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A tubular co-flow reactor to produce macroporous polymer beads by polymerization of medium and high internal phase emulsion (M/HIPE) templates was developed. This reactor allows for improved production rates compared to tubing based microfluidic devices. Water-in-oil (W/O) M/HIPEs, containing methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA) monomers in the continuous phase, were injected into a re-circulating carrier phase. The continuous phase of the emulsion droplets was UV polymerized in situ, resulting in polyM/HIPE beads. The emulsion composition was adjusted to produce poly(MMA-co-EGDMA) porous polymer beads with a protective crust and an interconnected internal pore structure. HCl loaded beads were produced by adding the active ingredient into the dispersed emulsion phase, leading to HCl encapsulation in the porous structure of the beads after polymerization. Even after exposure to ambient conditions for 24 h, 60% of the HCl remained in the beads, indicating good encapsulation efficiencies. Thus, it is possible to use such macroporous beads as delivery vehicles.

Micromixers made from emulsion templated macroporous polymers (poly-Pickering-HIPEs) were used to continuously produce polymerizable high internal phase emulsions (HIPE) by injecting a monomer containing continuous phase and aqueous internal phase into micromixers. The interconnected and complex flow path through poly-Pickering-HIPE micromixers resulted in effective mixing by creating local vortices and shear. The emulsion phase volume fraction of the produced HIPE templates can be varied during the process. PolyHIPEs with a porosity gradient ranging from 74% to 89% were produced by altering the phase volume ratio during the emulsification in poly-Pickering-HIPE micromixers. The average pore size of the produced polyHIPEs can be tailored by using poly-Pickering-HIPE micromixers with degrees of interconnectivity ranging from 0.028 to 0.06. The lower the degree of interconnectivity of the micromixer the smaller the droplet size of the produced HIPEs and thus the average pore size of the resulting polyHIPEs.

The abstract is available here: https://uscholar.univie.ac.at/o:1633047

Polyetheretherketone (PEEK) is a high-performance semi-crystalline thermoplastic polymer with outstanding mechanical properties, high thermal stability, resistance to most common solvents, and good biocompatibility. A high temperature thermally induced phase separation technique was used to produce PEEK foams with controlled foam density from PEEK in 4-phenylphenol (4PPH) solutions. Physical and mechanical properties, foam and bulk density, surface area, and pore morphology of foamed PEEK were characterized and the role of PEEK concentration and cooling rate was investigated. Porous PEEK with densities ranging from 110 to 360 kg/m

The abstract is available here: https://uscholar.univie.ac.at/o:1586494

Flexible epoxy foams were successfully prepared by curing medium internal phase emulsions (MIPEs) with a continuous organic phase containing epoxy resin and hardener, surfactant and carbon nanotubes and an aqueous internal phase. Curing the MIPEs at ambient temperature resulted in interconnected polyepoxide foams with average pore size of about 10 μm, while curing the MIPEs (with carbon nanotubes as a thickening agent) at 50 °C resulted in epoxy foams with pore sizes of one magnitude higher. The polyepoxide foams were compressible up to a strain of 70% of their original height and did not fracture. The polyepoxide foams were resilient with energy loss coefficients ranging from 40% to 60%, representing their energy adsorption during cyclic loading.

There is increasing focus on the development of bioactive scaffolds for tissue engineering and regenerative medicine that mimic the native nanofibrillar extracellular matrix. Solution blow spinning (SBS) is a rapid, simple technique that produces nanofibers with open fiber networks for enhanced cell infiltration. In this work, highly porous bioactive fibers were produced by combining SBS with thermally induced phase separation. Fibers composed of poly(d,l-lactide) (PLA) and dimethyl carbonate were sprayed directly into a cryogenic environment and subsequently lyophilized, rendering them highly porous. The surface areas of the porous fibers were an order of magnitude higher in comparison with smooth control fibers of the same diameter (43.5 m2·g–1 for porous fibers produced from 15% w/v PLA in dimethyl carbonate) and exhibited elongated surface pores. Macroporous scaffolds were produced by spraying water droplets simultaneously with fiber formation, creating a network of fibers and ice microspheres, which act as in situ macroporosifiers. Subsequent lyophilization resulted in three-dimensional (3D) scaffolds formed of porous nanofibers with interconnected macropores due to the presence of the ice spheres. Nanobioactive glass was incorporated for the production of 3D macroporous, bioactive, therapeutic-ion-releasing scaffolds with potential applications in non-load-bearing bone tissue engineering. The bioactive characteristics of the fibers were assessed in vitro through immersion in simulated body fluid. The release of soluble silica ions was faster for the porous fibers within the first 24 h, with confirmation of hydroxyapatite on the fiber surface within 84 h.

