

Tissue Engineering is the use of polymer scaffolds to grow tissue cells in vitro and then implant them. The polymer is designed to degrade as the cells grow into functional tissue in vivo. These scaffolds must be porous, strong, flexible, and ultimately degrade into harmless biomasses. The polymer scaffold is usually a natural or synthetic polymer in a fiber, foam, or fabric form. Synthetic polymers are preferred due to their easily tailored properties. For specialized tissues such as arteries, the scaffold fabric is formed into a tube. While the cells are being developed prior to implantation, nutrients are pumped through the tube. The engineered artery is ready to be implanted when it has acclimated itself to blood-pumping pressures. Other engineered tissues include heart, liver, bone, cartilage, nerves, and skin.

P20 and Beyond: Mold Steel for New Challenges
Nick Cerwin, May 2000

The mold steel designated as P20 has a long history of successful service in the plastics molding industry. The characteristics of this steel that have established it as the grade of choice among molders and moldmakers is reviewed as well as recent variations such as P20 Hi-Hard and P20 Premium (double melted) that offer advantages for some molding applications. Alternate grades of mold steel offering distinctly different characteristics from P20 are increasingly employed in specialized applications. Grades such as Long-Run mold steel, molybdenum modified 420 Stainless Steel, and age-hardening grades RA40 and Mar-X will be reviewed for a clearer understanding of their appropriate roles in plastics molding.

Process and Tooling Factors Affecting Sink Marks for Amorphous and Crystalline Resins
Dan Tursi, S.P. Bistany, May 2000

A plaque tool was built to facilitate changing rib features that include rib-to-wall (R/W) ratio, proximity to the gate, orientation with respect to flow, rib-base radius, and tool steel type. Gate type was also studied along with several process conditions using crystalline and amorphous resins. A Screening study was performed to determine the most influential factors affecting sink and followed by a Response Surface study to better define the relationships. A profilometer was used to measure sink depth. Optical microscopy and DSC were used to observed crystallization and molecular orientation differences between plaques exhibiting high and low degrees of sink. Low molding temperatures, high dwell times and high hold pressures helped reduce sink depth as did positioning ribs closer to the gate and perpendicular to the flow direction. Using a Beryllium Copper mold material also reduced sink while increasing rib-base radius significantly increased sink.

Melting Phenomena and Mechanism in Polymer Processing Equipment
Costas G. Gogos, Myung Ho Kim, May 2000

The research work presented here examines the heating and melting phenomena taking place, when individual polymer particulates or compacted polymer particulate systems are subjected to stresses which force them to deform and flow. The heating/ melting behavior in compression experiments of single polymer cylinders and in co-rotating twin screw extruders was examined. Different polymers and different polymer particulate solid systems were used, over a range of processing conditions. The results of this work shed light on the important roles that solid dissipative deformation and interparticle frictional phenomena play in generating the heat necessary to melt polymer particulate systems. This paper also attempts to deal with the modification of the Thermal Energy Balance Equation, so that it includes the above heat generating dissipative source terms.

Rheological and Mechanical Properties of Recycled Polycarbonate
Ruifeng Liang, Rakesh K. Gupta, May 2000

Polycarbonate (PC) is used in computer and electronic housings, and here it was sought to reuse this polymer after having been separated from electronic shredder residue. The separated stream was not pure PC; there was some cross-contamination. The separated polymer was characterized by rheological, thermal and mechanical methods; the measured properties were only slightly inferior to those of comparable virgin materials. Recovered plastic and virgin polymer were blended using a TSE to determine the minimum virgin content needed to mask the effects of addition of recycled material on the rheological and mechanical properties of the blend. Differences in processing behavior and mechanical performance of the blends as a function of composition are discussed in relation to potential material recycling strategies.

Characterizing Scrap Vinyl Flooring to Determine Feasible Reuse Options
Andrew Lawrence, May 2000

The manufacturing waste generated during the production of vinyl floor tiles is typically sent to landfills, rather than recycled, because of a lack of reuse options for this material. This waste is typically PVC loaded with approximately 80% limestone. The goals of this research are to characterize this material to determine the feasibility of reprocessing it and to measure the mechanical properties of the processed material. This study will also attempt to suggest an injection molding or extrusion application for the mixture.

A Method to Characterize the Impact Properties of Hand Tools
John Stanko, John Kennerknecht, May 2000

There does not currently exist a method for the characterization of the impact properties of hand tools, specifically screwdrivers. Without a scientific method of collecting data for various designs, it is difficult for manufacturers to determine the effect of material or design changes on the impact properties of the product. The most demanding application for these hand tools can often be a hammer blow to the handle of the product, and therefore this abuse must be strongly considered in the design criteria.

Predicting Creep in Bottle Design
Ivan McCracken, May 2000

Experimental creep is data collected to drive an FEA program, ultimately used to predict bottle deformation caused by an internal pressure. The results indicate that it is possible to predict bottle deformation using existing creep data, but it is a highly manual process. The FEA program is beneficial in determining stresses caused by internal pressures, which can then be used to calculate deformations. True deformations can be calculated for segments of a bottle using FEA, but a new approach has been suggested, which will allow the FEA program to calculate the deformations along the entire sidewall of the bottle.

Crystalline but Fully Transparent - A New Polyamide with Outstanding Properties
Hans-Peter Hauck, May 2000

Requirements for chemical resistance and transparency are usually mutually exclusive in plastics, especially for polyamides. While aromatic constituents are used to produce most amorphous polyamides, this new transparent polyamide (designated according ISO 1874: PA PACM 12, herein PA means polyamide, PACM = Bis(p-aminocyclohexyl) methane) is based on aliphatic monomers. The monomer building blocks form very small crystallites that do not scatter visible light, so consequently parts made of this polyamide are clear as glass. This so called microcrystalline structure counts for a well-balanced combination of properties, e.g. good UV-stability, high level of impact behavior, low water absorption and isotropic shrinkage. Especially its chemical resistance is superior to other transparent materials such as polycarbonate, polymethacrylate or all amorphous polyamides.

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