Rubber Elephant in the Room
Malaysian researchers think that rubber pollution needs to be dealt with before it repeats the problems that have arisen with plastics
Could Rubber Pollution Be the Next Environmental Crisis?
This opinion piece first appeared in the New Straits Times. It has been written by Dr. Desmond Ang Teck Chye and Ms. Natasya Nabilla of the Department of Chemistry, University of Malaya. It highlights the elephant in the room, the problem of waste rubber. The call for action in the final paragraph sums up the need for joined-up thinking around the world.
Environmental pollution from excessive use of conventional plastic is widely known and has been making headlines throughout the globe. The focus of this article is not to further elaborate on the pollution caused by plastic wastes, but to articulate the potential of rubber as the next environmental pollutant.
Perhaps due to the overwhelming volume of plastic consumption, the amount of other commodity polymers used in our daily life is given very little attention. The term plastic pollution is so commonly used and repeated that the public may not realize that other materials may possess the same hazards too.
The problem with plastic pollution largely arose from the material’s huge molecular weight and inert property, allowing it to persist for decades or centuries after they were discarded. Many polymers out there share those similar characteristics with plastics, and one of them is rubber.
Rubber can be natural or synthetic in origin, and they have both found niche applications in various industries and in our daily life. Natural rubber is produced from the rubber trees, while synthetic ones are produced from the polymerization of one or several types of petroleum-based chemicals. Some of the widely used synthetic rubbers include SBR, NBR, and neoprene.
The issue on biodegradable material has been somewhat controversial and such label is often exploited for marketing purposes. There are several 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 the mineral salt medium using rubber as the source of carbon, and the rubber is perceived as biodegradable if the microbes, which usually comprised of either bacteria or fungi can make use of the rubber as a carbon source for its growth.
It is however noteworthy that positive result from such test simply shows that the rubber, just like some of the plastics, can be degraded or digested by the specific few microbes but this does not necessarily equate to the ability of the rubber to undergo biodegradation when they are discarded and left floating in the ocean, or buried deep in the landfill. In those laboratory setups, parameters such as humidity, the concentration of various salt nutrients, presence of specific bacteria strains, temperature etc. are carefully controlled to optimize the growth of the microbes, and oftentimes this does not reflect the actual environment out there.
Despite many studies carried out, many questions related to biodegradation of the material remain unanswered:
How long does a discarded vulcanized rubber articles remain in the environment?
How does the rate of biodegradation of synthetic rubber compare to natural rubber?
How well does the result from the laboratory biodegradation test translate to the biodegradability of the rubber articles in the actual environment?
Some of the synthetic rubbers are carefully engineered to exhibit superior chemical resistance and inertness, and logically such rubber is expected to be even more difficult to biodegrade. This concern is not unfounded as a group of researchers has published their findings in Journal of Rubber Research demonstrating that even in a composting environment, conventional NBR glove hardly undergoes biodegradation, with only 1 – 3% weight loss recorded after 6 months of composting. If such insignificant degradation reported at elevated temperature and in the presence of compost, what more to expect if the discarded nitrile rubber ends up in the environment?
Although the volume of rubber production is comparatively less than plastics, millions of tons of rubber produced annually is not an amount that one can sweep under the carpet. The impending problems related to the unsustainable use of rubber is just a matter of time and it does not take a genius to figure this out. It is literally a simple mathematical equation. When the rate of production of new rubber articles greatly exceeds the rate of decomposition of the used rubber articles, it equates to the accumulation of rubber waste. This is the exact situation with the current plastic crisis. Before déjà vu strikes again with rubber, it is best to nip the problem in the bud.
Fortunately, there are several options that can be practiced when it comes to treating end-of-life rubber articles or rubber waste. One of the reported initiatives in valorizing rubber waste include mechanically reprocess partially worn-out rubber products to a state where it is fit to use again, and one example of such practice is the retreading of used tyres. As for totally worn-out rubber products or rubber waste, they can be ground and pulverized into small particles and subsequently embedded and utilized in various rubberized materials such as concrete, asphalt, conveyor asphalt, conveyor belt, and playground matting. There are also ongoing practices to convert waste rubber into fuel via pyrolysis. The process involves heating the rubber waste at temperatures as high as 400 – 800 °C in the absence of oxygen. Lastly, rubber waste can also be incinerated for energy recovery purposes.
However, implementation of these initiatives has its own limitations and restrictions such as lack of proper infrastructure, lack of an established system to collect suitable rubber waste, segregation of waste, economic challenges, as well as the emission of toxic pollutants in some of the treatments. If we truly want the consumption of rubber and other polymeric materials to be more sustainable, there is a need for concerted efforts from various stakeholders, ranging from policymakers to consumers. It is our hope that everyone can strive together to do our part to make the world a greener place for future generations.
Dr. Desmond Ang Teck Chye, Natasya Nabilla, Department of Chemistry, University of Malaya