Februaky 1, 1919. 



THE INDIA RUBBER WORLD 



251 



What the Rubber Chemists Are Doing. 



INVESTIGATIONS OF THK VULCANIZATION PROCESS. p^,,o„, HeATINC OK Raw RuBBEK AN. THE Vo.CANXZATIOK 



Accelerators. Coefficient 

 INSPECTION of the following tabulated results will show Experiments by Van Heurn demonstrated that one can in- 

 1 that some compounds, especialh- the basic, or such as are crease the velocity of vulcanization considerably and thus im- 

 transformed at the vulcanizmg temperature into bases, cause prove the mechanical properties, by heating Hevca crepe for 

 strong acceleration. Other compounds have no influence, while four hours in a current of carbon dioxide at 130 de-rees C 

 the acid compounds show distinctly a retarding influence. If the heating is continued beyond four hours the me^'chanical 

 Influence of \-ariou5 Inorganic Compounds on the Velocity properties again decline, approaching normal. How far the 

 OF Vulcanization (\an Heubnj. ^ change observed on heating in carbon dioxide is due to the in- 

 Extra addition of one per cent. ' ^Co'efficient"" ' fluence of that gas and whether the same result may be obtained 



None 3.1, ' 3 jg on heating in another indifferent gas, will be determined by 



Magnesium oxide 6.90 6.80 future experiments. 



Ammonium carbonate 5.85 5 20 



Banum hydroxide 5. 05 PlASTICIZING AND THE MECHANICAL PROPERTIES OF VuLC,A,NI7ED 



Lithir" '""'''''' "'^^ *•" Rubber. 



s'oVuT bicarbonate"!'.'!'.'.!!!!!"'.'.!!.'^!';;!.'!! 4!" \'% Continued plasticizing causes the diminishing of the breaking 



Ammonium phosphate !!..!!!!!!!!!! 3!86 4!29 'oad and the elongation at break. When plasticizing takes place 



Magnesium carbonate 3.93 during periods within those of ordinary practice such influence 



AmmZium'"surh% ^'^ ^ '^^ is not noticeable. The Institute has unpublished tests showing 



Ammonium oxaUtf .!!!!!!!!!!!!!!!!!!!!!!!!!! 312 ^'" 2. 86 *^^' °" energetically plasticizing, but not to such an extent that 



Ammonium chloride ....:....!!!!..!!!!!!!!!!! 2!77 3!o8 '''e velocity of vulcanization diminishes, the course of the curve 



Zinc oxide 2.75 2.70 is not altered, but its end point is shifted. Possibly this fact 



Ammonium borate 2.57 2.65 may be attributable to air, imprisoned during plasticizing, which 



PoTssruTbisulphate' !!!!!!!!!!!!!!'!!' !■!!'■' \'n I'fe ''°" "°' "^''""^ ""P^ '^"""^ vulcanization. The course of 



rsr , , -a ■■■■■■■■■■■.■■■ ■ . the curve is practically independent of the degree of plasticizing. 



Of much greater influence is the action of organic accelerators -y, „ & v &■ 



as can be seen in the following table, which relates to vulcaniza- ^™.^ °^ ^"""^ ^=^'° ^^^ Mechanical Properties. 



tions according to the "standard method" in the oil bath. _'^^^ PO'"* investigated was whether a rubber with a low 



,-, ^ ,, ,, viscosity can yield on prolonged vulcanization as good a orodiict 



Influence of Organic Compounds on the Velocity of Vulcanization . , ... . . *„, "'>-'»"'-«'"uii .is guuu d prouuct 



(Van Heurn). ... ^' ""^ ^^"" ^ "'Sn viscosity. The answer is affirmative. 



None'" ^•''^'''''" °^ '^ °* 1 P'"' '^'■"'- 7 46^°''''^'^'^" 2 II' ^"^•■^'^'^^ LOAD AND ELONGATION AT BrEAK WITH INCREASING 



Accelerene"!!!.'! !.'.'.'.'!!!!.'.'!.'.'!.'.'.'!.'.'.'.'.'!..'.'.'.....' .' 8.04 7^90 TiME OF V0LCANIZ.ATION. 



