New 'super-paper' is stronger than cast iron

Punching your way out of a paper bag could become a lot harder,
thanks to the development of a new kind of paper that is stronger than
cast iron.

The
new paper could be used to reinforce conventional paper, produce
extra-strong sticky tape or help create tough synthetic replacements
for biological tissues, says Lars Berglund from the Swedish Royal Institute of Technology in Stockholm, Sweden.

Despite
its great strength, Berglund's "nanopaper" is produced from a
biological material found in conventional paper: cellulose. This long
sugar molecule is a principal component of plant cell walls and is the
most common organic compound on Earth.

Wood is typically about half cellulose, mixed with other structural compounds.

Support network

In
plant cell walls individual cellulose molecules bind together to
produce fibres around 20 nanometres in diameter, 5000 times thinner
than a human hair. These fibres form tough networks that provide the
cell walls with structural support.

"Cellulose
nanofibres are the main reinforcement in all plant structures and are
characterised by nanoscale dimensions, high strength and toughness,"
Berglund told New Scientist.

Cellulose
is extracted from wood to make paper, is the basis of cellophane, and
has also recently been used by materials scientists developing novel
plastic materials. But they have used it only as a cheap filler
material, ignoring its mechanical properties.

However,
the mechanical processes used to pulp wood and process it into paper
damage the individual cellulose fibres, greatly reducing their
strength. So Berglund and colleagues have developed a gentler process
that preserves the fibres' strength.

Tough as iron

The
new method involves breaking down wood pulp with enzymes and then
fragmenting it using a mechanical beater. The shear forces produced
cause the cellulose to gently disintegrate into its component fibres.

The
end result is undamaged cellulose fibres suspended in water. When the
water is drained away Berglund found that the fibres join together into
networks held by hydrogen bonds, forming flat sheets of "nanopaper".

Mechanical
testing shows it has a tensile strength of 214 megapascals, making it
stronger than cast iron (130 MPa) and almost as strong as structural
steel (250 MPa).

Normal
paper has a tensile strength less than 1 MPa. The tests used strips 40
millimetres long by 5mm wide and about 50 micrometres thick.

http://technology.newscientist.com/article/dn14084-new-superpaper-is-stronger-than-cast-iron.html?DCMP=ILC-hmts&nsref=news1_head_dn14084