Enthalpy recovery in low molecular weight PMMA

Effect of physical aging on nano- and macroscopic properties of poly(methyl methacrylate) glass

“…This peak increases in magnitude and it appears at higher temperature when the aging is performed at temperature closer to T g . Such effect of physical aging was reported earlier in literature [26,27] and was observed also for other thermally aged amorphous polymers like polystyrene [28] or poly(ethylene terephthalate) [29]. The calculations of the fictive temperature -T f show that the T f is the highest for reference sample (111 8C), while for the aged samples T f values are smaller and equal: 103 8C (sample aged 3 weeks at 95 8C), 104 8C (sample aged 3 weeks at 80 8C) and 108 8C (sample aged 9 months at 25 8C).…”

Structural recovery of a single polystyrene thin film using nanocalorimetry to extend the aging time and temperature range

“…The prediction of changes in glass properties as a function of time and temperature is essential for practical applications, especially for polymeric glass formers, which can be used in structural applications, such as in aerospace composites. The majority of works [3][4][5][6][7][8][9][10][11][12][13][14] show smooth evolution of properties towards the extrapolated equilibrium line and that the extrapolated equilibrium line is reached at long enough times, but there are some groups claiming that the extrapolated equilibrium line is not reached [15][16][17][18] or that the change in properties shows stepwise changes with multiple time scales [19,20].…”

“…For example, most enthalpy recovery experiments using conventional differential scanning calorimetry (DSC) [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] cannot accurately determine enthalpy changes for aging times of less than 1 min because the small changes in enthalpy are difficult to measure coupled with uncertainties concerning the sample's thermal history and the associated temperature gradient in the sample. In addition, aging temperatures are generally limited to temperatures below the nominal glass transition temperature T g [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17], because the timescales for relaxation at higher temperatures are too short relative to the instrument response time.…”

Structural relaxation of an unentangled polymer in terms of a simple phenomenological approach

“…Such value was experimentally obtained only for the two highest annealing temperatures; for the others the approximated relation 8,31 ⌬H͑T a , ϱ͒ = ⌬C p ͑T g ͒ · ͑T g − T a ͒ was assumed to hold. Such value was experimentally obtained only for the two highest annealing temperatures; for the others the approximated relation 8,31 ⌬H͑T a , ϱ͒ = ⌬C p ͑T g ͒ · ͑T g − T a ͒ was assumed to hold.…”

“…Such value was experimentally obtained only for the two highest annealing temperatures; for the others the approximated relation 8,31 ⌬H͑T a , ϱ͒ = ⌬C p ͑T g ͒ · ͑T g − T a ͒ was assumed to hold. 31, where Fig. 1 the good agreement between theory and experi-ments is apparent at all the investigated temperatures.…”