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Mohammad Hosain Beheshty - One of the best experts on this subject based on the ideXlab platform.

  • A new latent accelerator and study of its effect on physical, mechanical and shelf-life of carbon fiber epoxy prepreg
    Iranian Polymer Journal, 2019
    Co-Authors: Mina Niazi, Mohammad Hosain Beheshty
    Abstract:

    The effects of a new latent accelerator and those of two common accelerators of 1-methyl imidazole and 2,4,6-tris(dimethylaminomethyl)phenol (DMP) have been studied in relation to the properties of Dicyandiamide (Dicy) cured epoxy resin and its prepregs with unidirectional carbon fiber. The new prepared accelerator is an adduct based on DMP (A_DMP). The results showed that the curing behavior of epoxy/Dicy did not change when the appropriate amount of new accelerator was used. The amount of 5 phr of new latent accelerator is equal to the amount of 0.6 phr of DMP accelerator and by increasing the amount of new accelerator, the curing reaction of epoxy/Dicy increased significantly. Viscosity build-up results and gel time measurements showed the high pot-life of resin system (epoxy/Dicy/A_DMP) and the high shelf-life of their prepreg. The results showed that the lap shear strength of sample containing 5 phr of the new accelerator (A_DMP5) was increased by 127% in comparison to the sample containing 0.6 phr of DMP. Transverse tensile strength and strain-at-break were increased by 27% and 31.7%, respectively. Transverse flexural strength, flexural strain-at-break and flexural modulus increased by 52%, 11% and 60%, respectively. On the other hand, fracture toughness and fracture energy increased significantly by 214% and 700%, respectively. This increase in mechanical properties was due to the bulkiness of the new latent accelerator acting as a toughening agent and also the good adhesion of fiber to the matrix as revealed by scanning electron microscopy.

  • Effect of tertiary amine accelerators with different substituents on curing kinetics and reactivity of epoxy/Dicyandiamide system
    Polymer Testing, 2017
    Co-Authors: Mohammad-nabi Hesabi, Ali Salimi, Mohammad Hosain Beheshty
    Abstract:

    Abstract Non-isothermal Differential Scanning Calorimetry and gel time measurements were employed to study the effects of four different tertiary amine accelerators with different molecular structure and substituents on the curing behavior and reactivity of epoxy/Dicyandiamide (Dicy) system. Results showed that the acceleration behavior depends on three factors: the bulkiness, the number of nitrogen atoms in molecular structure and the electron density of accelerator. Among these, the former two factors demonstrated stronger effect. The results of model fitting kinetic demonstrated that Sestak–Berggren model can well simulate the reaction rates especially for the samples accelerated by 2,4,6-tris(dimethylaminomethyl)-phenol and (Dimethylaminomethyl)phenol. The activation energy projected by Flynn-Wall-Ozawa and Kissinger–Akahira–Sunose methods exposed different amounts for each accelerator while both models revealed similar trends. Moreover, 1-methylimidazol-accelerated samples showed shortest storage life and gel time mainly due to the presence of two nitrogen atoms in a compact structure of accelerator.

  • Toughening of Dicyandiamide-cured DGEBA-based epoxy resins using flexible diamine
    Iranian Polymer Journal, 2015
    Co-Authors: Hajar Jamshidi, Reza Akbari, Mohammad Hosain Beheshty
    Abstract:

