Flexible multilayer packaging has been successfully used for the
preservation of food and other products. However, once it has been
used represents a serious environmental problem as an important
part of solid wastes.
Multilayer packaging has a multicomposite structure made
with paper, aluminum and polyethylene films which are gathered
by temperature or by copolymerization with some additives
as acrylic acid or vinyl acetate, where the cellulose part
represents 75% of the total weight of the packaging, while aluminum
films are estimated in 5%. These films are coated and joined
by polyethylene layers to avoid the contact of food with
aluminum and to protect from external agents.
Although cellulose is recovered and reused in paper industry, the
remaining solid wastes, namely, a mixture of low density polyethylene
and aluminum composites, are still a demanding challenge
today. An outstanding characteristic of polyethylene–aluminum
(PE–Al) composites derived from postconsumer aseptic
packaging is that both plastic and metal components are strongly
adhered and they are hard to separate by mechanical processes.
Therefore, the treatment and disposal protocols for this kind of
wastes are limited. Currently, PE–Al composites are used as an alternative
energy source by pyrolysis or they are
reprocessed to plastics for secondary uses, or they are incinerated. In all these cases, the total waste disposal problem is not
completely resolved because residual aluminum and carbon dioxide
are formed, or the selling prices of reprocessed materials are lower
than those if aluminum and polyethylene were separately
commercialized.
Inspired by these facts, we initiated an investigation in order to
design a non-destructive procedure for the recovery of polyethylene
from PE–Al composites. In this regard, we considered that certain
solvents can solubilize polyethylene, besides
other plastics such as polystyrene are recycled by dissolution with
appropriate solvents. Taking these precedent
reports, we proposed in Fig. 1a recovery process for polyethylene
from PE–Al composites using a plastic dissolution as recovery
strategy. Herein is described a summary of our recent successful
endeavors in this area.