| Since the advent of carbon fiber,its outstanding properties such as high specific strength,high specific modulus and high temperature resistance have attracted much attention.During the preparation of composite materials,the reaction between carbon fiber and matrix materials will cause the degration of carbon fiber,which cannot give full play to the excellent properties of fibers.Carbon coating on the surface of carbon fibers can inhibit the damage of carbon fiber,and regulate the interface between fiber and matrix.According to the high cost and long production cycle of the traditional carbon coating process,this paper puts forward a method that uses cheap glucose as a carbon source to achieve the preparation of carbon fiber carbon coating by simple and operable hydrothermal reaction,which has the advantages of low cost,short production cycle and environmental protection.Therefore,it is of great significance to study the preparation of carbon coating by hydrothermal reaction of glucose.In the process of hydrothermal reaction,the solution p H value,reaction temperature,reaction time,solution concentration and reaction times have important influence on the coating quality.When the p H value was greater than 3,there were spherical adhesion on the surface of the coating.When p H value was 7,the coating thickness was about 200 nm,and the sphere size was about 900 nm.When the p H value was less than 2,the coating was smooth and continuous and the thickness of the coating was about 1 ?m.The threshold of reaction time and reaction temperature had been revealed.The thickness of the coating was controlled in the light of the need.When the solution concentration increased from 6 wt.% to 30 wt.%,the coating thickness was gradually increased to 1.7 ?m.After five times of reaction,the coating thickness was increased to 3 ?m.The physical and chemical properties of the solid and liquid products were studied after the reaction.The mechanism was revealed that the strong acid condition catalyzed the isomerization of glucose to fructose and further promoted the conversion of fructose to 5-hydroxymethyl furfural.The relationship between the growth of nuclei and the growth of the coating in the hydrothermal reaction was established.When the p H value of glucose solution was 1,multiple nucleation occured in the reaction.When heterogeneous carbon fibers existed,heterogeneous nucleation and growth was more likely to occur,resulting in a smooth coating.When the p H value is 7,single nucleation occured.It is difficult to give priority to the heterogenous nucleation,resulting in spherical adhesion on the surface of the coating,whose component was the same as the the coating.The composition of the coating was studied indirectly through hydrothermal solid products.The hydrothermal solid product was consisted of the main structure of poly 5-hydroxymethyl furfural with embedded levulinic acid,which did not contain any free carbon structure.Elemental analysis showed that the carbon content increased from 40 wt.% to 67.94 wt.% after reaction,and its surface carbon content was greater than internal.The carbon content increased with the increase of hydrothermal reaction time and temperature,and decreased with the increase of glucose concentration.In the heat treatment process,the hydrothermal solid phase products showed two obvious weight loss intervals of 130 °C-250 °C,250 °C-750 °C,and the total residual mass was 47.1%.The coating exhibited uniform shrinkage and no damage during heat treatment.Structural analysis showed that organic matter changed to a free carbon structure,and its carbon content and graphitization degree increased with the increase of treatment temperature. |
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