Synthesis,characterization, and mechanical properties evaluation of thermally stable apophyllite vinyl ester nanocomposites

The objective of this study is to prepare layered organosilicates with enhanced thermal stability that can be used to formulate high‐temperature polymer nanocomposites. Fourier transform infrared (FTIR) spectroscopy, wide‐angle X‐ray diffraction (WAXD), and thermal gravimetric analysis (TGA) characterization results of the modified silicates indicate that the organic pendant group has been chemically grafted on to the backbone of layered silicate and the organically modified apophyllite is thermally stable up to approximately 430°C. The organically modified apophyllite was mixed along with vinyl ester resin and styrene diluent in a sonic dismembrator and the mixture cured to form a nanocomposite specimen. Transmission electron microscopy (TEM) results of the nanocomposites showed mixed morphology with predominant fraction of organosilicates exhibiting an intercalated structure. Tapping mode atomic force microscopy (TMAFM) observation of the nanocomposite showed striated layered silicates dispersed in the resin matrix. The nanocomposites formulated with organosilicates containing reactive terminal pendant group were found to have a higher tensile strain than the nanocomposites formulated with organosilicates containing inert pendant group. Copyright © 2007 John Wiley & Sons, Ltd.     

Thermal properties and moisture absorption of nanofillers‐filled epoxy composite thin film for electronic application

This current study aimed to enhance the thermal conductivity of thin film composites without compromising other polymer qualities. The effect of adding high thermal conductivity nanoparticles on the thermal properties and moisture absorption of thin film epoxy composites was investigated. Three types of fillers in nanosize with high thermal conductivity properties, boron nitride (BN), synthetic diamond (SD), and silicon nitride (Si₃N₄) were studied. SN was later used as an abbreviation for Si₃N₄. The contents of fillers varied between 0 and 2 vol.%. An epoxy nanocomposite solution filled with high thermal conductivity fillers was spun at 1500–2000 rpm to produce thin film 40–60 µm thick. The effects of the fillers on thermal properties and moisture absorption were studied. The addition of 2 vol.% SD produced the largest improvement with 78% increment in thermal conductivity compared with the unfilled epoxy. SD‐filled epoxy thin film also showed good thermal stability with the lowest coefficients of thermal expansion, 19 and 124 ppm, before and after T_g, respectively, which are much lower compared with SN‐filled and BN‐filled epoxy thin film composites. However the SD‐filled epoxy film has its drawback as it absorbs more moisture compared with BN‐filled and SN‐filled epoxy film. Copyright © 2012 John Wiley & Sons, Ltd.     

Imidazole‐type thermal latent curing agents with high miscibility for one‐component epoxy thermosetting resins

Epoxy resins are important thermosetting resins widely employed in industrial fields. Although the epoxy–imidazole curing system has attracted attention because of its reactivity, solidification of a liquid epoxy resin containing imidazoles proceeds gradually even at room temperature. This makes it difficult to use them for one‐component epoxy resin materials. Though powder‐type latent curing agents have been used for one‐component epoxy resin materials, they are difficult to apply for fabrication of fine industrial products due to their poor miscibility. To overcome this situation and to improve the shelf life of epoxy–imidazole compositions, we have developed a liquid‐type thermal latent curing agent 1 , generating an imidazole with a thermal trigger via a retro‐Michael addition reaction. The latent curing agent 1 has superior miscibility toward epoxy resins; in addition, it was confirmed that the epoxy resin composition has both high reactivity at 150 °C, and long‐term storage stability at room temperature. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2680–2688     

Exploitation of introducing of catalytic centers into layer galleries of layered silicates and related epoxy nanocomposites. I. Epoxy nanocomposites derived from montmorillonite modified with catalytic surfactant‐bearing carboxyl groups

