Hypothesis: The desirable tack and viscosity in prepregs are mostly obtained by pre-curing, but the main problem with this method is the decremental storage life of prepreg because of the ongoing curing reaction. One of the appropriate strategies to overcome this problem is to eliminate the pre-curing stage in the prepreg process and achieve the appropriate viscosity through epoxy formulations with different molecular weights. With this method, it is possible to obtain a prepreg with single-stage curability and longer storage life. Methods: By using low molecular weight epoxy resin (Epon828) and solid epoxy resin with high molecular weight (Ker3003) in the presence of MEK as solvent, DICY as curing agent and diuron as accelerator, two types of formulations including 3S7L (30% (wt) Ker3003 and 70% (wt) Epon828) and 4S6L (40% (wt) Ker3003 and 60% (wt) Epon828) were designed. Based on the obtained formulations, prepregs were manufactured and then cured to obtain the final composites. Different characterization techniques including FTIR, DSC, DMTA, ILSS, tensile strength, viscosity and drapability were used to determine the properties of formulated resins, prepregs and composites. Results: Appropriate prepregs were obtained based on the designed resin formulations without pre-curing stage. The results showed that the curing initiation temperatures of the formulated resins were about 15°, C higher than that of Epon828 epoxy resin. The 4S6L formulation maintains the desired tack and viscosity of the prepreg up to 45°, C. ILSS for composites based on 3S7L formulation was about 14% and 11% higher than the values obtained for composites based 4S6L and Epon828 resins, respectively. Flexural rigidity as representative of the drapability of the prepregs was obtained 3230 and 3460 μ, J/m, respectively. For prepregs based on 3S7L and 4S6L formulations, there is an indication of high drapability of the prepregs based on designed formulations.

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.

Epoxy resins are the most commercially important polymers, which have found a broad range of applications because of their excellent adhesion, toughness, insulation and good physical and chemical properties. In this project, liquid epoxy resin with narrow molecular weight distribution was synthesized by polymerization reaction of epichlorohydrin and bisphenol A in molar ratio of 12 to 1 in presence of sodium hydroxide. This product was characterized by FTIR and 1H NMR spectroscopy and its thermal degradation was studied by using DSC and TGA thermograms. Epoxy equivalent and chlorine content were determined by chemical analysis. Some effective parameters such as the method employed and the adding amount of sodium hydroxide in the reaction system were changed in order to gain qualified epoxy resin. Epoxy equivalent of this resin was 0.53 per 100 g of resin and its chlorine content was 0.25 percent. Epoxy equivalent weight of this resin was 169 g per one equivalent of resin. Viscosity of the product was studied at different temperatures and the constituting liquid epoxy resin was determined by TLC.

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.

To determine the kinetics characteristics of thermoset resins, it is required to optimize curing conditions due to their dependency on time, temperature and curing conditions. In this work, curing kinetics of epoxy resin 5052, with amine-based hardener was investigated using DSC at nonisothermal conditions with various heating rates. Kinetic parameters were firstly deduced experimentally using isoconversional method, which was introduced by Malek. Then, by choosing Sestak-Berggren model, the experimental data obtained from DSC showed good agreement with this model. Considering this model, it is able to interpret the curing behavior of resin at various thermal and time dependent conditions.

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.

Various amounts of dicyandiamide (Dicy), two grades of epoxy resins, i.e. Epiran 06 and Epikote 828, and three different accelerators including benzyl dimethyl amine (BDMA), 3-(4-chlorophenyl)-1, 1-dimethyl urea (Monuron) and 2-methyl imidazole (Im) were used in curing of Dicy/epoxy resin system. Both of the used epoxy resins were based on diglycidyl ether of bisphenol A (DGEBA). The effects of type and concentration of accelerators on curing behavior were studied by differential scanning calorimetry (DSC) method in dynamic or non-isothermal mode. The optimum concentration of Dicy for curing of epoxy resins was obtained based on the glass transition temperature of the cured epoxy/Dicy formulations. The maximum glass transition temperature of 139oC was obtained at the stoichiometric ratio of Dicy to epoxy of 0.65. The results showed that BDMA has a broader curing peak in DSC and starts the cure reaction earlier than the others. However, Monuron has a narrow curing reaction peak with good cure latency. The tensile properties of Dicy-cured Epiran 06 and Epikote 828 epoxy resins reinforced with chopped strand mat showed that these two epoxy resins have similar mechanical properties. For composites based on the Epiran 06 and Epikote 828 reinforced with 40 wt % glass chopped strand mat, tensile strength and modulus were 156 and 153.4 MPa and 11.6 and 12.4 GPa, respectively.