New technology in alloying, compatibilizers & reactive compounding.
Novel thermoplastic alloys, developments in compatibilizers, and new data revealing the effects of twin-screw extruder die design on resin morphology highlighted Compalloy '90, the Second International Conference on Compatibilizers and Reactive Polymer Alloying, held recently in New Orleans.
The burgeoning field of proprietary compatibilizers, reactive compounding, and polymer alloys remains at the forefront of new materials development for the 1990s. Awareness of the vast progress being made in this area is gaining momentum and fueling a slow unveiling of information in what is among the most secretive technical areas in plastics development. A rare early glimpse of research advancements in alloying and compatibilizers was provided by PLASTICS TECHNOLOGY last year (see PT Feb. '89, p 60). Here's what's going on now.
A new alloy developed by Daicel Chemical Industries Ltd. of Japan features the rare combination of two crystalline thermoplastics--nylon 6 and PBT--through use of a compatibilizer that is a random copolymer of styrene, maleic anhydride and glycidyl methacrylate (SGM). Six grades of the material, three of them glass-filled, are available here in test-sample quantities through Daicel's office in Fort Lee, N.J. Three different blend ratios (each available filled and unfilled) are offered: 70/30 nylon/PBT, 50/50, and 30/70. Akihiro Izuka, research scientist, said it would be at least a year before the material is fully commercialized, and speculated it eventually would be priced in a range similar to nylon and PBT.
Izuka said the idea behind the crystalline alloy was to create a material that improved upon the weak points of the two resins partners: dimensional stability in nylon 6, and hot-water hydrolysis in PBT.
Test parts were made by Daicel by injection and compression molding. Izuka said the alloy's processability is aided by the similar glass-transition and melt temperatures of the two crystalline resins.
Formulation of the new alloy involves mixing various levels of nylon 6 and PBT with up to 5% of SGM. The mixture is melt blended in a twin-screw extruder at 518 F. Izuka said the SGM causes an "unconventional" chemical coupling between the two crystalline resins, establishing an interfacial area that "almost becomes a thermoset." However, the resulting alloy is a thermoplastic. (CIRCLE 36)
Two grades of a new random terpolymer elastomer, designed for use as compatibilized impact modifiers in nylons and thermoplastic polyesters, were introduced by Sartomer Co., West Chester, Pa. The material, marketed by Sartomer in the U.S., is produced by Norsolor, a French affiliate firm.
Two distinct formulations have been developed for the new terpolymer. Lotader 4700 ($1.60/lb) is a copolymer of ethylene, acrylic ester, and maleic anhydride, designed for use in various nylon grades. Lotader 8660 ($2/lb) substitutes glycidyl methacrylate for maleic anhydride among its comonomers, and is for use in PBT and PET. Both are available in commercial quantities.
Richard Costin, technical manager of specialty polymers for Sartomer, said they were developed as impact modifiers because conventional rubbers lack compatibility with nylons and TP polyesters. Lotader forms a chemical bond with both resins. Costin said the ethylene component serves to compatibilize the matrix resin with the acrylic ester elastomer, which also lowers the crystallinity and improves wettability. In high-temperature blending or extrusion compounding, the maleic anhydride in the 4700 grade reacts with the free amine of nylon, while the glycidyl methacrylate epoxy group of the 8660 grade reacts with the free carboxylic acid groups of polyester.
Initial test results show that Lotader 4700 is most successful when used with nylon 66. A 30% concentration of Lotader 4700 in nylon 66 provides a 20-fold improvement in impact properties, as compared with virgin nylon 66. A 20% addition of Lotader 4700 significantly increases the notched Izod and elongation percentage at break of the material, while heat-deflection temperature, flexural modulus, and tensile strength decline (see table).
When the terpolymer was added to nylon 6 and 610 in 30% concentrations, the relative impact properties were improved between 8- and 10-fold. Development work is under way at Norsolor to improve impact enhancement in these nylons.
