جستجوی مقالات مرتبط با کلیدواژه "epoxy resin" در نشریات گروه "مهندسی شیمی، نفت و پلیمر"

Hypothesis: 

Some adducts were prepared from three kinds of DGEBA-based epoxy resins, phthalic anhydride and an alkanol amine accelerator, as a latent accelerator for one-pot epoxy/dicy systems. These adducts come with two kinds of accelerators: DMP-30 A, which is lab-grade and Ax-10, which is industrial-grade, as well as DGEBA based epoxy resins Epikote 828, Epiran 06 and ML 504. The adduct made of Epikote 828 and DMP-30 A was considered as a reference. It seems that it might be possible to prepare a new efficient latent accelerator with change of epoxy resin and accelerator.

For this purpose, four different adducts with resins and accelerators and four different epoxy/dicy mixtures with four adduct types and AX-10 accelerator and one with no adduct as a reference were prepared. Measuring the melting point, viscosity build-up versus time, gelation time, non-isothermal differential scanning calorimetry (DSC) and glass transition temperature characterization and also lap shear, interlaminar shear strength, transvers tensile and scanning electron microscope (SEM) were used to study the latent properties of the prepared adducts in the epoxy/dicy system and find its effect on mechanical properties of the final composites and all were compared with references.

Melting point of all adducts is above room temperature, so they are solid at room temperature. The results show that the adducts containing the industrial accelerator in one-pot epoxy/dicy system has lower gel time at high temperature, higher viscosity changes at ambient temperature and pot life and has made no significant change in cure temperature. The mechanical properties of the composite made with an adduct consisting of ML 504 resin are accompanied by a decrease in the related values. In general, the adduct made with Epiran 06 or Epikote 828 resin and industrial accelerator is an efficient and new latent accelerator and is suitable for preparing one-pot epoxy/dicy systems.

The purpose of the present research is to investigate the shear modulus of the polymer matrix composite. For this purpose, 3D orthogonal fabric was used to strengthen the composite. Threads in the woven structure produced by the orthogonal method have less wrinkling compared to other 3D fabric production methods. Composite samples in two different types, one with a high volume fraction of HVF fibers and the other with a low volume fraction of LVF fibers, were produced with two types of epoxy resin and polyester using the vacuum pump method and were subjected to torsion testing. In the next step, numerical modeling was done in Abaqus software. The results showed that the shear modulus and torsional strength of LVF composite with epoxy matrix increased by 7% and 11%, respectively. Comparison of the simulation results with the experimental method showed that the shear modulus obtained from the modeling had an error of less than 10% compared to the shear modulus of the composite, so the simulation method can be used to predict the mechanical properties of the composite.

The process of curing the epoxy resins with hardeners leads to an increase in crosslink density and the properties of the hardened resin are affected, depending on the curing conditions. To improve the final properties of epoxy resins, the use of organic and inorganic nanoparticles has been suggested. One of the recently attended nanoparticles is graphene oxide and its derivatives. In this paper, various models presented in the curing kinetics of epoxy/ graphene oxide hybrid compounds have been evaluated and the reasons for the deviation of laboratory and experimental results with modeling results have been explained. Also, comparison of each of these models with experimental results has shown that Sestak-Berggren and Kamal model has higher adaptation to experimental results than the other models and can be used as a reliable basis for describing the curing process of epoxy resins containing graphene oxide nanoparticles.

Epoxy resins usually have a brittle structure due to the cross-linked structure and poor resistance to crack growth. Therefore, increasing the toughness of epoxy resins in the presence of polymer nanoparticles is one of the fields of interest for researchers. Studying the degradation of epoxy nanocomposites and modeling the degradation kinetics have become widely used as an essential tool for engineers to predict the thermal stability of materials before using in industry, which leads to reduction in costs and an increase in product quality. Surface modification of carbon nanotubes and dispersion of nanoparticles are two important factors in the thermal stability of epoxy nanocomposites in the presence of carbon nanotubes. Hybrid epoxy nanocomposite in the presence of multi-walled carbon nanotubes and clay nanoparticles showed that the simultaneous presence of these nanoparticles can act as a preventive agent against thermal degradation and increase the activation energy of the degradation reaction. In this article, the effect of carbon nanotubes on morphology, rheological and mechanical properties, thermal gravimetric analysis, thermal stability of epoxy resin, and modeling of degradation kinetics of epoxy nanocomposites in the presence of carbon nanotubes are reviewed.

