纤维素/氧化石墨烯复合气凝胶的制备及其阻燃性能研究
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摘要
为了提高纤维素气凝胶的阻燃性能,用具有阻隔效应和催化成碳能力的氧化石墨烯(GO)作为阻燃剂,通过简单的冷冻干燥的方法制备了具有阻燃功能的纤维素/GO复合气凝胶。结果表明,GO在纤维素黏液中的最佳添加量是5%(质量分数,下同);在此条件下,GO在纤维素中分散良好,可以形成有序的三维多孔气凝胶结构;GO和纤维素之间的作用力为氢键;在最佳添加量条件下,G5C95气凝胶始终处于阴燃状态,其燃烧速率从纯的纤维素气凝胶的5.67 mm/s降低为0.57 mm/s;相对于纯的纤维素气凝胶,GO阻燃纤维素气凝胶的峰值热释放速率减少了57.7%,总热释放量也明显降低,显示出较好的阻燃性能;相对于纯的纤维素气凝胶,GO阻燃气凝胶的残炭更加致密;GO提高了残炭的石墨化程度;由于GO的物理屏障效应和催化成碳能力,其不仅能增加残碳量,而且能提高残碳致密度和石墨化程度,从而有效提高纤维素气凝胶的阻燃性能。
To improve the flame retardancy of cellulose aerogels, graphene oxide(GO) nanosheets were employed as a flame retardant to prepare cellulose/GO composite aerogels by a simple freeze-drying method. Scanning electron microscopy implied that the optimum dosage of GO was 5 wt %in cellulose mucus, and GO was well dispersed in cellulose to form ordered three-dimensional porous aerogels under this condition. X-ray photoelectron spectrometry confirmed that the interaction between GO and cellulose was due to hydrogen bonding. The composite aerogels were well flame-retarded by GO at an optimum dosage of 5 wt %, and their combustion rate decreased to 0.57 mm/s from 5.67 mm/s of pure cellulose aerogel. Micro cone calorimetric resultsindicated that the peak heat release rate of the composite aerogelsdecreased by 57.7 % at the optimum dosage of GO compared to that of pure cellulose aerogel, suggesting a good flame-retardant effect. Theresidual char of the composite aerogels was found to become denser than that of cellulose aerogel, and their graphitization degree was enhanced due to the incorporation of GO nanosheets. In summary, the char yield of the composite aerogels was improved and their density and degree graphitization were enhanced due to the physical barrier effect and the catalytic charring capability of GO. As a result, the flame retardancy of the cellulose aerogels was improved effectively.
To improve the flame retardancy of cellulose aerogels, graphene oxide(GO) nanosheets were employed as a flame retardant to prepare cellulose/GO composite aerogels by a simple freeze-drying method. Scanning electron microscopy implied that the optimum dosage of GO was 5 wt %in cellulose mucus, and GO was well dispersed in cellulose to form ordered three-dimensional porous aerogels under this condition. X-ray photoelectron spectrometry confirmed that the interaction between GO and cellulose was due to hydrogen bonding. The composite aerogels were well flame-retarded by GO at an optimum dosage of 5 wt %, and their combustion rate decreased to 0.57 mm/s from 5.67 mm/s of pure cellulose aerogel. Micro cone calorimetric resultsindicated that the peak heat release rate of the composite aerogelsdecreased by 57.7 % at the optimum dosage of GO compared to that of pure cellulose aerogel, suggesting a good flame-retardant effect. Theresidual char of the composite aerogels was found to become denser than that of cellulose aerogel, and their graphitization degree was enhanced due to the incorporation of GO nanosheets. In summary, the char yield of the composite aerogels was improved and their density and degree graphitization were enhanced due to the physical barrier effect and the catalytic charring capability of GO. As a result, the flame retardancy of the cellulose aerogels was improved effectively.
引文
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[3] ZHENG Q F, CAI Z Y, MA Z Q, et al. CelluloseNanofibril/Reduced Graphene Oxide/Carbon Nanotube HybridAerogels for Highly Flexible and All-solid-stateSupercapacitors[J]. ACS Applied Materials & Interfaces, 2015, 7(5): 3 263-3 271.
[4] WANG Y G, YADAV S, HEINLEIN T, et al. Ultra-light Nanocomposite Aerogels of Bacterial Cellulose and Reduced Graphene Oxide for Specific Absorption and Separation of Organic Liquids[J]. RSC Advances, 2014, 4(41): 21 553-21 558.
