Yuezhen Bin

Polymer casting of ultralight graphene aerogels for the production of conductive nanocomposites with low filling content

We report a convenient and effective method to fabricate monolithic and conductive nanocomposites with various morphologies by directly infiltrating epoxy resin into the pores of ultralight graphene aerogels (ULGAs) with desired morphologies, followed by curing. These composites show linear ohmic behavior even with graphene filling content as low as 0.28 wt%. The electrical conductivity of the composites can be modulated in the range from 3.3 × 10−2 to 4.8 × 10−1 S m−1, superior to that of traditional composites by directly mixing the powdery graphene with the polymer. Furthermore, the conductivity of the nanocomposites remains unchanged in a wide range of temperature which may allow the structures to be promising candidates as resistance elements for integrated circuits (ICs).

Mechanical Properties of Poly (Lactic Acid)/Hemp Fiber Composites Prepared with a Novel Method

This research dealt with a novel method of fabricating green composites with biodegradable poly (lactic acid) (PLA) and natural hemp fiber. The new preparation method was that hemp fibers were firstly blending-spun with a small amount of PLA fibers to form compound fiber pellets, and then the traditional twin-screw extruding and injection-molding method were applied for preparing the composites containing 10–40xa0wt% hemp fibers with PLA pellets and compound fiber pellets. This method was very effective to control the feeding and dispersing of fibers uniformly in the matrix thus much powerful for improving the mechanical properties. The tensile strength and modulus were improved by 39 and 92xa0%, respectively without a significant decrease in elongation at break, and the corresponding flexural strength and modulus of composites were also improved by 62 and 90xa0%, respectively, when the hemp fiber content was 40xa0wt%. The impact strength of composite with 20xa0wt% hemp fiber was improved nearly 68xa0% compared with the neat PLA. The application of the silane coupling agent promoted further the mechanical properties of composites attributed to the improvement of interaction between fiber and resin matrix.

Synergetic effects of carbon nanotubes and carbon fibers on electrical and self-heating properties of high-density polyethylene composites

High-density polyethylene (HDPE) composite films filled with carbon fibers (CF), carbon nanotubes (CNT) as well as hybrid filler of CF and CNT were prepared by melt mixing. The electrical and self-heating properties of the composite films were investigated. Results showed that: when the total content of filler was the same, (i) the electrical resistivity of composite films filled with hybrid fillers was lower than those with single filler; (ii) the composite films filled with hybrid fillers displayed more excellent self-heating performance such as a higher surface temperature (Ts), a more rapid temperature response, and a better thermal stability. This indicates the synergetic effect of combination of CNT and CF on improvement of the electrical and self-heating properties of HDPE-based composite films. The synergy can be considered to be the result of the fibrous filler CF acting as long distance charge transporters and the CNT serving as an interconnection between the fibers by forming local conductive paths.

Facile fabrication of polyaniline@γ-MnOOH on a buckypaper ternary composite electrode for free-standing supercapacitors

Ternary composites as electrode materials have attracted extensive attention due to their excellent electrochemical performance in energy-storage technologies as compared to single or binary composites. Herein, we demonstrated a facile two-step method to construct a new hierarchical nanocomposite by combing buckypaper (BP) with γ-MnOOH nanorods and polyaniline. BP is used as a conductive substrate for the synthesis of free-standing hierarchical electrodes. The structural characterizations revealed the growth of a hierarchical porous structure of the ternary electrode. The synthesized polyaniline@γ-MnOOH–BP ternary composite electrode shows a maximum specific capacitance of 567.5 F g−1 at a current density of 0.5 A g−1 and a relatively high areal capacitance of 301.2 mF cm−2 at a current density of 0.27 mA cm−2. This intriguing result is ascribed to the good combination of BP, γ-MnOOH, and PANI. We believe that this ternary composite electrode has potential in portable, environmentally friendly, and wearable applications for next generation energy-storage devices.

Synthesis of vinylferrocene and the ligand-exchange reaction between its copolymer and carbon nanotubes

To improve the dispersibility of carbon nanotubes (CNTs), poly(vinylferrocene-co-styrene) (poly (Vf-co-St)), was grafted onto the surface of CNTs by a ligand-exchange reaction. Poly(Vf-co-St) was obtained by a radical copolymerization reaction using styrene and vinylferrocene as the monomers. The vinylferrocene was synthesized from ferrocene via a Friedel-Crafts acylation. The molecular weight, molecular weight distribution, and amount of Vf in the poly(Vf-co-St) were 1.32 × 104, 1.69 and 17.6% respectively. The degree of grafting of the copolymer onto the CNTs surface was calculated from thermogravimetric analysis and varied from 27.1% to 79.7%. The addition of the poly(Vf-co-St) greatly promoted the dispersibility of the modified CNTs in anhydrous alcohol. The electrical conductivity of composites prepared from the polymer-grafted CNTs and copolymer (acrylonitrile, 1,3-butadiene and styrene, ABS) strongly depended on the degree of grafting. These results show that the amount of polymer grafted onto the surface of CNTs can be controlled and that the electrical properties of composites prepared with these grafted polymers can be tuned.

