Zhenhu Cao

Polypropylene nanocomposites based on C60-decorated carbon nanotubes: thermal properties, flammability, and mechanical properties

In the present study, the effects of covalently functionalized carbon nanotubes (CNTs) decorated with C60 (abbr. C60-d-CNT) on thermal, flame retardancy and mechanical properties of polypropylene (PP) are investigated. Compared with pristine CNTs, the C60-d-CNT is more easily dispersed in the PP matrix through reactive compatibilization. With the incorporation of C60-d-CNT, thermal oxidation degradation of PP is considerably delayed. Compared to PP, at 1.0 wt% loading of C60-d-CNT, the initial degradation temperature (T5) and maximum weight loss temperature (Tmax) in air are enhanced by 68 °C and 87 °C, respectively. Furthermore, incorporating 1.0 wt% C60-d-CNT can remarkably reduce the peak heat release rate (PHRR) by 71% relative to that of PP, and slow down the combustion process to some extent. The free-radical trapping effect of C60 and the CNTs network are responsible for the improved thermal and flame retardancy properties. Meanwhile, addition of C60-d-CNT also causes enhanced mechanical properties of PP nanocomposites to a certain degree.

Thermal stability and rheological behaviors of high-density polyethylene/fullerene nanocomposites

High-density polyethylene/fullerene (HDPE/C60) nanocomposites with the C60 loading that varied from 0.5 to 5.0% by weight were prepared via melt compounding. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) results showed that the presence of C60 could remarkably enhance the thermal properties of HDPE. A very low C60 loading (0.5wt%) increased the onset degradation temperature from 389°C to 459°C and decreased the heat release from 3176 J/g to 1490 J/g. The larger the loading level of C60, the better the thermal stability of HDPE/C60 nanocomposites. Rheological investigation results showed that the free radical trapping effect of C60 was responsible for the improved thermal stability of HDPE.

Effect of Lignin Incorporation and Reactive Compatibilization on the Morphological, Rheological, and Mechanical Properties of ABS Resin

In order to develop the potential application of industrial alkali lignin, its acrylonitrile-butadiene-styrene (ABS) composites were fabricated via melt blending in the absence/presence of a compatibilizer. The lignin can uniformly disperse in the ABS matrix with number-average dispersed-phase domains of sub-micron scale, ranging from 150–250 nm, as observed by scanning electron microscopy. Infrared spectroscopy reveals that strong intermolecular interactions, mainly hydrogen bonding, were responsible for their good interfacial compatibility. Rheological behaviors show that the presence of lignin restricts to some extent the relaxation of polymer chains without affecting the processing properties of ABS resin. The presence of lignin increases storage modulus and glass transition temperature (T g) of ABS. Incorporating small amounts of lignin, e.g. 5 wt%, can produce ABS composites with enhanced tensile strength and modulus, while higher loading of lignin will reduce mechanical properties. The latter, however, can be improved by reactive compatibilization.

The effect of fullerene on the resistance to thermal degradation of polymers with different degradation processes

Investigations were made about the effect of fullerene (C60) on the resistance to thermal degradation of high density polyethylene (HDPE), polypropylene (PP), polymethyl methacrylate (PMMA), and bisphenol A polycarbonate (PC) matrix by using thermogravimetric analysis coupled to Fourier transform infrared spectroscopy. The results showed that the influences of C60 on the resistance to the thermal degradation of different polymers were dependent on their thermal degradation mechanism. The resistance to the thermal degradation of HDPE, PP, and PMMA were improved with the addition of C60, especially for HDPE matrix, which indicated that the radical trapping played a dominant role. PP and PMMA released more gaseous products at high temperature by the random scission of C–C backbone; owing to the lower bond dissociation energy of C–C in the backbone for the existence of side chains. Meanwhile, the steric hindrance of side chains also made the radicals hard to recombine with each other and accelerated the random scission, leading to the less effect on the resistance to the thermal degradation of PP and PMMA. However, few changes of resistance to the thermal degradation were found in PC matrix with the addition of C60 for its non-radical degradation mechanism.

Influence of fullerene on the kinetics of thermal and thermo-oxidative degradation of high-density polyethylene by capturing free radicals

The influence of fullerene (C60) on the thermal and thermal-oxidative degradation of high-density polyethylene (HDPE) was studied using non-isothermal thermogravimetric analysis under nitrogen (N2) and air atmosphere. Kinetic parameters of the degradation were evaluated using the Flynn–Wall–Ozawa method, which does not require the knowledge of the reaction mechanism. The results showed that the addition of C60 enhanced the thermal stability of HDPE and increased the activation energy both in N2 and air atmosphere and especially affected the initial stage of degradation. In N2, C60-trapped carbon-centered radical originated from the degradation of HDPE to improve the thermal stability and increase the activation energy. While in air, C60 trapped the alkyl radicals and alkyl peroxide radicals to inhibit the hydrogen abstraction (especially the initial stage of thermo-oxidative degradation) and form more stable species, which improved the thermal stability and increased the activation energy during the thermal degradation of HDPE. Comparing with that of pure HDPE, the changes of activation energy for HDPE/C60 nanocomposites were higher in air than in N2, especially in the initial stage.