664 



THE INDIA RUBBER WORLD 



JlNE 1, 1921 



lor one hour at 2SU ilcgrcis F. These vulcanized samples 

 were allowed to rest for 24 hours. Then test pieces ^-inch 

 in width were cut from each slab with a suitable die, each 

 piece was marked with linos two inches apart and physical 

 tests were made by use of a Scott testing niacliiiic, the rate 

 of speed being 20 inches per minute. 



The results recorded below for tensile strength, elongation 

 and Set at break represent the average results of three tests 

 of each sample. In taking the permanent set, the original 

 marks two inches apart were stretched to twelve inches and 

 so held for ten minutes, then allowed to recover for ten min- 

 utes, when measurements were taken and tlic percentage in- 

 crease in length recorded. 



RESULTS 



\\'hcn cured and tested as described above, Compound 

 Xo. 1 (see Table 1) gave the following results: 



Tensile strength per sq. in 1,915 prunds 



lilonKation, or stretch 750 per cent 



Permanent set 9 per cent 



Set at breaking lead 13.5 per cent 



The first lead compound compared with litharge in accel- 

 erating action was sublimed white lead. It was found to 

 require seven per cent of this compound to obtain results at 

 all comparable with those given by one per cent of litharge. 

 Six and five per cent of sublimed white lead gave tcnsiles 

 far below that of one per cent of litharge. 



T.VBLE 2 

 Results Obt.\ined With Sublimed White Le.\d 



5% 6% 7% 



Tensile strength per sq. in lbs. 907 1,552 2,195 



Klongation. nr stretch 700% 8S5% 800% 



Permanent set 15% 7.5% 8% 



Set at breaking lead 16% 18% 15% 



Basic lead carbonate was next compared with litharge in 

 accelerating action and it was found to require 3 per cent of 

 this compound to give results approximating those given by 

 one per cent of litharge. 



T.ABLE 3 

 Results Obt.\ined With Basic Lead Carbonate 



3"; 4% 6% 



Tensile rtrength per s.;. in lbs. 1.853 1.635 2,079 



Elonjaiion. or stretch 800% 800% 850% 



Permanent set 8.5% 7.5% 4% 



Set at breaking load 19% 



Finally, sublimed blue lead was compared with litharge in 

 accelerating action. The nearest approach to the results 

 obtained with one per cent of litharge, was obtained with 

 three per cent of sublimed blue lead. Further addition of this 

 lead compound indicated decided overvulcanization; while 

 one and two per cent indicated that the samples tested were 

 very much undercurcd. 



Table 4 

 Results Obtained With Sublimed Blue Lead 



1% 2% 3% 5% 7% 



Tensile strenfith per sq. in... lbs. 210 779 1,663 1,733 2,125 



Elongation, or stretch 800% 800% 800% 800% 750% 



Permanent set 25% 11.5% 6.5% 4.5% 3.5% 



Set at breaking load 43.6% 17.8% 12.8% 13% 12.5% 



The results thus indicated that basic lead carbonate and 

 sublimed blue lead have approximately the same accelerating 

 action in the vulcanization of rubber. 



In the course of his investigations, the writer tried com- 

 binations of lead compounds with hexamethylene tetramine, 

 with remarkable results. It was found that such combina- 

 tions enable one to greatly reduce the percentage of hexa- 

 methylene tetramine used; and when the price was high, this 

 was quite an item of cost. 



To further test the relative accelerating action of basic 

 lead carbonate and of subliined 1)!ue lead, and also to de- 

 termine whether the accelerating action of basic lead car- 

 bonate is entirely dependent upon the lead hydroxide pres- 

 ent, three per cent each of basic lead carbonate, of sublimed 



blue lead; and ul chemically pure normal lead carbonate were 

 introduced separately into the following formula and the 

 compounds thus obtained were then cured in a press for 40 

 minutes at 290 degrees F. and tested as described above. 



Formula of Compound No. 13 



Per Cent 



Smoked sheet 65 



Sulphur 2K 



Zinc oxide 2 



Blanc fixe 5 



Barytcs 22J<2 



Hexamethylene tetramine ^ 



Basic lead carbonate or sublimed blue lead, or normal 



lead carbonate 3 



100 



In this connection, it may be stated that tests were made 

 with the formula as given above, using blanc fixe and barytes 

 in place of barytes alone. The results were sufficiently in- 

 teresting to warrant further work that is now in process, 

 the results of uliich will be presented in tin- near future. 



T.\BLE 5 

 Results Obtained With Basic Lead C.\rbonate, Sublimed Blue Lead 



AND KoKMAL LeaD CaRBONATE IN COMPOUND No. 13 



3% Basic 3% Sub- 3% Normal 



Lead limed Blue Lead 



Carbonate Lead Carbonate 



Tensile strength per sq. in.... lbs. 1,487 1,475 1,481 



Elongation, c;r stretch 700%, 750% 750% 



Permanent set 8% 8% 9% 



Set at breaking load 18% 19% 20% 



Three per cent of sublimed white lead and of chemically 

 pure lead sulidiate was introduced separately into the same 

 formula. 



T.\BLE 6 



Results Obtained With Sublimed White Lead and Chemically Pure 

 Lead Sulphate 



Tensile strength per sq. in lbs. 872 906 



Elongation, or stretch 750% 725% 



Permanent set 10% 10% 



Set at breaking load 20% 16.5% 



SUMMARY 



The conclusions to be drawn from this investigation are: 



1. That, of the most coinmonly used lead compounds, 

 litharge possesses the greatest accelerating action. 



2. That the relative accelerating action of basic lead car- 

 bonate to that ot litharge is in approximately the proportion 

 of 3 to 1. 



3. That the relative accelerating action of sublimed blue 

 lead is appro.ximately the same as that of basic lead carbonate. 



4. That the relative accelerating action of sublimed white 

 lead is much below tliat of the other compounds of lead. 



5. That it may be questioned whether the accelerating 

 action of basic lead carbonate is entirely dependent upon the 

 lead liydroxide present. 



6. That combinations of lead compounds with hexamethyl- 

 ene tetramine enable one to greatly reduce the percentage of 

 the organic accelerator used. 



THE ACTION OF CERTAIN ORGANIC ACCELERA- 

 TORS IN THE VULCANIZATION OF RUBBER— II' 

 By C. D. Kralz, A. H. Flower and B. J. Shapiro" 



/^XE of the early patents' for the use of syntlictic iiitro- 

 ^^ genous organic substances in the vulcanization of rubber 

 refers to the dissociation constant of 1 X 10-' as the dividing 

 line between accelerating and non-accelerating bases. On the other 

 hand, Peachcy' has pointed out that certain other substances which 

 are not basic, or but slightly so. are aljo exceedingly active as 

 accelerators. The number of examples in tliis class, however, is 

 relatively small. 



'Presented before the Rubber Division of the .American Chemical Society 

 at Chicago. Illinois. Seiitcniber 6 to 10. 1920. 

 -The Falls Rubber Co.. Cuvahoga Falls, Ohio. 

 ^Oerman patent No. 280.198. 1914 

 '.Tniirnal of the Society of Chemicil Industry. 36, 1917. 950. 



