Gang Sui

A plant fiber reinforced polymer composite prepared by a twin-screw extruder.

Polypropylene (PP) composites reinforced using a novel plant fiber, sunflower hull sanding dust (SHSD), were prepared using a twin-screw extruder. Thermal and mechanical properties of the SHSD/PP composites were characterized and compared to an organically modified clay (organo-clay)/PP composite. Differential scanning calorimetry (DSC) analysis showed that the crystallization temperature and the degree of crystallinity of PP exhibited changes with addition of SHSD and organo-clay. Mechanical properties of the PP were enhanced with the addition of SHSDs. Both the flexural strength and flexural modulus of the PP composites containing 5% (w/w) SHSD were comparable to that of the 5% (w/w) organo-clay reinforced PP. Scanning electron microscope (SEM) observation showed that no obvious agglomeration of SHSD existed in the PP matrix. Compared to the neat PP and organo-clay/PP, the SHSD/PP composites exhibited a relatively decreasing rate of thermal degradation with increase in temperature. Experimental results suggest that SHSD, as a sunflower processing byproduct, may find promising applications in composite materials.

Novel MnO/carbon composite anode material with multi-modal pore structure for high performance lithium-ion batteries

A new type of MnO/carbon composite particle with multi-modal pore structure was designed and prepared as anode materials of lithium-ion batteries through a promoted template method. The porous MnO/carbon composite anode materials exhibited the superior electrochemical performance, including excellent stability under different current density, high reversible capacity (as high as 1210.9 mA h g−1 after 700 cycles at 1.0 A g−1), good rate capability and high initial coulomb efficiency of over 80%, which had benefited from the reasonable material composition, special multi-modal pore structure, desirable micro-morphology and good structural integrity. The complex multiphase structure consisting of MnO crystal grains, abundant nanopores and uniform carbon layers can effectively improve cyclic stability and rate capability of the anode materials, and thus will have an important application value in high-performance energy supply devices.

Degradable cellulose acetate/poly-L-lactic acid/halloysite nanotube composite nanofiber membranes with outstanding performance for gel polymer electrolytes

The biodegraded cellulose acetate (CA)/poly-L-lactic acid (PLLA)/Halloysite nanotube composite nanofiber membranes were fabricated for the preparation of gel polymer electrolytes (GPEs) used in lithium-ion batteries. The microstructure, crystallization behaviour and thermal stability of nanofiber membranes were analysed. The testing results showed that the crystallization behaviour of the polymeric materials was significantly inhibited, and that the thermal stability of the polymer nanofiber membranes was improved due to the addition of the halloysite nanotubes (HNTs). The composite GPEs based on the CA/PLLA/HNT nanofiber membranes presented a satisfactory electrochemical performance, including high ionic conductivities, proper lithium-ion transference numbers, and good electrochemical stability. An ionic conductivity of 1.52 × 10−3 S cm−1 was obtained from the above mentioned GPEs, which is far greater than the existing bio-based GPEs. Moreover, the initial discharge capacities, cycle performance and rate performance of the Li/GPE/LiCoO2 cells involved with the CA/PLLA/HNT nanofiber membranes was superior to those of the commercial Celgard® 2500. Therefore, through the proper collocation of biodegradable polymer materials and functional nanoparticles, the resulting composite GPEs exhibited the recommendable integrated performance. The CA/PLLA/HNT composite nanofiber membranes can be used as novel green skeleton materials in GPEs for high performance lithium-ion batteries, which provide a perfect combination of high performance and environmental protection.

Structures and properties of polyimide fibers containing fluorine groups

A series of copolyimide (co-PI) fibers containing fluorine groups were successfully obtained based on 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), p-phenylenediamine (p-PDA), 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) and 4,4′-oxydianiline (ODA) via a typical two-step wet-spinning method. The increased 6FDA moieties in the system resulted in unexpected great changes on the structures and properties of the resultant PI fibers. Regarding mechanical performances of the PI fibers, the tensile strength and initial modulus of the fibers decreased from 2.56 to 0.13 GPa and 91.55 to 2.99 GPa, respectively. Two-dimensional wide angle X-ray diffraction (2D WAXD) confirmed the existence of highly oriented structures along the fiber axial direction, while this feature gradually disappeared after the introduction of bulky trifluoromethyl pendant groups. SEM results suggested the presence of defects such as macrovoids structures with the increased 6FDA moieties. Besides, the dielectric permittivity was found to decrease from 3.46 to 2.78 in the frequency of 10 MHz as a result of the incorporation of 6FDA. Moreover, the co-PI fibers possessed excellent thermal-oxidative stabilities with the 5% weight loss temperature ranging from 495 to 552 °C under nitrogen atmosphere.

Carbon nanofiber/polyetherimide composite membranes with special dielectric properties

Negative dielectric constants in the frequency range from 10−2 to 107 Hz were gained from a type of carbon nanofiber/polyetherimide composite membranes with a thickness of ca. 20 µm, in particular, substantial negative values at the lower frequency region were discovered, which hold promise as an important resource for the preparation of meta-materials and their applications.

