Enhanced fracture toughness of epoxy resins with novel amine‐terminated poly(arylene ether sulfone)–carboxylic‐terminated butadiene‐acrylonitrile–poly(arylene ether sulfone) triblock copolymers

Amine‐terminated poly(arylene ether sulfone)–carboxylic‐terminated butadiene‐acrylonitrile–poly(arylene ether sulfone) (PES‐CTBN‐PES) triblock copolymers with controlled molecular weights of 15,000 (15K) or 20,000 (20K) g/mol were synthesized from amine‐terminated PES oligomer and commercial CTBN rubber (CTBN 1300x13). The copolymers were utilized to modify a diglycidyl ether of bisphenol A epoxy resin by varying the loading from 5 to 40 wt %. The epoxy resins were cured with 4,4′‐diaminodiphenylsulfone and subjected to tests for thermal properties, plane strain fracture toughness (K_IC), flexural properties, and solvent resistance measurements. The fracture surfaces were analyzed with SEM to elucidate the toughening mechanism. The properties of copolymer‐toughened epoxy resins were compared to those of samples modified by PES/CTBN blends, PES oligomer, or CTBN. The PES‐CTBN‐PES copolymer (20K) showed a K_IC of 2.33 MPa m^0.5 at 40 wt % loading while maintaining good flexural properties and chemical resistance. However, the epoxy resin modified with a CTBN/8K PES blend (2:1) exhibited lower K_IC (1.82 MPa m^0.5), lower flexural properties, and poorer thermal properties and solvent resistance compared to the 20K PES‐CTBN‐PES copolymer‐toughened samples. The high fracture toughness with the PES‐CTBN‐PES copolymer is believed to be due to the ductile fracture of the continuous PES‐rich phases, as well as the cavitation of the rubber‐rich phases. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1556–1565, 2002; DOI 10.1002/app.10390     

Mechanical and dielectric properties of epoxy resin modified using reactive liquid rubber (HTPB)

In the present study, hydroxyl‐terminated polybutadiene (HTPB) liquid rubber was employed to modify epoxy resin using 2,4,6‐tri (dimethylaminomethyl) phenol as a catalyst, and methyl hexahydrophthalic anhydride as a curing agent. The reactions between HTPB and epoxy were monitored by Fourier transform infrared (FTIR); the mechanical and dielectric properties of HTPB modified epoxies were evaluated and the morphology was investigated through scanning electronic microscopy (SEM). The FTIR analysis evidenced the occurrence of a chemical reaction between the two components. The mechanical results indicated that the impact strength of HTPB‐modified epoxy was superior to that of the pure epoxy. As the HTPB content increased up to 10 phr the best mechanical performances in terms of tensile and flexural properties were achieved when compared to the unmodified epoxy. Higher concentration of HTPB resulted in larger particles and gave lower mechanical strength values. The incorporation of HTPB into epoxy decreased the dielectric constant and dissipation factor over a wide frequency range from 1 to 10⁶ Hz, and improved the electrical resistivity. SEM micrographs showed that the modified epoxy exhibited a two‐phase morphology where the spherical rubber domains were dispersed in the epoxy matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Modification of epoxy resin by isocyanate‐terminated polybutadiene

Hydroxy‐terminated polybutadiene was functionalized with isocyanate groups and employed in preparation of a block copolymer of polybutadiene and bisphenol A diglycidyl ether (DGEBA)‐based epoxy resin. The block copolymer was characterized by Fourier transform infrared (FTIR) spectroscopy and size‐exclusion chromatography (SEC). Cured blends of epoxy resin and hydroxy‐terminated polybutadiene (HTPB) or a corresponding block copolymer were characterized by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMTA), and scanning electron microscopy (SEM). All modified epoxy resin networks presented improved impact resistance with the addition of the rubber component at a proportion up to 10 wt % when compared to the neat cured resin. The modification with HTPB resulted in milky cured materials with phase‐separated morphology. Epoxy resin blends with the block copolymer resulted in cured transparent and flexible materials with outstanding impact resistance and lower glass transition temperatures. No phase separation was discernible in blends with the block copolymer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 838–849, 2002     

