Elizabeth Henderson
Product Development Manager ITAC Ltd |
Natural rubber is polyisoprene, and its properties need
modifying for it to be hard, flexible and sufficiently weather resistant for
industrial applications. In particular, the vulcanisation of rubber is achieved
by milling sulphur into the hydrocarbon chains. These chains are strengthened
by the presence of carbon-sulphur bonds in the matrix. The bonds cannot be
formed without the presence of catalytic quantities of zinc oxide being included
in the milling. Zinc reacts readily with sulphur, forming a labile compound
which makes the sulphur available for incorporation in the hydrocarbon chain.
The amount of zinc oxide required is typically 5 parts per hundred parts of
rubber.
As well as using zinc oxide as a catalyst in these
reactions, Itac exploits its bacteriacidal properties in adhesives for medical
applications. Zinc oxide acts on bacterial cell surfaces causing the cells to
leak, and as the zinc oxide leaks into the cell it causes ‘oxidative stress’,
which is an imbalance between anti-oxidants and pro-oxidants in the cell. This
inhibits cell growth and eventually causes death of the cells.
Itac also uses zinc pyrithione as an additive in coatings for
food-bearing conveyor belts. Its presence inhibits the growth of algae and
fungi in the polyurethane matrix coating the belts. Exposure of yeast cells to
zinc pyrithione renders them unable to prevent the uptake of toxic copper from
their surroundings. Copper is incorporated by the yeast cells as copper
pyrithione, and this compound targets iron-sulphur proteins in the cells,
killing them.