86 



THE INDIA RUBBER WORLD 



[NOVEMBKR 1, 1919. 



The stability of a vulcanized rubber varies with the sulphur 

 content of the acetone-extracted rubber, that is, the "combined" 

 sulphur. I have shown by physical tests ("Journal of the 

 Society of Chemical Industry," 1916, 872; 1918, 395 t and 340 t), 

 that a vulcanized rubber of this type is fairly stable over a 

 period of 2 — 3 years under ordinary atmospheric conditions when 

 the coethcient° does not exceed 3. With higher coefficients, 

 such as 6 or 7. decomposition sets in quickly, so that the rubber 

 is brittle or "perished" in a few weeks. It was therefore of 

 interest to compare the behavior to benzene of vulcanized rubber 

 both with relatively low and high coetiiicients. A has a relatively 

 low coefficient (about 4.3). To compare with A, a rubber, D, 

 was taken which after one week's extraction with acetone gave 

 9.36, 9.42 per cent sulphur. It was placed in a desiccator for 26 

 days and the sulphur redetermined. Suplhur^7.41, 7.63 per cent, 

 that is to say, an apparent loss of nearly 20 per cent of sulphur 

 in 21 days. This compares with an apparent loss of approximately 

 12 per cent in several weeks for sample A. 



A great part of this apparent loss is explained by an increase 

 in weight which was found to take place while the rubber was 

 aging." To obtain uniform results, aging was carried out 

 in an incubator at 30 degrees C. A vulcanized rubber, E, was 

 extracted with (1) alcohol one week and acetone one week, 



(2) as (1) followed by benzene extraction for one week, and 



(3) benzene extraction only for one week. The extracted 

 samples were dried at a low temperature for a few hours and 

 analyzed without delay. (1) 4.05, 3.95; (2) 4.10, 3.89; (3) 3.90, 

 3.97 per cent sulphur. These figures show that the vulcanized rub- 

 ber was in all cases exhaustively extracted and contained no sul- 

 phur soluble in organic solvents. The extracts consisted almost 

 entirely of sulphur. 



Portions of (1) and (2) were weighed after extraction and 

 placed in the incubator at 30 degrees C. They showed the 

 following increases in weight :— 



Day!, Aging. (1) Per Cent. (2) Per Cent. 



19.2 



18.7 



At this Stage the specimens contained (1) 3.49 per cent, (2) 

 3.38 per cent of sulphur. 



Assuming the apparent loss of sulphur to be due entirely to 

 the increase in weight, the calculated figures would be (1) 3.35 

 and (2) 3.37 per cent. During aging, vulcanized rubber emits 

 a peculiar odor and gives off acid vapors due to a trace of a 

 volatile product containing sulphur. When passed into water, 

 the substance is retained and the solution reduces ammoniacal 

 silver nitrate. A trace of sulphur is therefore lost in a volatile 

 form. 



Conclusions. 



(1) No sharp distinction can be drawn between the "solubility" 

 and "insolubility" of vulcanized rubber in organic solvents. 



(2) The more fully the rubber is vulcanized, that is, th» 

 higher the percentage of "combined" sulphur, the less is the 

 tendency to dissolve. 



(3) Fully vulcanized rubber, such as that containing 3—4 

 per cent of "combined" sulphur, is almost insoluble in benzene. 



(4) Vulcanized rubber rapidly oxidizes after extraction with 

 alcohol or acetone, and becomes soluble to an increasing extent 

 in benzene. "Overcured" rubber with 9—10 per cent of com- 

 bined sulphur oxidizes more rapidly than rubber with 3 — 4 per 

 cent of combined sulphur. 



(5) Vulcanized rubber recovered from the solution in benzene 

 becomes almost completely insoluble in benzene, provided the 



"The coefficient is the percentage of combined sulphur calculated on 

 the raw rubber present in the vulcanized rubber. 



»In a similar manner a rubber not acetone-extracted but vulcanized to 

 give a relatively high coefficient (say over 4) shows a loss of combined 

 sulphur on agiuK owing to an increase in the weight of the rubber due 

 to oxidation which accompanies "perishing." Previous acetone extraction of 

 the rubber increases the tendency to oxidation and "perishing" and conse- 

 quently the apparent loss of combined sulphur is more marked. 



original rubber was not oxidized (perished). This recovered 

 rubber possesses the nature and general physical properties of 

 vulcanized rubber. 



