Why Does Natural Rubber Products Become Soft On Ageing?

Manufacturer: We manufacture rubber products using both synthetic and natural rubber. We observe that those made from natural rubber behaves differently compared to those made from synthetic rubbers after ageing (i.e. oxidation).

Unlike synthetic rubber products, natural rubber products tend to become soft after ageing. Why?

John Woon (Senior Latex Consultant): Oxidation is a free radicals chain process initiated when the rubber (polymer) chains are broken and carbon radical formed as a result.

Oxidation of rubbers leads to either hardening or softening of the rubbers. The free radicals are highly reactive and unstable having the tendency to form more stable products. For some synthetic rubbers, these free radicals form cross-links and the rubbers become harder.

In the case of natural rubber, the hindrance caused by the bulky methyl side group prevent the formation of such cross-links and the end result is "chain cleavage" or "chain scission" which breaks down the polymer chain. This means a reduction in the molecular weight and hence the rubber becomes soft.

Hartalega’s Plan to Expand Capacity Welcomed by Analysts

Analysts are upbeat on Hartalega Holdings Bhd's ambitious plans to triple its current annual production capacity with a RM1.5bil plant to be built over two four-year phases.

On Friday, Hartalega, via its wholly-owned subsidiary, Hartalega NGC Sdn Bhd (HNGC), revealed more details it had put in place to set up a new major rubber glove manufacturing project.

Affin Investment Bank, in a report, said it was positive on the HNGC project, as it clarified Hartalega's expansion plan beyond Plant 6, which was slated to commence its first phase of production in September 2012.

Image on the left shows a robotic glove-dipping simulator developed and used by Hartalega. Maybank says the company’s plant expansion, coupled with ongoing automation, will greatly improve economies of scale and enable Hartalega to come up with more competitive prices.


“Funding is not an issue, we gather that the project will be financed via a combination of borrowings and internally generated funds, considering its net cash of RM136mil as at December 2011,” it said........CLICK HERE to read more.

Loss of Viscosity in Coatings on Storage

Manufacturer: I chanced upon your website by accident and am amazed by your effort in helping the latex industry in overcoming many of the common problems encountered by manufacturers. We only hope that there are similar consultants online who could also help us in the coating industry.

Since I'm already in your site I thought I should try my luck in throwing a question to you too.




We manufacture coatings and paints based on cellulose lacquers and Polyvinyl acetate/acrylics emulsions. Our problem is the loss of viscosity on storage. Any idea what causes this?

John Woon (Senior Latex Consultant): I'm no expert in coatings. However, certain aspects of the basic science and technology of latex are also applicable to the coating technology.

Let me make an attempt in answering your question and hope you'd find it useful.

1) Some cellulose lacquers are prone to loss of viscosity on storage. This might be inherently due to the base material - cotton. However, this only happens initially after production and it would eventually stabilise at some point. If higher viscosity is required, I suggest you start off with a higher viscosity.

Some basic salts in pigments (or even acidic materials) might degrade the nitrocellulose molecule and hence causing a drop in viscosity.

2) When pigments are not sufficiently wetted or the wetting process is too slow, the paint may lose viscosity as wetting proceeds during storage.

3) As regards the reduction of viscosity of paints based on emulsions (e.g. PVac latex), the cause could be the degradation of the thickening agent by bacterial attack.