machines, and calculators. Here again the textile machine designer is not to be outdone. Figure 24 shows how one manufacturer has used molded nylon gears. His customers employ thousands of spindles so equipped which have given exceptional service over periods as long as 4 years, to date, without replacement. The advantages are: 1. Elimination of lubrication avoids adherence of yarn particles and abrasion, which ground and pitted steel gears rapidly 2. Cost is one third less than steel gears 3. They are quiet and neither moisture nor cleaning solvents corrode them 4. They will not chip or break MISCELLANEOUS APPLICATIONS
An interesting use of plastics, which is undergoing experimental evaluation in our plants, is not confined to textile fibers plants, but has application wherever air-conditioning air washers are used. It is the use of plastic instead of metal for eliminator blades on air-conditioning air washers. The purpose of these blades is to catch and remove entrained water from the stream of air leaving the air washers. These blades usually are made of aluminum or galvanized iron. They are subject to some corrosion and require frequent cleaning. Test installations of extruded polystyrene blades have been made and have proved very successful. The advantages of the plastic blades are that they do not corrode, do not collect dirt readily, and the slight accumulations of dirt on the surface which occur after long operating intervals can be wiped clean. However, these blades have one serious disadvantage which has prevented a more widespread application-
flammability. Air supply systems are not an ideal place to use flammable materials for eliminator blades or duct work, and, therefore, in the interest of safety and fire protection further extension of this use for plastics is suspended pending a complete study of the hazards involved and the possibility of substituting less flammable varieties of plastic in this application. SUMMARY
In appraising plastics for use in textile fibers plants, today we believe that corrosion alone is the easiest problem to solve with the materials now available. Were this the only problem, it would be relatively easy to find a plastic that would meet successfully most of the corrosion problems encountered in textile fibers plants. The big minus value which is encountered, particularly in piping, is the temperature limitation. If permissible operating temperatures could be raised another 50' to 60' C., or even half of that, without loss of chemical resistance or ~ O E E of physical strength, there would be a considerable immediate increase in application possibilities. Judging from what has already been done and the rate of growth in machine component applications for molded plastics, there seems to be no limit to what can be done and justified. ACKNOWLEDGMENT
The authors wish to thank those men of the D u Pont Co. Textile Fibers, Polychemicals, and Engineering Departments who supplied material and assisted in the preparation of this paper. RRCEIVED for review September 17, 1954.
AC~EPTED May 10, 1954.
Food Processing Plants LAWRENCE J. TURNEY T h e H . W . Madison Co., Medina, Ohio
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ECAUSE of the possible consequences of toxicity and contamination, food processors must give these factors more careful consideration than manufacturers of most other products. The food industry is generally reluctant to accept new or different materials of construction without complete toxicological and chemical resistance data. Since foods are never pure chemical compounds, the possibility of plastic deterioration as a result of reaction between the plasticizer and the ingredients of the food product is a strongly limiting factor Copper and iron as contaminants may accelerate the development of rancidity in vegetable oils and will discolor vinegar and vegetables. Rubber and metals, when attacked, will impair the taste and aroma of food products. We have learned that certain materials of construction are apparently not attacked by either of two food ingredients individually but may be by a combination of them. For example, Type 316 stainless steel is quite resistant to sodium chloride solutions and acetic acid but is more readily attacked by a solution containing both. The food industry has learned these and many other facts about currently used materials of constructmion. However, relatively little is known about the results which may be obtained through the use of plastics. Through honest, intelligent recommendations, the plastics industry can do much to hasten the widespread use of their materials in food processing plants. The Food and Drug Administration through its divisions of Pharmacology and Food has already done L good deal of work
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that should prove helpful in evaluating resins, plasticizers, stabilizers, release agents, antioxidants, accelerators, colorants, and emulsifiers. Many of the materials are considered not acceptable because of inadequate toxicological data. A list of the materials considered as well as the criteria and procedures used for the evaluations may be obtained from the agencies. The plastics industry would do well not only to cooperate with the Food and Drug Administration in this work but to conduct separate studies to determine which of their materials may be acceptable and to find substitutes for those which are not. This is a procedure that must be followed by all suppliers interested in introducing a new substance into food products. The food industry i s much in need of materials superior to those presently used. Many types of stainless steel are commonly used, but for some applications they are not entirely satisfactory and are quite expensive. Plastics may alleviate some of these conditions that are accepted as necessary. It is difficult for those not familiar with food processing plants to realize the corrosiveness of sodium chloride, acetic, lactic, and other food acids as well as the aromatic hydrocarbons and spices. However, I believe that manufacturers of stainless steel will readily admit that the food industry presents serious corrosion and erosion problems to which their products have merely come closest to a distant solution. Many food manufacturers and processors have been conducting experiments with various types of plastics as possible replace-
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 7
Plastics Construction Materials There are few industries so urgently in need of superior materials of construction as the food industry. Because of the consequences of toxicity and contamination, these characteristics must be given more careful consideration than in other industries. Experimental applications of some plastics for piping, tubing, tank car and tank truck lining, dead plating, protective coatings, agitators, mixing tanks, bearings, and pistons indicate that some of the problems of contamination, corrosion, erosion, and friction may soon be somewhat alleviated. The advantages and limitations of each type must be considered prior to selection for each application. A review of the properties of the presently available plastics indicates where they may be used with hope for success. Better machining methods as well as more complete handling knowledge are essential before a successful widespread use of plastics may be realized. The potential field for these materials is tremendous but suppliers must be conscious of the dangers of misuse, especially where toxicological data is incomplete. Such errors may do much harm to the food manufacturer as well as to the plastic suppliers.