Montmorillonite (MMT) was modified with the acidified cocamidopropyl betaine (CAB) and the resulting organo‐montmorillonite (O‐MMT) was dispersed in an epoxy/methyl tetrahydrophthalic anhydride system to form epoxy nanocomposites. The intercalation and exfoliation behavior of the epoxy nanocomposites were examined by X‐ray diffraction and transmission electron microscopy. The curing behavior and thermal property were investigated by in situ Fourier transform infrared spectroscopy and DSC, respectively. The results showed that MMT could be highly intercalated by acidified CAB, and O‐MMT could be easily dispersed in epoxy resin to form intercalated/exfoliated epoxy nanocomposites. When the O‐MMT loading was lower than 8 phr (relative to 100 phr resin), exfoliated nanocomposites were achieved. The glass‐transition temperatures (T_g's) of the exfoliated nanocomposite were 20 °C higher than that of the neat resin. At higher O‐MMT loading, partial exfoliation was achieved, and those samples possessed moderately higher T_g's as compared with the neat resin. O‐MMT showed an obviously catalytic nature toward the curing of epoxy resin. The curing rate of the epoxy compound increased with O‐MMT loading. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1192–1198, 2004     

Immobilization of flame retardant onto silica nanoparticle surface and properties of epoxy resin filled with the flame retardant‐immobilized silica

To prepare silica nanoparticle having flame retardant activity, the immobilization of flame retardant onto hyperbranched poly(amidoamine) (PAMAM)‐grafted silica was investigated. Grafting of PAMAM onto a silica surface was achieved in a solvent‐free dry‐system using PAMAM dendrimer synthesis methodology. The immobilization of bromine flame retardant, poly(2,2′,6,6′‐tetrabromobisphenol‐A) diglycidyl ether (PTBBA), was successfully achieved by the reaction of terminal amino groups of PAMAM‐grafted silica (Silica‐PAMAM) with epoxy groups of PTBBA. The immobilization of PTBBA was confirmed by FTIR and thermal decomposition GC‐MS. The amount of PTBBA immobilized onto Silica‐PAMAM was determined to be 60 wt %. PTBBA‐immobilized Silica‐PAMAM (Silica‐PAMAM‐PTBBA) was dispersed uniformly in a epoxy resin, and the epoxy resin was cured in the presence of hexamethylenediamine. Flame retardant activity of the epoxy resin filled with Silica‐PAMAM‐PTBBA was estimated by limiting oxygen index (LOI). The LOI of epoxy resin filled with Silica‐PAMAM‐PTBBA was higher than that filled with untreated silica and free PTBBA. It was confirmed that the flame retardant activity of epoxy resin was improved by the addition of the Silica‐PAMAM‐PTBBA. The elimination of PTBBA from the epoxy resin filled with Silica‐PAMAM‐PTBBA into boiling water was hardly observed by immobilization of PTBBA onto silica surface. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6145–6152, 2009     

Synthesis of hydroxyl‐terminated poly(ether ether ketone) with pendent tert‐butyl groups and its use as a toughener for epoxy resins

Hydroxyl‐terminated poly(ether ether ketone) with pendent tert‐butyl groups (PEEKTOH) was synthesized by the nucleophilic substitution reaction of 4,4′‐difluorobenzophenone with tert‐butyl hydroquinone with potassium carbonate as a catalyst and N‐methyl‐2‐pyrrolidone as a solvent. Diglycidyl ether of bisphenol A epoxy resin was toughened with PEEKTOHs having different molecular weights. The melt‐mixed binary blends were homogeneous and showed a single composition‐dependent glass‐transition temperature (T_g). Kelley–Bueche and Gordon–Taylor equations gave good correlation with the experimental T_g. Scanning electron microscopy studies of the cured blends revealed a two‐phase morphology. A sea‐island morphology in which the thermoplastic was dispersed in a continuous matrix of epoxy resin was observed. Phase separation occurred by a nucleation and growth mechanism. The dynamic mechanical spectrum of the blends gave two peaks corresponding to epoxy‐rich and thermoplastic‐rich phases. The T_g of the epoxy‐rich phase was lower than that of the unmodified epoxy resin, indicating the presence of dissolved PEEKTOH in the epoxy matrix. There was an increase in the tensile strength with the addition of PEEKTOH. The fracture toughness increased by 135% with the addition of high‐molecular‐weight PEEKTOH. The improvement in the fracture toughness was dependent on the molecular weight and concentration of the oligomers present in the blend. Fracture mechanisms such as crack path deflection, ductile tearing of the thermoplastic, and local plastic deformation of the matrix occurred in the blends. The thermal stability of the blends was not affected by blending with PEEKTOH. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 541–556, 2006     

Diglycidyl ether of bisphenol‐A epoxy resin modified using poly(ether ether ketone) with pendent tert‐butyl groups

