CTBN rubber

The epoxy-nitrile adhesives were introduced commercially in the late 1960s. They consisted primarily of DGEBA epoxy resin modified with carboxyl-terminated butadiene nitrile (CTBN) rubber. These first nitrile copolymers were available from B.F. Goodrich under the trade name of Hycar. The most convenient form of epoxy nitrile adhesive, especially when one is bonding large parts (aircraft structures), is a supported film. However, solvent solutions of epoxy-nitrile adhesives have also been commercially available. 

The use of rubbers (particularly epoxy-terminated butadiene nitrile, ETBN, rubber or carboxy-termi-nated butadiene acrylonitrile, CTBN, rubber) to toughen thermoset polymers is perhaps the most widely explored method and has been applied with some measure of success in epoxy resins. Phase separation of the second rubbery phase occurs during cure and its incorporation in the epoxy matrix can significantly enhance the fracture toughness of the thermoset. Although the rubber has a low shear modulus, its bulk modulus is comparable to the value measured for the epoxy, ensuring that the rubber inclusions introduced... 

The material used was a diglycidyl ether of bisphenol A (DGEBA) based epoxy resin (Ciba-Geigy, GY250) cured using stoichiometric amounts of 4,4 -diamin-odiphenyl sulfone (DDS). The rubber used for the modifications was Hycar car-boxy-teminated butadiene-acrylonitrile (CTBN) rubber (1300 x 13). The curing schedule for all the rubber-modified epoxy-DDS systems was as follows first the rubber and then DDS were mixed with the epoxy resin and stirred at 135 °C until the DDS was dissolved the systems were cured for 24 h at 120 °C and then postured for 4 h at 180 °C. The control epoxies were cured according to the same schedule. 

The characteristics of fracture surfaces of F-185 neat resin and those of F-185 matrix In the composites are similar to those reported In the literature ( ). The fact that the fracture surfaces of F-185 neat resin and F-185 matrix In the composites show typical ductile fracture behavior, while the unmodified HX-205 shows brittle fracture behavior, seems to Indicate the toughening effect of F-185 as a result of Incorporation of CTBN rubber. The fracture energies of these materials are being... 

The criterion was chosen since the toughening mechanism of CTPnBA/ Epon 828 systems was expected to be effective with this resin ratio range, based on CTBN rubber studies (10.14). The results suggested that the upper limiting molecular weight for the solubility of CTPnBA in Epon 828 was around Mn = 4400. 

Thermoplastic rubber block copolymers, with completely new adhesive performance, were developed in 1965 [21]. The first commercial product was Shell Chemical s Kraton 101, of styrene polybutadiene-styrene composition. This development led to the carboxy-terminated nitrile (CTBN) rubber modifiers used to flexibilize epoxy and other brittle resin adhesives in the late 1960s. Today, the thermoplastic rubber block copolymer adhesives are used in hot melt-, solvent- and water-based adhesives, and as hot melt- and solvent-based sealants. Major applications are as pressure-sensitive adhesives, construction adhesives and sealants, and general assembly adhesives. 

Zha Zhang, K., Berglund, A. Deformation and fracture of glass bead/CTBN-rubber/epoxy composites. Polym. Eng. Sci. 33 (1993) 100-107. 

Fig. 24 TEM micrographs of ternary epoxy, CTBN rubber and octadecyl ammonium-treated montmorillonite nanocomposites which were investigated with different polarity rubbers, (a) shows a broad view of the less polar rubber and the clay tactoids, clearly separated and (b) shows a close up of the more polar rubber close to silicate layers...

DGEBA/CTBN resin studies were made with DGEBA cured with 5 parts per hundred piperidine reinforced with 5, 10 and 15 parts per hundred CTBN rubber cured at 120 C for 16 h. It was found from this study that there is epoxy present in the separated rubbery particles, and that rubber is dissolved in the epoxy matrix. 

If a notched epoxy specimen toughened with CTBN is found to fell when the strain energy release rate is 5.95x10 kJ/m, calculate the fracture energy for a sample with a thickness of 3.2 mm. How does this compare with the value for Gj, found in Table 1 Based upon your answer, is CTBN rubber an effective toughener for epoxy ... 

For a thick epoxy sample modified by addition of CTBN rubber and glass spheres, Young s modulus was found to be 38 MPa, Gj, had the value 3 kJm, and was 3.41x10 Pa/m. Estimate the value of Poisson s ratio for this sample. 

Incorporating a CTBN rubber [51,52] concomitant with a significant loss of high temperature properties and poor long term aging stability at 200°C. 

The most conunonly used materials are the Hycar range from Noveon, which are butadiene, or more usually, acrylonitrile-butadieue telomers which are epoxy- (uo prereaction needed), amino-, vinyl- or, as here carboxyl-terminated. These latter are the well-known CTBN rubbers , which have a molecular weight generally in the region of 3000 to 4000. 

All these theoretical predictions are consistent with the results observed by Yee and Person [120, 131], which clearly show shear bands between cavitated particles in rubber-toughened epoxy materials. They also found that the ability of CTBN rubber to toughen epoxy is closely related to CTBN rubber cavitation, which is seen as thick dark circle within the rubber particles under optical microscopy. The need of internal cavitation of rubber particles has been questioned by others [152, 153], but these researchers have considered only the case of uniaxial tension, which have been shown to be quite different than the triaxial stress seen at the crack tip. 

The second ABCP-type materials of commerce are the rubber-toughened epoxy resinsUsually the epoxy resins are based on the diglycidyl ether of bisphenol A (DGEBA). Carboxyl-terminated butadiene-acrylonitrile (CTBN) rubber is the elastomer of preference. A typical composition is ... 

Valenza A and Calabrese L (2(X)3), liffect of CTBN rubber inclusions on the curing kinetic of DGliBA-IXjEiBF epoxy resin , Eur Polym J, 39, 1355-1363. doi 10.1016/ 80014-3057(02)00390-7. 

Several methods have been investigated to improve the fracture toughness of BMI resins, the most used technique being the incorporation of a second phase formed by the dispersion of rubber particles into the cross-linked matrix. Carboxyl-terminated butadiene-acrylonitrile elastomers (CTBN), which are very effective with epoxy resins, are also frequently added to BMI adhesives. The general formula of CTBN rubbers is ... 

Figure 25 Changes of the fracture energy (a) and flexural modulus at 25°C (b) and 250°C (c) for CTBN-BMI adhesives as a function of the CTBN-rubber content [69].

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