Drain covers made from polyurethane composites could soon replace the old cast iron manhole covers, according to recent news reports. The advantages are fairly obvious the modern manhole covers will be less dense and so easier to handle, they will be essentially worthless to metal thieves and given the state of the art in composite formulations will probably show greater wear resistance. It got me thinking…we entered the plastic age, as I mentioned in a previous blog post, quite some time ago. But, are metals now redundant?

It seemed like an original thought, but as is often the case a quick web search revealed that another blogger over on the polymers group page of the InnovateUK website had beat me to it. The author of the post, whom I believe is as Alan Wood of Victrex plc (although the byline is labelled as Matthew Thornton)  suggests that since the Bronze Age of 2500 BCE, metals have been humanity's material of choice for engineering and other applications from swords to ploughshares. One might argue that the natural polymer composite we know generically as wood was for a time a more ubiquitous material, but for technological advances in the modern era metals and alloys have stood firm.  Wood, the ironically named author of the blog post suggests that just as metals superseded other materials perhaps as the plastic age reaches true maturity metals will themselves be superseded.

Aside from plastic manhole covers, the concerns about ceramic knives on aircraft slicing through airport security metal detectors, also hints at how even that most common of metal products, the blade could be replaced by composite-type materials, while the advent of conducting polymers on which I first reported for New Scientist and Science back in the very early 1990s, might ultimately make copper wiring and connectors redundant too; there are many other examples.

Wood offers six bullet points as to why polymers might outstrip metals.
These are: far superior corrosion performance (assuming we are not talking biodegradable or photodegradable polymers, of course), toughness low friction, lower density, mass produceability and lack of "finishing/polishing" operations and finally the possibility of amalgamating sub-components (perhaps with the 3D polymer printer allowing almost any object or component to be fabricated). Vehicles and aircraft benefit from easier maintenance and lower fuel consumption, lower cost and many other advantages. Although it is not yet possible to replace engines and other high-temperature components with plastic, that day might come eventually too, especially if power technology emerges that precludes the need for "infernal" combustion. Wood also muses on the fact that the machines for producing polymers and fabricating them into useful components do, by necessity, require metal parts at the moment, but hints that they too might one day be displaced.

There are various issues yet to be addressed, the biggest being the feedstock from which the growing tonnages of polymer displacing metals are to be sourced. There is also the obvious dichotomy we face when talking about a low-carbon world if we are to displace ubiquitous metals that can be recycled in a fairly straightforward manner with myriad polymers that generally cannot. We have almost 5 millennia of metal work experience, but the age of plastic is very much in its infancy, the first truly synthetic polymers emerging from our ingenuity only in the last century. But look at the advances we have made with polymers in such a short time. Give the polymer chemists and materials scientists a little more time and solutions will be spun out...

Further reading

Polyurethane composites replacing iron for manhole cover manufacture - http://www.materialsviews.com/polyurethane-composites-replacing-iron-for-manhole-cover-manufacture
Are Metals Redundant Materials? -

David Bradley blogs at http://www.sciencebase.com and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".