Carboxy-terminated Butadiene Acrylonitrile Research Articles

Effect of Bond Thickness on the Fracture Toughness of Adhesive Joints

The effect of bond thickness on the fracture toughness of adhesive joints was investigated from a microstructural perspective, using compact tension (CT) adhesive-joint specimens with different bond thicknesses. The adhesive material was a rubber-modified epoxy resin with 12.5 wt% carboxy-terminated butadiene acrylonitrile (CTBN) elastomer. The shapes of the rubber particles dispersed in adhesive layers of damaged and undamaged specimens were observed with an optical microscope. The damage was distributed along the interfaces between the adhesive layer and the two adherends. The results show that the primary causes of variations in the fracture toughness of an adhesive joint with the bond thickness are not only a damage zone around a crack tip but also the combination of a damage zone around a crack tip and additional damage zones along the interfaces.

Toughened carbon/epoxy composites made by using core/shell particles

Toughened epoxy resin composites have been prepared by resin-transfer moulding by using a range of toughening agents. Two types of epoxy-functional preformed toughening particles were investigated and have a three-layer morphology in which the inner core is crosslinked poly(methyl methacrylate), the intermediate layer is crosslinked poly(butyl acrylate) rubber and the outer layer is a poly[(methyl methacrylate)- co-(ethyl acrylate)- co-(glycidyl methacrylate)]. The presence of glycidyl groups in the outer layer facilitates chemical reaction with the matrix epoxy resin during curing. Comparisons were made with acrylic toughening particles that have a similar structure, but which do not have the epoxy functionality in the outer shell, and with a conventional carboxy-terminated butadiene acrylonitrile (CTBN) liquid rubber toughening agent. The composites were characterised by using tensile, compression and impact testing. The fracture surfaces and sections through the moulded composites were examined by means of optical and scanning electron microscopy. Short-beam shear tests and fragmentation tests were used to investigate the interfacial properties of the composites. In general, use of the epoxy-functionalised toughening particles gave rise to superior properties compared with both the non-functionalised acrylic toughening particles and CTBN.

Water absorption in a rubber-modified epoxy resin; carboxy terminated butadiene acrylonitrile-amine cured epoxy resin system

Gravimetric and dielectric measurements of water uptake by a series of carboxy terminated butadiene acrylonitrile (CTBN) -amine cured epoxy resin systems are reported. The amount of water absorbed and rate of diffusion increases up to approximately 15 w/w% CTBN content. Anomalous behaviour is observed around a composition of approximately 20% CTBN which is coincident with the occurrence of a co-continuous phase structure in the resin. Dynamic mechanical analysis and atomic force microscopy studies provide evidence for phase separation and inversion of phase structure at 20% CTBN. The increase in the water uptake with increasing CTBN content reflects the ability of the highly polar acrylonitrile group to bind water. The general increase in the diffusion coefficient is consistent with CTBN being initially dispersed in the epoxy matrix tending to a lowering of the effective segment density inhibiting mobility of the water molecules. In the co-continuous region subtle effects of mutual solubility of components and generation of a long percolation path leads to the observed anomalous behaviour. Dynamic mechanical thermal analysis (DMTA) indicated that water absorption suprisingly leads to an increase in the glass transition temperature and is associated with a densification of the matrix structure. Atomic force microscopy measurements reveal that the surface roughness changes with composition with a marked increase in the surface roughness at 20% CTBN.

Effect of the addition of aramid-CTBN block copolymer on adhesive properties of cured epoxy resins modified with CTBN

To improve the bond strength of carboxy-terminated butadiene acrylonitrile (CTBN)-modified epoxy resin, aramid-CTBN block copolymer was used as an additive to a bisphenol-A-type epoxy resin modified with CTBN. With the addition of aramid-CTBN block copolymer, the fracture energy values of the adhesive joints were more than twice that of the CTBN-modified system and about twelve times that of the unmodified system. Observations of the adhesive layers using an optical microscope revealed that the width of the damage zone near the crack-tip in the double cantilever specimen increased with the addition of the aramid-CTBN block copolymer. TEM micrographs showed that the diameter of the CTBN-dispersed phases decreased and a number of fine CTBN phases were dispersed in the epoxy matrix with the addition of the block copolymer. It is concluded that addition of the block copolymer leads to an increase in the dispersibility of the CTBN elastomer into the epoxy matrix and thus the bond strength of the block copolyme...