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ments for stainless steel, iron, glass, wood, etc. Plastics are now in use as piping, tubing, tank car and tank truck lining, bearings, pistons, conveyors, mixing tanks, and head spacers, and where the best available type has been used they have compared favorably with thc materials they have replaced. I n the Madison plants we are experimenting with styreneacrylonitrile copolymer blends and rigid poly(viny1 chloride) for piping; tetrafluoroethylene for dead plates, label pressers, head spacers, and bearings; epoxy resins and vinyls for protective coatings and polyethylene for containers. I n the future a 10,000-gallon concrete tank will be lined with the resin considered to be most satisfactory. A similar tank will be constructed of tile with furan or another suitable plastic grouting material. Experiments are currently being conducted to determine which of these methods would be most practical. We also have tank trailers used for hauling vegetables in brine for which we hope to find satisfactory plastic coatings or castings. At present these tanks are constructed of Type 316 stainless steel. Although this is the most satisfactory material used for this purpose, it requires frequent maintenance and is expensive. Tetrafluoroethylene has been used for dead plates became of its corrosion and erosion resistance, its low coefficient of friction, and zero moisture absorption. This material is well suited to cover label pressers because of its nonadhesive properties. One of our suppliers has used it to line capper hoppers and for packing material because of its low coefficient of friction, chemical inertness, and ability t o withstand relatively high temperatures. Rigid poly(viny1 chloride) piping has been used throughout our vinegar plant as well as in many installations in our pickle plant because of its low cost and resistance to acetic acid. Piping of styrene-acrylonitrile copolymer blends is used because of its low cost, resistance to acetic acid, sucrose, and sodium chloride and somewhat greater temperature range than poly(viny1 chloride). I n the food industry, coolers, mixing tanks, agitators, piping and all materials of construction are subjected to damp, highly corrosive conditions, and it is believed that plastics in some forms, because of their resistance to corrosion and sweating, may serve well in these applications While there are a great number of possible uses for plastics in the food industry, i t appears that the most promising volume outlets are for containers, piping, protective coating, and flooring.
Except for poly(viny1 chloride) linings for cans and vinylidene chloride coatings for caps, polyethylene has monopolized the container field. I n selecting a material for piping, pressures, temperatures, resistance to the materials to be handled, and the limitations of the layout should be considered. All plastic piping is much less rigid, softer, of lower tensile strength, and higher thermal expansion than iron. However, when properly selected, it has greater corrosion resistance, is lighter, has higher flow rates, has little tendency t o build up internal deposits, is less likely to contaminate sensitive solutions, and does less sweating than iron pipe. It is likely that the most fruitless of the food processors’ efforts have been directed toward securing satisfactory materials for heavy duty flooring. Epoxy resins have been used as a protective coating for the floor of a new vinegar plant. This appears to be satisfactory for the purpose, but such material would not be suitable for heavy duty floors. The work of Seymour and his associates of Atlas Mineral Products Co. indicates that properly joined hard-burned shale or fire-clay brick or tile gives the best service. The jointing material to be used is dictated b y the type of corrosives to which i t is to be subjected. We have studied with a great deal of interest the chemical inertness, heat resistance, nonadhesive properties, erosion resistance, low coefficient of friction, zero moisture absorption, dielectric properties, and weather resistance of tetrafluoroethylene and fluoroethylene resins. Beyond question this type of material could be used b y the food industry as pump and valve packing, gaskets, tank linings, and numerous other applications. The most frequent objection to the fluoroethylene resins has been lack of available engineering and handling knowledge, a need for specialized tools, and high original cost. The food industry is a needy and possibly large outlet for plastic materials. However, the suppliers must be conscious of their responsibility to society and of the gravity of the misuse of their materials. They should make every effort to impress on potential customers that each type of plastic has its limitations, and although it may be excellent for one application it may be worthless or impractical for another. RECEIVED for review September 17, 1954.
ACCEPTBDMay 17, 1955.
END OF SYMPOSIUM Reprints of this symposium may b e purchased for $1.75 each from the Reprint Department, American Chemical Society, 1 155 Sixteenth St., N.W., Washington 6, D. C.
July 1955
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