Complex mixtures of long chain organic compounds often show overlapping glass transition temperatures (Tgs) when analyzed by differential scanning calorimetry (DSC) or modulated DSC (MDSC). In such cases, subjective and inconsistent
smoothing of data acquired under different conditions can lead to the misinterpretation of results. A quantitative method
for the selection of smoothing factors for the analysis and comparison of (M)DSC results is presented. The method is most
useful for the analysis of the derivative of the heat capacity, dCp/dt or dCp/dT, plots which best highlight overlapping Tgs. Four equations are shown to relate the heating rate and the smoothing factor. The equations allow a comparison of data
acquired i) at different heating rates and plotted vs. temperature, ii) at a single heating rate and plotted vs. both time and temperature, i.e., dCp/dt vs. dCp/dT, iii) at different heating rates and plotted vs. both time and temperature, and iv) at different heating rates, and shown exclusively in the time domain. Examples of the use of the equations are provided
for the analysis of bitumen, a complex mixture of natural origin.
Polyaniline/γ-Al2O3 (PANI/γ-Al2O3) composites were synthesized by in-situ polymerization at the presence of HCl as dopant by adding γ-Al2O3 nanoparticles into aniline solution. The composites were characterized by FTIR and XRD. The thermogravimetry (TG) and modulated
differential scanning calorimetry (MDSC) were used to study the thermal stability and glass transition temperature (Tg) of the composites, respectively.
The results of FTIR showed that γ-Al2O3 nanoparticles connected with the PANI chains and affected the absorption characteristics of the composite through the interaction
between PANI and nano-sized γ-Al2O3. And the results of XRD indicated that the peaks intensity of the PANI/γ-Al2O3 composite were weaker than that of the pure PANI. From TG and derivative thermogravimetry (DTG) curves, it was found that
the pure PANI and the PANI/γ-Al2O3 composites were all one step degradation. And the PANI/γ-Al2O3 composites were more thermal stable than the pure PANI. The MDSC curves showed that the nano-sized γ-Al2O3 heightened the glass transition temperature (Tg) of PANI.
The toughness of amorphous copolyester sheets was assessed by the essential work of fracture (EWF) concept. While the yielding-related
work of fracture terms did not change significantly, the necking-related parameters strongly decreased with decreasing entanglement
density of the copolyesters having different amounts of cyclohexylenedimethylene (CHDM) units in their backbones. Furthermore, copolyesters with high CHDM content and thus less entanglement density showed full recovery of the necked region beyond the glass transition temperature,
i.e. the ‘plastic’ zone in the related specimens formed by cold drawing and not by true plastic deformation. By contrast,
the copolyester with negligible amount of CHDM did not show this shape recovery. Modulated differential scanning calorimetry (MDSC) revealed that the necking in the latter
system was accompanied by strain-induced crystallization. The superior work hardening in the necking stage of the respective
poly(ethylene terephthalate) (PET) specimens can thus be ascribed to stretching of the entanglement network with superimposed crystallization.
Different grades of linear low density polyethylenes (LLDPEs) have been quenched cooled step-wise and crystallised isothermally
at (a series of increasing) temperatures in a DSC (thermal fractionated samples). These samples have been investigated by
temperature modulated DSC (MDSC). The heat flow curves of the thermal fractionated materials were compared with those obtained
from samples crystallised at a relatively slow cooling rate of 2 K min-1(standard samples).
The melting enthalpy obtained from the total heat flow of the thermal fractionated samples was 0-10 J g-1higher than those of standard samples. The melting enthalpy obtained from the reversing heat flows was 13-31 J g-1lower in the thermal fractionated samples than in the standard samples. The ratio of the reversing melting enthalpy to the
total melting enthalpy increased with decreasing density of the PE. The melting temperature of the endotherms formed by the
step-wise cooling was 9 K higher than the crystallisation temperature.
The tensile loading-induced necking in notched specimens of an amorphous copolyester (aCOP) was studied by modulated differential
scanning calorimetry (MDSC). It was shown that necking occurred by cold drawing since the enthalpy of cold crystallization
and that of the subsequent melting agreed fairly with each other. Increasing deformation in the necking zone and increasing
deformation rate of the specimens shifted the onset of cold crystallization toward lower temperatures and yielded a slightly
higher glass transition temperature (Tg). This was attributed to the molecular orientation caused by mechanical loading. The finding that the melting contained a
non-reversing part was considered as appearance of possible microcrystallinity. The Tg range was strongly influenced by the deformation rate and reflects the thermomechanical history of the samples accordingly.
