crystallinity calculated from the heat of fusion.
In the present work, the effect of the rigidamorphousfraction (RAF) on the traditional amorphous fraction (TAF) will be discussed: the hysteresis peak at the glass transition of the TAF disappears under
Volumetric thermal analysis of semicrystalline poly(ethylene terephthalate), PET, with different content of crystalline phase
was carried out using mercury-in-glass dilatometry. The effect of crystals on the thermal properties of amorphous phase (glass
transition temperature, Tg, thermal expansion coefficients, α) were determined. At cold-crystallization (106°C, up to 4 h), crystalline content of 2.4–25.3
vol.% was achieved. Increasing content of crystalline phase broadens the glass transition region and increases Tg. The change of thermal expansion coefficient during glass transition is lower than that predicted by the two-phase model,
which indicates the presence of a third fraction — rigid amorphous fraction (RAF), whose content steadily increases during
crystallization. However, its relative portion (specific RAF) is significantly reduced. Further significant decrease in specific
RAF appears after annealing at a higher temperature.
A three-phase model, comprising crystalline, mobile amorphous, and rigid amorphous fractions (χc, χMA, χRA, respectively) has been applied in the study of semicrystalline Nylon-6. The samples studied were Nylon-6 alpha phase prepared
by subsequent annealing of a parent sample slowly cooled from the melt. The treated samples were annealed at 110°C, then briefly
heated to 136°C, then re-annealed at 110°C. Temperature-modulated differential scanning calorimetry (TMDSC) measurements allow
the devitrification of the rigid amorphous fraction to be examined.
We observe a lower endotherm, termed the ‘annealing’ peak in the non-reversing heat flow after annealing at 110°C. By brief
heating above this lower endotherm and immediately quenching in LN2-cooled glass beads, the glass transition temperature and χRA decrease substantially, χMA increases, and the annealing peak disappears. The annealing peak corresponds to the point at which partial de-vitrification
of the rigid amorphous fraction (RAF) occurs. Re-annealing at 110°C causes the glass transition and χRA to increase, and χMA to decrease. None of these treatments affected the measured degree of crystallinity, but it cannot be excluded that crystal
reorganization or recrystallization may also occur at the annealing peak, contributing to the de-vitrification of the rigid
Using a combined approach of thermal analysis with wide and small angle X-ray scattering, we analyze the location of the rigid
amorphous and mobile amorphous fractions within the context of the Heterogeneous and Homogeneous Stack Models. Results show
the homogeneous stack model is the correct one for Nylon-6. The cooperativity length (ξA) increases with a decrease of rigid amorphous fraction, or, increase of the mobile amorphous fraction. Devitrification of
some of the RAF leads to the broadening of the glass transition region and shift of Tg.
The increment of heat capacity at the glass transition for semi-crystalline poly(ethylene terephthalate) (PET) observed by
temperature-modulated differential scanning calorimetry (TMDSC) shows significant deviations from a simple crystalline/amorphous
two-phase model. Introduction of a rigid amorphous fraction, which is non-crystalline but which also does not participate
in the normal glass transition, allows a much better description of the transition behaviour in semi-crystalline PET. Certain
questions arise such as what is the rigid amorphous fraction and over what temperature range do these rigid amorphous segments
devitrify? These TMDSC results show that the rigid amorphous component may be treated as an interphase between amorphous and
crystalline phases. This interphase does not exhibit a separate glass transition temperature at temperatures above the normal
Tg. The suggestion is made that the glass transition of the rigid amorphous component occurs continually between the glass transition
temperature of the amorphous phase and up to about 135C for this particular sample of PET.
Authors:L. Torre, J. Kenny, A. Recca, V. Siracusa, A. Tarzia, and A. Maffezzoli
An analysis of the crystallization behaviour of a new poly(aryl-ether-ether-ketone-ketone), PK99, by differential scanning
calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) is presented. Isothermal crystallization TG were obtained in the
whole range between the glass transition temperature (Tg) and the melting temperature (Tm) as a consequence of the slow crystallization kinetics stemming from the closeness of these transitions. The calorimetric
results, compared with WAXD data, were applied to determine the theoretical melting temperature and crystallization enthalpy.
The DSC and WAXD data were combined in order to calculate the total amount of the crystallizable fraction of the polymer,
and a model was proposed to explain the difference between the fractions of crystallinity observed with these techniques.
The thermal and X-ray data were also correlated with different lamellar morphologies arising from the crystallization conditions.
Finally, DSC experiments on the crystallized sample were used to detect the presence of a rigid amorphous phase which does
not relax at Tg.
hindering the large-amplitude motion close to boundaries to a more rigid phase or by applying external strain, as in drawn fibers. Both of these latter restraints may produce a rigidamorphousfractions ( RAF ) [ 18 ]. The ATHAS Data Bank provides the
We report a thermal analysis study of the effect of molecular weight on the amorphous phase structure of poly(phenylene sulfide),
PPS, crystallized at temperatures just above the glass transition temperature. Thermal properties of Fortron PPS, having viscosity
average molecular weights of 30000 to 91000, were characterized using temperature modulated differential scanning calorimetry
(MDSC). We find that while crystallinity varies little with molecular weight, the heat capacity increment at the glass transition
decreases as molecular weight decreases. This leads to a smaller liquid-like amorphous phase, and a larger rigid amorphous
fraction, in the lower molecular weight PPS. For all molecular weights, constrained fraction decreases as the scan rate decreases.
Authors:C. Schick, J. Dobbertin, M. Pötter, H. Dehne, A. Hensel, A. Wurm, A. Ghoneim, and S. Weyer
The relaxation strength at the glass transition for semi-crystalline polymers observed by different experimental methods shows
significant deviations from a simple two-phase model. Introduction of a rigid amorphous fraction, which is non-crystalline
but does not participate in the glass transition, allows a description of the relaxation behavior of such systems. The question
arises when does this amorphous material vitrify. Our measurements on PET identify no separate glass transition and no devitrification
over a broad temperature range. Measurements on a low molecular weight compound which partly crystallizes supports the idea
that vitrification of the rigid amorphous material occurs during formation of crystallites. The reason for vitrification is
the immobilization of co-operative motions due to the fixation of parts of the molecules in the crystallites. Local movements
(Β-relaxation) are only slightly influenced by the crystallites and occur in the whole non-crystalline fraction.