Carboxyl-terminated Butadiene Acrylonitrile Research Articles

Effect of carboxyl-terminated poly(butadiene- co-acrylonitrile) (CTBN) concentration on thermal and mechanical properties of binary blends of diglycidyl ether of bisphenol-A (DGEBA) epoxy resin

Six blend samples were prepared by physical mixing of epoxy resin with varying concentrations of liquid carboxyl-terminated butadiene acrylonitrile (CTBN) copolymer having 27% acrylonitrile content. The blend samples were cured with aromatic amine. A comparative study of Fourier-transform infrared (FTIR) spectra showed the modification as a result of chemical reactions between epoxide group, curing agent and CTBN. The tensile strength of cured blend samples decreased slightly from 11 to 46% where as the elongation-at-break showed an increasing trend with increasing rubber content, i.e., up to 25 phr, in the blend samples. Appreciable improvements in impact strength were also observed in the prepared blend systems. The glass transition temperature ( T g) of the epoxy resin matrix was slightly reduced on the addition of CTBN. The cured resin showed a two-phase morphology where the spherical rubber domains were dispersed in the epoxy matrix.

Electrochromic devices based on copolymers of 3-Trimethoxysilanylpropyl-N-aniline-2,5-Dimethoxyaniline

Abstract Electrochemical copolymerization of 3-trimethoxysilanyl-propyl-N-aniline (TMSPA) with 2,5-dimethoxyaniline (DMA) was performed in 1 M HCl aqueous solution for different feed ratios of TMSPA using cyclic voltammetry. The deposition rate of TMSPA–DMA copolymer is higher than that of PTMSPA but lower than that of PDMA. (TMSPA-co-DMA) film was deposited using electrochemical polymerization as conducting film on indium tin oxide (ITO) electrode and used as an electrode in an electrochromic device. Poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) was spin-coated on ITO as the other electrode. Carboxyl-terminated- butadiene-acrylonitrile (CTBN) blended with LiClO4 was used as solid polymer electrolyte. A total solid electrochromic device was assembled as follows: ITO|P(TMSPA-co-DMA)∥LiClO4-CTBN∥PEDOT:PSS|ITO. The columbic efficiency of the devices reached to 104% for P(TMSPA-co-DMA) film with TMSPA feed ratio of 0.25. The optical contrast (ΔT, %) of the single electrode and the device were determined by UV–vis spectroelectrochemical studies. The stability of ΔT was improved during color switching from +1.5 to −1.5 V (vs. PEDOT) for this device. The device was pale yellow at −1.5 V and blue at +1.5 V.

Interaction of toughening mechanisms in a hybrid epoxy system

AbstractInteraction between different toughening mechanisms is studied using a heat treated hybrid system, consisting of carboxyl‐terminated butadiene acrylonitrile (CTBN) rubber and EXPANCEL (expandable hollow microspheres) as modifiers for an epoxy resin. It was found that the fracture toughness of the hybrid system is higher than that of either individually EXPANCEL‐ or CTBN‐modified system for a given content of modifier, although the maximum toughness was not substantially high compared with maxima of single modifier systems. Microscopic examination revealed that damage zone due to CTBN particles ahead of the crack reduces due to the presence of EXPANCEL particles and nevertheless its fracture toughness increased. A possibility was deduced that the cavitation due to CTBN assists with promoting compressive stresses around EXPANCEL particles ahead of the crack tip, resulting in increase in fracture toughness. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4470–4475, 2006

Toughening of cyanate ester resin by carboxyl terminated nitrile rubber

AbstractThe carboxyl terminated butadiene‐acrylonitrile (CTBN) rubber was used to improve the toughness of the cyanate ester (CE) resin. The toughness of the modified blends depended on the CTBN content. The addition of 10 phr (g/100gCE) CTBN in CE resin led to a 200% increase in the impact strength with a loss of storage modulus. The transmission electron microscopy result showed the existence of rubber particles, inferring that phase separation had occured after curing. The thermogravimetric analysis curve of CTBN indicated the presence of cavities which also can be observed on the fractured surface in the scanning electron microscopy pictures using high magnification. Thus, phase‐separation and cavities toughening mechanisms function together to improve the toughness. Copyright © 2004 John Wiley & Sons, Ltd.

