Mao Peng

Carbon Nanotubes Noncovalently Functionalized by an Organic−Inorganic Hybrid: New Building Blocks for Constructing Superhydrophobic Conductive Coatings

A facile method for constructing superhydrophobic, conductive, and transparent/translucent coatings is presented. Pristine multiwalled carbon nanotubes (MWNTs) are first noncovalently (wrapped) modified by an organic-inorganic hybrid of an amphiphilic copolymer of styrene and maleic anhydride and silica with the existence of gamma-aminopropyltriethoxysilane (a silane coupling agent). The modified MWNTs were mixed with tetraethyl orthosilicate in ethanol, air sprayed, coated with a fluoroalkylsilane, and then heat treated to obtain the superhydrophobic, conductive, and transparent/translucent coatings. Scanning electron microscopy shows that the coatings have a micrometer- and nanometer-scale hierarchical structure similar to that of lotus leaves; therefore, they show both high water contact angles (>160 degrees) and low sliding angles (<2 degrees). The coatings also exhibit good transmittance and greatly improved conductivities. This method is convenient, inexpensive, and easy to scale up. Moreover, it does not require any chemical modification of the MWNTs or use any harsh chemicals.

Green Preparation of Epoxy/Graphene Oxide Nanocomposites Using a Glycidylamine Epoxy Resin as the Surface Modifier and Phase Transfer Agent of Graphene Oxide

In studies of epoxy/graphene oxide (GO) nanocomposites, organic solvents are commonly used to disperse GO, and vigorous mechanical processes and complicated modification of GO are usually required, increasing the cost and hindering the development and application of epoxy nanocomposites. Here, we report a green, facile, and efficient method of preparing epoxy/GO nanocomposites. When triglycidyl para-aminophenol (TGPAP), a commercially available glycidyl amine epoxy resin with one tertiary amine group per molecule, is used as both the surface modifier and phase transfer agent of GO, GO can be directly and rapidly transferred from water to diglycidyl ether of bisphenol A and other types of epoxy resins by manual stirring under ambient conditions, whereas GO cannot be transferred to these epoxy resins in the absence of TGPAP. The interaction between TGPAP and GO and the effect of the TGPAP content on the dispersion of GO in the epoxy matrix were investigated systematically. Superior dispersion and exfoliation of GO nanosheets and remarkably improved mechanical properties, including tensile and flexural properties, toughness, storage modulus, and microhardness, of the epoxy/GO nanocomposites with a suitable amount of TGPAP were demonstrated. This method is organic-solvent-free and technically feasible for large-scale preparation of high-performance nanocomposites; it opens up new opportunities for exploiting the unique properties of graphene or even other nanofillers for a wide range of applications.

Synthesis of aromatic diamine-based benzoxazines and effect of their backbone structure on thermal and flammability properties of polymers

Three kinds of novel aromatic diamine-based benzoxazines containing naphthalene, propane-2,2-diyldibenzene and neopentyl groups in the backbone, respectively (designated as BAPNCP, BAPBACP and BAPNPGCP, respectively), were synthesized and characterized. In addition, the effects of backbone structures on curing behaviors of the monomers and thermal and flammability properties of the resulting polymers were systematically studied. The results indicated that BAPNPGCP displayed the highest enthalpy of the curing reaction associated with the ring-opening of benzoxazine, which was due to the effect of benzoxazine ring content per unit mass. Interestingly, the 5 wt% weight loss temperature and char residue after thermogravimetric test for poly(BAPNPGCP) were 8 °C and 7% higher than those of poly(BAPBACP). Meanwhile, the total heat release of poly(BAPNPGCP) was less than half of that for poly(BAPBACP), indicating the substantial effect of benzoxazine ring content on flammability and char formation. Furthermore, it was found that poly(BAPNCP) gave the best thermal stability and flame retardancy, which was due to the synergistic effect between naphthalene group and benzoxazine ring content. This study provides new insight into the curing behavior of benzoxazine and further understanding on the high performance of polybenzoxazine.

Crystallization of high density polyethylene: effect of contact with NdFeB magnetic powder substrates

Abstract Remarkable heterogeneous nucleation effect of rare earth neodymium–iron–boron (NdFeB) magnetic powder on high density polyethylene (HDPE) matrix was found. HDPE transcrystallinity was observed through polarization microscope, and the crystallization of HDPE loaded by NdFeB powder with various weight fraction were characterized using difference scanning calorimetry (DSC) and wide angle X-ray diffractometer (WAXD).

Effect of oscillatory shear on the mechanical properties and crystalline morphology of linear low density polyethylene

In this study, effects of oscillatory shear with different frequencies (0–2.5 Hz) and amplitudes (0–20 mm) on the mechanical properties and crystalline morphology of linear low density polyethylene (LLDPE) were investigated. It was found that the mechanical properties of LLDPE are improved because of the more perfect crystalline structure when LLDPE crystallizes under low-frequency and small-amplitude (0.2 Hz/4 mm) oscillatory shear. The mechanical properties can be further improved by increasing either the frequency or the amplitude of oscillatory shear. The Young’s modulus and tensile strength of LLDPE are improved by 27% and 20%, respectively, when the frequency is increased to 2.5 Hz and the amplitude is maintained at 4 mm; while the Young’s modulus and tensile strength are improved by 49% and 47%, respectively, when the amplitude is increased to 20 mm and the frequency is remained as 0.2 Hz. The crystallinity and microstructure of LLDPE under different oscillatory shear conditions were investigated by using differential scanning calorimetry, wide angle X-ray diffraction and scanning electron microscopy to shed light on the mechanism for the improvement of mechanical properties.

Combination of a bio-based polyphosphonate and modified graphene oxide toward superior flame retardant polylactic acid

Superior flame retardant polylactic acid (PLA) composites were prepared using bio-based polyphosphonate (BPPT) and polyethyleneimine-modified graphene oxide (M-GO) to be used as a flame retardant, the total amount of which is only 3 wt%. With 2.4 wt% BPPT and 0.6 wt% M-GO in the polymer matrix, the as-prepared PLA composites can achieve the UL94 V0 grade and a LOI value of 36.0. Analysis of the residual char and pyrolytic products revealed that the conjunction of a gas-phase and condensed-phase mechanism contributes to the good flame retardant performance. Moreover, the tensile toughness of PLA was also enhanced. The PLA composite with 2.1 wt% BPPT and 0.9 wt% M-GO displayed an elongation at break of 13.1% and maintained a tensile strength of 39.1 MPa. The debonding between the M-GO and PLA matrix and the plastic deformation around the M-GO particles were responsible for the improved tensile toughness.