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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 20, No. 8
Softeners and Antisofteners' Erle C. Zimmerman and Leslie V. Cooper THE FIRESTONS TIREA N D RUBBERCOMPANY, AKRON,OHIO
' has none of these objectioninitely affect plasticity of features* the rubber. I n other words, In the manufacture of rubber goods various materials As it is necessary to have no is given to are incorporated with the rubber in order to produce a standard grade of rubber which affect the a mixture that will process more easily. Such mafor use in all experiments, Of raw-rubber terials are usually called,.fluxesor softeners. mixtures chiefly through a each batch is made up Of A simple method of determining the relative effects pieces of rubber cut from lubricationOr dispersing of such materials is described. This consists in mixing various sheets from differtion on the pigments-i. e., the material in rubber under standardized conditions ent bales. It s h o u l d b e substances w h i c h a c t . and determining the plasticity of the product by the noted that the blend is not through their influence on Williamsmethod. the interfacial tension, or massed' No piece Some materials show stiffening instead of softening should exceed 100 grams in affect the wettability Of the action and both types are shown in the results reported weight. Six hundred grams pigment. in this paper. Benzidine and p-amidophenol are of rubber will process easily N o a t t e m p t has been examples of materials which stiffen rubber. on a 30-cm. (12-inch) mill made to study shrinkage, with 15-cm. (6-inch) rolls which. although an imDorand as a 30-gram sample is tant item in the processing of a rubber mixture, may be eliminated by correctly using removed for crude rubber plasticity during the test, the initial materials which produce the proper plasticity. If true soften- amount of rubber used is 630 grams. Of equal importance is the initial temperature of the mill ing is obtained the shrinkage is reduced, but if the reverse action, antisoftening, occurs, shrinkage may become pro- rolls. By experiment 60" C. has been found to be the most nounced. Shrinkage also results when set-up or premature satisfactory, as a higher temperature gives too hot a batch vulcanization takes place and is always caused by the genera- to work with,and a lower temperature makes the test unnecessarily long. This initial temperature should always be tion of too much heat in processing stiff stock. obtained by heating a cool mill up to temperature by milling Determination of Softening Effects of Various Materials rubber. The temperature of 60" C. can be measured by the use of a thermocouple pad and potentiometer but may also Much has been written on various rubber softeners, but be gaged by feel after the operator has become proficient. there is little available which gives a numerical evaluation. After this initial temperature is obtained, it is made certain Two instruments have been developed for the measurement that both steam and water are shut off so that the temperature of crude rubber plasticity-the Marzetti extrusion apparatus2 of the mill may rise as it will. and the Williams press.3 Both types have been modified The third necessary standard is the method of milling. by several investigators and Burbridge' in his r o r k used a In this work a mill with 10:9 ratio and front roll speed of 30 modification of the Williams press. revolutions is used and the time periods given in Table I The work of Burbridge is an outstanding contribution and may not hold true for all mills, but the procedure may be his method can be briefly summarized as follows: A batch adapted to any mill with a little allowance for the new speed. of standard stock is milled for 25 minutes. The formula Table I-Milling Cycle for this batch is: massed pale crepe 100, zinc oxide 1, sulfur TIMEELAPSEPROM START 5, and diphenylguanidine 0.25 parts. Into this master batch Minutes Seconds various percentages of several substances are incorporated 0 0 Crepe rubber through once 0 15 Open mill to 3 mm. (1/8 inch) and start massing by milling. Plasticity figures are obtained on the crude 3 30 Cut rubber back and forth four times 5 0 Remove sample A rubber, the massed rubber, and the finished batch. I n de5 10 Start adding material t o be tested termining the softening action a comparison is made of the 7 40 Cut mix back and forth four times 9 0 Remove from the mill finished batches with and without softener. 1 Presented before the Division of Rubber Chemistry at the 75th MeetThe first creping operation insures the rubber massing ing of the American Chemical Society, St. Louis, Mo.,April 16 to 19, 1928. continuously and not lodging in a ball on top of the rolls. 2 Giorn. chim. ind. applicafa, 6 , 342 (1923). The time of knitting together should be between 2 minutes 8 IND. ENG. CHEM.,16, 362 (1924). 45 seconds and 3 minutes and is a definite check on all varia4 T r a n s . Insl. Rubber Ind., 1, 429 (1926).
