Epoxy resins (ER) are considered as one of the most important classes of thermosetting polymers and are extensively used in various applications. But they are very brittle, with poor resistance to crack propagation and have low impact strength. In the present work, a series of hydroxyl terminated polybutadiene (HTPB) was directly dispersed in the epoxy resin. Then, the dispersed phase was cross-linked by divinylbenzene (DVB) that was previously added to HTPB. Different content of DVB and HTPB are evaluated for effecting on the most of physico-chemical properties of the epoxy resin. The FTIR analysis evidenced the occurrence of a chemical reaction between HTPB and DVB and also ER which was led to improved compatibility. The DMTA analysis of samples indicated different Tg for HTPB/DVB and ER in the mixture and explaining the phase separation between rubber and matrix phases. On adding DVB the stress-at-break increased accompanied by an increase in the elongation-at-break value. Maximum impact strength is obtained by adding 20 phr of DVB and 5 phr HTPB. Finally, SEM analysis showed that modified rubber particles’ diameter is about 5 mm (corresponding to maximum of toughness).

To improve the toughness of epoxy resin, and clarify the complex interrelationship between the miscibility, morphology, toughness and composition of epoxy resin/graft copolymer blends, amphiphilic polysiloxane graft copolymers (F6-PMSs) with different contents of polyether were synthesized via hydrosilylation between epoxy-immiscible poly(methylhydrosiloxane) and epoxy-miscible allyl polyoxyethylene polyoxypropylene ether (F6) to modify diglycidyl ether of bisphenol A (DGEBA). The miscibility of amphiphilic graft copolymers with epoxy resin was investigated by observing the transparency of the modified epoxies before and after curing and by detecting the glass transition temperature (Tg) of the cured epoxies using differential scanning calorimetry. The morphologies of the cured epoxies were studied by scanning electron microscopy, and the toughness in terms of tensile and impact strength were examined by tensile and impact testing. Results indicated to higher miscibility of polysiloxane with DGEBA by grafting with polyether. Relative to the neat epoxy network, the polysiloxane modified epoxies exhibited lower Tgs and with the increased polyether in graft copolymer, there was a decreasing trend noticed in Tg. The nanostructures were obtained for the modified epoxies with different F6 to PMS ratios (5 wt% of DGEBA). The formation of the nanostructures in the thermosetting composites was judged by following the self-assembly and reaction-induced mechanisms, mainly dependent on the miscibility of graft copolymer with epoxy resin. Moreover, toughness of the epoxy networks was greatly improved by F6-PMS of 100/100 weight ratio at relatively low addition levels.

A new kind of reactive toughening agent, defined as liquid crystalline polyurethane (LCPB), having both flexible chain and rigid biphenyl mesogenic groups was synthesized by polyaddition of 2,4-toluenediisocyanate (TDI) with diethylene glycol and 4,4'-dihydroxybiphenyl in DMF. The structure and morphology of the LCPB were investigated systematically by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), wide angle X-ray diffractometry (WAXD) and polarizing optical microscopy (POM), respectively. The POM observation confirmed that the LCPB exhibited nematic texture and good mesophase stability. The LCPB was used to modify the epoxy resin as toughening agents. The mechanical properties, dynamic mechanical behaviour, fracture surface morphology and apparent activation energy (Ea) of the modified systems were systematically investigated. The experimental results revealed that the impact strength of the epoxy resin modified with LCPB reached the highest value of 47.21 kJ/m2, and it is 1.8 times higher than that of the unmodified system when the content of LCPB loading reached 5 wt%. In addition, the tensile strength and the fracture strength also enhanced with increasing concentration of LCPB. The DMA results showed that the storage modulus in rubbery state and glass transition temperature (Tg) of the modified systems were higher than those of the unmodified system, indicating that the motion of epoxy matrix chains was strongly restricted by the rigidity of mesogenic units, while the Ea at glassy relaxation process of modified system was about 100-120 kJ/mol higher than that of the unmodified system. The effects of reinforcement on mechanisms of the damaging process of the modified systems were investigated by scanning electron microscopy. 

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.

This study investigates the use of three different types of Epoxy Resin materialsviz., EXPACRETE SNE1, LAPOX B-47 and HARDENER K-46, and CONBEXTRA EP10, 65 & 120 for repairing the reinforced concrete beams. In this research, 6 standard size beams (150x230x1500mm) for M50 grade of concrete were distress in flexure by applying two points load by taking 90% of the ultimate load. Then, these distressed beams were repaired and retested up to ultimate failure load.The aim of this study is to determine the suitability of Epoxy Resin material type to be used in RCC beams for repairing and restoring good strength and for considering economical aspects. Hardened concrete specimens were tested for compression, and flexural test. The results of these experiments show that the beams repaired using Epoxy Resin material (EXPACRETE SNE1) gave higher increase in the ultimate load than other Epoxy Resin materials. The flexural strength increased significantly up to about 15 percent for concrete beams repaired with epoxy resin material (EXPACRETE SNE1) compared to other epoxy resin materials. Deflections were smaller in reinforced concrete beams with epoxy resin compared to conventional concrete beams. Compare to all the three types of epoxy resin materials used i.e. EXPACRETE SNE1 is cheaper than other two materials. Though reinforced concrete beams repaired with epoxy resins is costlier comparatively, it is cheaper than to reconstruct the structure.

