Page 206 - Materials Chemistry, Second Edition

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Sustainability of Municipal Solid Waste Management
Waste beverage carton 185

Shredding

Soaking

Hydrapulping Beating

Screening

Pulp PE/Al mixture
FIGURE 5.20 Composite packaging recycling process

Repulping: Two alternative technologies are used for repulping to separate
pulp from Al and PE. The first alternative uses a hydrapulper which acts like
a blender. The cut carton material and water are added in the hydrapulper
where they are vigorously mixed resulting in friction forces between the
materials that accordingly leads to the separation of the fibers from the poly-
ethylene and aluminum material producing pulp. A schematic drawing of
the hydrapulper is shown in Figure 5.21.
The second alternative uses a beater. The cut carton material and
water are added in the beater and circulate in its oval tank discussed before
as shown in Figure 5.9. As they circulate, they pass in between a rotating
drum and a bed plate. This leads to the separation of the paper fibers due to
impact and high friction. Continuous circulation of the material in the tank
results in refining the fibers.
Screening: Screens are used to remove the pulp from the polyethylene and
aluminum materials. Water and the repulped material are added to the screen-
ing device from the top. An air injection system is used to blow air through
the water containing the suspended materials for a few minutes to avoid
blocking the screens and to allow efficient separation of the materials from
each other. The air flow is stopped and a water valve at the bottom of the
device is opened for draining water. The pulp produced is obtained by being
removed from the screen at the bottom. A schematic drawing of the screening
device is shown in Figure 5.22.