Electronics and Computer Scrap
Almost 100 billion pounds of plastics are produced in the U.S. each year, and these
include such common materials as polyethylene, polypropylene, polystyrene and PVC;
these are routinely turned into fibers, films, tubing, containers, and molded articles. From
the viewpoint of both energy and resource conservation and environmental protection, it
is desirable to recycle and reuse as much of the plastic as possible. Indeed, there have
been large programs directed at recycling nylon carpet fibers, polyethylene milk jugs and
PET beverage bottles. However, these efforts are hampered by the low resale value and
poor quality of the recycled materials, especially in an environment where high-quality
virgin polymers are freely available at lower cost. It is, therefore, logical to blend
recovered plastics with virgin plastics, but it should be noted that for a material to be
termed "green" it must have a reasonably high recycle content. Additionally, any materia
must satisfy all performance requirements for the intended application.
In this research, we have focused on recycling plastics used in electronic applications
such as computer and printer housings. There are two reasons for this choice: (i)
Computers are discarded after only three or four years of use, and a large amount of
plastic is likely to end-up in landfills; this material may have to be treated as hazardous
waste due to contamination with mercury and lead that are found in computers and
computer monitors. (ii) The plastics used in electronic applications are polymers such as
acrylonitrile-butadiene-styrene (ABS), polycarbonate (PC) and their blends, and these are
relatively expensive polymers. Attempting to recover and reuse ABS and PC is
economically less challenging than recycling polyethylene and polypropylene. A total of
about 150 million pounds of such plastic goes into electronic applications each year.
Objective
The key challenge in recycling polymers used in computers is that a given computer
housing contains more than one kind of plastic. Also, different computer makers do not
use the same polymer for the same application; the choice typically depends on the price
and performance behavior of an available polymer. The result is that a facility built to
recycle electronic polymers has to deal with mixed polymer waste. Unfortunately, mixed
plastics have unacceptably poor mechanical, flow and thermal properties. As a
consequence, recovered (but mixed) material cannot be reused to make new computer
housings. Mixed waste must be separated by chemical type before any recycling is
attempted, and a relevant question is the purity level that must be achieved in such a separation process. Furthermore, the separated material has to be standardized.
This is
because polymers are large molecules, and there is typically a distribution in sizes in any
given sample. Unless this size distribution can be kept the same, flow properties vary
from batch to batch. The initial objectives of our work have, therefore, been to determine
the necessary purity level of separated polymers and to come up with a strategy for
standardizing the size distribution in the recovered material.
Approach
The general approach to the recycling of mixed plastics is to grind the plastic parts
into small chunks, remove labels and non-plastic parts, and then to use wet processing to
separate the different plastics by chemical type to different purity levels. Each of the
different plastics is then melted in an extruder where it is mixed with various additives
and converted into little pellets that can be processed back into moldings. The effect of
purity level and the subsequent compounding operation can be assessed by measuring the
mechanical, thermal and flow properties of the compounded and pelletized polymer.
Conservation benefits of appliance recycling
Even when landfilled properly, electronic equipment poses a threat to environmental and public health. Reusing and recycling electronic equipment reduces the amount of toxic and hazardous substances that may enter the environment through disposal. By extending the useful life of products, reuse conserves the energy and raw materials needed to manufacture new products.
17.04.2007. 00:05
This article hasn't been commented yet.
Write a comment