Morphology and performance of epoxy nanocomposites modified with organoclay and rubber

AbstractHybrid epoxy nanocomposites modified with carboxyl‐terminated butadiene acrylonitrile (CTBN) rubber and organoclay were synthesized. The morphology of those nanocomposites was studied with X‐ray diffraction (XRD), Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The results showed that most of the organoclay in the nanocomposites was exfoliated and high cure temperatures benefit the formation of exfoliated nanocomposites. Organoclay simultaneously improved fracture toughness, compressive modulus, yield strength and ultimate strength of the epoxy resin. Organoclay not only enhanced Tg, yield strength and ultimate strength of rubber‐modified epoxies, but also further improved their fracture toughness. There was a superposition effect on fracture toughness of the hybrid epoxy nanocomposites modified with both rubber and organoclay. Polym. Eng. Sci. 44:1178–1186, 2004. © 2004 Society of Plastics Engineers.

Cryogenic microcracking of rubber toughened composites

AbstractThis study investigated the influence of carboxyl‐terminated butadiene acrylonitrile (CTBN) liquid rubbers on the microcracking response of polymeric composite materials to cryogenic cycling. Matrices of carbon fiber/epoxy prepregs were modified with different concentrations of two CTBN liquid rubbers. The glass transition temperature and the interlaminar shear strength of the laminate systems were depressed as a result of the presence of CTBN in the epoxy phase. An increase in total rubber concentration with the continuous phase was found to decrease and in some cases eliminate microcracking in laminates exposed to cryogenic cycling.

Influence of Dipole Interactions on Mechanical Behavior of Modified Epoxy Resins

In this article, Influence of dipole interactions on tensile properties, fracture toughness and glass transition of epoxy resins was investigated by comparing the poly ethylene glycol (PEG) and carboxyl-terminated butadiene acrylonitrile (CTBN) modified epoxy systems. The infrared spectroscopy (IR) spectrums proved that there existed polar interactions between epoxy network and PEG chain. The results showed that dipole interactions played a significant role in influencing on toughness and strength of epoxy resins but had little effect on their glass transition temperature.

Characterization in the Toughening Process of CTBN Modified Epoxy Resins Induced by Electron Beam Radiation

Epoxy resins are widely utilized as high performance thermosetting resins for many industrial applications but characterized by a relatively low toughness. Electron beam (EB) curing of polymer resins has a number of advantages over conventional thermal curing, such as shorter curing time, low energy consumption, low cure temperature, dimensional stability, reduced manufacturing cost. In the present work liquid carboxyl-terminated butadiene acrylonitrile (CTBN) copolymers containing 8% acrylonitrile is added at different contents to improve the toughness of diglycidyl ether of bisphenol A (DGEBA) epoxy resins using triarylsulfonium hexafluoroanimonate as a photointiator. The EB irradiation was conducted 5 kGy to 250 kGy in nitrogen. The physics properties of CTBN modified epoxy resins were examined by determine gel content, DMA (dynamic mechanical analysis), UTM (Instron model 4443), SEM (scanning electron microscopy).

Elastomer modification of epoxy based film adhesives: adhesive and mechanical properties

Three approaches were employed to improve the flow and sandwich bonding properties of a nylon-carrier supported film adhesive based on carboxyl terminated butadiene acrylonitrile (CTBN)-modified novolac epoxy resin. These included the addition of a commercial acrylate flow modifier, replacement of novolac epoxy partly with solid diglycidyl ether of bisphenol A (DGEBA) resins, and replacement of CTBN partly with an epoxy functional acrylate terpolymer (EPOBAN). Adhesive properties such as lap shear strength (LSS), T-peel strength (TPS) and flatwise tensile strength (FTS) on honeycomb core bonded sandwich specimens were evaluated using aluminium adherends. The addition of the flow modifier in low concentrations enhanced the flexibility of the system and resulted in a marginal increase in LSS, TPS and FTS. Replacing novolac epoxy partly with solid DGEBA resulted in a less brittle system with enhanced LSS and TPS, but with reduced FTS due to the decreased flow characteristics. A substantial increase in FTS was observed when CTBN was partly replaced with EPOBAN. The introduction of EPOBAN resulted in good flow and fillet properties and the optimum FTS was obtained for the composition based on 25/75 CTBN/EPOBAN ratio. Mechanical properties of selected systems were also studied in addition to adhesive properties.