IhTDCSTRIAL A-VD EXGINEERING CHEMISTRY
August, 1928
bles up to this point. Sample A is obtained by removing a strip, weighing out 30 grams, and returning the exce$s to the mill immediately. Five per cent of softener is about the maximum amount used commercially so this percentage was adopted as the standard. Sample B is cut from the finished batch and may be any convenient size. As these batches contain neither sulfur nor accelerator, it is permissible to obtain a plasticity figure as though the batch were crude rubber. The machine used is the one designed by william^,^ and Y value after 5 minutes in the press is obtained on samples A and B. The ratio of difference of the Y values of A and R to the Y value of A is the total softening percentage and is due to two causes-(1) the effect of the additional 4 minutes of milling, and (2) the effect of the ingredient added to the rubber. The total softening effect, minus the percentage drop due to milling as obtained by a control run in which no softener is used, is the effective softening action of the ingredients added. For example, the Y value of A of the control is 296, and of B is 256. Thus the percentage drop due to milling is 40 divided by 296 or 13.5 per cent. The Y value of the A sample before addition of hardwood pitch is 295 and of the B sample is 239, a drop of 56 points, or 19 per cent, which gives an effective softening action due to hardwood pitch of 19 minus 13.5, or 5.5 per cent. Table 11-Softening Stearic acid Pine tar Liquid asphalt Pine oil Degras Rosin oil Stearin pitch
Action Expressed i n Percentage C h a n g e i n Plasticity Per cenf Per rent 22 Perilla oil 11 16.5 Vaseline 9 16.6 Mineral rubber 8 16 Straw paraffin oil S 16 Cottonseed oil S 13 Hardwood pitch 6.6 11 Carnauba wax 5
Softeners
In Table I1 are listed a few of the better known softeners. It may be noted that pine oil and pine tar are similar in
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softening action, which probably explains why various viscosities of pine tar are about alike in their effect on plasticity. Also stearic acid by its superior power justifies a premium in price due to this property alone. Burbridge4 stated that carnauba wax is a stiffener and that it is hard to incorporate, but it has been found to he a softener similar to hardwood pitch. Perhaps the previous investigator did not consider the fact that in raising the initial temperature of the mill he greatly reduced the amount of breakdown. Antisofteners
Khen the total percentage drop of any batch is less than the percentage drop of the control, it is evident that the substance added is a stiffener. It is a well-known fact that some antioxidants exert softening action to such an extent that tubed articles lose their shape due to their weight alone. Several ways are open to overcome this and one of them is to use an antisoftener in the compound. Benzidine, an antioxidant, accelerator-activator, and a fair stiffener of cured stock, is a stiffener of uncured stock of high degree, as evidenced by Table 111. Table 111--Antisoftening Action of Benzidine BENZIDIKE TO ACTUAL TRUE STIFFENING RUBBER STIFFENING Per cent Per cent Per cenl
Another material which behaves in a manner similar to benzidine is p-amidophenol, which gives its optimum stiffening action (43 per cent) when 0.5 per cent on the rubber is used. Other stiffeners which have been noted are 8-phenylenediamine, 8-naphthylamine, a-naphthylamine, tolidine, quinone, and dianisidine.
A Study of Auto-Ignition Temperatures' 11-Pure
Compounds
Henry James Masson and William F. Hamilton? LABORATORY OF CHEMICAL ENGINEERIXG, DEPARTMENT OF CHEMISTRY, KEWYORKUNIVERSITY, NEWYORK,N. Y.
S U M B E R of o b The auto-ignition temperatures of an additional range of auto-ignition terns e r v e r s 1 t o 5,* have number of pure organic compounds have been deterperatures was far wider than p o i n t e d out the immined in air at ordinary pressures. The compounds was anticipated. The range portance of auto-ignition ternselected cover a wide range of properties and structures of the pyrometer was therep e r a t u r e s in arriving a t a in order to provide data for use in studying various fore extended to make possicombustion reactions. A study has also been made better understanding of the ble the study of a larger nummolecular structure of organic of the catalytic effect of various surfaces on autober of compounds. The wellignition temperatures. known catalytic activity of compounds, and the mechanism of their c o m b u s t i o n , p l a t i n u m has indicated the and in determining the suitability of certain mixtures of them desirability of determining auto-ignition temperatures on as fuels for use in the internal-combustion engine. Although various surfaces other than this metal. the auto-ignition temperatures of several pure substances The previous paper6 describes the apparatus used, the have been reported by the authorsI6it was considered desir- experimental method followed, and the results obtained for a able to determine these temperatures for additional pure number of pure organic compounds. The results given in substances of widely different properties and structure before Table I include for comparison determinations previously studying the various mixtures as represented by typical com- reported as well as those subsequently made. The commercial fuels. Previous determinations showed that the pounds have been arranged according to the conventional organic groupings in order to facilitate comparisons. I Received April 25, 1928. A comparison of these results with those of other investiResearch fellow, Atlantic Refining Company Fellowship. * Numbers refer to bibliography a t the end of the article. gators shows a fair general agreement. Owing, however, to
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