

THE INDIA RUBBER WORLD 



| September 1. 1915. 



Rubber Substitutes and Their Analysis. 



B:K reclaimed rubber came into vogue rubber substitutes 

 the <>nly adulterants used in the European manufai 



i i rubber g Is and even now their use has not la-en 



iletely abandoned. The following paragraphs descriptive of 

 different rubber substitutes are translated from a recent number 

 iutchouc X la i .nii.i Percha" . 

 Rubber substitutes, as indicated bj the name, closelj resemble 

 r, with which thej can be mixed, in proportions oi one to 

 and even more, without materially affecting the elastic 

 tj of the rubber. This is due to the euri.ni> mechan 

 ical consi ubstitutes which, although they 



have no great tensile strength, have a high degree of elasticity. 

 When substitutes are added to rubber the latter's strength is re- 

 duced, but there i- no proportional lessening of its elasticity. 

 titutes containing neither mineral oils nor wax and having 

 a density varying between 0.98 and 1.020 are the only substituti 

 that can lie used in combination with floating rubbers other than 

 black rubber, and they are therefore of considerable interest. 

 White substitutes were discovered during the first half of lasl 

 iy and brown substitutes later on, and the manufacture 

 of both has been perfected in the last decade. Rubber substitute 

 i- the result of the reaction of sulphur chloride at a moderate 

 temperature — 80 to 100 degrees Centigrade (176 to 212 degrees 

 Fahrenheit)— or of sulphur at a higher temperature— 160 to 200 

 entigrade (320 to 392 degrees Fahrenheit)— on crude 

 blown oil Many features of the manufacture of rubber sub- 

 stituti n i nbli those of the manufacture of rubber itself. 



Different oils are used, acci rding to the market price, but best 

 Its are obtained with castor oil or rape oil. The reaction of 

 sulphur chloride produce- a -lightly colored substitute commer- 

 known as white substitute or white factice. Pure sulphur 

 produce- brown factice or brown substitute. When blown or 

 oxidized oils are used the amount of the sulphur or of the 

 sulphur chloride addition can be materially reduced, which is an 

 advantage in white substitutes where high vulcanization tem- 

 peratures injuriously affect the stability of the composition. The 

 usual amount of sulphur doe- not exceed 6 or 7 per cent, for 

 white substitutes, whereas brown substitutes can contain from 7 

 to 20 per cent, of sulphur. Cheap qualities of soft sulphur can 

 be used only for -trough oxidized oils and produce quite differ- 

 ent substitutes from those made with fine sulphur, which is gen- 

 erally used with crude oils. 



Rubber substitutes are solid substances of about the same con- 

 sistencj as stiff jelly. Thej will not dissolve in rubber solvents, 

 which will, however, swell the substitute into a light jelly. Al- 

 though rubber substitutes are. as a rule, chemically inert, they 

 are essentiallj a ' ueous alkalis decompose rubbei 



substitutes easilj ; alcoholic alkalis readily change them into 

 rim and fatty acids that produce alkaline salts which are 

 soluble in water. Brown substitutes are most generally used in 

 - that are to be heat cured. White substitutes are 

 used lor cold cured article- and. in -mall quantities, in heat cured 

 ds 

 ["hi normal coi f rubber substitutes i- a- follows: 



1 N'on-vulcanized ! ' 



2 Free sulphur. 



3. Rubber substitute properh so railed, containing sulphur and 

 irine. 



■own substitutes also contain mixtures of paraffin am! 



I hese are mixed with the oil before vulcan- 



fer more th dvantage from a manufacturing 



■ of view. "Rubber manufacturers do not cot sider the add- 



:\n or petroleum a fraudulent adulteration as 



•heir presence in the substitute and 



I '.rown substitute is sold commercially in compact cakes meas- 

 uring HI \ .ill centimeters (4 x ll ! i inches). White substitute 

 comi - either in irregularly shaped amber colored pieces or in the 

 form of a white powder of light consistency and having the 

 appearance oi lucid crumbs. 



It is important to note that the chemical composition of com- 

 pacl lubber substitute i- not homogeneous but varies consider- 

 ably from one point to another. For this reason the analysis of 

 a shipment cannot be determined by analyzing a small fragment 

 of it: at least a pound must lie taken and worked cold in a 

 mixing mill or calender. 



ANALYSIS <H' RUBBER SUBSTITUTI - 



Two mam- of substitute are placed in a funnel filter on top 

 of purified cotton and are extracted with acetone during 10 

 hour- in a Saxhlet or in a Knofler extractor. The extract is 

 then dried at 1U0 degrees Centigrade (230 degrees Fahrenheit). 

 1 1 ci mtains : 



1. Non-vulcanized oil. 



2. Non-saponifiable substances. 



3. Free sulphur. 



The presence of paraffin is characterized by its crystallization 

 in the acetone ; the presence of mineral oil by its fluorescence. 



Non-vulcanized oils are only slightly soluble in acetone and 

 often -ettle in heavy drops. This product is not composed of 

 non-modified fatty oils, for they always contain from one to two 

 per cent, of combined sulphur. However, it is really oil, very dis- 

 tinct from the substitute that is a gelatinous solid, so that the 

 designation "non-vulcanized oil" is not a misnomer. 



DETERMINATION OF SULPHUR. 



For this purpose one of the methods for determining the pro- 

 portion of sulphur in vulcanized rubber can be used. The most 

 expeditious method is to treat the extracted acetone with sulphur- 

 saturated petroleum, but this system can only be adopted where 

 there are large quantities of sulphur and when the crystals have 

 settled. The Davis and Fouchard process gives very exact re- 

 sults where there are small or even large quantities of sulphur, 

 but this process is not reliable where there is chlorine, as in 

 white substitutes. The method by oxidation presents the dis- 

 advantage that the small quantity of combined sulphur that is in 

 the substitute is also oxidized and the figure representing free 

 sulphur in this manner slightly increased. Large quantities of 

 sulphur denote defective preparation of the substitute. White 

 substitute generally contains from one to two per cent, and 

 sometimes more free sulphur that is produced by the reaction 

 of the sulphur chloride on the oil. The presence of free sulphur 

 maj also be due to a reversion of the substitute after its manu- 

 facture. 



PROPORTION OF NON-SAPONIFIABLE SUBSTANCES 



The proportion of non-saponifiable substances is determined by 

 treating the acetone extract of 2 gram- of substitute, the extract 

 being boiled for two hours with 40 c c of normal alcoholic potash. 



The -ubsequent treatment varies according to the kind 

 of non-saponifiable substance. This is easily discovered 

 by cooling the alcoholic potash or by diluting it with water. 

 When the non-saponifiable part is liquid, like vaseline or 

 mineral oil. the alcohol should be distilled, the residue 

 taken up with water and extracted twice or even three times 

 with ether, the ether extract decanted, evaporated, dried at 

 110 degree- Centigrade (230 degree- Fahrenheit) and weighed. 

 If the non-saponifiable part i- solid, like paraffin or ceresin, or 

 extracted by petroleum ether, the alcoholic liquid is not evapo- 

 rated, but an equal volume of water i- added and then extraction 