Bisphenol‐A‐based difunctional epoxy resin was modified with poly(ether ether ketone) with pendent tert‐butyl groups (PEEKT). PEEKT was synthesized by the nucleophilic substitution reaction of 4,4′‐difluoro benzophenone with tert‐butyl hydroquinone in N‐methyl‐2‐pyrrolidone. Blends with various amounts of PEEKT were prepared by melt‐mixing. All the blends were homogeneous in the uncured state. The glass transition temperature of the binary epoxy/PEEKT blends was predicted using several equations. Reaction‐induced phase separation was found to occur upon curing with a diamine 4,4′‐diaminodiphenyl sulfone. The phase morphology of the blends was studied using scanning electron microscopy. From the micrographs, it was found that PEEKT‐rich phase was dispersed in a continuous epoxy matrix. The domain size increased with the amount of PEEKT in the blends. The increase in domain size was due to the coalescence of the domains after phase separation. Dynamic mechanical analysis of the blends gave two peaks corresponding to epoxy‐rich phase and thermoplastic‐rich phase. The tensile strength and modulus of the blends remained close to that of the unmodified resin, while the flexural properties decreased with the addition of PEEKT to epoxy resin. The fracture toughness of the epoxy resin increased with the addition of PEEKT. Investigation of the fracture surfaces revealed evidences for local plastic deformation of the matrix, crack pinning, crack path deflection, and ductile tearing of PEEKT‐rich phase. Thermogravimetric analysis revealed that the initial decomposition temperature of the blends were close to that of the unmodified resin. Finally, the properties of the blends were compared with other modified PEEK/epoxy blends. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2481–2496, 2007     

Study of the fire resistant behavior of unfilled and carbon nanofibers reinforced polybenzimidazole coating for structural applications

With increasing interest in epoxy‐based carbon fiber composites for structural applications, it is important to improve the fire resistant properties of these materials. The fire resistant performance of these materials can be improved either by using high performance epoxy resin for manufacturing carbon fiber composite or by protecting the previously used epoxy‐based composite with some fire resistant coating. In this context, work is carried out to evaluate the fire resistance performance of recently emerged high performance polybenzimidazole (PBI) when used as a coating material. Furthermore, the effect of carbon nanofibers (CNFs) on fire resistant properties of inherently flame retardant PBI coating was studied. Thermogravimetric analysis of carbon/epoxy composite, unfilled PBI and nano‐filled PBI shows that the carbon/epoxy composite maintained its thermal stability up to a temperature of 400°C and afterwards showed a large decrease in mass, while both unfilled PBI and nano‐filled PBI have shown thermal stability up to a temperature of 575°C corresponding to only 11% weight loss. Cone calorimeter test results show that unfilled PBI coating did not improve the fire retardant performance of carbon/epoxy composite. Conversely, nano‐filled PBI coating has shown a significant improvement in fire retardant performance of the carbon/epoxy composite in terms of increased ignition time, reduced average and peak heat release rate and reduced smoke and carbon monoxide emission. These results indicate that addition of carbon nanofibers to inherently flame retardant coating can significantly be helpful for improving the fire resistance performance of composite materials even with low coating thickness. Copyright © 2013 John Wiley & Sons, Ltd.     

Nonaqueous synthesis of nanosilica in epoxy resin matrix and thermal properties of their cured nanocomposites

Nonaqueous synthesis of nanosilica in diglycidyl ether of bisphenol‐A epoxy (DGEBA) resin has been successfully achieved in this study by reacting tetraethoxysilane (TEOS) directly with DGEBA epoxy matrix, at 80 °C for 4 h under the catalysis of boron trifluoride monoethylamine (BF₃MEA). BF₃MEA was proved to be an effective catalyst for the formation of nanosilica in DGEBA epoxy under thermal heating process. FTIR and ²⁹Si NMR spectra have been used to characterize the structures of nanosilica obtained from this direct thermal synthetic process. The morphology of the nanosilica synthesized in epoxy matrix has also been analyzed by TEM and SEM studies. The effects of both the concentration of BF₃MEA catalyst and amount of TEOS on the diameters of nanosilica in the DGEBA epoxy resin have been discussed in this study. From the DSC analysis, it was found that the nanosilica containing epoxy exhibited the same curing profile as pure epoxy resin, during the curing reaction with 4,4′‐diaminodiphenysulfone (DDS). The thermal‐cured epoxy–nanosilica composites from 40% of TEOS exhibited high glass transition temperature of 221 °C, which was almost 50 °C higher than that of pure DGEBA–DDS–BF₃MEA‐cured resin network. Almost 60 °C increase in thermal degradation temperature has been observed during the TGA of the DDS‐cured epoxy–nanosilica composites containing 40% of TEOS. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 757–768, 2006     

