Preparation And Properties Of Cellulose/Graphene Composites

With the development of the polymer synthetic industry, lots of environmental issues come into beings, such as white pollution, air and water pollution, which threat the existence of human being, have attracted more and more concerns. Making effective use of natural polymer may be a good way to prevent and finally solve these environmental issues. In our work, we focus on cellulose, which is from a wide variety of sources and can be easily dissolved in aqueous solution. By the addition of graphene with high electrical and thermal conductivity during dissolution, we can obtain cellulose/graphene composites. Polyethylene glycol (PEG) can be impregnated into cellulose/graphene aerogels to form phase change materials with good shape stability, high thermal conductivity, and large latent heat. Details are as follows:Firstly, we use the alkali/urea aqueous system to dissolve cellulose, and successfully prepare a three-dimensional cellulose/graphene oxide (GO) hydrogel by addition of graphene oxide. Ascorbic acid is used to reduce cellulose/GO hydrogel, and the cellulose/reduced GO (RGO) hydrogel with both good mechanical properties and high electrical conductivity is obtained. The cellulose/graphene conductive hydrogel is immersed into aqueous solution of PEG 200, and the water contained in the hydrogel is partially replaced by PEG 200. The resulting hydrogel maintains its high electrical conductivity and has a substantial increase of compressive strength. Also, the compressive strength of this hydrogel can be easily controlled by changing the concentration of PEG 200 aqueous solution.Secondly, through above method, we further increase the content of RGO in cellulose/RGO hydrogel. The water contained in hydrogel is fully replaced with PEG 1000 to fabricate a PEG/cellulose/RGO three-dimensional phase change composite. Due to the strong hydrogen bonds between cellulose and PEG, this obtained three-dimensional composite has excellent shape stability. The addition of graphene also improves thermal conductivity of the composite to accelerate rate of heat transfer.Thirdly, we replace RGO in PEG/cellulose/RGO hydrogel by high-quality graphene nanoplatelets (GNPs), which was reduced under 2800℃. When compared to RGO, these GNPs have fewer defects and higher thermal and electrical conductivity. So these GNPs are used to improve the thermal properties of PEG/cellulose/GNP phase change composite. In addition, cellulose/GNP aerogel fabricated by freeze-drying is easily filled with a high loading of PEG 6000 through vacuum assisted impregnation. The obtained PEG 6000/cellulose/GNP composites have a larger latent heat than PEG 1000/cellulose/RGO composite, due to the larger intrinsic latent heat and higher loading of PEG 6000. Therefore, we have prepared a PEG/cellulose/GNP phase change composite with both excellent shape stability, large latent heat and high thermal conductivity.