High-pressure differential thermal analysis of polymers

Melting behavior under high pressure of nylon 6, nylon 6-clay hybrid (NCH) and poly(butylene terephthalate) was investigated by high-pressure differen tial thermal analysis (DTA). It was found that the melting temperature and the pressure dependency of the melting temperature of NCH were low compared with those of nylon 6. Using the melting temperature, the pressure depende ncy of the melting temperature, and the heat of fusion (the enthalpy of fus ion), the Clausius-Clapeyron equation was used to determine the volume chan ges on melting of the polymers at atmospheric pressure DeltaV(m0)(DTA). Del taV(m0)(DTA) of NCH was lower than that of the nylon 6 alpha -form. The sma ller DeltaV(m0)(DTA) of NCH was attributed to the presence of nylon 6 gamma -form in NCH. The values of DeltaV(m0)(DTA) for nylon 6 and poly(butylene terephthalate) were similar to those obtained from pressure-volume-temperat ure relationships DeltaV(m0)(PVT) of those polymers. The entropies of fusio n were constant and independent of pressures up to 100 MPa. The volume chan ges on melting (DeltaV(m) in cm(3)/K) under high pressure can be approximat ely described by the following equation: DeltaV(m) = 0.165T(m)V(w) (dT(m)/d P)/ (dT(m0)/dP)/298, where T-m and T-m0 are the melting temperatures (in K) under high pressure and atmospheric pressure, respectively and V-w is the van der Waals volume of the polymer (cm(3)/g). (C) 2001 John Wiley & Sons, Inc.