Fabrication of Waterborne Polyurethane (WPU) Porous Layers Through Binary Particle Stabilized Pickering Foam Templating

As important raw materials utilized in fire-proof, sound insulation, thermal insulation, gas sorption, etc., the traditional solvent phase inversion methods to produce porous materials have resulted in air/water pollution and residual VOCs in the products, which have been restricted by many countries. Waterborne polymer products possess the superiority of being eco-friendly during manufacturing but are limited by foam stability. Pickering foam is an air-water mixture whose interface is stabilized by the particles without interfacial activity. Excess particle desorption energy from the air-water interface over surfactants ensures superior stability and potential templating porous material production. The classic view of Pickering foam requires specific particle wettability, explained through the maximum capillary pressure concept, which hinders its application in industry.<br/><br/>We have reported a new strategy to prepare ultra-stable aqueous foams from PVA-Silica binary component system1. A series of Pickering aqueous foams were therefore achieved as the hydrophilic polymer and hydrophobic colloidal particles stabilized the Janus bilayer air-water interface in one step without massive particle wettability modification. The resulting Pickering foam afforded convincing stability over one month and templated the porous materials monolith. The work opened a new door for binary component Pickering foam and waterborne composite porous materials preparation.<br/><br/>In our recent work, the stabilization mechanism and kinetics of binary colloidal particles stabilized Pickering foam are under investigation. We are seeking for the potential to get the typical Pickering foam applied as a low-cost and eco-friendly scheme for porous materials industrial production. The Pickering aqueous foam systems, including hydrophilic-hydrophobic and hydrophilic-hydrophilic colloidal particles systems, are derived from waterborne polyurethane (WPU), hydrophobic silica particles (SP), and cellulose nanofibrils (NF) with typical wettability, surface charge, size distribution have been achieved.<br/><br/>Key Words: Porous material, Pickering foam, WPU, Silica particles, Cellulose nanofibrils<br/><br/>Reference<br/>1. Y. Sheng, K. Lin, B. P. Binks and T. Ngai, J Colloid Interface Sci, 2020, 579, 628-636.