Extension-dominated improved dispersive mixing in single-screw extrusion. Part 2: Comparative analysis with twin-screw extruder

In Part 1 of this work, the possibility of improving single-screw extruders (SSE) better dispersive mixer was explored by harnessing extensional flows provided by the hyperbolic contracting–diverging channels of extensional mixing elements (EME). Addition of the EME to the pin screw generated enhanced breakup for polymer blends and nanocomposite systems without significant penalty in flow rate. In Part 2, experiments are performed on immiscible polymer blends (low-viscosity ratio and high-viscosity ratio) and nanocomposites on both SSE and twin-screw extruder (TSE) with the same rotation speed and throughput. Morphological results show tremendous improvement in dispersive mixing capability of SSE when equipped with EME that are mainly comparable to conventional TSE that is, with kneading blocks as mixing sections, although not as good as TSEs equipped with EMEs. Mechanical results also show enhanced modulus when EME is used in SSE operations.     

An improved strategy to synthesize graphite oxide with controllable interlayer spacing as coatings for anticorrosion application

A facile method to synthesize nanoscale graphene oxide (GO) with controllable interlayer spacing was carried out using two-step oxidation process and much less acid to improve the efficiency of the oxidation. The X-ray diffraction results demonstrated that GO had been successfully prepared from graphite because of disappearance of characteristic peaks of pristine graphite at about 2θ = 26.5° along with appearance of a sharp major peak of GO at about 2θ = 9.4°. The increased basal spacing d₀₀₁ of as-prepared GO could reach as high as 9.39 Å, suggesting higher degree of oxidation than that prepared by the classical Hummers' synthesis, and characterization results from Fourier transform infrared spectrometer, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy further confirmed this conclusion. The influence of GO on anti-corrosion performance of nanocomposite coatings composited with the 2,5-dimethoxyaniline (DMA) conductive polymer was examined via potentiodynamic polarization curve tests in 3.5 wt% NaCl aqueous solution. The results demonstrated that the incorporation of GO significantly decreased the corrosion current density (i_corr = 2.62 μA/cm²) in the case of GO-PDMA coating, reflecting excellent physical isolation of GO and its synergistic effect with PDMA against the infiltration of water and corrosive electrolyte.     

Antistatic packaging based on PTT/PTT-g-MA/ABS/MWCNT nanocomposites: Effect of the chemical functionalization of MWCNTs

Polymer/carbon nanotube nanocomposites have attracted high interest for a wide spectrum of applications, including antistatic packaging used to protect electronic devices against electrostatic discharge. Polytrimethylene terephthalate (PTT)/maleic-anhydride-grafted PTT (PTT-g-MA)/acrylonitrile butadiene styrene (ABS) blend-based multiwall carbon nanotubes (MWCNTs) nanocomposites were prepared through extrusion. It was conducted chemical functionalization on the MWCNTs by oxidation using nitric acid to introduce functional groups. The effect of the amount (0.5 or 1.0 wt%) and functionalization of MWCNTs on the nanocomposites was investigated. Despite the poor barrier properties of PTT/PTT-g-MA/ABS/MWCNT nanocomposites due to the presence of voids confirmed by scanning electron microscopy (SEM), the nanocomposites with functionalized MWCNT (MWCNTf) showed excellent barrier properties, indicating that the functionalization process improved the interaction between the MWCNTs and the matrix. The addition of MWCNTs into PTT/PTT-g-MA/ABS blend decreased the electrical resistivity by eight orders of magnitude. The use of MWCNTf may still disrupt the electrical network pathway and slightly decreasing the electrical resistivity, but the nanocomposites present the desired properties required for antistatic packaging.     

