Effect of inorganic particles gradation on the properties of high-filled unsaturated polyester resin/CaCO₃ composites

The preparation of high-filled composites by compounding with calcium carbonate (CaCO3) and polymer has received much attention. However, challenges such as enhancing the interaction between CaCO3 and the polymer and improving the performance of the resulting composites need to be addressed. In this paper, composites with a high filler content were made by adding fillers of various CaCO3 gradations into unsaturated polyester resin (UPR). The mechanical properties, curing degree, component distribution, and structural phases of resulting blends were analyzed by a universal testing machine, differential scanning calorimeter, Raman, and scanning electron microscope/energy-dispersive x-ray spectroscopy (EDX), respectively. Based on the research findings, optimizing the CaCO3 gradation significantly increased the strength of the resulting blends. The average flexural strength increased by 343.5%, while the average compressive strength increased by 888.9%. The composites with an optimized gradation of filler showed a significant reduction in uncured domains, leading to an improvement in the curing degree of the composites. The interfacial defects between the optimized graded CaCO3 filler and the UPR were reduced, resulting in a uniform distribution with no visible interface. The Raman and EDX analyses show that the gradation optimization technique has successfully prevented structural phase separation and enhanced the tendency to agglomerate between CaCO3 and UPR. This study proposes an effective method for developing high-performance UPR/CaCO3 composites with a high filler content.