660 



THE INDIA RUBBER WORLD 



Jink 1. 1921 



currcnce of several forms of caoutchouc, representing, he sup- 

 poses, different degrees of polymerization; (3) the behavior of 

 caoutchouc in some respects as a saturated hydrocarbon, namely, 

 its failure to become reduced by hydrogen in the presence of 

 platinum black or palladium. 



POLYMERIZATION 

 Mention may be made of a recent very interesting paper on 

 the general subject of polymerization in which Professor Staud- 

 inger' strongly urges the view that polymerization processes 

 should and can be regarded as involving only normal valences, 

 and that auxiliary or partial valences should not be called in to 

 explain polymerization. In accord with this view, he favors the 

 closed-chain formula for caoutchouc proposed by Pickles. He 

 also interprets on the basis of a similar closed-chain formula 

 the results of Steimmig who obtained as scission products of 

 samples of caoutchouc prepared by the polymerization of isoprene 

 with sodium, not only lacvulinic acid, but also acetonylacetone and 



succinic acid. 



VULCANIZATION 



Among Harries' most recent work on rubber are some obser- 

 vations on the nature of the vulcanization process. Harries 

 distinguishes between primary vulcanization and aftervulcaniza- 

 tion. In primary vulcanization sulphur becomes adsorbed, but 

 not chemically combined. The essential change is in the condi- 

 tion of the caoutchouc from a metastabile form, soluble in organic 

 solvents, to a stabile form insoluble in such solvents. The stabile 

 caoutchouc, as obtained after the exhaustive extraction of sulphur 

 from the primary vulcanized material, he found to be unvulcan- 

 izable. No chemical difference between the two forms could be 

 ascertained by an e.xamination of the ozonides. 



In addition to an account of his work on natural caoutchouc, 

 Harries' recently published volume gives an interesting review of 

 his work on synthetic caoutchouc derived, by a variety of poly- 

 merization methods, from butadiene, isoprene, piperylene and di- 

 methylbutadienc. 



'Berichte, 1920. p.ige 1073. 



VARIATION IN FINE HARD PARAS AND PLANTATION RUBBER i 



From the earliest plantation days fine hard Para rubber has 

 served as a standard by which plantation rubber has been judged. 

 It is now generally agreed that much first latex plantation rubber 

 is on an average f4uite equal to fine hard Para but shows greater 

 variation in rate of cure. It is generally assumed that the latter 

 shows no appreciable variation in this respect and various theories 

 have been put forward to explain the difference between it and 

 plantation grades. But few comparative tests between different 

 samples of these rubbers, have been made. It seems, therefore, 

 that adequate experimental proof of the superior uniformity of 

 fine hard Para in rate of cure does not exist. 



The results of his own work and that of others is summarized 

 by Stevens in the following table, remarking that the variations 

 calculated on the basis of the average deviation from the average 

 allows an approximate comparison in spite of the difference in the 

 number of samples. 



.\vcrage deviation 

 from {he average; per 

 cent of time of cure 

 Eaton and his collaborators on 26 samples (probably 



each a mixture from different balls of fine bard Para) 6.1 



Stevens on 5 samples from different balls of fine hard 



Para :-. 9.5 



Stevens on 23 samples of crepe prepared for testing 



on different occasions under uniform conditions 4.8 



De Vries and Spoon on — 



193 samples of smc»ked sheet 10.5 



131 samples of first latex crepe 5.1 



Assuming that the conclusions arrived at arc correct, namely, 

 that fine hard Para rubber shows much the same variation in 

 rate of cure as probably smoked sheet, we are faced with the 



Tiy Dr. H. P. Stevens. Bulletin of the Rubber Growers' Association, 

 September, 1920, p3?e 347. 



difficulty of explaining the manufacturer's preference for fine hard 

 Para and his complaints as to the variability of plantation rubber. 

 It should be noted that plantation ruljber is not all first latex and 

 quite a considerable proportion originates from native holdings. 

 This fact is sufficient explanation of the variation in plantation 

 rubber apart from other contributory causes. 



EFFECT OF ACIDS IN RETARDING THE RATE OF CURE ' 



In general as regards rate of cure, the effect of treatment with 

 hydrochloric acid is intermediate between that of sulphuric 

 acid and that of acetic acid. Hydrochloric acid, like sulphuric 

 acid, reduces the rate of cure, although to a lesser extent, and 

 the rate of cure is restored more completely by soaking in water 

 than in the case of sulphuric acid. The amount of hydrochloric 

 acid retained by the rubber is very small and similar in quantity 

 to the amount of acetic acid retained under similar circumstances, 

 and much smaller tlian the amount of sulphuric acid retained. 

 This is in accordance with the volatility of hydrochloric acid, and 

 a large part appears to be lost by evaporation when the crepe 

 rubber is hung to air dry. The relative action of acetic, hydro- 

 chloric and sulphuric acids on rate of cure therefore is not pro- 

 portional to the amounts of these acids retained by the rubber. 

 Hydrochloric acid has probably a greater retarding effect than 

 sulphuric acid, having regard to the very small amount retained. 



From this point of view, hydrochloric acid is very unsuitable 

 for latex coagulation. It is also unsuitable because rubber so 

 coagulated frequently becomes soft and tacky on keeping. This 

 does not happen with sulphuric acid, and it is evident that hydro- 

 chloric acid has a degrading or oxidizing effect on raw rubber, 

 and it should never be used for coagulating late.x under any cir- 

 cumstances. 



'By Henry P. Stevens. Bulletin of the Rubber Growers' Association, 

 November, 1920, page 435. 



SYNTHETIC RUBBER 



In the Allgeme'me Autoiiwbil-Zcituiig Dr. Albert Xeuburger 

 sketches the historical development of synthetic rubber in Ger- 

 iriany, referring to its usefulness during the war, and advances 

 the opinion thst under economic conditions which prevail in Ger- 

 many, synthetic rubber may be perfected to actually compete 

 seriously with the natural product. It is planned to develop the 

 German coal industry intensively, and by distilling the coal at 

 the mines, conserve all its by-products. These supplies of acetone 

 and benzol will give the necessary source materials. 



The important consideration is the possibility of developing 

 synthetic rubber with essentially the same technical character- 

 istics as the natural product. Germany, since the war, naturally 

 retains greater interest in the future prospects of synthetic rub- 

 ber than any other country. Dr. Neuburger, in fact, suggests 

 that it is possible that Germany in time may not need to import 

 natural rubber. 



CHEMICAL PATENTS 



THE UNITED STATES 



PROCESS OF Treating Vii-camzeu Rubber, consisting of re- 

 ducing it to a finely divided state under conditions of exclu- 

 sion of oxygen, adding a small quantity of new, unvulcanized rub- 

 ber in solution, sufficient merely to film the particles of old rub- 

 ber, expelling the solvent, and fomiing and vulcanizing in the 

 usual manner. — Joseph Porzel, Buffalo, Xew 'i'crk. assignor, by 

 mesne assignments, to Superior Rubber Co., Pittsburgh, Pennsyl- 

 vania. United States patent No. 1,374.231. 



.Admesute Cement and Process of Manufacture. A cement 

 consisting of rubber, and water as solvent for the dextrin. — 

 Thomas Edwards, Milton, Massachusetts. United States patent 

 Xo. 1,374,992. 



Vulcanized Oil Product Proiess. Depoi.vmerizing a vul- 

 canized oil product in the presence of gasemis hydrochloric acid. — 



