Elastic zinc compounds

Table 4.1-135 Elastic constants c, (in GPa) of zinc compounds, cont.

Vulcanization The treatment of natural rubber with sulfur to reduce its tackiness and improve its strength and elasticity. Invented independently by C. Goodyear and N. Hayward in the United States in 1839, and by T. Hancock in London in 1842 to 1843. Goodyear was honored for his invention by Napoleon III, but he died in a debtors prison in Paris. Various chemicals other than elemental sulfur are effective, for example, sulfur monochloride, selenium, and /v-quinonc dioxime. The chemical mechanism of this process is still not fully understood some believe that traces of zinc, derived from the zinc oxide used in compounding, are essential. 

Until they are vulcanized, elastic, amorphous ethylene-olefinic copolymers have very little possible utility except as components of caulks or sealants. However, grafting MA on the copolymers, using peroxide initiators, and compounding the modified materials with zinc oxide provides improved rubbers. A typical recipe would consist of 100 parts ethylene-propylene copolymer, 20 parts zinc oxide, 7 parts MA, and 2 parts BPO. Curing is carried out at 160°C for 30-45 min. Previously grafted copolymers, containing 2-5 MA residues, can also be cured with N-phenyl-B-naphthylamine initiator, steric acid modifier, and zinc oxide crosslinker. 

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