Abstract:

Objective Cotton fabrics have the advantages of breathable moisture permeability and comfort, and is widely used for summer clothing. However, cotton fabrics are weak in UV protection. It is known that excessive ultraviolet irradiation, particularly in the summer, causes great harm to the human body, but the common anti-ultraviolet finishing agent is easy to be washed off during laundering. It is necessary to improve the fastness of anti-ultraviolet agents on cotton fabrics. In this research, BN-CQDs and isocyanate microcapsules are used to finish cotton fabric.

Method BN-CQDs were fixed to the fabric using microcapsule core material isophorone diisocyanate. In this research, the structure and surface morphology of finished cotton fabric and microcapsules were studied, and characterized by Fourier infrared spectroscopy, three-purpose ultraviolet analyzer and video microscope. In addition, the UV protection factor (UPF) of the finished cotton fabric was measured to examine the effect of the volume proportion of different modified liquid on the UV protection and UV water-resistant properties of the fabric. The moisture permeability of the cotton fabric was tested to study whether the finished fabric was qualified in the moisture permeability.

Results Isocyanate group and —NH appeared in the prepared microcapsules at 2 257 cm^-1 and 3 365 cm^-1, respectively, while the isocyanate group was stronger in the pure core material and there was no —NH (Fig. 1). Isocyanate-type microcapsules showed smooth surface without wrinkles, particle size of about 200 nm and relatively concentrated distribution, core material mass fraction of microcapsules reaches 42%, and encapsulation efficiency is 75% (Fig. 2, Fig. 3 and Fig. 4). As the content of microcapsules in the modified solution increased, the strength of the hydroxyl group in the finished fabric also decreased (Fig. 5). The original fabric appeared almost white under ultraviolet lamp, while the cotton fabric after finishing illustrated bright blue fluorescence. The fluorescence of pure BN-CQDs finishing fabric became weaker sharply after 20 times of washing. However, after the same washing, the fluorescence intensity of the BN-CQDs/ microcapsules composite reinforced by the finished fabric was only reduced slightly, and the blue fluorescence of microcapsules was also slightly improved with the increase of microcapsule content in the modified solution (Fig. 6). The UPF value of the original fabric was low, and the UPF value of the BN-CQDs fabric only was increased slightly to 19 and the UV transmittance of the two fabrics was greater than 5%. The UPF value of BN-CQDs/ microcapsule fabric was maintained at 34-36, which reached the level for ptoviding better protection, and increased by 192.6%-207.7% compared with the original. After 20 washes, the UPF value of the BN-CQDs fabric was decreased to 14, and the declining rate of the UPF value of the BN-CQDs/ microcapsule fabric also decreased with the increase of the microcapsule content in the modified solution. Because IPDI reacted with the cellulose and the surface OH of the BN-CQDs, it was fixed on the fabric. However, when its content reached 3 mL, the decrease rate of its UPF value did not change much. For example, the UPF value of A6 fabric was still as high as 32, representing a decrease by 11%, and the ultraviolet transmittance of A1-A5 fabrics were less than 5% (Fig. 7 and Fig. 8). For the finished fabric, the moisture permeability was found in the range of 2 712-3 101 g/(m²·d), in comparison to the moisture permeability of 3 154 g/(m²·d) untreated fabric, representing a reduction from 2% to 14%, meeting the moisture permeability requirement (Fig. 9).

Conclusion Isocyanate microcapsules have smooth surface, complete morphology, uniform dispersion and no agglomeration. The original fabric and BN-CQDs are not up to the "requirements of UV protection products", and the addition of BN-CQDs on the surface of the fabric will improve its UV protection performance, at the same time adding isoferone diisocyanate microcapsules not only improve the UV water resistance, but also reduce the UV transmittance, BN-CQDs/ Microcapsule fabric meets the requirements of "UV protection products". BN-CQDs/ microcapsule finishing can reduce the moisture permeability of fabric slightly, but still meet all the requirements of moisture permeability.

Key words: carbon quantum dots, UV protective property, polyurethane, microcapsule, ultraviolet protection factor, washing durability