TECHNOLOGY
Ashland offers water-extended polyester Resin can be extended with as much as 90% water; 50-50 blend gives best strength upon curing As resin extenders go, water is about the cheapest there is. And when it makes up 50rA or more of a finished product, it can have a decided effect on the economics of raw material costs. Especially if the raw material is a 25 cent-per-pound polyester resin, as it is in Ashland Chemical's WEP (for water-extended polyester) material. Ashland Chemical, formerly ADM Chemicals, is just now bringing the material out of its early market development phase. The Minneapolisbased company will say nothing about the chemistry involved. Patent applications have been made on the material and its uses. But the enthusiasm of the research and development people is obvious in their "will-you-lookat-that?" attitude toward the material itself. In its cured form, the material is a hard, white, fine-grained substance. It consists of a plastic matrix containing microscopic particles of water fixed permanently and uniformly. The water droplets in the closed-cell matrix are between 2 and 5 microns in size. The resin can be extended with as much as 90% water, although the material develops optimum strength at 50 to 607c Also, at 50 to 607c water, cell walls are strong enough to withstand freeze-thaw cycling to temperatures as low as - 3 0 ° F. Before casting and curing, WEP unsaturated polyester resin is mixed with the water to form a milkshakelike emulsion. Catalyst is added and the material cures spontaneously. Actually, Ashland plans a family of resins, according to Dr. Richard Coderre, venture manager for WEP in the company's resins and plastics division. It will include resins ranging from rigid to resilient. Some, pointed toward specific uses, are still under development. So far, Ashland has devoted most of its market development effort to decorative moldings, Dr. Coderre says. WEP plastics, he points out, can replace plaster of Paris, filled polyesters, and concrete. In some applications it is stronger, in some cheaper. Statuary, flooring, and structural materials for military shelters are also potential applications. The resins are only the basic material for what will be essentially custom 34 C&EN JAN. 8, 1968
formulations made up by the user. Users can, for example, strike their own balances between strength and cost by varying the water loading. At 50% loading, which gives about the optimum strength, tensile strengths go up to about 2000 p.s.i., compressive strengths (at failure) to 5000 p.s.i., and flexural strengths to 3600 p.s.i. The strength of WEP materials is somewhat less than that of unmodified polyesters. Density can be varied as well. At 50 to 607^ water, densities of WEP materials are about 63 to 66 pounds per cu. ft. In comparison, conventional polyesters filled with calcium carbonate or silica run about 110 pounds per cu. ft., concrete about 130 to 140 pounds per cu. ft. With WEP materials, density can be decreased by adding lightweight fillers or by driving out water by baking. Water is retained almost indefinitely in WEP materials with water loadings of 50 to 607c The resin itself can be designed, however, to be hydrophobic or hydrophilic so that after water is driven out by baking, the material will soak up water again or repel it. At high water loadings—above 757c—the material dries out readily because the cell walls are thin and there is rapid cell-to-cell diffusion. In any event, whether retained or baked out, water has no effect on the material's strength. Pigments are another variation that can be made in formulations. They can be organic or inorganic, water soluble or oil dispersed. Two-component systems can be formulated, with pigment and filler in the resin and catalyst in the water. Water serves primarily as an inexpensive bulking agent. As such, it brings the cost of materials for WEP castings down to 10 to 12 cents per pound (about $6.00 to $8.00 per cubic foot). But the water has a technological function, too, that becomes particularly significant with large castings. It dissipates heat and thus moderates the curing exotherm. Dr. Robert Leitheiser, who developed the material, explains that conventional polyesters, on curing, develop exotherms up to 300° F. It would be difficult, he says, to make a pure rigid polyester casting because it would begin to crack and craze at
THICK added, cream. sible by
CREAM. When hardener is WEP's consistency resembles Thick castings are made posheat sink of trapped water
