The influence of multi-walled carbon nanotubes (0–5 wt%) on the crystallization process in isotactic polypropylene has been investigated by DSC and fast scanning calorimetry. In the non-isothermal ...experiments the crystallization temperature shifts to higher temperatures with increasing nanotube content, αCNT, whereas the polymer crystallinity was not significantly influenced. The critical cooling rate, βc, at which the PP does not crystallize, increases with increasing of αCNT. From βc and αCNT a nucleation efficiency parameter was derived, which is independent of crystallization temperature and filler content. Isothermal crystallization experiments allow differentiating between α-phase and mesophase crystallization. Nanotubes accelerate only the α-phase formation. To describe the efficiency of a nucleation agent an acceleration factor, ε, was introduced, which is the ratio of the characteristic crystallization time of unfilled and filled polymer. For the α-phase formation the acceleration factor ε is related to the number of nuclei per nanotube and the specific effect of the filler on the growth rate.
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•Study of PP-MWCNT crystallization versus temperature, cooling rate and composition.•MWCNT accelerates the α-phase formation, but has no impact on mesophase formation.•Models are derived for the acceleration of crystallization due to nucleating agent.•The model parameters characterize the efficiency of a nucleating agent.
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•The cooling rate dependence of the glass transition is measured in a cooling rate range of more than six decades.•The cooling rate dependence of the glass transition can be described ...by a Vogel–Fulcher–Tammann–Hesse equation.•The influence of the heat transfer conditions in a Flash DSC is discussed.
The thermal glass transition of polystyrene (PS) is measured in a range between 0.003K/s and 4000K/s using a conventional DSC 1 and a Flash DSC 1 from Mettler-Toledo. The dependency between the cooling rate and the glass transition temperature is in accordance with the Vogel–Fulcher–Tammann–Hesse (VFTH) equation, as it is usually used for description of the frequency–temperature relationship of the dynamic glass transition (or main relaxation process). Furthermore we discuss the influence of the thermal lag on the measurement and develop correction methods.
Resins are important for enhancing both the processability and performance of rubber. Their efficient utilization requires knowledge about their influence on the dynamic glass transition and their ...miscibility behavior in the specific rubber compound. The resins investigated, poly-(α-methylstyrene) (AMS) and indene-coumarone (IC), differ in molecular rigidity but have a similar aromaticity degree and glass transition temperature. Transmission electron microscopy (TEM) investigations show an accumulation of IC around the silanized silica in styrene–butadiene rubber (SBR) at high contents, while AMS does not show this effect. This higher affinity between IC and the silica surface leads to an increased compactness of the filler network, as determined by dynamic mechanical analysis (DMA). The influence of the resin content on the glass transition of the rubber compounds is evaluated in the sense of the Gordon–Taylor equation and suggests a rigid amorphous fraction for the accumulated IC. Broadband dielectric spectroscopy (BDS) and fast differential scanning calorimetry (FDSC) are applied for the characterization of the dielectric and thermal relaxations as well as for the corresponding vitrification kinetics. The cooling rate dependence of the vitrification process is combined with the thermal and dielectric relaxation time by one single Vogel–Fulcher–Tammann–Hesse equation, showing an increased fragility of the rubber containing AMS.
The non-isothermal crystallization of 11 different homopolymers and one copolymer is measured by fast differential scanning calorimetry (FDSC) with various cooling rates. A new method to evaluate the ...kinetics of polymer crystallization based on the Gibbs free energy difference between liquid and crystal is proposed. As a result a surface parameter, κ, is introduced characterizing the surface free energy of the crystals in respect to the molecular packing density. Regarding this surface parameter the homopolymers can be grouped in three groups. Polyamides and polyesters behave differently compared to the other polymers investigated here. Inside a group of polymers the ratio between surface tension and crystalline package density is widely invariant regarding crystal perfectness and chemical structure.
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•Non-isothermal crystallization of 12 polymers at cooling between 0.1 and 10000 K s−1.•Introducing of a new evaluation method based on the Gibbs free energy difference.•Polymers can be grouped in three groups regarding a surface tension parameter, κ.•κ is linked to the ratio of surface free energy and the packing density of crystals.•A fast method to determine the surface free energy of crystals is proposed.
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•The thermal lag causes the heating-rate-dependent onset of melting temperature.•At larger samples, the onset temperature increases linearly with the heating rate.•At smaller sample ...mass, the onset temperature behaves nonlinearly.•This behavior is explained by using a heat flow model and an equation is derived.•The heating rate dependence for small samples and fast heating is corrected.
The thermal lag of DSC is a heating rate independent constant and influences the measured onset temperature of melting peaks and must be taken into account during the temperature calibration. In the literature, however, non-linear behavior of the measured onset temperature is reported for the case of high scanning rates and the use of small samples. Based on a conventional heat transfer model of a DSC a general relation of the heating rate and sample mass dependence of the onset temperature is derived. The reason of this unusual behavior is that the time for the melting event is less than the equilibration time of the DSC. The approach presented can be used to correct the onset temperatures in the case of non-linear behavior, which may occur in conventional DSC and Fast DSC (using chip sensors).
•The KJMA equation is modified to minimize experimental uncertainties.•Crystallization kinetics of iPP at high supercooling measured by FDSC.•Mesophase formation is homogeneously nucleated and ...diffusion controlled.•α-phase growth is heterogeneously nucleated and could be diffusion controlled.•The α-phase crystallization in CaCO3 filled PP could be homogeneously nucleated.
A robust procedure for isothermal kinetic evaluation of Differential Scanning Calorimetry (DSC) measurements of polymers using the Kolmogorov-Johnson-Mehl-Avrami (KJMA) equation is proposed. This procedure takes into account the experimental uncertainties for short (initial deflection) and long (secondary crystallization) measurement times. This procedure is applied to the isothermal crystallization of various commercially available isotactic polypropylenes (iPP) in the temperature range between 10°C and 120°C. Further measurements are performed on unfilled iPP and iPP highly filled with calcium carbonate. The measurements were performed using Fast Differential Scanning Calorimetry (FDSC).
Evaluation of the crystallization kinetics indicates homogeneous nucleation in the temperature range of mesophase formation below 60°C. With decreasing temperature, the crystallization is more affected by diffusion control and/or termination of growth at an early crystallization stage
During α-phase formation (above 60°C), crystallization is heterogeneously nucleated. Depending on the sample, growth occurs at a constant rate or is diffusion controlled.
Polypropylene highly filled with calcium carbonate shows an additional α-phase crystallization process. The KJMA evaluation indicates that this process is homogeneously nucleated.
