Gelatin hydrate formation

Of particular interest in connexion with our subject is the case of compound formation by a macromolecular solid e. g., the hydrate formation by cellulose and gelatin or the formation of an addition compound between nitrocellulose and acetone. Whereas in ordinary low molecular hydrates the composition of the successive compounds X, X. HgO, X. 2HaO etc. differs considerably as regards the percentage of water and, hence, the Gibbs potentials of these compounds differ by considerable jumps, the situation is different in macromolecular substances. If e.g., each monomeric residue R of a molecule consisting of a chain of n residues can bind one water molecule, the following hydrates are possible ... 

Since swelling is intrinsically a process of dissolution, be it one of partial dissolution, or even, in its initial phases bound up with the formation of addition compounds (or hydrates if water is concerned), the volume contractions do not represent any new or specific phenomenon In cellulose and gelatin gels, by far the main part of the total contraction coincides with the range of hydrate formation. (cf. p. 541) and hence, may be connected with a chemical reaction, like the contraction occurring in the system sulphuric acid-water, or upon formation of crystalline hydrates of salts. It is known from numerous other examples that compound formation gives rise to a volume contraction. 

Benzylatnine. Warm an alcoholic suspension of 118-5 g. of finely-powdered benzyl phthalimide with 25 g. of 100 per cent, hydrazine hydrate (CAUTION corrosive liquid) a white, gelatinous precipitate is produced rapidly. Decompose the latter (when its formation appears complete) by heating with excess of hydrochloric acid on a steam bath. Collect the phthalyl hydrazide which separates by suction filtration, and wash it with a little water. Concentrate the filtrate by distillation to remove alcohol, cool, filter from the small amount of precipitated phthalyl hydrazide, render alkaline with excess of sodium hydroxide solution, and extract the liberated benzylamine with ether. Dry the ethereal solution with potassium hydroxide pellets, remove the solvent (compare Fig. //, 13, 4) on a water bath and finally distil the residue. Collect the benzylamine at 185-187° the 3ueld is 50 g. 

It will be noticed that all the properties of the gel with the exception of the turbidity and foam have minimum values at or near the isoelectric point P = 4 7, whilst these two attain their maximum values at this point. Evidently as the data for the swelling and viscosity indicate the hydration of the gelatine particles is at a minimum at the isoelectric point (see Chiari, Bioohem. Zeit xxxili. 167, 1911) where as indicated by the alcohol number it is most readily precipitated from solutions to form large aggregates to which the turbidity and the foam formation are due. 

The gelatin of the original solution may be replaced by gum acacia, and the hydrogen by such reducing agents as formaldehyde, hydrazine hydrate, hydroxylamine, or hypophosphorous acid. Both nickel acetate and freshly precipitated nickel hydroxide behave in an analogous manner to the formate. 

Germanic solutions are characterized by the formation with HjS of a white sulfide, GeS2, soluble in ammonium sulfide, also by the formation of a gelatinous precipitate, K2GeF , when KC1 and HF are added to GeF,. This precipitate becomes crystalline on standing. The hydrated dioxide is partially precipitated by ammonia, ammonium carbonate, and sodium carbonate. The fixed alkalies produce no precipitate because of the ready formation of the germanates. 

Although the analytical results give therefore no support for the conception of complex coacervation as simple formation of a gelatin-arabinate hydrate of constant composition, it will nevertheless be seen from the following subsections... 

Several processing factors can affect the binder performance during extrusion and spheronization processes including hydration level, extruder speed, shape, hole size, spheronizer speed, and residence time. While the use of microcrystalline cellulose alone or in combination with lactose is widely adopted, the addition of binders can aid in the formation of a plastic mass than can be easily extruded and spheronized. Increasing the PVP or starch/gelatin level increases the pellet size and decreases their friability (59). 

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