High-Pressure/High-Temperature Dilatometry of SMC Low Profile Additives

A high-pressure/high-temperature volumetric dilatometer has been designed and constructed. This equipment can be operated at temperatures as high as 250°C and pressures as high as 14 MPa. The sample chamber of this unit is composed of two concentric, double wall, stainless steel cylinders with ceramic and epoxy attachments and two thermocouples. The test sample is placed in the cavity between the two cylinders, and hence a very rapid and efficient heat transfer is achieved. The volume changes of the sample during the experiement are monitored by recording voltage changes caused by vari ations in the resistance of a circuit of the graphite rod in the pool of mercury. Using SMC paste samples, it has been demonstrated that the role of low profile additive is not affected by the maturation viscosity of the paste. Also, it was observed that the onset of volume ex pansion caused by the low profile additive occurs at about 110°C, whereas, the onset of the volume shrinkage due to chemical reaction does not coincide with this point and occurs at 135°C. This observation explains why, in general there is a major volume expansion and shrinkage associated with the cure of SMC.