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- ItemCharge Separating Microfiltration Membrane with pH-Dependent Selectivity(Basel : MDPI, 2018-12-20) Breite, Daniel; Went, Marco; Prager, Andrea; Kuehnert, Mathias; Schulze, AgnesMembrane filters are designed for selective separation of components from a mixture. While separation by size might be the most common approach, other characteristics like charge can also be used for separation as presented in this study. Here, a polyether sulfone membrane was modified to create a zwitterionic surface. Depending on the pH value of the surrounding solution the membrane surface will be either negatively or positively charged. Thus, the charged state can be easily adjusted even by small changes of the pH value of the solution. Charged polystyrene beads were used as model reagent to investigate the pH dependent selectivity of the membrane. It was found that electrostatic forces are dominating the interactions between polystyrene beads and membrane surface during the filtration. This enables a complete control of the membrane’s selectivity according to the electrostatic interactions. Furthermore, differently charged beads marked with fluorescent dyes were used to investigate the selectivity of mixtures of charged components. These different components were successfully separated according to their charged state proving the selectivity of the invented membrane.
- ItemTailoring Membrane Surface Charges: A Novel Study on Electrostatic Interactions during Membrane Fouling(Basel : MDPI, 2015) Breite, Daniel; Went, Marco; Prager, Andrea; Schulze, AgnesIn this work we aim to show that the overall surface potential is a key factor to understand and predict anti-fouling characteristics of a polymer membrane. Therefore, polyvinylidene fluoride membranes were modified by electron beam-induced grafting reactions forming neutral, acidic, alkaline or zwitterionic structures on the membrane surface. The differently charged membranes were investigated regarding their surface properties using diverse analytical methods: zeta potential, static and dynamic water contact angle, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Porosimetry measurements proved that there is no pore blocking due to the modifications. Monodisperse suspensions of differently charged polystyrene beads were synthesized by a radical emulsion polymerization reaction and were used as a model fouling reagent, preventing comparability problems known from current literature. To simulate membrane fouling, different bead suspensions were filtered through the membranes. The fouling characteristics were investigated regarding permeation flux decline and concentration of model fouling reagent in filtrate as well as by SEM. By considering electrostatic interactions equal to hydrophobic interactions we developed a novel fouling test system, which enables the prediction of a membrane’s fouling tendency. Electrostatic forces are dominating, especially when charged fouling reagents are present, and can help to explain fouling characteristics that cannot be explained considering the surface wettability.
- ItemBio-Inspired Polymer Membrane Surface Cleaning(Basel : MDPI, 2017-3-9) Schulze, Agnes; Breite, Daniel; Kim, Yongkyum; Schmidt, Martin; Thomas, Isabell; Went, Marco; Fischer, Kristina; Prager, AndreaTo generate polyethersulfone membranes with a biocatalytically active surface, pancreatin was covalently immobilized. Pancreatin is a mixture of digestive enzymes such as protease, lipase, and amylase. The resulting membranes exhibit self-cleaning properties after “switching on” the respective enzyme by adjusting pH and temperature. Thus, the membrane surface can actively degrade a fouling layer on its surface and regain initial permeability. Fouling tests with solutions of protein, oil, and mixtures of both, were performed, and the membrane’s ability to self-clean the fouled surface was characterized. Membrane characterization was conducted by investigation of the immobilized enzyme concentration, enzyme activity, water permeation flux, fouling tests, porosimetry, X-ray photoelectron spectroscopy, and scanning electron microscopy.
- ItemDegradation of Polyester Polyurethane by Bacterial Polyester Hydrolases(Basel : MDPI, 2017-2-16) Schmidt, Juliane; Wei, Ren; Oeser, Thorsten; Dedavid e Silva, Lukas Andre; Breite, Daniel; Schulze, Agnes; Zimmermann, WolfgangPolyurethanes (PU) are widely used synthetic polymers. The growing amount of PU used industrially has resulted in a worldwide increase of plastic wastes. The related environmental pollution as well as the limited availability of the raw materials based on petrochemicals requires novel solutions for their efficient degradation and recycling. The degradation of the polyester PU Impranil DLN by the polyester hydrolases LC cutinase (LCC), TfCut2, Tcur1278 and Tcur0390 was analyzed using a turbidimetric assay. The highest hydrolysis rates were obtained with TfCut2 and Tcur0390. TfCut2 also showed a significantly higher substrate affinity for Impranil DLN than the other three enzymes, indicated by a higher adsorption constant K. Significant weight losses of the solid thermoplastic polyester PU (TPU) Elastollan B85A-10 and C85A-10 were detected as a result of the enzymatic degradation by all four polyester hydrolases. Within a reaction time of 200 h at 70 °C, LCC caused weight losses of up to 4.9% and 4.1% of Elastollan B85A-10 and C85A-10, respectively. Gel permeation chromatography confirmed a preferential degradation of the larger polymer chains. Scanning electron microscopy revealed cracks at the surface of the TPU cubes as a result of enzymatic surface erosion. Analysis by Fourier transform infrared spectroscopy indicated that the observed weight losses were a result of the cleavage of ester bonds of the polyester TPU.