Influence of matrix modulus on the mechanical and interfacial properties of carbon fiber filament wound composites

The effect of epoxy resin matrix modulus on the mechanical and interfacial properties of T700 carbon fiber and T800 carbon fiber filament wound composites was investigated. Different aromatic amine curing agents were selected to change the modulus of the same kind of resin matrix. The mechanical properties of carbon fiber filament wound composites were characterized through Naval Ordinance Laboratory-ring (NOL) burst tests, and interlaminar shear strength (ILSS) tests. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and dynamic mechanical thermal analysis (DMA) were used to characterize the failure surfaces and interfacial properties of the resulting composites. The results showed that, even if carbon fibers were fully impregnated with epoxy resin, the mechanical properties of composites and the mode of interfacial failure were closely related to the modulus of the resin matrix. The resin matrix with a high modulus was found to be an essential prerequisite to excellent mechanical and interfacial properties of the resulting composites.

Porous carbon derived from Ailanthus altissima with unique honeycomb-like microstructure for high-performance supercapacitors

Biomass-derived porous activated carbon (AC) with high surface area of up to 1776.9 m2 g−1 was prepared by KOH and urea activation of Ailanthus altissima stems with unique honeycomb-like microstructure at 800 °C. As an electrode material for supercapacitors, the AC samples exhibited a remarkably large capacitance of 300.6 F g−1 at 0.5 A g−1 in 1 M H2SO4 and retained up to 213.4 F g−1 even at a current density of 20 A g−1. It is worth noting that no obvious capacitance loss was observed over 5000 charge/discharge cycles, clearly demonstrating the robust long-term stability. The excellent performance of the special carbon electrode can be attributed to the inherent honeycomb-like porous microstructure of Ailanthus altissima stems, which can offer more surfaces for activation by KOH to generate a more microporous network. This work provides a promising strategy to take full advantage of the unique microstructure of raw materials from nature via simple technologies to achieve sustainable energy development.

The curing and thermal transition behavior of epoxy resin: a molecular simulation and experimental study

Curing and thermal transition behavior of two epoxy resins i.e. 2,2′-dimethyl-4,4′-diaminobiphenyl (MTB)–4,5-epoxycyclohexyl-1,2-diglycidyl diformate (TDE85) and 2,2′-bis(trifluoromethyl)-4,4′-diamino biphenyl (TFMB)–4,5-epoxycyclohexyl-1,2-diglycidyl diformate (TDE85) with different chemical structures were experimentally and theoretically investigated via molecular simulations to establish the structure–property relationships. The slight modification in the diamine structure resulted in significant changes in the curing and glass transition behavior of epoxy resin. As the side group of the diamine was changed from methyl to trifluoromethyl, the reactivity of the diamine toward epoxy decreased and the glass transition temperature increased from about 164 °C to about 191 °C. These phenomena can be illustrated by the change of the reaction energy barrier, flexibility of chains and the cohesive energy density in the molecular simulation of the curing process. The simulated values show good agreement with experimental data, and can be used to predict the related material characteristics for the different amine curing agent–epoxy systems.

Effect of epoxy monomer structure on the curing process and thermo-mechanical characteristics of tri-functional epoxy/amine systems: a methodology combining atomistic molecular simulation with experimental analyses

The curing kinetics and thermo-mechanical characteristics of two kinds of high-performance amine cured tri-functional epoxy resin compounds, including diglycidyl-4,5-epoxycyclohexane-1,2-dicarboxylate and N,N-diglycidyl-4-glycidyloxyaniline, were systematically studied herein. Different to the simple bi-functional epoxy resins studied before, the increase in epoxy functionality and resultant asymmetric monomer structure made the whole curing behaviour more difficult to analyse. Nevertheless, there is an urgent demand to provide a thorough understanding of the tri-functional epoxy resin/amine system in order to obtain the desired macro-performance. In this paper, a methodology, which combines atomistic molecular simulation with experimental research, was established to expound the effect of the asymmetric epoxy monomer structure on the reaction kinetics and ultimate performance of the tri-functional epoxy/amine system. It can be utilized to efficiently analyse the cross-linking procedure and the microstructure–property relationships of epoxy resin with poly-functionality and asymmetric monomer structures, thereby serving as guidance to design high-performance polymer matrices for advanced composites.

Highly moisture-resistant epoxy composites: an approach based on liquid nano-reinforcement containing well-dispersed activated montmorillonite

The effects of butyl glycidyl ether (BGE) activated montmorillonites (BGE-MMTs) on moisture-resistant characteristics of epoxy-based composites were evaluated. The activated MMTs were prepared by intercalating BGE into the inter-layer surfaces of octadecyl ammonium modified MMTs (O-MMTs) under ultrasonication, and in the form of liquid nano-reinforcement. It showed advantages of low viscosity, excellent dispersibility and high chemical reactivity in the epoxy matrix. The enhancements in tensile and flexural properties of BGE-MMTs/epoxy composites confirmed the well dispersion of BGE-MMTs in epoxy matrix and the strong interfacial adhesion between the two components. More importantly, the well-dispersed BGE-MMTs in epoxy matrix led to significant enhancement in the moisture-barrier properties of epoxy composites. In comparison with that of neat epoxy, the moisture diffusion coefficient of BGE-MMTs/epoxy composites significantly decreased from 10.1 × 10−6 to 0.3 × 10−6 cm2 s−1. The enhancement in moisture-barrier properties was ascribed to the exfoliated two-dimensional lamellar structure of MMTs extending the effective penetration paths of water molecules into tortuous forms. A model concerning moisture diffusion in BGE-MMTs/epoxy composites was suggested.