Nowadays, the use of prepregs has accelerated the composite manufacturing and has facilitated their processing. To prepare the epoxy prepregs, it is necessary to cure the resin slightly in order to maintain the overall shape of the prepreg and to hold the fibers together. Since epoxy resins require heat for curing and heat is release during the curing reaction, it is always difficult to control the degree of cure in the precuring stage. The progress of precuring reaction determines the mechanical properties and processability of the prepregs. One of the methods to control the degree of cure of epoxy resin for use in prepregs is to use two different curing systems with different conditions for each stage called dual curing system. In this article, while introducing the types of dual curing systems used for epoxy resin such as epoxy-acrylate, epoxy-phenol, epoxy-thiol, epoxy-siloxane, epoxy-sulfonium salt and epoxy-amine, the application of each system is reviewed. Due to the diversity of dual curing systems, different systems can be used to control the prepregs properties such as viscosity, curing percentage, shelf life and also improve the properties of the final composite. Studies show that, in order to increase the shelf life of prepregs using the click reaction with an optical initiator to perform the reaction of the first stage of curing and the thermal click reaction for the second stage of curing are most effective.

 Epoxy resin is used in various industries such as adhesives, paints and coatings, aerospace and electronics due to its unique attributes. Epoxy curing agents can be generally classified in two groups of normal (room or high temperature) and latent curing agents. Latent curing agents are mixed with epoxy resins to obtain stable compounds at normal conditions. These compounds can cure epoxy resins rapidly when exposed to external stimulation, such as heat. Capsulation of curing agent as a cost-effective method has attracted an extensive attention to prepare non-reactive or latent curing agents. The concentration of microencapsulated latent curing agent significantly affects the final mechanical properties of cured epoxy resins.

The effect of concentration of microcapsules containing curing agent of 1-methyl imidazole by solid epoxy shell on the mechanical properties of epoxy resin was investigated using dynamic mechanical thermal analysis.

The effect of 20, 25, 30 and 35 phr (per hundred resin) microcapsules concentration in liquid epoxy on storage modulus (E′) and phase angle tangent (Tanδ) was investigated. The results showed that increasing the concentration of microcapsules in cured samples causes to advance storage modulus due to increasing the amount of curing agent and consequently increasing the density of crosslinks. On the other hand, it was found that liquid epoxy resin cured with 30 phr microcapsules has the highest glass transition temperature (48°C). The hardness test results also confirmed the results of thermal-mechanical dynamic test at the optimum microcapsule concentration. The results also indicated that at 30°C the storage module decreased by increasing microcapsule concentration from 20 to 25 phr.  The storage modulus of cured epoxy resins increased to higher values by increases in microcapsule concentration. Therefore, the epoxy resin cured by 35 phr microcapsule showed the highest storage module (723 MPa).

The sudy of degradation kinetics of epoxy nanocomposites is very important because it can determine the temperature range and service life of the sysem. Degradation kinetics modeling has become widely used as an essential tool for engineers to predict the thermal durability of materials before their usage in indusry, leading to reduced coss and product development, manufacturing coss, time and quality of the designed product. Dispersion and disribution of clay nanoparticles in epoxy resin matrix are two important factors in the physical and mechanical properties of epoxy nanocomposites. Also, the inhibitory properties of clay nanoparticles or layered silicates agains hydrogen and oxygen, as well as the type of sructure can cause thermal sability of epoxy resin. Surface modifcation of the clay nanoparticles could play a delaying role in the degradation reaction of epoxy nanocomposites. The content of the added clay nanoparticles and the type of production process  are two important factors in invesigating the degradation kinetics of epoxy resin in the presence of clay nanoparticles. In this paper, the efect of modifed and unmodifed clay nanoparticles on the degradation kinetics of epoxy resin and diferent models of degradation kinetics, activation energy, thermogravimetric analysis and weight loss percentage and the efect of diferent types of clay nanoparticles on the degradation kinetics of epoxy resin are reviewed.

