Atomically thin hydroxylation boron nitride nanosheets for excellent water-based lubricant additives

Hexagonal Boron nitride (BN) can be used as a lubricant additive, which can dramatically reduce friction energy. However, due to the accumulation of BN in the water-based lubricants and the difficulty of entering the friction contact area, the tribological performance of BN becomes worse. To address this issue, the atomically thin hydroxylated boron nitride nanosheets (HO-BNNS) were successfully prepared. The thickness of HO-BNNS is only 0.6-0.8 nm. Meanwhile, the HO-BNNS has excellent dispersion stability in water-based lubricants because of the hydroxyl group on the surface of HO-BNNS. The as-prepared HO-BNNS exhibits unique friction properties as a water-based dispersible lubricant additive. Additionally, the average wear scar diameter, average friction coefficient, and mean wear volume of HO-BNNS/water-based (0.05 wt%) drop by about 64.7%, 60%, and 95.73%. Finally, the introduction of HO-BNNS can well control the temperature of water-based lubricant.     

氮化硼表面修饰及其对氮化硼/硅橡胶复合材料热性能的影响

研究氮化硼表面改性及其对氮化硼/硅橡胶复合材料热性能的影响。结果表明:活化可以提高氮化硼表面接枝率,偶联剂CA1对氮化硼的改性效果优于偶联剂KH570;随着氮化硼用量的增大,氮化硼/硅橡胶复合材料的热导率增大;加入氮化硼的复合材料热稳定性提高,但改性氮化硼/硅橡胶复合材料的热稳定性下降。     

Boron nitride and fluoropolymer combinations: Interactions and their performance as processing aids

In this work, we studied the adsorption capacity of boron nitride (BN) for fluoropolymer and polyethylene (PE) to gain a better understanding of the interactions and the performance of BN and fluoropolymer, and their combinations as processing aids in the extrusion of Ziegler‐Natta PEs. We found that BN has a relatively high adsorption capacity for both PE and fluoropolymer. As a result, simultaneous compounding of BN and fluoropolymer into the host polymer causes fluoropolymer to be trapped within the bulk of the polymer, and prevents the fluoropolymer particles from coating the die wall during flow. This limits the effectiveness of fluoropolymer and BN as processing aids. To avoid this interaction, we added fluoropolymer separately in a dry form just prior to extrusion. In this case, the synergistic effect of BN and fluoropolymer as a combination processing aid was evident. POLYM. ENG. SCI., 45:669–677, 2005. © 2005 Society of Plastics Engineers     

BiOI/g-C3N4光催化降解甲基橙研究

以三聚氰胺为前驱物采用热聚合法制备了石墨相氮化碳（g-C₃N₄）,并在其表面原位合成了碘氧化铋（BiOI）,构筑了石墨相氮化碳-碘氧化铋复合材料。采用X射线衍射仪（XRD）、傅里叶变换红外光谱仪（FT-IR）、紫外可见漫反射仪（UV-Vis-DRS）等对催化剂进行了表征。结果表明,当BiOI与g-C₃N₄物质的量比为0.5时,BiOI/g-C₃N₄催化剂具有高分散的BiOI颗粒及适中的禁带宽度,吸附和降解甲基橙性能最佳。回流温度为120 ℃时制备的BiOI/g-C₃N₄催化剂具有适中的粒径、比表面积和表面羟基浓度,吸附和降解甲基橙性能最佳,且该催化剂具有良好的重复使用性能。     

Gas-assisted exfoliation of boron nitride nanosheets enhancing adsorption performance

A gas exfoliation strategy for controllable preparation of boron nitride (BN) nanosheets with few-layered structure were reported. The green exfoliation process provides the BN nanosheets remarkable increment of adsorption capacities to organic contaminants, which is ascribed to better exposure of active sites originating from the larger surface area and thinner layer. Moreover, the prepared BN also exhibits outstanding recyclability.     

Pore size regulation of BN fibers and its effect on tetracycline adsorption

The environmental hazards caused by antibiotics are becoming more and more serious, especially tetracycline antibiotics, which not only destroy the water balance, but even threaten people's lives. Therefore, the hierarchical micro-mesoporous boron nitride (BN) fibers with high adsorption capacity were prepared by in situ synthesis. The results indicated that the pore size extremes of the hierarchical micro-mesoporous BN fibers were distributed at 1.2, 2.9, and 23.4 nm, and the total pore volume reached 0.295 cm³/g. Importantly, mesopores were conducive to diffusion while microporous structure was conducive to capture the tetracycline molecules. The maximum adsorption capacity of hierarchical porous BN fibers for tetracycline reached 870.29 mg/g, which was 1.99 times the maximum adsorption capacity reported in the existing literature. This was attributed to the synergistic enhancement between the mass transfer trapping effect and the intermolecular bonding in the BN fibers, which enabled the vertical adsorption of tetracycline molecules on the surface and between the layers of the BN molecules. In addition, the adsorption removal rate of the hierarchical porous BN for tetracycline was still as high as 99.93% after reusing five times. This hierarchical micro-mesoporous BN fiber has broad application prospects in the fields of antibiotic adsorption and water purification.     

