Polybenzoxazine based high performance nanofibers via electrospinning
Polybenzoxazines are newly developing phenolic type thermoset resins having fascinating properties which overcome the shortcomings of the traditional resins. In recent years, polybenzoxazines are attracting much interest because of their outstanding features, such as near-zero volumetric change upon curing, no by-products during curing, low water absorption, high glass transition temperature and high char yield. In addition, the molecular structure of polybenzoxazines facilitates immense design flexibility which enables tailoring the properties of the cured material for a wide range of application. Electrospinning is a widely used simple and cost-effective technique to produce nanofibers from various polymers, polymer blends, inorganic materials, supramolecular structures and composites. In principle, a continuous filament is formed from polymer solution or melt under high electric field which resulted in fibers with diameters ranging from tens of nanometers to few microns. Nanofibers produced with electrospinning technique show unique physical/chemical properties due to their very high surface area and nanoporous structures. In this thesis, we have produced polybenzoxazine based high performance nanofibrous materials via electrospinning by using two approaches. In the first approach, main-chain polybenzoxazines (MCPBz) were synthesized to produce bead free and uniform nanofibers without using polymeric carrier matrix. However, it was observed that these nanofibers lost the fiber morphology at low temperatures and they formed film before cross-linking. Subsequently, novel photo/thermal curable MCPBz resins were designed and synthesized readily owing to the design flexibility of polybenzoxazines in order to enhance thermal stability of MCPBz nanofibers. Therefore, firstly photo curing was performed to improve the thermal stability of nanofibers and then, thermal curing was carried out at high temperatures to obtain cross-linked MCPBz nanofibers with good thermal and mechanical properties. In addition, it was shown that these cross-linked and highly porous MCPBz nanofibers are very stable in various organic solvents, highly concentrated acid solutions and at high temperatures which make these nanofibers quite useful for the certain filtration applications requiring high temperatures and harsh environmental conditions. In the second approach, we produced polybenzoxazine based composite nanofibers from both polymeric materials and non-polymeric systems (cyclodextrins) with enhanced thermal and mechanical properties. At the same time, PAHs, dye molecules and heavy metal ions removal experiments were performed with polybenzoxazine based composite nanofibers to demonstrate their potential application for the waste water treatment.