April, 1922
THE JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY
279
Changes in Some Varnish Resins on Heating’ By F. H.Rhodes2 and H.F. Johnson DEPARTXENT O F CHEMISTRY, CORNELL UNIVERSITY, ITHACA, NEW YORK
In uarnish manufacture resins are rendered soluble in oil by a preliminary heating (“running”) at 325” to 350” C. The present paper deals with the nature and extent of changes in the acid and iodine numbers of resins on heating. Determinations were made on Congo copal, East India copal, Manila copal, Pontianak. and kauri, on the original resins and on samples which had been heated to 300”, 350”, and 390” C. In every instance heating caused a decrease in acid ualue, the extent wrying with different resins. The iodine number of Congo copal decreased upon heating, and that of East India copal increased. For the other resins, the ualue increased slightly when they were heated to 300 C. but decreased at higher temperatures. There i s no apparent relation between the change in iodine number, acid ualue, and loss in weight on heating.
S is well known, ordinary oleoresinous varnishes consist essentially of solutions of ‘‘varnish resins” in drying oils Among the resins which are most commonly used in varnish-making are various natural resins of fossil or semifossil origin-Congo, EaPt India, Manila, and Pontianak copals, and kauri. These resins are not, in general, directly and completely soluble in oil, but may be rendered soluble by heating to fusion and partial decomposition. In actual practice, this preliminary heating or “running” of the resin is effected by heating it to temperature of approximately 325” to 350” c. When the resin is thus heated a certain amount of decomposition takes place, volatile products are given off, and the residue becomes more soluble in oil or other solvents than was the original resin. Very little work has been done to determine the actual chemical changes which take place in the resins on heating, and little or nothing is known as to the exact nature of the chemical reactions which occur in “running” the varnish resins. A number of investigators have determined the analytical constants of the various fossil and semifossil resins. Worstall3 determined the acid numbers and the iodine values (Hubl) of a rather large number of samples of Manila, Pontianak, South African, West African, Sierra Leone and Brazilian copals, kauri, and dammar. He also showed that some of these fossil resins, when finely ground and exposed to air for 4 mo., showed an increase in the acid number and a decrease in iodine value. These changes he attributed to the oxidation of the resin. Williams4 determined the “KOH absorption” and the iodine value of a kauri and copal, both before and after He examined, however, only one sample of each type of resin, and gives no information as to the type or source of the copal which he used. Moreover, he does not state the temperature to mhich the resin was heated during “running.” LewkowitschE determined the analytical constants of ti number of varnish resins, both before heating and after heating to 300” C. The results obtained with the original resins differ markedly from Worstall’s results for the same constants of similar types of resins. Moreover, in “running” his resins, Lewkowitsch heated the resins to a temperature of 300” C. only, whereas in the actual manufacture of var-
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Received December 22, 1921. Professor of Industrial Chemistry. 8 J . Am. Chem. Soc., 26 (1903), 860. 1 Analyst, 28 (1898), 254. 6 Ibid., 26 (1901),37. 1
2
nishes the resins are usually heated to temperatures appreciably higher than this. The work described in this present article was done for the purpose of determining the nature and extent of the changes in the acid numbers and the iodine numbers of the varnish resins when these resins are heated to various temperatures. It was hoped that the results thus obtained would afford some information as to the nature of the chemical changes which occur in the “running” of varnish resins. MATERIALS AND METHOD The following resins were used: CONGOCOPAL,bold amber, donated by S. C. Johnson & Sou Co. KAURI,Grade No. I, donated by S. C. Johnson & Son Co. EASTINDIACOPAL,nubs, dondted by S. C. Jobnson & Son Co. PONTIANAK COPAL,selected fine, donated by A. Hlipstein & Co. MANILACOPAL, bright amber, from Patterson, Boardman, Rnirpp Co.
In all cases, the iodine numbers of the resins were determined by the Hubl method, following the exact procedure described in Lewkowitsch’s “Chemical Technology and Analysis of Oils, Fats and Waxes.”6 The acid numbers were determined by the indirect method used and described by W o r ~ t a l l . ~ To 1 g. of the finely powdered res,in weighed out in a glassst#opperedbottle, 15 cc. of benzene, 5 cc. of alcohol, and 15 cc. of 0.2 N alcoholic potash solution were added. After 18 hrs., 25 cc. of alcohol and a few drops of phenolphthalein were added and the excess of alkali was titrated wit.h 0 . 2 N sulfuric acid. The number of milligrams of potassium hydroxide neutralized by the gram of resin was taken as the acid value of the resin. This method would, of course, give incorrect results if t h e resins contained esters well as free acid or APPARATUS USED POR “RUNNING” RESINS acid anhydrides, but Worstall has shown that esters are not normally present in these fossil or semifossil resins. When the original Manila and Pontianak copals were analyzed by this method, the resins dissolved completely in the mixed solvent. The original East India and Congo copals and kauri resin, however, did not dissolve completely even on long standing, and therefore the acid values obtained for these results are possibly lower .than the true 6
5th editioii, I , 39,5.
