Preparation And Characteristics Of Polyimide Fiber Paper

Polyimide is a novel kind of special engineering plastic which has properties of high strength, high modulus coupled with good thermal stability and radiation resistance. Made from spinning, polyimide is now widely used in domains of aerospace, personal protection, dust removal under conditions of high temperature. Nevertheless, application of polyimide fibers in the paper field is still in its infancy.Polyimide fiber has smooth surface as well as the low binding force between fibers, as a result of which, addition of precipitation fibers as binder is necessary to improve the strength of paper. Slotted beater polyimide has been used for fiber beating and then fiber length, curl and other forms with time difference has been correlated. Three kinds of fibers with different length after beating with two polyimide fibrids have been used to made paper. The effect of fiber length and fibrids properties has been studied on the properties of paper. The results show that polyimide cannot broom even after the intensive beating. The length and morphology of fibers have a lot to do with the paper made. The optimal fiber length is 5.1mm and the optimal ratio of polyimide to No.1 precipitation fibers is 6:4. Under such conditions, the paper made has the best properties of strength.Paper density made of polyimide staple fiber and polyimide fibrid is only 0.25g/cm3 and therefore bonding area between fibers is small, the bonding strength between fibers is weak. Besides, tear index and tensile index of fiber paper without autoclaved is only and 8.3mN·m2/g and 8.6N·m/g respectively. In order to increase the strength of the polyimide fiber paper, a dual roll pressing machine has been used to autoclaved the paper. Using isothermal boost, isobaric heating, isothermal compression speed hot pressing process, the performance changes of polyimide fiber paper have been explored.The results show that the mechanical property of the paper increases along with the sintering temperature increase and it decreases but increases afterwards with increasing pressure to increase hot. With hot temperature of 210℃, hot pressure of 120N/m and pressing speed of 1m/min, polyimide fiber paper has been observed to achieve the best performance. In this case, the density of the polyimide fiber paper was 0.70g/cm3, tensile index reached 20.7 N·m/g, tearing index for 19.6 mN·m2/g, Dielectric strength for 11.8kV / mm.Mega-aramid fiber paper was developed by DuPont in the 1970 s. It is widely used in electric motor insulation and so on. This study is intended to develop a product with mega-aramid fiber paper as reference product. By comparison of the trial productions of polyimide fiber paper and mega-aramid fiber paper, the results that the strength of the polyimide fiber paper is far below mega-aramid fiber paper are concluded. Strength of the paper is the combined effects of its own strength between the fibers and fiber bonding strength. With polyimide fibrid, mega-aramid fibrids, para-aramid pulp treated by beating process, paper was made of three kinds of fibrids and short fibers. The results show that fibrid size effect on the ultimate strength of a paper fiber paper is larger, but little effect on the electrical properties. And the paper has good thermal stability also, which provides a theoretical basis to next research and development.Despite a little insufficient in terms of strength, novel polyimide fiber paper has a more excellent electrical performance, compared to conventional aramid fiber paper 1313. Therefore, polyimide fiber paper can be used for less demanding electrode cable insulation materials. Operating temperature of large motor can reach 180 ℃and even higher, and the cable insulation material expose to bright light for a long time, photoaging may occur, thus reducing its insulating properties. Therefore, to explore the performance of polyimide fiber paper by the light and heat aging effects influence cannot be more necessary. With the use of aramid fiber paper handsheets 1313 as a reference, the two fiber paper were placed at three different temperature and two light irradiation intensity of photoaging.The results show that with heat aging temperature going up, the two fibrous sheet exhibit a significant increase in tensile index and the tear index decreased slowly. After aging 300 ℃, polyimide fiber sheet exhibits almost no deformation. But aramid fiber 1313 has an obvious dimensional shrinkage. Thermal aging treatment has little effect on the electrical properties of the polyimide fiber paper, but will have a significant impact on the electrical properties of aramid fiber paper of 1313. Mechanical properties of the two fibers decline with the time of photoaging, Polyimide fiber paper has better resistance to light aging performance than aramid fiber paper. However, the electrical properties of the two fibrous sheet is lowered in light aging.To improve the strength of the polyimide fiber paper, water-based epoxy resin is used to impregnate paper with and without hot processing. The effect of impregnated amount on mechanical properties and electrical breakdown of polyimide fiber has been studied. The results show that when the solid content of the impregnating liquid is 15%, the tensile index of paper achieved the best. There is a significant decline of the tear index with increasing amount of impregnation. Using an aqueous rings impregnated with epoxy resin does not significantly improve the breakdown strength of the paper.