MATERIAL SPECIAL New
self-healing plastics developed through crosslinking reaction
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Self-healing
materials can repair themselves by restoring their initial molecular
structure after the damage. Scientists of the Karlsruhe Institute of
Technology and Evonik Industries have developed a chemical crosslinking
reaction that ensures good short-term healing properties of the material
under mild heating. The research results have now been published in the Advanced
Materials journal. The KIT group headed by Christopher Barner-Kowollik
uses the possibility of crosslinking functionalized fibres or small molecules
by a reversible chemical reaction for the production of self-healing
materials. These so-called switchable networks can be decomposed into their
initial constituents and reassembled again after the damage. The advantage is
that the self-healing mechanism can be initiated any time by heat, light or
by the addition of a chemical substance. "Our method does not need any
catalyst, no additive is required," Prof. Barner-Kowollik says.
Excellent healing properties in few minutes
It
took about four years of research for the working group of Barner-Kowollik,
together with the Project House Composites of Creavis, the strategic
innovation unit of Evonik, to develop a novel polymer network. At comparably
low temperatures from 50°C to 120°C, the network exhibits excellent healing
properties within a few minutes. Reducing the time needed for healing and
optimizing the external conditions, under which the healing process takes
place, are the major challenges of research relating to self-healing
materials. Using the healing cycle developed by them, the KIT researchers
have found a large number of intermolecular compounds that close again within
a very short term during cooling.
Mechanical
tests, such as tensile and viscosity tests, confirmed that the original
properties of the material can be restored completely. "We succeeded in
demonstrating that test specimens after first healing were bound even more
strongly than before," Barner-Kowollik says.
The
self-healing properties can be transferred to a large range of plastics
known. Apart from self-healing, the material is given another advantageous
property: As flowability is enhanced at higher temperatures, the material can
be molded well. A potential field of application lies in the production of
fiber-reinforced plastics components for automotive and aircraft industries.
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CHWKLY 140422