Pickering aqueous foam templating: a promising strategy to fabricate porous waterborne polyurethane coatings

Abstract

Graphical abstract

Porous Waterborne Polyurethane Films Templated from Pickering Foams for Fabrication of Synthetic Leather

“…21 Nevertheless, WPU-based synthetic leather manufactured via phase inversion features a lower water-vapor permeability than solvent-based PU coatings. 25,26 Porous structures prepared using a physical blowing agent 27 or via particle templating (i.e., solvent casting and particle leaching) 28 and emulsion templating 29 have demonstrated promising water-vapor transmission abilities, but such methods are no longer favored in the leather industry owing to restrictions on the use of volatile organic compounds (VOCs). The use of wet foam as a template for preparing porous materials was suggested because the approach is organic solvent-free in nature and processing-friendly.…”

“…Moreover, WPU has gained considerable attention owing to its nontoxicity, odorlessness, convenient storage properties, safety, and environmental friendliness . Nevertheless, WPU-based synthetic leather manufactured via phase inversion features a lower water-vapor permeability than solvent-based PU coatings. , Porous structures prepared using a physical blowing agent or via particle templating (i.e., solvent casting and particle leaching) and emulsion templating have demonstrated promising water-vapor transmission abilities, but such methods are no longer favored in the leather industry owing to restrictions on the use of volatile organic compounds (VOCs).…”

“…This is because the particles irreversibly adhere to the air–water interface. , Hydrophilic particles, with water contact angles of 60–70°, are considered ideal stabilizers for Pickering foams, whereas hydrophobic particles are considered defoamers. ,, A recent study has demonstrated that particles with higher hydrophobicity improve the aqueous foam stability by cooperating along with other hydrophilic components at the air–water interface during the formation of binary component stabilized Pickering foam . Despite Pickering foam exhibiting superior stability in comparison to other types of foam, the drainage inside the foam’s continuous phases causes the liquid thin film among bubbles to become weaker, finally resulting in the rupture of the foam bubbles . Therefore, it is crucial to solidify the continuous phase of a Pickering foam in order to establish it as a template for achieving a highly porous structure .…”

“… 39 Despite Pickering foam exhibiting superior stability in comparison to other types of foam, the drainage inside the foam’s continuous phases causes the liquid thin film among bubbles to become weaker, finally resulting in the rupture of the foam bubbles. 26 Therefore, it is crucial to solidify the continuous phase of a Pickering foam in order to establish it as a template for achieving a highly porous structure. 37 A gel-like continuous phase has been created by establishing a physically interconnected network between hydrophobic silica particles (SPs) and cellulose nanofibers, which effectively prevents the wet Pickering foam from collapsing upon drying.…”

Bioactive Porous Protein Scaffolds Enabled by High Internal Phase Emulsion Templates

“…In this regard, the ideal porous scaffolds need not only good bioactivity and biodegradability but also high porosity and interconnected porous structure to facilitate the input of nutrients and oxygen, metabolic waste discharge, and cell adhesion and proliferation . The toolkits for preparing porous scaffolds, including particle leaching, three-dimensional (3D) printing, and electrospinning, are associated with significant limitations such as low porosity, low pore interconnectivity, special equipment required, uncontrollable pore size, and high preparation cost. − Recently, high internal phase emulsions (HIPEs) stabilized by solid particles are particularly attractive for the fabrication of porous scaffolds with hierarchical structure . Unfortunately, most of the scaffolds obtained from this method are hydrophobic synthetic polymers and hardly possess both appropriate pore size and high porosity, which is unfavorable for cell adhesion and proliferation in scaffolds. − Besides, the scaffolds templated from HIPEs solely stabilized by solid particles exhibit low pore interconnectivity owing to the solid particles surrounding the droplets acting as barriers …”