The mechanical strain-induced βα-transition of a β-phase isotactic polypropylene (β-iPP) was studied by modulated differential
scanning calorimetry (MDSC). Samples were taken after tensile fracture of a double notched specimen from its process and plastic
zones, respectively, and the related calorimetric response was compared to that of the bulk material. In contrast to conventional
DSC results, it was found that the βα-transformation was not completed in the process zone. Furthermore, the melting of the
α-iPP showed both non-reversing and reversing characteristics, whereas the melting of the β-phase proved to be a reversing
process. Therefore, it was recommended to consider the conversion grade of the βα-transformation by the relative change in
the melt flux of the reversing β-melting peak.
The DSC characterisation of the morphology of the metastable a phase of stoichiometric nickel sulphide was carried out using
two calorimeters; a TA Instruments 2920 MDSC and a Perkin Elmer DSC-7, and two quenching histories. Based on these quenching
histories, significant differences were observed in the heat flow curves, including the observation of a second exothermic
peak which is tentatively assigned to be a metastable phase to metastable phase transformation. The kinetic constants for
the a to b recrystallisation were determined as a function of degree of conversion using a mechanism free isoconversional
model. Variations in the values of the kinetic constants were also ascribed to the quenching histories. Although the differences
in morphology observed were ascribed to the processing history, the shift in the position of the a to b recrystallisation
peak was partially attributed to the thermal resistances of the instruments used.
This article discusses AFM-based localized thermal analysis of crosslinked polymer coatings based on a recent breakthrough
in nanoscale thermal probe technology. The addition of a thermal tip to a conventional AFM adds a new and valuable capability
of spatially resolved thermal analysis to the AFM. It is particularly useful for thin films since it enables the measurement
of transition temperatures (melting (Tm) or glass (Tg)) on selected regions of the sample aiding in the identification and characterization of phases on the length scales approaching
macromolecular dimensions. Examples include the monitoring of the softening point of automotive clearcoat systems, as a function
of cure time and cure temperature and characterization of degradation and embrittlement of weathered acrylic-polyurethane
coatings. Comparison of nano thermal analysis with bulk DSC and MDSC is made and its inherent advantages over DSC in analyzing
surfaces, is demonstrated.
The polymerization of a cyclic butylene terephthalate
(CBT) oligomer was studied as a function of temperature (T=200
and 260C, respectively) by modulated DSC (MDSC). The first heating was
followed by cooling after various holding times (5, 15 and 30 min) prior to
the second heating which ended always at T=260C.
This allowed us to study the crystallization and melting behavior of the resulting
polybutylene terephthalate (PBT), as well. In contrary to the usual belief,
the CBT polymerization is exothermic and the related process is superimposed
to that of the CBT melting. The melting behavior of the PBT was affected by
the polymerization mode (performed below or above the melting temperature
of the PBT product) of the CBT. Annealing above the melting temperature of
PBT yielded a product featuring double melting. This was attributed to the
presence of crystallites with different degrees of perfection. The crystals
perfection which occurred via recrystallization/remelting was manifested by
a pronounced exothermic peak in the non-reversing trace.
The DSC curve obtained in conventional equipment usually only shows the resultant thermal effect due to simultaneous phenomena,
which may occur during isothermal or dynamic analyses. This does not allow one to identify the processes properly and may
cause an erroneous interpretation of the resulting curves.
Modulated DSC equipment enhances the operating conditions and the analysis capacity of conventional DSC by superimposing a
sinusoidal temperature modulation on the linear temperature control. Thus reversing and non-reversing heat flow curves are
obtained, which are, respectively, the heat capacity and kinetic components of the DSC curve. Therefore, events that are related
to these components can be separately analyzed.
A method to obtain curves similar to the MDSC reversing and non-reversing components was developed using conventional DSC
equipment in a non-conventional way. It was applied to analyze samples of poly(ethylene terephthalate) (PET) taken from bottles
of mineral water. The second PET crystallization step that occurs during its melting was quantified and an apparent initial
crystallinity was obtained from the resulting data.