The effect of a small amount of modified microfibrillated cellulose and ethylene–glycidyl methacrylate copolymer on the crystallization behaviors and mechanical properties of polylactic acid

With the purpose of improving the crystallization rate and toughness of polylactic acid (PLA) comprehensively, chemical modified microfibrillated cellulose (MMFC) and ethylene–glycidyl methacrylate copolymer (EGMA) were used in the preparation of the PLA/MMFC/EGMA composite. After controlled acetylation using acetic anhydride, MMFC exhibited an improved hydrophobicity, resulting in a much better dispersion in PLA matrix. To clarify the impact of MMFC on the crystallization behaviors and mechanical properties of PLA, PLA/MMFC composites with 1–20xa0wt% of MMFC were characterized using differential scanning calorimetry (DSC) analysis and stress–strain curves. It was revealed that in the presence of only a small amount of MMFC (3xa0wt%), the crystallization rate of PLA was enlarged for seven times when the crystallization occurred at 120xa0°C, and the tensile modulus and tensile strength were both increased by 25% compared with pure PLA. The effect of EGMA component on the crystallization and mechanical properties of PLA was considered based on the characterization of the PLA/MMFC/EGMA composite. It was confirmed from DSC thermograms that a small amount of EGMA (5xa0wt%) did not exhibit any negative impact on the crystallization of PLA in the case of PLA/MMFC-3xa0wt%/EGMA-5xa0wt% composite. Meanwhile, in the presence of the EGMA, PLA/MMFC-3xa0wt%/EGMA-5xa0wt% composite showed an obvious increase of elongation-at-break from 9.1 to 20.8 compared with pure PLA. A remarkable improvement of crystallization behavior and toughness of PLA was achieved due to cooperative effect of the small amount of MMFC and EGMA in the PLA composite.

Study of the structural orientation and mechanical strength of the electrospun nanofibers from polymers with different chain rigidity and geometry

Structure of nano amorphous matter has not been studied sufficiently yet due to the difficulty in both operation of nano matter and characterization of their structure. In this work, a detailed study of the structural orientation within amorphous polymeric nanofiber and its mechanical strength was conducted for a highly thermal resistant amorphous polymer: poly(phthalazinone ether ketone) (PPEK). Poly(butylene terephthalate) (PBT), a semi-crystalline polymer with partial difference in chain flexibility and geometry to PPEK, was chosen for a comparative discussion. For the method, highly aligned PPEK and PBT nanofiber bundles were prepared by electrospinning with a home-made book-like collecting device. X-ray experiments were conducted to research their structural orientation, and tension experiments were conducted to research their mechanical properties. It was found that the amorphous PPEK nanofibers showed relatively low orientation degree of polymer chain limited by its rigid and twisted segments within the polymer chain, while PBT nanofibers showed not only highly ordered crystal structure but also very large shish length, beneficial from the co-existence of rigid and flexible segments. The above structural information was well supported by their uniaxial tensile behaviors, where PBT nanofiber manifested much larger ultimate stress σ, failure strain ε, Young’s modulus E and toughness than those of PPEK nanofibers and commercial PBT plastic. However, the electrospun PBT nanofibers’ orientation degree, within the range of 0.45–0.7, is much lower than that of some reported melt-spun PBT fibers with the orientation degree above 0.9. Therefore, it can be concluded that the instinct characterization of polymer chain and processing technique have a much more significant influence than size effect on the structural orientation and mechanical strength of nanofibers rather than size effect.

Improved electrical heating properties for polymer nanocomposites by electron beam irradiation

Nowadays, light weight heating materials are attractive and conductive polymer nanocomposites (CPC) were potential applications in being used as Joule heating materials. To prepare CPCs with high efficiency and stable heating, nanocomposites of high density polyethylene (HDPE) and carbon nanotubes (CNTs) were treated by electron beam (EB) irradiation. The influence of EB irradiation on the composites was characterized by DSC, TGA, TMA, SEM, and DMA. The results showed that gel content and thermal decomposition temperature increased and the thermal expansion coefficient decreased with increasing the irradiation dose. Meanwhile, electrical and thermal conductivity of irradiated samples also increased. These were attributed to crosslinking of HDPE by EB irradiation. As a result, surface temperature (Ts) of samples after irradiation was heightened and the correspondence heat efficiency was improved. Mechanical properties of the composites were significantly improved after irradiation, especially at the temperatures which were higher than melting point of HDPE, indicating the improvement of thermal stability by irradiation crosslinking. It made the irradiated HDPE/CNTs composites good candidates for application in the electrical heating.

Transcrystallization in Polymer Composites and Nanocomposites

Abstract This chapter summarizes the transcrystalline morphology and transcrystallization behavior observed in a wide range of polymer composites and nanocomposites. It begins with an introduction of the materials and preparation techniques that are usually used to obtain transcrystalline structures. Then it introduces the characterization of the morphology, crystal modification, lamellar structure, and mechanical property of the transcrystalline region. The formation mechanism of the transcrystalline structure and numerical model in simulating the transcrystallization are also discussed. The transcrystalline morphology and transcrystallization behavior are compared with those of the spherulite with the purpose of clarifying the impact of nucleation and growth on the lamellar structure, morphology, and mechanical property of various polymer composites and nanocomposites.