Jelly Glue

The Use of Jelly Glue

Jelly glue or technical gelatin has many uses that depend on it's gelling or on it's surface properties. The most common use for jelly glue is as an adhesive solution where its gap filling properties added to its great dry strength are its main advantages. However jelly glue must penetrate the surfaces to be bonded so one must ensure that the penetration of the liquid occurs before the glue gels. Surfaces can be joined with jelly glue if one of the surfaces is permeable to water. In practice jelly glue is used hot and sufficiently so to ensure penetration before gelation. The rapidly developed tackiness of jelly glue as it sets to a gel makes it useful in such application as sticking cloth to wood, bookbinding, in the manufacture of cartons on high speed machines and manufacture of “gummed” tape.

Other examples of its uses as an adhesive is in woodworking, cardboard case closing, match head bonding to the stick and the bonding of abrasives to paper for use as sandpaper.

The glue on drying forms a very strong film. This film forming property is used in paper seizing and cardboard manufacture and for decorative picture frame moldings.

Glue films are so strong that as they dry and shrink, if the glue is well keyed to glass the drying film rips some glass from the surface. This is the basis for the process called glass chipping and is also the reason why you never let glue dry in a glass container.

Jelly Glue being a protein does not burn and this property is used to control the rate of combustion of dry match head formulations, as well as in fireworks and in firearm propellants. Jelly glue solution gels on cooling and this property is used in retaining match heads on match sticks during the drying process and in the manufacture of printing machine rollers.

To prevent glue solutions from drying, polyhydric alcohol humectants can be added to the solution before gelation.

Finally, gelatin modifies the deposition environment (zeta potential) during electroplating allowing a smooth surfaced ingot to be formed in place of an ingot full of spikes, due to uneven electrolytic deposition of metal from solution. The glue also improves the efficiency and cost of deposition. In refining metal the glue is used as an additive in the electrolytic process. Especially used in refining copper.

Types of Jelly Glue

Dissolving Glue

 

When stirring machinery is available, glue solutions can be prepared by adding dry powdered glue to hot water. The temperature of the water should be such that it drops to about 60℃ after the addition of the glue. The mix is then stirred at this temperature until the glue has dissolved. An initial temperature of about 80℃ is satisfactory when concentrated solutions are being prepared.
If solutions are to be prepared without mechanical stirring, the glue should be soaked in cold water until the water has penetrated to the centre of every particle. The time required depends on the state of subdivision. For powdered glue 15-30min may be sufficient but cubes or pearls may require one or two hours. After swelling the glue will dissolve very readily on warming with gentle hand stirring.

Concentration of Solutions

 

In general the solutions are required to be at the maximum concentration at which they can be spread easily. This depends on the grade, or more exactly the viscosity of the glue. Since, however, glues are graded mainly by jelly strength and since there is some correlation between jelly strength and viscosity, concentrations are recommended in terms of jelly strength.

Manufacture of Jelly Glue

That the presence of reducing sugars such as corn or invert sugars in jelly glue adhesives results in what is herein referred to as a resinification reaction, indicated by a progressive increase in viscosity and a tough, rubbery texture, eventually reaching a point where the adhesive becomes unusable. This resinification reaction is greatly accelerated by heat. Flexible glues are made by heating jelly glue, water, and plasticizer to a homogeneous dispersion, and allowing the material to cool in molds so as to form semi-rigid slabs. In order to use the glue it must again be melted down by heat (with or without addition of water) so as to regain its fluid form. The resinification reaction, accelerated by the heat, may thicken and rubberize the composition during its manufacture. Or, it may continue, over a longer period of time, in the slabs, resulting in the eventual insolubilization of the glue cake, that is, it can no longer be caused to revert to the fluid, usable form. On the'other hand, if the glue cake is melted down before the jelly glue-reducing sugar resinification reaction has insolubilized it, the reaction nevertheless continues at an accelerated rate in the heated liquid adhesive, so that in a relatively short time it is converted into a thick, rubbery, unusable mass.

That the addition of any chemical compound containing the ammonium radical restrains, the jelly glue-reducing sugar resinification reaction and thus acts as the resinification inhibitor. Regardless of the other radical or radicals in the particular ammonium compound chosen, it is the ammonium radical itself which functions as the resinification inhibitor. Thus, suitable resinification inhibitors would include ammonium sulphate, ammonium phosphate, ammonium acetate, ammonium chloride, ammonium nitrate, ammonium thiocyanate, as well as the other known compounds containing the ammonium radical. A preferred inhibitor is ammonium sulphate because it is relatively inexpensive and readily available.

In selecting a particular ammonium compound, the effect that the portion of the compound other than the ammonium radical may have on the glue composition should also be considered. Thus, for example, it is well known that chlorides, nitrates and thiocyanates tend to thin or liquiiy jelly glues, and, therefore, in manufacturing a flexible glue composition Where a semi-rigid slab is the desired final product, other resinification inhibitors than ammonium nitrate or ammonium chloride Or ammonium thiocyanate should be selected. On the other hand, in certain liquid jelly glue compositions these salts would be entirely suitable. In any case, the ammonium radical serves to retard resinification between the reducing sugar and the jelly glue, regardless of any additional effect brought about by the remainder of the ammonium compound.

The amount of ammonium compound to be added depends upon several variables, such as the particular type of ammonium chemical used and the amount of reducing sugar present. The resinification restraining effect is noticeable even with the use of only a fraction of one per cent of the ammonium compound. However, for average jelly glue compositions, using ammonium sulphate, I prefer to use from 0.5% to 30%. Percentages are by Weight, and are based upon the dry weight of the jelly glue in the composition.