Preparation of High Performance Copolyimide Fibers via Increasing Draw Ratios

Abstract

High performance fibers based on copolyimide (co-PI) containing benzimidazole and ether moieties were prepared via a two-step wet spinning method. The effects of draw ratio on the structures and properties of the fibers are investigated. The mechanical properties of the co-PI fibers are improved greatly by increasing draw ratio at temperatures above 400 8C, reaching the optimum tensile strength of 2.8 GPa and modulus of 136 GPa, which is due to the development of the molecular orientation along the fiber direction. The hot drawing process roughens the fiber surface and stretches the molecules in the fibers. Moreover, the fiber structure evolutions during the drawing process were also discussed and a ''smectic A liquid crystal-like'' model was proposed.

Polyimide fibers prepared by a dry‐spinning process: Enhanced mechanical properties of fibers containing biphenyl units

“…13 When it was heated to 300 8C, the characteristic peaks of the sample at 1370 and 1770 cm 21 were attributed to the CAN stretching and C@O symmetric stretching of the imide ring, respectively; these peaks illustrated the formation of fully imidized PI-1 fibers. 14,15 In our last work, 16 we reported that the peak at 1370 cm 21 could be used to quantitatively calculate the ID by the following equation because of its very strong characteristic features:…”

“…The imidization process of PAA-1 was easily identified by the disappearance of the amiderelated bands and the appearance of the corresponding imide bands as the heating temperature increased. At 100 8C, the precursor PAA fiber vibrations included three bands: the carbonyl stretching of the carboxylic acid at 1726 cm 21 , the carbonyl stretching of the amide I mode at 1670 cm 21 (C@O, CONH), and the CANH stretching of the amide II mode at 1540 cm 21 . 13 When it was heated to 300 8C, the characteristic peaks of the sample at 1370 and 1770 cm 21 were attributed to the CAN stretching and C@O symmetric stretching of the imide ring, respectively; these peaks illustrated the formation of fully imidized PI-1 fibers.…”

“…At 100 8C, the precursor PAA fiber vibrations included three bands: the carbonyl stretching of the carboxylic acid at 1726 cm 21 , the carbonyl stretching of the amide I mode at 1670 cm 21 (C@O, CONH), and the CANH stretching of the amide II mode at 1540 cm 21 . 13 When it was heated to 300 8C, the characteristic peaks of the sample at 1370 and 1770 cm 21 were attributed to the CAN stretching and C@O symmetric stretching of the imide ring, respectively; these peaks illustrated the formation of fully imidized PI-1 fibers. 14,15 In our last work, 16 we reported that the peak at 1370 cm 21 could be used to quantitatively calculate the ID by the following equation because of its very strong characteristic features:…”

“…where a is the ID, and (D 1370 /D 1500 ) T1 is the ratio of the height of the peak at 1370 cm 21 to that of the peak at 1500 cm 21 at the curing temperature (T 1 ), and (D 1370 /D 1500 ) T300 is the ratio value after complete imidization at a curing temperature of 300 8C. The same method was used to evaluate the conversion degrees of the PAA-0, PAA-2, and PAA-3 precursor fibers.…”

“…The crystal orientation in the fibers was measured on the basis of the following Hermans' equation 21 :…”