Studies on rheological and mechanical properties of EVA/CaCO 3 composites prepared by twin-screw kneading method

This study employed a twin-screw kneading method to prepare ethylene-vinyl acetate (EVA)/calcium carbonate (CaCO3) composites and investigated their rheological and morphological behavior at filler contents up to 80 wt% CaCO3. We evaluated the effects of processing temperatures (70–105°C) and different particle sizes of CaCO3 (7.3 μm, 641.5 μm) on the dispersion efficiency and mechanical properties of the composite. Rheological analysis showed that EVA underwent a semi-crystalline to fully molten transformation at 105°C, at which point the viscosity decreased to ~10 Pa·s, and exhibited significant shear-thinning behavior. Experimental results indicated that the EVA/CaCO3, processed at 105°C with 80 wt% large-particle CaCO3, resulted in phase separation. The composite with small-particle CaCO3 formed a uniform morphology, with a maximum stress of 3.93 MPa and an elongation at break of 18.91%. However, lowering the processing temperature to 85°C led to a sharp increase in viscosity, resulting in flow stagnation and incomplete wetting. These findings indicate that high CaCO3 content systems have a narrow processing range, and high temperatures are crucial for reducing the viscosity of the composite, thereby promoting the wetting of high specific surface area fillers. This study provides a rheological framework for optimizing the processing flow of highly filled thermoplastic adhesives.