Almost half of the zinc emissions from the wearing of tyres take place in urban arears, where they are capture with the rainwater, end up in STP's and are not released to the environment. Along regional roads the zinc load at the target zone is of the same order of magnitude as background deposition. The impact will be minimanl. Along highways the zinc load at the target zone is of the same order of magnitude as in fertilised agricultural land. In The Netherands only 1.1 to, or 0.5 % of the 184 ton of zinc released per year from tyre wear and guard rail corrosion will enter this target zone along highways. This amount will further decrease by the use of porous asphalt. Special cases such as bridges, crossings and squares are to be considered where the release of zinc may be a source of local pollution. A proper management of the solids in drains or on the top soil of the road border is required and should be determined on a case by case basis.

There is pressure on the rubber industry to reduce, or even remove, the zinc oxide used in rubber compounds, because of concerns that zinc chemicals may have adverse affects on the aquatic environment. An EU-supported project, entitled ‘Ecozinc’, was set up to determine the scope for reducing, or eliminating, the zinc chemicals, predominantly zinc oxide, used in a wide range of rubber products, including tyres and articles manufactured from latex. The project’s partners include rubber product manufacturers, rubber chemical suppliers and rubber research institutes. A variety of studies conducted by the project’s partners have indicated that the zinc oxide content in sulphur-vulcanised rubber compounds can generally be reduced to about 2 phr. In a major application, SBR/BR passenger tyre treads, much larger reductions of zinc oxide level, from 3 phr down to 0.5 phr, or even removing zinc oxide completely, appear to be feasible. Parallel studies indicate that the crosslinking chemistry in the high-vinyl solution SBR, used in these passenger tread compounds, is quite different from that found in other rubbers. This may explain the markedly different dependence on zinc oxide. The use of more active forms of zinc oxide, additional phase transfer catalysts, or other zinc chemicals (such as zinc sulphide or zinc accelerator complexes) have not substantially further reduced the minimum zinc content that can be achieved with standard zinc oxide, contrary to indications in the literature, although a zinc soap combination shows more promise. However, the dispersion of high-surface-area zinc oxide during mixing was found to be significantly better, which could enable low levels of this zinc oxide to be used in industry with more confidence. Inclusion of an anti-reversion agent, or a combination of anti-reversion agents, in an NR compound can enable the minimum zinc oxide level to be further reduced from 2 to 1.5 phr. Combinations of calcium or magnesium oxide with a zinc soap also show improved reversion, compared with the equivalent zinc oxide level of 1 phr, but other properties are still not satisfactory. So far, zinc-free alternatives based on ‘activated’ calcium or magnesium chemicals have shown no promise. Our studies have generally shown that zinc oxide can be removed from peroxide-cured compounds with little or no effect on properties, although in some applications there is evidence that severe-ageing performance may be affected. The minimum zinc oxide found to be required for sulphur curing of NR latex compounds, 0.1-0.3 phr, is much less than required for dry rubber. Our findings indicate that the main role of zinc oxide in XNBR latex compounds is to act as a base; replacement by other bases is being investigated.

In het kader van een innovatief onderzoek programma (IOP) is een onderzoek uitgevoerd om de hoeveelheid zink in rubber compounds te reduceren door de beschikbaarheid van het zinkion te vergroten. De beschikbaarheid kan worden vergroot door een dragermateriaal te beladen met de benodigde ionen. Dit is een techniek die met name in de katalyse veelvuldig wordt toegepast. Voordeel van deze techniek is dat de drager(klei) relatief goedkoop is en de hoeveelheid zink drastisch kan worden gereduceerd. De belading van het dragermateriaal kan bijvoorbeeld plaatsvinden door middel van een ionenuitwisselingsproces. De eigenschappen zijn vergelijkbaar met conventionele bandencompounds.