Abstract:

Objective Polyethylene terephthalate (PET) fibers have excellent mechanical properties, stable thermal and chemical properties, and are widely used in industrial, home textile, and apparel fields. However, because of its regular macromolecular chain structure and the lack of hydrophilic groups, the softness and moisture absorption of the fibre and fabrics made from it are poor, leading to low wearing comfort. This research aims to improve the softness and high moisture absorption of PET fiber.

Method Two series of modified PET fibers containing different molar fractions (3%, 6%, 9% and 12%) of modified monomers and different drafting multipliers were prepared by melt spinning ethylene terephthalate (BHET) copolymerized with glutaramide adipate (PA56 salt) and its derivative p-adipic acid diamide (APA56), respectively, combined with the two-step method of spinning undrafted yarn followed by progressive drafting. The properties of modified PET fibers were tested and analyzed with the aid of an acoustic velocity orientation meter, an X-ray diffractometer, and a yarn tensiometer.

Results The orientation and crystallinity of modified PET fibers were found lower than those of PET fibers, and the orientation and crystallinity decreased gradually with the increase of the molar fraction of modified monomers, but increased with the increase of the draft multiple (Fig. 1 and Fig. 3). The modified PET fiber was still trigonal as PET and the crystal shape does not change, but the diffraction peak was gradually weakened and the peak broadened as the molar fraction of the modified monomer was increased (Fig. 2). The breaking strength and initial modulus of modified PET fibers also decreased with the increase of the molar fraction of modified monomer, and the strength of fibers decreased while the softness increased. When the molar fraction was below 6%, the breaking strength of fibers could reach more than 2.0 cN/dtex, illustrating better mechanical properties (Fig. 4 and Fig. 5). For the same molar fraction of PA56 salt and APA56 modified PET fiber, the former showed higher breaking strength and initial modulus than the latter at the same drafting times, so the APA56 modified PET fiber became more flexible. The relative bending stiffness test results further showed improved softness of the modified PET fibers, with relative bending stiffness reduced by 18% to 71% and 40% to 88%, respectively(Fig. 6). APA56 show better softness than PA56 salt modified PET fibers, and the softness basically reached the level of fine wool when the molar fraction of modified monomers reached 6% and above. The moisture regain of PA56 salt and APA56 modified PET fibers increased by 39% to 200% and 53% to 213%, respectively, compared with PET fibers when the molar fraction of modified monomers was 3% to 12%. The modification of PA56 salt and APA56 significantly improved the moisture absorption of PET fibers, and the moisture absorption of APA56 modified PET fibers was better (Fig. 7).

Conclusion Two series of modified PET fibers were prepared by melt spinning using PA56 salt and APA56 as the modifying monomer, respectively, for copolymerization modification of PET. Compared with PET fibers, the orientation, crystallinity, and fracture strength of the modified PET fibers were reduced by the introduction of the modified monomers, and the molar fraction of the modified monomers increased, but the presence of flexible methylene chain segments and amide groups in the modified monomers significantly improved the softness and moisture absorption of the fibers, and the softness and moisture absorption of APA56 were better than those of PA56 salt. When the molar fraction of the modified monomer reaches 6% and above, the softness can reach the level of fine wool, and the mechanical property test shows that the fiber with a 6% molar fraction of modified monomer can reach the breaking strength of 2.0 cN/dtex and above, which retains good mechanical properties and can meet the requirements of the service performance, and will provide the possibility of replacing cotton and other natural fibers in the field of clothing in the future. It will provide the possibility of replacing cotton and other natural fibers in the apparel field in the future.

Key words: glutaric diamine adipate, p-adipic acid glutaramide, modified polyester fiber, softness, hydrophilicity