Search

Polarized optical micrographs of PEN/H-ZnOc blends: (a) 0 wt%, (b) 0.4 wt%, (c) 0.6 wt%, (d) 1.0 wt%, (e) 1.5 wt% isothermally crystallized at 200 °C for 40 min.

In order to overcome the low crystallization rate of poly(ethylene terephthalate) (PET), bicyclo[2.2.1]heptane-2,3-dicarboxylic acid disodium salt (HPN-68L), a highly active organic nucleating agent for polypropylene, was selected to replace the special nucleating agent of PET to improve PET crystallization due to its carboxylate anion structure, which usually shows a high induced nucleation ability for PET. The crystallization and properties of the composites were systematically investigated. It was found that HPN-68L had a significant nucleation effect on PET. The crystallization temperature and the nucleation efficiency of PET was increased by approximately 14 °C and 68.4%, respectively at a very low content of 0.6 wt% HPN-68L. Moreover, the half-time of crystallization and isothermal crystallization activation energy decreased upon the addition of HPN-68L. The long period of PET decreased and the number of spherulites increased after adding HPN-68L, while the crystal form of PET did not change. In addition, the nucleation mechanism of HPN-68L induced PET crystallization was studied and a chemical degradation nucleation mechanism was proposed. The flexural strength and modulus of PET were improved, whereas the impact strength decreased to a certain extent upon the addition of HPN-68L.

Intermolecular hydrogen-bonding could be formed between poly(butylene terephthalate) (PBT) and 4,4′-thiodiphenol (TDP) which was verified using advanced quantum-chemistry calculations. Blends of PBT and TDP were prepared through melt blending and the intermolecular hydrogen-bonding was characterized using Fourier transform infrared spectroscopy (FTIR). The results showed that intermolecular hydrogen-bonding formed between the carbonyl group of PBT and hydroxyl group of TDP, the carbonyl and hydroxyl absorption bands shifted to a lower wavenumber and the shape of the hydroxyl peaks became wider asymmetrically with increasing TDP content. The effects of hydrogen bonding on the crystallization and melting behaviors of PBT were investigated using differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide angle X-ray diffraction (WAXD). The results showed that both the non-isothermal melt-crystallization behavior and isothermal crystallization kinetics of PBT were inhibited by the addition of TDP. The overall isothermal crystallization rates of PBT in the PBT/TDP blends were obviously slower than that of pure PBT at the same crystallization temperature. The crystal structure of PBT did not change through the incorporation of TDP, while the crystallinity and the crystal size of PBT decreased with increasing TDP content.

Poly(ethylene terephthalate) (PET) and aryl amide derivative (TMB-5) blends were prepared by melt blending. It was found that TMB-5 shows a significant nucleation effect on PET and especially the non-isothermal nucleation efficiency reached up to 80.7% at a very low content of 0.6 wt% TMB-5. The effects of TMB-5 on the crystallization behavior and mechanical properties of PET were systematically investigated. DSC results show that crystallization temperature of PET apparently increased by nearly 20 °C with the addition of 0.6 wt% TMB-5 during the cooling process. A remarkable acceleration in the crystallization rate of PET was achieved as analyzed using the Avrami equation. Wide angle X-ray diffraction (WAXD) and polarized optical microscopy (POM) results show that the addition of TMB-5 remarkably increases the crystallinity and nuclei density of PET. Small angle X-ray scattering (SAXS) measurements reveal that the long period of PET decreased and lamellar thickness increased with an increase in TMB-5 content. The impact strength of PET was greatly enhanced by the addition of TMB-5, and a toughening mechanism was proposed.

In this study, we synthesized a new multifunctional benzoxazine monomer Azo-COOH-Py BZ—featuring an azobenzene unit, a carboxylic acid group, and a pyrene moiety—through the reaction of 4-(4-hydroxyphenylazo)benzoic acid (Azo-COOH), paraformaldehyde, and aminopyrene (Py-NH2) in 1,4-dioxane. Fourier transform infrared (FTIR) spectroscopy and 1H and 13C nuclear magnetic resonance spectroscopy confirmed the structure of this new monomer. Using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and FTIR spectroscopy, we monitored the curing behavior of Azo-COOH-Py BZ leading to the formation of poly(Azo-COOH-Py BZ); we found that the carboxylic acid and azobenzene units acted as catalysts for the ring opening reaction of the benzoxazine unit. The pyrene moiety of Azo-COOH-Py BZ enhanced the dispersibility of carbon nanotubes (CNTs) in THF, leading to the formation of highly dispersible Azo-COOH-Py BZ/CNT nanocomposites stabilized through π–π stacking of the pyrene and CNT units, as detected through fluorescence emission spectroscopy. We also used DSC and TGA to examine the curing behavior of Azo-COOH-Py BZ/CNTs to form poly(Azopy-COOH-Py BZ)/CNTs nanocomposites. Interestingly, DSC profiles revealed that the maximum exothermic peak representing the ring opening polymerization of the benzoxazine unit of Azo-COOH-Py BZ shifted to much lower temperature upon increasing the content of single-walled CNTs (SWCNTs) or multiwalled CNTs (MWCNTs), suggesting that the CNTs acted as catalysts for the ring opening reaction of the benzoxazine. In addition, the curing temperatures for the SWCNT composites were lower than those for the MWCNT composites, suggesting that the SWCNTs were dispersed better than the MWCNTs in their composites and that the thermal stability of the SWCNT nanocomposites was higher than that of the MWCNT nanocomposites. The combination of photoresponsive azobenzene units, carboxylic acid groups, and CNTs enhanced the thermal stability and char yields of the polybenzoxazine matrixes, as determined through TGA analyses.