Yusheng Tang

Hierarchically porous silicon–carbon–nitrogen hybrid materials towards highly efficient and selective adsorption of organic dyes

The hierarchically macro/micro-porous silicon–carbon–nitrogen (Si–C–N) hybrid material was presented with novel functionalities of totally selective and highly efficient adsorption for organic dyes. The hybrid material was conveniently generated by the pyrolysis of commercial polysilazane precursors using polydivinylbenzene microspheres as sacrificial templates. Owing to the Van der Waals force between sp2-hybridized carbon domains and triphenyl structure of dyes, and electrostatic interaction between dyes and Si-C-N matrix, it exhibites high adsorption capacity and good regeneration and recycling ability for the dyes with triphenyl structure, such as methyl blue (MB), acid fuchsin (AF), basic fuchsin and malachite green. The adsorption process is determined by both surface adsorption and intraparticle diffusion. According to the Langmuir model, the adsorption capacity is 1327.7 mg·g−1 and 1084.5 mg·g−1 for MB and AF, respectively, which is much higher than that of many other adsorbents. On the contrary, the hybrid materials do not adsorb the dyes with azo benzene structures, such as methyl orange, methyl red and congro red. Thus, the hierarchically porous Si–C–N hybrid material from a facile and low cost polymer-derived strategy provides a new perspective and possesses a significant potential in the treatment of wastewater with complex organic pollutants.

Ultralow dielectric, fluoride-containing cyanate ester resins with improved mechanical properties and high thermal and dimensional stabilities

In this contribution, we present a new strategy for the fabrication of modified cyanate ester resins combined with ultralow dielectric properties, improved mechanical properties and high thermal and dimensional stabilities. The fluoride-containing compound 2-((3-(trifluoromethyl)phenoxy)methyl)oxirane (TFMPMO), synthesized from m-(trifluoromethyl)phenol (TFMP) and epichlorohydrin (ECH), was used to modify bisphenol A dicyanate ester (BADCy) resins via copolymerization reaction. The BADCy resin modified with 15 wt% TFMPMO presented ultralow dielectric constant (e, 2.75) and dielectric loss tangent values (tan δ, 6.7 × 10−3), high mechanical properties (impact strength of 15.4 kJ m−2 and flexural strength of 141.0 MPa), and superior thermal and dimensional stability (THeat-resistance index of 206 °C and coefficient of thermal expansion of 6.4 × 10−5), and it possesses great potential application in radomes and antenna systems of aircraft.

Reinforced Cyanate Ester Resins with Carbon Nanotubes: Surface Modification, Reaction Activity and Mechanical Properties Analyses

The reinforcement and toughness of cyanate ester (CE) resins with multiwalls carbon nanotubes (MW-CNTs) were investigated in this paper. Based on the surface modification of MW-CNTs, the reaction activity of CE resins, desperation of MW-CNTs, mechanical properties and thermal properties of MW-CNTs/CE composites were addressed. TEM and XRD analyses demonstrate that the MW-CNTs with regular arrangement and perfect crystals structures can be achieved after the treatments with pyrolysis and dense HNO3/H2SO4 acids oxidation. The reaction activity of CE systems with MW-CNTs is increased with the incorporation of carbon nanotubes. The mechanical analysis, dynamic mechanical analysis (DMA), and thermal gravimetric analysis (TGA) indicate that the addition of MW-CNTs can enhance both impact strength and flexural strength of cured CE resins without decreasing their thermal stability. The storage module for the MW-CNTs/CE composites is much higher than that of the pure CE sample in a wide temperature range. After aging in boiling distilled water, the water absorption of is less than that of CE resins.

Study on Preparation of SiO2/Epoxy Resin Hybrid Materials by Means of Sol-Gel

Silicon dioxide/epoxy resin hybrid material was prepared by means of Sol-Gel based on epoxy resin, tetraethyl orthosioate (TEOS), [H2N(CH2)3Si(OC2H5)3](KH-550), Methyltetrahydrophthalic anhydride (MeTHPA), dimethyl phthalate (DMP-30) and (HOCH2CH2)N. The contents of TEOS, KH-550 and reacting temperature influencing on the properties of hybrid materials were studied. The behaviors of the hybrid materials were characterized by differential scanning calorimentry (DSC), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Fourier transform-infrared ray (FT-IR) spectroscopy. The results showed that the properties of the material was optimal at approximately 3% TEOS, 2% KH-550, reacting at 60°C, and the mechanical and thermal properties were significantly improved compared with the pure epoxy resin. The dimension of SiO2 particles was about 20 nm, and distributed homogeneously in the system.

