Plastics News reporter Bill Bregar has recapped a few of the more than 600 technical papers presented at the Society of Plastics Engineers' Annual Technical Conference, held May 8-11 in Boston. For people who did not attendANTEC, the complete, three-volume proceedings are available from Technomic Publishing Co. Inc. of Lancaster, Pa. Cost is $525.
Robert Peret of custom molder Nypro Inc. of Clinton, Mass., described a process he uses to estimate the cost of secondary finishing operations.
His paper, ``Using Predetermined Time Standards for Secondary Quoting,'' explains how to create a database that groups different elements of Methods-Time Measurement into categories.
Peret said the technique allows a molder to produce quotes quickly for hand assembly work.
New gas-assisted system described
A high-pressure, gas-proportional controller for gas-assisted injection molding is described in a paper by Ed Lasch and Desi Csongor of DMX Inc. of Manchester, Mass., and Vineet Kapila and Nick Schott of the Institute for Plastics Innovation at the University of Massachusetts at Lowell.
The paper examines a microprocessor-controlled system, sending gas through the mold, that functions according to the screw position signal that sets a timer. The timing system controls two solenoid valves - a high-pressure valve to allow gas flow into the mold and a valve to operate a shut-off nozzle to prevent gas from entering the barrel.
A patent application has been made for the technology.
Martin Stephenson and Mi-chael Ryan of the State University of New York at Buffalo studied sagging of styrenic sheets when heated for thermoforming.
Thermoformers need more knowledge about sagging because they are pursuing markets that require tight tolerances and reliable repeatability, Stephenson and Ryan argued. They studied sagging of sheet made of a 50-50 blend of styrene-butadiene block copolymer and polystyrene.
They concluded that initial orientation present in the sheet has a major influence on its sagging behavior later. Also, samples clamped around the perimeter exhibit much less sagging than samples clamped only at the ends.
Document examines PP-wood composites
How to improve mechanical properties of polypropylene-wood fiber composites by compounding and in-line maleation was examined by a paper from Minqui Lu, J.R. Collier and B.J. Collier of Louisiana State University in Baton Rouge, La.
Wood fiber is an attractive filler for thermoplastics. However, it faces problems with mixing, poor dispersion and surface wetting, no chemical bonding, poor adhesion and chemical instability of wood fibers at high temperatures.
According to the Louisiana State researchers, those problems can be overcome by using processing aids to promote rapid dispersion and wetting of the wood by the molten polymer or by using compatibilizers.
The paper concludes that maleated PP is a very effective coupling agent for PP-wood fiber composites.
Only a small amount of maleated PP significantly improves tensile properties, the paper stated.
Gulf War technology can aid blow molders
Thermal imaging - the same technology used by heat-seeking missiles in the Gulf War - can be used to determine temperature accurately in blow molding.
Author M.S. Mitchell of blow molder Constar International Inc. of Atlanta, is enthusiastic: ``I cannot overemphasize the fact that the application of this technology is limited only by one's imagination.''
The imaging equipment can freeze a frame for analysis, allowing measurement of temperatures on objects that are moving and that have increasing or decreasing temperatures.
Paper urges change in plastic lumber
The ``shape'' of plastic lumber to come was discussed by a paper by Franz Koch of Recycling Technology Assistance Partnership in Seattle.
``Plastic lumber producers must change the shapes of their current products,'' Koch said.
He said wood lumber makers have created new ``composite'' shapes, such as plywood and oriented strandboard, that have higher shear values than virgin wood.
One example could be plastic lumber extruded into an H-beam shape, he said.
Recycled plastic use limited in Mexico
``Recycled'' is still a dirty word in Mexico, as it applies to plastic products.
A survey showed that 65 percent of Mexicans would not use a product made of recycled plastic.
That finding means more must be done to educate Mexico on recycling, said a paper by E. Mendiz bal, R.M. Jimunez-Amezcua, C. Ortiz and V.M. Gonz lez of the Department of Chemical Engineering at the University of Guadalajara, Mexico.
They found that plastic accounts for about 13.5 percent by weight of the household waste generated in Guadalajara.
There is a supply of about 340,000 pounds of plastics per day, including high and low density polyethylene, polystyrene, polypropylene, PVC, PET, acrylic, ABS, polyurethane and cellophane. All of the area's 27 recycling companies accept industrial plastic, but they rarely recycle household waste because the plastic usually is very contaminated.
Recyclers also say there is no guarantee of a constant supply. Only two or three neighborhoods collect plastic, paper and glass.
The authors conclude that there are business opportunities in some recycled plastics, but first a collection program must be started.
Metallocene paper finds few difference
There is no dramatic difference between the solid-state properties of semicrystalline polyolefin elastomers formed by copolymerization with propylene and octene, according to a metallocene paper by Douglas Turek and Brian Landes of Dow Chemical Co. in Midland, Mich., and Mark Winter, Kalyan Sehanobish and Steve Chum at Dow in Freeport, Texas.
The paper discusses Dow's Insite single-site metallocene catalyst technology.
The researchers compared the solid-state properties of uncured ethylene octene-based elasto-mers, including Dow's Engage grades, with various ethlyene-propylene and ethylene diene propylene monomer rubber.