High Performance Aramid Fibers With High Surface Activity And UV-resistance Through Layer-by-layer Self-assembly Technique

Aramid fiber?AF?is a kind of high-tech organic synthetic fiber,which has a broad application prospect in a variety of cutting-edge fields beacuse of its excellent comprehensive properties?such as ultrahigh strength and modulus,impact resistance,light weight,etc.?.Low surface activity and poor ultraviolet?UV?resistance are two inherent disadvantages of AFs.To overcome the two bottlenecks,our researches reported in this thesis aim to construct a new kind of AFs with high surface activity,heat-resistance and UV-resistance.The specific research contents are divided into two parts.?1?Study on self-assembled AF with MgAlFe LDH and SiO₂Layered double hydroxide?LDH?containing Mg,Al and Fe ions was synthesized through a solvothermal method,and positively charged inorganic nanosheets?LDH-NS?were prepared by an exfoliation process.A new kind of modified aramid fiber?n BL-AF,n is the number of layers?with specific surface structure?inorganic nanosheets/inorganic nanoparticles?was constructed through a simple and green layer-by-layer self-assembly method using SiO₂ colloidal dispersion as negative charge source.The effect of layer number on the structure and properties of BL-AF was systematically studied.Results show that the structure and properties of BL-AF can be controlled by adjusting the number of self-assembly.Compared with AF,nBL-AF?n?3?fibers have significantly improved surface activity,heat resistance,mechanical properties and UV resistance.This is due to the high strength,high heat resistance and excellent UV absorption of LDH and SiO₂.Typically,for 3BL-AF,its initial thermal decomposition temperature(T_di)is increased by about 92°C,its tensile strength,energy to break,modulus,elongation at break are increased by 12%,13%,11%,5%,respectively;the retentions of tensile properties of3BL-AF under 168 h UV irradiation are as high as 91-95%while the retention of AF is only 62-81%.In addition,the surface free energy of BL-AF increases with the increase of self-assembly number,and the surface free energy of 9BL-AF reaches the maximum,about1.8 times of that of AF.?2?Study on self-assembled AF with SiO₂By using the positive charge of SiO₂ aqueous solution?Ludox-CL?and the negative charge of SiO₂,inorganic nanoparticles/inorganic nanoparticles multilayers were fabricated on the surface of AF through layer-by-layer self-assembly,namely a new modified aramid fiber?BL-AFp?.The self-assembly process does not involve the use of organic solvents,and this is completely green.Prior to self-assembly,dopamine modified AF is used to introduce reactive groups?-OH,-NH₂?without destroying structure and properties of AF.FTIR,SEM and EDX were used to track the self-assembly process,and the effect of self-assembly number on the structure and properties of BL-AFp were studied.Results show that the n BL-AFp?n?5?fibers have improved surface activity,heat resistance,mechanical properties and UV resistance,which are equivalent with the integrated performances of n BL-AF?n?3?.Indicating that in the premise of using dopamine instead of phosphoric acid modified AF,the performances of inorganic nanoparticles/inorganic nanoparticles modified fibers can achieve the equivalent extent with those of inorganic nanosheets/inorganic nanoparticles modified fibers.