Jin Zheng

Preparation and Properties of Poly(ethylene terephthalate)/Silica Nanocomposites

A kind of poly(ethylene terephthalate) (PET)/Silica nanocomposite (PETS) was synthesized via in situ polymerization using the compatibility between silica nanoparticles and ethylene glycol (EG). Transmission electron microscopy (TEM) micrographs revealed that the silica nanoparticles were well dispersed in the PET matrix, the particle size was about 10 nm with narrow distribution, and there existed strong interaction between the particles and the polymer chains. Differential scanning calorimetry (DSC) results indicated that the thermal properties of PETS with 2 wt% silica (PETS‐2) are different from those of pure PET (PETS‐0). The properties of the as‐spun fibers show that the tenacity and LASE‐5 (load at a specified elongation of 5%) of PETS‐2 were higher than those of PETS‐0, while the heat shrinkage of PETS‐2 was lower than that of PETS‐0. We suggest that the increasing of crystallinity and the strong interface interaction of the nanocomposite caused the fibers of PETS‐2 to not only have higher tenacity and LASE‐5 but also to have lower heat shrinkage.

Relationship between Microstructure and Tensile Properties of PET/Silica Nanocomposite Fibers

The influence of silica nanoparticles on the tensile properties of poly(ethylene terephthalate)(PET) fibers was investigated. The results showed that mechanical properties of PET fibers were improved through nano‐silica incorporation. Two maxima of the modulus‐strain curves of PET/silica nanocomposites (PETS) fibers are always higher than those of pure PET (PET0) fibers. The results of microstructure investigations suggested that the amorphous orientation factor of PETS fibers is higher than that of PET0 fibers. It is suggested that the increase of amorphous orientation factor contributed to the improvement of tensile properties of PET fibers. Considering the difference in modulus‐strain curves of PET0 and PETS fibers, it is believed that the addition of nanoparticles not only improved the amorphous orientation factor but also changed the load units of PET fibers when strained, which also resulted in the improvement of tensile properties.

Isothermal Crystallization and Subsequent Melting Behavior of Poly(ethylene terephthalate)/Silica Nanocomposites

The crystallization process of poly(ethylene terephthalate)/silica nanocomposites were investigated by differential scanning calorimetry (DSC) and then analyzed using the Avrami method. The results indicated that the crystallization of pure poly(ethylene terephthalate) (PET) was fitted for thermal nucleation and three‐dimensional spherical growth throughout the whole process, whereas the crystallization of PET/silica nanocomposites exhibits two stages. The first stage corresponds to athermal nucleation and three‐dimensional spherical growth, and the second stage corresponds to recrystallization caused by the earlier spherulites impingement. The crystallization rate increases remarkably and the activation energies decrease considerably when silica nanoparticles are added. The subsequent melting behavior of the crystallized samples shows that the melting point (T m) of nanocomposites is higher than that of pure PET, which might be caused by two factors: (1) The higher melting point might be due to some hindrance to the PET chains caused by the nanoparticles at the beginning of the melting process; (2) it might also be the case that more perfect crystals can be formed due to the higher crystallization temperatures and lower activation energies of PET/silica nanocomposites.

Non-Isothermal Crystallization Kinetics of Poly(Butylene Terephthalate)/Silica Nanocomposites

Poly(butylene terephthalate)/silica nanocomposites were prepared by in situ polymerization of terephthalic acid, 1,4-butanediol and silica. Transmission electron microscopy (TEM) was used to examine the quality of the dispersion of silica in the PBT matrix. The non-isothermal crystallization behavior of pure PBT and its nanocomposites was studied by differential scanning calorimetry (DSC). The results show that the crystallization peak temperatures of PBT/silica nanocomposites are higher than that of pure PBT at a given cooling rate. The values of halftime of crystallization indicate that silica could act as a heterogeneous nucleating agent in PBT crystallization and lead to an acceleration of crystallization. The non-isothermal crystallization data were analyzed with the Avrami, Ozawa, and Mo et al. models. The non-isothermal crystallization process of pure PBT and PBT/silica nanocomposites can be best described by the model developed by Mo et al. According to the Kissinger equation, the activation energies were found to be −217.1, −226.4, −259.2, and −260.2 kJ/mol for pure PBT and PBT/silica nanocomposites with silica weight content of 1, 3 and 5 wt%, respectively.

ISOTHERMAL CRYSTALLIZATION AND SUBSEQUENT MELTING BEHAVIOR OF POLY(ETHYLENE TEREPHTHALATE)/SILICA NANOCOMPOSITES

The crystallization process of nanocomposites was investigated by differential scanning calorimetry (DSC) and analyzed by the Avrami method. It was found that the crystallization of pure poly(ethylene terephthalate) (PET) is fitted for thermal nucleation and three-dimensional spherical growth in the whole process, while the crystallization of PET/silica nanocomposites exhibits two stages: the first stage corresponds to athermal nucleation and three-dimensional spherical growth, and the second one corresponds to recrystallization caused by the earlier spherulite impingement. The crystallization rate increases markedly and the activation energies decrease greatly with adding silica nanoparticles. The subsequent melting behavior of the crystallized samples shows that the melting point (Tm) of nanocomposites is higher than that of pure PET, which might result from two reasons: (1) some hindrance to the PET chains caused by the nanoparticles at the beginning of the melting process; and (2) more perfect crystals being formed due to the higher crystallization temperature and lower activation energy of PET/silica nanocomposites.

Synthesis and Nonisothermal Crystallization Behavior of Poly(ethylene terephthalate)/Attapulgite Nanocomposites

Poly(ethylene terephthalate)/attapulgite nanocomposites were prepared by in situ polymerization. The nanoscaled AT rods were well dispersed in the PET matrix. The crystallization and melting behavior of PET in the composites were investigated by differential scanning calorimetry. The results show that the degree of crystallinity and the peak temperature of crystallization of PET/AT nanocomposites are higher than that of pure PET. The AT nanorods have a remarkable heterogeneous nucleation effect in PET. Several different analysis methods were used to describe the process of nonisothermal crystallization. The combination of the Avrami and Ozawa equations could describe the nonisothermal crystallization of the composites very well. By using a method proposed by Kissinger, activation energies have been evaluated to be 169, 197, 223, and 222 kJ/mol for nonisothermal crystallization of pure PET and PET/AT nanocomposites with AT loadings of 0.5, 1, and 2 wt.%, respectively.

The Suppression of Isothermal Cold Crystallization in PET Through Nano‐Silica Incorporation

Isothermal crystallization from the glassy state of pure poly(ethylene terephthalate)(PET) and PET/Silica nanocomposites films was studied. The results showed that addition of nano‐silica increased the crystallinity of filled PET compared to pure PET, suggesting that nano‐silica is an effective nucleating agent. However, the induction period prior to crystallization was prolonged and the overall crystallization rate decreased through nano‐silica incorporation. This is a result of the cold crystallization rate being primarily controlled by diffusion of PET chains, rather than being controlled by the nucleation rate. The strong interaction between the nanoparticles and PET chains confined the movement of the macromolecular chains and decreased the cold crystallization rate.