Yongqiang Guo

Significantly enhanced and precisely modeled thermal conductivity in polyimide nanocomposites with chemically modified graphene via in situ polymerization and electrospinning-hot press technology

Both aminopropylisobutyl polyhedral oligomeric silsesquioxane (NH2-POSS) and hydrazine monohydrate were utilized to functionalize graphene oxide (GO), and to obtain chemically modified graphene (CMG), which was then used for preparing thermally conductive CMG/polyimide (CMG/PI) nanocomposites via a sequential in situ polymerization and electrospinning-hot press technology. NH2-POSS molecules were grafted on the GO surface, and CMG was obtained by the reaction between NH2-POSS and GO. The thermal conductivity coefficient (λ), glass transition temperature (Tg) and heat resistance index (THRI) of the prepared CMG/PI nanocomposites were all increased with increasing the CMG loading. The λ value of the CMG/PI nanocomposites with 5 wt% CMG was significantly improved to 1.05 W m−1 K−1, about 4 times higher than that of the pristine PI matrix (0.28 W m−1 K−1). The corresponding Tg and THRI values were also increased to 213.0 and 282.3 °C, respectively. Moreover, an improved thermal conductivity model was proposed and predicted the λ values of the nanocomposites more precisely than those obtained from the typical Maxwell, Russell and Bruggemen classical models.

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.

A review on thermally conductive polymeric composites: classification, measurement, model and equations, mechanism and fabrication methods

AbstractWith the fast-developing miniaturization and integration of microelectronics packaging materials, ultrahigh-voltage electrical devices, light-emitting diodes (LEDs), and in areas which require good heat dissipation and low thermal expansion, the investigations on the polymeric composites with highly thermal conductivities and excellent thermal stabilities are urgently required, which would be beneficial to transferring the heat to the outside of the products, finally to effectively avoid substantial overheating and prolong their working life. Our article reviews recent progress in the classification, measurement methods, model and equations, mechanisms, commonly used thermally conductive fillers, and the correlative fabrication methods for the thermally conductive polymeric composites, aiming to understand and grasp how to enhance the λ value effectively. And future perspectives, focusing scientific problems and technical difficulties of the present thermally conductive polymeric composites are also described and evaluated. Graphical abstractThermally conductive polymeric composites: classification, measurement, model and equations, mechanism and fabrication methods.

Novel Reusable Porous Polyimide Fibers for Hot-oil Adsorption

The development of oil sorbents with high thermal stability, adsorption capacity, reusability and recoverability is of great significance for hot oil leakage protection, especially for oil spillage of oil refinery, petrochemical industry and cars. In our work, highly efficient hot oil adsorption of polyimide (PI) fibers with excellent thermal stability was successfully prepared by a facile electrospinning method followed by post-treatment. The corresponding morphologies, structures and oil adsorption properties of as-prepared PI fibers at different temperatures were analyzed and characterized. Results showed that PI fibers presented a stable morphology and pore structure at 200°C. The oil adsorption capacity of porous PI fibers for hot motor oil (200°C) was about 57.4gg-1, higher than that of PI fibers (32.7gg-1) with non-porous structure for the motor oil at room temperature. Even after ten adsorption cycles, porous PI fibers still maintained a comparable oil sorption capacity (oil retention of 4.2%). The obtained porous PI fibers exhibited excellent hot oil adsorption capacity, reusability and recoverability, which would broaden the application of electrospun fibers in oil spill cleanup and further provide a versatile platform for exploring the technologies of nanofibers in hot oil adsorption field.