反应性端基聚丁二烯系列液体橡胶在环氧树脂改性增韧方面的应用

综述了含反应性端基聚丁二烯系列液体橡胶（以下简单PBLR）品种、性能及特点，概括比较了PBLR改性增韧环氧树脂方法及特点；分别列举了PBLR改性环氧树脂在微机电浇注料，树脂砂轮，水利机械涂敷，电子灌封及飞机粘合剂等方面的应用。     

Thermal stability and kinetics analysis of rubber‐modified epoxy resin by high‐resolution thermogravimetric analysis

A dynamic heating rate mode of high‐resolution thermogravimetric analysis was used to study the thermal and thermal‐oxidative stability, as well as kinetics analyses, of a model liquid rubber‐modified epoxy resin, Ep/CTBN, made up of bisphenol A diglycidyl ether‐based epoxy and carboxyl‐terminated butadiene acrylonitrile rubber (CTBN). Results show that the thermal degradation of Ep/CTBN resin in nitrogen and air consists of two and three independent steps, respectively. Moreover, Ep/CTBN has a higher initial degradation temperature and higher activation energy than those of pure epoxy resin in both gases, indicating that the addition of CTBN to epoxy can improve the thermal and thermal‐oxidative stability of pristine epoxy resin. Kinetic parameters such as activation energy, reaction order, and preexponential factor of each degradation step of both Ep/CTBN and pure epoxy resins in air and nitrogen were calculated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3594–3600, 2003     

Synthesis and architecture study of a reactive polybutadiene polyamine as a toughening agent for epoxy resin

In this study, a novel reactive toughener for the epoxy resin was developed and compared with traditional hydroxyl‐terminated polybutadiene (HTPB). For this purpose, the highly reactive aliphatic amine‐terminated polybutadiene (ATPB) was synthesized at ambient conditions by nucleophilic substitution amination. The characterizations of the product were provided by Fourier transform infrared and ¹H NMR spectroscopy. According to the mechanical test results, incorporation of ATPB into epoxy networks can significantly toughen the epoxy matrix. The addition of 10 phr ATPB increased the critical stress intensity factor (K_IC) and critical strain energy release rate (G_IC) of the epoxy from 0.85 to 2.16 MPa m^1/2 and from 0.38 to 3.02 kJ m^?2, respectively. Furthermore, unlike HTPB, the presence of the ATPB did not deteriorate the tensile strength of the matrix. The toughening and failure mechanisms were discussed based on the epoxy network morphological characteristics. The reduction in cross‐linking density and glass transition temperature of the epoxy system upon modification with liquid rubbers was confirmed by dynamic mechanical analysis. This article opens up the possibility of utilizing reactive flexible diamines with polybutadiene backbone as effective toughening agents for thermoset polymers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44061.     

含活性官能团液体橡胶增韧环氧树脂及其应用

介绍了含活性官能团的聚丁二烯系列液体橡胶 (以下简称PBLR)的品种、性能及特点 ;概括比较了PBLR改性增韧环氧树脂的方法及特点 ;分别列举了PBLR改性环氧树脂在微电机浇注料、树脂砂轮、水利机械涂敷、电子灌封及飞机粘合剂等方面的应用。     

Cure kinetics of ternary blends of epoxy resins studied by nonisothermal DSC data

The curing kinetics of blends of diglycidyl ether of bisphenol A (DGEBA), cycloaliphatic epoxy resins, and carboxyl‐terminated butadiene‐acrylonitrile random copolymer (CTBN) in presence of 4,4′‐diamino diphenyl sulfone (DDS) as the curing agent was studied by nonisothermal differential scanning calorimetry (DSC) technique at different heating rates. The kinetic parameters of the curing process were determined by isoconversional method given by Malek for the kinetic analysis of the data obtained by the thermal treatment. A two‐parameter (m, n) autocatalytic model (Sestak‐Berggren equation) was found to be the most adequate selected to describe the cure kinetics of the studied epoxy resins. The values of E_a were found to be 88.6 kJ mol^?1 and 61.6 kJ mol^?1, respectively, for the studied two sample series. Nonisothermal DSC curves obtained using the experimental data show a good agreement with that theoretically calculated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Elastomer‐modified epoxy/amine systems in a resin transfer moulding process