Hyperbranched polyborosilazane and boron nitride modified cyanate ester composite with low dielectric loss and desirable thermal conductivity

In this paper, we presented a new strategy for fabrication of polymeric composites combined with low dielectric loss and desirable thermal conductivity. With the incorporation of hyperbranched polyborosilazane (hb-PBSZ) into bisphenol A cyanate ester (BADCy) matrix, the modified hb-PBSZ/BADCy resin with 4 wt% hb-PBSZ possessed a low dielectric constant (å) value of 2.37 and relatively low dielectric loss tangent value of 0.008 at 1MHz. Furthermore, by integrating micrometer boron nitride particles (mBN) into hb-PBSZ/BADCy matrix, the mBN/hb-PBSZ/BADCy composites presented relatively low å of 3.09, desirable thermally conductive coefficient (λ of 0.63 W/(m·K)) and thermal diffusivity (α of 0.42 mm2/s) values. It provides an important perspective for designing dielectric and thermally conductive polymeric composites for electrical packaging and energy storage fields.

Fabrication of novel wave-transparent HMPBO fibre/BADCy laminated composites

The method of “impregnation–winding–lamination–mould pressing” was performed to fabricate novel wave-transparent high modulus poly(p-phenylene-2,6-benzobisoxazole) fibre/bisphenol A cyanate ester resin (HMPBO fibre/BADCy) laminated composites. The “two-step approach” of methanesulfonic acid/γ-glycidoxy propyl trimethoxy silane (MSA/KH-560) was also proposed to functionalize the HMPBO fibres’ surface. Results revealed that KH-560 was grafted on the HMPBO fibres’ surface successfully. The functionalized HMPBO fibre/BADCy laminated composites possessed better ILSS & flexural strength, lower e & tan δ, and higher heat-resistance index & Tg. The ILSS and flexural strength of the functionalized HMPBO/BADCy laminated composites were increased to 53.7 MPa and 753.7 MPa, respectively. The corresponding e and tan δ were decreased to 2.93 and 0.00097, respectively. The corresponding heat-resistance index and Tg were increased to 219 °C and 236 °C, respectively. The functionalized HMPBO fibre/BADCy laminated composites display potential application in radomes and the antenna systems of aircrafts.

Enhanced surface property of HMPBO fibers by using γ-aminopropyl triethoxy silane

The silane coupling agent of γ-aminopropyl triethoxy silane combined with ultrasonic vibration was employed to modify the surface of high modulus poly (p-phenylene-2, 6-benzobisoxazole) (HMPBO) fibers. The results showed that polar hydroxyl groups were successfully introduced on the HMPBO surface. The contact angles on HMPBO fibers both for water (θwater) and for glycol (θglycol) gradually were decreased, and the surface roughness of HMPBO fibers was also increased. Meanwhile, the single fiber pull-out strength of HMPBO was increased accordingly.

Synchronously improved dielectric and mechanical properties of wave-transparent laminated composites combined with outstanding thermal stability by incorporating iysozyme/POSS functionalized PBO fibers

Modified bisphenol A dicyanate ester (m-BADCy) wave-transparent laminated composites reinforced with functionalized poly(p-phenylene-2,6-benzobisoxazole) (f-PBO) fibers were fabricated using an optimized method of impregnation-winding followed by lamination-molding. m-BADCy was synthesized from copolymerization between (2-((3-trifluoromethyl)phenoxy)methyl)oxirane and the BADCy matrix. f-PBO fibers were obtained by modifying with lysozyme followed by polyhedral oligomericsilsesquioxane (POSS). Lysozyme was coated on the surface of PBO fibers (PBO@lysozyme) and polyhedral oligomericsilsesquioxane (POSS) was grafted onto the PBO@lysozyme fibers (POSS-g-PBO@lysozyme, f-PBO fibers). The dielectric constant (e), 2.81, and dielectric loss (tan δ), 0.0028, for f-PBO fiber/m-BADCy wave-transparent laminated composites were lower than those of PBO fiber/m-BADCy wave-transparent laminated composites (e = 2.91 and tan δ = 0.0043). The interlaminar shear strength (ILSS) and the flexural strength of the f-PBO fiber/m-BADCy wave-transparent laminated composites were significantly increased to 47.6 and 805.8 MPa, increased by 23.0% and 33.5% in comparison to those of PBO fiber/m-BADCy wave-transparent laminated composites (ILSS = 38.7 MPa and flexural strength = 603.5 MPa), respectively. In addition, the corresponding heat resistance index (THRI, representing thermal stability) and glass transition temperature (Tg) of the f-PBO fiber/m-BADCy wave-transparent laminated composites were 228.3 and 252.1 °C, respectively.

Fabrication and properties of BADCy modified by epoxy-capped polyhedral oligomeric silsesquioxane

Epoxy-capped polyhedral oligomeric silsesquioxane (EP-POSS) is performed to modify bisphenol A cyanate ester (BADCy) to regulate its dielectric constant and thermal resistance. EP-POSS can be incorporated in the cross-linked network of BADCy via covalent bonds, which catalyzes BADCy self-polymerization to decease the initial temperature of forming triazine rings. EP-POSS is distributed in the BADCy matrix uniformly and there is no aggregation and phase separation between EP-POSS and BADCy matrix at a micrometer scale. The dielectric constant values of EP-POSS/BADCy are decreased with the addition of EP-POSS, but increased slightly when the mass fraction of the EP-POSS is more than 2 wt%. The thermal resistance of EP-POSS/BADCy is increased slightly with the addition of EP-POSS.