High mechanical and thermal performance of Sasobit-modified epoxy resin,prepared via vacuum shock technique

In this study, thermal and mechanical properties of novel nanocomposite, epoxy resin reinforced with octadecylamine functionalized graphene oxide (GO-ODA) and Sasobit, prepared via creative vacuum shock technique, were investigated. By introducing 1, 3 and 5 wt% Sasobit to the neat epoxy resin, the tensile strength increased remarkably by 104%, 315% and 266%, respectively due to the unique stiff and crystalline structure of Sasobit. In addition, considerable enhancement of 125% in Young's modulus, 351% in toughness, 562% in impact resistance, ~19 °C in thermal stability and ~7 °C in glass transition temperature of epoxy resin with 3 wt% Sasobit loading was demonstrated. The composite containing 3 wt% Sasobit alone, were found to have even superior properties than GO-ODA/epoxy nanocomposite, as surprisingly 3, 2.9, 2.2 and 2 times more improvement, respectively in tensile strength, toughness, impact strength and thermal stability of epoxy resin compared to reinforcement with GO-ODA were obtained.     

Preparation and characterization of epoxy/SiO2 nanocomposites by cationic photopolymerization and sol–gel process

Epoxy/SiO₂ nanocomposite materials were prepared by cationic photopolymerization and sol–gel process using a novel epoxy oligomer (EP‐Si(OC₂H₅)₃) prepared by 3‐isocyanatopropyltriethoxysilane (IPTS)‐grafted bisphenol A epoxy resin and tetraethyl orthosilicate as inorganic precursor. The chemical structures of EP‐Si(OC₂H₅)₃ were characterized by Fourier transformed infrared spectroscopy. Transmission electron microscopy showed that the in situ generated nano‐SiO₂ dispersed uniformly in the EP matrix, and its average diameter is around 40 nm. The relationship between nanocomposite materials' thermal/mechanical properties and nano‐SiO₂ introduced were studied by thermogravimetric analysis, dynamic mechanical analysis, and impact strength test. The results showed that the nanocomposite materials' thermal and mechanical properties improved a lot with increase of the SiO₂ content. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis and thermal studies of flexible polyurethane nanocomposite foams obtained using nanoclay modified with flame retardant compound

This work presents thermal studies of nanocomposites based on the flexible polyurethane (PU) matrix and filled using montmorillonite organically modified with organophosphorus flame retardant compound. Flexible PU nanocomposite foams were prepared in the reaction carried out between reactive alcoholic hydroxyl and isocyanate groups with the ratio of NCO to OH groups equal to 1.05. The amount of an organoclay ranging from 3 to 9 vol% was added to the polyol component of the resin before mixing with isocyanate. The apparent density of PU foams was ranging from 0.066 to 0.077 g cm^?1. Thermal properties of the flexible PU nanocomposite foams were investigated by thermogravimetry and dynamical mechanical analysis. Glass transition temperatures (T _g) were defined as maximum peak on tanδ curve. Thermal decomposition was observed at 310–320 °C (calculated from the onset of TG curve). Tensile strength of the PU foams was determined using mechanical test. The microstructure of the nanoparticles and the composites was investigated by X-ray diffraction. Finally, it was confirmed that the thermal and mechanical properties of flexible PU nanocomposite depend on the amount of nanoclay.     

The preparation of inorganic/organic hybrid nanomaterials containing silsesquioxane and its reinforcement for an epoxy resin network

A series of new inorganic/organic hybrid nanomaterials were prepared through the reaction of cage octa(γ-aminopropylsilsesquioxane) with n-butyl glycidyl ether. The structures and properties of these hybrid materials were characterized by Fourier transform infrared spectroscopy, ²⁹Si nuclear magnetic resonance (NMR), ¹H-NMR, and mass spectrometry spectra. The hybrid materials were used for improving mechanical and thermal properties of epoxy resin E-51. The results showed that appropriate amount of addition of the hybrids could enhance the fracture elongation ratio and impact strength. The tensile strength decreased with the addition of the hybrids. The thermal properties such as glass transition temperature, antioxidant index, decomposition temperature, and Vicat softening temperature were obviously improved. Scanning electron microscope observation displayed a rough structure inside the cured epoxy resin by the addition of the hybrids. Kinetic study indicated that the curing process was continuous with average activation energy of 48.06 kJ/mol which was based on Kissinger and Flynn–Wall–Ozawa models.     