The effect of the elastomer structure on toughening highly crosslinked epoxy systems in a resin transfer moulding process (RTM) was investigated. Two kinds of elastomers containing carboxyl functionalized groups were used: (1) a reactive liquid elastomer based on carboxyl‐terminated butadiene‐acrylonitrile copolymer (CTBN), (2) a preformed core‐shell rubber (CSR). The introduction of CTBN rubber caused the modification in the glass transition temperature due to the miscibility in the epoxy matrix, whereas CSR particles did not. During cure, these elastomers affected the morphological, rheological and dielectric behaviour of epoxy/amine systems. A blend of 5% CTBN and 5% CSR exhibited a bimodal distribution of rubber particle sizes (analyzed by transmission electron microscopy) whereas scanning electron microscopy showed the glass fibre‐matrix cohesion in fracture surfaces. A semi‐empirical model was used (developed by Castro‐Macosko for describing chemorheological behaviour of epoxy/amine systems for the RTM process). The increase in viscosity and the reduction in ion conductivity were the two key parameters to monitor the cure process. The presence of rubber affected the rheological behaviour involving initial viscosity and gel point. The investigation of temperatures, pressures and ionic conductivities in various glass fibre layers was conducted to control the front flow filling and the cure reaction. The introduction of rubber modified the inflexion area of the cured rubber–epoxy blends by changing the cure rate. Copyright © 2004 Society of Chemical Industry     

Partially miscible blends of epoxy resin and epoxidized rubber: Structural characterization of the epoxidized rubber and mechanical properties of the blends

The cure process and the mechanical properties of blends of diglycidyl ether of bisphenol-A–based epoxy resin and hydroxyl terminated, internally epoxidized polybutadiene rubber have been studied. Internal oxirane groups are characterized by a main absorption at 885 cm^?1 in the infrared spectrum while the terminal oxirane groups of the diepoxide monomer absorb at 913 cm^?1. In the absence of prereaction of the rubber, gelation of the epoxy matrix occurs much faster than any reaction involving the internal oxirane groups or the terminal hydroxyl groups. Therefore, only weak chemical bonding between the rubber particles and the epoxy matrix exists and the fracture toughness of the blends does not show any significant improvement. Upon prereaction of the rubber with an excess diepoxide monomers, a 40% improvement in the value of the critical stress intensity factor is obtained. However, dynamic mechanical spectra of these blends acquired in the rubbery plateau region uniquely demonstrate that this improvement is due to the incorporation of the rubber into the epoxy network rather than to the presence of phase-separated rubber particles. © 1994 John Wiley & Sons, Inc.     

Mechanical,thermal, and viscoelastic response of novel in situ CTBN/POSS/epoxy hybrid composite system

The present study focuses on the preparation of a novel hybrid epoxy nanocomposite with glycidyl polyhedral oligomeric silsesquioxane (POSS) as nanofiller, carboxyl terminated poly(acrylonitrile‐co‐butadiene) (CTBN) as modifying agent and diglycidyl ether of bisphenol A (DGEBA) as matrix polymer. The reaction between DGEBA, CTBN, and glycidyl POSS was carefully monitored and interpreted by using Fourier transform infrared (FTIR) and differential scanning calorimetry (DSC). An exclusive mechanism of the reaction between the modifier, nanofiller, and the matrix is proposed herein, which attempts to explains the chemistry behind the formation of an intricate network between POSS, CTBN, and DGEBA. The mechanical properties, such as tensile strength, and fracture toughness, were also carefully examined. The fracture toughness increases for epoxy/CTBN, epoxy/POSS, and epoxy/CTBN/POSS hybrid systems with respect to neat epoxy, but for hybrid composites toughening capability of soft rubber particles is lost by the presence of POSS. Field emission scanning electron micrographs (FESEM) of fractured surfaces were examined to understand the toughening mechanism. The viscoelastic properties of epoxy/CTBN, epoxy/POSS, and epoxy/CTBN/POSS hybrid systems were analyzed using dynamic mechanical thermal analysis (DMTA). The storage modulus shows a complex behavior for the epoxy/POSS composites due to the existence of lower and higher crosslink density sites. However, the storage modulus of the epoxy phase decreases with the addition of soft CTBN phase. The T_g corresponding to epoxy‐rich phase was evident from the dynamic mechanical spectrum. For hybrid systems, the T_g is intermediate between the epoxy/rubber and epoxy/POSS systems. Finally, TGA (thermo gravimetric analysis) studies were employed to evaluate the thermal stability of prepared blends and composites. POLYM. COMPOS., 37:2109–2120, 2016. © 2015 Society of Plastics Engineers     

