April 1, 1920.] 



THE INDIA RUBBER WORLD 



427 



What the Rubber Chemists Are Doing. 



THE DETERMINATION OF CELLULOSE IN RUBBER GOODS.^ 



A PROPOSED METHOD for the determination of cellulose in rub- 

 ber goods has been worked out by S. W. Epstein and R. 

 L. Moore, assistant chemists of the Bureau of Standards. 



The authors find that the method usually employed for the 

 determination of the rubber content of mixing by difference will 

 give worthless results whenever there arc present ingredients 

 which are driven off in the ashing or are not included in the 

 other determinations. Unless these ingredients are determmed 

 separately the figure for rubber hydrocarbonation is necessarily- 

 erroneous. Free carbon', glue', and cellulose are examples of 

 such ingredients. 



Rubber sheeting, raincoat materials, balloon fabrics, spread 

 goods and frictioned fabrics are cited as rubber products which 

 have cellulose impregnated with rubber in such a way that it 

 cannot be separated from it. In addition there is the type of mix- 

 ing which has fiber distributed throughout the compound, such 

 as fiber soles, special light compounds, and special packings. In 

 order to evaluate these products properly the fiber must be de- 

 termined separately. 



DETAILS OF METHOD. 



After having considered the essentials of a procedure for the 

 determination of cellulose in rubber goods, the following method 

 was devised : 



Digest 0.5 -gr. sample of rubber in a 2S0-cc. assay flask with 25 

 cc. of freshly distilled cresol (boiling point 198 degrees C.) for 

 four hours at 160-185 degrees C. The digestion can be carried 

 out on an electric hot-plate or better still in a constant tempera- 

 ture oven. Allow the cresol to cool completely and add 200 cc. 

 of petroleum ether (boiling point 45-50 degrees C.) very slowly 

 and with constant agitation. After the solution has settled com- 

 pletely and the supernatant liquid is perfectly clear, filter through 

 a Gooch crucible containing a fairly thick pad of acid treated 

 and ignited asbestos, and wash three times with petroleum ether. 

 Wash at least five times with hot benzene and then once or 

 twice with acetone. Treat the contents of the flask with hot 

 10 per cent solution of hydrochloric acid and transfer the entire 

 contents of the flask to the Gooch crucible with the aid of a 

 "policeman." Care must be taken in adding the first portion of 

 acid to the Gooch since in the presence of carbonates the effer- 

 vescence which ensues may cause some of the material to be 

 lost. It is best to add the acid a few drops at a time until there 

 is no more eflervescence. Continue to treat with hot ten per 

 cent solution of hydrochloric acid until the pad has been washed 

 to least ten times. Wash the pad free from chlorides with boil- 

 ing water and run small portions of acetone through it until 

 the filtrate comes through colorless. Treat with a mixture of 

 equal parts of acetone and carbon bisulhpide until the solvent 

 is no longer colored. Wash with alcohol and dry for one hour 

 and thirty minutes at 105 degrees C. Remove the pad from the 

 crucible with the help of a pair of sharp pointed tweezers and 

 place it in a weighing bottle that is large enough to contain 

 a 2S-CC. Gooch crucible or the size crucible that is being used. 

 Use the underneath portions of the pad as a swab to clean the 

 sides of the crucible. If necessary moisten this asbestos with 

 a little alcohol since this will facilitate the complete removal of 

 material which sometimes adheres tenaciously. Place the weigh- 



D. C. 



= "netermination of Free Carbon in Rubber Cloods." by A. H. Smith 

 and S. W. Epstein, The Indta Rubber World, January 1, 1919, page 197. 



» "Detection and Determination of Glue in Rubber Goods." by S. W. 

 Epstein and W. E. Lange, The India Rubber World, January I, 1920, 

 page 216. 



ing bottle and contents in the drying oven for about 15 minutes, 

 cool and weigh. Call this weight A. 



Transfer the contents of the weighing bottle to a 50-cc. beaker, 

 taking precautions that no material is lost during the transfer or 

 allowed to remain in the weighing bottle. Add 15 cc. of acetic 

 anhydride and 0.5-cc. of concentrated sulphuric acid and allow to 

 digest for 30 minutes at 75 degrees C. The steam bath can be con- 

 veniently used for this purpose. After the mixture has cooled 

 completely dilute with 25 cc. of 90 per cent acetic acid and filter 

 through a weighed Gooch containing a thick pad of properly 

 prepared asbestos. To guard against traces of material l)eing 

 carried through it is absolutely essential that this filtration as 

 well as the ones to follow be very slow and that only gentle 

 suction be used. Wash with hot 90 per cent acetic acid until 

 the filtrate comes through absolutely colorless and then wash at 

 least four limes more. Wash about five times with acetone. 

 After having taken care that all of the material has been washed 

 out of the beaker in which the acetylation took place, remove the 

 crucible from the funnel, clean the outside thoroughly, place it 

 inside of the same weighing bottle that was used to weigh the pad 

 and dry for two hours at 140 degrees C. Cool and weigh. Call 

 this weight B. Weight of Gooch crucible plus weight A, minus 

 weight B equals loss due to acetylation or cellulose. 



It is essential that all reagents given above be of chemically 

 pure quality and be filtered before using. 



When large numbers of determinations were carried out ac- 

 cording to the above procedure, it was found practical to distil 

 the filtrates and in this way recover a large part of the solvents 

 used. The combined filtrates containing petroleum ether, benzene 

 and cresol were distilled on the steam bath to recover the petrole- 

 um ether. The benzene was recovered as the temperature was 

 raised. Finally the w^ater condenser was replaced by an air con- 

 denser and the cresol distilled out at about 195-200 degrees C. 

 This distillate was usually only slightly yellow. 



Likewise the filtrates from the acetylation, which contain acetic 

 anhydride, acetic acid and small quantities of sulphuric acid were 

 collected and distilled. The distillate w^as collected between 105 

 and 115 degrees C. and was used for washing to take the place 

 of the 90 per cent acetic acid called for in the propcsed method. 

 RESULTS. 



Results obtained by the analysis of a number of prepared stocks 

 containing cellulose in the form of cotton fiber clearly indicated 

 that by this method it is very easy to determine widely varying 

 amounts of cotton fiber very accurately even when accompanied 

 by a miscellaneous collection of mineral fillers in the rubber com- 

 pound. Even in the presence of 15 per cent of carbon black 

 it was possible to get good results on cellulose because the weigh- 

 ings were all made in weighing bottles and therefore no error 

 was introduced by absorption of moisture bv the large amount 

 of carbon. 



The presence of large quantities of cellulose in some reclaims 

 necessitates looking for cellulose in finished rubber goods of 

 grades in which reclaims may be expected. 



The presence of considerable amounts of leather does not affect 

 the determination of cellulose. In the cases of wood and jute, 

 a comparatively accurate estimation of their quantity can be 

 obtained by using a modified procedure, in which the tempera- 

 ture of 120 degrees is used in place of 185 degrees C. in order to 

 dissolve the rubber. 



CONCLirSIONS. 



I. The method presented is readily applicable to the deter- 

 mination of fabric in rubber sheeting, raincoat materials, water- 

 proofed fabrics, spread goods, frictioned and calendered fabrics 

 in general. The results obtained by this method have been found 