Thermal and mechanical characterization of epoxy resins toughened using preformed particles

AbstractPreformed, multilayer particles have been used to toughen an epoxy resin. The particles were formed by emulsion polymerization and consist of alternate glassy and rubbery layers, the outer layer having glycidyl groups to give the possibility of chemical bonding of the particles in the cured resin. Two variants of this type of particle were used, termed GM(47/15) and GM(47/37); both types have an overall diameter of 0.5 µm, but the former have a thicker rubbery layer. For comparison, acrylic toughening particles (ATP) with no surface functionality and a liquid carboxyl‐terminated butadiene–acrylonitrile (CTBN) rubber were used as toughening agents. The epoxy resin system consisted of a commercial diglycidyl ether of bisphenol A (Shell Epon 828) with diamino‐3,5‐diethyl toluene as hardener, two commercial sources of which were used, namely Ethacure‐100 (Albemarle SA) and DX6509 (Shell Chemicals). These hardeners contain a mixture of two isomers, namely 2,6‐diamino‐3,5‐diethyltoluene and 2,4‐diamino‐3,5‐diethyltolueneThermogravimetry in nitrogen shows that the preformed toughening particles begin to degrade at 230 °C, whereas the cured resin begins to degrade rapidly at 350 °C. Thus, even though the particles are less thermally stable than the cured resin, their degradation temperature is well above the glass transition temperature of the resin, and their use does not affect the thermal stability of the toughened materials at normal use temperatures.The performance of the toughening agents was compared using Ethacure‐100 as the hardener. The GM(47/15) and GM(47/37) toughening particles gave rise to a greater toughening effect than the ATP and the CTBN. For example, the fracture energies were: 0.26 kJ m−2 for the unmodified resin; 0.60 kJ m−2 for the resin toughened with CTBN; and 0.69 kJ m−2 for the resin toughened with the GM(47/15) particles. The ultimate tensile stress of the unmodified epoxy resin was 43 MPa, which increased to 55 MPa when 20 wt% of GM(47/15) toughening particles were added.The toughness of resins cured with the DX6509 hardener were superior to those obtained with the Ethacure‐100 hardener, most probably due to DX6509 producing a less‐highly‐crosslinked network. This highlights the sensitivity of the toughening process to the hardener used, even for hardeners of a similar nature.© 2001 Society of Chemical Industry

Effect of modified rubber compound on the cure kinetics of DGEBA/MDA system by Kissinger and isoconversional methods

The cure kinetics of diglycidyl ether of bisphenol A (DGEBA)/4,4′-methylene dianiline (MDA) system with various contents of MDA-endcapped carboxyl-terminated butadiene acrylonitrile (CTBN) were studied by Kissinger and isoconversional methods. With increasing MDA-endcapped CTBN content, the exothermic heat decreased due to the diffusion control induced by rubber domain produced in the epoxy matrix, which disturbed the diffusion of functional groups, and the maximum exothermic peak value and the activation energy by Kissinger equation decreased due to the increasing content of amine group in rubber compound, which reacted with epoxy group and formed a hydroxyl group acted as a catalyst. In the isoconversional method, the activation energy decreased until minimum value in the initial stage and increased after that value. The decreasing in the initial stage was due to the autocatalytic cure reaction and the increasing after the minimum value was due to the increasing crosslink density and rubber domain.

Effect of MDA-endcapped CTBN on the cure kinetics of epoxy system by autocatalytic cure rate expression

The cure rate of diglycidyl ether of bisphenol A (DGEBA)/4,4′-methylene dianiline (MDA) system with or without MDA-endcapped carboxyl-terminated butadiene acrylonitrile (CTBN) rubber was studied by autocatalytic cure rate expression. All the cumulative conversion curves for DGEBA/MDA system with or without MDA-endcapped CTBN (20 phr) showed s-shape and this meant that the two systems followed the typical autocatalytic reaction. The cure rate of the system with MDA-endcapped CTBN (20 phr) was faster than that of the system without MDA-endcapped CTBN (20 phr). The activation energies of k 1 and k 2 for DGEBA/MDA system were 54.01 kJ/mol and 44.06 kJ/mol, respectively and those of k 1 and k 2 for the system with MDA-endcapped CTBN (20 phr) were 47.71 kJ/mol and 40.95 kJ/mol.