about 240° F. But since the water in WEP materials helps to dissipate the heat, the exotherm gets no higher than about 190° F. At high water loadings, it would probably not reach much higher than 140° F. Again, it would be necessary for a user to strike an economic balance. The higher the water loading, the lower the exotherm and the longer the cure time. Temperatures of 170° to 190° F. are probably the best for a good molding cycle, Dr. Leitheiser points out. Castings solidify within two to 10 minutes and can be demolded in less than 10 minutes after gel. Essentially full strength is obtained within an hour. The ability of cured material to form around and retain tiny water droplets derives in large part from the ability of the resin to form an emulsion with water. The emulsions formed with W E P are quite stable. Depending on how they are made, some will last for days, some for weeks. With a conventional resin, Dr. Leitheiser says, the water and resin would separate almost immediately. With the WEP resins, emulsions must be formed under high-shear mix-
ing conditions. Beyond that, however, there are essentially no restrictions. Batch or continuous mixing can be used to combine the resin with water from almost any source. There is no limit to the amount of material that can be poured into a mold at one time. Ashland, in some of its tests, has poured as much as 9 gallons per minute for 45 minutes to fill a crater 9 feet in diameter. Most common molding operations, Dr. Coderre says, would require only 1 or 2 gallons per minute. One application in which Ashland expects WEP resins to compete strongly is the overlap where the material is suitable for replacing injectionmolded thermoplastics. In such a situation, molding costs could strongly favor WEP, Ashland feels. The metal molds required for injection molding are expensive. Rubber molds, such as silicone or urethane, can be used with WEP. Silicone rubber has the advantage that it can be formed on a wood master, Dr. Leitheiser points out. Urethane rubber, on the other hand, would pick up water from the wood and form bubbles. But a urethane mold can be made at about a fourth the cost of a silicone rubber mold. It hasn't done so yet, but Ashland plans to investigate the use of the material as a replacement for concrete in castings such as planters, garden statues, and the like. With concrete, Dr. Coderre says, demolding is impossible in less than a day. Moreover, it takes up to several weeks for the casting to develop enough strength to be sold. Sand-filled WEP could be used in the same molds, he says, at a rate of two or three finished items per hour. On a cost basis, WEP materials can compete with plaster and wood for art objects, lamp bases, and the like. Finishing depends only on the skills of the product finishers. The materials can be painted or otherwise finished (if not pigmented already), and they can be sawed, cut, or nailed. On a molding basis, they can in some cases compete with molded rigid polyurethane foam, since the latter requires clamped molds, compared to the open molds for WEP. Ironically, the basic idea that led to the use of water as an extender for unsaturated polyesters has not yet proved practical. It originally came up, Ashland says, during a spring luncheon discussion several years ago when the Minnesota River was overflowing its banks below the Ashland research center in Bloomington, Minn. Dr. Leitheiser thought that flood control embankments could be built rapidly by encasing large amounts of water in thermoset plastics. His idea, which resulted in WEP, did not tame the Minnesota.
Fisher has a $325 vacuum oven with more usable sample space and a stainless-steel chamber. (It's worth looking into.) If this isn't enough, the new Model 48 can be operated under vacuums down to 3 0 " Hg, will respond to temperature changes of ± 1 . 0 ° over a range of 40°C to 200°C. You can use this compact unit efficiently as a vacuum-drying oven; as a controlled-atmosphere or ordinary air-filled chamber for static drying; and as a purged-atmosphere chamber. The %2"-thick, stainless-steel interior and removable stainless-steel shelves guard against corrosion. Usable sample space is 313 sq. in. Interested? Our free product bulletin will convince you that the Fisher Model 48 has everything you want. Look into it; write Fisher Scientific Company, 1011 Fisher Building, Pittsburgh, Pa. 15219. j-629
FISHER SCIENTIFIC CO. Instruments, apparatus, furniture and chemicals for laboratories • ATLANTA BOSTON CHICAGO CINCINNATI CLEVELAND HOUSTON PHILADELPHIA PITTSBURGH ST. LOUIS NEW YORK WASHINGTON EDMONTON MONTREAL TORONTO VANCOUVER JAN. 8, 1968 C&EN 35