Phase-inversion investigations of rubber-modified epoxies by electron microscopy and X-ray diffraction

The phase-inversion phenomena of diglycidyl ether of bisphenol A (DGEBA) incorporated with a carboxy-terminated butadiene-acrylonitrile (CTBN) containing 17 wt% bound acrylonitrile after curing with ethylene diamine (EDA) in a stoichiometric ratio were investigated by scanning and transmission electron microscopy (SEM and TEM), and wide-angle X-ray scattering (WAXS). The results of the SEM studies revealed that the rubber-rich phases in a size range of 1–30 Μm, which originally dispersed in an epoxy-rich matrix, gradually transformed to a co-continuous phase as the CTBN content reached 30 phr. As the CTBN content was increased to 50 phr, that phase inversion, as the continuous epoxy-rich phase transformed to a dispersed phase, took place. However, because the transformed dispersed phase was very small, the phase inversion could only be observed by TEM in specimens stained by osmium tetraoxide (OsO4). On the other hand, we also found that the phase inversion could be detected by WAXS, and this showed the absence of a characterization peak of the epoxy resin at the scattering vector,Q=4.1 nm−1. To the best of our knowledge, this was the first time in the literature that WAXS has been employed to detect a phase inversion.

The relationship between resin mechanical properties and Mode I delamination fracture toughness

The purpose of this investigation has been to define better the relationship between resin mechanical properties and the resultant Mode I delamination toughness. Five resin systems have been selected for study: (i) Hercules 3502 (a highly crosslinked epoxy); (ii) Hexcel F 155 (a rubber-toughened, moderate crosslink density system with epoxy equivalent weight of 280); (iii) Hexcel 155 without the rubber particle additions; (iv) Hexcel F185 (a rubber-toughened, low crosslink density system with epoxy equivalent weight of 410); and (v) Hexcel F185 without the rubber particles. The F155 system had 5.7% carboxyterminated butadiene acrylonitrile (CTBN) added to the resin. It was added in the form of 2.3% liquid and 3.4% solid rubber additions. The F185 had 8.1% liquid Hycar CTBN and 5.4% solid Hycar 1472 CTBN added to the resin [1]. It is possible that not all of the liquid CTBN precipitated as particles, but that some of it may have been retained in solution as a plasticizer. The neat resin mechanical properties which might correlate with delamination fracture toughness include tensile elongation, modulus, and neat resin critical energy release rate G~c. These neat resin properties have been measured for each of the resins along with the tensile strain to failure for transverse fracture of unidirectional laminates. These results have been correlated with Mode I delamination fracture toughness measurements made from unidirectional symmetric split laminate tests [2]. The neat resin fracture toughness was determined using compact tension specimens. The experimental results are summarized in Tables I to III. The non-linear component of the strain to failure was calculated by subtracting from the total elongation the linear elastic portion of the strain (the ratio of the strength to modulus). Fig. 1 shows the expected monotonic increase in fracture toughness with both non-linear strain to failure and total strain TAB LE I Mechanical properties of resins (measured at 22 ° C) Resin Resin Resin non-linear Resin Resin tensile system elongation strain to failure UTS modulus (%) (%) (MPa) (GPa)

Glass Fabric Reinforced Bismaleimide Composites: Effect of Elastomer/ Reactive Diluent on Properties

The paper deals with the effect of additions of amine terminated butadiene/acrylonitrile (ATBN), carboxy terminated butadiene/acrylonitrile (CTBN) elastomers and bismethacryloxy derivative of diglycidyl ether of bisphenol-A (vinyl ester resin, VE) on the properties of glass fabric reinforced bismaleimide resin composites. Flexural and interlaminar shear strength of the laminates increased in the presence of these elastomers (3 or 5%). Optimum mechanical properties were observed at — 3 % of VE resin. Glass transition temperatures of laminates were determined by dynamic mechanical analysis.

