656 



THE INDIA RUBBER WORLD 



ISkpthmber 1, 1916. 



What the Rubber Chemists Are Doing. 



\ ARlAltil.irY IN VlIlAXIZATIdN OK IM AM MULN 1' AKA. 



AN important study of the cause of variability in respect to 

 the rate of cure of plantation Para is being conducted 

 by B. J. Eaton and J. Grantham in tlie chemical laboratory 

 and experimental vulcanizing factory, Department of Agricul- 

 ture, Federated Malay States. 



The India Rubber World, October, 1915, page 11, and Decem- 

 ber, 1915, page 114, presented abstracts of the first communica- 

 tion on this research. The second communication, published in 

 "The Journal of the Society of Chemical Industry" (June 15, 

 1916) is abstracted below. 



In their previous paper, the authors indicated that the primary 

 cause of variability in rate of cure was attributable to the ac- 

 celerating action of a small quantity of some substance existing in 

 the latex or produced subsequently in the raw rubber from some 

 constituent present in the latex. 



Subsequent experiments have been directed to ascertaining the 

 nature of this substance and its behavior under different treat- 

 ments, to determine its probable constitution. These efforts have 

 resulted in the isolation or preparation of a substance or sub- 

 stances from the latex serum to which acceleration in rate of 

 cure can be attributed, and evidence has been oljtained of the 

 presence of a second substance which also has a similar effect. 



The experimental resuhs of the present paper confirm the 

 theory that the rate of cure is influenced by the amount of an 

 accelerating agent formed by the decomposition of some constit- 

 uent of the latex, and that this substance is a decomposition 

 product of the protein or nitrogenous constituents of the latex, 

 produced usually in the freshly coagulated raw rubber by the 

 action of micro-organisms, which gain access to the latex after- 

 it leaves the tree, or possibly in some cases decomposition by 

 chemical action. The retarding effect of smoking, on the rate 

 of cure, has proved to be a more complicated problem than at 

 first appeared. The retarding effect, though invariably shown 

 by slab, has been found not to be constant in sheet, especially 

 in thin sheet. This is due to the fact that, in smoking rubber, 

 more than one variable factor, influencing the rate of cure, is 

 present. 



In most of their experiments the authors used raw rubber in the 

 form of slab slightly pressed, or unpressed coagulum contain- 

 ing a large percentage of serum. The latex was coagulated one 

 day about noon, left in the serum till about 10 A. M. the follow- 

 ing day and then rolled undej- a wooden rolling pin on a sloping 

 table. All samples were eventually converted to thin crepe be- 

 fore vulcanizing. In order to demonstrate that the differences 

 obtained by the authors in their experimental samples were not 

 a special feature of the latex or rubber prepared in their factory, 

 tlveir methods of preparation were repeated for them on different 

 e>tates, with identical results. 

 The authors present their investigation in three divisions: 



PART 1.— EXPERIMENT.\U 

 Part I embraces a group of experiments for determining— 

 The time necessary to develop the change in slab rubber, caus- 

 ing an increase in rapidity of cure. 

 The effect of antiseptics, heat and cold. 

 The effect of formalin. 

 The effect of soaking in running water. 



COXCI.fSIOXS UXDKK P.\IM 1 



1. That the rate of vulcanization of rulibcr from any given 

 latex is determined by the extent to which a certain chan.ae takes 

 place subsequent to coagulation. 



2. This change is normally limited to the first few days after 

 coagulation. The change is progressive and rcaclus a maNimum 



in "slab" rubber (i. i'., coagulum containing a large proportion ui 

 the serum) in approximately six days after coagulation. 



3. The change can be arrested either partially or completely 

 by the action of formalin, heat, and cold. It is also arrested by 

 crepeing shortly after coagulation, which may be due either to the 

 larger surface exposed or to the more rapid drying, or both, com- 

 bined with the removal of most of the serum in machining to 

 crepe form. 



4. The complete arrest or inhibition of the change by forma- 

 lin (similar effects have been obtained with other antiseptics) 

 and by the action of both heat and cold, indicates the formation 

 by biological action of a substance which increases the rate of 

 cure of raw rubber, the decomposition being probably of an 

 anaerobic nature. There is no evidence that the change is due 

 to chemical agencies. 



In this connection experiments carried out on latex frozen 

 for several days at 12 to 15 degrees F., are of considerable interest, 

 since by freezing for this period, the rubber no longer cures 

 rapidly, even if left for a considerable period afterwards at 

 84 degrees F. 



[The method of freezing latex to produce rubber has been 

 patented in the Federated Malay States. Latex after freezing 

 for 4 to 5 hours is coagulated and, on thawing the solid block 

 thus formed, a solid coagulum is formed, whereas latex can be 

 frozen for a short period and on thawing is reconverted into 

 latex,] 



P.\RT II,— EXPERIMEXTAI.. 



Part II deals with the probable nature of the constituent of 

 the latex involved in the changes in raw rubber, and the nature 

 of the constituents which are responsible for the variations in 

 rate of cure of different rubbers. 



The experiments of Part II included the addition of proteins 

 to rubber and the effect was determined of the following addi- 

 linns : 



Casein and peptone. 



Decomposed casein. 



Protein from the latex. 



l-\aporated serum minus protein. 



Decomposed protein from serum. 



toxn.rsiox.s uxpkr part ii. 

 It is apparent from these experiments that there exist in the 

 serum two substances: (1) a substance of the nature of pro- 

 tein, precipitated or coagulated by heat, which is ineffective in 

 accelerating the rate of vulcanization unless decomposed ; (2) 

 a soluble substance, only obtained by evaporation and not easily 

 ilecomposed, which has itself an accelerating action or vulcaniza- 



Decomposed precipitated protein is effective in much smaller 

 quantity than serum residue obtained by .evaporation, after the 

 heat coagulated protein has been removed. 



In the ordinary preparation of sheet and crepe rubbers the 

 greater part of the serum is removed in machining the coagulum, 

 and the whole of the soluble products may be washed out in 

 crepeing, so that normally the accelerating effect of the soluble 

 serum is nothing. All of the experiments of the first part show 

 the gradual development of the accelerating substance during the 

 first few days after coagulation. This is attributed to the de- 

 composition of protein (similar in nature to that precipitated from 

 the serum by heat) which is precipitated with the rubber during 

 coagulation. 

 part III.— anat.ytical. nitrohex content of rubber 



AND THE rate OF VULCANIZATION. 

 The contrast between the high nitrogen content of a slow- 



