The diglycidyl ether of bisphenol A and boron trifluoride-diethylamine, mono-allylamine and piperidine complexes are used in a model system to investigate the cure reaction which occur during polymerization. Experiments using FT-IR at different temperatures show that boron trifluoride-amine complexes break down rapidly to tetrafluoroboric acid at 100 degrees C and above. Tetrafluoroboric acid forms complexes with epoxy groups, producing an activated monomer that reacts with epoxy in an etherification reaction. Dynamic DSC thermograms also show a small exotherm peak due to complex formation before the large exotherm peak of etherification reaction. A phenomenological approach is used to characterize the cure kinetics. Kinetic analysis, using integral procedure on dynamic data, indicates that the cure reaction data of diglycidyl ether of bisphenol A with boron trifluoride-amine complexes can be described well with the homogeneous first-order reaction model. The activation energies are found to be in the range of 90.85 kJ/mol for boron trifluoride-diethylamine; 96.88 kJ/mol for boron trifluoridemonoallylamine; and 94.45 kJ/mol for boron trifluoride-piperidine complexes.

Compared to thermoplastic, thermoset matrix composites and thermoset processes is more complex and less controllability.Cure kinetics, determine the network morphology in which the mechanical and physical properties of cured product may be assessed. So, knowing of thermoset curing kinetics is essential to process development, quality control and achieve desirable products. Hence, in this work, cure kinetics of an epoxy resin EPON/828 curing agent dicyandiamide / accelerator Duran system for the production of the epoxy/glass fiber prepreg using in wind turbine blades. For this, curing epoxy system was carried out using Differential Scanning Calorimetry and the effect of temperature and the nanosilica weight percent studied. To investigate the effect of temperature, isothermal DSC test was carried out at five different temperature without the presence of nanoparticles and to assess the influences nanosilica with 0, 4 and 6 weight percentage is done. Obtained figures by MATLAB curve fitting were fitted well with autocatalytic Kamal model and model parameters achieved for each tested sample. Results showed an increase in temperature of the isothermal test, leads the increase of the rate of cure and the complete of curing process. Addition of nanosilica cause the increase of the rate of cure at low value a but delay at the beginning of cure and decrease significantly overall heat of reaction.

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.

Phenolic resins are very well known for their high temperature and chemical resistance and good electrical properties. These thermoset resins are being used for a long time as friction materials, ablatives, decorative laminates and special domestic applications. The curing process of these resins, because of the required high temperature and pressure, is very complicated. The curing reaction mechanism of phenolic resins is a condensation type of reaction producing gaseous water or ammonia. The curing condition of this system is very important in order to eliminate any voids and achieve good mechanical properties. In this paper a preliminary curing cycle has been considered for a phenolic asbestos composite based on DSC thermograph of the resin. The effect of pressure, temperature and curing time on mechanical properties of this composite have been experimentally investigated. The optimized condition for achieving the highest mechanical properties has been determined. The results show that the optimum curing condition corresponds to 160oC, 60 bar pressure and 60 minutes for reaction time.

An investigation is conducted into the non-isothermal kinetics of the curing reaction of diglycidyl ether of bisphenol A (DGEBA) epoxy resin with two novel aromatic diamines, 4,4´-diaminostilbene (DAS) and 4,4´-diaminoazobenzene (DAAB), as curing agents. Kinetics analysis of the curing reaction of DGEBA with two different concentrations (29 wt% =0.13 mol% and 19 wt%=0.09 mol%) of the curing agents was studied using non-isothermal differential scanning calorimetry (DSC) technique. Two methods (Ozawa and Kissinger) for analysis of the scanning DSC data were applied to calculate the kinetic parameters and compared with kinetic parameters obtained from isothermal DSC tests using Kamal method. Activation energies in the range of 52.5-59.5 kJ/mol were obtained for both DGEBA/curing agent systems. The water absorption and resistance of the cured products against solutions of H2SO4 and NaOH were also studied. Water uptake curves for both systems are similar. Weight loss for the cured products of DGEBA/DAS and DGEBA/DAAB systems in 50% solution of NaOH reached the equilibrium values of 0.2% and 0.5%, respectively after about 80 h and weight gain of the cured products of both systems in 30% solution of sulphuric acid reached the equilibrium value of about 0.3% after about 40 h. The cured products from DGEBA/DAS system showed less weight loss during thermal degradation at 250°C but their water uptake was much higher.

