Chemical Surface Treatments of Luffa Fibers to Enhance the Interfacial Adhesion and Mechanical Properties of Unsaturated Polyester Composites

Abstract

: This study focuses on the reinforcement of thermosetting matrices with lignocellulosic fibers and the limited interfacial compatibility that remains a major obstacle to the structural use of bio-based composites. The effect of chemical surface treatment on the interfacial behavior and macroscopic performance of unsaturated polyester resin (UPR) reinforced with Luffa fibers (LF) is studied in depth. LF was treated with two different chemical treatments: (i) alkaline treatment with sodium hydroxide (NaOH) and (ii) a combined NaOH/acetic acid (CH 3 COOH) treatment. The structural and morphological characteristics of the LF treated were examined using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Composite specimens were fabricated through a contact molding technique. Mechanical performance was assessed via density, tensile strength, impact resistance, hardness test, and water absorption. Results demonstrate that composites containing 10 wt.% LF exhibits improvements in mechanical properties, with tensile strength, impact strength, and hardness increasing by 74%, 192%, and 16.2%, respectively. The chemical treatments further enhance performance by reducing water absorption and improving fiber–matrix interfacial densification. SEM observations indicate uniform fiber dispersion at low fiber contents, while higher loadings lead to fiber agglomeration. The results demonstrate that luffa fibers can serve as an eco-friendly strengthening material in unsaturated polyester resin composites.