Studies on the adhesive properties of solid elastomer-modified novolac epoxy resin

Adhesive properties like lap shear strength and T-peel strength of novolac epoxy resin modified with carboxyl terminated butadiene acrylonitrile (CTBN) solid resin and cured with two different curing agents namely, dicyandiamide (DICY) and 3,3′-diaminodiphenyl sulphone (DDS) were evaluated using aluminium adherends. Substantial improvement in adhesive properties was obtained by the inclusion of moderate concentrations of CTBN in the formulations. Adhesive properties of the formulations were evaluated when used as paste, nylon-carrier supported and unsupported film adhesives. Optimum concentrations of 20 parts by weight (pbw) and 25 pbw of solid CTBN in epoxy were obtained for the DICY and DDS cured systems, respectively. Inclusions of larger amounts of CTBN led to flexibilisation of the systems thereby reducing the adhesive properties. CTBN also reduced the glass transition temperatures and high-temperature strength retention of both the systems. The development of two-phase morphology for the CTBN-modified systems was evident from scanning electron micrographs (SEM).

Kinetics and thermal characterization of epoxy-amine systems

The curing behavior of epoxy resins was analyzed based on a simple kinetic model. We simulated the curing kinetics and found that it fits the experimental data well for both diglycidylether of bisphenol A–4,4′-methylene dianiline and diglycidylether of bisphenol A–carboxyl-terminated butadiene acrylonitrile–4,4′-methylene dianiline systems. The kinetic results showed the curing of epoxy resins involves different reactive process and reaction stages, and the value of activation energy is dependent on the degree of conversion. By analyzing the effect of vitrification, at low curing temperature, we found the curing reaction at the later stage was practically diffusion-controlled for unmodified resin, and the rubber component did not markedly decrease Tg at the early stage of reaction as would be expected. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2401–2408, 1999

Computer simulation of curing and toughening of epoxy systems

The crosslinking and toughening process of diglycidyl ether of bisphenol A (DGEBA) resin was simulated by various computational techniques, using a commercial polymer modeling software package. First, curing of DGEBA resin with three different curing agents was simulated using a Monte Carlo simulation technique. Results calculated for crosslinking conversion of the formed network showed that deviation from an ideal network due to loops and dangling chains increased with excess amounts of the curing agent and that the formed network is close to the ideal when stoichiometric concentrations are used. The maximal calculated modulus was an indication of the optimal curing agent concentration. The glassy modulus and Tg for the simulated systems were calculated using the group contribution method and semiempirical correlations. Second, the simulation results of multicomponent epoxy systems, comprising two curing agents, a reactive diluent and DGEBA resin, indicate that there is no difference in network quality compared with bicomponent epoxy systems, comprising DGEBA and a single curing agent. The simulation results exemplified the ability to choose optimal components concentration in a complicated multicomponent epoxy system. Third, the toughening process of amino-terminated butadiene acrylonitrile (ATBN) and carboxyl-terminated butadiene acrylonitrile (CTBN) in DGEBA resin was analyzed using the solubility parameter approach. This approach could explain the role of the rubber acrylonitrile group in epoxy/rubber blends. The interaction parameters of both systems (ATBN and CTBN) and their phase diagrams were estimated using modified Flory—Huggins theory. It was shown that this technique leads to good estimations of the optimal rubber concentration, leading to optimal mechanical properties.

Fracture of an epoxy polymer containing recycled elastomeric particles

The fracture behavior of elastomer-modified epoxy was investigated using compact-tension geometry. The elastomeric modifiers included a liquid carboxyl-terminated butadiene acrylonitrile and solid rubber particles of different sizes which were obtained from recycled automobile tires. When used with solid rubber alone, no significant improvement in the fracture toughness was observed. However, when used in combination with the liquid rubber modifier, it was observed that the fracture toughness of these hybrid epoxies was higher than that of those toughened with liquid rubber alone. This synergistic effect is explained in terms of crack deflection and localized shear yielding. Furthermore, we observed a slight improvement in the fracture toughness as the size of the solid rubber particles increased. Although using a combination of both reactive rubber liquids and solid rubber particles as toughening agents had been investigated previously, in this study, the solid rubber particles used were from recycled rubber tires. Therefore, we have clearly demonstrated an application of producing high-quality engineering epoxy systems using toughening modifiers that are relatively low in cost and created higher-value products for recycled solid rubber.

