Influences of molecular weight on the non-isothermal crystallization and melting behavior of β-nucleated isotactic polypropylene with different melt structures

Structure and Properties of Epoxy Resin/Graphene Oxide Composites Prepared from Silicon Dioxide-Modified Graphene Oxide

In this study, graphene oxide (GO) was modified via electrostatic interactions and chemical grafting by silica (SiO2), and two SiO2@GO hybrids (GO-A and GO-B, respectively) with different structures were obtained and carefully characterized. Results confirmed the successful grafting of SiO2 onto the GO surface using both strategies. The distribution of SiO2 particles on the surface of GO-A was denser and more agglomerated, while it was more uniform on the surface of GO-B. Then, epoxy resin (EP)/GO composites were prepared. The curing mechanism of EP/GO composites was studied by differential scanning calorimetry and in situ infrared spectra spectroscopy. Results of tensile tests, hardness tests, dynamic mechanical analysis, and dielectric measurement revealed that EP/GO-B exhibited the highest tensile properties, with a tensile strength of 79 MPa, a 43% increase compared to raw EP. Furthermore, the addition of fillers improved the hardness of EP, and EP/GO-B showed the highest energy storage modulus of 1900 MPa. The inclusion of SiO2@GO hybrid fillers enhanced the dielectric constant, volume resistivity, and breakdown voltage of EP/GO composites. Among these, EP/GO-B displayed the lowest dielectric loss, relatively good insulation, and relatively high volume resistivity and breakdown voltage. A related mechanism was proposed.

Effects of graphene oxide size on curing kinetics of epoxy resin

To study the effects of graphene oxide (GO) size on the curing kinetics of epoxy resin (EP), two kinds of GO were selected and characterized by Fourier transform infrared spectrometry (FT-IR), FT-Raman spectrometry (FTIR-Raman), thermo gravimetric analysis (TGA), dynamic light scattering (DLS), transmission electron microscopy (TEM), X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that the two kinds of GO had similar chemical structures but different sizes-the average particle size of GO-A was 190.1 nm and that of GO-B was 1510 nm, and GO-A has more oxidizing groups on its surface. The two kinds of GO were separately added to EP, and the curing kinetics of GO/EP composites and neat EP were investigated through differential scanning calorimetry (DSC). It can be seen that the addition of GO promoted the curing process of the EP system, and GO-A had a more significant catalytic effect. Furthermore, the curing activation energy (E a) was calculated by Kissinger model, and the change of E a in the whole curing reaction process was studied by Ozawa method to further understand the curing mechanism. It showed that the apparent E a of EP system increases with the increase of the conversion rate, and E a of EP-A is obviously lower in the early curing stage. However, as the curing reaction proceeds, E a of EP-B is a little lower than that of EP-A in the later curing stage. But EP-A has the lowest E a combined with the whole process from Kissinger method. To sum up, it can be concluded that the curing process of EP can be promoted by adding GO and the smaller size (190.1 nm) of GO had a greater effect and lower E a than the GO with particle size of 1510 nm. And the related mechanisms were discussed and analyzed.

Exploring Impacts of Hyper-Branched Polyester Surface Modification of Graphene Oxide on the Mechanical Performances of Acrylonitrile-Butadiene-Styrene

In this manuscript, the graphene oxide (GO) was modified by hyper-branched polyester (HBP). The effects of GO or modified GO (HBP-m-GO) on the mechanical performance and wearing properties were investigated. The results of X-ray photoelectron spectra (XPS), Fourier transform infrared spectroscopy (FT-IR), and transmission electron microscopy (TEM) revealed the successful grafting of HBP onto GO. The thermogravimetric analysis (TGA) indicated that the graft amount of HBP is calculated to be 9.6 wt%. The GO or HBP-m-GO was added into acrylonitrile-butadiene-styrene copolymer (ABS) to prepare the ABS/GO composites. The mechanical properties and wear performance of the composites were studied to comparatively study the impact of GO modification on the properties of the composites. The results revealed that the addition of GO has a significant effect on the mechanical properties of ABS, and when HBP-m-GO was added, the elastic modulus and tensile strength of ABS/HBP-m-GO increased evidently compared with ABS/GO. The tensile strength increased from 42.1 ± 0.6 MPa of pure ABS to 55.9 ± 0.9 MPa, up to 30%. Meanwhile, the elongation at break was significantly higher than ABS/GO to 20.1 ± 1.3%, slightly lower than that of pure ABS. For wear performance, the addition of raw GO decreased the friction coefficient, and when the HBP-m-GO was added, the friction coefficient of the ABS/HBP-m-GO dropped more evidently. Meanwhile, the weight loss during the wear test decreased evidently. The related mechanism was discussed.

Impacts of Modified Graphite Oxide on Crystallization, Thermal and Mechanical Properties of Polybutylene Terephthalate

In this study, the surface modification on graphene oxide (GO) was performed using octadecylamine (ODA). Furthermore, polybutylene terephthalate/GO (PBT/GO) composites were prepared to elucidate the role of GO surface modification on the mechanical performance, thermal stability and crystallization behavior. Results of Fourier transform infrared spectra (FT-IR), Raman spectrum, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and transmission electron microscope (TEM) revealed that ODA was successfully grafted on GO. Differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), tensile test, Izod impact strength test and TGA were carried out on the PBT/GO composites. Results indicated that the addition of raw GO can enhance the crystallization temperature and degree of crystallinity and can slightly improve the thermal stability and tensile strength of the composites. However, the impact strength and elongation at break were seriously decreased owing to the poor compatibility between the GO and PBT matrix. Once the modified GO was added, the crystallization temperature and degree of crystallinity were greatly increased. The tensile strength increased greatly while the elongation at break and Izod impact strength were efficiently maintained; these were evidently higher than those of PBT/raw GO. Moreover, thermal stability was greatly enhanced. SEM (scanning electron microscope) observation results on the impact-fractured surface clearly confirmed the improved compatibility between the modified GO and PBT matrix. A related mechanism had been discussed.