The fracture toughness of a polyester resin after immersion in aqueous liquids

The fracture toughness, K[sub]Ic' of a polyester resin after immersion for periods up to 1300 h at 30[degrees]C and 65[degrees]C in distilled H[sub]2O, 0.78M H[sub]2SO[sub]4, 0.78M NaC1 and 0.78M was measured. At 65[degrees]C, K[sub]Ic was found to fall, particularly in NaOH. The reduction is attributed to severe and widespread hydrolysis in the resin in NaOH. However in H[sub]2), H[sub2SO[sub]4 and NaC1 at 65[degrees]C, the reduction os attributed mainly to the absorbtion of liquid into the resin and in the latter two liquids the fall was slightly more than in the H[sub]2O which is accounted for by more sorbed moisture in the resin. Hydrolysis, leaching and possible further crosslinking in the resin was found not to have a significant influence on the K[sub]Ic on H[sub]2O, H[sub]2SO[sub]4 and NaC1. Disc shaped isolated cracks developed in the resin at 65[degrees]C after about 1500h in H[sub]20 and after about 3000h in H[sub]2SO[sub]4 and in NaC1. These cracks increased in size and number up to a certain period of time. Paradoxically, the generation of disc cracks which proved to be beneficial at first by retarding the water absorption into the resin, later turned out to be detrimental when the cracks began to interact, leading to an apparetn reduction in K[sub]Ic. In 0.78M NaOH cracks developed after about 2000h but did not become numerous as with the other liquids. At 30[degrees]C, a snall reduction in K[subIc was observed in all the liquids and is attributed primarily to absorption of liquid into the resin.