Epoxy resin is used as a wind turbine, coating, adhesive and base material for composites and is widely used in automotive, electronics, and construction industries. Modification of the surface of epoxy nanocomposites in the presence of silica nanoparticles, due to increased adhesion and covalent bonding, increases the impact strength and Also, by adding silica nanoparticles to epoxy resin, the Young's modulus increases linearly, which is due to the increase in nanoparticle dispersion and reduced stress concentration. By adding silica nanoparticles to epoxy resin, the maximum heat flow temperature decreases and the curing rate increases, and also causes the heat flow curve of epoxy nanocomposite to be wider. The presence of silica nanoparticles reduces the activation energy and silica nanoparticles act as a catalyst in the curing reaction with epoxy resin. Two important factors in reducing the thermal degradation of epoxy nanocomposites are proper dispersion of nanoparticles and non-agglomeration. Silica nanoparticles increase the maximum temperature of thermal degradation, thermal stability and the percentage of residual char. In this research, the modeling of curing kinetics of epoxy nanocomposites on morphology, rheological and mechanical properties, activation energy, curing degree, heat flow and investigation of thermal stability and thermal degradation has been reported.

Thermoset nanocomposites, due to their strength and special physical and mechanical properties compared to metal materials, are widely used in the manufacture of household appliances, electrical appliances, coatings and sports equipment, and sanitary wares. The thermal properties of epoxy nanocomposites depend on the adhesion between the nanoparticles and matrix. Also, designing high quality and efficient epoxy nanocomposites with suitable physical and mechanical properties requires understanding the phenomena that occur during the curing reaction. The reaction of epoxy resin and curing agent as well as the study of curing kinetics play an important role in controlling the deformation of the structure and physical and mechanical properties of the composites. Investigating the dispersion of nanoparticles and selecting the appropriate mixing method can improve the curing reaction or crosslinking of epoxy nanocomposites. It can also prevent the agglomeration of nanoparticles, that affect thermal reactions. Modified iron oxide nanoparticles reduce the reaction activation energy and the curing time. Reaction time and temperature are two important factors for evaluating chemical curing reactions. Modeling analysis of curing kinetics of epoxy nanocomposites is a solution to overcome the problems of thermal reactions that occur during the curing reactions. In this paper, the curing kinetics modeling of epoxy nanocomposites and the effect of adding modified and unmodified iron oxide nanoparticles on the amount of activation energy, curing index, and rheological, mechanical and thermal properties are introduced.

The main goal of this research is the preparation and study of nanocomposites based on carboxylated nitrile butadiene rubber )XNBR( and epoxy resin reinforced by halloysite nanotubes )HNTs(. The effect of various HNTs loadings on the cure characteristics, morphology, cure kinetics and mechanical properties of binary XNBR/Epoxy systems was investigated. The results of cure rheometer indicated that the introduction of HNTs into the XNBR/Epoxy matrix leads to a decreased scorch time up 25% and higher maximum torque values. The resulted SEM photomicrographs of fractured section from tension tests revealed a more rough fractured surface of nanocomposites containing HNTs with a distributed of nanotubes into the polymer matrix. The study of cure kinetics show that the introduction of HNTs into the polymer system decreases the activation energy needed for curing reaction up to 40% . The results of tension tests demonstrated a higher Young’s modulus up to 1.46 MPa and tensile strength up to 2.58 MPa with higher loadings of HNTs into the XNBR/ Epoxy matrix. The analyses of XNBR/Epoxy/HNTs nanocomposites indicated that with the natural and inexpensive reinforce nano materials, it is possible to make nanocomposites with higher mechanical strength up to 40% with respect to neat polymer.

