Annealing Test of PET/Clay Nanocomposites

The DSC scans of the annealed samples at 125°C, 165°C, and 205°C from the temperature rise process at 40°C show that the scan curves are similar in shape, but the temperature range and peak size of the melting peak appear with the annealing temperature. Certain changes. Specifically quantified by the peak temperatures and melting enthalpies shown in Tables 1 and 2 below.

From the data in Table 1 and Table 2, it can be seen that at the same temperature, the low-temperature melting peak temperatures of the annealed samples during the temperature increase process are not significantly different, and they are all slightly higher than the annealing temperature. Crystals with different degrees of perfectness have different melting points. It is believed that the annealed polymer contains a combination of crystals with different levels of pre-quench formation. When the sample is annealed at a certain temperature, the stabilized crystal has the same melting point as the annealing temperature. During the heating scan, the crystals are partially melted and recrystallized into more complete crystals, so that the melting peak appears at a temperature higher than the annealing temperature.

As the annealing temperature increases, the peak temperature of the low temperature peak (annealing peak) also increases, narrowing the peak shape and increasing the peak area. Because in this annealing temperature range, mainly due to the crystallization of some irregular molecular chains, its crystal perfection is very poor, so its low temperature melting peak temperature is low. As the annealing temperature increases, the molecular chains move more easily, and the number of participating crystals increases, showing an increase in the peak area. The degree of perfection of the imperfect crystals formed at the annealing temperature tends to be complete as the annealing temperature increases, and the peak temperature of the low-temperature endotherm correspondingly increases, and the peak shape correspondingly narrows. This can be attributed to an increase in the thickness of the flakes inside the spherical grains and a higher tendency to crystallize; however, it is also possible to relate to the shape of the crystals produced under different conditions of PET, and the annealing temperature is annealed at 125°C, 165°C, and 205°C. The treated samples had high temperature melting peak temperatures in the order: PET>tackified PET/clay nanocomposites>PET/clay nanocomposites. The crystal melting temperature is mainly related to the degree of grain refinement. In the PET/clay nanocomposites, the interaction between the PET molecules and the clay particles is enhanced due to the organicization of the clay, thereby limiting the PET molecular segments during the crystal growth process. The movement of the crystal hinders the growth of the crystal and impairs the integrity of the crystal grains, so that the melting temperature decreases. The tackified PET/clay nanocomposites, on the one hand, have a lower melting temperature than PET due to the damage to the grain integrity caused by the clay flakes dispersed in the polymer matrix; on the other hand, due to the tackifying effect ,The activity of the segment decreases during the heating process, and the melting temperature increases, so the total effect makes the melting temperature be between the first two kinds of samples. The melting temperature is lower than that of PET, and it is lower than that of PET/clay nanocomposite. The material is high.

3 Conclusion

1) Due to the slower and slower crystallization rate of PET, the quenched specimens have an amorphous internal structure. In the PET/clay nanocomposites, the dispersion of the nanoclay layer in PET increases the crystallinity and crystallization. As the rate increases, the cold crystallization temperature decreases during heating.

2) In PET/clay nanocomposites, due to the increase of the crystallization rate due to the distribution of the clay nanosheets in the matrix, the cold crystallization temperature decreases, the crystal perfection decreases, and the melting point decreases during heating and melting.

3) During the temperature rise of the annealed samples, there are two melting peaks, in which the melting peak temperature at low temperature is strongly dependent on and slightly higher than the annealing temperature, and the change trend of the peak melting temperature at the high temperature is consistent with the melting tendency of the quenched sample, which is known from the experimental results. : The order of melting peak temperatures of the three materials is: PET/clay nanocomposites <Tackified PET/clay nanocomposites
(Author/Bai Xiaoli, Xu Xuemeng Henan University of Technology)

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