Activity of Water-Soluble Dithiocarbamate Accelerator

Manufacturer: We were reviewing our natural rubber latex compound formulations to study the rate and efficiency of our accelerator systems. Our consultant advised us that for maximum rate of vulcanization, we should look into the use of water-soluble dithiocarbamate. However, we did not achieve the result expected by our consultant. Can you help?

John Woon (Senior Latex Consultant): This question had been asked before in this forum. 

I'm not surprised at all that you did not obtain better result from water-soluble accelerator because your consultant  was wrong!

Although the advantages of using water-soluble dithiocarbamates are the ease of use when being added to the latex and there is no concern over the dispersion and the particle size of the accelerator as experienced with the insoluble zinc salts, it is less active than the zinc salt counterparts. Also, it could be easily leached out before vulcanization.

Also, water-soluble accelerators might upset the alkalinity of the latex compound since they are considered as electrolytes.

Appearance of Whitish Powder on Rubber Products

Manufacturer: We are facing problem with the appearance of whitish powder on our finished products after storage. Our detailed latex compound formulations and samples of the good and defective products have been sent to you for your study. Please guide us on how we could overcome this problem.

John Woon (Senior Latex Consultant): Thanks for your samples and the compound recipe. After some initial tests and observation, I've concluded that this problem was very likely to be due to "blooming" of some of your additives, particularly the dithiocarbamate accelerators i.e. migration of some compounding chemicals to the surface of the rubber, as a result of low solubility in the rubber concerned.

All ingredients used in rubber compounding should have maximum solubility possible in the rubber.
Usually the higher the molecular weight of the accelerator, the more soluble it is in the rubber and hence lesser tendency to bloom.

My detailed report on how to prevent or minimize blooming has been sent to you separately. Hope you would find this useful.