August 1, 1921 



THE INDIA RUBBER WORLD 



821 



Pitch Hydrocarbons Used in the Rubber hidustry^ 



By Frederic Dannerth, Ph.D. 



A Study of Technical Properties, Sources, Definitions and Uses of Solid Hydrocarbon Residues, Both 



Natural and Industrial 



AT a time when the market price of standard pitches varies 

 from $25 to $50 a ton, many large manufacturers of rubber 

 goods, and especially those making rubber-coated fabrics, 

 might well consider the desirability of installing their own pitch- 

 mixing departments. The maiuifacturcr, knowing the chemical 

 character of the materials which are put into the compounds, 

 could then control his processes more accurately. The fact that 

 pitch is a "specific material" 

 for correcting microporosity, is 

 now generally acknowledged. 

 Aside from this it offers to the 

 compounder a clean and prac- 

 tical method for incorporating 

 finely divided carbon with the 

 rubber compound. 



The use of coal-tar for 

 waterproofing textile fabrics 

 dates back to about the year 

 1820, but the discovery that 

 high-melting-point pitches are 

 valuable and important com- 

 pounding materials is of far 

 more recent date. The word 

 "pitch" as used at present in 

 industrial work, designates all 

 those natural or artificial dis- 

 tillation residues, which are 

 black, soft and sticky at high 

 temperatures, but hard and 

 brittle at ordinary room tem- 

 perature. In certain cases they 

 may be tenacious or elastic at 

 ordinary temperatures. The 

 characteristic types are : lake 

 asphaltum occurring in Vene- 

 zuela and a nearby island; gil- 

 sonite from the mines of Utah ; 

 the residues from coal-tar, pe- 

 troleum, fatty acid, and hard- 

 Wdod distillation. 



SPECIFICATIONS 



The choice of a pitch for 

 compounding purposes will de- 

 pend in a great measure on the 



purposes for which the finished rubber product is to be used. 

 In other words, the "external influences*' to which the finished 

 rubber goods will be exposed. The questions which the con- 

 sumer must keep in mind are these : 



1. Will the black color of the pitch interfere with the use to 

 which the finished product will be put? 



2. Does it impart any peculiar or unpleasant odor to the 

 goods? 



3. Is the melting point of the pitch so low tliat the finished 

 product is too supple — that it has not enough "spring" or "come- 

 back" to it? 



4. Doe? it contain any matter which will volatilize below the 

 temperature at which the rubber compound will be vulcanized? 

 In other words, will the pitch cause blistering? 



5. What is the influence of high-pressure steam, volatile or- 



It appears necessary to say a word about the numerical 

 values quoted in connection with the present series of 

 articles on organic materials used in the rubber industry. 



Materials obtained from plants and animals, as a rule, 

 have two or three properties which are quite constant, 

 provided the material is a true chemical compound not 

 admixed or adulterated with any other substance havins- 

 similar properties. These three properties are called 

 "constants." They are: the melting point, the boilinj; 

 point, and the specific gravity. For example: commercial 

 90 per cent benzol if tested by the distillation test, will 

 show this property: 90 per cent of the liquid will boil 

 over or "distil" before the thermometer has registered 

 more than 100 degrees C. Pure benzol, however, is a chem- 

 ical entity, and its formula is well known to chemists. The 

 pure article has been examined by thousands of persons, 

 and wherever tested it is found to boil at a temperature 

 close to 80.5 or 81 degrees C. It has a freezing point of 4 

 degrees C, which means that it goes over into the solid 

 form of crystals at that temperature. It has a specific gravity 

 very close to 0.880 compared with water at 20 degrees C. 



In the case of oils, fats, waxes and resins the fluctuation 

 in the numerical values is at times very obvious. In such 

 cases the chemist concludes that he has before him sub- 

 stances not chemically pure and of indefinite chemical 

 composition. For that reason it is customary to differen. 

 tiale between "chemically pure" substances and "com- 

 mercial materials." Specimens of commercial materials are 

 frequently found to be admLxed with other materials in 

 indefinite proportions, or it may simply be that they have 

 been carelessly prepared. — The Author. 



ganic solvents and oils on rubber compounds containing this pitch? 



6. Do the rubber compounds containing it resist abrasion? 



7. What is the maximum percentage which can be used to 

 advantage in a recipe for a given type of rubber compound? 



8. To what extent will compounds containing this pitch resist 

 abrasion, hammer blows, and other physical influences? 



9. What is the best form in which to deliver it to the com- 



pounder so that it can be mixed 

 uniformly in the shortest pos- 

 sible time? Should the pitch be 

 granulated ? 



10. Is the vendor willing to 

 deliver it in metal drums to 

 avoid the danger of wood- 

 splinters in the compound? 

 DEFINITIONS 



The use of bituminous mate- 

 rials for building roads, pave- 

 ments, and roofing, as well as 

 for plastic masses, has led to 

 the formal definition of many 

 of the terms used in the indus- 

 try. Some of the most impor- 

 tant of these are: 



1. Asphalts. Solid or semi- 

 solid native bitumens; solid or 

 semi-solid bitumens obtained 

 by refining petroleum ; solid or 

 semi-solid bitumens which are 

 combinations of those already 

 mentioned with petroleums or 

 derivatives thereof. They melt 

 upon the application of heat, 

 and consist of a mixture of 

 hydrocarbons and their deriva- 

 tives. They are of complex 

 chemical structure, largely 

 cyclic and bridge compounds. 



2. Bitumens. Mixtures of 

 native or pyrogenous hydro- 

 carbons with their non-metallic 

 derivatives. These materials 

 are soluble in carbon disul- 

 phide. 



3. AsPH..\LTK.\ES. The components of the bitumen in pe- 

 troleum, petroleum products, malthas, asphalts, and solid native 

 bitumens which are soluble in carbon disulphide, and insoluble 

 in paraffinc naphtha (gasoline). 



4. C.\RBE.\ES. The components of the bittunen in petroleum, 

 petroleum products, malthas, asphalts, and solid native bitumens^ 

 which are soluble in carbon disulphide, but insoluble in carbon' 

 tetrachloride. 



5. Petrolene. That part of the bitumen which is soluble in 

 petroleum spirit is designated as petrolene. This extraction is to 

 be carried out first, and the extraction with carbon disulphide is 

 carried out secondly. It is of particular importance in the case 

 of petroleum pitches. 



6. Free carbon. That part of a pitch which is insoluble in 



"This article m.iy not. be reprinted without permission from the author 

 who reserves all publication rights. 



