Somewhere on teh intarwebs Chris Hogg wrote:
On Sat, 31 Jan 2009 00:11:22 GMT, Rusty_Hinge
wrote:

The message
from "Pete C" contains these words:
Sheila wrote:

How do I know which paper is bleached/unbleached? I have been
putting paper in my compost heap, but just read you shouldn't put
bleached in......oh no, how do I find out!

'White' paper is either bleached or dyed. I hate to think what is
in the dye!

You can't dye something white.

Actually, it is bleached and if glossy, white clay is added, and it
is heat-treated. (Basically, ironed...)

Paper these days is mostly made from softwood, i.e. fast growing
conifers. They are pulped, either mechanically or chemically with
alkali (or a combination of the two) to break down the lignins and
liberate the cellulose fibres, which are usually then bleached.
Chlorine used to be used extensively, but chlorine dioxide, oxygen,
hydrogen peroxide or ozone are used now to avoid the formation of
harmful dioxins. White mineral fillers are usually added to the pulp
slurry (e.g. chalk or china clay, aka kaolin), to give opacity and
improve whiteness. The pulp slurry, at a very low solids content
(little more than cloudy white water), is then run onto a continuous
conveyor belt of wire mesh, where the water is sucked through, leaving
a fragile web of wet fibres. This is continuously lifted off and
passed over a series of heated rollers and drying stages to
consolidate and strengthen it.

If the paper is destined for the glossy magazine market, it is
subsequently coated with a high-solids slurry of either china clay or
chalk, depending on the quality of finish required, together with an
adhesive to bind it. Historically, this might be casein, made from
milk, but synthetic latex adhesives are used now. Optical brighteners
can also be added. Under UV light these fluoresce into the visible
spectrum, making the paper look whiter than it really is. Similar
chemicals are added to washing powders, which is why some white shirts
glow under the UV lighting in discos, for example. Paper coating is
often done at very high speeds, hundreds of feet per minute. To give
gloss, the dried, coated paper is passed through a series of pairs of
heated polished steel rollers forced together under pressure, a bit
like a series of old-fashioned clothes mangles. There is a very slight
speed differential between opposite rollers which causes slip and
which polishes the paper.

The paper industry used to have a very poor reputation for polluting
rivers with waste, particularly waste water containing residual
cellulose fibres and chemical residues. This had a very high
biological oxygen demand (BOD) as it decayed, resulting in dead fish
and sterile rivers. But over the last few decades they've cleaned up
their act enormously, and most pulp mills in the western world have to
conform to very strict regulations, and AIUI many recycle everything
they use with virtually no effluent at all.

The suggestion that bleached paper is somehow harmful to living
organisms in a compost heap is, at best, outdated, and probably never
had any validity in the first place.

Thats exactly what I was going to say!

;-)
--
Shaun.

"Build a man a fire, and he`ll be warm for a day. Set a man on fire, and
he`ll be warm for the rest of his life." Terry Pratchett, Jingo