518 



THE INDIA RUBBER WORLD 



[June 1, 1917. 



fereiiliated from the simpler amino compounds produced by 

 their putrefaction or from the synthetical accelerators. These 

 simpler bodies are far more effective in promoting vulcanization. 

 Hence they accelerate vulcanization in a rubber such as ordinary 

 washed crepe already containing sufficient protein matter for 

 normal vulcanization. A complex substance, such as peptone, 

 is not so active and consequently does not produce appreciable 

 acceleration. We require to distinguish clearly between the 

 complex nitrogenous substance (protein) which is necessary for 

 normal vulcanization but which can hardly be termed an ac- 

 celerator, and simpler nitrogenous derivatives which are more 

 effective than proteins and are true accelerators. The latter are 

 able to produce appreciable acceleration in an ordinary raw rub- 

 ber, while the former cannot. To gage the effect of the former 

 substances as catalysts or promoters of vulcanization, it is neces- 

 sary to start with a rubber from which the natural insoluble 

 nitrogenous constituent has been removed. A series of experi- 

 ments has now been made with rubber from which practically 

 the whole of the nitrogenous material has been removed by 

 standing for a period of one to two years in the dark with cold 

 benzene. The clear supernatant solution of rubber was then 

 poured off and the rubber recovered from this by spontaneous 

 evaporation without arti.'icial heat. The original raw material 

 was an unsmoked sheet rubber containing 0.48 per cent of ni- 

 trogen. After removal of the insoluble matter the "protein-free" 

 rubber contained only 0.07 per cent of nitrogen. Separation of 

 the insoluble matter was very complete, and it is possible that 

 this small residue of nitrogen was present in some soluble form. 

 The following ''mixes" were made up, on the simple formula 

 of rubber 100 parts, sulphur 10 parts. 



1. Untreated sheet. 



2. "Protein free" sheet. 



3. ''Protein free" rubber plus tliree per cent of the lieat co- 

 agulable proteins which separated out as a flocculent precipitate 

 on concentrating the serum expressed in sheet making. 



4. ''Protein free" rubber plus one and one-half per cent of 

 the evaporated liquors after removal of the flocculent precipitate 

 referred to above. 



5. "Protein free" rubber pkis three per cent of /-methyl — 

 inositol extracted from the residual liquors. This represents 

 about the maximum amount of this crystalline substance ordi- 

 narily found in sheet rubber. 



6. Rubber rich in protein, being the residue of rubber and 

 solvent after pouring off the clear benzene solution. 



The following results were obtained, all samples being cured 

 under the same conditions (three hours at 135 degrees C.) so as 

 to illustrate the effect of the different constituents: 



1. 2. 3. 4. 5. 6. 



Breaking load, grams per square 



millimeter 1,360 590 70O 940 280 810 



Final length (original length = 



100) 1,010 1,160 1,040 860 1,110 630 



Tensile product 136 68 73 81 32 51 



Coefficient of vulcanization 3.66 1.60 3.08 5.28 1.32 6.44 



Nitrogen calculated on raw rub- 

 ber, per cent..^. 0.48 0.05 0.57 0.35 0.05 1.81 



In experiments of this type particular attention should be paid 

 to the figures for the coefficient of vulcanization. Tensile figures 

 are more difficult of interpretation, as a low breaking load may 

 be caused not only by under or over-vulcanization, but by the 

 adulteration of the rubber itself. 



The results clearly show the effect of the different nitrogenous 

 constituents on the vulcanizing properties of the rubber. 



(2) Shows that the removal of the insoluble nitrogenous mat- 

 ter causes a greatly reduced rate of cure. The breaking load has 

 fallen to less than one-half. The elongation is gfeater and the 

 coefficient of vulcanization is much lower. 



(3) Shows that the addition of the insoluble matter which 

 separates from the mother liquor or serum on evaporation causes 

 an increased rate of vulcanization. This insoluble matter behaves 



like the natural protein matter retained in ordinary crepe rubber. 

 '1 he coefficient of vulcanization is almost equal to that of the 

 original untreated rubber. Although tlic effect of adding the in- 

 soluble matter to sample (2) is so marked, it is quite possible that 

 the effect of adding it to sample (1) would have been in- 

 appreciable. 



(4j The effect of the addition of soluble nitrogenous matter 

 is similar to that of the insoluble nitrogenous matter in sample 

 (3), but is much more pronounced. The coefficient of vulcaniza- 

 tion much exceeds that of the original rubber, sample (1). The 

 efficiency of this soluble matter is no doubt due to its containing 

 protein decomposition products. In the main it will consist of 

 /-mcthylinositol. 



(5) Shows that the effect of the addition of the mcthylinositol 

 is to retard vulcanization. ' 



(6) This sample contains a large excess of the insoluble nitro- 

 genous matter ( protein ) naturally present in rubber. Its effect 

 has been to increase the rate of cure. Both samples (4) and (6) 

 are much over-vulcanized. The percentage of nitrogen in sample 

 (6) is 1.81, in sample (4) it is only 0.35. Yet the effect of the 

 larger proportion of nitrogenous matter on the coefficient of vul- 

 canization and physical properties in sample (6) has not been 

 very much greater than that of the small proportion of soluble 

 nitrogenous matter in sample (4). This clearly illustrates the 

 difference between the action of the insoluble and soluble nitro- 

 genous matters. 



The conclusions to be drawn from these results are that com- 

 plex nitrogenous matter (protein) promotes vulcanization, and 

 that naturally present in the rubber is necessary to secure vul- 

 canization within reasonable limits of time and temperature. 

 There are, however, simpler nitrogenous substances, probably 

 formed by the decomposition or gradual breaking up of the com- 

 plex proteins by the action of micro-organisms which are far more 

 active as vulcanizing agents than the proteins themselves. 



Some measure of the efficiency of the organic bases produced 

 during putrefaction of latex serum was worked out experiment- 

 alh, resulting in this conclusion, namely: The organic bases 

 separated and used in these experiments are not volatile or not 

 readily volatile. The putrefaction of latex serum might well 

 give rise to volatile bases and such are indeed formed. Their 

 presence can be shown by cutting up inatured slab into small 

 pieces and distilling in steam. 



In general the experimental results show that the rapid curing 

 property of matured coagulum is due to organic nitrogenous 

 bases formed during putrefaction, as small quantities of these 

 bases can be extracted from the rapidly curing rubber which has 

 undergone putrefaction, while only a trace can be extracted from 

 the ordinary pale crepe. Further, that similar bases can be ex- 

 tracted from the residual liquors and very small quantities of 

 these bases have been shown to have very marked effect in pro- 

 moting vulcanization. 



COAGULATION OF LATEX IN PRESENCE OF SUGARS. 



The work of Gorter and Swart on the coagulation of latex 

 in the presence of sugars is presented in Bulletin No. 6 of the 

 West Java Rubber Testing Station and given here as condensed 

 by "Chemical Abstracts." 



Gorter and Swart confirm the observations of Eaton and 

 Grantham that coagulation results from the action of micro- 

 organisms and is favored by the presence of sugars. They also 

 further find that the sugar undergoes a complicated fermentation, 

 producing lactic acid (mainly) with some acetic and succinic 

 acids. The resultant acidity is the real cause of the coagulation. 

 The amount of acid formed is dependent on the amount of 

 sugar present, but excess sugar inhibits fermentation and con- 

 sequent acidity. Lactic acid plays an important part in the slow 

 coagulation with acetic acid in minimum quantities. Latex con- 

 tains 2.3 grams of sugar per liter, which is too little to help 



