Indentation of poly(methyl methacrylate) under high-pressure gases

The variation of the indentation hardness of a high molecular weight poly(m ethyl methacrylate) (PMMA) subjected to CO2 and Ar at high pressure was mea sured in situ. The samples were subjected to gas exposure for 3 h at 40 deg reesC before a conical indenter of an included angle at 105 degrees, with a fixed load of 0.237 kg, was applied for a loading time of 60 s. The data s how that both CO2 and Ar reduce the hardness of PMMA to a comparable extent at low pressures. The hardness of PMMA subjected to Ax indicates a minimum at about 4 MPa. and then increases. CO2 produced a monotone decreasing tre nd in hardness in the pressure range studied, and the glass-transition temp erature (T-g) was achieved at about 6.0 MPa. The change in hardness is attr ibuted to plasticization of the polymer matrix that is more extensive for C O2, The relationship between the change in hardness for this PMMA subjected to high-pressure CO2 the corresponding change in the T-g, and the associat ed swelling of the polymer is discussed. (C) 2001 John Wiley & Sons, Inc.*.