HIGH DUCTILITY IN POLY(METHYL METHACRYLATE) INDUCED BY ABSORPTION ANDDESORPTION OF AN ACETONITRILE AQUEOUS-SOLUTION

Tension tests were conducted in air at room temperature on PMMA sheet specimens which had been previously soaked in a 40 vol% acetonitrile a queous solution at 20 degrees C for 24 h and then dried in air at room temperature for 480 h. In contrast with an untreated specimen which f ractured at a stress of 84 MPa and a strain of 9%, shear yielding clea rly took place at 42 MPa and the elongational fracture strain increase d to about 148%. No crazes were observed on the specimen surface and a s a result the transparency of the PMMA was thoroughly maintained unti l fracture. Thus this soaking treatment may change PMMA to a completel y ductile polymer without a crazing mechanism. The results of the dyna mic viscoelastic measurements at 1 Hz show that the glass transition t emperature was lowered to about 80 degrees C (as compared to about 110 degrees C), and the beta relaxation became much sharper with a higher peak value of 20 degrees C (as compared to a broad curve with a peak at 50 degrees C). This clear beta relaxation at room temperature may c ontribute to shear yielding and large plastic elongation of the treate d PMMA.