Tannins as Bio-Based UV-Blocking Agents for Textiles: Chemistry, Mechanisms, Processing Strategies, and Functional Performance

Abstract

Growing concern over ultraviolet (UV) radiation exposure and the environmental limitations of conventional synthetic UV absorbers has accelerated the search for sustainable alternatives in textile finishing. Among emerging bio-based materials, tannins have attracted significant attention due to their renewable origin, strong UV absorption capability, and multifunctional performance. This review provides a comprehensive and integrated analysis of tannins as natural UV-blocking agents for textiles by systematically linking molecular chemistry, processing strategies, and functional performance. The structural characteristics of hydrolysable, condensed, and complex tannins are examined in relation to their photophysical behavior, with particular emphasis on aromatic chromophores, phenolic hydroxyl groups, conjugated π-electron systems, and textile-level shielding effects, which collectively influence UV attenuation and energy dissipation. Mechanisms underlying UV protection, including photon absorption, radical scavenging, metal–polyphenol coordination, and formation of protective surface films, are critically discussed alongside fiber–tannin interaction pathways across cellulosic, protein, and synthetic substrates. The review further evaluates extraction approaches, sustainable processing routes, and textile application techniques such as exhaustion, pad–dry–cure, layer-by-layer deposition, encapsulation, and hybrid sol–gel systems. Reported studies demonstrate substantial enhancement of UPF, frequently achieving excellent protection levels (UPF ≥ 50 +), particularly when optimized concentrations, fabric structures, and fixation systems are employed. Despite promising performance, challenges related to durability, color control, and process standardization remain. By consolidating dispersed research findings, this work establishes a mechanistic and technological framework that supports the development of scalable, environmentally responsible UV-protective textile finishes based on tannin chemistry.

Graphical Abstract