Hybrid anion exchange membranes with adjustable ion transport channels designed by compounding SEBS and homo-polystyrene

Hybrid anion exchange membranes (AEMs) were prepared via chemically functionalizing and crosslinking poly(styrene-b-[ethylene-co-butylene]-b-styrene) (SEBS) copolymers and low molecular weight homo-polystyrene (hPS). Via sequential chloromethylation, crosslinking, quaternization, and alkalization, a series of hPS/SEBS AEMs were obtained with varying content of hPS. Systematic structural, morphological, mechanical, absorption, and transport measurements reveal that these properties depend on the total PS content in the membranes. Particularly, increasing total PS content causes (a) PS domains in the AEMs transition the cylindrical morphology to lamella-like morphology with comparable correlation length; (b) Young's modulus, water uptake, swelling ratio, ionic exchange capacity and ionic conductivity of the AEMs, and T_g of PS phase increase. In addition, the alkaline stability of the hPS/SEBS AEMs is also improved by addition of hPS. These findings suggest that the proposed method can develop high performance SEBS AEMs that are suitable for fuel cell applications.     

Effect of modified layered double hydroxide on the flammability of intumescent flame retardant PP nanocomposites

The dodecyl sulfate intercalated CaMgAl-hydrotalcites (layered double hydroxides [LDHs]) were successfully prepared by co-precipitation method, and characterized by X-ray diffraction analysis, infrared spectroscopy (Fourier transform infrared spectra [FT-IR]), thermogravimetry (TG-DTA), scanning electron microscope, and Brunner−Emmet−Teller (BET). The prepared LDHs were added to the intumescent flame retardant (IFR) polypropylene (PP) nanocomposites, and the limiting oxygen index method (LOI), vertical combustion method (UL-94), cone calorimetry (CCT), and other test methods were used to study its thermal stability and combustion performance. The results showed that when the flame retardant was composed of 23 wt% IFR and 2 wt% O-SDS-LDHs, the LOI value of the material was increased to 31.5%, reaching the V-0 level, and the flame retardant performance was significantly improved. The results also showed that there was a significant synergistic effect between IFR and O-SDS-LDHs, which could improve the thermal stability and graphitization degree of PP nanocomposites. In addition, the peak heat release rate, total heat release, and total smoke production of the PP/IFR/O-SDS-LDHs system were 177 kW/m², 101 MJ/m², and 15.4 m², respectively, which were 82.2%, 51.0%, and 23.0% lower than those of pure PP, respectively. These improvements could be attributed to the presence of dense and continuous char layer formed by the synergistic effect.     

Sustainability-guided life-cycle design and assessment for bio-based composite foams: Integrate flame retardancy/lightweight in usage and energy utilization after service

Sustainable development strategy has aroused a great interest in biomass resources as alternative raw materials. A kind of biomass-derived poly(butylene succinate) (PBS), has been developed as porous foams to reduce resource exhaustion and meet lightweight demands. For fire-safety in-service, graphene oxide (GO) was functionalized by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) to combine flame-retardant elements and heat-barrier function. Hence, a very low loading level of P-containing GO as only 5 wt% could reduce peak heat release rate (pHRR) and total heat release (THR) of PBS-based foams by 58.5% and 22.3%, respectively. Meanwhile, N-/P-doped mesoporous char with a specific surface area of 136 m²/g, which derived from combustion of flame-retardant foaming PBS, contributes to a potential of energy storage applications in the capacitor or the anode of Li-ion battery with long-term stability. Overall, the sustainability of bio-based polyester could integrate lightweight of foaming, and be extended to utilization after use via facile combustion inspired by flame-retardancy design.     

Ultrahigh molecular weight polyethylene with improved crosslink density,oxidation stability,and microbial inhibition by chemical crosslinking and tea polyphenols for total joint replacements

Highly crosslinked ultrahigh molecular weight polyethylene (UHMWPE) stabilized by vitamin E (VE) is widely applied in artificial joints as the bearings. Despite the approval, there is a discord that VE lowers the crosslinking efficiency, limiting its use at high concentration. In this work, we aim to obtain highly crosslinked and oxidation resistant UHMWPE through the conjunction of tea polyphenol and chemical crosslinking. We hypothesized that highly incorporated tea polyphenol with multiple reactive sites can ameliorate crosslinking efficiency of chemical crosslinked UHMWPE in comparison to VE. Epigallocatechin gallate (EGCG) as representative tea polyphenol was incorporated into UHMWPE at high concentration (2–8 wt%), followed by chemical crosslinking with 2 wt% organic peroxide. Unlike VE/UHMWPE blends as the control, chemical crosslinking achieved an increasing trend in crosslink density of EGCG/UHMWPE blends with increasing antioxidant concentration. High concentration of EGCG also enhanced the oxidation stability of UHMWPE. Intriguingly, EGCG endowed UHMWPE with an excellent antimicrobial property, which was inefficient in VE/UHMWPE. Cell viability was hardly affected by the high loaded antioxidant and peroxide. The chemically crosslinked UHMWPE blended with EGCG is proved to be a reasonable, cost effective and realistic alternative for use in artificial joints.     

