Shulin Ma

The reuse of nonmetals recycled from waste printed circuit boards as reinforcing fillers in the polypropylene composites

The feasibility of reusing nonmetals recycled from waste printed circuit boards (PCBs) as reinforcing fillers in the polypropylene (PP) composites is studied by using both mechanical and vicat softening temperature (VST) tests. The concentration of Cu leaded from the composites is also tested. The mechanical test shows that both tensile and flexural properties of the nonmetals/PP composites can be significantly improved by adding the nonmetals into PP. The maximum increment of tensile strength, tensile modulus, flexural strength and flexural modulus of the PP composites is 28.4%, 62.9%, 87.8% and 133.0%, respectively. As much as 30 wt% nonmetals recycled from waste PCBs can be added in the PP composites without violating the environmental regulation. The VST test shows that the presence of nonmetals can improve the heat resistance of the nonmetals/PP composites for their potential applications. The optimum particle is the fine or medium nonmetals recycled from waste PCBs, and the optimum content of the nonmetals is 30 wt% basing on the comprehensive consideration. All the above results indicate that the reuse of nonmetals as reinforcing fillers in the PP composites represents a promising way for recycling resources and resolving the environmental pollutions.

Achieving concentrated graphene dispersions in water/acetone mixtures by the strategy of tailoring Hansen solubility parameters

Although exfoliating graphite to give graphene paves a new way for graphene preparation, a general strategy of low-boiling-point solvents and high graphene concentration is still highly required. In this study, using the strategy of tailoring Hansen solubility parameters (HSP), a method based on exfoliation of graphite in water/acetone mixtures is demonstrated to achieve concentrated graphene dispersions. It is found that in the scope of blending two mediocre solvents, tailoring the HSP of water/acetone mixtures to approach the HSP of graphene could yield graphene dispersions at a high concentration of up to 0.21 mg ml−1. The experimentally determined optimum composition of the mixtures occurs at an acetone mass fraction of ~75%. The trend of concentration varying with mixture compositions could be well predicated by the model, which relates the concentration to the mixing enthalpy within the scope of HSP theory. The resultant dispersion is highly stabilized. Atomic force microscopic statistical analysis shows that up to ~50% of the prepared nanosheets are less than 1 nm thick after 4 h sonication and 114g centrifugation. Analyses based on diverse characterizations indicate the graphene sheets to be largely free of basal plane defects and oxidation. The filtered films are also investigated in terms of their electrical and optical properties to show reasonable conductivity and transparency. The strategy of tailoring HSP, which can be easily extended to various solvent systems, and water/acetone mixtures here, extends the scope for large-scale production of graphene in low-boiling-point solutions.

A novel approach to recycling of glass fibers from nonmetal materials of waste printed circuit boards

The printed circuit boards (PCBs) contain nearly 70% nonmetal materials, which usually are abandoned as an industrial solid-waste byproduct during the recycling of waste PCBs. However those materials have abundant high-value glass fibers. In this study, a novel fluidized bed process technology for recycling glass fibers from nonmetal materials of waste PCBs is studied. The recycled glass fibers (RGF) are analyzed by determination of their purity, morphology and surface chemical composition. This process technology is shown to be effective and robust in treating with nonmetal materials of waste PCBs. The thermoset resins in the nonmetal materials are decomposed in the temperature range from 400 degrees C to 600 degrees C. And the glass fibers are collected at high purity and recovery rate by the cyclone separators without violating the environmental regulation. This novel fluidized bed technology for recycling high-value glass fibers from nonmetal materials of waste PCBs represents a promising way for recycling resources and resolving the environmental pollutions during recycling of waste PCBs.

A study of the reaction characteristics and mechanism of Kapton in a plasma-type ground-based atomic oxygen effects simulation facility

Kapton, a commonly used spacecraft material, is studied to investigate the atomic oxygen (AO) erosion effects in a plasma-type ground-based AO effects simulation facility. The samples before and after the experiments are compared in aspect, mass and surface morphology. The reaction characteristics of the material in the facility are obtained. The contribution of AO and ionic oxygen to mass loss in the sample and the reaction mechanism between the different particles and samples are analysed. It is concluded that neutral AO is the major cause of material erosion and mass loss and that the collision of energetic ions may accelerate the oxidation reaction.

A green, rapid and size-controlled production of high-quality graphene sheets by hydrodynamic forces

Based on a hydrodynamic mechanism, a novel, scalable and rapid production of relatively defect-free graphene nanosheets (GNSs) by a high shear mixer is proposed in this paper. The synergistic enhancement of shear forces and collision effects can result in an effective exfoliation of ultrathin GNSs. Moreover, the productivity and dimension distribution of GNSs can be easily controlled by adjusting hydrodynamic forces. Utilizing the small stator, the concentration of mono- and multi-layer GNSs prepared for 1 h in 40 vol% IPA–water mixtures can reach 0.27 mg ml−1. Almost all GNSs are less than 1 μm in average size and 2 nm in thickness. Furthermore, the mixtures of isopropanol (IPA) and water are low boiling, green, inexpensive, and have excellent solubility for GNSs. The optimal volume fraction of IPA–water mixtures for preparing GNSs is co-determined by the Hansen solubility parameter distance (Ra), surface tension and viscosity. More importantly, graphite particles have strong physical interactions with hydrodynamic forces, but GNSs structure also can remain relatively defect-free. Consequently, this scalable, rapid and high-yield method can be satisfactorily applied in the production of GNSs and other two-dimensional (2D) materials.

