The effect of network architecture on the thermal and mechanical behavior of epoxy resins

✍ Scribed by Emmett Crawford; Alan J. Lesser

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 263 KB
• Volume: 36
• Category: Article
• ISSN: 0887-6266
• DOI: 10.1002/(sici)1099-0488(199806)36:8<1371::aid-polb11>3.0.co;2-4

✦ Synopsis

The effects of crosslink functionality ( f c ), molecular weight between crosslinks (M c ), and chain stiffness display on the thermal and mechanical behavior of epoxy networks are determined. Both f c and M c are controlled by blending different functionality amines with a difunctional epoxy resin. Chain stiffness is controlled by changing the chemical structure of the various amines. In agreement with rubber elasticity theory, the rubbery moduli are dependent on f c and M c , but independent of chain stiffness. The glassy moduli and secondary relaxations of these networks are relatively independent of f c , M c , and chain stiffness. However, the glass transition temperatures (T g ) of these networks are dependent on all three structural variables. This trend is consistent with free volume theory and entropic theories of T g . f c , M c , and chain stiffness control the yield strength of these networks in a manner similar to that of T g and is the result that both properties involve flow or relaxation processes. Fracture toughness, as measured by the critical stress intensity factor ( K Ic ), revealed that f c and M c are both critical parameters. The fracture behavior is the result of the fracture toughness being controlled by the ability of the network to yield in front of the crack tip.