    This study has examined the toughening of Dicyandiamide-cured diglycidyl ether of bisphenol-A (DGEBA)-based epoxy resin with a flexible diamine. Eight different formulations were prepared by mixing DGEBA resin with a mixture of two curing agents of Dicyandiamide (Dicy) and flexible polyoxypropylene diamine (Jeffamine D-400) in the presence and the absence of Monuron as an accelerator. The effect of curing agents on the curing behavior of epoxy systems was studied using differential scanning calorimetry (DSC). The fracture surfaces of the tensile test samples were examined by scanning electron microscopy (SEM). The DSC results showed that the reaction between Jeffamine and epoxy resin occurred within a much wider range of temperatures than the reaction of Dicy in the presence of accelerator. The tensile strength of the modified epoxies was much higher than the tensile strength of samples cured by one curing agent alone, due to the synergistic effect of the former. The tensile modulus of all samples was approximately equal and the Izod notched impact strength remained fairly constant up to 60 % Jeffamine and then increased beyond this amount. The fracture toughness increased as the Jeffamine content increased. All samples containing Jeffamine showed greater elongation-at-break. This behavior was a confirmation that Jeffamine increased the flexibility and toughness of Dicy-cured epoxy resin, even at 20 % Jeffamine content. The glass transition temperature ( T _g) for epoxy resin containing 100 % Dicy (116 °C) was higher than that containing 100 % Jeffamine (73 °C). SEM observation showed a homogeneous phase with no phase separation and that the crack area increased as the content of the flexible curing agent increased.

  • Curing behavior of Dicyandiamide/epoxy resin system using different accelerators
    Iranian Polymer Journal, 2013
    Co-Authors: Mehran Hayaty, Hengameh Honarkar, Mohammad Hosain Beheshty
    Abstract:

    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 139 °C 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.

  • Modification of Dicyandiamide-cured epoxy resin with different molecular weights of polyethylene glycol and its effect on epoxy/glass prepreg characteristics:
    High Performance Polymers, 2013
    Co-Authors: Navid Mahnam, Mohammad Hosain Beheshty, Mohammad Barmar, Mahdieh Shervin
    Abstract:

    Epoxy resins are widely used in the manufacture of structural composites; however, the inherent brittleness of epoxy matrices has restricted their applications. In this work, a diglycidyl ether of bisphenol-A epoxy resin cured by Dicyandiamide (Dicy) was modified by adding polyethylene glycol (PEG) with molecular weights of 2000 and 4000 g/mol in amounts of 10, 20, and 30 phr. The effect of these PEGs on the mechanical properties and fracture toughness of epoxy resin was studied. Toughness (the area under the stress–strain curve) increased approximately four- and eightfold upon the addition of 20 and 30 phr of the PEGs, respectively. Results of this study also showed a 73% increase in fracture toughness (KIC) and increases in 300% and 425% in fracture energy (GIC) following the addition of 30 phr of PEGs 2000 and 4000, respectively. Subsequently, prepregs having 50 wt% resin content were prepared. Then relevant prepreg tests such as rheology, resin flow, and lap shear strength were performed. Increasing t...

Takeshi Endo - One of the best experts on this subject based on the ideXlab platform.

  • Storage stability and curing behavior of epoxy‐Dicyandiamide systems with carbonyldiimidazole‐Cu (II) complexes as the accelerator
    Journal of Polymer Science Part A: Polymer Chemistry, 2013
    Co-Authors: Xiang Dong Liu, Atsushi Sudo, Chun Hua Zhao, Takeshi Endo
    Abstract:

    The reaction between carbonyldiimidazole (CDI) and copper (II) nitrate produces a new Cu (II) complex with nitrate as the counter anion. TGA, UV, and FTIR analyses confirmed that the coordination number of CDI in this complex is two. The acceleration effect of the complex in epoxy-Dicyandiamide (Dicy) curing systems has been evaluated by DSC and TMA, and the increasing viscosity of the mixture was monitored during the storage. The results revealed that the complex is not only very effective for the acceleration of epoxy-Dicy systems, leading to a rapid gelation within 21 min at 120 °C, but it is also chemically stable at ambient temperature. This is reflected by the slow increase of viscosity of the accelerated curing systems stored at 35 °C, even over 56 days. In addition, the effects of the [Cu(CDI)2]2+ complex with different counter anions, that is, bromide, chloride, nitrate, sulfate, phthalate, and acetate, were compared using a series of tests. By comparing with N,N-dimethyl-N′-phenylurea (fenuron), the widely used latent accelerator for Dicy-epoxy curing systems, the complexes with bromide and nitride were found to be better, both regarding storage stability and for their acceleration effect. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3470–3476

