Beyond Flexible Polymers Rigid Amorphous Fraction

6 Beyond Flexible Polymers Rigid Amorphous Fraction 

Similar to polyethylenes the morphology of these polymers is also described as a lamellar stack of crystalline and non-crystalline layers. This so-called two phase model is applied for the interpretation of X-ray diffraction data as well as for heat of fusion or density measurements. However, it is well known that several mechanical properties, as well as the relaxation strength at the glass transition temperature, cannot be described by such a simplistic two-phase approach, as discussed by Gupta [59]. Prom standard DSC measurements [60], dielectric spectroscopy, shear spectroscopy [61], NMR [62], and other techniques probing molecular dynamics at the glass transition (a-relaxation) temperature, the measured relaxation strength is always smaller than expected 

Lin et al. [66] have exploited this variation in specific volume of the RAF to control the barrier properties of polyester films. An attempt to correlate the mechanical deformation of PET with the amount of RAF present in these films has been made recently. Moreover, the observations have been that a Sample having a greater amount of RAF, on imiaxial compression, shows considerable loss in crystallinity compared to a sample having lesser amoimt of RAF. These findings have been reported in a recent pubhcation [67]. 

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Beyond flexible polymers rigid amorphous fraction. 189... 

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