Latex DRC loss with storage time

Latex Producer: I observed that the DRC (Dry Rubber Content) of our latex concentrates tends to reduce on storage after some months. Why?

JohnWoon: Strictly speaking, in the standard testing method that most of us are using for DRC, the actual rubber content does not truly contain 100% rubber. Besides the rubber, you have the so-called non-rubbers. These non-rubbers on the rubber particles in time could get hydrolysed and dissociate itself from the rubber, hence the lower DRC content you observed.

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Effect of air on Latex MST (Mechanical Stability Time)

Manufacturer: We have been observing some interesting findings of MST (mechanical stability time)results of our centrifuged latex concentrates between samples kept in full bottles and those in partially filled bottles. The former very often shows a higher MST. Can you offer some explanation to our observation?

JohnWoon: Depending on the source of your latex, this observation some times does occur. This is the effect of the latex absorbing the air (oxygen) in the partially filled bottles. This was first reported about 50 years ago! Hence we always advise that after opening the sample bottle, latex sample must be tested as soon as possible - within 24 hours.

As regards the reason for the increase in MST when exposed to air, there is no clear explanation to date although some suggested the possibility of the formation of hydroperoxide groups on the polyisoprene molecule. But I can't see how this could increase the MST. Another explanation might make more sense:

The aldehyde groups of the rubber molecule could be oxidised forming carboxylic groups and this ionised groups could in turn migrate to the rubber particle surface thereby increasing the negative charge at the particle-water interface.

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.