LETTERS: The term plastic pollution is so commonly used that the public may not realise that other materials may possess the same hazards, and one of them is rubber.
Rubber can be natural or synthetic in origin, and both have found niche applications in industries and in people's lives.
Natural rubber is produced from rubber trees, while synthetic ones are produced from polymerisation of one or several types of petroleum-based chemicals.
Some of the widely used synthetic rubbers include SBR, NBR and neoprene.
There are scientific reports on the biodegradation of rubber, with some showing evidence of biodegradability of rubber articles.
One of the most employed biodegradation test methods is to quantitate the growth of specific microbes in a mineral salt medium using rubber as a source of carbon.
The rubber is perceived as being biodegradable if the microbes, which usually comprise of either bacteria or fungi, can make use of the rubber as a carbon source for its growth.
It is, however, noteworthy that positive results from these tests simply show that the rubber, just like some plastics, can be degraded or digested by specific few microbes, but it does not necessarily equate to the ability of the rubber to undergo biodegradation when it is discarded and left in oceans or landfills.
In those laboratory setups, parameters — humidity, concentration of salt nutrients, presence of specific bacteria strains and temperature — are controlled to optimise the growth of the microbes, and oftentimes this does not reflect the environment out there.
Despite many studies carried out, questions related to the biodegradation of the material remain unanswered, including how long does a discarded vulcanised rubber article remain in the environment and how does the rate of biodegradation of synthetic rubber compare with natural rubber?
Some synthetic rubbers are engineered to exhibit superior chemical resistance and inertness, and logically, these rubbers are expected to be even more difficult to biodegrade.
This concern is not unfounded as a group of researchers published its findings in the Journal of Rubber Research, demonstrating that even in a composting environment, conventional NBR gloves hardly undergo biodegradation, with only one to three per cent weight loss recorded after six months of composting.
Although the volume of rubber production is comparatively less than plastics, the millions of tonnes of rubber produced annually are not an amount that one can sweep under the carpet.
When the rate of production of new rubber articles greatly exceeds the rate of decomposition of the used rubber articles, it equates to an accumulation of rubber waste.
This is the exact situation with the plastic waste crisis. Before deja vu strikes again with rubber, it is best to nip the problem in the bud.
Fortunately, there are options when it comes to treating end-of-life rubber waste, including mechanically reprocessing partially worn-out rubber products to a state where it is fit to use again. One example is the rethreading of used tyres.
Totally worn-out rubber products or rubber waste can be grinded and pulverised into small particles and embedded and used in various rubberised materials, such as concrete, asphalt, conveyor asphalt, conveyor belt and playground mat.
Another is converting waste rubber into fuel via pyrolysis by heating the rubber waste at temperatures as high as 400 to 800 degrees in the absence of oxygen.
Lastly, rubber waste can be incinerated for energy recovery.
However, the implementation of these initiatives has limitations and restrictions, such as lack of proper infrastructure, lack of an established system to collect suitable rubber waste, segregation of waste, economic challenges and emission of toxic pollutants.
If we truly want the consumption of rubber and other polymeric materials to be more sustainable, we must make the world a greener place for future generations.
DR DESMOND ANG TECK CHYE and NATASYA NABILLA
Department of Chemistry, Universiti Malaya
The views expressed in this article are the author's own and do not necessarily reflect those of the New Straits Times