New strategy to improve acrylic/casein compatibilization in waterborne hybrid nanoparticles

Abstract

The grafting of casein to acrylic polymers is needed to fully exploit the possibilities of hybrid nanoparticles containing such materials. The explored alternative up to now, based on the primary radical formation onto the protein chains through the redox initiation between the casein amino groups and a hydroperoxide, produces a limited degree of compatibilization to guarantee the synergic effect between both components. A novel strategy that overcomes these limitations is presented. The strategy is based on the use of a crosslinkable casein, which in addition to the characteristic grafting capacity by redox initiation with hydroperoxides, contains acrylic groups able to radically polymerize. The degree of grafting of both acrylic and casein is significantly increased by functionalizing casein with varied amounts of pendant propagating points per protein. Moreover, it is observed that the improved degree of compatibility obtained when using the crosslinkable casein considerably enhanced the properties of the acrylic/casein films, such as their mechanical behavior and resistance to both water and organic solvent.

Waterborne Hybrid Acrylic/Protein Nanocomposites with Enhanced Hydrophobicity by Incorporating a Water Repelling Protein

“…These results are in agreement with those reported elsewhere, where the incorporation of a hard protein phase improved mechanical properties. 11,35 Furthermore, when employing the functionalized casein (A/C F and A/C F Z), materials were strengthened, decreasing their elongation at break but increasing tensile strength and hardness, compared to those obtained with native casein (A/C N and A/C N Z, respectively). Based on the PGE results, higher cross-linked films were obtained when methacrylated casein was used, which contributed to produce a cross-linked network, thus affecting mechanical performance.…”

“…9 Li et al 10 synthesize acrylic/ casein latexes by emulsion polymerization, where the grafting of the acrylic polymer onto casein chains was promoted by the redox initiation between an alkyl hydroperoxide and casein amine groups. According to Picchio et al, 11,12 such redox initiation allowed the production of acrylic/casein particles with a high degree of grafting (i.e., compatibility) when a low protein concentration is used. On the other hand, the hydrophilic character of casein and the low grafting degree reached when a high biomaterial content was used resulted in hybrid films with poor water resistance.…”

Proteins as Promising Biobased Building Blocks for Preparing Functional Hybrid Protein/Synthetic Polymer Nanoparticles

“…With the aim to maximize the GP, casein acrylation with acrylic acid (AA) was studied (see section Synthesis of Hybrid Protein Based NPs), but a low degree of protein modification was reached. 101 A more robust approach to overcome this difficulty was the use of highly methacrylated casein (HMC) in the latexes formulation, 81,82,102 which can be obtained through an amine−glycidyl ether reaction. 81 With this last procedure, the GP of the hybrid system was controlled by varying the content of methacrylic groups in the casein backbone.…”

“…Another approach to increase the grafting efficiency between protein and synthetic polymer consisted in adding vinyl functionalities to the protein, which then serve as propagating sites in a radical polymerization. With this aim Picchio et al 101 synthesized functionalized casein through the reaction of protein with AA, in the presence of N-(3-dimethylaminopropyl)-N′-ethylcarbodiimine hydrochloride (EDC). In this way, an amide bond is formed between the casein and the AA, 226 providing new acrylic functionality able to propagate via radical polymerization.…”

“…However, one limiting factor for acrylic/casein hybrid films reaching a commercial scale is the obtained low GP values when high casein concentrations are used in the latex formulation, which is highly desirable for a better exploitation of this renewable resource. With the aim to maximize the GP, casein acrylation with acrylic acid (AA) was studied (see section Synthesis of Hybrid Protein Based NPs ), but a low degree of protein modification was reached . A more robust approach to overcome this difficulty was the use of highly methacrylated casein (HMC) in the latexes formulation, ,, which can be obtained through an amine–glycidyl ether reaction .…”