Sept., 1922
T H E JOURNAL O F INDUSTRIAL A N D ENGINEERING CHEMISTRY
799
Vegetable Glue By C. K. Reiman RESEARCH LABORATORY, ARTHURD. LITTLE,INC.,CAMBRIDGE, MASS.
EGETABLE glue may be defined as a homogeneous mixture of starch, water, and a solvent for amylocellulose such as caustic soda, having the appearance and many of the adhesive properties of animal glue. Cassava (tapioca) starch generally forms the basis of this material. The water content varies from 2 to 4 times the weight of the starch and the caustic is generally about 5 per cent and may vary between 2 and 12 per cent of the welight of the starch. The vegetable glues find their widest use in the veneering industry. They produce a joint as strong as animal glue. They are mixed hot but used cold and they will keep ready for ust: without deterioration for weeks. They d.o not have the waterproof qualities of casein, being about the same in this respect as the animal glues. Their chief disadvantage is the tendency of some of these glues to stain certain woods.
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much water that drying was difficult, and a large percentage of failures occurred owing to opening up of the glue joints, Animal glue used for this purpose was generally mixed with 2 parts of water. When the raw starch was used with 2 parts of water the resulting glue was altogether too thick to spread, either by hand & by the mechanical spreaders then used with animal glue. It was after this point had been appreciated that the various parties interested in introducing vegetable glue into the veneering field turned for assistance to the almost forgotten patents concerning the partial hydrolysis of starch. When a starch base was used, which had been previously hydrolyzed according to the methods of Higgins or Gerson and Sasche, a glue could be prepared with caustic using the same amount of water that was used with animal glue. In 1912 the first of a series of patents in the vegetable glue field was granted to PATENT CONTROVERSY Perkins. This patent covered a large number of claims; some of which had to The earliest reference to such a material do with the processing of the starch by -oncerns apparatin, a product patented methods practically identical with those of nearly half a century ago (1874) by Gerthe earlier patents; some of which dealt ard. a Frenchman. This material con. _. with the soiution of the starch in caustic sisted of what is generally called a solution CLARENCE K . REIMAN with three or less parts of water, the of starch in caustic and water. It was lescribed as having excellent adhesive properties, and as patentability of which has been widely questioned; and ding useful in the field of textile sizing and as an adhesive other claims which covered the combination of these two steps. I n the only case that has come to the Court of for various purposes. Two others of the many patents dealing with such products Appeals the Perkins Patent has been upheld in Part, that is, deserve attention. I n 1897 a patent was granted to Higgins it was declared that neither step alone was Patentable but describing an adhesive prepared from a starch that had been that a combination of the two was. At the present time there are several large manufacturers partially hydrolyzed by treatment with dilute acids. The various stages through which the starch progressed during of these vegetable glues supplying the PlWood and veneering this treatment were accurately described. The fact was industries. Many of the users of these glues are to-daY pointed out that increased strength of joint was obtained defendants in suits brought by Perkins. A number of these by so treating the starch. I n 1906 Gerson and Sasche were glue manufacturers and certain organizations composed of granted a patent in Germany covering a process for the the users of these glues have banded together in the defense partial hydrolysis of starch by means of an alkaline oxidizing of these suits. As the outcome is uncertain, both sides are interested in forcing a decision in the near future which will agent, and the starch base so produced. Sinm that time a large patent literature has been pro- a t least serve to clear the air of the large amount of dust a t duced in various countries on this subject. To-day there present obscuring activities in these fields. CURRENT PRACTICE are a number of important suits in progress in which the courts are endeavoring to determine to whom should be given It is interesting to note that to-day current practice is the credit for the actual inventions declared in these many drifting away from the type of glue described in the Perkins patents. patents. Several of the glue manufacturers have discovered The reason for the court activity a t the present time over that it is unnecessary to process their starch with dilute these old patents is because of the considerable importance acid solutions or aEaline oxidizing agents in order to make a which vegetable glues have acquired in the woodworking workable glue when mixed with caustic and 2 or 2'12 parts industry. With the enormous growth in the production of of water. I n practice, if the raw starch is properly cooked plywood panels and veneered furniture, and with the gen- with the caustic a workable glue will result. I n fact, some erally rising price of animal glue the need of a cheaper adhesive of the important developments of recent date have been in for this purpose became more and more urgent. the opposite direction from that indicated by Perkins. It The first vegetable glues made for this use consisted of has been found possible to so adjust the gel properties of the raw starch, either potato or cassava, cooked with 8 or 10 starch by the addition of certain colloidal materials, that a per cent of caustic and 3 to 5 parts of water. A 3-ply or a product as strong as animal glue is obtained when 4 parts or 5-ply panel glued with this type of adhesive contained so more of water are added to the starch and caustic. It is
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