Epoxy resins are widely used as encapsulating materials in the electronic and electrical industries, transportation, coatings, adhesives, and advanced composite matrices owing to their excellent heat, moisture and chemical resistance, high tensile strength, low shrinkage on curing, and excellent dimensional stability. Epoxy resins are very flammable; this nature seriously restricts their widespread applications, especially in the areas requiring high flame retardancy. To address this challenging problem, several approaches, such as use of halogen-based flame retardant, organophosphorus compounds (e.g., ammonium polyphosphate and melamine polyphosphate), inorganic flame retardants (most widely used alumina trihydrate and magnesium hydroxide known as ATH and MDH, respectively), nitrogen-based flame retardants, silicon-based flame retardants, intumescent flame retardants, and nanomaterials have been proposed. Phosphorus-containing compounds are mostly used as substitutes for the halogenated compounds in flame-retardant epoxy resins. Various phosphorus compounds are used as additive or reactive flame retardants. Comparing the additive flame retardants, reactive organophosphorus compounds present excellent flame retardant efficiency in the case of epoxy resins and it can be chemically linked to the backbone of the network either through being part of the curing agent or through the structure of epoxy resins itself and giving intrinsic flame retardancy. In this review, classification of flame retardants (halogen-based flame retardants, organophosphorus compounds, inorganic flame retardants, nitrogen- and silicon-based flame retardants, intumescent flame retardants and nanocomposites), the combustion cycle of polymers and application of flame retardants, especially phosphorus-based flame retardants for epoxy resins are introduced and classified. Experimental test methods for evaluation of flame retardancy like UL-94, limiting oxygen index and cone calorimeter are also discussed.

Hypothesis: 

Organogels are hydrophobic macromolecular networks with ability to absorb and retain organic solvents. They have been used in various applications, e.g., production of disinfectant hygienic gels used in medicine and public health. The present paper is a preliminary report on the conversion of common epoxy resin (DGEBA) into a new superabsorbent organogel containing functional groups of furan, carbamate, and triazole.

The organogel was synthesized through a four-step strategy from epoxy resin and furfuryl alcohol. The furfurylated epoxy resin was converted to an isocyanate-terminated compound that then converted into a propargyl-terminated intermediate. The final product was produced by 1,3-dipolar cycloaddition polymerization reaction of a propargylated compound and a diazide compound prepared from epichlorohydrin. The intermediate compounds and the final product were characterized by Fourier transform infrared (FTIR) spectroscopy. The final product was characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Rheological behavior in solvent N-methyl-2-pyrrolidone (NMP) was preliminarily studied and swelling capacity of the organogel was determined in various solvents.

A novel polymeric organogel was synthesized without using a particular crosslinker. Its dried particles were found to have porosity with a pore diameter of ~680 nm. The organogel showed increased swelling capacity with dropping of solvent viscosity and increasing of solvent polarity. The high solvent uptake and storage capacity by this organogel has supported it as a superabsorbent organogelator. Its swelling capacity was determined in the solvents to be in order: ethylene glycol < chloroform < ethanol < acetonitrile < dimethylformamide < dimethylacetamide < dimethylsulfoxide < NMP. For instance, each gram of the organogel can absorb and gelate ~145 g ethanol, or ~1853 g NMP, within ~1 h. The super-swelling behavior of this solvent-retaining network was preliminarily attributed to a combination of limited crosslinkages as well as some polymer-polymer and polymer-solvent supramolecular interactions. The presence of 1,2,3-triazole groups is also expected to induce antibacterial properties in this organogel.

Epoxy resins are one of the most prominent resins in the world. Many factors affect the mechanical properties of this family of polymers, but the effects of parameters such as molecular packing on mechanical properties are less investigated. The most important factor in molecular packing and mechanical properties is the chemical structure of the curing agent. Herein, we report the effect of aromatic structure of the curing agent on the molecular packing and mechanical properties of the cured epoxy resin.

The curing of the epoxy resin was performed by melting the curing agent and addition of the epoxy resin. To study the effect of curing agent structure, three different curing agents including meta-phenylenediamine (m-PDA), ortho-phenylenediamine (o-PDA) and 2,4-diamino toluene (2,4-DAT) were used. The molecular packing was studied by X-ray diffraction (XRD) technique. Also, the density measurements of cured epoxy resins were carried out using the Archimedes method and finally, the effect of molecular packing on the mechanical properties was investigated by tensile test.

The results obtained from XRD and tensile test measurements showed that there is a direct relationship between the molecular packing and mechanical strength which by increases in the molecular packing the tensile strength increased as well. By changing the curing agent from m-PDA to o-PDA, the molecular packing was increased and consequently, led to an increase in the tensile strength of the epoxies. In using 2,4-DAT as a curing agent, the molecular packing and hence the mechanical strength were decreased due to the steric hindrance of the methyl group.

