Paper - ...Stronger than Iron?

[rhoenix]

Paper grocery bags that can hold a few liters of milk without tearing? That may not be too far off thanks to the development of a "nanopaper" that is tougher than cast iron. The material--made from nanosized whiskers of cellulose--is also lighter than conventional paper and could provide sturdy scaffolds for growing replacement tissues and organs.

Conventional paper is made from cellulose, a crystalline polymer of glucose that's the primary component of plant cell walls. At the nanoscale level, cellulose can be extremely strong, with individual fibers capable of withstanding more stress than glass fibers or steel wire. But paper processing generates relatively large cellulose microfibers riddled with defects that can break apart under stress. That leaves most commercial paper with a tensile strength that tops out at about 30 megapascals (MPa), says Lars Berglund, a lightweight structures engineering expert at the Royal Institute of Technology in Stockholm, Sweden.

To toughen paper up, Berglund and his colleagues kept the cellulose fibers small. They did this by breaking down wood pulp in water with a combination of enzymes and mechanically beating it further. The result: defect-free nanofibers about 1000 times smaller than typical cellulose fibers. As a final step, the researchers treated their nanofibers with carboxymethanol, which coated the fibers in carboxyl groups. These groups readily form hydrogen bonds that helped the fibers make tight contacts with one another, further strengthening the material. The final result--published in the current issue of Biomacromolecules--was a paper with a tensile strength of 214 MPa, far above the 130 MPa of cast iron and the previous record of 103 MPa for a high-strength paper. In addition to improving paper products directly, the new cellulose nanofibers could help create reinforced plastic composites cheaper than those reinforced by carbon fibers, the researchers say.

The new nanopaper is "quite interesting," says Mike Wolcott, a materials scientist and cellulose fiber expert at Washington State University in Pullman. In addition to making paper stronger, the nanopaper has large pores between the fibers, which should also make it easier and cheaper to dry, thus reducing the cost of any final product, he says. And because cellulose is the most abundant organic compound on the planet, nanopaper has the potential to be cheaper than more-exotic, expensive-to-produce nanomaterials such as carbon nanotubes, says John Simonsen, a physical chemist and nanocrystalline cellulose expert at Oregon State University in Corvallis.

This is fascinating. Does anyone else suspect this might lead to the innovation of more biodegradable heavy parts?

[Ra]

Gives the paper tiger a whole different perspective.

If it's stronger than steel, I wonder if it's strong enough for a space elevator? Think of it; a paper tower to the stars.

But aside from that, if they run with this it could mean the end of our over-reliance on oil derived plastics; or at least reduce it considerably. Plastic bags at the checkout, plastic components in lots of everyday containers and things, gone.

And if it can compete with carbon fiber, we're talking (potentially) biodegradable aircraft fuselages, among other things. Depends on how flamable it is, and if they can add fireproofing in any epoxy they apply, though I'm hardly an expert on that sort of thing.

It's a very cool discovery, at any rate.

[Destructionator XV]

So many of these new materials talk about their great tensile strength being superior to that of iron or steel, but that alone doesn't make it a stronger material than iron. Cast iron is a poor example of good tensile strength anyway.

Moving on, tensile strength comes into play when you pull two ends of a string. A string with good tensile strength can be pulled very hardly and not break. But, if you compress a string, it doesn't hold its shape. If you yank it parallel to its grains, it will probably come apart. It lacks compressive and shear strength. If you heat it up, it just burns away.

Steel, on the other hand, is pretty strong all around. It weakens greatly if you heat it, but at room temperature, it can take a lot of different kinds of punishment. That is why it is so useful.


These new materials will have their uses, no doubt, but they won't replace good old steel.

[rhoenix]

Replace steel? No. Supplement steel? Yes - I can see new paper alloys (heh) becoming more wide-spread, if the material strength and biodegradability are as touted.