Scalable preparation of hollow polymer and carbon microspheres by spray drying and their application in low-density syntactic foam

Abstract

Monodispersed hollow polymer microspheres (HPMs) and hollow carbon microspheres (HCMs) are prepared by a low-cost and rapid spray-drying technique using resorcinol-formaldehyde as precursors. By spraying the precursor solution into a high-temperature chamber, micrometer-scale hollow structure can be immediately obtained. To achieve the required morphology, the factors of influencing the products morphology and purity are systematically optimized. The as-obtained HPMs have a low bulk density of 0.089 g/cm3, narrow particle size distribution of 15–80 μm with a mean size of 37 μm, a high floatation ratio of 96.3% and high mechanical strength. Followed by a simple carbonization, HCMs with a bulk density of ca. 0.1 g/cm3 and a mean size of 23 μm are achieved. This spray-drying strategy could drastically reduce their production times and costs, enabling continuous and scalable synthesis of hollow microspheres for practical use. As a proof-of-concept application, a series of syntactic foam consisting of HPMs and HCMs as fillers and phenolic resin as matrix are prepared via a hot-press molding. The resulting composite materials have low bulk densities but improved mechanical properties, which highlights the possibility for the manufacturing of light-weight materials using these kinds of hollow microspheres.