  • Accelerating effects of N‐aryl‐N′,N′‐dialkyl ureas on epoxy‐Dicyandiamide curing system
    Journal of Polymer Science Part A: Polymer Chemistry, 2010
    Co-Authors: Xiang Dong Liu, Mika Kimura, Atsushi Sudo, Takeshi Endo
    Abstract:

    This report focuses on epoxy-Dicyandiamide (Dicy) curing system accelerated by N-aryl-N′,N′-dialkyl urea, aiming at clarifying the accelerating mechanism and the relationship between accelerating effect and molecular structure of the accelerators. Nine N-aryl-N′,N′-dialkyl ureas were synthesized and investigated with measurements of differential scanning calorimetry, thermo gravimetric/differential thermal analysis and NMR spectroscopy. The results revealed that the ureas released the corresponding secondary amines by the thermal dissociation in the presence of epoxide, which led to the formation of tertiary amines that catalyze the addition reaction of Dicy to epoxide. Moreover, a tendency that the ureas able to release more compact amines exhibited higher acceleration effects was discovered. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Ke-hsuan Wang - One of the best experts on this subject based on the ideXlab platform.

  • Polymeric g-C_3N_4 Derived from the Mixture of Dicyandiamide and Mushroom Waste for Photocatalytic Degradation of Methyl Blue
    Topics in Catalysis, 2020
    Co-Authors: Hung-chun Yang, Miao-ting Liu, Ming-wei Chao, Ke-hsuan Wang
    Abstract:

    Metal-free, visible light-responsive, carbon-based graphitic carbon nitride (g-C_3N_4) is a well-known photocatalyst. It is necessary to develop a g-C_3N_4 for use as a photocatalyst in a green, economically viable, and effective manner. In this study, a waste-derived g-C_3N_4 was successfully prepared from the mixture of Dicyandiamide (Dicy) and mushroom waste (MW). The waste-derived g-C_3N_4 (1MDCN) exhibited enhanced photocatalytic activity compared to the conventional Dicyandiamide-derived g-C_3N_4 for the degradation of an azo dye, methyl blue (MB), which is a most commonly used dye in the pharmaceutical industry. Under visible light irradiation, the improved activity could be attributed to its greater graphitic degree and fewer pyrrolic-N forming repeated tri-s-triazine units oriented along the [100] plane, which was evidenced by high-resolution X-ray photoelectron spectroscopy. In addition, the waste-derived g-C_3N_4 in this study is less harmful and exhibited good cell viability for Chinese hamster ovary cells, with over 50% of the cells surviving, whereas more than 85% of the cells were killed using melamine-derived g-C_3N_4 at a concentration of 1000 μg mL^−1. The present study shows that g-C_3N_4 derived from the mixture of Dicy and MW can be a harmless, economically viable, and effective photocatalyst for environmental remediation. Graphic Abstract

  • Polymeric g-C3N4 Derived from the Mixture of Dicyandiamide and Mushroom Waste for Photocatalytic Degradation of Methyl Blue
    Topics in Catalysis, 2020
    Co-Authors: Hung-chun Yang, Miao-ting Liu, Ming-wei Chao, Ke-hsuan Wang
    Abstract:

    Metal-free, visible light-responsive, carbon-based graphitic carbon nitride (g-C3N4) is a well-known photocatalyst. It is necessary to develop a g-C3N4 for use as a photocatalyst in a green, economically viable, and effective manner. In this study, a waste-derived g-C3N4 was successfully prepared from the mixture of Dicyandiamide (Dicy) and mushroom waste (MW). The waste-derived g-C3N4 (1MDCN) exhibited enhanced photocatalytic activity compared to the conventional Dicyandiamide-derived g-C3N4 for the degradation of an azo dye, methyl blue (MB), which is a most commonly used dye in the pharmaceutical industry. Under visible light irradiation, the improved activity could be attributed to its greater graphitic degree and fewer pyrrolic-N forming repeated tri-s-triazine units oriented along the [100] plane, which was evidenced by high-resolution X-ray photoelectron spectroscopy. In addition, the waste-derived g-C3N4 in this study is less harmful and exhibited good cell viability for Chinese hamster ovary cells, with over 50% of the cells surviving, whereas more than 85% of the cells were killed using melamine-derived g-C3N4 at a concentration of 1000 μg mL−1. The present study shows that g-C3N4 derived from the mixture of Dicy and MW can be a harmless, economically viable, and effective photocatalyst for environmental remediation.

