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 Bioplastics
Mirel Structure and Properties
3. Mechanical Properties
Metabolix Mirels cover an enormous range of physical properties. The following
chart shows the range of tensile strength and elongation at break for
unformulated Mirels when tested according to ASTM D 638-01. Mirels can behave
both as traditional thermoplastic polymers and as elastomers. While
some polymers such as polyethylene, flexible PVC, and thermoplastic
elastomers have high elongation at break figures, they yield irreversibly
at high levels of extension. Metabolix has developed truly elastomeric
grades that have high levels of recovery (typically >80-90%), even
under high levels of deformation (e.g. > 500% ultimate elongation
at break). These materials can be used for adhesives, stretch coatings,
and fibers, and have properties competing with some vulcanized rubbers.
4. Surface Energy
The surface energy of a polymer film is an extremely important property
for printability or lamination. For example polyolefin films produced
directly from blown or cast film processes have very low surface energies
that make high quality printing extremely difficult. The surface has
to be chemically modified (usually by flame or corona treatment) to
introduce polar groups onto the surface for improved adhesion of the
printing inks. Similarly, the surface of polyethylene terephthalate
(PET) film has to be coated to provide surfaces suitable for printing
or heat sealing (microwave food products).
The following chart shows that, to a first approximation, there is a
linear relationship between the average length of the alkyl side chain
and the surface energy. This means that Mirels can be constructed with
surface energies ranging between those of PP and PET.
• Molecular Weight • Thermal
Properties • Mechanical Properties • Surface Energy • Gas Barrier Properties • Biodegradability • Stability
to hydrolysis • UV Stability
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