INDUSTRIAL AND ENGINEERING CHEMISTRY
952 50.000
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Vol. 37, No. 10
Compositions corresponding to formulas A-17, -18, -20, and -21 of Table I were prepared, and heating was continued for approximately 4 hours aftkr the glue had been dispersed. Table I1 lists the properties of the overcooked compositions and those prepared in the standard manner. The difference in results is most noticeable in the gel strength determinations. The degradation of the glue in this fashion, a t a constant pH, is apparently a function of time, temperature, and concentration of glue. Thus, certain of the 1: 1 compositions were cooked for a long time without noticeable degradation, but high-softener or high-water-content glue formulas seem to be greatly aff ccted by such trcatment. The discrepancies noted in the 25” C. gel strength (Figure 4A) are probably traceable t o this trouble. Apparently, for the same reason the 25’ C. gel strengths for sorbitol-glycerol cornpositions were too erratic t o plot. The present data are based on glue having a gel strength of 415 grams and are therefore strictly applicable to the preparation of formulas from such a glue. However, they have been used for comparative purposes with some success for glues with gel strength ranging from 200 to 465 grams. CONCLUSIONS
Ratio of Softener t o Glue Figure 10. Variation of Physical Properties of Glue Compositions with Composition of Softener at 20% Water Content and 1.75-1 Softener-Glue Ratio Figure 10 illustrates the variation of physical properties with changing composition of softener (at constant softener-glue ratio and at constant water content). It is generally conceded that, with prolonged heating, glue compositions undergo deterioration. I n the present work i t was not feasible to standardize on a single heating time for all compositions since the time required for complete dkpersions of the glue was much shorter at high softener-high water contents than when the glue content was high. Furthermore, it was evident t h a t the degradation was more severe when the water content was high so that the practice throughout this study was to pour each batch as soon as there were no detectable particles of swollen glue in it. Serious degradation by overcooking is illustrated in the following experiments.
The curves show that the replacement of glycerol by sorbitol in glue compositions increases the viscosity, tensile strength, and gel strength. I n most applications, these are desirable treAds. Thus, in printers rollers, higher tensile and gel strengths, particularly a t elevated temperatures, permit higher press speeds and operating temperature. The higher viscosity of sorbitolcontaining compositions may necessitate modification of operating procedure and formulation. I n printers roller formulas, particularly, it is undesirable to increase the fluidity for ease in casting by increasing the water content since this would increase the risk of roller shrinkage. The proper modification is to raise the casting temperature or to increase the softener-glue ratio (or a combination of the two). It was not feasible to include in this study all of the properties pertaining t o the quality of a roller. Thus, resiliency, tack, etc., are important factors. I n general, it has been found in plant tests that a roller of excellent wearing properties combined with good printing characteristics is obtained when approximately equal quantities of glycerol and sorbitol are used. LITERATURE CITED
(1) Alexander, Jerome, ‘Glue and Gelatin”, A.C.S. Monograph 11, 1st ed., p. 227, New York, Chemical Catalog Co., 1923; Allen’s “Commercial Organic Analysis”, 5th ed., Vol. 10, Chapter on Scleroproteins, 1933. (2) Almy, Griffin, and Wilcox, IND.ENQ.CKEM.,ANAL.ED., 12, 392-6 (1940). (3) Government Printing Office, Tech. Bull. 24 (1942). (4) Griffin, IND. ENG.CHEM.,to be published. (5) Hoeppler, F., Chem.-Ztg., 57, 62-3 (1933). (6) Hopppler, F., 2. tech. Physik, 14, 165 9 (1933).
Correlating Vapor Compositions and Related Properties of Solutions-Correction A mistake in this paper which appeared in the September, 1944, issue has been called t o my attention. I n the discussion under “Partial Heats of Solution” on page 860, the second sentence reads: “The heat required to vaporize one mole of one component ( L ) from a solution is equal to the latent heat of the pure com-
ponent ( L ” ) ,plus its partial heat of solution ( H ) , etc.” This sign should be minus rather than plus, as well as those in the corresponding formulas of Table I, the second line for pi. This line should read as follows:
D. F. OTHMER
