Thermoplasticization of Bamboo Fibers via Solvent-Free Heterogeneous Esterification with Long-Chain Fatty Acids: Effect of Lignin Removal and Carbon Chain Length

Abstract The development of bio-based thermoplastics from lignocellulosic biomass is of considerable interest for reducing dependence on petroleum-derived plastics. In this work, a solvent-free strategy was proposed to fabricate thermoplasticized bamboo fibers (TBF) via heterogeneous esterification of bamboo fibers with long-chain fatty acids (C10, C12, C14, C16, and C18), combined with controlled delignification. The influences of lignin removal and alkyl chain length on the chemical structure, thermal behavior, mechanical performance, optical properties, and surface wettability of the resulting TBF were systematically investigated. The results showed that delignification promoted the accessibility of reactive hydroxyl groups and increased the degree of esterification. Structural characterization revealed that the introduction of long-chain fatty acyl groups disrupted intermolecular hydrogen bonding and transformed the native crystalline structure into an amorphous state. The improved molecular mobility of esterified bamboo fibers enabled them to be readily hot-pressed into continuous and flexible films at 140 °C, demonstrating their excellent thermoplastic processability. The mechanical performance of hot-pressed TBF films exhibited a strong dependence on structural parameters, with moderate chain lengths (e.g., C12) achieving optimal toughness (elongation at break up to 217%), while excessive chain length led to reduced ductility due to side-chain ordering effects. Thermogravimetric analysis demonstrated improved thermal stability after esterification, and the films also exhibited excellent ultraviolet (UV)-blocking performance, maintaining transmittance below 0.3% in the UVC and UVB regions. These findings demonstrate that the combined regulation of lignin content and fatty acid side-chain structure is an effective approach for tailoring the properties of bamboo-based thermoplastics and provides a sustainable pathway for the high-value utilization of lignocellulosic biomass.