Stored energy of cold work in polystyrene

Abstract

The energy stored in polystyrene after plastic deformation is measured by the differential scanning calorimetry (DSC) technique. Similar to metals, the stored energy increases with plastic straining, first rapidly, and then more slowly, and finally the stored energy seems to approach a saturation value (about 1 cal/gram). By comparing to the plastic work done, the fraction stored ranges from 30 percent after 10 percent compression to 10 percent after 60 percent compression. The fraction is about twice as large as that of copper. The release of stored energy has two distinct parts, one below Tg and the other above Tg. Most of the strain recovery seems to accompany the second part. By using the Kissinger plot, the second part has an activation energy, of 142 kcal/mole which is about 10 percent larger than that of compressive strain recovery.

Post-yield compressed semicrystalline poly(butylene terephthalate): energy storage and release

“…7. This ratio is clearly decreasing as the strain level increases in good accordance with the data reported by Li and co-workers [10,11] on glassy polymers. More recently, Shenogin et al [50] measured the fraction of the inelastic deformation work stored as internal energy in many different amorphous polymers, such as polystyrene, poly(methyl methacrylate), polycarbonate and a cured epoxy, in the pre-yield region by a new deformational calorimeter.…”

Investigation of nonelastic response of semicrystalline polymers at high strain levels

“…The speed at which both components recover at high temperature is such that anelastic and plastic recovery are no longer distinguishable. Similar to the behavior of fully amorphous polymers,1–10 the thermomechanically activated nature of strain recovery for semicrystalline polymers can be seen. Experimental data points at T rec > 25°C were corrected by subtracting the specimen thermal expansion evaluated by using the following coefficients of linear thermal expansion: α T = 9 × 10 −5 /°C for PA615 and 1.7 × 10 −5 /°C for PET19 and PEN.…”

“…Studies on yield and postyield behavior of amorphous glassy polymers1–10 show the existence of two distinct nonelastic strain components. In particular, when the material is deformed in the glassy state, one can distinguish between an anelastic (ε an ) component that can recover in a certain interval of time, even at a temperature well below the glass transition, and a permanent plastic (ε pl ) component.…”

Energy storage and strain‐recovery processes in highly deformed semicrystalline poly(butylene terephthalate)

“…Many researchers1–6, 9, 12, 13, 22, 25, 28, 29 have found in DSC traces of highly deformed polymers an exothermal peak or plateau that for glassy polymers extends typically from the temperature of deformation up to the T g or little above 3, 4, 9, 12, 13. The area under the peak, Δ H exo , has been attributed to the energy released for the nonelastic strain recovery 3, 4, 9, 12, 13, 22, 25. The results here obtained suggest that the reversible component of the deformation is associated with relaxation processes that require temperatures well above T g to be activated.…”

“…In amorphous glassy polymers three of the following components of deformation are commonly distinguished: elastic, anelastic, and plastic 1–13. The elastic strain component recovers instantaneously after sample unloading, whereas both the anelastic and plastic components recover with time, although the former has faster kinetics 7.…”