Page 205 - Materials Chemistry, Second Edition

Ch005-P373623.qxd 3/22/07 5:34 PM Page 184
Sustainable Industrial Design and Waste Management
184
The plate is then cooled and pressed in a cooling press to the desired thick-
ness. The produced plate has moisture resistance and sound-deadening proper-
ties that are suitable for office furniture, flooring, interior decoration as well as
other products.

Repulping of beverage cartons
Anonymous (2001) presented a pulping technique for processing used bever-
age cartons for pulp production. Beverage cartons are first shredded into palm-
sized pieces then conveyed into a drum which is a metal cylinder about 22 m
long with a diameter of about 3 m. This drum is divided up into two parts, a
separation drum that is 10 m long followed by a sorting drum of about 12 m
long. The shredded cartons are softened by water; rotating paddles inside the
drum transport the material upwards, after which it drops back down. The
impact causes the softened paper fraction in the shredded cartons to disinte-
grate into fibers and become detached from the other material; no chemicals
are required. As a result of this process, a brown fiber pulp slurry is produced
that is washed away through small holes, cleaned, concentrated, and then
pumped to a paper machine to be converted into new paper or board products.
The residual PE/Al mixture is discharged at the end of the drum and dried.
Charlier and Sjoberg (1995) presented a different mechanical pulping
technique for recovering the fiber portion in the used beverage cartons in
repulping facilities available in paper mills. Through the process of hydra-
pulping, batches of used beverage cartons are mechanically heavily mixed
with warm water leading to the separation of fibers from the other polyethy-
lene and aluminum constituents of the laminates. The resulting fiber slurry
is then separated and transferred to join the pulp and paper production route
in the paper mill. A wet residue mainly of polyethylene and aluminum foil
together with some fibers and foreign objects remains.

Process of paper pulp separation
The process of recycling paper constituted in used cartons requires the sep-
aration of the paper fraction from the aluminum and polyethylene layers.
The process steps involved are cutting, soaking, repulping, and screening as
illustrated in Figure 5.20. The different recycling stages are presented below
in more detail.
Cutting: Used beverage cartons are cut by scissors into four pieces to
decrease their size and increase their specific area. Cutting is necessary to
facilitate the repulping process for paper recycling and reduce the time
required to refine the fiber and form the pulp.
Soaking: The cut cartons are put in a tank filled with water and left
overnight before pulping. This reduces the time required to refine the fibers
for pulping and accordingly increases the pulper’s capacity.