Abstract:

Objective Special protective clothing are used against high temperature, acid and alkali corrosion, fire and other special environments, and high-performance fibers are essential for special protective clothing. Polyphenylene sulfide (PPS) fiber is a high-performance fiber with excellent mechanical properties, chemical resistance, self-flame retardancy and insulation and other outstanding properties, and it is a suitable raw material for special protective clothing. However, the poor moisture absorption, dyeing performance and light resistance of PPS fiber, limit the applications in apparel.

Method PPS fibers were modified with sodium polyacrylate (PAAS) and nano-TiO₂ to obtain PPS/PAAS/TiO₂ composite fibers with better hygroscopic property, dyeing performance and UV resistance. The PPS/PAAS/TiO₂ composite masterbatches were prepared by melt blending the vacuum-dried PPS with PAAS and nano-TiO₂ using a twin-screw extruder before these composite masterbatches were vacuum dried at 130 ℃ for 13 h. The composite fibers were prepared by a one-step spinning and drawing process using melt spinning. The spinning speed was 800 m/min, the pump supply was 22 g/min, and two-zone drafting was used, with the temperature of each drafting hot plate setting at 88, 102 and 108 ℃, and the drafting multiplier was 3.2. The mechanical properties, moisture absorption properties, dyeing rate, color fastness, and ultraviolet(UV) resistance of the prepared fibers were characterized.

Results PAAS and nano-TiO₂ were able to disperse uniformly in the polyphenylene sulfide (PPS) fiber matrix and form a good cross-compatibility (Fig.2), but when the mass fraction of PAAS exceeded 3%, agglomeration appeared and the poor dispersion led to poor spinnability of PPS composite fibers (Tab. 1). The use of Nano-TiO₂ improved the crystallinity of PPS fibers, while PAAS made the glass transition temperature and crystallinity of composite fibers decrease (Fig. 3 and Tab. 2). Increasing the internal free volume and amorphous zone of fibers resulted in a slight decrease in the breaking strength of PPS fibers compared with pure PPS fibers, but the elongation at break increases (Fig. 4). When the mass fraction of PAAS was 2%, the breaking strength of PPS/PAAS/TiO₂ composite fiber reached 3.06 cN/dtex and the elongation at break 30.4%, indicating the mechanical properties meeting the requirements of fabrics for apparel. The moisture absorption performance and dyeing performance of the PPS/PAAS/TiO₂ composite fiber was improved, the water contact angle decreased with the increase of PAAS content from 73.7° for the pure PPS fiber to 51.2° for the PPS-5 composite fiber (Fig. 5). The standard moisture regain rate increased with the increase of PAAS content from 0.22% for the pure PPS fiber to 3.9% for the PPS-5 composite fiber (Fig. 6). Under the same dyeing conditions, the dyeing rate of PPS-4 composite fiber (90.9%) was twice as high as that of the pure PPS fiber (44.8%) (Fig. 7). The color fastness of PPS/PAAS/TiO₂ composite fiber all reached levels 5 and 5 for soaping resistance (Tab. 3), and 6 and 7 for light fastness. The resistance of PPS composite fibers to light aging was significantly improved by addition of nano-TiO₂, and the strength remained at more than 85% after 120 h, although there was also strength loss with time (Fig. 8).

Conclusion The hygroscopic property, dyeing performance and UV resistant of PPS/PAAS/TiO₂ composite fibers are all enhanced to a certain extent, partly because of the functional groups of PAAS and nano-TiO₂, and partly because of the formation of a good spatial cross-linked network structure with the PPS matrix (Fig. 9). PAAS itself has a long molecular chain entanglement cross-linked structure. There are many reactive —COONa, —COOH groups inside the network, which have super hygroscopic ability. It is proved that nano TiO₂ plays a role in preventing UV aging by absorbing and reflecting ultraviolet light and the scattering and shielding ultraviolet light. Water molecules and dyestuffs that penetrate and diffuse into the interior of PPS fibers produce certain hydrogen bonding with the functional groups, resulting in improved moisture regain and color fastness of the fibers. On the basis of maintaining the original properties of PPS fibers, improved moisture absorption, dyeing and UV resistant properties make it a prospective candidate fibre for apparel applications. For further development, it is necessary to focus on the deterioration of the spinnability and mechanical properties of PPS fibers that occur after the PAAS content is increased.

Key words: polyphenylene sulfide fiber, modification for clothing, hygroscopic property, dyeing property, UV resistant, sodium polyacrylate, TiO₂