Microgel polymer composite fibres

Doctoral thesis English OPEN
Kehren, Dominic (2014)
  • Publisher: Publikationsserver der RWTH Aachen University
  • Subject: Mikrogel | Nanofaser | Elektrospinnen | Miniemulsion | Naturwissenschaften | Kompositfasern | degradable Materialien | microgel | nanofiber | electrospinning | degradable materials
    • ddc: ddc:500

In this thesis some novel ideas and advancements in the field of polymer composite fibres, specifically microgel-based polymer composite fibres have been achieved. The main task was to investigate and understand the electrospinning process of microgels and polymers and the interplay of parameter influences, in order to fabricate reproducible and continuously homogenous composite fibres. The main aim was to fabricate a composite material which combines the special properties of polymer fibres and thermo-sensitive microgels, as well as properties given by the specific choice of the fibre polymer and the microgels co-monomers. Furthermore, these fibres are supposed to enable a macroscopic access to the microgel properties, because their usual dispersion state is not applicable for many tasks, but a macroscopic fibre nonwoven consisting of microscopic fibres decorated with nanoscopic microgels will provide this opportunity, without losing the “nano” aspect. In a first step, using PVA it was already shown that the microgels retain their thermo-sensitive, smart swelling properties in the fibre structure, which gives the fibres tuneable swelling properties as well. Additional ways to crosslink these fibres chemically or physically are shown. In the next step, PCL, a polymer with more special properties (hydrophobic, degradable), was chosen to achieve fibres with these properties and to show how much these properties can be influenced by the addition of microgels. Moreover, different fibre morphologies have been fabricated, fibres with microgels located only in the core and fibres with microgels located only on the surface, which not only show differences in the tuneable swelling behaviour and the degradation process, but it also opens opportunities to more specific applications. The different morphologies were achieved by using different solvent systems: methanol/toluene and chloroform/DMF. Additionally, it should be mentioned that the simple one step electrospinning process of hydrophilic microgels and hydrophobic PCL gives access to an elegant way to completely change the hydrophobicity of the general polymer fibres. To give a possibility for a better exploitation of the newly achieved PCL fibres with microgel exclusively on the fibre surface, microgels with a special property combination have been created: microgels, crosslinked with a star-shaped acrylate-functionalised poly(epsilon-caprolactone) crosslinker, that are degradable due to the same functionality as PCL, having additionally hydrophobic domains to immobilise hydrophobic drugs. The synthesis was done via a specialised miniemulsion polymerisation and uptake as well as release of ibuprofen was shown. Fibres with these microgels on the surface could deliver drugs targeted to specific places and are completely degradable under physiological conditions. The results of a preliminary study for a project with the aim of creating PLA based stents, with a neutral degradation process for a higher tolerance in the human body. A combination of VIm modified microgels with polylactide fibres was chosen to achieve this. The fibres are successfully realised and analysed regarding their swelling properties, in the same manner as the other composite fibres presented in this work. Two small preliminary studies about different topics, which are still in an early stage, but that already show promising results are also presented in this thesis. Fibres with iron(III) oxide nanoparticles and phosphazene microsphere have also been fabricated using the same technique shown for the PCL-microgel fibres with microgel exclusively on the surface. These fibres give an insight in the process and show its limitations and possibilities. Furthermore, hollow fibre membranes with microgels as additive have been prepared using a wet spinning process, to show other options to fabricate composite materials with microgels, accessing the field of filtration and separation.
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