Structural Colors Derived from the Combination of Core–Shell Particles with Cellulose

Combining cellulose-based components with functional materials is highly interesting in various research fields due to the improved strength and stiffness of the materials combined with their low weight. Herein, the mechanical properties of opal films are improved by incorporating cellulose fibers and microcrystalline cellulose. This is evidenced by the increase in tensile strength of 162.8% after adding 10 wt% of microcrystalline cellulose. For this purpose, core–shell particles with a rigid, crosslinked polystyrene core and a soft shell of poly(ethyl acrylate) and poly(ethyl acrylate-co-hydroxyethyl methacrylate) are synthesized via starved-feed emulsion polymerization. The synthesized particles’ well-defined shape, morphology, and thermal properties are analyzed using transmission electron microscopy, scanning electron microscopy, and differential scanning calorimetry measurements. Free-standing mechanochromic opal films with incorporated cellulose and structural colors are obtained after processing the core–shell particles with cellulose via extrusion and the melt-shear organization technique. The homogeneous distribution of the cellulose within the composite material is investigated using fluorescent-labeled cellulose. The opal film's angle-dependent structural color is demonstrated using reflection spectroscopy.