February 1, 1919.] 



THE INDIA RUBBER WORLD 



249 



been using, we shall study some types belonging in each 

 category. 



Among the sulphydric accelerators we may reckon the resin 

 oils, crude petroleum, waxes and ozokerite, certain bitumens, 

 sodium, calcium, potassium in the form of paraffinated powder, 

 tannin, and turpentine. These substances permit the rapid 

 formation of sulphydric acid, they diminish a little the length 

 of time necessary for curing and, above all, they allow the work 

 to be done at a lower temperature. They must be classified 

 according to whether the vulcanization takes place with dry 

 heat, under pressure, by steam, or with hot air with or without 

 pressure. A substance which behaves admirably in one case 

 acts badly in another. A group of sulphydric accelerators 

 corresponds to every source of heat. This remark is general 

 and applies not only to accelerators, but also to vitalizers, and 

 to vitalizing accelerators. 



Sulphurous accelerators are found chiefly among the me- 

 tallic oxides and peroxides. We have long known the action 

 of litharge and of light magnesia, of which the accelerating 

 qualities have been empirically demonstrated. 



Iron oxide has similar qualities but it seems that they attain 

 their maximum effect only in the presence of brown factices. 



The oxide of manganese, especially Weldon's earth, is a good 

 accelerator, but must be used in very small quantities, as it 

 reacts on the caoutchouc, oxidizes it and makes it easy to break. 



Black copper oxide cannot be used, but the red oxide is an 

 excellent accelerator ; a one per cent mixture easily vulcanizes 

 in 30 minutes: but, unforunately, this oxide gives a green 

 color to the gum. 



Peroxide of zinc, peroxide of magnesium, peroxide of sodium, 

 the alkaline carbonates and persulphates and the plumbates, 

 in quantities of 0.5 to 0.2 per cent, are good sulphurous ac- 

 celerators. 



The same thing can be said of the mixture of chlorate of 

 barium and vanadium salts, but all these substances must be 

 used in very small quantities, with great precaution and, as 

 far as possible, in the presence of sulphydric accelerators, such 

 as resins or lanolin. Their use shortens the time necessary 

 for vulcanization and allows lowering the temperature for the 

 reaction. 



The importance of these has greatly diminished since the 

 discovery of vitalizing accelerators by using which both re- 

 actions can be obtained at the same time, without risking injury 

 to the quality of the manufactured product. 



Certain substances which are also classed among the accel- 

 erators can give both the sulphurous and the sulphydric re- 

 action ; they are those containing easily decomposable hydrox- 

 ides. Certain alcohols, such as amyl alcohol, glycerine, ter- 

 pineol, most of the phenols, particularly the diphenols, have 

 these qualities. They accelerate vulcanization, but as their dis- 

 sociation takes place only at a rather high temperature, no 

 lowering of the heat during curing is possible. 



We can include in this class also several alkaline oxides, 

 such as sodium, potassium and barium hydrate, of which the 

 accelerating action has long been known. The rapidity with 

 which alkaline-reclaimed rubbers vulcanize is due to the pres- 

 ence of traces of sodium which acts to accelerate cure. 



As a real vitalizer we can mention hardly anything but cyan- 

 hydric acid or the alkaline cyanides. The best is the cyanide 

 of ammonium (CNNH,), but it can be used only in the 

 presence of sulphide of carbon. The reaction takes place ac- 

 cording to the following equation : 



CNNH. -I- CS, + S = (CNSH), + H,S. 



The substance behaves under these conditions as an accel- 

 erating sulphydric vitalizer. 



The addition of the vitalizer (mixture of cyanide of ammon- 

 ium and of sulphide of carbon saturated with sulphur) is made 

 when the mixture of the caoutchouc and charges is finished, 



and the incorporation is insured by mixing on cold rolls to 

 prevent too rapid evaporation of the sulphide of carbon. One 

 can slacken this evaporation to a certain extent by adding tetra- 

 chloride of carbon to the sulphide, part for part. On account 

 of their poisonous qualities, the use of cyanides cannot be 

 recommended. 



The sulphydric accelerating vitalizers are the most numerous 

 and, practically, the easiest to use. Theoretically, every organic 

 base, all amines and all iraines can, under certain conditions, 

 give the reaction of vitalization and of sulphydric acceleration. 

 Such is the case of aniline, one of the first substances used 

 as an accelerating vitalizer. The reaction is rather complex. 

 In the presence of sulphur the benzene ring is broken up, form- 

 ing a molecule of sulphocyanic acid, a molecule of sulphydric 

 acid, two molecules of acetylene and one molecule of sulphide 

 of carbon, at about 140 degrees C. The equation is : 



Ce.Hj.NH, -f 4S = CNHS -|- 2 (CK=CH) -f H^S + CS,. 



In the class of the imines we can mention as giving very 



good results, piperidine or imino pentane : 



CH, ■ CH, 



CH, NH 



CH, . CH, 



The reaction again takes place by the breaking up of the ring, 

 forming acetylene, sulphocyanic acid and sulpliydric acid. The 

 equation is : 



C5H10NH -f 2S = CNHS -f H,S + 2 (CH =CH). 



A mixture composed of plantation crepe, 60 parts ; oxide of 

 zinc, 33 parts; sulphur, 6 parts, and piperidine, 1 part, gives, 

 under three atmospheres, a well-vulcanized product in 40 min- 

 utes and the following physical constants : 



Breaking strength per square millimeter 1.905 grams 



Elongation at break 5.9 



Permanent elongation 1.08 



In order to obtain a perfect result it is necessary to add the 

 piperidine to the sulphur before making the mixture. The crepe 

 and the oxide of zinc are uniformly mixed and the steam shut 

 off from the rolls before the mixture of sulphur and of piperi- 

 dine is added. The mixture must be allowed to rest 24 hours 

 hours before being cured. 



Paraphenylene diamine, aldehyde ammonia, sodium amide, ben- 

 zylamine, naphthylene diamine, and all quaternary ammonium 

 bases behave in the same way. Among these substances it is 

 best to choose, as being the most energetic, those which can fur- 

 nish most sulphydric acid and most sulphocyanic acid. 



From this explanation it seems that the more atoms of nitro- 

 gen an amined or imined compound substance has, the greater 

 will be its energy as a vitalizer. This is not always true, for, 

 besides the nitrogen, the atoms of carbon and of hydrogen neces- 

 sary to form the active bodies, sulphydric acid and sulphocyanic 

 acid, will often be lacking. One way of remedying this defect 

 is to condense the amines with the aldehydes. 



The type of this formation is the combination of formalde- 

 hyde with ammonia, which produces successively three accelerat- 

 ing vitalizers. 



1. Trimethylene triamine. 



CH^ 