Fabrication of thermally conductive composite with surface modified boron nitride by epoxy wetting method

Boron nitride (BN) particles fabricated with different surface treatments were used to prepare thermally conductive polymer composites by epoxy wetting. The polar functionality present on the BN particles allowed the permeation of the epoxy resin because of a secondary interaction, which allowed the fabrication of a composite containing high filler concentration. The different cohesive energy densities of the synthesized material due to a functional-group-induced surface treatment effect on surface free energy and wettability determined the thermal and mechanical properties of the polymer. The results indicate that surface-curing agents interrupt the interaction between the filler and matrix, and do not always enhance thermal conductivity. Moreover, the composites showed maximum thermal conductivity at 30 wt% epoxy loading when the fixed-pore volume fraction reached in the filtrated BN film. The measured storage modulus was also enhanced by surface treatment because of the sufficient interface produced and interaction between the large amount of the filler and epoxy.     

Alkylation of mixed micro‐ and nanocellulose to improve dispersion in polylactide

Nanocellulose tends to be aggregated due to the hydrogen bonding between three of the hydroxyl groups in each repeat unit, resulting in poor dispersion in non‐polar polymer matrices. In this research, to improve the dispersion of cellulose particles in a polymer matrix, a long hydrophobic alkyl chain was substituted for hydrogen in the hydroxyl group of cellulose via a bimolecular nucleophilic substitution (S_N2) reaction with alkyl bromide. Octyl (? C₈H₁₇) and dodecyl (? C₁₂H₂₅) groups were applied in this reaction, which is faster and simpler than other substitution reactions. The chemical structures of octyl and dodecyl ether cellulose were identified using Fourier transform infrared and NMR analyses. The contact angle with water and methylene iodide was measured to calculate the surface energy of alkyl nanocellulose. The surface energy was decreased by the substituted alkyl chain. The thermal properties, morphology and crystal structure of octyl and dodecyl ether cellulose were also investigated to determine the possibility of use as a reinforcement. Furthermore, polylactide/alkyl ether cellulose composites were prepared to make certain of sufficient dispersion of the alkyl ether cellulose in the polylactide matrix. The thermal and mechanical properties of the polylactide composite films were investigated. The optical transmittance of the polylactide composites was measured to confirm the relative dispersity. © 2014 Society of Chemical Industry     

Simple approach to developing high‐efficiency neutron shielding composites

Three distributions of boron nitride (BN) particles were designed: random, oriented, and periodic. The BN particles in multilayered high‐density polyethylene/boron nitride (HDPE/BN) composites were oriented along the extrusion direction and arranged regularly, and the BN/HDPE layers containing oriented BN particles exhibited periodic distribution in multilayered HDPE/(HDPE/BN) composites. Compared to the random distribution of BN particles, these structures could help reduce neutron transmittance and improve the linear and mass attenuation coefficients. Moreover, the neutron shielding efficiency could rapidly improve as the number of layers of the multilayered composites increased. Meanwhile, the crosslinking effect of the HDPE matrix caused by secondary radiation could be weakened as the number of layers of the multilayered composites increased. This study also introduced a novel idea for designing neutron shielding materials. POLYM. ENG. SCI., 59:E348–E355, 2019. © 2019 Society of Plastics Engineers     

Investigation on two abnormal phenomena about thermal conductivity enhancement of BN/EG nanofluids

The thermal conductivity of boron nitride/ethylene glycol (BN/EG) nanofluids was investigated by transient hot-wire method and two abnormal phenomena was reported. One is the abnormal higher thermal conductivity enhancement for BN/EG nanofluids at very low-volume fraction of particles, and the other is the thermal conductivity enhancement of BN/EG nanofluids synthesized with large BN nanoparticles (140 nm) which is higher than that synthesized with small BN nanoparticles (70 nm). The chain-like loose aggregation of nanoparticles is responsible for the abnormal increment of thermal conductivity enhancement for the BN/EG nanofluids at very low particles volume fraction. And the difference in specific surface area and aspect ratio of BN nanoparticles may be the main reasons for the abnormal difference between thermal conductivity enhancements for BN/EG nanofluids prepared with 140- and 70-nm BN nanoparticles, respectively.     

