January 1, 1917.] 



THE INDIA RUBBER WORLD 



195 



What the Rubber Chemists Are Doing. 



VARIABILITY OF PLANTATION RUBBER IN TECHNICAL 

 MIXINGS. 



THE variability of plantation Para rubber, when vulcanized 

 with various technical mixings in addition to sulphur, has 

 been investigated by Eaton and Grantham, Agricultural 

 Department, Federated Malay States. Their results appear in the 

 "Journal of the Society of Chemical Industry," (October 31, 

 1916). In the experiments described by them zinc oxide, litharge 

 and magnesium oxide with a small percentage of sulphur were 

 used in several combinations. Vulcanization was effected in molds 

 in a steam-jacketed vulcanizer at 140 degrees C. and tests 

 made with ring specimens on the Schopper-Dalen testing machine. 

 Regarding the stability of their vulcanized samples kept six 

 months or a year before testing, their experiments show that, 

 with the 10 per cent sulphur mixing the rubber continues to 

 vulcanize slowly during six months. This extra vulcanization 

 represents about a quarter-hour cure at 140 degrees C. A cer- 

 tain amount of deterioration in tensile properties also takes 

 place. While the 10 per cent mixing is excellent to ascertain 

 variations in rate of vulcanization between different rubbers, 

 especially when it is required to test the samples shortly after 

 vulcanization, it is not a good mixing for testing the aging prop- 

 erties of different rubbers after vulcanization, because the large 

 amount of free sulphur gradually exudes, leaving the sample 

 porous and easily oxidizable. The authors append their paper 

 with the following conclusions : 



1. The variability of plantation Para rubber in respect to 

 rate of cure continues to exist in various technical mixings in 

 which the rubber is loaded with mineral constituents in addition 

 to sulphur, and also in rubber-sulphur mixings containing dif- 

 ferent proportions of sulphur. 



2. The variability is not of the same degree as with mixings 

 containing 8 to 10 per cent sulphur. 



3. The use of strong accelerating agents, such as oxide of 

 lead, tends to obscure these differences which are produced in 

 the raw rubber by the presence of a natural accelerator. 



4. Other substances, caustic soda and potash and various 

 organic nitrogenous accelerators, also obscure these differences, 

 since these substances behave in a somewhat similar manner to 

 the natural accelerators present in raw rubber. 



5. To ilhistrate the differences in rate of -cure between dif- 

 ferent rubbers, which is the most important variability in planta- 

 tion Para "first latex" rubbers, and 8 or 10 per cent sulphur 

 mi.xing, without other addition, is very satisfactory, although not 

 suitable for stability or aging experiments. 



SYNTHETIC RUBBER FROM ALCOHOL. 



Ostromyslenski's method of producing erythrene rubber is 

 given in "Chemical Abstracts," as follows : The mixed vapors 

 of ethyl alcohol and air are passed through spirals of copper 

 and silver gauze and the products are converted into erythrene 

 by being passed in a gaseous or liquid state through a series of 

 metal tubes containing aluminum oxide heated to 824 to 860 

 degrees F. Erythrene is converted into rubber in an autoclave 

 containing a small quantity of a catylitic substance. In order 

 to give the synthetic rubber all the properties of natural rubber 

 it is necessary to add to it certain substances found in the 

 latter. These additions amount to about IS per cent and consist 

 of pure nitrogenous substances, litharge and colophony, or 

 Canada balsam, as a substitute for the resins of natural rubber. 



In connection with the above it should be noted that Dr. Ivan 

 Kondakorr, in a communication to "Le Caoutchouc & la Gutta- 

 percha" (November, 1916), refers to this synthesis as nothing 

 new and to Ostromyslenski's recently published researches as a 

 confirmation of previous knowledge rather than new discoveries. 



VULCANIZATION TESTS. 



Two reports made by the Imperial Institute to the Rubber 

 Research Committee in Ceylon (Department of Agriculture Bul- 

 letin, Ceylon, No. 23), on vulcanization tests of plantation Para, 

 deal with the following points: (1) The effect of different 

 methods of coagulation . (2) The effect of adding ammonia, 

 sodium bisulphite and formaldehyde to latex before coagulation. 

 (3) The effect of the form of the rubber (sheet, crepe, etc.) 

 TENSILE STRENGTH. 



The maximum tensile strength of 64 specimens was 2,571 

 pounds, minimum, 1,607 pounds. Two samples of best fine hard 

 Para gave, in comparison, 2,276 pounds and 2,312 pounds. Rub- 

 ber prepared by spontaneous coagulation has tensile value equal 

 to that coagulated by acids. Scrap rubber shows low tensile 

 strength in every case. The use of different acids for coagula- 

 tion has little effect on the tensile strength of the rubber pro- 

 duced. Double the usual amount of acid had no marked effect 

 on the tensile strength. The addition of fractionaj percentages of 

 ammonia, sodium bisulphite or formaldehyde to the latex before 

 coagulation had no marked effect on the strength of the rubber. 

 Hand-made and machine-made sheets seem to give rubbers of 

 practically equal strength. Thick crepe is slightly higher in 

 tensile strength than thin crepe. 



ELONGATION. 

 The elongations at heating point ranged from 787 to 919 per 

 cent. Two samples of best fine hard Para gave in comparison, 

 880 and 893 per cent. 



TIME OF VULCANIZATION. 



This was tested on a standard mixing of 90 parts rubber and 

 10 parts sulphur, vulcanized at a constant steam pressure of 50 

 pounds. 



The results are thus summarized : 



Hand-made sheet cured more quickly than machine-made. 

 Crepe cured more quickly than thin crepe. Thin crepe required 

 longer to cure than the corresponding sheet. 



Rubber prepared from the same sample of bulked latex by 

 coagulation with different acids had approximately the same 

 time of cure. When double the minimum amounts of acid were 

 used, the time of cure was not much affected. 



Addition of ammonia and sodium bisulphite to the latex before 

 coagulation had no constant effect on the time of cure, but an 

 excess of formaldehyde lengthened the time very considerably. 



Differences in the tensile strengths of washed and unwashed 

 rubber were comparatively small. 



RUBBER OF UNIFORM COLOR. 



The production of rubber of uniform color has been specially 

 studied by Clayton Beadle and Stevens and their results pub- 

 lished in a paper presented at the Congress of Ratavia. In brief 

 they find that such rubber can be produced only by the e.Kercise 

 of special precautions in the coagulation of the latex. It is pos- 

 sible to obtain uniformly pale rubber if the latex is rapidly 

 coagulated by an excess of acetic acid, the coagulum rapidly 

 washed in a machine, followed by rapid drying in warm air or 

 in a vacuum chamber. The reason for this is simple. 



Rubber latex contains an enzyme, an oxydase which causes 

 rapid absorption of oxygen from the air by the fresh coagulum. 

 This oxygen reacts rapidly on certain organic substances con- 

 tained in the latex, producing black coloring matters. Color 

 is not an indication of quality, but manufacturers and dealers 

 regard variations of color with suspicion. For this reason large 

 dealers sort their cargoes and repack for external appearances, 

 with no regard to the sources or origin of the rubber. 