Toughened cycloaliphatic epoxy resin for demanding thermal applications and surface coatings

An epoxy resin based on nonglycidyl ether and varying content of carboxyl‐terminated (poly)butadiene acrylonitrile copolymer was cured using an aromatic amine hardener. The ultimate aim of the study was to modify the brittle epoxy matrix by the liquid rubber to improve toughness characteristics. Fourier transform infrared spectroscopic analysis of the modified was performed to understand the structural transformations taking place during the uncured and cured stage of the modified systems. The decreasing trend in exothermal heat of reaction with increasing rubber content in the epoxy resin can be explained by the fact that the increase of carboxyl‐terminated butadiene acrylonitrile copolymer (CTBN) modifier might induce a high reactivity of the end groups with the epoxide ring and resulting shorter curing times and, hence, the faster curing process than the unmodified resin. Tensile strength, impact strength, and elongation‐at‐break behaviors of neat as well as modified networks have been studied to observe the effect of rubber modification. Blends sample exhibits better properties as compared to pure epoxy resin in terms of increase in impact strength and elongation‐at‐break of the casting and gloss, scratch hardness, adhesion, and flexibility of the film. The improvement in these properties indicate that the rubber‐modified resin would be more durable than the epoxy based on di glycidyl ether of bis‐phenol‐A and other epoxies. The films of coating based on epoxy with 15 wt % CTBN offered the maximum resistance toward different concentrations of acids, alkalies, and solvents as compared to the cured films of other blend samples. The thermal stability of the cycloaliphatic‐based epoxy resin was increased with the addition of 15 wt % CTBN in epoxy matrix. Cycloaliphatic‐based epoxy network modified with CTBN displayed two phase separated morphology with dispersed rubber globules in the matrix resin, i.e., they revealed the presence of two phase morphological features. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Adhesive properties of epoxy resin modified by end‐functionalized liquid polybutadiene

Adhesive properties of epoxy resin networks modified with different functionalized liquid polybutadiene were evaluated by using aluminum adherent. The end‐functionalized polybutadiene rubbers were hydroxyl‐ (HTPB), carboxyl‐ (CTPB), and isocyanate‐terminated polybutadiene (NCOTPB). The adhesive properties depend upon the morphology and the degree of interaction between the rubber–epoxy system. The most effective adhesive for Al–Al joint in both butt and single‐lap shear testing was epoxy resin–NCOTPB system. This system presents stronger rubber–epoxy interactions and a higher degree of rubber particle dispersion with particle size diameter in the nanoscale range. These characteristics were not important for improving the toughness of the bulk network but are fundamental for the improvement of adhesive strength. The effect of the pretreatment of the aluminum surface on the roughness was also evaluated by using profilometry analysis. The type of failure was also investigated by analyzing the adhered surfaces after fracture by scanning electron microscopy and profilometry. A proportion of cohesion failure higher than 90% was observed in all systems. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2370–2378, 2004     

A Probe on the Failure Mechanism in Rubber-Modified Epoxy Blends: Morphological and Acoustic Emission Analysis

