THE INDIA RUBBER WORLD 



I May 1, 1916. 



What the Rubber Chemists Are Doing. 



AS1-:R1H.S of researches on the synthesis, structure and 

 vulcanization of caoutchouc has been carried out liy I. I. 

 Ostroinyslenski. Abstracts follow from the "Juurnal of 

 ihe Society of Chemical Industry" (March 31) : 



NKW ^[ETHOU OF COI.l) VULCANIZATION. 



A mi.xture of a primary or secondary aliphatic amine with a 

 metallic o.xide either accelerates vulcanization of natural and 

 synthetic caoutchoucs or considerably lowers the temperature of 

 vulcanization. In the presence of such mixtures, vulcanization 

 takes place at the ordinary temperature. The process is espe- 

 cially rapid with chemically pure caoutchouc obtained synthetical- 

 ly. In the air or ordinary molds the vulcanization occupies from 

 a few weeks up to three months, according to the purity of the 

 original caoutcliouc. With natural caoutchoucs the vulcaniza- 

 ti<in requires from two to si.x months at the ordinary tem- 

 perature. 



N'ulcanization by means of trinitrobenzene or benzoyl pero.Kide 

 also takes place at ordinary temperature, no special catalyst being 

 necessary. O.xides of zinc, magnesium, and particularly lead ac- 

 celerate the action when the nitro-compound is used, but these 

 o.xides retard cold vulcanization by benzoyl peroxide and also 

 diminish the value of the vulcanized material. When trinitro- 

 lunzene is used, time is saved by preliminary heating of the mix- 

 ture at 122 to 140 degrees F., or by preparing it with hot rolls. 

 Rolling with benzoyl peroxide must be carried out at the ordinary 

 temperature, otherwise a sticky mass results. Cautious heating 

 of the mixed mass at 86 to 176 degrees F., for 10 to 40 seconds 

 \i also necessary in this case, but access of air must be avoided, 



ACTK.t.V OF .\MIXES AND METALLIC OXIDES ON THE VULCANI- 

 Z.^TION OF CAOUTCHOUC. 



In a mixture of caoutchouc, sulphur, amine and metallic oxide, 

 the sulphur and the amine first react with formation of the corre- 

 sponding thiozonide. This reaction proceeds only in the presence 

 of a catalyst such as an oxide. The unstable thiozonide then 

 transmits its sulphur to the caoutchouc, the amine being re- 

 generated, or the aminic residue, under the influence of the oxide, 

 uniting with a fresh portion of sulphur to give thiozonide. The 

 ]irocess is one of double catalysis. The metallic oxide catalyses 

 the formation of the thiozonide of the amine, which in turn accel- 

 erates the formation of the caoutchouc thiozonide and so catalyses 

 the vulcanization. Only primary and secondary amines give 

 thiozonides and these are also the only amines which catalyse 

 the vulcanization of caoutchouc. Thiozonides of aromatic amines 

 are relatively stable compounds, incapable of functioning as 

 sulphur carriers. An explanation is thus afforded of the observa- 

 tion that aromatic amines have practically no catalytic action on 

 the vulcanization of caoutchouc. 



From Bernstein's observation that the ordinary vulcanization 

 of caoutchouc proceeds at the ordinary temperature under the 

 action of ultra-violet light, it is concluded that, in the absence of 

 air, this light activates sulphur by converting it into thiozone. 

 The vulcanization is then effected partly by the latter and partly by 

 the ozone formed simultaneously. Thiozone is also formed when 

 ordinary sulphur is dissolved in a primary or secondary aliphatic 

 amine, such as piperidine with a side chain, and the solution 

 either heated for 20 to SO minutes with lead oxide in a reflux appa- 

 ratus on a water bath, or left at the room temperature. 



VULCANIZATION OF CAOUTCHOUC BV HALOGEN COMPOUNDS. 

 In the formation of vulcanite-like substances by the action of 

 bromine, iodine or iodine bromide on caoutchouc, the first phase 

 of the change consists in the formation of the caoutchouc halo- 

 genide. The unchanged caoutchouc then absorbs tlii> new com- 



pound or forms a swollen mass with it. This process may also 

 he carried out liy treatment of the caoutchouc with its halogenide. 

 The latter acts eitlier freshly prepared or old. All three halo- 

 genides of either natural or synthetic caoutchouc may be em- 

 ployed. Caouprene chloride or bromide exert a similar action on 

 caoutchouc. The products obtained from the chloride are espe- 

 cially valuable because of their great stability and relatively low 

 elastic point, and are easily obtained chemically pure. The 

 amount of caoutchouc used need not exceed 7 to 10 parts per 100 

 parts of caouprene chloride. Similar vulcanization is effected by 

 the action of the hydrochloride of natural caoutchouc, but not by 

 that of aluminum chloride. The products obtained by the above 

 methods have the black color of ordinary ebonite, are electrical 

 non-conductors, may be scratched with the nail, keep well even 

 in moist air, and take a high polish. 



NATl'RAL C.AS AND SYNTHETIC RUBBER. 



In recent investigations by Singer, natural gas below the freez- 

 ing point was subjected to successive pressures, according to 

 "Le Caoutchouc & la Gutta-Percha." The first compression, 

 of 3"/S atmospheres, yielded liquids having a density of 0.6935 

 to 0.6720; and those of the second compression, of 24 atmos- 

 pheres, showed a specific weight of 0.6365 to 0.6160. 



The first part contained 30 per cent of pentane, 30 per cent of 

 hexane and 7 per cent of butane. The second part was composed 

 of ethane, propane and he.xane, and appeared to be similar to the 

 gas oil studied by Colson, 



These products may serve as low cost material for transforma- 

 tion into isoprene or butadiene. 



METHODS OF ANALYSIS. 



ANALYSIS OF VULCANIZED RUBBER GOODS. 



'T'HE following scheme for analysis is reported by J. A. S. 

 *■ Morrison of Glastonbury, England : 



Tlie usual estimations are : rubber resins, free sulphur, mineral 

 matter, vulcanized rubber and rubber substitutes. 



Rubber Resins. — Rasp the sample into small pieces; weigh out 

 4 grams and extract with acetone in a Soxhlet extractor for two 

 days. Dry the extract at 212 degrees F. and weigh. This extract 

 contains the rubber resins and free sulphur, the latter being esti- 

 mated in the extract as described later. The total extract minus 

 the free sulphur gives the rubber resins. Keep the residue from 

 the extraction in order to determine the rubber substitutes. 



Mineral Matter.— To determine the mineral matter, 1 or 2 

 grams of the sample are boiled with 50 cc. of nitrobenzene in a 

 fat flask with air reflux. It is then cooled and washed into a 300 cc. 

 tall beaker with a mixture of 2 vols, sulphuric ether and 1 

 vol. ethyl alcohol. Dilute to about 250 cc. with this mixture, stir 

 and stand over night to settle. Viscous deposits are due to in- 

 sufficient ether, and more should be added if these occur. Filter 

 the insoluble matter on a tared filter, dry and weigh. This gives 

 organic matter insoluble in nitrobenzene plus mineral matter. 



Wash the tared filter with warm dilute hydrochloric acid. 

 Wash out acid with water, dry and weigh. Finally ash the paper 

 and residue and weigh ash. Ash plus loss due to hydrochloric 

 acid washing gives total mineral matter. The extraction with 

 hydrochloric acid is carried out in order to extract carbonates 

 as such. 



The difference between the total nitrobenzene residue on the 

 tared filter and the total mineral matter gives the organic matter 

 insoluble in nitrobenzene. Carbon if used as a filling will be in- 

 cluded in this figure. 