Thermal properties and fracture toughness of epoxy resins cured by phosphonium and pyrazinium salts as latent cationic initiators

In this work, the latent thermal cationic initiators triphenyl benzyl phosphonium hexafluoroantimonate (TBPH) and benzyl‐2‐methylpyrazinium hexafluoroantimonate (BMPH) were newly synthesized and characterized with IR, ¹H NMR, and P NMR spectroscopy. The thermal and mechanical properties of difunctional epoxy [diglycidyl ether of bisphenol A (DGEBA)] resins cured by 1 phr of either TBPH or BMPH were investigated. The DGEBA/TBPH system showed a higher curing temperature and a higher critical stress intensity factor than the epoxy/BMPH system. This could be interpreted in terms of the slow thermal diffusion rate and bulk structure of the four phenyl groups in TBPH. However, the decomposition activation energy derived from the Coats–Redfern method was lower for epoxy/TBPH. This result was probably due to the fact that a broken short‐chain structure was developed by the steric hindrance of TBPH in the difunctional epoxy resin. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2393–2403, 2003     

Structure–initiator activity dependence of aminimides as thermally latent initiators in the polymerization of glycidyl phenyl ether

Novel aliphatic aminimides were synthesized from the corresponding carboxylic acid esters, 1,1‐dimethylhydrazine, and epoxides in 54–95% yields. Bulk polymerization of glycidyl phenyl ether (GPE) with 3 mol % of the aminimides was evaluated by DSC as a model process for curing of epoxy resin. All the aminimides showed no exothermic DSC peak below 120 °C but showed sharp exothermic peaks above 137 °C, indicating good thermal latency. Good relationships were observed between the calculated bond length from the carbonyl carbon to the α‐carbon of the aliphatic group (R C), DSC onset temperatures, and the thermal dissociation temperatures (T_d 's) of the aminimides. The aminimide with a longer R C bond length showed lower T_d and DSC onset temperature, that is, higher activity. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3428–3433, 2000     

Synthesis and characterization of novel epoxy resins‐filled microcapsules with organic/inorganic hybrid shell for the self‐healing of high performance resins

Novel microcapsules (MCs) with organic/inorganic hybrid shell were successfully fabricated using epoxy resin as core material and nano boron nitride (BN) and mesoporous silica (SBA‐15) as inorganic shell materials in aqueous solution containing a water‐compatible epoxy resin curing agent. The morphologies, thermal properties and Young's moduli of MCs were investigated. The results indicated that epoxy resins were encapsulated by BN/SBA‐15/epoxy polymer hybrid layer, the resulting MCs were spherical in shape and the introduction of inorganic particles made MCs had rough surface morphology. The mean modulus value of MCs was from 2.8 to 3.1 GPa. The initial decomposition temperature (T_di) of MCs at 5 wt% weight loss was from 309 to 312°C. MCs showed excellent thermal stability below 260°C. The structures and properties of MCs could be tailored by controlling the weight ratio of inorganic particle. When the weight ratio of BN to SBA‐15 was 0.15:0.10, MCs had the highest T_di and modulus. The resulting MCs were applied to high performance 4,4′‐bismaleimidodiphenylmethane/O,O′‐diallylbisphenol A (BMI/DBA) system to design high performance BMI/DBA/MC systems. Appropriate content of MCs could improve the fracture toughness and maintain the glass transition temperature (T_g) of BMI/DBA system. The core materials released from fractured MCs could bond the fracture surfaces of the BMI/DBA matrix through the polymerization of epoxy resins. When the healing temperature schedule of 100°C/2h+150°C/1h was applied, 15 wt% MCs recovered 98% of the virgin fracture toughness of BMI/DBA. Copyright © 2016 John Wiley & Sons, Ltd.     

