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

Abstract The preparation of high‐filled composites by compounding with calcium carbonate (CaCO 3 ) and polymer has received much attention. However, challenges such as enhancing the interaction between CaCO 3 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 CaCO 3 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 CaCO 3 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 CaCO 3 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 CaCO 3 and UPR. This study proposes an effective method for developing high‐performance UPR/CaCO 3 composites with a high filler content. Highlights The optimized gradation of CaCO 3 was used as filler to address the weak interaction of CaCO 3 with the UPR in a high‐filled UPR/CaCO 3 composite system while improving the performance of the composite. The gradation optimization of CaCO 3 filler can improve the morphology and reduce the porosity of the high‐filled UPR composites. The gradation optimization of CaCO 3 filler can effectively improve the curing effect of UPR. Optimizing the CaCO 3 gradation resulted in a significant increase in the average flexural strength (by 343.5%) and average compressive strength (by 888.9%) of the resulting blends.