United States Patent Office Patented Nov
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3,411,972 United States Patent Office Patented Nov. 19, 1968 2 Surface due to insufficient flow of the gelatin; they possess 3,411,972 poor mechanical strength, and are soluble in water to METHOD FORMOLDING GE LATIN PRODUCTS Iyal O. Salyer and James L. Schwendeman, Dayton, Ohio, about the same extent as the unmolded particles. In order assignors to Monsanto Research Corporation, St. Louis, to obtain smooth pieces, it is necessary to treat them care Mo., a corporation of Delaware fully with wet steam for obtaining just enough solubiliza No Drawing. Continuation-in-part of application Ser. No. tion of the surface to provide, upon drying, a hardened 296,450, July 22, 1963. This application June 30, 1966, gel as a coating. Hence, molding at ordinary atmospheric Ser. No. 561,754 temperatures at very high pressures does not provide a 3 Claims. (CI. 156-336) commercially feasible means of converting gelatin to struc tural units. Not only is the extreme pressure impracticable; 10 but, also consisting shaping to dimensional tolerance is ABSTRACT OF THE DISCLOSURE problematic and steaming of rough surfaces to make them Chemically unreacted gelatin having a water content of smooth requires mechanical provision for coping with from 12 to 14 weight percent is molded at 100-160 stickiness. Also, when a moisture-resistant material is de C./50-3,000 p.s.i. to obtain a very tough solid. Laminates sired, use of extreme pressures at ordinary atmospheric are prepared by first impregnating a permeable support temperature is futile, since the compressed gelatin thereby with an aqueous solution of gelatin and drying to give a obtained is as water-susceptible as the starting material. coating of gelatin having the above water content, stack Although chemically unmodified gelatin is known to be ing, and molding the stack under the above conditions of degraded upon heating, we have found that very useful temperature and pressure. 20 structural materials are obtainable by employing discrete solid, finely comminuted gelatin containing from 12% to -mmunism 40% by weight of water and molding it at from about This application is a continuation-in-part of our applica 100° C. to about 160° C. at a moderate pressure of, say, tions Ser. Nos. 296,450 and 296,480, both filed on July 22, from about 50 p.s.i. to about 3000 p.s. i. and preferably at 1963, and both now abandoned. 25 from about 500 p.s.i. to about 1000 p.s.i. The invention relates to strong, molded bodies and The manner in which water is retained in solid gelatin more particularly to materials of construction compris is not definitely known. Hydrogen bonding may be present ing gelatin and to the method of producing the same. or there may exist merely a solute/solvent relationship. Although gelatin has been widely employed industrially, However, it is not believed that the gelatin is chemically e.g., for the preparation of medicinal capsules, phoo 30 modified by its water content, i.e., it does not appear that graphic films, and adhesives, its sensitivity to heat and a molecule of water has reacted chemically with one or moisture and the brittle nature of the unplasticized, solid more of the functional groups present in gelatin. Hence, gelatin have hampered its application as a material of as used herein, the term "chemically unmodified gelatin' construction. Also, although resistance to heat and mois includes moisture-containing gelatin; it does not include ture is improved by tanning it, i.e., by reacting the gelatin gelatin which has been modified by treatment with an agent with tannic acid or the natural tannins, or with chromium that reacts chemically with a functional group present in salts, or with phenolic and/or aldehydic compounds, the gelatin. thus chemically modified gelatin usually is a horny mate The moisture content of commercial gelatin in Solid rial which, owing to its complex composition, is not suit form may vary widely, depending upon the method of able for producing units of uniform shape and structure. 40 manufacture, temperature and extent of drying, storage Gelatin, itself, varies in composition with its method of conditions, etc. However, the moisture content equilibrates production and when it is reacted with such active mono very rapidly with the environment. Hence, irrespective of meric compounds as, say, formaldehyde, tannic acid, pyro its water content as received, when gelatin is stored at gallol, chronic acid or the salts thereof, a variety of re ordinarily encountered relative humidity, a moisture con action products are formed owing to condensation at Some tent which is within the at least 12% limitation is easily or all of the functional groups present in gelatin, and/or arrived at. For example, a moisture content of about fragmentation and/or convolution of the gelatin chain. 