Page 224 - Materials Chemistry, Second Edition

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Recycling of Municipal Solid Waste Rejects
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The production of interlocks was much more profitable than brick, as they
did not need adhesives. The cost of silica-plast interlocks is 30–50% of the
traditional types of interlock depending on top layer coating. The appearance
of the interlocks can be improved by coating the top layer of the interlock
with better quality plastic waste. The top layer of plastic waste shown in
Figure 6.5 is a cheap coating layer since it is made out of plastic waste. The
plastic waste that was used were clothes hangers that were crushed and melted
in the heater, put in the mold, and pressed with the reject paste to produce this
top layer.
Bricks proved to be unstable due to the difficulty to maintain adhesion
because of water absorption. Interlocks proved to be very competitive, as the
plastic coat was optimum because it is made out of clean waste plastic. This
plastic coat completely covered the black color of the rejects and it was proved
to be durable.
The brick/interlock material was composed of a mixture of plastic rejects
and natural sand. The utilized plastic rejects included unsorted thermoplas-
tic wastes from MSW, the plastics recycling industry, thermoplastic wastes
from the packaging industry, etc. The major waste constituents were LDPE
(low density polyethylene) and HDPE (high density polyethylene), which
together comprised about 80% of the total waste. Small fractions of PS (poly-
styrene), PET (polyethylene terephthalate) and PVC were also present at a
weight percentage of 10–15% while the remaining balance contained other
minor waste constituents such as paper, wood, cardboard, small pieces of glass,

FIGURE 6.5 Development of interlocks