[5] CHONG K Y, CHIA C H, ZAKARIA S, et al. CaCO3-decorated Cellulose Aerogel for Removal ofCongo Red from Aqueous Solution[J]. Cellulose, 2015, 22(4): 2 683-2 691.
[6] XIONG R, LU C H, WANG Y R, et al. Nanofibrillated Cellulose as the Support and Reductant for the Facile Synthesis of Fe3O4/Ag Nanocomposites with Catalytic and Antibacterial Activity[J]. Journal of Materials Chemistry A, 2013, 1(47): 14 910-14 918.
[7] WANG L, SANCHEZ-SOTO M. Green Bio-based Aerogels Prepared from Recycled Cellulose Suspensions[J]. RSC Advances, 2015, 5(40): 31 384-31 391.
[8] GUO L M, CHEN Z L, LYU S Y, et al. Highly Flexible Cross-linked Cellulose Nanofibril Sponge-like Aerogels with Improved Mechanical Property and Enhanced Flame Retardancy[J]. Carbohydrate Polymers, 2018, 179: 333-340.
[9] YANG L, MUKHOPADHYAY A, JIAO Y C, et al. Ultralight, Highly Thermally Insulating and Fire Resistant Aerogel by Encapsulating Cellulose Nanofibers with Two-dimensional MoS2[J]. Nanoscale, 2017, 9(32): 11 452-11 462.
[10] HAN Y Y, ZHANG X X, WU X D, et al. Flame Retardant, Heat Insulating Cellulose Aerogels from Waste Cotton Fabrics by In Situ Formation of Magnesium Hydroxide Nanoparticles in Cellulose Gel Nanostructures[J]. ACS Sustainable Chemistry & Engineering, 2015, 3(8): 1 853-1 859.
[11] YUAN B, ZHANG J M, MI Q Y, et al. Transparent Cellulose-silica Composite Aerogels with Excellent Flame Retardancyvia In Situ Sol-gel Process[J]. ACS Sustainable Chemistry & Engineering, 2017, 5: 11 117-11 123.
[12] SANG B, LI Z W,LI X H, et al. Graphene-based Flame Retardants: A Review[J].Journal of Materials Science, 2016, 51:8 271-8 295.
[13] HUANG G B, GAO J R, WANG X, et al. How can graphene reduce the flammability of Polymer Nanocomposites?[J]. Materials Letters, 2012, 66(1): 187-189.
[14] LIU S, YANH Q, FANG Z P, et al. Effect of Graphene Nanosheets on Morphology, Thermal Stability AndFlame Retardancyof Epoxy Resin[J]. Composites Science Technology, 2014, 90(10):40-47.
[15] BAOC L, GUO Y Q, YUAN B H, et al. Functionalizaed Graphene Oxide for Fire Safety Applications of Polymers: a Combination of Condensed Phase Flame Retardant Strategies[J]. Journalof Materials Chemistry, 2012, 22:23 057-23 063.
[16] JIANGS D, BAIZ M, TANG G, et al. Fabrication of Ce-doped MnO2 Decorated Graphene Sheets for Fire Safety Applications of Epoxy Composites: Flame Retardancy, Smoke Suppression and Mechanism[J]. Journal of Materials Chemistry A, 2014, 2:17 341-17 351.
[17] YANG C Z, LI Z W, YU L G, et al. Mesoporous Zinc Ferrite Microsphere-decorated Graphene Oxide as a Flame Retardant Additive: Preparation, Characterization, and Flame Retardance Evaluation[J]. Industrial & Engineering Chemistry Research, 2017, 56:7 720-7 729.
[18] LIU G Y, SANG B, ZHOU Z Q, et al. Platinum-dopedTitanate Nanotubes/Reduced Graphene Oxide: Photocatalytic Activity and Flame Retardancy[J]. Materials Research Express, 2018, 015018.
[19] SANG B, LI Z W, LI X H, et al. Titanate Nanotubes Decorated Graphene Oxide Nanocomposites: Preparation, Flame Retardancy, and Photodegradation[J].Nanoscale Research Letters, 2017, 12:441.
[20] GAO T T, CHEN L C, LI Z W, et al. Preparation of zinc Hydroxystannate-decorated Graphene Oxide Nanohybrids and Their Synergistic Reinforcement on Reducing Fire Hazards of Flexible Poly (vinyl chloride)[J]. Nanoscale Research Letters, 2016, 11: 192.
[21] HUMMERS W S, OFFEMAN R E. Preparation of Graphitic Oxide[J]. Journal of the American Chemical Society, 1958, 80(6): 1 339-1 339.