Thermoplastic Toughened Epoxy Resins

Fig. 6. Scanning electron micrographs of various morphologies produced with tailor-made thermoplastics toughened epoxy resins (A) homogeneous, (B) particulate, (C) phase inverted, (D) and (E) cocontinu-ous. (From Flamerton, L, Ed. Chemistry and Technology of Cyanate Ester Resins, Blackie Academic and Professional Glasgow, 1994.)...

Ale Alessi, S., Conduruta, D., Pitarresi, G., Dispenza, C., Spadaro, G. Accelerated ageing due to moisture absorption of thermally cured epoxy resin/polyethersulphone blends Thermal, mechanical and morphological behaviour. Polym. Degradation Stability 96 (2011) 642-648. llAsi Asif, A., Rao, V. L., Ninan, K. N. Preparation, characterization, thermo-mechanical, and barrier properties of exfoliated thermoplastic toughened epoxy clay ternary nanocomposites. Polym. Adv. Technol. 22 (2011) 437 47. 

J. C. Hedrick, N. M. Patel, and J. E. McGrath, Toughening of Epoxy Resin Networks with Functionalized Engineering Thermoplastics, in Rubber Toughened Plastics, K. Riew (Ed.), American Chemical Society, Washington, DC, 1993. 

Chemical functionalization of the thermoplastics was found to improve toughness without such detractions. High-molecular-weight resins based on amine-terminated PES oligomers or chain extension of bismaleimide resin with the same amine-terminated PES were found to have improved fracture resistance and reduced thermal shrinkage.14 Also a mechanism was found to toughen cyanate esters by incorporating epoxy resins, which can react with the ester.15... 

Gilbert, A.H. Bucknall, C.B. Epoxy resins toughened with thermoplastic. In Makromol. Chem. Macromol. Symp, Vol. 45, 289-298. 

One way of overcoming this is to have the second phase already separated before cure, i.e. the toughener is insoluble in the epoxy resin before cure. Examples are found in toughened thermoplastics, where core-shell particles that optimize adhesion and compatibility and have a particle-size distribution to maximize toughness have been synthesized. These particles can be added at the desired volume fraction to achieve toughness without compromising performance rather than relying on the phase trajectory to achieve the desired... 

It was noted in the previous section that the carboxyl end groups on the CTBN elastomer affected the final performance of the material as a toughener since these groups would co-react with the epoxy resin and facilitate stress transfer from the brittle matrix to the phase-separated elastomer. Without this adhesion the particles could debond prematurely, which would lead to poor dissipation of the energy of the growing crack. It has also been noted that excessive adhesion between an epoxy resin and a thermoplastic could be deleterious to the performance (Williams et al, 1997). The process of toughening of a thermoset... 

A variant of thermosetting has been described in that PPE resins are dissolved in epoxy resins. A variety of polymers can be dissolved in epoxy resins." In order to facilitate the processability of PPE, the PPE is dissolved in an epoxy resin as processing aid. After processing by kneading, the epoxy resin is cured. In contrast to other approaches where the thermoplastic polymer acts as a toughener for the epoxy matrix, the amount of epoxy resin added can be adjusted so that the PPE will form the continuous phase in the final state. 

The study considered here employed materials obtained from McDonnell Aircraft Co., through Dexter Hysol, under the Air Force program Development of Ultra Lightweight Materials . They contained the Courtaulds Research Apollo 45-850, consisting of 5 pm diameter carbon fibers in Dexter Hysol s HC 9106-3 di-, tri- and tetrafunctional epoxy resin, toughened by addition of the thermoplastic polyether sulfone (PES). The thermoplastic PEIS toughening agent, present in this epoxy matrix, is presumed to phase separate out once it has cured. These panels were fabricated in an autoclave by Dexter Hysol. 

Hou Hourston, D. J., Lane, J. M., MacBeath, N. A. Toughening of epoxy resins with thermoplastics. 

Wu Wu, H., Xu, J., Liu, Y., Heiden, P. Investigation of readily processable thermoplastic-toughened thermosets. V. Epoxy resin toughened with hyperbranched polyester. J. Appl. Polym. Sci. 72 (1999) 151-163. 

OlMim Mimura, K., Ito, H., Fujioka, H. Toughening of epoxy resin modified with in situ polymersized thermoplastic polymers. Polymer 42 (2001) 9223-9233. 

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