October 1, 191 = 



THE INDIA RUBBER WORLD 



What the Ruhber Chemists Are Doing. 



VARIATION IN RATE OF VULCANIZATION OF RUBBER. lum, which was left in this form for some days, a really new 



THE "Malay Mail" reports a lecture on "The Variability type of rubber has been discovered. It vulcanizes more 



of Rubber," delivered in July at Klang by B. J. Eaton, rapidly than fine hard Para and ordinary plantation grades, 



chemist of the a.yricultural department of the Fed- which take medium time. Only eight or nine samples of 



erated Malay States. fine hard Para have been tested so far, but it is remarkable 



The lecturer referred to two terms of frequent occurrence — that all vulcanized in about the same time, 



standardization and uniformity — both as yet hazy and inde- It is, therefore, natural for the small manufacturer to rely 



terminate. There is a marked tendency to look to fine hard on fine hard Para. The reason for its lack of variation is 



Para as the standard because manufacturers have had ex- attributable to the uniform method of its preparation, and 



perience with it extending over many years. That, how- not because of any intrinsic value of the method. As it 



ever, is the only argument in its favor. The term uniformity, may require two or three months to prepare a ball of fine 



as applied to rubber, means rubber of the same type. Dil- hard Para, any variations in its quality are averaged, 



ferent types of rubber may vary in mechanical strength, but The formation of the accelerating substance is believed to 



variation in vulcanizing quality is far more important to be effected by bacteriological action. Rapid curing samples 



the rubber manufacturer. The matter of form and appear- show better mechanical tests than those that cure slowly, 



ance is of little consequence to the manufacturer, although Rapid vulcanization eliminates the danger of overheating, 



important to the broker, buying and selling on looks rather and that is probably the reason for the increase of strength, 



than by test. The lecturer credits Dr. Schidrowitz with first pointing out 



In vulcanizing rubber with sulphur the manufacturer has this variability in rate of cure in plantation rubber, of which 



recourse to three methods in securing a given result. He the experiments at the agricultural department first showed 



may vary the amount of sulphur, or the temperature and time the cause. It is possible now to prepare a rubber which will 



of vulcanization. In the experimental work of the agricul- vulcanize correctly at any particular time, within certain 



tural department, the sulphur and temperature were fixed limits. 



and the time varied. In the original experiments all the In conclusion, Lawrence Lewton-Brain, director of agri- 

 rubbers tested gave their best results in 2}/^ to 2^4 hours. culture, Federated Malay States, remarks that, although an 

 DiiTerent mechanical results were obtained by changing the insufficient number of experiments have been completed, the 

 time of cure. Subsequently a piece of Byrne-cured (smoked) results already obtained indicate that the variability in the 

 slab rubber gave its maximum mechanical results at lyj rate of cure is probably caused by a difference in the quantity 

 hours' vulcanization. Ordinary Byrne-cured loaf vulcanized or quality of certain non-caoutchouc constituents of the 

 in the normal time of 2J^ to 2^ hours, and the inference was latex, which remain in the rubber after coagulation. There 

 drawn that the Byrne method of smoke curing has no effect may be other factors, such as the physical condition of the 

 on the rapidity of cure. caoutchouc which afTect the quality of the material as re- 



To demonstrate this point rubber slabs were made and gards elongation and tensile strength. This problem is now 



smoked in an ordinary smoke house, and these were vulcan- being investigated. 



ized in 1J4 to V/z hours. Then unsmoked slabs of pan coagulum, POT\SH FROM HEVE\ 



made the same thickness as the smoked slabs, were tested „,.,,. , . , , ' , ■ • r , 



and found to vulcanize much more quickly than either the ^he followmg analytical data appeared m a review of the 



Byrne-cured slab or the ordinary smoked slab. Evidently ^^'^^^ ''^'^f^°" S'^^" ^"^"""^ '" °"^ °^ ^^e papers published 



this was due to the form in which the rubber was prepared, '" ^^ ™P ^' ^5,, Potash, 



and had nothing to do with the smoking which actually re- Hevea: Percent. Percent. 



tarded the vulcanization. l^^^- ■:;:;:;:;::::::;::: '"j oil Z l^ 



Further experiments led to the conclusion that an altera- Leaves, old 4.4 4.7 on ash 



. , , , • , , J Wood 6.0 13.5 on ash 



tion or a presence in the latex, and in the coagulum. caused Seed husk 1.6 0.31 on sample 



this marked variability in the rate of vulcanization. La?ex '".'!'!. '.'.■.■.■.■.■.■.■.■.■.■.■.: '. 0.35 43'.6' on Ish "'' 



Rubber consists approximately of 94 per cent, of caout- Crepe 0.4 23.4 on ash 



chouc, 1 per cent, of mineral salts, 2 to 3 per cent, of resins, 



and 2 to 3 per cent, of protein. The ingredient most liable SULPHIDE OF CARBON AS A VULCANIZER. 

 to change is the protein, and probably some substance de- Mathews and Strange have discovered that a solution of 

 rived from this acts as an accelerator. Experimentally it was natural or synthetic rubber subjected to 40 per cent, carbon 

 found that this change occurs in the coagulum if left for six disulphide in a closed vessel, turns into "gel" which, when 

 days before being crcped No evidence of this change can dried, is vulcanized rubber, 

 be detected in the appearance of the rubber, which in conse- 

 quence requires to be tested to ascertain its vulcanizing COAGULATION OF L.-\TEX BY ELECTRICITY, 

 quality. Coagulation of rubber latex by electricity has been successfully 



.-\s concerns rubber estate practice several factors affect performed on plantations where acetic acid was scarce. This co- 

 vulcanization. These are tliickness. i. c, amount of serum agulation is effected in a porous vessel with carbon electrodes, 

 removed; smoking, which retards vulcanization; the use of using a low tension current. The latex is slightly diluted with 

 formalin or other preservatives; amount of acetic acid used water and the gum separates very rapidly. It is perfectly clear 

 in coagulation, and the dilution of the latex. The age of the ^„^ limpid. 



tree also affects the proportion of protein and other constit- ^^^^^^^^^^^ ^^ PROTEINS AND RESINS UPON VULCANIZATION. 



uents of the latex. . , „ , ,, • □ ^c 



The more uniform methods now adopted on many estates In a very mteresting study Stevens shows the influence of 



tend to greater uniformity of product; but variability is due these two substances upon vulcanization. Rubber, completely 



chiefly to the difference in rubber from different estates. freed of its proteins and resms, only sets l.S per cent, of su - 



In these experiments, in preparing the block of pan coagu- phur, whereas when simply washed it sets 2.86 per cent, of sul- 



