Biobased urea nowadays attracts increasing attention as a biomass resource with giant potential,which benefits from the development of biobased ammonia and ecological sanitation system.Urea is an ideal feedstock for c...Biobased urea nowadays attracts increasing attention as a biomass resource with giant potential,which benefits from the development of biobased ammonia and ecological sanitation system.Urea is an ideal feedstock for chemical industry and developing new urea-based polymer materials can take advantage of the urea resource.In this work,a class of renewable linear polyesters,namely polyisocyanuratoesters(PICEs)were synthesized from a urea-based monomer bis(2-carbomethoxyethyl)isocyanurate and biobased aliphatic diols.Compared with conventional aliphatic polyesters,PICEs containing isocyanurate rings in the polymer chain backbone exhibit outstanding flame retardancy that both PICE-4(the number‘4’refers to the number of methylene in diols,e.g.4 for butylene and 6 for hexylene)and PICE-6 have high limiting oxygen index values over 30%.In the UL 94 tests,PICE-6 reaches V-1 rating;while V-2 is found for PICE-10.All PICEs exhibit similar pyrolysis behavior that the temperatures of 5%weight loss are around 320°C.PICEs are found to have glass transition among 20°C-45°C.No crystallization behavior is observed without annealing except for PICE-10,which can crystallize even at room temperature.展开更多
Despite recent progress in the synthesis and application of graphene-based aerogels, some challenges such as scalable and cost-effective production, and miniaturization still remain, which hinder the practical applica...Despite recent progress in the synthesis and application of graphene-based aerogels, some challenges such as scalable and cost-effective production, and miniaturization still remain, which hinder the practical application of these materials. Here we report a large-scale electrospinning method to generate graphene-based aerogel microspheres （AMs）, which show broadband, tunable and high-performance microwave absorption. Graphene/Fe3O4 AMs with a large number of openings with hierarchical connecting radial microcharmels can be obtained via electrospinning-freeze drying followed by calcination. Importantly, for a given Fe3O4：graphene mass ratio, altering the shape of aerogel monoliths or powders into aerogel microspheres leads to unique electromagnetic wave properties. As expected, the reflection loss of graphene/Fe3O4 AMs-1：1 with only 5 wt.% absorber loading reaches -51.5 dB at 9.2 GHz with a thickness of 4.0 mm and a broad absorption bandwidth （RL 〈-10 dB） of 6.5 GHz. Furthermore, switching to coaxial electrospinning enables the fabrication of SiO2 coatings to construct graphene/Fe3O4@SiO2 core-shell AMs. The coatings influence the electromagnetic wave absorption of graphene/Fe3O4 AMs significantly. In view of these advantages, we believe that this processing technique may be extended to fabricate a wide range of unique graphene-based architectures for functional design and applications.展开更多
基金The authors are grateful for the financial supports of the National Science Foundation of China(21404040)the Fundamental Research Funds for the Central Universities(2015ZM053)the State Key Laboratory of Pulp and Paper Engineering(201538).
文摘Biobased urea nowadays attracts increasing attention as a biomass resource with giant potential,which benefits from the development of biobased ammonia and ecological sanitation system.Urea is an ideal feedstock for chemical industry and developing new urea-based polymer materials can take advantage of the urea resource.In this work,a class of renewable linear polyesters,namely polyisocyanuratoesters(PICEs)were synthesized from a urea-based monomer bis(2-carbomethoxyethyl)isocyanurate and biobased aliphatic diols.Compared with conventional aliphatic polyesters,PICEs containing isocyanurate rings in the polymer chain backbone exhibit outstanding flame retardancy that both PICE-4(the number‘4’refers to the number of methylene in diols,e.g.4 for butylene and 6 for hexylene)and PICE-6 have high limiting oxygen index values over 30%.In the UL 94 tests,PICE-6 reaches V-1 rating;while V-2 is found for PICE-10.All PICEs exhibit similar pyrolysis behavior that the temperatures of 5%weight loss are around 320°C.PICEs are found to have glass transition among 20°C-45°C.No crystallization behavior is observed without annealing except for PICE-10,which can crystallize even at room temperature.
基金This work was financially supported by the National Natural Science Foundation of China （No. 51573149）, the Science and Technology Planning Project of Sichuan Province （No. 2016GZ0224）, the Fundamental Research Funds for the Central Universities （No. 2682016CX069） and the Student Research Training Program （No. 2017005）.
文摘Despite recent progress in the synthesis and application of graphene-based aerogels, some challenges such as scalable and cost-effective production, and miniaturization still remain, which hinder the practical application of these materials. Here we report a large-scale electrospinning method to generate graphene-based aerogel microspheres （AMs）, which show broadband, tunable and high-performance microwave absorption. Graphene/Fe3O4 AMs with a large number of openings with hierarchical connecting radial microcharmels can be obtained via electrospinning-freeze drying followed by calcination. Importantly, for a given Fe3O4：graphene mass ratio, altering the shape of aerogel monoliths or powders into aerogel microspheres leads to unique electromagnetic wave properties. As expected, the reflection loss of graphene/Fe3O4 AMs-1：1 with only 5 wt.% absorber loading reaches -51.5 dB at 9.2 GHz with a thickness of 4.0 mm and a broad absorption bandwidth （RL 〈-10 dB） of 6.5 GHz. Furthermore, switching to coaxial electrospinning enables the fabrication of SiO2 coatings to construct graphene/Fe3O4@SiO2 core-shell AMs. The coatings influence the electromagnetic wave absorption of graphene/Fe3O4 AMs significantly. In view of these advantages, we believe that this processing technique may be extended to fabricate a wide range of unique graphene-based architectures for functional design and applications.
