Sodium montmorillonite concentration effect on Bis-GMA/TEGDMA resin to prepare clay polymer nanocomposites for dental applications

The aim of this work was to evaluate the effect of the addition of sodium montmorillonite (Na ⁺Mt) on the flexural strength, flexural modulus, degree of conversion, steady state shear viscosity and complex viscosity of the Bis-GMA (2,2-bis-[4-(methacryloxypropoxy)-phenyl] propane)/TEGDMA (ethane-1,2-diylbis(oxy)) bis (ethane-2,1-diyl) bis(2-methylacrylate) resin. Two types of clay polymer nanocomposites (CPN) were prepared, the first one by using sodium montmorillonite as received (Na ⁺Mt) and the second one by adding sodium montmorillonite previously dispersed in water (Na ⁺Mt/H ₂O). Sodium montmorillonite was added at different contents: 0.1, 0.2, 0.3, 0.4 parts per hundred of resin (phr) to Bis-GMA/TEGDMA resin for each type of CPN. A Bis-GMA/TEGDMA resin, without sodium montmorillonite, was used as control. Two-way ANOVA and Tukey`s test were applied for statistical analysis. Comparisons were performed using a significance level of α = 0.05. Statistical analysis revealed that the addition of sodium montmorillonite as received or dispersed in water, had no effect on flexural strength ( p = .886), flexural modulus ( p = .809) and degree of conversion of resin ( p = .742). Nevertheless, the content of sodium montmorillonite significantly influenced the flexural strength ( p = .004) and flexural modulus ( p < .001) of the two types of CPN. Flexural strength was increased when 0.1, 0.2 and 0.3 phr of Na ⁺Mt or Na ⁺Mt/H ₂O was used. Flexural modulus increased when 0.3 and 0.4 phr of Na ⁺Mt or Na ⁺Mt/H ₂O were added to resin. X-ray diffraction measurements showed that polymer chains were successfully introduced in the interlayer space of the clay mineral producing polymer intercalation. Scanning electron microscopy showed a rough surface for both CPN groups evaluated which evidenced electrostatic interactions between the clay mineral and the polymer matrix. Rheological behavior evidenced the physical interaction between clay mineral layers and polymer matrix. The incorporation up to 0.3 phr of sodium montmorillonite improved the mechanical and chemical properties of the Bis-GMA/TEGDMA resin.