Ask A Scientist Chemistry Archive

name         John A.
status       educator
age          40s

Question -   I am interested in knowing what is the best procedure to
melt recycled plastic and mixing it with fine recycled rubber crumb.
have given 10 students the task to manufacture a rubber mat using these
recycled products.
I want to use the recycled plastic as the binding agent mixed in with the
rubber crumb.
I believe that some recycled plastic is not conducive to melting , so I
would appreciate some information to what types of plastic recycled
material would best suit this process.
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Your inquiry raises a number of questions in addition to the one you asked
explicitly. There are two general types of plastics: thermosetting and
thermoplastic. The former will not melt when heated, just decompose and/or
oxidize; the latter will soften when heated. Rubber, Bakelite,
urea-formaldehyde copolymers are examples of thermosetting polymers; methyl
methacrylate (Plexiglas), polystyrene, polyethylene are examples of
thermoplastic polymers. Some acrylate, styrene, and polyethylene polymers
can be found in both thermoplastic and thermosetting forms. You will need to
use thermoplastic recycle.

When the thermoplastic polymer is heated, say in the range of 100-300 C. the
melt will be VERY viscous. You will require some heavy duty blending
equipment such as "dough" mixers, "roller" mills, or extruders. Otherwise it
will not be possible to obtain a uniform blend of binder polymer and rubber
crumb. In addition, these types of equipment are potentially very dangerous,
and should not be used by untrained personnel. Close supervision is a must.
You will need the elevated temperature also in order to "wet" the rubber
crumb with the binding polymer. Hot polymer melts are also VERY hazardous
because if they come into contact with skin, they cannot be wiped or brushed
off. They will cause serious deep burns.

The mixing process will have to be done with ventilating exhaust because
some of the polymers will de-polymerize (polystyrene and methyl methacrylate
for example) and/or contain volatile components that you cannot allow to be
released into the facility for safety reasons.

The crumb/binder ratio will have to be determined, if it has not been done
previously, because this will have a large effect on both the melt viscosity
and properties of the final product.

If the "mix" is made successfully, how will the mats be fabricated? What are
the wear properties of the mats -- both interior and exterior? That is, will
the mats leave black marks on light linoleum? Will the mats withstand the
abrasion of wiping sand and/or mud? Will the mats weather well -- that is,
withstand freeze/thaw cycling, water immersion, exposure to sunlight?

Yours is a pretty complex project that will require careful planning and
execution.

Vince Calder
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