Study the influence of growth conditions on the mechanical behavior of unidirectional and woven plant fibers polyester composites

Abstract

The aim of this thesis is to contribute to the advancement of scientific research on understanding the factors that influence the overall performance of plant fibers, with the objective of improving their properties and enhancing their functional behavior. In this context, a comprehensive study was carried out to evaluate the suitability of Alfa fibers (Stipa tenacissima L) as reinforcement in composite materials. The study investigated the effects of seasonal variations, and growth sites on the physical, chemical, thermal, morphological, and mechanical properties of fibers. Samples of Alfa fibers were collected from five different regions in Algeria throughout the four seasons of the year. Various analyses were performed, including chemical composition, thermal (TGA-DTG), structural (XRD), spectroscopic (ATR-FTIR), and morphological characterization using scanning electron microscopy (SEM). Additionally, the physical and mechanical properties of the fibers were evaluated. To improve fiber performance and enhance compatibility with the polymer matrix, Alfa fibers from the M’sila region were selected and chemically treated using sodium hydroxide and potassium permanganate. The structural, physicochemical, and morphological characteristics of the fibers were assessed, while the interfacial shear strength (IFSS) between treated and untreated fibers and the polyester matrix was determined through micro-bond test. Weibull statistical analysis was applied to evaluate the variability of IFSS values and to highlight the influence of chemical treatment on fiber structure and surface behavior. Furthermore, intra-ply woven fabrics combining treated and untreated Alfa fibers with jute yarns were developed to investigate the effect of fiber orientation within the matrix. Based on these hybrid fabrics, as well as unidirectional ply of Alfa fibers, polyester-based composite materials were fabricated, and their physical, mechanical, and morphological properties were analyzed. The results revealed a significant enhancement in the mechanical performance of the composite materials following chemical treatment, along with improved interfacial adhesion between the fibers and the polymer matrix. The findings also confirmed the strong influence of environmental and climatic factors on the chemical, structural, physical, and mechanical characteristics of Alfa fibers, providing valuable insights for determining the optimal harvesting period to achieve the desired properties and for guiding their targeted use in advanced industrial and engineering applications. Overall, this study highlights the great potential of Alfa fibers as a sustainable and efficient reinforcement material for high performance composites and contributes to a deeper understanding of local lignocellulosic fibers in green material development