Rigid amorphous fraction

Beyond flexible polymers rigid amorphous fraction. 189... 

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. 

Differential scanning calorimetric (DSC) evidence suggests the possibility of using this thermal method to identify a rigid, amorphous fraction formed by the immobilization of a surface layer of binder in contact with aggregate. 

Lin, J., Shenogin, S., and Nazarenko, S., Oxygen solubility and specific volume of rigid amorphous fraction in semicrystalline poly(ethylene terephthalate). Polymer, 43, 4733 (2002). 

Prigogine, Trappeniers, and Mathot pressure-volume-temperature measurements lead zirconate titanate quaternary ammonium salts quasi-two-parameter theory rigid amorphous fraction Rheometrics extensional rheometer Rheometrics elongational rheometer for melts room temperature small-angle neutron scattering small-amplitude oscillatory shear flow small-angle x-ray scattering side-chain LCP... 

Annealing the drawn fiber, as shown in Fig. 4.150, introduces sufficient crystallinity to cause the shrinkage to occur continually between the glass and melting temperatures. One would interpret this behavior in terms of the existence of a rigid amorphous fraction that gradually becomes mobile at temperatures well above the... 

The dimensions of the crystal and amorphous subsystems vary from nanometers to micrometers, i.e., polymeric materials are nanophase- or microphase-separated and have only a partial crystallinity. If we treat homopolymers as one-component systems, the phase rule of Sect. 2.5.7 does not permit equilibrium between two phases, except at the transition temperature. Partially crystalline homopolymers are, thus, not in equilibrium. The properties of semicrystalline polymers are critically influenced by the interactions between the amorphous and crystalline domains, as is seen in the formation of rigid amorphous fractions, discussed in Sect. 6.1.3 and 6.3.4. 

For bulk materials, all techniques based on structure-insensitive properties, as described in this section and elsewhere, yield closely similar data. The crystallinity model is thus a valid defect concept to describe structure-insensitive properties of semicrystalline polymers. It breaks down for three-phase systems, consisting, for example, of a crystalline phase, a mobile amorphous phase, and a rigid-amorphous fraction (see Chap. 6). In addition, one does not expect valid answers for structure-sensitive properties. 

The glass transition of the amorphous phase can be used to estimate the strain introduced into the metastable, amorphous nanophases by the interfaces with the crystals. The local strain manifests itself in an increase of the glass-transition temperature and the possible presence of a rigid amorphous fraction that does not show a contribution to the increase in heat capacity at T, as is discussed in Sect 6.1.3. Most bulk-crystallized macromolecules which do not exhibit intervening mesophases are described by the phase areas 7 and 8 of Fig. 6.1. 

The reversing heat capacity and the total heat-flow rate of an initially amorphous poly(3-hydroxybutyrate), PHB, are illustrated in Fig. 6.18 [21]. The quasi-isothermal study of the development of the crystallinity was made at 296 K, within the cold-crystallization range. The reversing specific heat capacity gives a measure of the crystallization kinetics by showing the drop of the heat capacity from the supercooled melt to the value of the solid as a function of time, while the total heat-Uow rate is a direct measure of the evolution of the latent heat of crystallization. From the heat of fusion, one expects a crystallinity of 64%, the total amount of solid material, however, when estimated from the specific heat capacity of PHB using the ATHAS Data Bank of Appendix 1, is 88%, an indication of a rigid-amorphous fraction of 24%. 

Figures 6.127 and 6.128 illustrate that for the two macromolecules the strain on the amorphous fraction is so large that a portion of the amorphous phase remains rigid up to the transition region and a lower increase in heat capacity at Tg results than is expected from the fraction of the amorphous sample, (1 - wj. This fraction is called the rigid-amorphous fraction, RAF. The method of its evaluation is described in Figs. 6.16-18 for the case of poly(oxymethylene). For PEEK, the RAF is illustrated in Fig. 6.127. It is calculated as the ratio to the total amorphous fraction and increases...

Rigid-amorphous Fraction of Poly(thio-1,4-phenylene), PP6... 

Besides T, the breadth of the ttansition region, and ACp, partial crystallization affects also the hysteresis behavior (enthalpy relaxation) of the amorphous fraction. Figure 6.129 in its bottom curve depicts a typical enthalpy relaxation in amorphous PET that can be used to study the thermal history, as outlined for polystyrene in Figs. 4.125-127. The DSC curves for the samples with increasing crystallinity show that the hysteresis disappears faster than the step in ACp at the glass transition. The top sample in Fig. 6.129 of 31% crystallinity shows a smaller change in heat capacity than expected for an amorphous content of 69%, due to some rigid-amorphous fraction, but the hysteresis peak seems to have disappeared completely. 

A drawn film was also included in the analysis [66]. The quasi-isothermal TMDSC of this drawn sample is reproduced in Fig. 6.109. It was produced out of practically amorphous PET by biaxial drawing at 368 K. The sample retains no residual cold crystalhzation and has a higher rigid-amorphous fraction than the semicrystalline reference PET of Fig. 3.92. Long-time aimealing causes an aimealing peak of the crystals, as described in Sect. 6.22, but displays no hysteresis peak, as was also observed for the slowly cooled, undrawn PET samples with similar crystallinity used as an example in Fig. 6.129. 

Schick C, Wurm A, Mohammed A (2001) Vitrification and Devitrification of the Rigid Amorphous Fraction of Semicrystalline Polymers Revealed from Frequency-dependent Heat Capacity. Colloid Polymer Sci 279 800-806. 

P The glass transition temperature of semicrystalline PBT is seen at Tg from 310 to 325 K. In addition, it shows the existence of a rigid-amorphous fraction [53]. The quenched sample shows some small transition at 248 K which is probably not the Tg, as assumed earlier [72]. 

Above Tg, poorly crystallized samples show a rigid-amorphous fraction that does not contribute to the increase in heat capacity at Tg [35]. 

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