(6) Vulcanized rubber dissolves more readily in benzene the 

 more it is oxidized. At the same time the recovered rubber 

 becomes more inelastic or "resinous" and dissolves more readily 

 in benzene. 



(7) The increase in weight due to the oxidation of acetone- 

 extracted vulcanized rubber fully accounts for the apparent 

 loss of sulphur which takes place. But a trace of sulphur is lost 

 in the form of a volatile product of an acid and reducing nature 

 and containing sulphur. 



(8) Extraction with benzene does not allow of the separation 

 of a vulcanized rubber into parts vulcanized to different degrees 

 having different coefficients. 



CHEMICAL PATENTS. 



THE UNITED STATES. 



pKicK-^"^ OF M.\KiNG Waterproofing Compositions, compris- 

 ^ i'ng heating melted wax, a resinous substance, and dissolved 

 rubber to about 305 degrees F., adding to the mass at 140 de- 

 grees F. a resinous substance dissolved in alcohol and a light 

 hydrocarbon oil, then raising the temperature of the mass to 

 about 180 degrees F. (the amount of light hydrocarbon oil added 

 being sufficient to dilute the mass to the desired degree) ; finally 

 adding to the mass, while at 60 to 80 degrees F., carbon bisulphide. 

 (Guy M. Garlick, Kalamazoo, Michigan, assignor to William 

 S. Mitchell, Gary, Indiana. United States patent No. 1,315,109.) 



Waterproofing Composition, consisting of paraffine wax, dis- 

 solved rubber, a resinous substance dissolved in alcohol, a light 

 hydrocarbon oil, and carbon bisulphide. (Guy M. Garlick, Kal- 

 amazoo, Michigan, assignor to William S. Mitchell, Gary, In- 

 diana. United States patent No. 1,315,110.) 



Process and Products of Treating Vulcanized Oils com- 

 prising the depolymerizing of a vulcanized oil and repolymeriz- 

 ing the product to a plastic material without vulcanization, pro- 

 ducing a product that is similar in elasticity and plasticity to 

 gum chicle. (Walter O. Snelling, Pittsburgh, Pa. United States 

 patent No. 1,315,246.) 



Process of Making Tire Fillers consisting of subjecting to vul- 

 canization in a mold by heat and pressure a mass composed 

 ot small particles of soft rubber, rubber cement, gasoline and 

 kerosene. (Edward F. Aycock, Midlothian, Texas. United States 

 patent No. 1,315,652.) 



Impregnating Fibrous Material. A new material for articles 

 of footwear comprising a sheet of felted material, and a stiffen- 

 ing composition of resin, oxidizable oil and a drier incorporated 

 for the purpose of making the product transpiratory. (William 

 B. Wiegand and Walter Uffelman, Montreal, Quebec, Canada, 

 assignors to Rubber Regenerating Co., Naugatuck, Conn. United 

 States patent No. 1,317,340.) 



THE UNITED KINGDOM. 



VuLCA.NiziNG Rubber with Sulphur, accelerated by compounds 

 resulting from the interaction of strong alkalies or strongly 

 basic substances and monohydroxy derivatives of benzene or its 

 derivatives. Sodium phenate is one such compound in which 

 the hydrogen of the hydroxy! groups is replaced by the metal or 

 equivalent radical. In others the meta or para-cresol or beta- 

 naphthol may be the acidic group. (North British Rubber Co. 

 and B. D. Porritt, Castle Mills, Fountainbridge, Edinburgh. 

 British patent No. 129,798.) 



Vulcanizing India Rubber in the Cold by alternate treat- 

 ment with sulphur dioxide and hydrogen sulphide, the two gases 

 yielding sulphur within the substance of the rubber. A solu- 

 tion of hydrogen disulphide in benzene may be used instead of 

 the gas after treatment with sulphur dioxide. The process may 

 be used for the vulcanization of rubber dissolved in a solvent 



