Preparation,Modification And Properties Of Phenolic-based Activated Carbon Fibers

Phenolic fiber is an organic fiber with excellent properties such as good heat resistance,low toxicity,smoke-free,flame retardant and chemical resistance.It is widely used in aerospace and other military industries and the raw materials with special requirements.In addition,phenolic fibers are ideal precursors for the preparation of activated carbon fibers because of their high char yield,low density,and high porosity.However,domestic phenolic fibers mainly rely on imports.Although many researchers are studying related aspects of phenolic fibers,there is still some way to go before the industrial production of phenolic fibers in China.In this dissertation,the phenolic fiber was prepared by melt-spinning with novolac as raw material,and the phenolic-based activated carbon fiber with high specific surface area was obtained through curing,carbonization and activation.The factors affecting the degree of cross-linking of phenolic fibers in the spinning process and the curing process of preparing phenolic fibers were studied and analyzed,and better process conditions were obtained;the modification of nano-Al₂O₃ and nano-SiO₂ was performed on phenolic fibers;The properties of the obtained phenolic activated carbon fiber were studied and analyzed.The main conclusions are as follows:?1?The thermodynamic properties and molecular structure of the phenolic resin before and after spinning are not changed;the best process conditions for the curing of the phenolic fiber are:the solidified solution is composed of an aqueous solution of 18.5%formaldehyde and 15%hydrochloric acid,and the heating rate At 20°C/h,a solid-to-liquid ratio of 1:50 and a curing temperature of100°C,the resulting cross-linked unmodified phenolic fibers had a carbon residue of 68.8%and a tensile strength of up to 225 MPa.After activation,the surface of the phenolic fibers becomes rough,resulting in an infinite number of uniformly distributed pores,and the morphology of the fibers still maintains the original fibrous shape of the fibers.The specific surface area of direct carbonization of phenolic fibers is as high as 410 m²·g^-1.When the activation time is 90min,the corresponding specific surface area reaches 2160 m²·g^-1.?2?The doping of nano-Al₂O₃ into phenolic fibers can increase the curing efficiency to a certain extent,so that the degree of cross-linking of cured phenolic fibers is higher,and the thermal stability and residual carbon content of the fibers are improved.With the different content of nano-Al₂O₃ doped,the residual carbon and tensile strength of the fiber have improved to varying degrees.When the content of nano-Al₂O₃ was 1.5%,the residual carbon ratio of phenolic fibers reached 66.40%,the residual carbon ratio increased by 13.6%compared with pure phenolic fibers,and the tensile strength of the fibers reached 201 MPa,an increase of 6.91 MPa.The specific surface area of carbon fibers prepared by carbonization of nano-Al₂O₃ modified phenolic fibers was as high as 630 m2/g,and the specific surface area of unmodified phenolic carbon fibers was increased by 53.6%,the average pore diameters were 0.86 nm and0.85 nm,and the activation time was 90 minutes.The specific surface areas of the phenolic-based activated carbon fibers before and after the modification were as high as 2160 m²·g^-1 and 2410 m²·g^-1,and the pore diameters were1.01 nm and 1.02nm,respectively.?3?Nano-SiO₂ modified phenolic fibers The hydroxyl groups in the hydroxyl-modified nano-SiO₂ will undergo condensation reaction with the phenolic hydroxyl groups in the phenolic aldehyde molecules,so that the resulting phenolic fiber precursor has better stability in the air,and is not easy to It is oxidized and discolored;when the nano-Si O₂ doping content is 2%,the residual carbon content of the fiber is 62.4%,which is increased by 17.9%,and the strength reaches 205MPa;when the activation time is 90 min,the phenolic-based activated carbon fiber before and after the nano-SiO₂modification is obtained.The specific surface area of 2160 m²·g^-1 and 2430 m²·g^-1 respectively increased the specific surface area by 270 m²·g^-1.