Epoxies are generally cross-linked by the addition of a hardener, most of the time a diamine such as diamine diphenyl sulphone, oxydianiline or methylene diamine, and then thermocured. These formulations are quite often used, particularly in the aerospace industry for making structural materials, prepregs or composites. In this paper we have investigated the cross-linking reactions of a difunctional cycloaliphatic epoxide monomer 3,4-epoxycyclohexylmethyl-3', 4'-epoxycyclohexane carboxylate initiated by UV-irradiation and compared the kinetics with N,N-diglycidyl- 4-glycidyloxyaniline (a nitrogen-containing monomer with a functionality of three) and 4,4'-methylenebis (N,N-diglycidylaniline) (another nitrogen-containing monomer with a functionality of four). Kinetics is followed using a differential photocalorimetry (DPC) technique. Upon UV irradiation in the presence of cationic photoinitiator, the difunctional cycloaliphatic epoxide monomer shows an exotherm peak whereas for the latter two monomers, no exotherm peaks were observed from the sample as a result of exposure to the UV source. To explain the phenomenon observed, the effect of addition of two amines with wide difference in the basicity of p-nitroaniline and pyridine, has been studied on the UV-curing of epoxy resins. It has been found that the presence of amines does retard the rate of photopolymerization and the extent of retardation is dependent on the basicity of the amine. Of the two amines used, pyridine and p-nitroaniline, the former is a stronger inhibitor, because of the ready availability of the lone pair of electrons. The results explain the non-reactivity of nitrogencontaining epoxy monomers N,N-diglycidyl-4-glycidyloxyaniline and 4,4'-methylenebis (N,N-diglycidylaniline) to cationic polymerization upon exposure to UV-radiation.

Epoxy resins are considered as one of the most important classes of thermosetting polymers for many industrial applications, but unfortunately they are characterized by a relatively low toughness. In this respect, many efforts have been made to improve the toughness of cured epoxy resins by the introduction of rigid particles, reactive rubbers, interpenetrating polymer networks and thermoplastics within the matrix. In this work, hydroxyl-terminated polybutadiene (HTPB) as a modifier, firstly, was crosslinked by variable content of divinylbenzene (DVB) in the presence of epoxy resin (ER) and then the modified matrix was cured with 1-methylimidazole as a curing agent. Infrared spectra showed the existence of a chemical reaction between modified HTPB (MHTPB) and the ER. Most of the tensile properties attained a peak at an approximately 20 phr (part per hundred rubber) DVB content, where the toughening reached its maximum. For both notched and un-notched specimens, a two-fold increase in izod impact strength was obtained by the addition of just 20 phr DVB compared to the neat resin. On the addition of DVB, the Izod impact strength varied from 0.54 to 0.71 kJ/m2 for notched specimens and from 1.43 to 6.66 kJ/m2 for un-notched specimens. Whereas, KIC varied from 1.35 to 2.59 MPa.m1/2 with increasing DVB content. By SEM analysis the average diameter was found to be about 5 mm (corresponding to maximum of toughness) for modified rubber particles. The overall results have shown that it is possible to obtain excellent impact strength and good mechanical properties with the use of MHTPB as a toughening agent for the epoxy resins.

Maleimide modified epoxy compounds were prepared by reacting N-(4-hydroxyphenyl) maleimide (HPM) with diglycidylether of bisphenol-A. Triphenylphosphine was used as a catalyst and methylethylketone as a solvent. The resulting compound possessed both the oxirane ring and maleimide group. The curing reaction of the maleimide-epoxy compound with amine curing agents such as ethylenediamine (EDA), diethylenetriamine (DETA) and triethylenetetramine (TETA) were studied. Incorporation of maleimide groups in the epoxy resin provides cyclic imide structure and high cross-linking density to the cured resins. The cured samples were found to have good thermal stability, chemical (acid/alkali/solvent) and water absorption resistance. The morphology of cured epoxy systems were also studied by scanning electron microscopy (SEM).

Toughening of a diglycidyl ether of bisphenol-A (DGEBA)-based epoxy resin with liquid carboxyl-terminated butadiene acrylonitrile (CTBN) copolymer has been investigated. For this purpose six blend samples were prepared by mixing DGEBA with different concentrations of CTBN from 0 to 25 phr with an increment of 5 phr. The samples were cured with dicyandiamide curing agent accelerated by Monuron. The reactions between oxirane groups of DGEBA and carboxyl groups of CTBN were followed by Fourier-transform infrared (FTIR) spectroscopy. Tensile, impact, fracture toughness and dynamic mechanical analysis of neat as well as the modified epoxies have been studied to observe the effect of CTBN modification. The tensile strength of the blend systems increased by 26 % when 5 phr CTBN was added, and it remained almost unchanged up to 15 phr of CTBN. The elongation-at-break and Izod notched impact strength increased significantly, whereas tensile modulus decreased gradually upon the addition of CTBN. The maximum toughness of the prepared samples was achieved at optimum concentration of 15 phr of CTBN, whereas the fracture toughness (K IC) remained stable for all blend compositions of more than 10 phr of CTBN. The glass transition temperature (T g) of the epoxy resin significantly increased (11.3oC) upon the inclusion of 25 phr of CTBN. Fractured surfaces of tensile test samples have been studied by scanning electron microscopic analysis. This latter test showed a two-phase morphology where the rubber particles were distributed in the epoxy resin with a tendency towards co-continuous phase upon the inclusion of 25 phr of CTBN.