DECEMBER, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
American users of a protein-base fiber will doubtless demand a strength capable of withstanding reasonable carding, combing, and spinning operation without help from other fibers. They will require dyeing properties similar to wool, under the same conditions of dyeing, because casein fiber and wool will be frequently mixed. Felting properties should be good in mixtures with feltable materials. The product must have a permanency which will avoid any breakdown by bacteria, mold, etc. It must withstand all common cleansing agents under normal conditions of use. In general, a satisfac-
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tory fiber must go into a textile mill, be blended with other fibers, and withstand all the operations common to a textile plant without requiring any change in operating conditions. When, and if, a casein-base fiber is produced and offered to our domestic trade, which meets the above requirements, it will doubtless fmd a successful use in many classes of textile goods. In addition, such a fiber will have many properties unique to itself and, without supplanting or interfering with the use of any present textile fibers, will add materially to the versatility of the textile industry.
Soybean Protein Fibers Experimental Production R. A. BOYER, Ford Motor Company, Dearborn, Mich.
Production of fiber from soybean protein is described. Difficulties encountered in obtaining uniform protein necessitate strict control of the variety of the soybeans and thorough chemical analysis and fertilization of the soil on which they are grown. When good protein is used, spinning solutions containing 20 per cent protein can be obtained. Soybean fiber as made at present has about 80 per cent the strength of wool, has more elongation both wet and dry, and does not wet so easily as wool or casein fiber. It does not promote mold growth so readily as casein fiber. The fiber blends well with wool and cotton and has been processed satisfactorily on both cotton and worsted textile equipment. Plans are being made for a pilot plant capable of producing 1000 pounds per day of soybean fiber.
YNTHETIC fiber production has been one of the most active and fertile fields for chemical research during the past twenty years. The tremendous growth of the rayon industry has stimulated the interest in work along this line, not only of textile chemists but of those employed in unrelated fields. Until recent years the greater part of the work was devoted to production and improvement of cellulose fibers such as viscose, cuprammonium, and acetate. I n 1936, however, Ferretti in Italy published his work on a new type of protein fiber produced from milk casein. This fiber called “lanital” achieved a reputation commercially as a wool substitute because of its chemical and physical similarity to wool. The success of lanital inspired fiber research on a great many other proteins, among them, fish protein, regenerated silk, peanut, corn zein, and soybean. The Ford research chemists had several years background of soybean research in 1937 and undertook the development of a fiber from soybean protein a t that time. The soybean in many ways is an outstanding source of protein for fiber work. Economically it is sound. The supply of soybeans is large and increasing yearly. The large use of soybean meal a t present is for cattle food, and this tends to keep the price stable and low. The bean is easily grown and finds favor with the farmers. Soybean oil, which
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is fast becoming one of our most important vegetable oils, is recovered in the first step of the fiber production.
Production of Fiber from Soybeans EXTRACTION OF OIL. The continuous solvent extraction method is used to extract the oil. The crushed beans are washed countercurrently with hexane which removes the oil. The resulting oil-free meal is passed through a steam-jacketed pipe for removal of the solvent. Although the Ford extraction equipment is different, the whole operation is standard in the soybean industry with the exception that meal prepared for fiber work is treated at much lower temperatures than meal prepared for cattle food. EXTRACTION OF PROTEIN FROM OIL-FREE MEAL. This is a critical and important part of the fiber preparation. Although protein extraction is a relatively simple operation, extreme care must be exercised in order to produce uniform batches. There are many ways of extracting protein, some of which are closely guarded secrets. The indications are that the simpler methods will be the most satisfactory. One method is to treat carefully sized oil-free meal with a weakly alkaline solvent, such as 0.1 per cent sodium sulfite solution, for a half hour. The resulting solution is clarified either by filtering or centrifuging. The protein in the solution is precipitated with an acid, and the resulting curd is washed and dried. Because of the discoloration of protein by iron, each one of these steps must be carried out in stainless steel or glass lined equipment (Figure 1). The pH must be checked and controlled constantly. For instance, no two batches of soybean meal will have the same pH when treated with the same amount of sodium hydroxide under similar conditions. Accordingly the alkali is adjusted to bring each batch to the same pH. Clarifying an alkaline solution of protein setisfactorily is a difficult chemical engineering problem. At present stainless steel centrifuges with automatic unloading devices are being used (Figure l). However much more work remains to be done on this point. Precipitation must be carried out a t exactly the right temperature and p H in order to get a curd that can be satisfactorily handled during the subsequent washing and drying. In spite of all these precautions we have found variations in the proteins. We have traced these back to differences in the variety of the bean from which the protein was extracted.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 32, NO, 12
