Introduction: Many endodontic sealers are available, but search for the ideal sealer continues. This study aimed to assess the cytotoxicity of two experimental endodontic sealers in comparison with AH-26 resin sealer. Methods and Materials: This in vitro study was conducted on conventional and experimental root canal sealers: AH-26, an epoxy resin experimental sealer A (ES-A) composed of calcium tungstate, zirconium oxide, aerosil, bismuth oxide, titanium oxide, hexamine and an epoxy resin and experimental sealer B (ES-B) with compositions similar to ES-A except for the presence of imidazoline as a catalyst. The experimental sealers containing nano-particles were mixed with 37. 5% of an epoxy resin. The extraction of five samples of each experimental sealer (A, B) and AH-26 sealer were subjected to MTT assay in the form of set and fresh at 1, 24 and 72 h with 1, 10, 100% dilution according to the International Standard ISO: 10993-2012. Data were analyzed using the one-way ANOVA. Results: The set ES-A had the least cytotoxicity from the first hour but the cytotoxicity of ES-B and AH-26 extraction decreased over time. In fresh form, except for 100% concentration, ESA showed the least cytotoxicity compared to the other two sealers. Conclusion: All three sealers had high cytotoxicity in 100% concentration but had low cytotoxicity in 10% and 1% concentrations.

To enhance the properties of epoxy composites, the biphenyl diol formaldehyde resin (BPFR) and glycidyloxypropyl polyhedral oligomeric silsesquioxane (G-POSS) were synthesized and used for modification of fiber-glass reinforced composites of epoxy resin (ER). The BPFR was employed to cure epoxy resin with different G-POSS contents and the laminates of fiber-glass reinforced hybrid composites prepared from BPFR, ER and G-POSS. The dynamic mechanical properties, thermal properties, mechanical and electrical properties of the hybrid composites were characterized by dynamic mechanical analyzer, thermogravimetric analyzer and electroproperty detector. The results showed that the T g of the composites is increased with the addition of G-POSS. When the content of G-POSS is 5 wt%, the tensile and impact strength of the hybrid composites are 249.87 MPa and 63.83 kJ/m2, respectively, which are all 30 % higher than those of non-added composites. At G-POSS content of 7 wt%, T g of the material is 9.6 °C higher than pure BPFR/ER composite, and the initial decomposition temperature, T id, is enhanced by about 29 °C. Dielectric constant, e, and dielectric loss, tand, of the hybrid composites are between 0.53–0.7 and between 0.004-0.012, respectively.

The aerospace and automotive industries widely use composite materials due to their weight-to-strength ratios. One of the most significant problems with composites is repair and maintenance. This study attempts to repair glass epoxy composites. The repair process involves two stages: 1)optimization of the position of the hole and 2) repair work. To optimize the repair techniques, two distinct holes were performed: 1) at the center of the specimen and 2) at the edges of the specimen. As a result, the hole drilled at the center gives higher strength than the hole drilled at the edges. After the optimization, samples were repaired with a single hole in the center and peak loads of 60% and 90%. The cracked and delaminated areas were repaired with epoxy/hardener. The repaired samples were subjected to a three-point bending test, and the results were compared with the Neat GFRP samples. The results show that the curves of the repaired samples aligned with both the post and the residual flexural strength. The residual flexural strength of the 60% and 90% peak-loaded repaired samples retains about 47% and 76%, respectively.

Current research work focuses on the synthesis of phosphorus-and silicon-containing amine curing agent (PSA) for epoxy resins. PSA was synthesized using phenyl phosphonic dichloride and ethylenediamine as raw materials and further modification with 3-glycidoxypropyltrimethoxysilane. NMR, FTIR and amine value analysis were performed for the structure confirmation of the obtained product and intermediate. PSA was taken in different molar ratios for the crosslinking with epoxy resin before which the sol–, gel technique was performed onto the product for self-crosslinking of the methoxy groups. The obtained formulations were applied onto the mild steel panels and cured in an oven. The thermal and mechanical properties of cured epoxy resins were analyzed by TGA, DSC, impact resistance, pencil hardness and flexibility. The thermal and mechanical properties were increased along with the heat resistance index temperature (THRI) toward the loading of PSA into the coating formulations. The flame retardant properties were also checked and found to be increased with respect to the increasing concentration of PSA because of the synergistic effect of P and Si atoms. The formulation with the highest amount of PSA showed the highest LOI as 29 with self-extinguishing behavior in the UL-94 test.