Mitigation of Delamination Between Bilayer Membranes with Low Affinity to Enable Roll-to-Roll Fabrication

Single-layer membranes, despite their ease of fabrication and performance, often face material characteristic limitations that are employed for membrane fabrication, such as polymer fouling propensity and low mechanical strength. To mitigate such material drawbacks, bilayer membranes were developed to use multiple materials with the potential to mitigate the disadvantages of using a single material. When fabricating bilayer membranes with different polymers, varying affinities between the polymers can lead to significant challenges. Specifically, if the affinity between the polymers is low, delamination often occurs. This phenomenon poses a substantial limitation on the combinations of polymers that can be utilized in the construction of bilayer membranes. Understanding and addressing the affinity issues are crucial for membrane performance and expanding the range of applicable materials. This work explores the behavior of two low-affinity polymeric membrane materials: polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) and polysulfone (PSf), which are prone to delamination. PSf and PVDF-HFP were selected due to their relative RED values and their established applications in membrane fabrication. A scalable process incorporating slot-die coating on a roll-to-roll (R2R) system followed by non-solvent-induced phase inversion (NIPS) is used to fabricate the bilayer membranes. To mitigate delamination between these polymers, additive polymers were strategically employed: poly(methyl methacrylate) (PMMA) to enhance interfacial affinity, or polydopamine (PDA) to promote hydrogen bonding. This approach yielded an ultrafiltration bilayer membrane that achieved a 2B rating on the ASTM D3359-B standard for adhesion at the interface between layers. Scaled fabrication of bilayer membranes is enabled by this work.