Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

This thesis focussed on understanding the relationship between the structure and the properties of a partially soluble polymer, PEDOT, in a suspension of EG. In this suspension, conjugated structures of amorphous and crystalline phases of PEDOT are formed with EG. Solution-induced crystallization of the suspension was investigated in situ in order to study the effects of PEDOT concentration and temperature on the final properties. Firstly, the conductivity of solid PEDOT was studied by using a dielectric set-up. The conductivity was shown to be limited due to the low amount of dopant added during synthesis of PEDOT. However, it was demonstrated that a slower cooling rate of the crystallization process could significantly enhance the resulting conductivity. The established increase in the conductivity was linked to the larger fraction of the crystalline phase by DSC analysis. The conductivity could be increased by approximately three decades by decreasing the cooling rate from 5 to 0.1 °C/min. This was calculated to correspond to a crystallinity increase of around 30 %. Secondly, the influence of concentration and temperature was investigated by performing rheological and conductivity experiments. In order to do so, the suspension preparation was optimized by focussing on decreasing the aggregate size, which mainly influenced the sedimentation rate and suspension stability. Rheological experiments showed that a rheological percolation was achieved at a concentration of 10 mg/mL, resulting in an increase of the storage modulus by approximately three decades. Conductivity experiments did not show a significant increase at these conditions. However, at a concentration of 40 mg/mL, a twofold increase of conductivity could be obtained. A study of the influence of temperature on the rheological percolation kinetics was performed to ascertain the optimal temperature for solution-induced crystallization, which followed an Arrhenius dependency. Finally, the contribution of the amorphous and crystalline phases to the bulk properties were separated by heating above the melting temperature. At these conditions, rheological experiments showed that the rheological percolation was destroyed. This indicated that the rheological percolation was mostly formed by the connectivity of the crystalline phase of PEDOT. At similar conditions, a concurrent change in the conducting properties was however restricted.

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

The Rare Earth Elements (REEs), including europium and yttrium, are classified as critical materials with a large supply risk. Therefore, it becomes important to recycle end-of-life products containing these elements to close the loop. Photochemical recycling in organic and aqueous media is studied before in batch reactors, but was not yet fully optimized to be used in a continuous manner that is more aimed towards industrial applications. An assessment of separation of Eu and Y was done in methanol using dibuthylphosphate. The aim was to use a two-stage process for the separation whereby the first step includes the photoreduction of Eu(III) and the second step deals with the precipitation of Y that could be separated in space using two separate reactors. This assessment did not yield favourable results for this principle and alternatives in the separation such as the use of extractants, selective crystallisation or selective precipitation were not suitable for Eu/Y separation. The two-stage procedure as explained before could not be used as photochemical reduction and precipitation in aqueous media are inherently connected in the principle, which means that clogging in the reactor should be avoided. A model for photochemical reactors was derived, making it possible to determine the outflow of the reactor based upon the feed concentration as well as determining the reaction rate at each point in the reactor and optimizing the reactor for best light distribution and utilisation. The model is used to estimate the conversion in the continuous flow reactor. The reactor was build using a low-pressure mercury lamp (LPML) which was used to asses the separation of Eu and Y. Separation was achieved faster up to a factor 40 for space-time and space-time yield for removal up to 50\% of the available Eu in solutions containing no Y. The reactor was constructed as such that the light was used more efficiently as the photochemical space-time yield (PSTY) is 20 times better at 50\% removal of Eu. The model as derived before matched the results seen in the continuous flow reactor well up to 50\% recovery of Eu, after this point, deviations started to occur as the model did not account for solid particles, gas bubbles and dark spots in the reactor. Only 75\% conversion was achieved in the current reactor with a possibility to achieve a higher conversion at higher retention times, but with large deviations compared to the model. Reducing the amount of dark spots in the reactor by pulsing the feed did not yield an increase in conversion, but by seeding the reactor an increase from 33\% to 42\% conversion was seen at the same residence time. Separation of Eu/Y solutions was assessed as well. Artificial YOX solutions (having the same composition as YOX, but with lab-grade chemicals) were introduced into the reactor, but separation was poor as only 25\% conversion was observed with a decrease at higher residence times due to clogging of the reactor. Reaction rate was higher compared to batch results, but this was not truly comparable as no near full conversion could be achieved. As YOX was introduced in the reactor, no conversion of Eu was measured, batch results did already confirm difficult separation as an increased induction time was seen. It is likely that the induction time was longer than the residence time of the YOX in the reactor. YOX separation was more difficult than recovery of Eu from solutions without Y. Y does not react or interfere with