Deformation recovery

The deformation recovery theory implies that the shapes of the disintegrant particles are distorted during compression, and that the particles return to their preeompression shape upon wetting, thereby causing the tablet to break apart. Hess [20], with the aid of photomicrographs, showed that deformed stareh particles returned to their original shape when exposed to moisture. 

The deformation recovery theory implies that the shapes of the disintegrant particles are distorted during com-... 

Because of the complexities involved, the mechanism of action of super disintegrants is not well understood. Some of the proposed mechanisms include water wick-ing, swelling, deformation recovery, particle repulsion, and heat of wetting. Water uptake is a necessary... 

Viscoelastic foams show a stress-relaxation phenomenon, i.e., delay of complete deformation recovery after compression. These foams usually take 2 to 30 seconds to recover after 50% compression. In contrast, HR foams and conventional flexible polyurethane foams show very short deformation-recovery times, e.g., less than 1 second. This means that these foams have low viscoelasticity or small energy absorption. 

Zhu et al. studied a biocompatible shape memory polymer blend based on poly(e-caprolactone) (PCL) and polymethylvinylsiloxane (PVMS). Pure PCL was subject to scission rather than cross-linking under irradiahon. In the presence of a small amoimt of PVMS (<20 wt%), both polymers are miscible in the amorphous phase and the radiation cross-linking of PCL is enhanced. Mechanical properties were improved, and a strong shape memory behavior was achieved. Above the melhng point of PCL, the blend exhibited a rubber-like state and could be deformed. The switch temperature was the melting temperature of PCL. With 5 to 15 wt% of PVMS and under 100 kGy y-irradiation, the deformation fixation ratio and the deformation recovery ratio were 100%. 

For a viscoelastic material under a constant applied stress, the strain e(t) shows a delay in response to the applied stress see Fig. la(4). When the load is removed at t = t, a viscoelastic liquid will recover partially its deformation at t = over a period of time. Some deformation remains permanently. In contrast, for a viscoelastic solid, on load removal, the deformation recovery over time is relatively faster, and almost all the deformation may be recovered over a sufficiently long period of time. 

Since PS progressively lose their deformation recovery properties with increase of plasticiser levels and yield to systems of little practical value, usually they are used neat , without... 

The force of deformation recovery = fejAdx = —du r)/dr. The force constant approximates the second-order differential of the respective Mx(r) at equilibrium, and the points always against the direction of deformation. 

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