This interesting article about using sound to recycle paper many more
times than is possible with current technologies. An excerpt from the
article is included below with the full article being at the following
URL;
http://www.discover.com/science_news/gthere.html?article=envirscience.html
Sameer Madanshetty, a mechanical engineer at Kansas State University,
has come up with another way. He has devised a recycling procedure that
dispenses with chemicals entirely; it also does so little damage to the
paper fibers that pages can be reused multiple times. And all he needs
to do it is some water and precisely controlled pulses of sound.
As a sound wave travels, it creates a ripple of expansion and
compression: a low-pressure pulse followed by a high pressure pulse, and
so on. Tiny bubbles that can sometimes form in water and other liquids
react to this change in pressure. The low pressure pulse expands the
bubbles and the high pressure pulse makes them contract.
With certain sound waves, the contraction caused by the high pressure
part of the sound wave can be strong and fast enough to make the bubble
collapse in on itself, creating a surprisingly large concentration of
energy.
Called cavitation, this process is powerful enough that it can damage
things like ship propellers and water pipes, eventually eroding them
away. Engineers therefore usually try to create cavitation-proof
designs, but this goal is hampered by the unpredictable nature of
cavitation.
Madanshetty does not see cavitation as a bad thing. "It's such a
fascinating energy manifestation, but we are removing it because we
don't understand it and we can't control it," he says. "If you think of
fire, any fire is devastating, but if you contain it you can do some
good cooking."
Indeed, Madanshetty has found a way to control when and where cavitation
will occur. Along with a strong sound pulse that causes the bubbles to
expand and contract, he uses a weaker background sound wave that
destabilizes the bubbles so that they collapse at a lower pressure; the
result is that they release less energy and their effect is more
localized.
When a piece of paper is placed in water, tiny bubbles are most likely
to form around the inked parts of the page, because the ink repels
water.
Madanshetty's sound system blasts these microbubbles; when they
collapse, they literally explode the ink off the page. "It's like
micro-jackhammers," he explains. "It chisels away the ink and throws it
up." The process can strip the ink from a page in a few seconds, and the
ink particles can then be filtered out of the water.
Although the bubbles have enough energy to destroy the ink,
Madanshetty's control process keeps them weak enough that they do not
seriously damage the paper fibers below. In most cases, the paper need
not be mashed up to be recycled--the microbubbles erase the ink
effectively enough that the original paper is as good as new,
Madanshetty says.
"Present practice mechanically pulps the paper, and in the churning
process they damage the paper fibers, so it limits the recycleability to
three times," he notes. "In this case, you are not touching the paper
fibers at all, so the number of times you can recycle the paper would be
endless."
-- Jerry Wayne Decker / jdecker@keelynet.com http://keelynet.com / "From an Art to a Science" Voice : (214) 324-8741 / FAX : (214) 324-3501 KeelyNet - PO BOX 870716 - Mesquite - Republic of Texas - 75187