Yuansen Liu

Super long-life supercapacitor electrode materials based on hierarchical porous hollow carbon microcapsules

Remarkable supercapacitor electrodes with a high specific supercapacitance and a super long cycle life were achieved by using hierarchical porous hollow carbon microcapsules (HPHCMs) as active materials. HPHCMs were prepared by a facile chemical route based on pyrolysis of a soft sacrificial template involving a non-crosslinked core of poly(styrene-r-methylacrylic acid) and a crosslinked shell of poly(styrene-r-divinylbenzene-r-methylacrylic acid), which were synthesized by using traditional radical polymerization and emulsion polymerization. The results of scanning electron microscopy, transmission electron microscopy and Brunauer–Emmett–Teller characterizations revealed that HPHCM possessed the desired pore structure with apparent macro-/meso- and micropores, which not only provided a continuous electron-transfer pathway to ensure good electrical contact, but also facilitated ion transport by shortening diffusion pathways. As electrode materials for supercapacitor, a high specific capacitance of 278.0 F g−1 was obtained at the current density of 5 mA cm−2. Importantly, after 5000 potential cycles in 2 M KOH electrolyte at the discharge current density of 20 mA cm−2, the capacitance actually increased from 125 to 160 F g−1 and then remained 151 F g−1, corresponding to a capacitance retention of 120%, likely due to electrochemical self-activation.

The preparation and application of a graphene-based hybrid flame retardant containing a long-chain phosphaphenanthrene

A novel hybrid flame retardant combining graphene oxide (GO) with long-chain phosphaphenanthrene was fabricated via surface grafting reaction. Taking advantageous of the double barrier effects, including the physical shield contributed by graphene nanoplates during the initial stage and the chemical char contributed by phosphaphenanthrene during the later stage, greatly decreased the release rate of decomposed volatiles from the resin, as well as minimized the release of oxygen and combustion heat. Hence, such hybrid flame retardant can overcome the shortcomings of early acid catalyzed degradation effects caused by conventional flame retardants containing phosphorus. Satisfactory flame retardance was achieved (UL94 V-0 rating) with only 4% addition of the hybrid flame retardant to the epoxy resin laminate. Due to the long-chain and bulky phosphaphenanthrene groups, the interlayer attractive forces of the modified GO were effectively weakened, thus favoring the exfoliation and dispersion of graphene sheets. As a result, the incorporation of the flame retardant slightly enhanced the mechanical properties of the polymer composites, rather than deteriorating them, as occurs with traditional additive flame retardants. As a potential application for graphene, it is believed that the reported hybrid flame retardant has promising future prospect.

Self-assembly Behavior of Aryl Amide Nucleating Agent under Supercritical Carbon dioxide and its Influence on Polypropylene

ABSTRACT Supercritical carbon dioxide-assisted extrusion was adopted to prepare polypropylene containing aryl amide β nucleating agent. The experimental results showed that supercritical carbon dioxide did not affect the nucleating efficiency of β nucleating agent on polypropylene but acted as a carrier to facilitate the dissolution and self-assembly in polymer melts, so as to promote polypropylene crystallize into rich β-modification of needle-like crystals with outstanding toughening effect at low temperature. GRAPHICAL ABSTRACT

Synergistic Flame-retardant Effect and Mechanism of Nitrogen–Phosphorus-Containing Compounds for Glass Fiber-reinforced Polyamide 66

ABSTRACT The system based on aluminum phosphinate (OP) and melamine polyphosphate was applied in flame-retardant glass fiber-reinforced polyamide 66. From a qualitative and quantitative point of view, the incorporation of OP played a positive role in obtaining the homodisperse of flame-retardant particles throughout the composites. A two-step cooling mode during the degradation process was established to play an effective role in absorbing heat to retard the flame spread rate and provide enough time for barrier generation. In condensed phase, the cross-linked structure formed in residue promoted the construction of the high-quality barrier layer. GRAPHICAL ABSTRACT

A shear pan mill for preparation of ultrafine polyamide 66 powder using sodium sulfate ionic crystals as grinding aid

ABSTRACT Fine polyamide 66 (PA66) powder was prepared in a shear pan mill that was designed and developed in our laboratories. In contrast with discontinuous impacts in the ball mill, the size reduction operation in the pan mill is characterized by application of uninterrupted strong shear forces on particles. It has been found that as compared to the ball mill, much finer pulverization of the polymer material is achieved in the pan mill, in spite of the high strength and ductility of the polymer. Sodium sulfate ionic crystals with hard and pointed edge were co-milled with PA66 to further cut the fine polymer particles into ultrafine powder (2–5 µm). Besides acting as a grinding aid, the ionic crystals also prevented conglutination and aggregation of the polymer powder. Furthermore, PA66 powder could be conveniently separated and purified from the co-milled grinding aid-polymer mixture by simple water washing and filtration. Thus, an energy efficient and environment-friendly technology has been developed to prepare the ultrafine plastic powder at room temperature. This process holds a good promise for commercial applications.

