Resistance to Copper-Catalysed Oxidation and Surfactants for Fillers in Latex

Manufacturer:  We have two questions:

1) How to improve ageing resistance of our latex dipped products that are going to be exposed to an environment that contains heavy metal ions such as copper and iron during service?
2) What is the requirement of surfactants for adding filler in dry form (i.e. powder) and wet from (i.e. slurry).

We manufature both household gloves and examination gloves.


John Woon (Senior Latex and Rubber Consultant): Please see my comment below:

1) You need to use a combination of both your curatives and antioxidants at the right levels.
2) You need different levels of surfactant for both types of fillers with higher level for dry filler. Also, the particle size of the fillers play an important part in deciding the surfactant types and levels. Calcium carbonate, talc and clay are to be treated differently.

Details of my answers have been sent to you separately at your request.

Volatile Fatty Acids (VFA) in Natural Rubber Latex Concentrates

 
Manufacturer: We are producer of natural rubber latex concentrates and our sister company manufactures latex dipped products. Both companies have often experienced latex storage stability problem despite keeping the VFA Number low during production. We found that the VFA Number could suddenly increase on storage despite a reasonable level of hygiene standard. Can you explain why?

 
John Woon (Senior Latex and Rubber Consultant):  VFA i.e. volatile fatty acids which primarily consist of acetic acid with traces of propionic and formic acid, are formed as a result of bacterial breakdown of carbohydrates. Hence low VFA Number is usually welcomed as a sign of latex concentrates having been carefully prepared as far as bacterial contamination is concerned.

However, an initial low VFA could not always guarantee that the latex would continue to be stable because some live bacteria that are present in the latex could be inactive and dormant. But they could burst into activity weeks later by some external stimulation such as addition of ingredients which could act as nutrients for bacteria and the usual agitation.

One way to find out whether there would be any further damage done by bacterial action is to do a culturing of a sample of the latex on a suitable medium and carrying out a plate count of the bacteria present. If the result is nil, then the VFA Number would remain low on storage bearing  in mind, of course, that there are other factors such as the breakdown of protein which would also affect negatively the storage stability of latex concentrates.

To understand fully the whole picture of latex stability of which VFA is only a small part, you need to attend my lecture on "Latex Properties and Stability".