Hydrodynamics-assisted scalable production of boron nitride nanosheets and their application in improving oxygen-atom erosion resistance of polymeric composites

Searching for a method for low-cost, easily manageable, and scalable production of boron nitride nanosheets (BNNSs) and exploring their novel applications are highly important. For the first time we demonstrate that a novel and effective hydrodynamics method, which involves multiple exfoliation mechanisms and thus leads to much higher yield and efficiency, can realize large-scale production of BNNSs. The exfoliation mechanisms that multiple fluid dynamics events contribute towards normal and lateral exfoliation processes could be applied to other layered materials. Up to ~95% of the prepared BNNSs are less than 3.5 nm thick with a monolayer fraction of ~37%. Compared to the conventional sonication and ball milling-based methods, the hydrodynamics method has the advantages of possessing multiple efficient ways for exfoliating BN, being low-cost and environmentally-friendly, producing high quality BNNSs in high yield and efficiency, and achieving concentrated BNNSs dispersions even in mediocre solvents. It is also shown for the first time that BNNSs can be utilized as fillers to improve the oxygen-atom erosion resistance of epoxy composites which are widely used for spacecraft in low earth orbit (LEO) where atom oxygen abounds. An addition of only 0.5 wt% BNNSs can result in a 70% decrease in the mass loss of epoxy composites after atom oxygen exposure equivalent to 160 days in an orbit of ~300 km. Overall, the demonstrated hydrodynamics method shows great potential in large-scale production of BNNSs in industry in terms of yield, efficiency, and environmental friendliness; and the innovative application of BNNSs to enhancing oxygen-atom erosion resistance of polymeric composites in space may provide a novel route for designing light spacecraft in LEO.

Graphene for reducing bubble defects and enhancing mechanical properties of graphene/cellulose acetate composite films

In this study, we have demonstrated a strategy by which graphene was used to reduce the bubble defects and enhance the mechanical properties in graphene/cellulose acetate (Gr/CA) composite films. Mono- and multilayer graphene flakes were successfully prepared in the water–acetone mixtures by a jet cavitation method. Moreover, outstanding enhancement of mechanical properties of Gr/CA composite films were obtained at relatively low concentration of graphene flakes. Young’s modulus of these composite films increased linearly with the graphene flakes loading, due to the significantly high surface area of graphene and strong interactions between graphene flake and CA. Furthermore, three-dimensional channel formed by graphene flakes could increase the degassing speed and reduce the negative effects of bubbles. The Gr/CA composite has excellent mechanical properties and, more importantly, it is a natural and environmentally friendly polymer composite.

Vessel diameter and liquid height dependent sonication-assisted production of few-layer graphene

Sonication-assisted liquid-phase exfoliation of graphite makes facile, scalable, and low-cost graphene production possible, but there is little information about how sonication-related factors such as vessel diameter (D) and liquid height (H) affect this process and how to scale-up this technique. In this article, the dependence of the sonication-assisted few-layer graphene (FLG) production on D and H was investigated based on experiments and numerical simulation which was performed by finite element method to determine cavitation-related parameters. It was found that by essentially changing the cavitation phenomenon, D and H could critically affect the FLG concentration, FLG yield, injected power, and production efficiency. Combined experimental and simulational analyses reveal that though D and H can change both cavitation volume and cavitation volume fraction, it is the cavitation volume fraction that directly relates to the FLG concentration and production efficiency with a monotonically increasing trend, while the FLG yield and injected power are almost proportional to the cavitation volume, which in turn follows a linear increasing trend with the sample volume. The practical importance for industrial FLG production may lie in the following: (1) D and H should be carefully designed to obtain high cavitation volume fraction to gain high production efficiency and FLG concentration or output-input ratio and (2) large D, H, or sample volume is necessary for achieving large cavitation volume to enhance the FLG yield. Moreover, enhancement in pressure amplitude or cavitation intensity could also favor FLG production. These results have verified the importance of D and H which are often ignored when studying graphene production, and will provide important information on designing large-sized vessels for mass-producing graphene by sonication.

One-step green synthesis of graphene nanomesh by fluid-based method

A fluid-based method is demonstrated for preparing graphene nanomeshes (GNMs) directly from pristine graphite flakes by a one-step process. The high efficiency is attributed to the combination of fluid-assisted exfoliation and perforation of the graphene sheets. Atomic force microscopy shows that the as-produced GNMs are less than 1.5 nm thick. The total area of the pores within 1 μm2 of the GNM sheet is estimated as ∼0.15 μm2 and the pore density as ∼22 μm−2, The yield of GNMs from pristine graphite powder and the power consumption for per gram GNM synthesis are evaluated as 5 wt% and 120 kW h, respectively. X-ray photoelectron spectroscopy, infrared spectroscopy, elemental analysis and Raman spectroscopy results indicate the purity of the GNMs and thus it is a green efficient method. The present work is expected to facilitate the production of GNMs in large scale.

Morphology and structure of mono- and few-layer graphene produced by jet cavitation

We prepared mono- and few-layer graphene with micrometer-sized dimensions in aqueous solution by a jet cavitation method starting from common crystal graphite, which is totally green, facile, low-cost, and laborsaving. The graphene yield by our method is estimated as ∼4 wt. % by statistical analysis. Diverse microscopy is used to characterize the morphology, microstructure, and near-edge fine structure of the prepared nanosheets. It is found that partial folding allows realization of rotational stacking fault in otherwise perfect samples. The folded graphene with Morie patterns could be ideal specimens for experimentally probing band structure and electronic properties of graphene with different stacking styles.