Statement of problem: Although acrylic resin materials have great features for making artificial dentures, but still dimensional change is a common problem in processing them.Purpose: The aim of this study was to compare the linear dimensional changes of two heat-cure acrylic resins. Materials and Method: In this descriptive study, twenty specimens in two groups were made by “Acropars” and “Meliodent” acrylic resins according to the manufacturer’s recommendations in a metallic mold. Dimensional changes were measured at one, thirty and sixty weeks after processing with a digital caliper. The results were analyzed using T-test, T-paired test and repeated measure ANOVA.Results: Considering the dimensional changes, there was a difference in the first day equal to 0.42± 0.28 mm, in day thirty: -0.09±0.42 mm, and in day sixty: 0.07±0.22mm between the two acrylic resins, showing no statistically significant differences (r =0.21). However, there were significant differences between different times of measurements (r =0.001).Conclusion: “Meliodent” acrylic resin had more dimensional stability when compared to “Acropars” resin but there was not any significant difference between the two acrylic resins in the day sixty. There were significant differences between different times of measurements; the maximum difference between these two types of acrylic resins was in first day after polymerization.

Background and Aim: Cold-cure acrylic resins are commonly used for making interim prostheses, orthodontic appliances, denture repairs and special trays. Acrylic resins exhibit certain unavoidable changes that may affect on appliances accuracy. The aim of this study was to compare the linear dimensional changes of two cold - cure acrylic resins: Acropars and Meliodent.Materials and Methods: In this experimental laboratory study, twenty specimens in two groups of ten were made by Acropars OP and Meliodent acrylic resins according to the manufacturer's instructions. Dimensional changes were measured at 24, 48 and 72 hours after setting by a digital collis. The results were analyzed using t-test, t-paired test and repeated measure ANOVA.Results: In Acropars OP specimens, the difference between 48 hours and 72 hours (96.20±0.20 vs. 96.33±0.17) was significant (P3=0.006) but the differences between 24 (96.20±0.25) and 48 hours (P1 =0.958) and between 24 and 72 hours (P2=0.123) were not significant. In Melidoent specimens, the differences between all 3 days (0.37±0.47, 0.15±0.28 and 0.18±0.24) were significant (Pl=0.005, P=0.001 and P3=0.005). Moreover, the differences between Acropars and Meliodent acrylic resins on all three days (first: 95.82±0.25, second: 96.05±0.11 and third 96.15±0.10) were significant (P=0.003). The differences between mean groups and metallic dye, after three days, were significant in Meliodent group (P=0.000), but in significant in Acropars group (P=0.774).Conclusion: Meliodent self-cure resin had considerable dimensional changes when compared to Acropars resin. Maximum differences between these two types of acrylic resins were in the first 24 hours and the minimum difference was at 48 hours after polymerization.