Ionic liquid modified graphene oxide for enhanced flame retardancy and mechanical properties of epoxy resin

In this work, to improve its dispersion and flame retardancy, graphene oxide (GO) was functionalized by silane coupling agent KH550 and 1-butyl-3-methylimidazole hexafluorophosphate (PF₆-ILs), and characteristics of the PF₆-ILs@GO was obtained by transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Then, the synergistic flame retardant of GO or PF₆-ILs@GO and melamine pyrophosphate (MPP) were applied for epoxy resin (EP) materials. Specifically, the limiting oxygen index (LOI) value of EP with 0.1 wt% PF₆-ILs@GO was increased to 29.2% from 27.5% of EP/MPP composites, and the UL-94 test reached the V-0 rating. The CCT results showed that the total heat release (THR) and total smoke release (TSP) of EP/MPP/PF₆-ILs@GO composites were significantly 24.4% and 53.4% lower than that of EP/MPP composites. Besides, the thermal behavior investigated by TGA indicated that the char-forming effect of GO and PF₆-ILs@GO was great, the residual char of EP/MPP/PF₆-ILs@GO composites was as high as 19.5% at 700°C, and its thermal stability was higher than that of EP/MPP composites. On the other hand, the tensile strength of EP/MPP/GO and EP/MPP/PF₆-ILs@GO composites were increased by 15.6% and 28.3% compared with EP/MPP composites. According to SEM analysis, the EP/MPP/GO composites formed a good protective char layer, which can effectively improve flame retardancy of EP. This research represents a new method of flame retardant modified GO to improve the flame retardancy and mechanical properties of polymers.     

需求侧能量共享:概念、机制与展望

分布式可再生能源的蓬勃发展为建设清洁高效智能电网提供了新途径,但同时也导致了需求侧用户行为更随机、能量管理更困难、设备利用更低效等问题。为应对这些新挑战,充分调动需求侧灵活性,能量共享作为一种分布式运营新范式应运而生。文中给出了需求侧能量共享的概念,分析了其在平抑不确定性、提升运行经济性和提高设备利用效率等方面的潜力,并对能量共享机制的设计要点及基本要求进行了详细阐述。在此基础上,从合作博弈与非合作博弈2个角度将国内外能量共享机制设计相关研究归纳为5类,总结了当前的研究进展与亟待解决的问题。最后,从需求侧能量共享市场内部设计与外部衔接2个方面,对未来的研究方向进行了展望。     

氮硼掺杂菌糠炭：蜂窝结构用于电极材料

绿色可再生、储量丰富且成本低廉的农林废弃物在能源转化利用领域具有重要位置。本文利用中国北方最常见的农林废弃物菌糠为原料,分别以氢氧化钾、硼酸铵为活化剂和掺杂剂,通过简单的高温煅烧法制备了具有蜂窝结构的氮硼双掺杂菌糠炭（NBFC）。NBFC的微观形貌和物理结构表征结果显示：NBFC-3为表面粗糙的蜂窝状多孔材料,孔径集中在2nm左右,比表面积高达2968.48m²/g,具有相互连接的微介孔网络结构。电化学性能测试结果表明：当电流密度为0.5A/g时,NBFC-3的比电容高达297.2F/g。即使当电流密度增加到10A/g后,比电容仍可达218.5F/g,在循环5000圈后（电流密度为5A/g）,比电容保持率为94.5%,展现了良好的倍率性能和显著的电化学稳定性。综上,NBFC是一种极有潜力的电化学储能材料。该研究也为农林废弃物菌糠的高效利用提供了新思路。