Obective With the frequent occurrence of global acute infectious disease outbreaks, people are increasingly aware of individual protection. In order to protect textiles from microbial contamination and protect human health, it is important to endow textiles with antibacterial properties. However, with the gradual deterioration of white pollution, biodegradable environment-friendly polymer materials are receiving more and more attentions from researchers worldwide. Therefore, this research is committed to develop a green antibacterial fiber.
Method Polylactic acid (PLA) with good biodegradability and the natural antibacterial agent thymol were mixed evenly using a temperature control blending device before the PLA antibacterial fibers were prepared by melt spinning. The apparent morphology, chemical structure, crystallization, thermal and mechanical properties of PLA antimicrobial fibers with different thymol mass fraction were investigated by scanning electron microscopy, Fourier infrared spectroscopy, X-ray diffraction, single fibers strength meter and comprehensive thermal analyzer. The antibacterial properties of the fibers were tested by using oscillatory flask method.
Results After the addition of thymol, the two phases of PLA and thymol were interconnected without any obvious interface, and the two phase assembly led to good overall dispersion of thymol particles in the fibers, and excellent the compatibility between PLA and thymol, as evidenced in Fig. 2. In this study, the characteristic peak of C—H bending vibration on the benzene ring appeared at 800 cm-1. The hydroxyl group of thymol can interact with the carbonyl group in PLA to form valence bonds, indicating the existence of chemical bonding interactions between thymol and PLA matrix. Furthermore, the electron microscopic morphology results indicated that the chemical bonding between thymol and PLA promotes their dispersion, as shown in Fig. 4. As the mass fraction of thymol increases, the melting temperature of PLA antibacterial fibers gradually decreases(as shown in Fig. 5). There were two stages of thermal decomposition of PLA antimicrobial fibers. The first stage occurs in 100-200 ℃, which is due to the volatilization and thermal decomposition of thymol in the system. The second stage takes place in 310-395 ℃, and the maximum degradation rate is shown around 375-381 ℃, and the mass loss gradually increases up to 99.28%. This is because of the decomposition of PLA macromolecules and short chain segments, and oligomers and lactide esters are produced during the melting process, as shown in Fig.6. With the increase of thymol mass fraction, the crystallinity of PLA antibacterial fibers gradually increases(as shown in Fig.7). When the mass fraction of thymol is 15%, the elongation at break of PLA antibacterial fibers can reach 320.98%, which was 90 times more than that of pure PLA fibers, and the flexibility is greatly improved, and these are shown in Fig. 8 and Tab. 3. Moreover, the higher the thymol mass fraction, the better the antibacterial properties of antibacterial fiber's. When the mass fraction of thymol is greater than or equal to 15%, the antibacterial rate of PLA antibacterial fibers becomes higher than 99.99%, which can inhibit the growth of Escherichia coli and Staphylococcus aureus completely. Besides, the antibacterial property of thymol on Staphylococcus aureus is better than that on Escherichia coli, as shown in Tab. 4.
Conclusion During the fiber formation process, thymol will adhere to the outer surface of the fibers to show antibacterial effect. With the increase of thymol mass fraction, the elongation at break of antibacterial PLA fibers shows a trend of rapid increase and then slowly decrease, and the elongation at break of PLA antibacterial fibers with thymol mass fraction of 15% can reach 320.98%, which is 90 times of pure PLA fibers. This indicates that the addition of thymol is beneficial to improve the flexibility of PLA. In addition, with the increase of thymol mass fraction, the melting temperature of PLA antimicrobial fibers gradually reduce and the crystallinity gradually increase, which illustrates that the addition of thymol promotes the formation of the α' crystalline form of PLA. When the mass fraction of thymol is more than 15%, the antibacterial property of PLA antimicrobial fibers reaches more than 99.99%, which can completely inhibit the growth of Staphylococcus aureus and Escherichia coli. In summary, the addition of thymol can impart excellent antibacterial properties to the fibers, improve the wearability of PLA fibers, and make them better used in textiles. Subsequent studies can optimize the wearability by improving the spinning conditions and processes to achieve the mass production of antibacterial fibers.