Macroporous, low-density polyetheretherketone, polyetherketoneketone, and polyetherimide foams are produced using a high-temperature, thermally induced phase separation method. A high-boiling-point solvent, which is suitable to dissolve at least 20 wt% of these high-performance polymers at temperatures above 250 °C, is identified. The foam morphology is controlled by the cooling procedure. The resulting polymer foams have porosities close to 80% with surface areas up to 140 m2 g-1 and elastic moduli up to 97 MPa.

The surface properties of original high strength and preoxidized high modulus carbon fibers were altered by electrocopolymerizing acryl amide and carbazole and therefore depositing a copolymer coating onto the fibers. Scanning electron microscopy and zeta-potential measurements confirmed the presence of a rough but dense and continuous electrocoating with a basic surface character. Therefore, ‘good’ adhesion behavior between the electrocoated carbon fibers and an epoxy resin matrix should be expected. The interfacial adhesion was measured using the single fiber pull-out and single fiber indentation test. It was shown that only ‘intermediate’ adhesion was present between the carbon fibers and the electrocoating, but superior adhesion between the coating and epoxy resin exists. The single fiber model composites always failed at the fiber/electrocoating interface. However, as shown by using the indentation test, the interfacial adhesion between fibers and electrocoating can be significantly improved if preoxidized fibers are used as substrate for electropolymerization. A very high tensile strength for the electrocoating can be expected as derived from the single fiber pull-out tests.

High Internal Phase Emulsions (HIPEs) are important for a wide range of applications in the food, cosmetic, pharmaceutical and petroleum industries. If the continuous phase is polymerizable, HIPEs can be used as templates for the synthesis of highly porous polymers with potential applications as low weight structures or scaffolds in tissue engineering. HIPEs are characterized by a minimum internal phase volume ratio of 0.74 but Lissant first defined this minimum as 0.7. HIPEs consisting of a continuous organic phase and an internal aqueous phase (w/o emulsion), are commonly stabilized by large amounts of surfactants. Particle-stabilized emulsions also known as Pickering-emulsions have recently attracted much interest. Unlike surfactants, particles irreversibly adsorb at the interface of emulsions due to their high energy of attachment which makes them good emulsifiers. The ability of particles to adsorb at the interface between the two phases is primarily dependent on the wettability of the particles. Hydrophilic particles such as metal oxides tend to stabilize o/w emulsion while hydrophobic particles such as carbon tend to stabilize w/o emulsions. Nevertheless, it is possible to modify the wettability of particles by adsorbing surfactant molecules onto the particle surfaces or by silanation. All reports on particle-stabilized emulsions deal with emulsions having internal phase levels elow 70 vol.-%. Kralchevsky et al. developed a thermodynamic model, which predicts that

High temperature activation of carbon nanotubes (CNTs) provides a new and highly versatile functionalisation strategy. The reaction allows the attachment of a wide variety of functional species onto the nanotube surface at grafting ratios between 1–8 wt%, whilst maintaining the intrinsic properties of the untreated materials. The underlying, radical-based, reaction mechanism has been established by quenching experiments and EPR studies. The distribution of the functionalised sites has been investigated at the microscopic scale using tagging reactions. The grafted products have been characterized by electron microscopy, thermal analysis (TGA), Raman spectroscopy, and inverse gas chromatography (IGC). The change in the CNT surface properties after grafting has been quantified in terms of dispersive and specific surface energies, and altered dispersibilities in a broad range of solvents. It is possible to carry out the reaction using gas phase reagents, providing a clean, efficient, and scalable methodology, relevant to a diverse range of applications.

Fully renewable macroporous thermosetting and UV-cured cellulose nanocomposites have been synthesized from medium and high internal phase water-in-acrylated soybean oil emulsions stabilized solely by hydrophobized bacterial cellulose nano-fibrils.

Hybrid sol–gel inorganic–organic fibres offer great potential in tissue engineering and regenerative medicine. A significant challenge is to process them using scalable technologies into useful scaffolds that provide control over fibre diameter, morphology, mechanical properties, ion release, degradation and cell response. In this work we develop formulations that are amenable to processing via solution blow spinning (SBS), a rapid technique using simple equipment to spray nano-/micro-fibres without any electric fields. The technique is extended to produce porous class I and II hybrid fibres using cryogenic SBS, with formulations developed based on tetraethyl orthosilicate/gelatin that are relatively facile to lyophilise. The formulations developed here take advantage of the reversible thermally activated conformation change of gelatin in aqueous solutions from random coil to triple helix to enable viscosity tuning and therefore fibre spinning. Gelatin is functionalised with (3-glycidyloxypropyl)trimethoxysilane to produce class II hybrids which exhibit controllable time- and temperature-dependent viscosity profiles which can be tuned for spinning into highly porous fibres.