Verification of the Specific Gravity of Rubber before and after Its Vulcanization

1. Every hot vulcanization of a rubber compound leads to a volume decrease of the vulcanized material, or to an increase of its specific gravity. 2. The increase of the specific gravity of a rubber system depends directly on the condensation of rubber only, and does not depend on fillers. 3. The extent of the increase of the specific gravity of a vulcanized material is proportional to the quantity of rubber in the compound and to the degree of vulcanization. 4. Active fillers, as ZnO, and accelerators can influence the growth of the specific gravity of a vulcanized compound as agents promoting vulcanization; hence carbon black, contrary to Ditmar's opinion, can hardly contribute to condensation.