Study On The Improvement Of Aramid Nanofibers On The UV Aging Resistance Of Aramid Paper-Based Materials

Aramid paper-based materials are blended from aramid chopped fibers and fibrids.Due to their characteristics of light specific gravity,high specific strength and stiffness,strong impact resistance,excellent insulation and thermal stability,aramid paper-based materials have been widely used in aerospace,rail transit,national defense and military fields,and have become an important national strategic material.However,in the process of using aramid paper-based materials,due to the photoaging behavior of aramid fiber,the durability of the aramid fiber in a long time outdoor environment decreases sharply,which greatly reduces the service life of the paper-based materials and also restrictes their further development.Therefore,it is urgent to improve the UV aging resistance of aramid paper-based materials.Aramid nanofiber(ANF),as a polymer nanofiber that has been developing rapidly in recent years,has the dual advantages of high-performance aramid fiber and nanofiber.Compared with the macroscopic aramid fibers,aramid nanofibers have better UV absorption property and surface activity.Therefore,the introduction of aramid nanofibers into the paper-based materials is expected to improve their UV aging resistance.Firstly,the para-aramid fibers were dissolved in DMSO/KOH/H2O system to prepare ANF.Then,ANF was compounded with para-aramid fiber and meta-aramid fiber respectively by vacuum-assisted filtration method,to explore the effect of ANF on improving the UV aging resistance of the two fibers.The results showed that after a long period of ultraviolet radiation(168h),the surface showed accumulation of fine particles,and some nano-scale pores appeared on the surface.The tensile strength and modulus of ANF paper were reduced from 207.19 MPa and 5.26 GPa to 164.59 MPa and 4.02 GPa,respectively.The retention rates of these values reached 79.37%and 76.43%respectively,which proved the good UV aging resistance.Further results showed that the addition of ANF can improve the UV aging resistance performance of meta and para-aramid paper-based materials.However,in the compounding process,due to the higher rigidity and lower amide bond activity of the para-chopped fiber than the meta fiber,the dispersibility of the para-chopped fiber in the ANF solution was relatively poor.When the content of para-chopped fiber in the materials exceeds 20 wt.%,the fibers were obviously flocculated inside the paper-based materials;thus,the maximum content of meta-chopped fibers in the materials could reach 60 wt.%.Secondly,the para-aramid chopped fiber was impregnated with ANF solution to coat the surface of the chopped fiber with ANF.By controlling the impregnation time of ANF,it was found that when the impregnation time was 10 minutes,the single-filament tensile strength of the fiber reached the best value(1.44 GPa),which was 30.91%higher than the original chopped fiber.The ultraviolet accelerated aging test was performed on the fiber,it was found that after 168 h of UV radiation,the strength retention rate of ANF coated fiber could reach 50.69%,which was 17.96%higher than the original fiber.These results indicated that this simple treatment method could effectively improve the mechanical properties and UV aging resistance of a single chopped fiber.In addition,by using the wet process of papermaking,ANF-coated chopped fibers and aramid fibrids were mixed to form paper.It was found that the tensile strength of ANF-coated paper-based materials(AOP)was 9.41 MPa,which was 10.41%higher than that of original paper(OP).After 168 h of UV radiation,the strength retention rate of AOP increased by 16.93%compared with OP,showing that the treatment of ANF could improve the mechanical properties and UV aging resistance of a single macro-fiber and paper-based materials.In order to further improve the UV aging resistance of aramid paper-based materials,nano-ZnO with excellent ultraviolet light absorption properties was introduced on the basis of the previous study.The ANF/ZnO composite was synthesized by electrostatic self-assembly of zinc salt and negatively charged anf through hydrothermal method using ANF as template,with the control of system pH control and the ratio of ANF/Zn2+.It was found that when the system pH was 10 and the mass ratio of ANF to Zn2+was 4:1,the UV absorption effect of ANF/ZnO reached the best.With the addition optimal ANF/ZnO ratio was selected,the results showed that when the ANF/ZnO content was 15 wt.%,the paper-based materials(ANF/ZnO(15%))had the best performance.The tensile strength,elongation at break and modulus of resultant materials were 13.45 MPa,2.36%and 0.88 GPa,which were 12.45%,10.02%and 33.33%higher than AOP,respectively.With the extension of UV radiation time,the tensile strength and elongation at break of ANF/ZnO(15%)showed a trend of first rising and then falling,reaching the maximum values at 120h,16.96 MPa and 2.75%;these values were increased by 26.30%and 16.53%respectively compared to those before radiation.When the UV radiation reaches 168 h,the tensile strength,elongation at break and modulus of ANF/ZnO(15%)were 16.73 MPa,2.70%and 1.02 GPa respectively,and the retention rate could reach 126.10%,114.41%and 159.10%respectively,indicating that the introduction of ANF/ZnO can greatly improve the UV aging resistance of aramid paper-based materials.