Epoxy resins are widely used in composites, aerospace, construction, electronic, adhesive and coatings industries due to their high physical and mechanical, thermal resistance, electrical and chemical properties. For curing epoxy resins, a chemical material, called curing agent or hardener, must be used. Curing agents have strong effect on the processing conditions and final properties of the cured resins. In general, epoxy curing agents can be classified in two groups of normal (room or high temperature) and latent curing agents. Normal curing agents increase the resin viscosity at room temperature due to crosslinking or curing reactions and the resin is gelled and finally cured. The rate of viscosity increment would be different and depends on the kind of curing agent. On the other hand, latent curing agents cannot react with epoxy resin at room temperature and do not increase the resin viscosity. Therefore, they are being used for preparing one-part epoxy resins. Latent curing agents are not active at room temperature, but they will react with epoxy resin by the application of an external force like heat or light. Thermally-latent curing agents are well-known and they are widely used. They include substances with active hydrogen, and are catalyzed and protected by chemical groups and microcapsules. Selection of a latent curing system for an application is an important issue which affects the processing conditions and final properties of the cured resins. In this paper, the latest achievements in this area are reviewed.

Hypothesis: Thermally stable nanocomposites were prepared by incorporation of carbon nanotubes (CNT) into the epoxy resin matrix cured by novolac resin. CNT modified with epoxy functional groups is capable of reaction with hydroxyl groups of novolac resin. Therefore, a new and robust method was planned for development of covalent bonding between the filler and matrix. On the other hand, due to slow reaction of epoxy and hydroxyl groups in the absence of catalyst, triphenylphosphine was used as the catalyst to accelerate the curing process.

CNT was modified with nitric acid to obtain oxidized CNT (CNTCOOH). After grafting of butane diol at the surface of CNTCOOH, hydroxyl-containing CNT (CNTOH) was prepared. Afterward, epoxy functional groups were applied at the surface of CNTOH through its modification with (3-glycidyloxypropyl) triethoxysilane in order to prepare epoxy-containing CNT (CNTG). Finally, CNTG and epoxy resin were placed in the hybrid network through the curing process with novolac resin. Finding: The results of FTIR-spectroscopy and X-ray photoelectron spectroscopy showed that modification of CNT was effectively carried out. X-ray diffraction analysis confirmed uniform distribution of CNTG in the matrix of cured epoxy resin. As thermogravimetric analysis exhibited, char yield of the cured epoxy resin (26.6%) was considerably increased to 32.8% and 38.2% through incorporation of 2 and 4 wt% of CNTG into the network, respectively. According to the scanning electron microscopy and transmission electron microscopy images, CNT showed tubular and entangled structure with smooth and uniform surface which even retained its structure after modification reaction. Finally, this approach can be successfully used for production of thermally-resistant thermoset hybrids for thermal protection applications

Epoxy, one of the most important thermosetting polymers, is used in a wide range of applications as adhesives, coatings, and materials for composite structures due to its outstanding performance, low processing capacity and low cost. Due to the superior properties of carbon nanomaterials in thermal conductivity, flame retardation, mechanical stability, electrical conductivity and environmental compatibility, these nanomaterials have attracted global attention. In the present article, a review of past literature on improving the performance of epoxy resin by adding carbon nanomaterials is presented. The correlation of structural performance for epoxy modified with various carbon nanomaterials has been closely analyzed. Improvement of mechanical, electrical, thermal conductivity and flame deterioration for epoxy resin has been investigated. Challenges and opportunities in the composite of functionalized nano-materials epoxy are also discussed. The purpose of this research is to provide a comprehensive understanding of the multi-purpose epoxy resins including carbon nanomaterials to date and assess its future prospects. Also, the relationship and comparison of the structure and performance of various carbon nanomaterials has been evaluated. The improvement of mechanical, electrical, thermal conductivity and carbon dioxide epoxy flame retardant properties has been thoroughly investigated. Finally, the conclusions and prospects for the future and the hope of facilitating progress are presented at the end of the paper.

