What does "vulcanize" mean?

Vulcanize: To change the properties of, as caoutchouc, or India rubber, by the process of vulcanization. Vulcanized fiber, paper, paper pulp, or other fiber, chemically treated, as with metallic chlorides, so as to form a substance resembling ebonite in texture, hardness, etc. Knight. -- Vulcanized rubber, India rubber, vulcanized.