Process for the preparation of un-vulcanised india-rubber in crumb or powder form

摘要

Rubber in the form of powder or crumb is made by adding a salt of nitrous acid, such as sodium nitrite, to latex, coagulating with an acid, lightly pressing the coagulum, and disintegrating. 1-50 per cent of sodium nitrate may be added to latex, and the amount of acid added should be sufficient to coagulate the rubber, and also to react with the nitrite, and to neutralize any ammonia &c. present. If the latex has been preserved with ammonia, it is desirable to add a protective colloid such as casein to ensure gradual coagulation. According to an example, to 1000 gm. ammonia preserved 40 per cent latex is added 50 ccm. of a solution containing 10 gm. casein per 100 ccm. of 10 per cent ammonia, and 10 gm. sodium nitrite in 100 ccm. of water. Coagulation is effected by the addition of 50 gm. glacial acetic acid in 500 ccm. of water. The coagulum is washed in a filter cloth, and pressed into a slab, which is rubbed through a sieve. The powder obtained is dried in thin layers. Specification 395,774 is referred to.