Octylamine-Modified Cellulose Nanocrystal-Enhanced Stabilization of Pickering Emulsions for Self-Healing Composite Coatings

Abstract

Linseed oil-in-water Pickering emulsions are stabilized by both sulfated CNCs (sCNCs) and octylamine-modified CNCs (oCNCs). oCNCs with hydrophobic moieties grafted on the surfaces of otherwise intact nanocrystals provided emulsions exhibiting stronger resistance to creaming of oil droplets, compared with unmodified sCNCs. sCNCs were not able to completely stabilize linseed oil in water at low CNC concentrations while oCNCs provided emulsions with no unemulsified oil residue at the same concentrations. Oil droplets in oCNC emulsions were smaller than those in samples stabilized by sCNCs, corresponding with an increased hydrophobicity of oCNCs. Cryo-SEM imaging of stabilized droplets demonstrated the formation of a CNC network at the oil–water interface, protecting the oil droplets from coalescence even after compaction under centrifugal force. These oil droplets, protected by a stabilized CNC network, were dispersed in a water-based commercial varnish, to generate a composite coating. Scratches made on these coatings self-healed as a result of the reaction of the linseed oil bled from the damaged droplets with oxygen. The leakage and drying of the linseed oil at the location of the scratches happened without intervention and was accelerated by the application of heat.

Amphiphilic Cellulose Nanocrystals for Aqueous Processing of Thermoplastics

“…Modification of Sulfated CNCs with Alkyl Groups and Characterization. The details of the modification process have been previously reported 23,24 and are presented in more detail in the Supporting Information. Briefly, the modification, schematically represented in Figure S1 (Supporting Information), involves a twostep process starting with oxidation of sulfated CNCs with potassium periodate to form dialdehyde CNCs.…”

“…The details of the modification process have been previously reported , and are presented in more detail in the Supporting Information. Briefly, the modification, schematically represented in Figure S1 (Supporting Information), involves a two-step process starting with oxidation of sulfated CNCs with potassium periodate to form dialdehyde CNCs. , This is followed by the coupling of octylamine or hexadecylamine to dialdehyde CNCs via a reductive amination route.…”

“…These include grafting of hydrophobic moieties such as 6–12 carbon chain alkyl groups, , polystyrene, benzyl-polyethyleneimine, and n -butyl/isobutyl and tertbutyl groups . These so-called amphiphilic CNCs have been mainly prepared to act as emulsifiers in Pickering emulsions. − …”

“…In addition, the aqueous suspensions of alkylated CNCs in potassium chloride formed robust gels with higher storage moduli when compared with those of sulfated CNCs at the same weight loadings . Octyl-modified CNCs have also recently been used to stabilize linseed oil-water Pickering emulsions for self-healing composite coatings, showing their capacity to interact with hydrophobic materials . However, studies on the interaction of aqueous suspensions of amphiphilic CNCs with hydrophobic thermoplastics are still lacking.…”

Progress in the Application of Food-Grade Emulsions

“…More specifically, Pickering emulsions find applications in the preparation of phase change materials [ 349 ] and the generation of hybrid foams exhibiting high-performance microwave absorption properties [ 350 ]. In addition, they have been applied to enhance the stabilization and paper sizing performance of various materials [ 351 ], to prepare self-healing composite coatings [ 352 ], and to limit the influx of metal ions [ 353 ]. Additionally, they can be used in cosmetic applications [ 354 ], such as in the case of a nanoemulgel that employs Argania spinosa microfibrillated cellulose and natural emulsifiers [ 355 ].…”