Polyethylene terephthalate (PET) is the most important mass‐produced thermoplastic polyester used as a packaging material. Recently, thermophilic polyester hydrolases such as TfCut2 from Thermobifida fusca have emerged as promising biocatalysts for an eco‐friendly PET recycling process. In this study, postconsumer PET food packaging containers are treated with TfCut2 and show weight losses of more than 50% after 96 h of incubation at 70 °C. Differential scanning calorimetry analysis indicates that the high linear degradation rates observed in the first 72 h of incubation is due to the high hydrolysis susceptibility of the mobile amorphous fraction (MAF) of PET. The physical aging process of PET occurring at 70 °C is shown to gradually convert MAF to polymer microstructures with limited accessibility to enzymatic hydrolysis. Analysis of the chain‐length distribution of degraded PET by nuclear magnetic resonance spectroscopy reveals that MAF is rapidly hydrolyzed via a combinatorial exo‐ and endo‐type degradation mechanism whereas the remaining PET microstructures are slowly degraded only by endo‐type chain scission causing no detectable weight loss. Hence, efficient thermostable biocatalysts are required to overcome the competitive physical aging process for the complete degradation of postconsumer PET materials close to the glass transition temperature of PET.

The efficient handling of wastewater pollutants is a must, since they are continuously defiling limited fresh water resources, seriously affecting the terrestrial, aquatic, and aerial flora and fauna. Our vision is to undertake an exhaustive examination of current research trends with a focus on nanomaterials (NMs) to considerably improve the performance of classical wastewater treatment technologies, e.g. adsorption, catalysis, separation, and disinfection. Additionally, NM-based sensor technologies are considered, since they have been significantly used for monitoring water contaminants. We also suggest future directions to inform investigators of potentially disruptive NM technologies that have to be investigated in more detail. The fate and environmental transformations of NMs, which need to be addressed before large-scale implementation of NMs for water purification, are also highlighted.

Removing pollutants from water by using the photocatalyst TiO 2 is a highly-promising method. A large amount of work has been done to increase the activity of TiO 2 , whereas the main two findings are increasing the surface area and applying mixed phase modifications (anatase, brookite, and rutile). Here, we present a method to directly synthesize non-agglomerated TiO 2 nanoparticles with different crystal phase ratios via low temperature dissolution-precipitation (LTDRP) on a porous microfiltration membrane (polyethersulfone). The amount of hydrochloric acid and the temperature was varied between 0.1-1 M and 25-130 • C, respectively, while the concentration of titanium precursor (titanium(IV) isopropoxide) was kept unchanged. The TiO 2 nanoparticles and the membrane were thoroughly characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), measuring the water contact angle and permeation flux, and examining the degradation of methylene blue. The mixed phase anatase/brookite with a main component being anatase exhibited the highest photocatalytic activity in removing methylene blue. Higher synthesis temperature induces enhanced crystallinity and, subsequently, the degradation rate of methylene blue was improved. Additionally, the photocatalytic activity remains high and unchanged for up to nine repeated cycles, i.e., full recovery of the photocatalytic properties is sustained.

Polyurethanes (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.

Poly(ethersulfone) membranes were surface modified in a one-step procedure. For this purpose, the membranes were soaked with aqueous solutions of different low-molecular weight molecules bearing diverse hydrophilic functionalities and subject to electron beam treatment. No catalysts, photoinitiators, organic solvents or other toxic reagents were used, and no additional synthetic or purification steps were required.

Electron-beam-induced grafting of hydrophilic polymers was applied to modify PVDF membranes for biomedical applications. Grafting was performed by immersing the membrane in an aqueous solution of different hydrophilic polymers followed by electron-beam irradiation. The two polymer types are able to cross-link by recombination of adjacent radicals formed via the irradiation. Although the untreated membrane was already quite hydrophilic, the modification resulted in even lower water contact angles at the membrane surface indicating improved water wettability. The presence of different functional groups originating from the hydrophilic polymers was detected on the membrane surface by electrokinetic measurements. SEM investigations as well as porosimetry experiments showed that the grafted hydrophilic polymer layer is very thin; therefore, the membrane pore structure is not negatively affected. Soxhlet extraction revealed the stability of the modification for selected polymers: surface contact angles were comparable after extraction, and total organic carbon investigation of the extraction water revealed no significant loss of organic material. Investigated mechanical properties confirmed an increased stability due to cross-linking of the polymers. Undesired hemolysis was not detected with hemocompatibility tests, and coagulation was decreased with selected hydrophilic polymers. Because of the absence of any toxic material during surface modification and the high stability of the product, this method is believed to be suitable for the modification of membranes for medical applications, e.g. for improving the hemo-or biocompatibility.

No abstract

Abstract:In 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.