The Very Long-Term Volume Recovery of Polycarbonate:  Is Self-Retardation Finite?

Abstract

The specific volume change of Bisphenol A polycarbonate was measured at room temperature for several years. The effects of formation conditions like cooling rate and pressure, the addition of low molecular additives, and injection molding and quenching were investigated. The volume shrinkage at long times was found to be much higher than extrapolated from short term measurements. A general pattern is observed in the volume recovery curves. They start with a small constant slope on the logarithmic time scale. After about 107 s a transition is observed to a much steeper slope. Whereas in the first section the characteristic increase in τeff is observed, the volume recovery during the transition can be fitted quite well with a single exponential. The sharp transition suggests that there is a long retardation time, which may represent the genuine α-relaxation. It also means that the self-retardation during physical aging is finite. The slope at long times (>107 s) scales with the distance from equilibrium, as extrapolated from measurements close to T g. The cooling rate during vitrification affects the slope in the first zone only, while the formation pressure leads to a vertical shift of the curves. Addition of low molecular weight additives leads to a dramatic densification and accelerates the volume recovery.

Diffusion mechanism for physical aging of polycarbonate far below the glass transition temperature studied by means of dielectric spectroscopy

“…In conclusion it is worth comparing our permittivity data with the volume relaxation data already reported in literature [23]. In this study, no specific volume reduction is observed for PC volume relaxation at 25°C in the time scale of several days, which is the time scale for our permittivity relaxation experiments.…”

Thickness dependence of structural relaxation in spin‐cast polynorbornene films with high glass transition temperatures (>613 K)

“…At 423 K, the apparent aging rate accelerates after 300 min as shown in Figure (a), which is counter to the typical slowdown in aging in the terminal region . There have been similar reports for acceleration in the densification of polycarbonates after long aging times (>10 7 s) . Here, this change in the apparent aging rate is accompanied by chemical modification of the polymer (Supporting Information, Fig.…”

Aging, Physical

“…Recent work (15) on polycarbonate (PC) suggests otherwise. At low aging temperatures, volume recovery appeared to be higher than expected (15). In addition, there was a sharp transition from a slow rate of volume recovery to a much faster aging rate at 10 7 s. The observations have been confirmed qualitatively for polycarbonate but not for polystyrene (PS) (16).…”

“…For enthalpy recovery, (dδ/dP) T = VT α and (dδ/dT) P = C p . The nonexponentiality of the structural recovery process is described by the nonexponentiality parameter β in equation (15); the history dependence is accounted for by the integral of the reduced time (dt/τ ); and the nonlinearity is incorporated into the model by allowing the characteristic relaxation time τ Vol. 1…”