Self-healing polymers and nanocomposites

Synthesis and properties of self-healing polymers and nanocomposites derived from cellulose

Universität des Saarlandes

Self-healing materials will be constructed by thermoreversible crosslinking of three components (a) cellulose derivatives, (b) flexible spacers, and (c) inorganic nanoparticles using the Diels-Alder (DA) reaction. Derivatisation of native cellulose will lead to processible liquid-crystalline polymers with pending furane substituents. Flexible oligomeres (e.g., PEG) will be terminated with maleimide groups. Also various inorganic nanoparticles (e.g., SiO2 and metal oxides) will be functionalized covalently with maleimide or furane groups. Crosslinked materials will be furnished from these three components by heating to around 60 °C by DA reaction. Heating to higher temperatures (around 130 °C) will lead to retro-DA reaction and allow self-healing of these materials. The purpose of cellulose is to achieve highly oriented specimen with high modulus and tensile strength. The introduction of flexible spacers should avoid brittleness of the material. The purposes of the nanoparticles are to limit crack propagation and to allow internal heating by alternating external electromagnetic fields to perform DA or retro-DA reactions. A homogeneous distribution of the components in the sample will be very important for the success of our concept. Self-healing efficiency will be tested by mechanical measurements of standardized specimen. Formation and healing of cracks will be observed by light and electron microscopy. On the long term, we attempt to mimic the mechanical properties of natural hierarchically ordered cellulosic systems, such as wood, showing the additional advantage of thermal processability.