In this work, diglycidyl ether of bisphenol A based epoxy resin (DGEBA) was modified with varying amounts of two liquid rubbers: carboxyl terminated copolymer of butadiene and acrylonitrile (CTBN); and a hydroxyl terminated polybutadiene (HTPB), using an anhydride hardener. The ultimate aim of this study was to investigate the failure mechanism operating in the rubber-modified epoxies and to evaluate this by correlating these results with the miscibility and interfacial adhesion between the components and the morphology of the cured network. Some of the mechanical and fracture properties, which are associated with the two-phase particulate morphology, were investigated. The visoelastic behavior of modified epoxies was also analyzed and variations in the shift of T _g values in toughened epoxies were explained. The samples were carefully analyzed by an acoustic emission technique to investigate the failure mechanism operating in them. From the response of force and number of acoustic events as well as from the amplitude of acoustic events, we were able to explain the failure mechanisms in the elastomer incorporated epoxy resins supplemented by morphological evidence.     

Influences of liquid elastomer additive on the behavior of short glass fiber reinforced epoxy

In this study, improvements in mechanical and thermal behavior of short glass fiber (GF) reinforced diglycidyl ether of bisphenol-A (DGEBA) based epoxy with hydroxyl terminated polybutadiene (HTPB) modification have been studied. A silane coupling agent (SCA) with a rubber reactive group was also used to improve the interfacial adhesion between glass fibers and an epoxy matrix. 10, 20, and 30 wt% GF reinforced composite specimens were prepared with and without silane coupling agent treatment of fibers and also HTPB modification of epoxy mixture. In the ruber modified specimens, hardener and HTPB were premixed and left at room temperature for 1 hr before epoxy addition. In order to observe the effects of short glass fiber reinforcement of epoxy matrix, silane treatment of fiber surfaces, and also rubber modification of epoxy on the mechanical behavior of specimens, tension and impact tests were performed. The fracture surfaces and thermal behavior of all specimens were examined by scanning electron microscope (SEM), and dynamic mechanical analysis (DMA), respectively. It can be concluded that increasing the short GF content increased the tensile and impact strengths of the specimens. Moreover, the surface treatment of GFs with SCA and HTPB modification of epoxy improved the mechanical properties because of the strong interaction between fibers, epoxy, and rubber. SEM studies showed that use of SCA improved interfacial bonding between the glass fibers and the epoxy matrix. Moreover, it was found that HTPB domains having relatively round shapes formed in the matrix. These rubber domains led to improved strength and toughness, due mainly to the “rubber toughening” effect in the brittle epoxy matrix.     

Burning‐rate enhancement of a high‐energy rocket composite solid propellant based on ferrocene‐grafted hydroxyl‐terminated polybutadiene binder

Four different samples of ferrocene‐grafted hydroxyl‐terminated polybutadiene (Fc‐HTPB), containing 0.20, 0.52, 0.90, and 1.50 wt % iron, were synthesized by the Friedel–Crafts alkylation of ferrocene with hydroxyl‐terminated polybutadiene (HTPB) in the presence of AlCl₃ as a (Lewis acid) catalyst. The effects of the reaction conditions on the extent of ferrocene substitution were investigated. The Fc‐HTPBs were characterized by IR, ultraviolet–visible, ¹H‐NMR, and ¹³C‐NMR spectra. The iron content and number of hydroxyl groups were estimated, and the properties, including thermal degradation, viscosity, and propellant burning rates (BRs), were also studied. The thermogravimetric data indicated two major weight loss stages around 395 and 500°C. These two weight losses were due to the depolymerization and decomposition of the cyclized product, respectively, with increasing temperature. The Fc‐HTPB was cured with toluene diisocyanate and isophorone diisocyanate separately with butanediol–trimethylolpropane crosslinker to study their mechanical properties. Better mechanical properties were obtained for the gumstock of Fc‐HTPB polyurethanes with higher NCO/OH ratios. The BRs of the ammonium perchlorate (AP)‐based propellant compositions having these Fc‐HTPBs (without dilution) as a binder were much higher (8.66 mm/s) than those achieved with the HTPB/AP propellant (5.4 mm/s). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Mechanical and Dielectric Properties of NiZn Ferrite Powders-CTBN Modified Epoxy Resin Coatings

