Amorphous calcium phosphate based composites: Effect of surfactants and poly(ethylene oxide) on filler and composite properties

The uncontrolled aggregation of amorphous calcium phosphate (ACP) particulate fillers and their uneven distribution within polymer matrices can have adverse effects on the properties of ACP composites. In this article, we assessed the influence of nonionic and anionic surfactants and poly(ethylene oxide) (PEO) introduced during the preparation of ACP on the particle size distribution and compositional properties of ACP. In addition, the mechanical strength of polymeric composites utilizing such fillers with a photo-activated binary methacrylate resin was evaluated. Zirconia-hybridized ACP (Zr-ACP) filler and its corresponding composite served as controls for this study. Surfactant- and PEO-ACPs had an average water content of 16.8% by mass. Introduction of the anionic surfactant reduced the median particle diameter about 45% (4.1 mu m versus 7.4 mu m for the Zr-ACP control). In the presence of PEO, however, the d(m) increased to 14.1 mu m. There was no improvement in the biaxial flexure strength (BFS) in any of the dry composite specimens prepared with the surfactant and/or PEO-ACPs compared to those formulated with Zr-ACP. The BFS of wet composite specimens decreased by 50% or more after a month-long exposure to saline solutions. Other types of surfactants and/or polymers as well as alternative surface modification protocols need to be explored for their potential to provide better dispersion of ACP into the matrix resin and better mechanical performance ACP composites.