Polyfunctional epoxies: Part II. Nonrubber versus rubber‐toughened brominated formulations for graphite composites

AbstractInitial screening of carboxy‐terminated butadiene acrylonitrile (CTBN) rubber‐toughened brominated formulations for graphite composites has been reported previously. This study is a further investigation, focusing on the performance of the brominated polymeric additives as a potential flexibilizing agent for graphite composites, using different molecular weights of the Br source. Increasing segment lengths of the polymeric backbone chain of brominated polymeric additives (BPA) are examined in a new development, trifunctional epoxy resin and is compared with a 10 percent rubber‐toughened formulation of the same epoxy resin. Results show that when the Br content in the graphite composite was increased without the use of rubber, the mechanical properties improved. Mechanical and other properties of the graphite composites are discussed.

Curing of epoxy resins with metal(II)4,4′,4″,4‴‐tetraamino phthalocyanines‐modification with elastomers

AbstractThe use of metal phthalocyanine tetraamines in curing epoxy resins to form high‐temperature‐resistant matrix polymers for composites has been reported earlier. The effect of adding carboxy‐terminated butadiene‐acrylonitrile (CTBN) elastomer is now described; preliminary measurements of tensile, flexural, and short‐beam shear strengths, dynamic moduli, resin content, and moisture absorption are presented, and the results of dynamic thermogravimetric analyses are given. In addition to their high char yield (86–87.5% at 800°C in a nitrogen atmosphere) and limiting oxygen index (48.3–50.3), the laminates showed good mechanical properties.

The fracture of an epoxy polymer containing elastomeric modifiers

The fracture energies of elastomer-modified epoxy polymers have been determined over a range of strain rates from 10−2 to 103 sec−1. The modifiers included a liquid carboxyterminated butadiene acrylonitrile and a solid rubber. They were used alone and also in combination. In all cases, the modifiers increased the toughness of the base resin by orders of magnitude and one combination of liquid and solid rubber increased toughness by 60 times. There was a general decrease in fracture energy with increasing strain rate but even during impact testing the modified epoxys were 10 to 20 times tougher than the base polymer. Scanning electron microscopy revealed that, when combined with the liquid rubber, the solid rubber induced a localized shear yielding.

Effect of Temperature on the Adhesive Fracture Behavior of an Elastomer-Epoxy Resin

Abstract The bulk and adhesive fracture behavior of a diglycidyl ether bisphenol-A epoxy modified with 15% carboxy-terminated butadiene acrylonitrile was determined as a function of temperature. The bulk fracture toughness increased sharply near the resin Tg in a manner similar to unmodified epoxy resins. The adhesive fracture energy exhibited a maximum with respect to bond thickness and this maximum broadened and shifted to larger bond thicknesses with increasing temperature. These results are discussed in terms of the size and stress condition of the crack tip deformation zone.

The fracture of epoxy- and elastomer-modified epoxy polymers in bulk and as adhesives

The fracture behavior of a piperidine/bisphenol A diglycidyl ether (A) resin has been determined in bulk and as an adhesive using the linear elastic fracture methods developed by Mostovoy1. The effect of adding carboxy-terminated butadiene–acrylonitrile (CTBN) elastomer to resin A was investigated. The opening-mode fracture energy () of resin A was 120 to 150 J/m2, and largely attributable to plastic deformation. Fractographic evidence was obtained for plastic flow at the crack tip during crack initiation. Propagation was unstable due to the rate dependence of the plasticity. There were no significant differences in the bulk and adhesive fracture behavior. Addition of 5–15% CTBN to resin A produced minute elastomer particles which increased to ∼4000J/m2 (at 15%). Further CTBN addition resulted in an elastomer–epoxy blend and a decrease in fracture energy. Fractography again indicated that crack initiation involved plastic deformation but that the elastomer had greatly increased the volume in which the deformation occurred. The adhesive fracture of the elastomer–epoxy was found to be strongly dependent on the crack-tip deformation zone size (ryc) in that was a maximum when bond thickness was equal to 2 ryc. At bond thicknesses less than 2 ryc, there was a restraint on the development of the plastic zone resulting in lower values.