High solid content preparation of size controllable BiOCl crystals as pearlescent pigment in solvent-free polyurethane coating

Abstract

In the current research, we are committed to solving the irreconcilable contradiction between fragmentation, agglomeration, poor size controllability, and high solid content in the preparation of BiOCl crystals. Water soluble block polymer polyethylene glycol monomethyl ether-b-polydimethylaminoethyl methacrylate (mPEG-b-PDMAEMA) was synthesized as dispersant to achieve high solid content by reducing the frequency of crystal collisions to avoid crystal fragments and agglomerates. With the reaction temperature of 80 °C, urea dosage of 40 g, bismuth salt solution addition rate of 0.45 ml/min, and variable amount of pre-added HCl in the reaction vessel, fragment-free BiOCl crystals of wide size ranges were successfully obtained with record-high solid content of above 10 wt%. Furthermore, bio-based pearlescent coatings were prepared by using as-synthesized BiOCl crystals as pearlescent pigments and polyglyceryl tetrastearate and polyphenyl polymethylene polyisocyanate (PAPI) as the formulations of two-component solvent free polyurethane. The decorative polyurethane coatings demonstrated excellent physical properties and corrosion resistance, which exhibited eye-catching gloss effects from pearl luster, glitter pearl luster, to shimmering luster derived from the size variation of 20, 50, and 70 µm, respectively. The large-scaled production of size controllable BiOCl crystals with high solid content in wide size range promises the practical applications in decorative coatings, cosmetics, clothing accessories, and car interior accessories.