Discolouration of Latex Dipped Products

Manufacturer: We observed discolouration of our dipped products made from natural rubber latex more than synthetic latex. Also, the colour could vary from batch to batch.

We would appreciate if you could explain why.

John Woon (Senior Latex Consultant): Natural rubber latex indeed is darker than most common synthetic latices. It is well known that natural rubber latex contains many constituents of non-rubbers. One possible cause of darkening of the dried rubber when exposed to air or oxygen is the enzymatic action of the naturally occurring polyphenol oxidase.

Another causative agent is from the Frey Wyssling particles which give the yellow colour due to the presence of carotenoids. Fortunately most of this is removed during the centrifugation process if done properly.

Since natural rubber latex is of botanical origin, the level of non-rubbers and hence its tendency to discolour is expected to vary from clones to clones and from time to time.

Efficient leaching is of utmost importance if you want to minimize the degree of discolouration. One of course must also bear in mind the possible discolouration caused by contamination with heavy metal such as copper and iron in compounded latex in which zinc dialky dithiocarbamates are used. This of course is expected to similarly occur with synthetic latex compounds using dithiocarbamates.