Phase rigid amorphous

The discussion of the influence of the interphase need not be limited to just linear polyethylenes. Interphases of several nm have been reported in polyesters and poly-hydroxy alkanoates. One major difference between the interphase of a flexible polymer like polyethylene and semi-flexible polymers like PET, PEN and PBT is the absence of regular chain folding in the latter materials. The interphase in these semi-flexible polymers is often defined as the rigid amorphous phase (or rigid amorphous fraction, RAF) existing between the crystalline and amorphous phases. The presence of the interphase is more easily discerned in these semi-flexible polymers containing phenylene groups, such as polyesters. 

A third phase, next to the amorphous phase x(a) and the crystalline phase x(c), is thought to be present in the temperature region between Tg and Tm of semi-crystalline polymers which is called the rigid amorphous phase x(r,a). 

This is amorphous material hindered to such a degree by the crystalline fraction that it behaves rigid [12, 13]. Assuming that a ACp-step at Tg of 0.115 J/g.C corresponds with a polymer weight fraction of 0.14, the extent of the possible rigid amorphous phase in PK terpolymer can be estimated. The sum of x(c), x(a) and x(r,a) is 1.00, thus might hold for PK terpolymer (after recrystallisation from the melt) ... 

Thus, PK terpolymer after recrystallisation from the melt might have a rigid amorphous phase (in the temperature region between Tg and Tm) of about 18 %wt. 

TABLE 12.1 PALS Parameters for the Rigid Amorphous Phases of Cold- and Melt-Crystallized PET at Room Temperature... 

Wunderlich, B., Reversible crystallization and the rigid-amorphous phase in semicrystalline macromolecules. Prog. Polym. Sci., 28, 383-450 (2003). 

The results on reversible crystallization and melting are reviewed in WunderhchB (2003) Reversible Crystallization and the Rigid Amorphous Phase in Semicrystalline Macromolecules. Progress in Polymer Science 28/3 383 50. 

Semicrystalline PPO shows the existence of a rigid-amorphous phase which governs the thermal properties from Tg to T ,. Fusion, superheating and annealing are directly affected by the rigid-amorphous phase [42]. 

The nearly 1000-fold difference in the values of of the crystalline and amorphous carbons in PE permit their separate observation. However, for semi-crystalline polymers with rigid amorphous phases characterized by high glass-transition temperatures, Tg, such a clean separation may not be possible. Although the chains in a glassy polymer sample are disordered, they may not be sufficiently mobile to rapidly sample all potentially accessible conformations. As a consequence, each amorphous conformational environment will contribute a different solid state chemical shift, producing a broad envelope of resonances for the disordered chains. Warming the semi-crystalline sample above Tg will... 

From the simultaneous SWD-experiments the following attempt to relate structure and dynamics can be made. For times shorter than a characteristic one t 90 min) the decrease of (Ae), Fig. 21.9a, indicates a significant reduction of the mobile material which follows the increase of crystalUnity (Fig. 21.9e). However, the reduction of (Ae), is stronger than the increment in crystallized material as determined by the increase of Xc- This effect, observed in different polymers [13,17], can be attributed to the formation of an immobilized amorphous phase frequently referred to as rigid amorphous phase (RAP) [40]. 

The glass transition of semicrystalline PLLA with different morphologies was studied by Picciochi et al. [49]. A three-phase model was proposed and the relative thicknesses of the three phases, that is, crystalline, mobile amorphous, and rigid amorphous phases, were obtained as presented in Figure 6.8. The decrease in Tg was found to be correlated with the changes in the thickness of the rigid amorphous phase as... 

A. Magon, E. Nowak-Pyda, R. C. Bopp, M. Pyda, Glass transition of the rigid amorphous phase of biodegradable poly(lactic acid), in Proceedings of the 35th NATAS Annual Corference on Thermal Analysis and Applications, 2007. 

---