Super non-adhesive membranes for sustainable water treatment – SUPERNAM

As planned we have started developping a microfluidic chip which would allow us to monitor the formation of fouling layers and their removal on surfaces modified by using co-polymer (di-block and tri-block synthesied at RDMCT in Taiwan).
In parallel we have developped a method for mapping the distribution of grafted polymers on a surface by ATR-FTIR, which seems very promising, as it helps to reveal heterogenities in the grafting density, which seems to be a key parameter highlightred by a new theoretical approach we have developped within the frame of the project.

As stated elsewhere, we have been able to maintain our objectives and follow the plan for a large part of the project.
Three families of copolymers were synthesized (di-blocks, tri-blocks and random) from base bricks, each with several molar masses, which gave a wide variety of possible solutions, all characterized chemically.
Essentially two modes of modification of membranes have been explored: the «coating« by adsorption of the copolymers and the blending of the copolymers before the manufacture of the membrane by inversion of phase by wet vapors. This part of the work has been reported on a mapping of possible membrane modification options, which is one of the project deliverables (D5).
As indicated, the microfluidic device could be realized and used but the results we were able to draw from it are below our expectations, despite a significant effort to develop and exploit it. In return, the use of the FTIR in «Mapping« mode, which was not foreseen, was the subject of numerous developments and an original publication (JMS 2016)
Membership measures could not be achieved by the project partners for technical reasons, but we were able to benefit from the collaboration of L Guttierez and JP Croue (Curtin Univ.), Who The observed differences between copolymers on a macroscopic scale.
We were able to test the membranes on wastewater in the laboratory, but we were not able to go as far as a large-scale production or a test under pilot conditions: One of the challenges today is to achieve this Part of the work, in order to test the effects of the modifications over the long term, the stability of the modifications in particular to the cycles of chemical cleaning of the membranes and the range of fluids that these membranes can treat while preserving good anti-adhesive properties.

During this project we were able to confirm the interest of the approach of surface modification of membranes provided that we choose precisely the bricks used for the modification and the base membrane support. We have not succeeded in completely eliminating adhesion, even on model media. A theoretical approach based on the physics of polymers offered an early explanation for this limitation, notably by highlighting the limitations inherent in the strategy chosen to avoid the adhesion of small molecules.
On the other hand, we have a much better understanding of the spatial structure of membrane modifications, which has allowed us to identify spatial heterogeneity at the submillimetric scale of the spatial properties of membranes as a lock to obtaining really resistant membranes To clogging, and to develop the appropriate technique for studying this parameter (FTIR-mapping).
This project, with its advances and conclusions, should lead to reorienting the work of the community towards the two aspects mentioned above, which constitute bottlenecks which can not be overcome if it is desired to obtain resistant membranes Clogging under industrial conditions.

* Surface Self-Assembled PEGylation of Fluoro-Based PVDF Membranes via Hydrophobic-Driven Copolymer Anchoring for Ultra-Stable Biofouling Resistance, N-J Lin, H-S Yang, Y Chang, K-L Tung, W-H Chen, H-W Cheng, S-W Hsiao, P Aimar, K Yamamoto and J-Y Lai, Langmuir 2013, 29, 10183-10193.
* Low-biofouling membranes prepared by liquid-induced phase separation of the PVDF/polystyrene-b-poly (ethylene glycol) methacrylate blend, Venault, A., Liu, Y.-H., Wu, J.-R., Yang, H.-S., Chang, Y., Lai, J.-Y., Aimar, P., 2014, J Membr Sci 450(2014)340-350.
* Fabricating hemocompatible bi-continuous PEGylated PVDF membranes via vapor-induced phase inversion, A Venault, J-RWu , Y Chang, P Aimar, J Membr Sci 470(2014)18–29.
* Hemocompatibility of PVDF/PS-b-PEGMA membranes prepared by LIPS process, Venault, A., Ballad, M.R.B., Liu, Y.-H., Aimar, P., Chang, Y., J Membr Sci, 477(2015)101-114
* Design of PVDF/PEGMA-b-PS-b-PEGMA membranes by VIPS for improved biofouling mitigation, Carretier, S., Chen, L.-A., Venault, A., (...), Aimar, P., Chang, Y., J Membr Sci, 510(2016)355-369.
* FTIR mapping as a simple and powerful approach to study membrane coating and fouling, Benavente, L., Coetsier, C., Venault, A., Chang Y, Bacchin, P., Aimar, P., J Membr Sci, 520(2016) 477-489.

Fouling takes today the largest share in the cost of building and running membrane processes for the production of drinking water or processing waste waters, for its impact on energy required, on downtime, cleaning chemicals and their disposal, membrane lifetime. Fouling cannot be avoided, but making it reversible would be a major impact in the way membrane water treatment processes, among others, are designed and run, in the cost of produced waters and mainly on the environment foot print. Therefore the project aims at developing a series of polymer membranes for the filtration of water or waste waters bearing super non-adhesive properties. By non-adhesive properties, we mean in this project that all types of component attachment mechanism would be made as reversible as possible. For this, our strategy is based on controlling two aspects of membrane properties: the physico-chemical properties of the material the membranes are made of and the pore structure of the final membranes, which also depends on the casting or spinning conditions.
Unlike many other studies which have been devoted to this question over the last ten years, we want to guide a) the synthesis of the polymers, b) the choice of the best way of attaching hydrophilic polymers onto a chemically and mechanically resistant matrix and c) the optimization of the membrane casting conditions by dedicated experiments allowing to assess the reversibility of fouling by a series of i) model solutes and particles, and ii) “real life” waters taken from water production plants or bio reactors.
In order to fulfill most of the requirements for industrial application, we have decided to work on a PVDF matrix which will provide the mechanical and thermal stability, which will be hydrophilized by adjunction of Poly ethylene glycol (PEGylation). A series of different copolymers will be synthetized on purpose. Various PEGylation routes will be explored and the propensity of the final material to adsorb macromolecules or attach to bacteria or colloidal particules will be assessed. This will require the development of specific micro-fluidics devices, simultaneously allowing the deposition and removal of fouling layer to be observed in real time and the flux / selectivity to be measured. Because this project is meant to generate a large number of membrane samples, each needing to be tested in different operating conditions, we plan to fit this design with parallel channels allowing to test several operating conditions at the same time.
This stage will help choosing polymers with excellent properties with regards to the reversibility of attachment of solutes / particles. Ultrafiltration or microfiltration membranes will then be prepared, and the preparation conditions will be explored so as to obtain a range of pore size and pore size distributions. These membranes will be characterized for their permeability and pore size distribution, and the reversibility of their fouling by e.g. surface waters and activated sludge will be assessed so as to select the optimal combination of material and structural properties.
A Taiwan-France workshop will be organized at the end of the project. Open to academics and industrialists, it will give a chance to share our conclusions and hopefully develop further the new material and processes with partners from Universities or Private companies.