Dual-Responsive Microgels for Structural Repair and Recovery of Nonwoven Membranes for Liquid Filtration

This study presents dual-responsive colloidal microgels to repair nonwoven fiber mats (NWFs) and recover their native morphological and functional properties. The formulation comprises poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAmco-AA) microgels loaded with iron oxide nanoparticles acting as magneto-responsive "bricks" and poly(N-isopropylacrylamide-co-N-4-benzoylphenyl acrylamide) (PNIPAm-co-BPAm) serving as photo-cross-linkable "mortar". The formulation is employed to repair small tears in meltblown polypropylene (PP) and polybutylene terephthalate (PBT) NWFs and recover the functional properties of the native membranes. Specifically, magnetically directed and UV-light-triggered repair recovers (i) the topological integrity, as shown by optical microscopy and image analysis of PP and PBT NWFs, (ii) the mechanical properties, as demonstrated by the values of tensile modulus of native, damaged, and repaired PP NWFs, and (iii) the permeability to sodium chloride of both PP and PBT NWFs. A comparative study of repair using magneto-responsive and photo-cross-linkable vs photo-cross-linkable-only formulations demonstrate that magnetic localization is vital to ensure rapid, spatially accurate, and effective recovery of the morphological and functional properties of damaged NWFs.