Application of Modified Natural Oils as Reactive Diluents for Epoxy Resins

Bisphenol A based low-molecular-weight epoxy resin was modified with epoxidized soybean oil, which exhibit viscosity reducing ability comparable to commercial grade active diluents. The studied compositions showed a non-Newtonian rheological behavior, typical for Bingham liquids. The values of the flow index (n) and the consistency index (k) for the compositions tested in the temperature range 25–65 °C were calculated from the Ostwald-de Waele rheological model and were used to calculate the flow-activation energy (E_a) using the Arhenius equation. Studies of co-crosslinking of mixed oil-resin compositions using isophorone diamine showed essential decrease of the reaction heat and peak maximum temperature. Mechanical properties, thermal stability, water absorption and chemical resistance of the epoxy resin modified with natural oil, were also investigated. Compositions of epoxy resin Ruetapox 0162, modified with the oil diluent, preserved very good mechanical properties of the epoxy resins and demonstrated relatively low water absorption as well as high chemical resistance. The compositions displayed even higher impact strength than pure epoxy resin due to plasticizing effect of the built-in oil. Compositions with the high contents (up to 60 weight %) of the oil were flexible materials with fast elastic recovery.     

Thermal and morphological characteristics of solution blended epoxy/NBR compound

Systematic study about the effect of acrylonitrile–butadiene rubber (NBR) concentration on the fracture toughness and thermal behavior of epoxy resin is conducted in this study. NBR is solved in an aromatic hydrocarbon solvent and is added to epoxy resin. We used diethylene-teriamin as the curing agent for epoxy resin. Tensile test results, performed followed by molding procedure, show that the toughness is improved owing to the increase of rubber content. Scanning electron microscopy (SEM) and atomic force microscopy besides thermogravimetric analysis (TG) are used to investigate the epoxy/rubber interface and chemical decomposition of the resultant mixture. The thermal behavior of cured epoxy resin was analyzed via TG instrument at different heating rates. Thermogravimetry curves showed that the thermal decomposition of epoxy system was occurred in only one stage regardless of the rubber content. The apparent activation energies of the rubber/epoxy systems containing 0, 5, and 10 phr of rubber were determined by Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, and Friedman methods. The results prove that the thermal stability of epoxy resin was decreased with enhancing the rubber content. However, the trend of changing activation energy versus conversions is totally different followed by adding the elastomer to the system compared to neat epoxy resin. Moreover, the results obtained via our proposed facile solution blending method are compared to those of resins modified with nano-powdered elastomer.     

Enhanced fracture toughness and mechanical properties of epoxy resin with rice husk-based nano-silica

This paper reports a novel approach to toughen epoxy resin with nano-silica fabricated from rice husk using a thermal treatment method with a particle size distribution in range of 40–80 nm. The nano-silica content was in the range, 0.03–0.10 phr, with respect to epoxy. The mechanical test showed that with the addition of 0.07 phr of rice husk based nano-silica, the fracture toughness of the neat epoxy resin increased 16.3% from 0.61 to 0.71 MPa m^1/2. The dynamic mechanical analysis test results showed that the glass transition temperature (T _g) of a 0.07 phr nano-silica dispersion in epoxy resin shifted to a higher temperature from 140 to 147°C compared to neat epoxy resin. SEM further showed that the nano-silica particles dispersed throughout the epoxy resin prevented and altered the path of crack growth along with a change in the fracture surface morphology of cured epoxy resin.     

Facile fabrication of fast recyclable and multiple self‐healing epoxy materials through diels‐alder adduct cross‐linker

A reversibly cross‐linked epoxy resin with efficient reprocessing and intrinsic self‐healing was prepared from a diamine Diels‐Alder (DA) adduct cross‐linker and a commercial epoxy oligomer. The newly synthesized diamine cross‐linker, comprising a DA adduct of furan and maleimide moieties, can cure epoxy monomer/oligomer with thermal reversibility. The reversible transition between cross‐linked state and linear architecture endows the cured epoxy with rapid recyclability and repeated healability. The reversibly cross‐linked epoxy fundamentally behaves as typical thermosets at ambient conditions yet can be fast reprocessed at elevated temperature like thermoplastics. As a potential reversible adhesive, the epoxy polymer with adhesive strength values about 3 MPa showed full recovery after repeated fracture‐thermal healing processes. The methodology explored in this contribution provides new insights in modification of conventional engineering plastics as functional materials. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2094–2103