Page 167 - Design for Environment A Guide to Sustainable Product Development

146 Cha pte r Ei g h t

Closed-Loop Material Recycling

Industrial processes can be de signed or retrofitted to increase scrap
utilization. With increasing attention to eco-efficiency, many compa-
nies have discovered that post-industrial scrap, such as trimmings,
off-spec product, and even dust can often be recovered and repro-
cessed cost-effectively (see the Owens Corning example in Chapter
17). This is effectively a dematerialization strategy, because it directly
reduces the quantity of materials required as process inputs (see
Section A.2, Design for Source Reduction).

End-of-Life Material Recovery
When products are disassembled, materials need to be sorted into
different categories for purposes of recovery and recycling. For this
reason, using similar or compatible materials can greatly reduce the
amount of end-of-life separation effort required. A key strategy for
separability, and an inexpensive one, is to facilitate identification of
materials by means of coding or marking. For example, the Inter -
national Organization for Standardization (ISO) has developed a
generic identification and marking standard, ISO 11469, to help
identify plastic products for purposes of handling, waste recovery,
or disposal.
Material homogeneity, purity, and reprocessability are important
considerations in determining their recovery value. Recyclable mate-
rials include thermoplastics, engineering plastics, metals, and glass.
As recycling technologies and materials science improve, we are
reaching the point where recyclable materials can be found for virtu-
ally any application. Factors to consider in material selection include
structural and aesthetic requirements as well as stability under vary-
ing conditions (e.g., temperature, moisture). For example, one of the
factors inhibiting wider use of bio-based plastics is their limited toler-
ance for high temperatures.
Composite materials, such as carbon fiber composites used in ten-
nis racquets, are prized for their light weight and superior mechanical
properties; for example, the use of composite auto parts can improve
fuel economy. However, composites can be problematic from an envi-
ronmental point of view because they cannot easily be separated into
their simpler and purer constituent materials. One viable approach is
to grind composite materials for use as fillers and reinforcements.
In general, the recyclability of a material depends on a number of
factors:
• The economic attractiveness of recycling the material and the
existence of end-use markets
• The volume, concentration, and purity of the recycled material
• The existence of recycling and separation technologies and
an adequate recycling infrastructure