Semicrystalline polymers interfacial phase

The study of the phase structure of semicrystalline polymers, particularly that of the interfacial region, is of foremost importance, since it has an intimate relationship with the macroscopic properties of polymers. Many techniques have been used to study this problem. To determine the mass fraction of each phase of the three-phase structure, such techniques as H broad-line NMR or Raman... 

In order for the ordered phase to crystallize from an amorphous melt a nucleation barrier must be overcome. This barrier is a result of interfacial energy between the ordered phase and the melt that causes super cooling. Sirota [44] suggested that in order for the nucleation barrier of the stable phase to be sufficiently high to form out of the melt, another phase with a lower nucleation barrier and a free energy intermediate between that of the stable phase and the melt must form. This, he points out, is implied by Oswald s rule [45] and evidence presented by Keller [35] that crystallization in semicrystalline polymer systems is mediated by a transient metastable phase [47, 48]. 

The above equation should be used with caution, however, because it does not account for the quality of interfacial contact between the plastic and the filler system. Poor interfacial contact has the same effect as a thermal contact resistance and can result in a significant lowering in the ability of the highly conducting filler particles to transmit heat to the low-conductivity polymer matrix. What complicates the matter further is that these systems may possess good interfacial contact while the polymer matrix is molten but then become lower in thermal conductivity as interfacial contact resistance develops between the filler and the now-solidified polymer. This can be particularly confusing in the case of some filled semicrystalline polymers, where the appearance of the crystalline phase upon solidification should result in increased thermal conductivity, while the actual value appears to decrease. For this reason, it is considered safer to measure the thermal conductivity of filled materials. 

The situation changes in the case of solid-phase (semicrystalline) polymer uniaxial drawing. As the experimental estimations shown [5], the Poisson s ratio value for initial pol5aneric materials (componors UHMPE-Al and UHMPE-bauxite) v 0.36 and for these materials extmdates with draw ratio X > 3-v 0.43. From the Eq. (14.3) it follows that A 0.857. This means componors volume obligatory increase, expressed in cracks formation on interfacial boundaries pol5nner matrix-filler [3] ... 

For PVDF and for other semicrystalline polar polymers, there are several different molecular and interfacial mechanisms that may lead to piezoelectricity, and their relative quantitative contributions are still not fully understood (Broadhurst and Davis 1984 Rollik et al. 1999 Katsouras etal. 2015). And in polyamide-11, one of the odd-numbered polyamides and, in other semicrystalline polymers, a rigid amorphous phase has been found to modify the mechanical deformation and thus also the piezoelectric response (Frubing et al. 2006). 

Although no exact correlation between experiment and model was produced by this exercise, it has been shown that the two polymers studied exhibit phase-separated morphologies that are similar in nature to the extent that they are subject to nearly identical polarizations. The large polarizations measured can only be explained by high interfacial areas, congruent with semicrystalline lamellar morphologies. Finally, the divergence of the observed polarizations from those predicted by the two-phase model is quite likely due to the existence of finite-thickness, transition zones between dissimilar domains. 

In a noncrystallizable polymer such as atactic polystyrene, is dose to 8wt%. In semicrystalline PE it is 5 wt%, presumably due to segregation of the CB to the noncrystalline phase or the phase boundaries in PE. This segregation is further enhanced in PE/PS blends when the composition allows for continuity of the PE phase and double percolation of the phases and conductive regions [27, 37]. This has been observed at a 45/55 ratio by weight of PE/PS in a melt-blended composition with more than 0.4 wt% (0.2 vol%) carbon black [27]. The effect seems to depend upon the relative interfacial tensions of the polymers and the CB in a manner consistent with the independent observations of Miyasaka et al. [38]. 

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