The damaging effect of certain solvent based glossing products on tyres

Technical explanation of one type of tyre failure - side-wall blowouts

Surface cracks in tyres that have been regularly exposed to solvents have been identified by one of the tyre manufacturers in South Africa as a potential cause for tyre failure and thus as one of the causes of tyre related accidents at high speed.

It has long been understood that certain solvents can penetrate rubber. Usually this applies most to smaller solvent molecules and medium sized molecules that evaporate slowly. Because one normally gets a very quick flash-off of very small molecules such as Ethanol and Isopropanol, the smallest molecules are not normally the problem. The molecules from the C4 to C9 ilk which evaporate slowest are the ones that penetrate rubber easiest. Also, it is usually the aromatic rather than the aliphatic compounds, or the Poly-Glycol Ethers that enter the lattice of the rubber the easiest.

Upon entering the rubber lattice, foreign solvent tends to puff the rubber slightly (sometimes not even noticeably), but the inner pressure then slowly again forces the solvent out of the rubber, usually in sync with the solvent’s natural evaporation rate. What happens next gets us to the crux of the problem. Some of the chemical compounds inside the rubber, such as the “internal” lubricant, which allows the tyre to stretch and wobble without becoming too hot, and also stop the tyre from perishing, become dissolved in the invader solvent, and as a result get squeezed out from the tyre along with the invader solvent over time.

By this mechanism, the chemistry of the rubber is changed, and accelerated aging of the rubber occurs. One of the symptoms of aging in tyres is the appearance of fine, hair-line cracks which are usually the only outward indication that not is all well with the outer layer of rubber in the tyre. Over time and with continued exposure to solvents, one may get to the point that a premature failure of the rubber occurs, hence the tyre may be subjected to a blow-out. As is well known, blow-outs, or catatonic tyre failures, normally happen at high speed. Through this explanation, it is evident that a linkage exists between using incorrect solvents in tyre-care products, and the introduction of an unnecessary element of danger for the drivers and passengers of vehicles.

When the main solvent used to prepare tyre-care compounds is water, the potential for damage is minimised since water is in itself basically repelled from rubber. For this reason, we generally recommend that Tyre Shine or Tyre Gloss is prepared as a water based emulsion with the glossing agent, namely Silicone Oil.

Although Silicone Oil is on its own a type of solvent, the molecules of Silicone Oil applied to tyres to give gloss are too large to be able to penetrate through the tyre surface, hence the idea that the Silicone Oil by itself may cause the leaching of chemicals from within tyres has been discounted in our opinion as being very, very, very unlikely.

Following the preceding reasoning, Ecwamix have developed water-based emulsions, which in addition to the obvious necessary facets of technical excellence as outlined herein, are also environmentally acceptable with respect to the chemistry employed. This gives our customers first-rate intermediate raw materials to put together products that they can confidently take to market and know that they can compete with any product that any competitor of theirs can present to their customers.

Bruce Rothmann

Ecwamix Chemical Systems cc