There are indications also that the composition of the soil on which the beans were growii has a marked effect on the protein. In order to have a uniform supply of beans for t.he fiber experiments, pure strains of soyheam are heing grown on fields that have been thoroughly analyzed and fertilized. The crop from them fields will be stored in special metal containerr in order to keep to a minimum any changes that may occur during storage. We hope by these methods to eliminate as many variables a t the source as possible. PREPARATION OF SOI,UTION FOR SPINNING. The third step in producing a fiber consists in dissolving the protein to produce a viscous stringy solution. It is desirable to obtain a solntion having a high solids content. Because of the tendency of proteins in high concentrations to form a gel, i t is difficult to prepare solutions having more than 12 per cent solids. However, by proper control during the extraction of the protein we have succeeded in producing solutions containing 20 per cent protein. These solutions have excellent spinning characteristics. They must, however, he aged at the right temperature for the correct time before the proper viscosity and “stringiness” are reached. The solution a t this point should contain no undissolved particles or air buhbles, BS the spinning continuity would be affected. SPINNING AND HARDENING. The fourth step consists in forcing the solution through the spinnerettes into the acid precipitating bath and collecting the filaments on a reel or bobbin. Although many variations in precipitating baths are possible, they nsnally consist of sulfuric acid, formaldehyde, and a salt such as sodium chloride or aluminum sulfate to facilitate dehydration of the filaments. Stretching is an important part of the precipitation. The filaments are pulled through the acid bath and over two glass pulleys called “Godet wheels” (Figure 2 ) . The second wheel revolves faster than the first and thus exerts a stretching effect between them on the filaments. For staple fiber work multihole spinnerettes are used; our usual practice calls for 500-hole spinnerettes. A spinning machine having the flexibility required for experimental work is quite complicated. In order to obtain all the features wanted, we hati to design and build our own machine. Recently we have been working with a continuous machine that will enable us to precipitate, harden, and carry out the aftertreatment of the filaments continuously. The uniformity of treatment obtained by the continuous machine is a great advantage in producing fibers bccause of their minute size and sensitivity. Control of stretching is important, as can be shown
F~GURE 1. (Above) STAINLESS STEELTANKS SEJZ-CLEANINC CENTRIFUGES
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DECEMBER, 1940
INDUSTRIAL AND ENGINEERING CIIEMISTKY
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Recent refinements in processing have produced a soybean fiber highly resistant to carboniaing and to boiling in dilute acid and alkali. The fiber has been handled on conventional cotton and worsted equipment. I t showsgreat promise as a new, distinctly different fiber eminently suited in wool blends for use in suitings and upholstery fabrics. The availability of the fiber in fine deniers, with a fine crimp and great resilience, indicates its usefulness with cotton and spun rayon in the development of many new materials. Still another development under investigation is the use of soybean fiber with wool in felt manufacture. While a tremendous amount of work remains to be done on soybean fiber, we feel that the r&Tb already obtained warrant proceeding with the program as fast as possible. Plans are now @ing forward for the installation of a complete pilot plant capable of producing 1000 pounds per day of finished fiber in the form of “top” suitable for blending with fibers FIGURE 2. EXPERIMENTAL SPINKINu MACHINE, SHoWINQFILAMENTS BEING 8PllETCHED used in automotive upholstery. In BETWEEN T W O (;ODET WHEELS developing tbis fiber we think that a definite contribution will have been made not only to the textile industry and its customers, by producing fibers made from the same solution with and hut also to the suppliers of the textile industry-the farmers. without stretcbing. Those made without stretcbing will be brittle and weak; those that are stretched during the treatment will have good elasticity and high yield points. X-ray diffraction studies of fibers show the value of stretching. Orientation occurs when the fiber is stretched under proper conditions, whereas indefinite x-ray patterns are obtained from unstretchcd fibers. AFTERTREATMENT AND DRYING. Aftertreatment of the fiber consists of a relatively long immersion of the fiber in a formaldehyde bath to set the fiber completely, cutting i t to the desired staple length, and drying i t under controlled humidity and temperature conditions (Figure 3). If the fiber has been properly treated, it will be in a loose fluffy condition resembling scoured wool.
Properties The finished fiber is white to light tan in color with medium luster; i t bas a warm soft feel, a natural crimp, and a high degree of resilience. The tensile strength of soybean fiber is about 80 per cent 8s compared to wool; its dry elongation of 40 per cent and wet elongation of 60 per cent are much higher. The tensile strength a t break is approximately the same dry and wet: however, the yield point is lower on the wet fiber. The specific gravity of soybean fiber is 1.31 measured in water. The fiber is nearly circular and has little pigmentation. Water does not wet soybean fiber so readily as it does casein fiber and wool. Preliminary experiments indicate that soybean fiber is very resistant to the action of mold as compared to casein fiber which is more readily attacked. Fiber sizes range from 1.5 to 5 deniers in staple lengths of 1.5to 6 inches. It can be produced in natural color or can be spun dyed, with or without a fixed, highly permanent crimp.
F I G U ~3.~ :DRYING SOYBEAN FIBERI N I ~ I ~ M I D I T Y - ~ ~ N TROLLED OVEN
