Comparatively few organic peroxides meet the rather exacting requirements of the ideal peroxidic curing agent for rubber. Only di-tertiary butyl peroxide has yet been found to give satisfactory vulcanization in black stocks. Pure gum vulcanizates of a high degree of transparency and good color have been obtained with two commercially-available non-hazardous peroxides which have also been used successfully with some non-black fillers. The incorporation of resorcinol overcomes a tendency to surface tackiness in peroxide cures and has a beneficial influence on tensile strength.
1. The rubber particles in Hevea brasiliensis latex have been partially purified by ;washing' with buffer solution, and separated into active fractions of different particle size. 2. The enzyme responsible for incorporating isopentenyl pyrophosphate into rubber is distributed between the surface of the rubber particles and the aqueous serum phase of the latex. The enzyme at the surface can be removed or inactivated if the rubber particles are washed sufficiently with buffer solution. Enzyme in the serum phase can be concentrated by fractional precipitation with ammonium sulphate. 3. To incorporate isopentenyl pyrophosphate into rubber in vitro, active rubber particles are required as well as enzyme and soluble cofactors. The activity of the rubber particles per unit surface area increases with diminishing particle size.
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