How important is the particle size of chemicals for latex products?

Manufacturer:
We are manufacturing both Nitrile and natural rubber latex gloves. Recently we’ve heard of chemical dispersion of sub-micron nano size being offered in the market. Is it important to use curative dispersion of nano size to ensure good physical properties of our gloves?

JohnWoon: Earlier work done by MRPRA in England suggests that the answer is "NO". This is because of the possibility of the curatives, namely sulphur, ZnO and accelerators forming sulphur-accelerator species in the serum of latex and becomes soluble very quickly in the presence of hydrophilic non-rubbers. Curatives of average particle size ranging from 1 to 5 microns have been and are being used without problems.

Also, ZnO is known to dissolve almost immediately when added to Nitrile latex due to its reaction with the carboxylic acids. Hence the question of the settling of the high-specific gravity ZnO and hence poor cross-linking does not arise.

Having said that, chemical dispersions with very fine particle size would be advantageous in reducing the degree of sedimentation of the particles in the dispersions on storage. This would make the job of pre-mixing the dispersions just before adding them to the latex easier. Also, if fillers are used, nano-sized versions are preferred.

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Water sensivity of latex products

Manufacturer: We are using potassium soap (fatty acid based) in our latex. Owing to production constraint we cannot implement the leaching process during or after production although our finished latex products are to have good resistance to water absorption. Please advise how best we could improve the resistance to water absorption without leaching. We do not use coagulant for our process.

JohnWoon: I’m afraid I have no easy solution for you if you do not intend to do leaching. At best my advice could only help you to have a partial improvement.

Try the approach of what I call the “fugitive soap technique”. Select soaps/surfactants that would revert to the corresponding fatty acids on drying. These are the ammonium and amine soaps. I must stress that you use this remedial action only as an interim step to solve your problem in the short term. I strongly advise that you set a long term objective to introduce a leaching stage in your process.

Good luck!

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