Page 78 - Materials Chemistry, Second Edition

60 LIFE CYCLE ASSESSMENT HANDBOOK

virgin and postconsumer content and different postconsumer recovery rates.
Because the system expansion and cut-off approaches focus on the material's
use in the current product system and the material's next use, the calculations
for these methods are more straightforward and require fewer assumptions
about prior and future uses of the material.
For recycling to be sustainable, there must be a balance between recycled
material supply and demand. If the supply of recycled material used by the
system is currently fully utilized (e.g., secondary aluminum), then the recy-
cling rate for a product must be equal to or greater than its recycled content
in order to be sustainable. If a system uses more of a fully utilized recycled
material than it produces (recycled content > recycling rate), then it creates a
u
net deficit in the recycled material supply that has to be made p with virgin
material. If the system's recycling rate is higher than its recycled content, then
it is a net producer of recycled material, and a credit can be applied for the vir-
gin material that is displaced by the surplus recovered material.

3.4.4 Converting Scrap
Scrap that is generated during material converting processes is referred to
as postindustrial or preconsumer scrap. Unlike postconsumer scrap, pre-
consumer material has not had a previous useful life in a product, so there
is no previous life to allocate virgin material burdens. However, the mate-
rial is often degraded to some extent during the converting process. For
example, the material may have been coated, had colorants added, or been
glued or laminated to other materials. The industrial scrap material usually
requires some degree of reprocessing before it can be used to produce a use-
ful product.
If the converting scrap is utilized internally at the same facility in the same
process that produced the scrap, then this internal recycling simply reduces
the net amount of virgin inputs required per unit of product output, and no
allocations are needed. The process burdens for manufacturing the primary
product should include the added burdens for any reprocessing of internal
scrap before it is returned to the process (e.g., regrinding of plastic molding
scrap before it is put back into an extruder).
If the scrap is used outside the boundaries of the system that produces the
scrap, then there are different approaches that can be used to allocate the virgin
material burdens associated with the scrap material. It is important to distin-
guish between the burdens associated with production of the material content
of the scrap and the burdens associated with the process that generates the
scrap. The burdens for the converting process that generates the scrap should
be assigned to the primary product, since the converting process adds no value
to the scrap material and usually reduces its value. For example, the processes
of applying coating to cartonboard and cutting it into carton blanks are done
for the purpose of producing a finished carton blank, so the environmental
burdens for these processes should be assigned to the carton blanks. The coat-
ing on the trim scrap generated from the converting process reduces the value