The Effect of Montmorillonite on the Rheological and Physico-mechanical Properties of a Thermosetting Polymer Composite

The study investigates a thermosetting polymer filled with montmorillonite. Montmorillonite is a naturally occurring layered mineral with particle sizes ranging from 8 to 12 µm. The thermosetting polymer was DER-330 epoxy resin and FCH-S hardener. Rheological and physical-mechanical studies of the properties of epoxy resin modified with montmorillonite were carried out. Viscosity versus shear rate is shown for uncured pure epoxy resin and resin modified with montmorillonite particles at room temperature. At low shear rates, a significant effect of montmorillonite on the properties of the composite is observed. The low shear rate further allowed epoxy molecules to leak between the layers of montmorillonite platelets, causing swelling and increasing the distance between them. As the shear rate increased from 8 to 20 s-1, the percolation time of montmorillonite decreased, which affected the decrease in viscosity. When the shear rate increases above 20 s-1, no significant changes in viscosity occur; for both samples a monotonic line is observed on the graph. The addition of montmorillonite to epoxy resin changes the chemical composition of the composite, which leads to changes in rheological and physical-mechanical properties. The addition of montmorillonite retards gelation, which can affect processability, cure time, and final properties of the composite. Morphological studies were carried out to determine the degree of dispersion of montmorillonite particles in the polymer composite using a transmission electron microscope. The uneven distribution of montmorillonite particles predominated in all samples. Apparently this is due to the curing conditions of the polymer composite and insufficient dispersion time. Physical and mechanical studies were carried out on samples made of a composite with montmorillonite in comparison with samples from pure epoxy resin. The flexural strength of samples made from the resulting composite is comparable to the strength of samples made from pure epoxy resin. In turn, the viscosity increased by 170%.