Vulcanisation and thickening of positively charged Natural Rubber and Nitrile latices (latexes)

Manufacturer: We managed to produce positive charged natural rubber latex and Nitrile latex. This is for coating and impregnating textiles which usually have negative charges. To our satisfaction, we found the adhesion of the latex to the textile to be superior compared to normal centrifuged natural rubber latex concentrates (i.e. CL 60 HA or LATZ) and standard Nitrile latex.

However, our problem is that the ageing resistance of the rubber is quite poor. To overcome this we decided to add curing agents to vulcanize the rubber. However we encountered latex stability problem during mixing of the latex compounds. Also, we had problems when we intended to increase the latex viscosity with acrylic types of thickener.

Your suggestions on how we could overcome these problems would be appreciated.


John Woon (Senior Latex Consultant): If you are using conventional dispersing agents for the preparation of your curative dispersions or you are using ready made dispersions from external sources, I won’t be surprised at all that you’re experiencing the latex stability problem you mentioned.

You should use only cationic surfactants and perhaps along with only non-ionic surfactants as your dispersing agents because your latex particles are positively charged, unlike the usual natural rubber and nitrile latex concentrates. Examples of the former are quaternary ammonium compounds such as cetyl trimethyl ammonium chlorides and cetyl pyridium bromide while examples of the latter are condensation products of ethylene oxide with fatty acids, alcohols or phenols.

As regards the latex thickeners, you should not use anionic type like sodium or ammonium polyacrylates. Your better bet should be those based on methyl cellulose.







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How to improve resistance to air permeability of Natural Rubber latex products?

Air Bladders Manufacturer: We manufacture a range of bladders using natural rubber latex. For some products the air permeability is too high resulting in premature deflation and therefore failure of the products. Can you suggest some quick solutions?

John Woon (Senior Latex Consultant): This question has been raised and answered at this site before.

If you don't already know, natural rubber has quite poor resistance to air permeability compared to most synthetic rubbers. You could try blending NR latex with other synthetic rubber latices such as Polychloroprene (e.g. Neoprene) and Nitrile latex but this normally requires quite a high level of the synthetic latex leading to the undesirable loss of flexibility, resilience and elongation.

Your best bet is to do "laminate dipping" whereby an over-dip with synthetic latex is carried out after the first NR latex dip. The sequence of the two dips can be changed depending whether you want the synthetic layer to be the external or internal surface. Products with an external polychloroprene layer could also render the products more resistant to ageing especially against ozone attack.

To further enhance the air impermeability, you could also add some laminar types of fillers an example of which is silica.

You are at the site for answers and solutions to all your problems in natural rubber latex processing and manufacturing of industrial, household and medical gloves, condoms, catheters, baby teats and baby pacifiers, toy balloons, latex foam products, latex threads etc.