Page 77 - Materials Chemistry, Second Edition

LIFE CYCLE INVENTORY MODELING IN PRACTICE 59

however, we will use the simplified equation, with 100% recovery and recy-
cling after each use.

Allocation equation applied to open-loop recycling: Open-loop recycling
describes a system in which a product is recovered at the end of its useful
life, and the recovered material is then used in a different type of product
system. Typically the second product is disposed after use, or the mate-
rial may be recovered and reused in a product that has a low recycling rate
and therefore a low probability of repeated use cycles. Open-loop recycling
often applies to materials with properties that degrade with repeated use
cycles, for example, paper fibers that become shorter with each repulping
and remanufacturing cycle. Open-loop recycling also applies to products
that have low recycling rates even though the material properties may be
suitable for repeated use cycles. In open-loop recycling, the total number of
useful lives of the material "n" is a small number. For example, if material is
used in a virgin product, recovered and recycled into a second product, and
the second product is disposed at end of life, then n=2, and each system that
uses the material is allocated half the virgin production burdens, recycling
burdens, and disposal burdens.

Allocation equation applied to closed-loop recycling: Closed-loop recy-
cling occurs when material is used in a product, the product is recovered
at end of life, and the recovered material goes back into the same type of
product, so that there are repeated recovery and reuse cycles. In order to
get a large number of use cycles out of the material, the material properties
must hold up through repeated use cycles (e.g., glass, metals). As the total
number of uses "n" increases, the virgin production burdens and disposal
burdens allocated to each use become smaller, and (n-l)/n (the allocation
factor for recycling burdens) approaches 1.

There are limitations to the allocated recycling approach. This method
requires assumptions about the total number of lifetime uses of the mate-
rial. For a given product application, it is only possible to state with certainty
whether incoming material is virgin material or postconsumer material. If the
material enters the system as postconsumer material, it has had at least one
previous life, but it is not possible to determine the total number of previous
uses. Similarly, if the current product is known to be recycled at end of life, the
material will have at least one subsequent use, but the fate of the material after
the next use is uncertain.
For durable products that have very long useful lives, there is additional
uncertainty about future recycling. If the product is in use for many years,
recycling rates and technologies at the end of the product's useful life may be
quite different from recycling rates and practices at the time the product was
manufactured.
Allocation calculations can become very complicated when adjusting for
reprocessing losses and sequential useful lives that have different mixes of