Polyurethane composite behavior influenced by the characteristics of the employed bentonite filler

Bentonite clays are widely used in polymer composites due to their ability to enhance mechanical and thermal properties. This study investigates the impact of various bentonite types on the rheology of polyurethane (PU) foam formulations and the stability of the resulting foams. Seven different bentonite samples, including both raw and activated forms, were characterized by using X-ray diffraction (XRD) and incorporated into polyurethane premixes. Rheological analysis revealed a significant correlation between bentonite content and viscosity hysteresis, which influenced foam stability. Results showed that certain bentonite types, such as natrium-activated bentonite from Hungary (B3 and B5), improved foam integrity by maintaining low hysteresis values, while others, such as calcium Romanian bentonite (B1), or Na-Ca-bentonite from Slovakia (B2) and standard Wyoming Na-bentonite from USA (B6), led to foam collapse at higher concentrations. Additionally, compressive strength tests demonstrated that small amounts of bentonite enhanced with 250% or more the mechanical properties of the foam. In the case of natrium-activated bentonite from Hungary (B3), catalytic effect is also revealed, decreasing the reaction time with 20%. This research provides insights into the role of bentonites as fillers in polyurethane composites, identifying key factors that determine their compatibility and usability.