Preparation And Properties Of Micro/nano Aramid Fiber Paper-based Composites

High-performance aramid fiber paper-based material is prepared from aramid chopped fibers and aramid pulp fibers/aramid fibrids by papermaking wet-forming technology,which have good chemical and thermal stability,excellent dielectric properties,high specific strength and modulus,and good reprocessing design,etc.It has great application potential in the fields of communication,aerospace,transportation,electrical and electronic,defense and military,etc.However,due to the smooth surface and extremely low surface chemical activity of aramid fibers,it is difficult to disperse uniformly them in aqueous medium,making it difficult to obtain a paper with good uniformity and strength,which seriously limits the application of aramid paper.Para-aramid nanofibers(PANFs)have prominent properties such as nano-morphology,high strength and stiffness,high specific surface area and excellent thermal stability.The DMAc(N,N-dimethylacetamide)/LiCl solution is a remarkable solution system,which can dissolve meta-aramid fibers efficiently.In this work,we firstly modified the aramid fiber with a coupling agent to increase the surface activity to maximize the formation of the original aramid paper.Then PANFs and DMAc/LiCl solution systems were introduced to improve the mechanical properties of aramid papers.The main research contents and important results are as follows:(1)Preparation of high performance gradient structure nano-aramid paper matrix composites.That is,the micron-sized para-aramid paper were reinforced by para nano-aramid fibers(PANFs)assisted by vacuum filtration.PANFs were loaded into the structure of paper thickness direction and distributed gradiently in the paper structure.The PANFs were electrostatic flocculated by adding a certain amount of DMDAAC solution to PANFs dispersion during vacuum filtration,which greatly reduced the filtration time from 20 hours and 30 minutes to 1 hour and 10 minutes.The obtained gradient structure nano-aramid paper has compact structure and tight bonding between fibers,and the tensile strength reaches 43.7MPa,which is 36.7 times higher than that of the base paper,and the specific strength and fracture energy are increased by 14.1 times and 78.0 times,respectively,compared with the original paper.(2)"Partial dissolution-regeneration welding"to prepare high-performance para/meta-aramid composite paper.That is,the DMAc/LiCl dissolution system is introduced to dissolve the meta-aramid,and the meta-aramid is dissolved and gradually filled in the paper structure.When it is regenerated,it has a better coating effect on the para-aramid fiber and fills most of the pores in the paper,so that the paper has a certain water resistance.The results of FT-IR analysis show that the paper has stronger hydrogen bonding between the fibers after strengthening,and the dry tensile strength,wet tensile strength,specific strength,interlayer bonding strength(ILSS)and folding resistance of the paper are 76.6 MPa,41.0MPa,139210 m~2/s~2,1096.3 J/m~2 and 732 times,respectively,which have increased by 2.2times,5.5 times,2.1 times,9.4 times and 34.7 times compared with the hot-pressed original paper.(3)"Partial dissolution-regeneration welding method"to prepare high-performance micro/nano-aramid fiber composite paper.On the basis of the above-mentioned enhancement method,PANFs with partial hydrogen protonation were introduced into the slurry system to prepare high-performance micro/nano-aramid fiber composite paper,and the influence of the amount of PANFs on the mechanical properties of the paper was studied.The results showed that the average tear index(47.8 mN·m~2/g)and ILSS(126.4 J/m~2)of hot-pressed original paper were the highest when the amount of PANFs was 8%,which increased by 41.6%and19.8%respectively compared with those of papers without PANFs,and the average tensile strength of paper was 37.8 MPa,which increased by 56.7%,only slightly less than that of paper with 10%PANFs(39.6 MPa).Subsequently,high performance micron/nano aramid fiber composite paper was obtained by partial dissolution-regeneration welding.The tensile strength of the paper reached 78.3 MPa,but the tear strength was lower than before.The three reinforcement methods adopted in this paper can effectively enhance the mechanical properties of aramid paper.The obtained paper has very excellent ultimate strength and specific strength,but also maintains good flexibility,and has a certain water resistance,which provides a new idea for the preparation of micro-nano aramid fiber paper-based composites with excellent properties.