13% is achieved by conditioning gelatin at 25 C. and Usually addition of the active compound to an aqueous 40% relative humidity until cessation of change in solution of gelatin causes almost immediate gelation, weight. Such equilibration is generally effected within thereby preventing proper impregnation in laminate struc 24 hours. Hence the present process generally presents ture; and drying of the gels gives a product of insufficient no problem of moisture control, insofar as most com flow for technically feasible molding operations. merically available gelatin is concerned. Even though Gelatin is known to be denatured by heating; therefore, gelatin has been dried, during manufacture, to significantly prior attempts to mold gelatin have involved compacting lower moisture content, during usual conditions of trans gelatin at ordinary atmosphere temperature. Obviously, portation and storage it will absorb moisture which is when finely comminuted, solid gelatin is mixed with Suffi at least 12% by weight of the solid gelatin, since a cient water to cause stickiness of the gelatin, the particles relative humidity of less than, say, 35% is rarely will adhere to each other. The resulting mass can then be encountered. The maximum content of moisture which dried to, say, a slab. However, here again uniformity of 60 may be present in the gelatin is limited only by the product is not achieved because the water has penetrated fact that the gelatin to be moulded must be in the solid into some of the particles to a greater extent than into state to permit molding under heat and pressure. As others and there is obtained a multiphase structure. On will be realized by those skilled in the art, proper forming the other hand, when the gelatin particles are not made requires that the molding mix be retained in the mold, sticky before compacting, extreme pressures, e.g., pres 65 i.e., flow must be limited to within the mold. We have sures of 20,000 p.s. i. and more, are required to cause found that comminuted films of gelatin, cast from Water coherence. Molded products thus obtained present a coarse solutions thereof and dried only to remove surface wetness 3,411,972 3 4. to the extent that fragmentation into discrete particles is precautions in this respect need be observed. Irrespective permitted, is a suitable charge for the mold. We have of the process by which the gelatin was prepared and the found that gelatin which has been stored to constant source from which it was derived and the Bloom strength weight at 100% relative humidity and thus containing and viscosity of the aqueous solutions from which it about 30% of water can be molded under heat and pres was cast into films or flaked, shaped articles of Sub sure to give solid, molded articles. The rate and extent stantially the same order of mechanical strength are of flow of moisture-containing gelatin is a function of obtained upon compression and injection molding so long not only the moisture content of the gelatin but also as the moisture content of the starting gelatins and the of the molding technique. As the moisture content of pH thereof are substantially of the same order and the gelatin in solid form is increased, the gelatin has an in O molding procedures and conditions are not too diverse. creasingly greater flow when subjected to heat and That the source and method of manufacture of the pressure. Injection molding requires higher flow than does starting gelatin has substantially on effect on the nature compression molding. Hence, a solid gelatin which is of products obtained therefrom under heat and pressure most suitable for injection molding will generally con is surprising, for in prior applications such factors were tain more moisture than that which is most suitable for 5 almost universally believed to be controlling. Their rela compression molding, e.g., it may contain from 25% to tive unimportance insofar as the present utility is con 35% by weight of water. Generally, the maximum cerned may be attributed to changes in the gelatin brought moisture content of the solid gelatin which is to molded about by heat and pressure which make for uniformity is about 40% by weight of the gelatin. For compression of the finished product irrespective of variation in starting molding at the usual operating pressures, a moisture con 20 material. It has long been known that gelatin is changed tent of say 13% to 16% will be found most useful at in some manner upon application of heat. In the present pressures of, say from 50 to 800 p.s. i. Whether or not process, the inherent properties of gelatin are radically the flow is suited to the molding technique is readily modified by simultaneously applied heat and pressure, and determined by the molding operator through simple the effects are demonstrated stepwise.