Fabrication of surface-treated BN/ETDS composites for enhanced thermal and mechanical properties

The ceramic/polymer composites based on epoxy-terminated dimethylsiloxane (ETDS) and boron nitride (BN) were prepared for use as thermal interface materials (TIMs). 250 µm-sized BN was used as a filler to achieve high-thermal-conductivity composites. To improve the interfacial adhesion between the BN particles and the ETDS matrix, the surface of BN particles were modified with silica via the sol–gel method with tetraethyl orthosilicate (TEOS). The interfacial adhesion properties of the composites were determined by the surface free energy of the particles using a contact angle test. The surface-modified BN/ETDS composites exhibited thermal conductivities ranging from 0.2 W/m K to 3.1 W/m K, exceeding those of raw BN/ETDS composites at the same weight fractions. Agari׳s model was used to analyze the measured thermal conductivity as a function of the SiO₂-BN concentration. Moreover, the storage modulus of the BN/ETDS composites was found to increase with surface modification of the BN particles.     

Preparation and properties of thermally conductive photosensitive polyimide/boron nitride nanocomposites

A new thermally conductive photoresist was developed. It was based on a dispersion of boron nitride (BN) nanoflakes in a negative‐tone photosensitive polyimide (PSPI) precursor. 3‐Mercaptopropionic acid was used as the surfactant to modify the BN nanoflake surface for the dispersion of BN nanoflakes in the polymer. The thermal conductivity of the composite films increased with increasing BN fraction. The thermal conductivity of the PSPI/BN nanocomposite was up to 0.47 W m⁻¹ K⁻¹ for a mixture containing 30 wt % nanosized BN filler in the polyimide matrix. Patterns with a resolution of 30 μm were obtained from the PSPI/BN nanocomposites. The PSPI/BN nanocomposites had excellent thermal properties. Their glass‐transition temperatures were above 360°C, and the thermal decomposition temperatures were over 460°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of Boron Nitride Coating on Carbon Nanotubes

A method to synthesize boron nitride coating on the surface of carbon nanotubes (nanofibers) without damaging the tube walls has been developed. A reaction between boric acid and ammonia was performed at moderate temperatures on the surface of carbon nanotubes to form boron nitride (BN) coatings. The surface structure of the carbon nanotubes significantly influences the morphology of the boron nitride coating. If the surface of the tubes is free of defects, highly crystallized insulating BN nanotubes can encapsulate carbon nanotubes. On the surface of carbon nanotubes with disordered wall structure, a polycrystalline BN sheath was produced.     

Electrical and mechanical properties of electrically conductive adhesives from epoxy,micro-silver flakes,and nano-hexagonal boron nitride particles after humid and thermal aging

In this study, we incorporated micro-silver flakes and nano-hexagonal boron nitride (BN) particles into a matrix resin to prepare electrically conductive adhesives (ECAs). The humid and thermal aging results under a constant relative humidity level of 85% at 85 °C revealed that the aged ECAs containing 3 wt% of nano-hexagonal BN particles had high reliability. The contact resistance was low and the shear strength high. Nano-hexagonal BN particles have a good effect on the reliability of ECAs that can be used to improve the properties of ECAs.     

Cold plasma modification of boron nitride fillers and its effect on the thermal conductivity of silicone rubber/boron nitride composites

Hexagonal boron nitride (h‐BN) fillers were first coated with low‐molecular‐weight polydimethylsiloxane (PDMS) by solution dispersion and then treated in argon plasma for different times. The modified h‐BN fillers were characterized by high‐resolution transmission electron microscopy, X‐ray photoelectron spectroscopy, and contact angle analysis. The results revealed that a thin PDMS film several nanometers thick was tightly coated on the surface of the h‐BN filler after plasma treatment, and this thin film could not be removed by 48 h Soxhlet extraction with n‐hexane at 120°C. Furthermore, the effect of plasma modification on the h‐BN filled silicone rubber composites was investigated. The results indicated that the plasma modification improved the interfacial interaction between h‐BN and the matrix, but hardly affected the distribution state of the h‐BN in the composites. The composites filled with the modified h‐BN exhibit significantly higher thermal conductivity than the composites filled with untreated h‐BN. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Effect of Interfacial Interaction on Morphology and Properties of Polyethylene/Boron Nitride Thermally Conductive Composites

In this study, polyethylene-g-maleic anhydride was utilized to enhance interfacial interaction between boron nitride and polyethylene. Moreover, KH550 was used as a surface treatment agent to improve interfacial interaction between boron nitride and polyethylene. It was found that surface functionalization of boron nitride particles and the addition of polyethylene-g-maleic anhydride can promote dispersion of boron nitride particles with reduced aggregation, resulting in the improvement of both tensile and impact strength of polyethylene/boron nitride composites. Compared to surface functionalization of boron nitride particles, the addition of polyethylene-g-maleic anhydride was much effective to enhance thermal conductivity of polyethylene/boron nitride composites and drop effectively rheological percolation threshold and gel point of polyethylene/boron nitride composites.     

