| Graphene is a kind of sheet carbon nanomaterials, which has a series of merits including high specific surface area, high mechanical strength, extraordinary electrical conductivity, superior thermal conductivity properties etc. Due to the wide range of research and application in terms of electronics, energy, materials and biochemistry, graphene has been listed as one of the most promising materials in the 21st century by a number of research institutions at home and abroad. The poly(ethylene terephthalate) products have many advantages, such as high mechanical strength, good dimensional stability, remarkable processing properties and excellent chemical stability, Thus, they have wide application in the national production and living. Graphene/poly(ethylene terephthalate) new composites have been developed via the combination graphene with poly(ethylene terephthalate). However, there are limited reports on graphene/poly (ethylene terephthalate) composites in domestic and international research. This paper aims to develop the graphene/poly(ethylene terephthalate) resin materials and study their processability and crystalline properties, providing experimental evidence and technical support for the application of graphene/poly(ethylene terephthalate) resin.In this paper, the graphene/poly(ethylene terephthalate) resin was synthesized using graphene as the modifier via in-situ polymerization. The structure and morphology of the graphene and the as-prepared modified polyester were characterized by dynamic light scattering(DLS), Fourier transform infrared spectroscopy(FT-IR) and scanning electron microscope(SEM). The crystalline morphology and the isothermal crystallization growth regularity of the modified polyester were investigated by polarizing microscope with heating and freezing stage. The crystallization properties, crystalline structure and thermal properties were also studied by differential scanning calorimetry(DSC), X-ray diffraction(XRD) and thermogravimetric analyzer(TG). The shear rheological properties of the modified polyester were analyzed by twin-bore capillary rheometer. The main conclusions were as follows:1. Selecting ethylene glycol antimony as the catalyst, a series of graphene/ poly(ethylene terephthalate) resin were successfully synthesized via in-situ polymerization adding different contents of ultrasonic well-dispersed graphene. Based on the test result of SEM and DLS, the particle size of the graphene was reduced when adopting the ultrasonic dispersion. FT-IR test results showed that there were still a small amount of hydroxyl group, a carboxyl group and an epoxy group and other reactive groups on the surface of the used graphene. According to the results of Fourier transform infrared spectroscopy(FT-IR) and the intrinsic viscosity test, the addition of a small amount of graphene during the synthesis process did not affect the main chain structure of PET and make the intrinsic viscosity of the polyester decrease a little, but the value could reach 0.6 dL/g.2. XRD indicated that the addition of the graphene particles did not impact the crystal structure of the PET, but made the crystallite size and the interplanar distance decrease. With the increase of the content of graphene, the grain size distribution became narrow, the size tended to be consistent. Graphene exhibited the effect of efficient heterogeneous nucleation. Compared with pure PET, adding a small amount of graphene into PET matrix could increase the spherulites number, but decrease the spherulites size, which indicated the spherulites accumulated densely. The glass transition temperature(Tg), the melt point (Tm), the crystallization temperature(Tc) and the crystallinity(Xc) were improved after addition of graphene. Compared with pure PET, the modified polyester at a loading of 0.3%graphene revealed a 2.6 ℃ increase in Tg, and showed around 7 ℃ increases in Tm, respectively. When the content of graphene was 0.05%, the modified polyester gave a 19% increase in the Tc. When the content of graphene approached 0.1%, the crystallinity (Xc) of the material increased from 26.9% to 29.6%. The non-isothermal crystallization studies demonstrated that, with the increase of cooling rate, the crystallization behavior was lagging behind, the crystallization peak temperature(Tp) decreased, the crystallization peak becomed wider, and the semi-crystallization time(t1 2) decreased. TG curves showed that the start degradation temperature and the stop degradation temperature of the modified polyester were improved, which indicated that the addition of graphene could improve the thermal stability of PET.3. The results of shear rheology showed that, the addition of graphene had not changed the flow type of poly(ethylene terephthalate) resin melt, graphene/poly(ethylene terephthalate) resin melt was still a pseudoplastic fluid. The content of graphene had a great influence on the apparent viscosity and the non-Newton index of the melt. With the increase of graphene content, the flowing resistance increased, and the apparent viscosity of the polyester melt increased gradually. At a shear rate of 500 s-1, with graphene content increased from 0 to 0.3%, the apparent viscosity of the melt increased from 21.61 Pa s to 49.07 Pa · s, higher than pure PET by 27.46 Pa · s. At the same shear rate, with the increase of the graphene content, the non-Newton index decreased, and the addition of graphene enhanced the non-Newtonian behavior of the melt, which implied it reinforced the dependence of the melt viscosity on the shear rate. |
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