Vinyltriethoxysilane-functionalized starch nanocrystals as Pickering stabilizer in emulsion polymerization of acrylic monomers. Application in nanocomposites and pressure-sensitive adhesives

Abstract

Emulsion polymerization provides a sustainable way to produce latex polymers for coatings and adhesives thanks to the use of water as a dispersion medium. This synthesis approach can be even more attractive if synthetic surfactant can be replaced by biobased solid particles as a stabilizer, through what is known as a "Pickering effect". Herein, latex dispersions with solid content up to 35 wt% were successfully produced by emulsion polymerization using starch nanocrystals (SNCs) as a sole stabilizer and H2O2/citric acid as a redox-initiator. The effect of the SNC modification with vinyltriethoxysilane (VTES) on the colloidal properties of the polymer dispersion and performance of the resulting nanocomposite film were investigated.As an application of this approach, pressure-sensitive adhesive (PSA) dispersions have been prepared via Pickering emulsion polymerization in the presence of 8 wt% SNCs. The use of VTES-SNCs has a beneficial impact on the performance of PSAs with improved peel strength and wettability. The possibility to use SNCs as a stabilizer to replace synthetic surfactants in emulsion polymerization opens new avenues for the application of SNCs as biobased Pickering stabilizers to produce latex for coatings, adhesives, inks, and textiles.

New Insights into the Formulation and Polymerization of Pickering Emulsions Stabilized by Natural Organic Particles

“…The use of an aqueous initiator can change the polymerization process from a (micro)suspension to a "Pickering heterogeneous emulsion polymerization" as showed by Ben Ayed and coworkers 172 This effect was also observed by Haaj et al 166,167 . They additionally found out that the presence of charges onto the growing polymer chains could dramatically impact the final size of the particles.…”

“…Consequently, the performances of the resulting composite in terms of mechanical resistance for instance, but also optical transparency, are much lower 160,196 . A way to overcome this issue and improve the material properties is the polymerization of Pickering emulsions stabilized by the agent (natural organic particles conferring targeted properties) 159,[172][173][174]179,182,197,198 . This so-called in-situ method is followed by the melting and casting of the produced latexes.…”

“…However, because of their inherent hydrophilicity, such particles cannot be well dispersed in hydrophobic polymer matrices (using the so-called ex situ method). Consequently, the performances of the resulting composite in terms of mechanical resistance, for instance, but also optical transparency, are much lower. , A way to overcome this issue and improve the material properties is the polymerization of Pickering emulsions stabilized by the agent (natural organic particles conferring targeted properties). ,− ,,,, This so-called in situ method is followed by the melting and casting of the produced latexes. Again, Pickering emulsions offer advantages compared to surfactants: no decrease of the mechanical or water resistance properties and lower toxicity. , Moreover, the particles herein act as stabilizers and loads ensuring their own good dispersion.…”

“…The use of an aqueous initiator can change the polymerization process from a (micro)suspension to a "Pickering heterogeneous emulsion polymerization" as showed by Ben Ayed and coworkers. 172 In their work, they used starch nanocrystals functionalized with vinyltriethoxysilane to stabilize Pickering emulsions of butyl methacrylate (BMA) in the presence of citric acid. The polymerization was triggered by addition of H 2 O 2 in the continuous phase.…”

Polysaccharide‐Based Nanoparticles as Pickering Emulsifiers in Emulsion Formulations and Heterogenous Polymerization Systems

“…Recently, Ben Ayed et al. [ 173 ] grafted SNCs with vinyltriethoxysilane (VTES‐SNC) which were subsequently applied as Pickering emulsifiers in the production of PBMA via surfactant‐free emulsion polymerization. Formulations with VTES‐SNC content ≥4 wt% of monomer produced stable latex dispersions, with monomodal size distributions (200–500 nm).…”