Sustainable and Recycled Particulate Fillers

Abstract

Environmental issues, such as life cycle impact and sustainability, are becoming important concerns for most industrial activities. Because of their scale of operation, composite materials are particularly affected, and this is filtering down to their major components, such as fillers.

In defense of using fillers at all, it has been shown that at least in some cases, replacing part of a synthetic polymer by fillers can reduce the environmental impact of a composite. While this is true, more could be done, and the main thrusts are for recycling and the use of renewables. The industry recognizes this; but, despite significant commercial activity, there are difficult obstacles to overcome and only limited success has been achieved so far. Recovery and recycling of fillers themselves is hampered by the low cost of many virgin products and has made little headway. Recycling of waste products from other industries has also made little progress, often due to competition from more valuable alternative applications for the wastes.

More progress has been made where the composite itself is recycled, examples being talc/polyolefin composites in automotive applications. This is much harder to accomplish in cross-linked polymers (thermosets and elastomers), which are inherently more difficult to recycle. The majority of fillers are currently from nonrenewable (although often vast) mineral resources. The exceptions are natural fibers, such as wood, cotton, and flax, and these are considered to be more sustainable.

Despite much effort from the tire companies on products such as starch, renewable particulate fillers have so far made little progress. It has, however, been demonstrated that carbon black can be made from biomass rather than petroleum oil, and this may develop as a significant commercial option in the future.

Despite the difficulties, pressure on the major volume products is only going to increase and we can expect more recycling and use of renewables in the future. This will mainly be in large volume products used in applications such as vehicles.