Wulff Possart - One of the best experts on this subject based on the ideXlab platform.

  • Dissolution, Transport and Reaction at a Dicy/DGEBA Interface
    The Journal of Adhesion, 2012
    Co-Authors: Ulrich Müller, Wulff Possart, Jan Christoph Gaukler, Martine Philipp, Roland Sanctuary, Jan-kristian Krüger
    Abstract:

    The curing of an epoxy consisting of the solid hardener Dicyandiamide (Dicy) and the resin diglycidyl ether of bisphenol A (DGEBA) is studied in a system consisting of a tablet of Dicy embedded in liquid DGEBA. Dissolution of Dicy within the liquid DGEBA in combination with the transport of dissolved Dicy from the tablet border into DGEBA and the chemical reaction of both reactants is studied by scanning Brillouin microscopy and infrared spectroscopy. Scanning Brillouin microscopy demonstrates the spatial and temporal evolution of the static and dynamic hypersonic properties in the course of curing in the vicinity of the Dicy tablet. Infrared spectroscopy performed on epoxy pieces extracted from the final sample at different distances from the tablet surface give information about the spatial evolution of the curing process. The results achieved by both techniques are finally combined to yield a better understanding of the curing of Dicy-based epoxies, which transform upon curing from strongly heterogeneo...

  • Functional nano fillers in epoxy-Dicyandiamide adhesives for prolonged shelf life and efficient cure
    e-Polymers, 2011
    Co-Authors: Jan Christoph Gaukler, Ulrich Müller, Jan-kristian Krüger, Wulff Possart
    Abstract:

    Shelf life at room temperature and curing behaviour at elevated temperature are studied for hot-curing accelerated epoxies (EP, diglycidylether of bisphenol A plus Dicyandiamide (Dicy)) by FTIR-spectroscopy and modulated DSC. The accelerator is added either directly or with nano-zeolite filler to the EP. Due to the immobilisation of the accelerator in the pores of the nano-zeolite, the shelf life of this EP is 5 times longer than for the EP containing free accelerator. While the free accelerator acts during the whole heating step to curing temperature, the nano-zeolite does not release the accelerator before ca. 100 °C. As monitored by light microscopy, the released accelerator not only supports the curing but also stimulates the dissolution of the solid Dicy. As the result, network formation at 170 °C finishes within less than 25 minutes for the nano-filled EP.

  • Reactive epoxies with functional zeolite fillers: IR spectroscopy and PALS studies
    Journal of Materials Research, 2011
    Co-Authors: Muhammad Quasim Shaikh, Wulff Possart, Klaus Rätzke, Jan Christian Gaukler, Franz Faupel
    Abstract:

    Epoxy–Dicyandiamide (Dicy) formulations frequently contain a free accelerator for reducing the curing temperature and the time for network formation, which reduces the shelf life of these adhesives. This study compared the reaction kinetics during the storage at 60 °C for a precured epoxy adhesive (EP = diglycidyl ether of bisphenol A and Dicy, mass ratio 100:6.7, precured at 150 °C for 1 h) mixed either with free accelerator (=EP_acc) or with the same concentration of accelerator immobilized in micro- or nanozeolite fillers (EP_μ-filled and EP_n-filled, respectively). During storage, the infrared (IR) study probed the chemical modifications. They lead to increasing cross-linking density and a loss of free volume as detected by positron annihilation lifetime spectroscopy (PALS). Cross-linking precedes to the chemical vitrification. Additionally, the glass transition and the free-volume parameters were investigated for the three EP’s as a function of temperature by PALS after thermal curing.