Efficient flame retardant polyvinyl alcohol membrane through surface graft method

The preparation of flame retardant polyvinyl alcohol (PVA) membranes with high performance is a challenge using conventional methods by physically mixing flame retardants with a PVA solution. In this study, the surface grafting of a flame retardant on neat PVA membrane was adopted instead of conventional physical mixing. The structure and grafting ratio of the flame retardant grafted chemically on a PVA membrane was examined and characterized. A comparison of the performance between the surface grafted and the conventional mixed flame retardant PVA membranes were conducted by cone calorimetry, vertical flame, thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), mechanical properties and transparency tests. The results showed that with the same flame retardant content, the one with the surface grafted had much better flame retardance, mechanical properties and transparence, as well as an enhanced melt point and thermal stability. In conclusion, the surface grafting of the flame retardant PVA membrane is very promising for many applications due to its remarkably improved properties.

Acid-base synergistic flame retardant wood pulp paper with high thermal stability

Acid-catalytic degradation caused by acid source flame retardants is the main reason for a decline in thermal stability of flame-retarded lignocellulosic materials. In the present research, a guanidine phosphate (GP)/borax (BX) flame retardant system based on acid-base synergistic interaction was designed and used in wood pulp paper (WPP) to solve this problem. Results showed that the treated WPP obtained good flame retardancy with a limiting oxygen index (LOI) value of 35.7%. As a basic flame retardant, borax could chemically combine with the acids released by guanidine phosphate, thus decreasing the acidity of the system in the initial heating stage. In this way, acid-catalytic degradation is greatly retarded on the lignocelluloses to improve thermal stability (the temperature of maximum degradation peak from 286°C to 314°C). Meanwhile, borax was also advantageous to form a denser and firmer condensed phase through reinforcement of the acid-base reaction product, borophosphates, allowing it to provide a protective barrier with higher quality.

Root-like natural fibers in polypropylene prepared via directed diffusion and self-assembly driven by hydrogen bonding

Interfacial properties govern effective transfer of load from a polymer matrix to a reinforced fiber, dictating the mechanical performance of the composite. This paper reports a facile and controlled strategy of preparing root-like natural fibers (NFs) in polypropylene (PP), where the two components are integrated via mechanical interlocking provided by the interfacial grown fiber. Specifically, driven by hydrogen bonding between amide groups of the self-assembling molecules (NAs) and abundant hydroxyl groups existing in the NF, the former selectively diffuses and aggregates on the latter and then self-assembles into branched fibers, which can be tailored finely by the annealing temperature and time as well as cooling rate. This study opens up an interfacial manipulation without preliminary surface modification and holds great potential in preparing NF-reinforced polymer composites.

Synthesis and properties of an intrinsic flame retardant silicone rubber containing phosphaphenanthrene structure

A novel intrinsic flame retardant silicone rubber (SR) containing phosphaphenanthrene structure was synthesized in the present research. A series of characterizations including vertical burning testing, limiting oxygen index (LOI), microscale combustion calorimetry (MCC), thermogravimetric (TG) analysis and scanning electronic microscopy (SEM) showed that this SR possessed much quicker self-extinguishment, lower heat release rate, higher LOI and thermal stability as well as better charring capacity compared with unmodified SR. The char residues of the materials had been investigated in detail by Fourier transform infrared spectra (FT-IR) and X-ray photoelectron spectroscopy (XPS) to reveal the interactions between phosphaphenanthrene group and siloxane in the condensed phase. In addition, the corresponding physical properties such as transparence, dynamic and static mechanical performances were also evaluated.

Investigation of crystallisation and interfacial nature of polyhedral oligomeric silsesquioxane/polypropylene composites in the presence of β-nucleating agent

ABSTRACT Polyhedral oligomeric silsesquioxane (POSS)/polypropylene (PP) composites in the presence of β-nucleating agent (β-NAs) were prepared by melt-blending, and the interfacial interaction and crystallisation behaviour were investigated. The experimental results indicated that strong hydrogen bonding interactions were generated between amino groups of β-NAs and silicon hydroxyl groups attached to POSS, allowing the absorption/anchoring of the former on the surface of latter. Compared to POSS, β-NAs exhibited higher nucleation effect on PP, as evidenced by an increment of the crystallisation temperature by 7°C in the presence of β-NAs. As a result, the absorbed β-NAs on the surface of POSS not only improved the interfacial interaction between POSS and polymer matrix using interfacial crystallisation but also promoted the formation of β-crystals with toughening effect, which is very important to prepare excellent-performance PP/POSS composite.