Epoxy resin has remarkable properties including excellent mechanical and electrical properties, thermal and chemical stability, and resistance to creep. On the other side, these resins are brittle with low resistance toward crack initiation and its growth. In order to solve this problem, thermoplastic polysulfone and graphene nanosheets have been used as filler for improving the flexibility of epoxy coatings. The effect of adding different amounts (1, 0.5, 2.5, 5 wt%) of polysulfone and 0.5 wt% of graphene nanosheets on the epoxy properties was investigated by thermal analysis (DSC), tensile strength, impact resistance and determining the gel content of samples. The results showed that the tensile strength of epoxy resin increased by adding polysulfone, and the graphene nanosheets could improve flexibility of the sample containing 1 wt% polysulfone. The study of thermal properties of cured samples by means of DSC analysis showed that the addition of polysulfone into the epoxy network resulted in changing the glass transition (Tg) of the resin. With incorporation of graphene nanosheets into the polymer matrix, the modulus decreased due to the reduction in number of crosslinks. The study in impact resistance of the samples showed that those containing 1 wt% polysulfone and 0.5 wt% graphene displayed high strength and impact resistance. These types of compounds can be used in flexible and anticorrosion coatings.

Thermoset polymers have excellent properties of high dimensional stability at elevated temperatures, low creep and good resistance against solvents due to their three-dimensional crosslinking structure. Proper thermal-mechanical properties for these polymers are based on such cured structures with high crosslink density. Due to its excellent mechanical properties, epoxy resin has been widely used in coatings, adhesives and composites. In recent years, a variety of modification procedures have been introduced for toughening of cured resin structure in order to minimize crack formation and improve their impact resistance. Chemical modification of epoxy resins with polyurethanes is one of the most efficient procedures to achieve this goal. Polyurethanes have unique properties including good abrasion resistance, ease of processing and high rupture strength. After a brief introduction of epoxy and polyurethane resins, the procedures and the mechanisms of fracture toughness in polyurethane-modified epoxy are reviewed in present article. Different polyurethanes with wide range of chemical structures are able to toughen the epoxy structure efficiently and provide improved resins for use indifferent applications.

Epoxy resins as one of the most important thermoset materials have shown various applications in production of composites، adhesives and surface coatings. Due to formation of the network structure، the cured epoxy resin shows brittleness and low impact resistance. The mechanical properties in the epoxy resin (especially the fracture toughness) can be modified by adding a softer phase preferably the rubber phase، thermoplastic fillers and even rigid particles. In comparison with other methods، the inclusion of rigid particles into epoxy resin improved the fracture toughness of epoxy resin without sacrificing the other main properties of epoxy resin such as the modulus (E) and glass transmission temperature (Tg). In recent years، the introduction of nanotechnology has shown some possibilities in toughening improvement of nanomaterials. Due to the special properties and different types of nanoparticles، a review study on effective nanoparticles would be useful in utilizing nanomaterials in toughening of the epoxy resin.

The mechanical properties of epoxy resin including tensile and flexural modulus، tensile and flexural strength for static conditions are currently studied. The frequency effect as significant parameter at room temperature is investigated and fatigue behavior of the epoxy resin in tension-tension loading conditions for different frequencies of 2، 3 and 5 Hz are obtained. The epoxy resin has been taken under flexural bending fatigue loading and fatigue life is investigated. The results of the experiments show the values of 2. 5 and 3 GPa of tensile and flexural modules and 59. 98 and 110. 02 MPa of tensile and flexural strengths for the resin، respectively. To achieve a linear load-deflection relationship in a three-point bending experiment، a maximum allowable deflection of 5 mm is acquired. The relationship between the frequency and fatigue life shows higher frequency results in lower fatigue life. Loading with frequency of 2 Hz has provided 5. 8 times more fatigue life compared with 5 Hz loading. For a tension-tension fatigue loading condition، the variation of tensile module of epoxy resin shows no noticeable change during the fatigue loading condition. This module decreases significantly only in the primary and failure cycles close to the fracture point. In further experiments، fatigue behavior of epoxy resin was tested under flexural bending fatigue loadings with controlled deflection at room temperature. Maximum applied normalized stresses versus the number of cycles to failure curve are illustrated and it can be performed in order to predict the number of cycles to failure for the resin in arbitrary applied normal stresses as well.