Statement of Problem: Composite reins have recently become popular for posterior teeth restorations.Gap formation and subsequent microleakage are of the complications resulting from such restorations.One of the techniques to overcome polymerization shrinkage of composite resins is sandwich technique (application of glass ionomer as a base beneath the composite resin). Since polymerization patterns in two types of composite resins (light cure and self cure) differ from each other, various effects on the bond strength between glass ionomer and dentin are expected.Purpose: The aim of this in vitro study was to evaluate the effects of self- cure and light- cure composite resins in sandwich technique on the bond strength of light cure glass ionomer and dentin.Materials and Methods: 40 extracted human premolars were selected and divided into four groups:Group 1: Light cure glass ionomer of 1mm thickness was placed on dentin.Group 2: 1mm thickness of light cure glass ionomer plus a mass of self cure composite resin of 2mm thickness were placed.Group 3: 1mm thickness of light cure glass ionomer plus light cure composite resin as two separate 1mm layer were placed.Group 4: 1mm thickness of light cure glass ionomer with 37% phosphoric acid etching followed by two separate layers of light cure composite resin of 1mm thickness were placed.SEM was used to determine gap size at GI- dentin and GI- composite interfaces. The findings were analyzed by ANOVA and t-student tests.Results: Groups 1 and 2 showed no gap at GI-dentin interface and also cracks were not observed in all these specimens. In group 3, there was gap between light cure GI and light cure composite resin and cracks were seen in GI, too. Group 4 showed gap at both interfaces and more cracks were seen in GI. Groups 1 and 2 showed the least gap formation and group 4 showed the most. Statistically significant difference was found between groups 3, 4 and group 1 (control), 2.Conclusion: Base on this study, the application of self-cure composite resin on light cure GI showed no gap and crack formation on GI-dentin and GI-composite interfaces and GI itself. However, light cure composite resins and glass ionomer etching aggregated crack and gap formation.

An investigation was conducted based on: (1) The study of cure mechanisms and kinetics of diglycidyl ether of bisphenol A (DGEBA) using imidazole (H-MI) and 1-methyl imidazol (1-MI) as the curing agents and, (2) the study of some of the properties of the cured epoxy resins. The cure kinetics of DGEBA was studied using dynamic differential scanning calorimetry (DSC) in various low concentrations (>0.5 mol%) of the curing agents. Kinetic analysis using integral procedure on dynamic DSC data indicates that both H-MI and 1-MI are effective curing agents. The curing reaction of DGEBA with H-MI took place almost 10oC lower than the temperature of its curing reaction with 1-MI. Small low temperature shoulder peaks were observed for both curing systems and for all studied concentrations which are related to the formation of adduct. The formed adduct will initiate the etherification reaction which appears as a large high temperature exothermic peak in dynamic DSC thermogram. Water absorption, chemical resistance toacetone and sodium hydroxide solution, and thermal oxidation of the cured systems are also studied. The DGEBA/H-MI and DGEBA/1-MI cured systems indicated similar properties.

The sluggish polymerization is one of the major problems of the high-performance phthalonitrile-based resins that needs to be solved urgently. In the present study, two types of new bisphthalonitrile resins 3, 3'-((propane-2, 2-diylbis(2-amino-4, 1-phenylene))bis(oxy))diphthalonitrile (PN-m) and 4, 4'-((propane-2, 2-diylbis(2-amino-4, 1-phenylene))bis(oxy))diphthalonitrile (PN-p) containing diamino groups were synthesized from 2, 2'-bis(3-amino-4-hydroxylphenyl)propane and 3-nitrophthalonitrile/4-nitrophthalonitrile by nucleophilic substitution. Fourier-transform infrared (FTIR), nuclear magnetic resonance (1HNMR and 13CNMR), and time of flight mass spectroscopy (TOF–, MS) were used to identify the chemical structures of new bisphthalonitrile resins. The different self-catalyzed curing behavior, owing to different positions of cyano groups on the benzene ring were confirmed by differential scanning calorimetry (DSC) and FTIR techniques. The thermal stability of the cured diamine-functional bisphthalonitriles was determined by thermogravimetric analysis (TGA) under a nitrogen atmosphere. The 5% mass-loss temperatures (T5%) and 10% mass-loss temperatures (T10%) of PN-p polymers were observed to be 413–, 498 °, C and 486–, 562 °, C, respectively, which were higher than those of the PN-m polymers (i. e., 408–, 497 °, C and 477–, 559 °, C, respectively). The char yields at 800 °, C for PN-m and PN-p under a nitrogen flow were 73. 58–, 78. 76% and 74. 22–, 79. 14%, respectively. After the thermal treatment at 375 °, C, the glass transition temperature (Tg) above 400 °, C has been observed for both polymers. Regarding the adhesive qualities, PN-p showed a comparatively high lap shear strength of more than 15 MPa at 300 °, C. Therefore, these diamine-functional bisphthalonitriles are suitable as resin matrices for structural metal-bonding applications.