Investigation into the use of ultrasonic velocity,photoacoustic, and thermoacoustic measurements for epoxy curing at coustant ambient temperature

Abstract

The epoxy cure was observed by ultrasonic lognitudinal velocity measurements at 19, 40, and $110\,^\circ\!C$ of curing temperatures. Three types of phase transition behavior of epoxy resin were due to the elastic modulus change during the cure of epoxy resin. Photoacoustic(PA) and thermoacoustic measurements were used to observe the curing of epoxy resin at $40\,^\circ\!C$ of ambient temperature. Five stages in PA and thermoacoustic signals showed the usual transition of liquid $\rightarrow$ rubber $\rightarrow$ glass state due to gelation and following vitrification. The variation of thermal diffusivity obtained by the phase-lag method also showed the five stage transitions reflecting the change of thermal properties.