Modification of polystyrene glass transition by high pressure methane

Polymers are currently processed in many different ways involving elevated temperatures and pressures as well as additional chemicals (mostly gases), this, being typically the case in foaming process. There is then a pressing need to assign the thermophysical properties of polymers in particular sta tes under precise thermodynamic conditions to obtain optimal performances. Thermal, mechanical and/or chemical stresses may induce modifications, poss ibly permanent, of the glass transition which consequently affect the chara cteristics of the material. Polystyrene (PS) has been submitted, in a scann ing transitiometer (ST), to pressures up to 200 MPa using as hydrostatic fl uid either mercury as a neutral fluid or methane as a "chemically active" f luid. Temperature modulated differential scanning calorimetry (TMDSC) has b een used to study the thermal behavior, especially the glass transition, of polystyrene modified by high pressure methane, in comparison with polystyr ene submitted to high pressure mercury as well as with "non-treated" (nativ e) polystyrene. (C) 2000 Elsevier Science Ltd. All rights reserved.