Cold crystallization enthalpy

In calorimetry, the cold crystallization enthalpy on heating or at isothermal conditions was found to be dependent on the number of previously formed nuclei.This was used to study isothermal nucieation and crystallization in PCL, covering times from 10" to 10 s and temperatures from about 25 K below the glass transition up to 330 K, which is close to the equilibrium melting. With the fast scanning calorimeter, it was possible to follow the development of crystals at one temperature over 9 orders of magnitude in time. ... 

Figure 34 shows the dependency of the overall latent heat and the cold crystallization enthalpies versus previous cooling rates for pure PCL and a heterogeneously nucleated PCL. 

For the pure PCL, the overall latent heat becomes zero within the error of measurement at previous cooling rates higher than 500 Ks . This means that no crystallization occurs on cooling under this condition. At cooling rates higher than 300Ks a reduaion of cold crystallization enthalpy is... 

Figure 34 Overall latent heat on heating, AWheaiing, and cold crystallization enthalpy, AWcc. as functions of the previous cooling rate measured for pure PCL and PCL mixed with 0.2 wt.% CNT (carbon nanotubes) functioning as added heterogeneous nuclei. The error bars include the influence of baseline construction on the results of integration. Reproduced with permission from Zhuravlev, E. Schmelzer, J. W. P. Wunderlich, B. Schick, C. Po/ymer2011, 52,1983-1997. ...

To study the kinetics of nudeation under isothermal conditions, experiments were performed for which the sample was cooled so fast (10 000 Ks" ) that no homogeneous nudeation occurs. If a sample were amorphous after annealing, it would show zero overall latent heat, but the cold crystallization enthalpy as well as its melting enthalpy would depend on the number of active nuclei in the sample. 

Elastomeric systems are quite commonly monitored by thermal techniques. Mohler [5] has discussed how DSC is used to characterize the quality of blends of elastomers. Changes in polymer Tg can point to miscible phases that might otherwise require a microscopic techmque to establish. The cold crystallization of a polymer in a blend can also be examined using the relaxation enthalpy of the sample. Vacuum TG can look at plasticizer content separate from polymer degradation. Dynamic mechanical analysis (DMA) is always a powerful technique with elastomers. Dimensional stability, storage modulus, loss modulus and loss factor are all important for this class of materials and are... 

Epoxidizedsoybean oil (ESO) is produced via conversion of the double bonds of soybean oil with peracids or peroxides, resulting in more reactive oxirane or epoxide moieties, promoting chemical reactions [230-232]. ESO is normally used to plasticize and/or stabilize poly(vinyl chloride) (PVC), chlorinated rubber, and PVOH emulsions [231, 232]. The effects of ESO as a PLA plasticizer were reported elsewhere [230, 233, 234]. In summary, ESO lowered Tg, cold crystallization temperature Tm. enthalpy of cold crystallization (AHcc), tensile strength, and tensile... 

AHm andAHc denotes the enthalpy of melting and cold crystallization, respectively, and 135 J/g is the enthalpy of fusion of PLLA [21]. 

Even if the enthalpy of 210 J/g is not the corresponding value for the crystallization enthalpy of MEl and ME2 it has been chosen in order to compare the variation of the crystallized fraction for all studied blends. The ME2 and DF have similar low percentages of crystals at —15 °C. However, ME 1 shows a high percentage of crystals at -15 " C. The cold flow parameters of pure compounds are listed in Table 13.3. The CFPP and PP were determined by DSC at 0.45 and 1 % of crystals, respectively, using the same AHcryst as mentioned above. Claudy et al. [9] realized a study on 40 different diesel fuels and established correlations between CFPP and PP determined by ASTM standards and CFPP and PP obtained by DSC measurements. The best correlations were obtained at 0.45 and 1 % of crystals, respectively. In our study, the same values have been retained in order to compare the samples. 

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