Recent Advances in Combining Waterborne Acrylic Dispersions with Biopolymers

Abstract

Water-based (meth)acrylic (co)polymer dispersions are produced on a large scale for various applications including coatings, adhesives, paints, and construction materials. A major benefit of waterborne polymer dispersions as compared to more traditional solvent-based alternatives is the low volatile organic compound (VOC) content, which results in an improved environmental profile. Following the trend of sustainability that has driven the growth of acrylic dispersions, recent research has focused on further enhancing the properties of these products by incorporating biobased materials such as polysaccharides (e.g., cellulose, starch, chitin, and chitosan), and proteins (e.g., casein, soy protein, and collagen). Amongst a large number of benefits, the incorporation of biomaterials can serve to decrease the amount of petroleum-based polymers in the formulation and can also contribute to enhance the physical properties of the resulting bio-composites. In this review, the beneficial role of these biopolymers when combined with waterborne acrylic systems is summarized. Recent advances in the use of these biobased and biodegradable materials are covered, aiming to provide guidance for the development of more sustainable, high-performance latex-based bio-composites with minimal environmental impact.

Keywords: biopolymers; casein; cellulose; chitin; chitosan; collagen; nanocellulose; soy protein; starch; waterborne acrylic latexes.

Figure 1

Chemical structure of acrylic acid, methacrylic acid, their ester derivatives, and some common vinyl comonomers used in waterborne acrylic latexes such as acrylonitrile, styrene, acrylamide, and methacrylamide. At the top, the principal compounds and main sources for their synthesis are indicated.

Figure 2

Schematic representation of (a) emulsion polymerization and (b) miniemulsion polymerization. The first step represents the initial conditions, where two different phases are present before agitation. Dispersed systems are formed and stabilized by surfactant with simple stirring for emulsion polymerization, which generate large monomer droplets and micelles swollen monomer, and strong shear forces, which produce smaller monomer droplets for miniemulsion polymerization. After polymerization, colloidal polymer particles form the latex in both procedures.

Figure 3

(a) Wettability effect of a solid particle at the oil–water interface. The contact angle (θ), measured through the aqueous phase, is shown in two scenarios: less than 90° (left), and greater than 90° (right). (b) Corresponding Pickering emulsions: when θ < 90°, an oil-in-water (o/w) emulsion can be formed (left), whereas when θ > 90°, a water-in-oil (w/o) emulsion would be formed (right). Reprinted and adapted with permission from reference [40]. Copyright © 2002 Elsevier. (c) Comparison between o/w droplet stabilized by surfactant and by solid particles.

Figure 4

Schematic steps of film-forming process of waterborne acrylic latexes.

Figure 5

Simplified representation of approaches for biopolymer addition into acrylic latexes. Top: ex situ addition where biopolymer is added on preformed latex. Bottom: in situ addition, where biopolymer is added before the polymerization.

Figure 6

Schematic illustration of casein micelles structure: black spheres represent the calcium phosphate nanoclusters; blue coils represent αS and β-caseins which can combine with nanoclusters; red lines present on the outermost part of the surface represent κ-caseins which provide steric and electrostatic stabilization. Reprinted and adapted with permission from reference [69]. Copyright © 2022 Elsevier.

Figure 7

Schematic representation of the two paths for the formation of amphiphilic core–shell nanoparticles and their corresponding SEM micrographs, adapted from [83]. (a) Redox radical generation, (1a) amino radical initiation, (1b) tert-butoxy radical initiation, (1c) tert-butoxy radical entering in casein micelles swollen with monomer, (2a) self-association of casein-g-polyacrylic, (2ba) oligomer entering in self-assembled micellar microdomain, (2b) oligomer stabilized by casein, (2bc) oligomer entering in casein micelles swollen with monomer, (3a) formation of compatibilized particle, (3b) and (2c) formation of polyacrylic particles stabilized with ungrafted casein. Reprinted and adapted with permission from reference [83]. Copyright © 2014 John Wiley and Sons. (b) Proposed mechanism for the graft copolymerization of MMA from water-soluble polymers containing amino groups, adapted from [82]. Reprinted and adapted with permission from reference [82]. Copyright © 2002 American Chemical Society.

Figure 8

Polycondensation reaction mechanism of caprolactam initiated by casein backbone moieties. Reprinted and adapted with permission from reference [89]. Copyright © 2012 Elsevier.

Figure 9

Chemical structure of different polysaccharides.

Figure 10

Schematic representation of the cellulose hierarchical structure from plant [126].

Figure 11

Amylose and amylopectin molecular structure and schematic arrangement of the different structures in the starch granules. Reprinted and adapted with permission from reference [167]. Copyright © 2014 Elsevier.

Figure 12

Upper: schematic illustrations for chitin structures and polymorphs, and for the preparations process of chitin nanocrystals and chitosan obtention from chitin deacetylation. Reprinted and adapted from [190]. Lower: deacetylation process for chitosan obtention.