In this study, the effects of carboxyl terminated butadiene-acrylonitrile liquid rubber (CTBN) addition on the mechanical and dielectric properties of NiZn ferrite powders-CTBN modified epoxy resin coatings were investigated. It was observed that the occurrence of the small, dispersed spherical CTBN domains in the epoxy resin resulted from the phase separation between epoxy and CTBN could enhance the toughness and dielectric constant at low frequency due to the increase in the phase boundary between ferrite powders and epoxy resin for the samples modified with proper CTBN. The addition of ferrite powders can effectively improve the thermal stability of epoxy resin.     

Flexibility improvement of epoxy resin by liquid rubber modification

The objective of this study was to improve the flexibility of diglycidyl ether of bisphenol‐A based epoxy resin by using a liquid rubber. For this purpose, hydroxyl terminated polybutadiene (HTPB) was used at two concentrations of 1 % and 1.5 % by weight. In order to improve compatibility between liquid rubber and epoxy, a silane coupling agent (SCA) was also used. Bending test specimens were moulded by using four different orders of mixing of HTPB with SCA and hardener to investigate the compatibility of HTPB and epoxy matrix. Three‐point bending tests indicated that the specimens containing HTPB rubber had higher flexibility than neat epoxy specimens. Moreover, liquid rubber modification resulted in increased plastic strain at failure due to the possible decrease in crosslinking density with the change in reactions path. Fractographic examinations under scanning electron microscope indicated the formation of rubber domains in the epoxy matrix. The deformed rubber domains and increased incidence of deformation lines, especially in the third and fourth group specimens, assessed the improvement in flexibility. © 2002 Society of Chemical Industry     

Morphology and toughness characterization of epoxy resins modified with amine and carboxyl terminated rubbers

The morphology (dispersed phase composition, size distribution, and particle/matrix interface shapes) of epoxy resins modified with 5–15 parts by weight (pbw) of carboxyl (CTBN) and amine (ATBN) terminated butadiene acrylonitrile rubber have been characterized. The characterization techniques were transmission electron microscopy coupled with energy dispersive X-ray analysis, differential scanning calorimetry and proton and ¹³C nuclear magnetic resonance. ATBN modified epoxies have a diffuse-appearing interface between the dispersed rubber phase and the epoxy matrix, in contrast to the sharp boundaries of CTBN particle interfaces. Interface mixing of epoxy and rubber, hypothesized initially to explain the interface diffuseness in ATBN modified epoxy, was not found in either CTBN or ATBN modified epoxy. The difference in interface appearance is attributed to ATBN particles having highly irregular shapes compared to the nearly spherical CTBN particles. Bimodal particle size distributions are observed with both modifiers. Both rubber modifiers also produce essentially identical toughness values which do not increase with rubber content in the range 5–15 pbw despite a commensurate increase in the population of large particles.     

Structure and properties of CE/CTBN/EP blends: II. Effect of EP on the mechanical properties and thermostability of the CE/CTBN system

Carboxyl‐terminated butadiene‐acrylonitrile rubber (CTBN) has often been used to improve the toughness of cyanate ester (CE) resin while sacrificing modulus and thermostability. In this paper, the addition of the appropriate amount of epoxy resin (EP) to the CE/CTBN system is shown to not only increase the modulus and thermostability of the blend, but also improve the toughness. The values of impact strength showed a maximum for the CE/CTBN/EP 100/5/5 blend. The temperature of 10 % weight loss (T₁₀) improves from 376 °C for CE/CTBN 100/5 to 407 °C for the CE/CTBN/EP 100/5/2.5 blend. It is proposed that addition of the appropriate amount of EP can decrease the mobility and increase the stability of CTBN via the reaction between the terminal carboxyl group of CTBN and the hydroxyl group of EP. But a very high EP concentration will decrease the crosslinking density of CE, consequently reducing the mechanical properties and thermostability of the blends. Copyright © 2004 Society of Chemical Industry