A 20% concentration of Lotader 8660 in PBT and recycled PET results in a 10-fold improvement in impact properties over the respective standard resins, Costin said. (CIRCLE 37)
Ultra-high-molecular-weight (UHMW) PE particles, surface modified through a proprietary gas-treatment process that creates reactive sites for alloying with nylons, polyurethanes and epoxies, was unveiled at the conference by Air Products & Chemicals Inc., Allentown, Pa. Thomas J. Kulikowski, market development manager for composite products, said the primary function of the UHMW-PE powder, called Primax UH-1000, is to improve the abrasion resistance of the host resin--which it does by as much as five times, according to Kulikowski. Along with abrasion resistance it also provides an overall reduction in the coefficient of friction for the base resin, serving as a lubricant for moving parts, gears, and bearings.
The UHMW-PE powder is treated with a highly oxidative gas at ambient temperature, which creates polar groups on the surface of the material that function as reactive sites for chemical bonding. Because of this compatibilization, the Primax powder is totally wettable and uniformly dispersed throughout the resin matrix, Kulikowski said.
Primax can be either batch blended or extrusion compounded into a matrix resin at typical loadings of 5-25%. Because of its ultra-high molecular weight, the powder doesnht melt in the compounding process, thus forming a true composite structure. Four particle sizes, ranging from 50 to 250 microns, have been commercialized. Prices start at $3.50/lb. (CIRCLE 38)
Besides UHMW-PE, Air Products is now developing the reactive gas-treatment process for various fibers, fabrics, and resins such as PP, PET, and PS. The company also has established a cost-sharing contract with the U.S. Dept. of Energy to surface-modify vulcanized-rubber particles from scrap automotive tires to be recycled and utilized as reactive elastomeric modifiers. (CIRCLE 39)
KEYS TO MORPHOLOGY CONTROL
Initial results of methods to control the size and shape of an alloy's dispersed phase and the resulting effect on physical and mechanical properties were presented by Basil D. Favis, program manager of polymer blends for the Industrial Materials Research Institute of the National Research Council of Canada, Boucherville, Quebec. Favis discussed surprising new findings on the significance of die design in a twin-screw extruder in controlling morphology in a resin blend. He also presented data on the interfacial modification and compatibilization of blended polymers in the dispersed phase. The latter effort, which is being conducted jointly with Polysar Ltd., seeks to find ways to boost mechanical properties of alloys through precise saturation levels of compatibilizing agents.
The research work of the Council, much of which is still in development, is intended to provide a more systematic, quantitative approach to the alloying process. "Our goal is to control at will the morphology of an alloy in a twin-screw extruder, and to be able to quantitatively maximize an alloy's physical and mechanical properties," Favis said.
The greatest effect on a blend's morphology, when processed on a twin-screw extruder, is produced by the geometry of the die, he reported. The screw's rate of rotation, shear stress, and volume level in the screw barrel all have "little or virtually no effect on an alloy's morphology," he reported. The Council's study also found that a twin-screw extruder was more effective than a batch mixer in alloying materials.
The Council is now involved in further research to determine the optimum configuration of die-land geometry, diameter ratios, and angle of entry for twin-screw extruder dies, in order to obtain the desired morphology. Favis declined to provide further details on this program. However, he reported that initial studies reveal that die configuration has greater importance for uncompatibilized resin blends, compared with compatibilized blends.
The Council's parallel development program with Polysar is working to develop a novel alloy of a styrene-maleic anhydride copolymer and bromobutyl elastomer, using dimethyl amino ethanol (DMAE) as the compatibilizing agent. Though it's not yet ready for commercialization, Favis said the significance of the blend is in matching a styrenic with an ultra-uv-stable elastomer.
Research showed that a precise saturation level of DMAE (about 5%) yielded a dramatic gain in impact strength (three-fold) and other mechanical properties for the alloy. He explained the key was to quantify the saturation point for this particular alloy, in order to attain the best interfacial adhesion between the styrenic and elastomer and yield the best physical properties.
Favis said the ongoing study has established that the desired physical properties of an alloy are determined by the equalization of phase sizes through the percentage of compatibilizers used in the blend. "We believe particle size and more uniform dispersion of the resins optimizes physical properties of an alloy," he said. "The level of saturation of compatibilizers at the interface of the alloyed materials is an important factor in creating a successful blend." He added that an interfacial modifier reduces the phase size of the alloy partners, giving rise to more uniform dispersion.
Proceedings of the conference are available from the sponsor, Schotland Business Research, Inc., Princeton, N.J. (CIRCLE 40)
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|Author:||Gabriele, Michael C.|
|Date:||May 1, 1990|
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