Polyimide fiber with high strength and high modulus and its preparation method

A high-strength high-modulus polyimide fiber obtained from random copolymerization of 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA), p-phenylenediamine (pPDA) and 2-(4-aminophenyl)-1H-benzimidazol-5-amine (BIA), wherein a molar ratio between pPDA and BPDA is 1:0.95˜1:1.05 and a molar ratio between pPDA and BIA is 1:10˜3:1;

• wherein the high-strength high-modulus polyimide fiber is prepared by:
• dissolving the pPDA and the BIA in a solvent, then adding the BPDA to obtain a solution with solid content of 5˜35 wt %, after reaction of the obtained solution under 2-5 gradient temperature sections with a temperature in each section being from 75° C. to −10° C. and with a total reaction time of 2-20 h, a polyamic acid (PAA) spinning solution is obtained;
• spinning the PAA spinning solution in a process, in which:
• after the PAA spinning solution is sprayed out from a spinneret plate, the PAA spinning solution continuously undergoes solidification in a coagulating bath to form PAA fiber, scrubbing the PAA fiber in a washing bath, treating the PAA fiber in at least four heat furnaces at different temperatures to obtain the high-strength high-modulus polyimide fiber;
• wherein treating the PAA fiber in at least four heat furnaces at different temperatures includes:
• drawing the PAA fiber in a first heat furnace at a temperature of 160-200° C. and a draw ratio of 1-2,
• drawing the PAA fiber obtained from the first heat furnace in a second heat furnace at a temperature of 240-280° C. and a draw ratio of 1-1.5,
• drawing the PAA fiber obtained from the second heat furnace in a third heat furnace at a temperature of 300-350° C. and a draw ratio of 1-1.3,
• drawing the PAA fiber obtained from the third heat furnace in a fourth heat furnace at a temperature of 400-550° C. and a draw ratio of 3-7,
• wherein the draw ratio in the first heat furnace is equal to or larger than the draw ratio in the second heat furnace, and the draw ratio in the second heat furnace is equal to or larger than the draw ratio in the third heat furnace.