Current and Future Applications for Pyrolysis Blacks
The large quantities involved and the present use of nonrenewables in their generation mean that there is a great incentive to recycle carbon blacks and this pressure is expected to intensify.
Unfortunately, the present discrepancy in properties between the pyrolysis blacks and the tire grades means that they can presently only be recycled at fairly low levels and into the least demanding tire parts, such as carcass and inner liner. This is unlikely to change much in the immediate future, although it is fairly new technology and improvements are steadily being made. Currently they are more suited to some general rubber goods applications, where they do not require such levels of reinforcement, and this is already happening to a limited extent. They can also be used to replace pigment blacks in some applications.
Significant property improvements are needed to make these products serious contenders for the larger volume tire and general rubber goods applications, however. In addition to improving the surface area and oil absorption properties, the questions of the ash content and dispersion difficulties also need resolving.
The present ash levels are much higher (more than an order of magnitude) than those of conventional blacks. In fairness, a significant amount of the ash is silica filler and zinc oxide which are common rubber ingredients anyway, but they dilute the effect of the black. Others may actually be detrimental. In theory, it should not be too difficult to reduce the ash content very significantly, but this will have cost implications. Most studies show poorer dispersion of pyrolysis blacks, and this may be part of the reason for the relatively low reinforcement observed. The dispersion issues are probably mainly due to carbonaceous material from the polymer degradation and may possibly be improved by developments in pyrolysis conditions. Better milling of the product is also said to be showing promise.
Probably the biggest threat to the pyrolysis black industry will come from the efforts on recycling filled rubber discussed in section “Carbon Black Recycling in Elastomer Compounds.”