The effectiveness of mulberry silk fabric in protecting against ultraviolet (UV) radiation is influenced by multiple factors, with the synergistic effect of its natural fiber structure and post-processing techniques determining its final protective performance. As a natural protein fiber, mulberry silk's UV protection primarily stems from its unique molecular composition. The aromatic amino acids such as tyrosine and tryptophan in silk protein can absorb some UVB rays, converting light energy into heat energy through molecular vibrations, thus reducing direct UV damage to the skin. This natural absorption mechanism gives untreated mulberry silk fabric basic protective functions, but achieving highly effective blocking requires the combination of other factors.
The physical structure of the fiber is one of the key factors affecting UV protection. Mulberry silk fibers are longitudinally arranged in a flat, smooth, and dense shape, forming a natural light-scattering layer. When UV rays come into contact with the fiber surface, some light is reflected in different directions, reducing penetration. Simultaneously, the microporous structure within the fiber further scatters the remaining light, forming multiple protective barriers. If the fiber arrangement is loose or defective, UV rays may penetrate directly into the skin through the pores; therefore, the integrity and uniformity of the fiber directly affect the protective effect. The fabric's weave structure significantly influences its UV protection performance. Tightly woven mulberry silk fabrics, such as plain weaves, significantly reduce UV penetration due to their small fiber spacing and high coverage. In contrast, loosely woven satin or twill weaves have relatively lower protection coefficients due to their higher porosity. Furthermore, increasing fabric thickness or the number of layers can lengthen the UV propagation path between fibers, enhancing overall protection through multiple reflections and absorptions. For example, double-layer mulberry silk fabric typically has a higher UPF value than single-layer fabric and maintains stable performance even in humid environments.
Finishing processes are a direct means of enhancing the UV protection of mulberry silk. By padding or coating techniques, inorganic UV-blocking agents such as titanium dioxide and zinc oxide can be attached to the fiber surface, forming a physical reflective layer. These nanoscale particles efficiently scatter all wavelengths of UV radiation (UVA and UVB), significantly increasing the fabric's UPF value. Some processes also incorporate organic UV absorbers, enhancing protective durability through chemical bonding. It is worth noting that excessive use of chemical finishing agents may damage the natural luster and breathability of mulberry silk; therefore, a balance must be struck between protective effect and wearing comfort.
The long-term impact of environmental factors on the UV protection performance of mulberry silk cannot be ignored. Prolonged exposure to ultraviolet rays can cause fiber molecular chain breakage, leading to yellowing and decreased strength, thus weakening its protective ability. Experiments show that after 150 days of natural aging, the whiteness and luster of mulberry silk fabric can decrease by more than 60%, and the breaking strength can decrease by more than 90%. Furthermore, the acidic or alkaline components in sweat can accelerate fiber hydrolysis, further reducing protective stability. Therefore, prolonged exposure to sunlight should be avoided in daily use, and sweat stains should be cleaned promptly to extend the fabric's lifespan.
The color and thickness of mulberry silk fabric also indirectly affect its UV protection. Darker fabrics, containing more natural pigments or dyes, absorb more ultraviolet rays and generally offer better protection than lighter colors. However, excessive dyeing can damage the fiber structure; therefore, environmentally friendly dyes should be chosen to balance protection and environmental friendliness. Regarding thickness, while heavier fabrics offer stronger protection, they may sacrifice breathability, leading to a stuffy feeling when worn in summer. Therefore, the appropriate thickness should be selected based on the usage scenario, or a multi-layered design should be used to balance protection and comfort.
The UV protection of mulberry silk fabric is the result of both its natural properties and human intervention. From fiber molecules to fabric structure, from finishing processes to the usage environment, every step requires precise control to achieve optimal protection. In the future, with the development of nanotechnology and green chemistry, mulberry silk fabric is expected to further improve its UV protection performance while maintaining its natural advantages, providing better solutions for outdoor apparel and health textiles.