Fracture of an epoxy polymer containing recycled elastomeric particles

The fracture behavior of elastomer-modified epoxy was investigated using compact-tension geometry. The elastomeric modifiers included a liquid carboxyl-terminated butadiene acrylonitrile and solid rubber particles of different sizes which were obtained from recycled automobile tires. When used with solid rubber alone, no significant improvement in the fracture toughness was observed. However, when used in combination with the liquid rubber modifier, it was observed that the fracture toughness of these hybrid epoxies was higher than that of those toughened with liquid rubber alone. This synergistic effect is explained in terms of crack deflection and localized shear yielding. Furthermore, we observed a slight improvement in the fracture toughness as the size of the solid rubber particles increased. Although using a combination of both reactive rubber liquids and solid rubber particles as toughening agents had been investigated previously, in this study, the solid rubber particles used were from recycled rubber tires. Therefore, we have clearly demonstrated an application of producing high-quality engineering epoxy systems using toughening modifiers that are relatively low in cost and created higher-value products for recycled solid rubber. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 271–277, 1997

Correlation between stress-whitening and fracture toughness in rubber-modified epoxies

Fracture toughness of rubber modified epoxy systems was evaluated in relation to stresswhitening. The epoxy systems consisted of diglycidyl ethers of bisphenol A (DGEBA)-based epoxy resin, 4,4′ diaminodiphenyl sulphone (DDS) as curing agent, and carboxylterminated butadiene-acrylonitrile (CTBN) rubber. It was found that a peak value of fracture toughness occurs at a small amount of rubber content (∼ 4 phr) and closely corresponds to that of stress-whitening size. Other properties such as flexural strength and flexural modulus were also found to display maxima at a similar amount of rubber content. © 1996 John Wiley & Sons, Inc.

Dielectric and thermally stimulated discharge current studies of rubber-modified epoxy resins

Abstract Comparison is drawn between data obtained from dielectric relaxation and thermally stimulated discharge current (TSDC) measurements on blends of carboxyl-terminated butadiene acrylonitrile (CTBN) with an epoxy resin (ER) obtained by reaction of the diglycidyl ether of bisphenol A (DGEBA) with either triethylenetetramine (TETA) or diamino-diphenylmethane (DDM). The effect of varying the composition of CTBN on the nature of the phase separation was examined using electron microscopy and was also evident from changes in the dielectric spectrum and the calculated activation energy for the molecular relaxation process. The morphology consists of spherical rubber particles dispersed in an epoxy matrix at low levels of CTBN, and at higher concentrations epoxy resin is observed to be precipitated as spheres within the rubbery phase. Detailed analysis of the dipolar spectra indicates that at low concentrations there appears to be some cosolution of the epoxy in the CTBN.

Dielectric and morphological investigations of phase separation and cure in rubber‐modified epoxy resins: Comparison between teta‐ and DDM‐based systems

AbstractReal‐time and equilibrium dielectric measurements, covering the frequency range 10−1–105 Hz, are reported on a series of rubber‐modified epoxy resins, based on reaction of the diglycidyl ether of bisphenol A (DGEBA) with either triethylenetetramine (TETA) or diaminodiphenylmethylene (DDM). The rubber modifier used was a carboxyl‐terminated butadiene acrylonitrile (CTBN) reactive oligomer and the phase‐separated structure, the results of which was examined using both dielectric and electron microscopic techniques. The mixture was initially homogeneous, but after a short period of time, it underwent phase separation and this process was marked by the appearance of a dielectric peak associated with ion‐charge migration within the occluded rubbery phase. Analysis of the peak provided information on the morphology of the system and these data were compared with information obtained from scanning electron microscopy. A phase‐separated morphology was observed consisting of spherical rubber particles dispersed in an epoxy matrix. For high concentrations of rubber ≥ 10 wt %, precipitation of epoxy domains within the rubbery phase was observed. Detailed dielectric studies of the peak associated with phase separation revealed that in the case of the TETA system the peak continued to shift after vitrification, whereas in the case of DDM, it was invariant with time. The point at which the peak appears was used to determine the time at which phase separation occurred. Differences observed in the lower temperature dielectric spectra were associated with variations in the form of the phase structure and possibly reflect different degrees of densification of the matrix. Good agreement was observed between the predictions of the Maxwell—Wagner—Sillers (MWS) theory and experimental observation for these systems. © 1993 John Wiley & Sons, Inc.