Dispersant-Binder Interactions in Aqueous Silicon Nitride Suspensions

The interaction of dispersant and binder on the surface of particles was studied to identify the effect of these additives on aqueous ceramic powder processing. Poly(methacrylic acid) (PMAA) and poly(vinyl alcohol) (PVA) were used as the dispersant and binder, respectively. The adsorption isotherms of the organic additives on silicon nitride were determined. The adsorption of PMAA was differentiated from PVA in the mixed additive system via ultraviolet spectroscopy. The electrokinetic behavior of silicon nitride was measured by using an electrokinetic sonic amplitude analyzer. As the PMAA concentration increased, the isoelectric point (pH_iep) of silicon nitride shifted from pH 6.7 ± 0.1 to acidic pH values. The magnitude of the shift depended on the surface coverage of PMAA. PVA did not affect the pH_iep of suspensions but did cause a moderate decrease in the near-surface potential. Finally, the rheological behavior of silicon nitride suspensions was measured to assess the stability of particles against flocculation in aqueous media; this behavior was subsequently correlated with the electrokinetic and adsorption isotherm data.     

Large scale fabrication of porous boron nitride microrods with tunable pore size for superior copper (II) ion adsorption

Herein, large scale fabrication of porous boron nitride (BN) microrods has been achieved via a facile process, which involves the synthesis of melamine diborate precursors and subsequent thermal treatment process. The fabrication can be scaled up to ultra-large scale which is limited by the furnace. The characterization results show that the as-obtained products are porous BN microrods with diameters in the range of ten to tens of micrometers and length of a few millimeters, respectively. The specific surface area and porosity of these porous BN microrods are tunable by adjusting the synthesis processes of precursors. A highest specific surface area of 653.66?m²/g is obtained for the sample of BN-4, corresponding to the differential pore volume of 0.289?cm³/(g?nm) and pore size of about 1.928?nm. Further measurement shows that the as-obtained porous BN microrods possess excellent copper ion adsorption property with a highest adsorption capacity of 365.4?mg/g. This adsorption capacity is superior to those of most copper ion adsorbents reported in recent literature. The high copper ion adsorption capacity combining with the unique properties of hexagonal BN makes them promising candidates for copper ions adsorption in practical wastewater treatment.     

Effect of nanoparticles on the performance of thermally conductive epoxy adhesives

Microsized or nanosized α‐alumina (Al₂O₃) and boron nitride (BN) were effectively treated by silanes or diisocyanate, and then filled into the epoxy to prepare thermally conductive adhesives. The effects of surface modification and particle size on the performance of thermally conductive epoxy adhesives were investigated. It was revealed that epoxy adhesives filled with nanosized particles performed higher thermal conductivity, electrical insulation, and mechanical strength than those filled with microsized ones. It was also indicated that surface modification of the particles was beneficial for improving thermal conductivity of the epoxy composites, which was due to the decrease of thermal contact resistance of the filler‐matrix through the improvement of the interface between filler and matrix by surface treatment. A synergic effect was found when epoxy adhesives were filled with combination of Al₂O₃ nanoparticles and microsized BN platelets, that is, the thermal conductivity was higher than that of any sole particles filled epoxy composites at a constant loading content. The heat conductive mechanism was proposed that conductive networks easily formed among nano‐Al₂O₃ particles and micro‐BN platelets and the thermal resistance decreased due to the contact between the nano‐Al₂O₃ and BN, which resulted in improving the thermal conductivity. POLYM. ENG. SCI., 50:1809–1819, 2010. © 2010 Society of Plastics Engineers     

Nano hexagonal boron nitride–Nafion composite membranes for proton exchange membrane fuel cells

This study investigates the proton conductivity and characterization of nano hexagonal boron nitride–Nafion composite membranes. Proton conducting composite membranes are prepared by mixing Nafion and nano hexagonal boron nitride (NhBN) particles with 3, 5, 10, and 15% weight ratios. Particle size distribution analysis is made for BN nanoparticles and the homogeneity of the membranes is proved by SEM and AFM. FTIR confirms the interaction between NhBN and Nafion. Methanol permeation and water absorption tests are made and it shows that hydrophobic NhBN particles decrease the swelling property and methanol retention of the membranes. X‐ray investigation of the composites supports semi‐crystalline nature of the composite materials. At dry conditions, the maximum proton conductivity was measured as 0.005 S/cm at 150°C for NafBN10, which is much higher than the pure Nafion. The results confirm that boron nitride nanoparticles have high contribution on the proton transfer, which may be explained with the formation of hydrogen bonds between amine and hydroxyl groups of boron nitride and sulfonic acid groups of Nafion. POLYM. COMPOS., 37:422–428, 2016. © 2014 Society of Plastics Engineers