Abstract:

Objective In order to prepare multifunctional alginate composite fibers, Zn²⁺- Ca²⁺, Cu²⁺- Ca²⁺, Sr²⁺- Ca²⁺ bimetal ion crosslinked alginate composite phase change fibers were prepared from sodium alginate (SA), silk fibroin (SF), lauric acid palmitic acid binary eutectic mixture (LA-PA) by wet spinning technology.

Method The influence of bimetal ion crosslinking system on hydrogen bonding of composite phase change fibers was studied by infrared spectroscopy and Gaussian fitting, and the influences of different bimetal ion crosslinking systems on the structure, mechanical properties, thermal stability, thermal properties, water resistance and bacteriostasis of composite phase change fibers were investigated by scanning electron microscope, thermogravimetric analysis, differential scanning calorimetry.

Results The type of double ions was found to have a great influence on the molecular action. In comparison to the single Ca²⁺ion crosslinking system, the content increase of intramolecular hydrogen bonds in the bimetal ion crosslinking system resulted in content decrease of intermolecular hydrogen bonds, while the content of free hydroxyl groups hardly changed (Fig.2 and Tab.1). In fibers β-the content of folded chains is an important factor affecting the mechanical properties of fibers, and the breaking strength of fibers varies with β-the content of the folded chain structure increases as it increases (Tab.2, Tab.4). Owing to the wet spinning forming mechanism, there are grooves along the fiber axis on the fiber surface. The Zn²⁺- Ca²⁺, Sr²⁺- Ca²⁺, Cu²⁺- Ca²⁺crosslinked composite phase change fiber showed denser grooves than the single Ca²⁺ crosslinked composite fiber. Metal ions participated in the forming process of the composite phase change fiber (Fig.3 and Tab.2). The thermal stability of Cu²⁺- Ca²⁺ion crosslinked composite phase change fiber was found lower than that of the other three composite phase change fibers (Fig.4). The maximum crystallization temperature and melting temperatures of the fibers are 26.19 and 36.71 ℃, respectively, and the maximum phase transition enthalpy is 25.95 J/g; The phase change enthalpy of Ca²⁺, Zn²⁺-Ca²⁺, Sr²⁺-Ca²⁺composite phase change fibers is 24-26 J/g, with a small difference, the phase change enthalpy of Cu²⁺-Ca²⁺composite phase change fibers is relatively small, ranging from 17 to 18 J/g (Fig.5, Tab.5). After 50 thermal cycles, the crystallization enthaly and melting enthalpy of the composite phase change fiber decreased by 0.15 and 0.50 J/g, respectively, and the crystallization and melting temperatures changed by 0.78 and 0.40 ℃, respectively (Fig.6, Tab.6). Zn²⁺-Ca²⁺composite phase change fibers have the highest swelling rate, followed by Ca²⁺, Sr²⁺-Ca²⁺composite phase change fibers, and Cu²⁺-Ca²⁺composite phase change fibers have the lowest swelling rate, which is mainly determined by the content of metal ions in the fibers (Fig.7, Tab.2). Owing to the large amount of Zn²⁺and Cu²⁺inside the fiber, which can extensively interact with the bacterial cell wall and lead to lysis or inactivation of proteins in the bacteria, thereby killing the bacteria. Therefore, there is no obvious inhibition circle around the Sr²⁺-Ca²⁺and Ca²⁺composite phase change fibers, while there is an obvious inhibition circle around the Cu²⁺-Ca²⁺and Zn²⁺-Ca²⁺composite phase change fibers(Fig.8).

Conclusion The type of bimetal ions has a great influence on the molecular interaction, and the combined effect of the metal ion radius and the metal ion content causes the change of hydrogen bond interaction of different bimetallic ion crosslinking systems. The proper bimetal ion crosslinking system is helpful to improve the mechanical properties of the composite phase change fiber β-the content of folded chain is an important factor affecting the mechanical properties of fibers. The bimetal ion crosslinked composite phase change fiber has a phase change temperature of 21-37 ℃ suitable for human body and a high phase change enthalpy of 17-26 J/g, which has broad application prospects in clothing and other fields. The phase change temperature and enthalpy of the composite phase change fiber before and after 50 thermal cycles have little difference, and the bimetal ion crosslinked composite phase change fiber has good heat storage durability. The water resistance of Cu²⁺- Ca²⁺composite phase change fiber is obviously superior to the other three composite phase change fibers. Cu²⁺- Ca²⁺and Zn²⁺- Ca²⁺composite phase-change fibers have good antibacterial properties against these two types of bacteria.

Key words: lauric acid-palmitic acid binary eutectic mixture, sodium alginate, silk fibroin, wet spinning, composite phase change fiber, heat storage material