Piplndi'ne ■.:":: : 700 l'% '^^^'^ ^^'■e ^^^^ '^'''' blanket crepe, viscosity 46; Hevea 



Accelerene is the trade name of a product consisting of para- "'^.% ^'''°''^ ?! =^"^ ^''^J" "^P^' ^•'=<=°=ity 70. The curing 



nitroso dimethylaniline, which is often sold containing a great ^^ ^^'^"^^'^ J™"^ °"<^ ^""^ '" '^ree, varying by intervals 



many impurities. Vulcacite seems to be a condensation product °^ -Ta"^''^^' ^T' T."^' ^ ^^ *^ '^"''°"'' '"'"'^^^ ^" 



from acetaldehyde and ammonia, according to researches made ^ t / ''f • '"'' "^°'"^^ *^' ^ '"^^^^ P'°^"='' 



at the Institute ^' P''°'°"Sed vulcanization, can yield as strong a product as a 



It is remarkable that this acceleration is not identical for all '''''''^ 'f^"' ^'ithout the danger of overvulcanization. It is 



species of rubber and it seems as if the combining with sulphur 1°""'"^'^ '^ "^^^^ '^\ conditions of vulcanizing diflfer from 



is less accelerated for highly viscous kinds than for those of low ^^e standard method only m time of cure, the vulcanization 



viscosity. One would be likely to conclude this from Van ^'>^^^'^''' "'"^■"^ a measure of the mechanical properties. 



Rossem's observations in the following table: Influence of Temperature and Quantity of Added Sulphur 



,. „ > _ ON THE Mechanical Properties. 



V uLcANiz.vriON Coefficients for Various Rubbers on .\dding the Same r- i . i . ... 



Quantity of Accelerene. Completely normal stress-strain diagrams were obtained 



Number of sample 54T 26T 98T 163T for rubbers vulcanized at 139.2 degrees C. (that is. nine degrees 



Viscosity number 3D 42 73 102 , , , , ^ ^ 



Vulcanization coefficients with standard lower tlian the chosen standard temperature"), by vulcanizing 



wifhoul addition)'^...''.''."". .**..!■" "..':•:. 2.3 3.1 4.3 4.7 ^°'' '"•°' "^""e^' ^°'"'' ^nd five hours, respectively. This is not 



^ . , [ H °! } Z° !•? \-l 'L l\ ^^^ "^e ^■'^e" ™°''e or 'ess sulphur than the standard quantity 



\ ulcanization coefficients af- 'A at I % 3.1 3.0 2.55 2.3 , j., ^^.^ ■ jj . ^ r\->, / ../•,, t- , 



ter :5 minutes' cure at] ^ of 1 % 3.6 3.6 2.7 2.9 o* ' /' Parts IS added to 92'^ parts of rubber. For example, 



1 .1 7 ' C. with accelerene. { H of 1 % 4.2 4.4 3.1 3.3 with 125^ parts of Sulphur to 87^ parts of rubber a much greater 



The above data suggest important aspects for technical appli- stress is required for a certain elongation than is necessary for 



cation. Before general conclusions can be drawn, further data a "normally" vulcanized rubber. This condition is noticeable 



will be required. with ten of sulphur to 90 of rubber. With less than 7y. 



.'Another point worth notice, confirmed by the Institute, is that parts the reverse is observed. The influence of excess sulphur 



Kerbosch-Schadt rubber, prepared by evaporating the latex, confirms the conclusion arrived at for catalysts, namely, that a 



possesses a high velocity of vulcanization, especially important greater rapidity of vulcanization causes, under similar circum- 



in connection with the low viscosity. It is undoubted that this stances, a stiflfer rubber than would be expected from the vul- 



high velocity must be ascribed to serum compounds. It is canization coefficient. 



further evident that there is no rea.sbn to give preference to Miscellaneous Factors and the Mechanical Properties of 



natural accelerators above artificial ones, when one desires to Vulcanized Rubber 



make "stiflf" goods, and only for those will the addition be of No exceptions have been met with at the Institute in which 



value. the elongation curve did not practically confirm expectation of 



~H!wtinned from The India Rubber World. January 1. 1919. pjfre 196. "'^ory regarding the correlation of viscositv and vulcanization, 



