Natural rubber

Natural rubber is a relatively low cost industrial material produced from the sap of the Pará rubber tree (Hevea brasiliensis). The raw latex is converted into a resilient and high strength material through chemical treatment and vulcanisation (reacted with sulphur at high temperature to harden it). Vulcanisation converts latex into a thermoset material that cannot be melted like thermoplastic elastomers (TPE). The advantage of this is a very durable and resistant material suitable for demanding applications in aerospace, transportation, industrial and manufacturing. The disadvantage is they cannot be recycled into new rubber. Instead, they are ground into crumb, which can be used as a filler material, such as in shock-absorbing floors and insulation. Some types of natural rubber and latex are biodegradable, but in general, they are considered non-biodegradable and take many years to breakdown. Along with synthetic rubber, dust and fragments, such as from tyre wear, contribute to air pollution and as microplastics in food, soil and water.

Natural rubber is resilient with excellent resistance to abrasion, but has poor resistance to oils, petroleum and weathering. Synthetic alternatives have evolved over the years to overcome its shortfalls and include a range of thermoset oil-based rubbers, including silicone and neoprene, as well as thermoplastic types (TPE) that are melt-processible. Even so, natural rubber remains one of the most widely used elastomers, largely due to its low price.

A fully synthetic version of natural rubber exists: polyisoprene (PI). Its consistency, purity and hypoallergenic nature (some people are allergic to the natural proteins in latex), mean it has replaced natural rubber in healthcare and medical items such as gloves, condoms, tubing and needle shields. It is also possible to deproteinise natural rubber to make it safe.

The majority of natural rubber production is not particularly sustainable – it uses harmful chemicals such as ammonia, sodium hydrogen sulphite and formic acid – but as a bio-based plastic, there is potential for it to be renewable and certified (FSC and PEFC for example). In the future, alternative sources may be commercialised that reduce our reliance on a single species of plant. For example, Yulex is scaling up production of certified rubber from the sap of the guayule plant (Parthenium argentatum). Its processes are sustainable and the raw materials are renewable, making this a very exciting development.

Yulex also produce rubber from the Hevea tree using more sustainable techniques – they are certified deforestation-free by PEFC and FSC, and use a water-based purification process – and their materials are biodegradable at the end of their useful life. Considering only around 3% of rubber production worldwide is certified, this is a great achievement.