bumpers that deform and recover rather than crack
and splinter, computer cases that withstand the occasional
rough encounter, and resilient coatings that can
withstand the ravages of the sun, may all be possible
if tiny functionalized rubbery particles are imbedded
in their plastic matrices, according to Penn State
"Plastics such as polypropylene, nylon, polycarbonate,
epoxy resins and other compounds are brittle and
fracture easily," says Dr. T.C. Chung, professor
of materials science and engineering. "Usually, manufacturers
take rubbery compounds and just mix them with the
plastic, but there are many issues with this approach."
The problems include difficulty in controlling the
mixing of the two components and adhesion between
the plastic and rubber. Chung, and Dr. Usama F. Kandil,
postdoctoral researcher in materials science and
engineering, looked at another way to embed rubbery
particles into a plastic matrix. They described their
work today (Aug. 29) at the 230th American Chemical
Society National Meeting in Washington, D.C.
The researchers used polyolefin ethylene-based elastomer,
a very inexpensive stable rubber that withstands
exposure to ultra violet radiation. This rubber is
often used as the sidewall in many automotive tires.
However, rather than simply produce micro particles
of polyolefin, Chung and Kandil produce a core-shell
particle structure with a tangle of polymerized polyolefin
rubber forming a ball with functionalized groups
hanging out like bristles.
"These functional groups can combine with the plastic
and improve the adhesion of the rubber with the plastic," says
Chung. The rubber particles embedded in other materials
absorb some of the energy of impact. Rather than
the brittle portion breaking on impact, the rubber
parts deform and absorb the energy without breaking.
Chung and Kandil believe if they can introduce the
rubber particles into other materials, such as ceramics,
the rubber would function in the same way, making
resilient ceramics. Plastics and rubbers are both
polymers, but have one significant difference. Plastics
have relatively high glass transition temperatures – the
temperature at which the materials cease being pliable
and become brittle like glass. Rubbers, especially
polyolefin, have very low glass transition temperatures.
"Tires never freeze above glass transition temperature," says
Chung. "So the material is always in a pliable state
at ambient temperatures. This can improve the toughness
of any material."
The functionalized groups on the outside of the
rubber balls can be tailored to join with any plastic
or ceramic, solving the problems of adhesion found
when using only untailored rubber particles. These
core and shell particles range in size from 30 nanometers
to 10 micrometers.
researchers manufacture their tiny rubber balls
in a one-pot procedure that causes the rubber components
to cross-link into the shape of a tiny rubber ball
with their functional groups intact. Addition of
a surfactant – a soap-like compound – causes the
polymers to entangle into a ball with some of the
functional groups sticking out from the surface.
By controlling the process, the researchers can control
the size of the particles from micron-sized to nano
The researchers have applied for a provisional patent
on this work.
Contact: A'ndrea Elyse Messer