  • Shelf Life and Controlled Cure of Epoxies by Loaded Zeolite
    Composite Interfaces, 2010
    Co-Authors: J. Ch Gaukler, Ulrich Müller, Jan-kristian Krüger, Wulff Possart
    Abstract:

    Epoxy formulations based on the multi-functional amine hardener, Dicyandiamide (Dicy), regularly contain a free accelerator for reducing the curing temperature and the time needed to complete the network formation. Unfortunately, all accelerators reduce the shelf life of these adhesives at 25°C. In order to solve this problem, accelerator-loaded zeolites fillers were developed, optimised with respect to host–guest interactions and characterised by Fraunhofer IFAM (Bremen, Germany) with regard to the release and curing behaviour in epoxy adhesive formulations. They are added to an epoxy adhesive (diglycidylether of bisphenol A (EP) and Dicyandiamide (Dicy), mass ratio 100:6.7), stored at 25°C in regular air or cured (heated with β = 10 K/min to 170°C subsequent isothermal curing for 45 min). That shelf life and curing behaviour are investigated by FT-IR spectroscopy and modulated DSC. Compared to the EP containing free accelerator, the zeolite-filled EP possesses a threefold increase in shelf life at 25°C ...

Xiang Dong Liu - One of the best experts on this subject based on the ideXlab platform.

  • Storage stability and curing behavior of epoxy‐Dicyandiamide systems with carbonyldiimidazole‐Cu (II) complexes as the accelerator
    Journal of Polymer Science Part A: Polymer Chemistry, 2013
    Co-Authors: Xiang Dong Liu, Atsushi Sudo, Chun Hua Zhao, Takeshi Endo
    Abstract:

    The reaction between carbonyldiimidazole (CDI) and copper (II) nitrate produces a new Cu (II) complex with nitrate as the counter anion. TGA, UV, and FTIR analyses confirmed that the coordination number of CDI in this complex is two. The acceleration effect of the complex in epoxy-Dicyandiamide (Dicy) curing systems has been evaluated by DSC and TMA, and the increasing viscosity of the mixture was monitored during the storage. The results revealed that the complex is not only very effective for the acceleration of epoxy-Dicy systems, leading to a rapid gelation within 21 min at 120 °C, but it is also chemically stable at ambient temperature. This is reflected by the slow increase of viscosity of the accelerated curing systems stored at 35 °C, even over 56 days. In addition, the effects of the [Cu(CDI)2]2+ complex with different counter anions, that is, bromide, chloride, nitrate, sulfate, phthalate, and acetate, were compared using a series of tests. By comparing with N,N-dimethyl-N′-phenylurea (fenuron), the widely used latent accelerator for Dicy-epoxy curing systems, the complexes with bromide and nitride were found to be better, both regarding storage stability and for their acceleration effect. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3470–3476

  • Accelerating effects of N‐aryl‐N′,N′‐dialkyl ureas on epoxy‐Dicyandiamide curing system
    Journal of Polymer Science Part A: Polymer Chemistry, 2010
    Co-Authors: Xiang Dong Liu, Mika Kimura, Atsushi Sudo, Takeshi Endo
    Abstract:

    This report focuses on epoxy-Dicyandiamide (Dicy) curing system accelerated by N-aryl-N′,N′-dialkyl urea, aiming at clarifying the accelerating mechanism and the relationship between accelerating effect and molecular structure of the accelerators. Nine N-aryl-N′,N′-dialkyl ureas were synthesized and investigated with measurements of differential scanning calorimetry, thermo gravimetric/differential thermal analysis and NMR spectroscopy. The results revealed that the ureas released the corresponding secondary amines by the thermal dissociation in the presence of epoxide, which led to the formation of tertiary amines that catalyze the addition reaction of Dicy to epoxide. Moreover, a tendency that the ureas able to release more compact amines exhibited higher acceleration effects was discovered. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010