Synthesis and characterization of composites: thermoplastic/lignocellulosic fibers from the Biskra region

Debabeche, Nedjla (2023) Synthesis and characterization of composites: thermoplastic/lignocellulosic fibers from the Biskra region. Doctoral thesis, Université Mohamed Khider (Biskra - Algérie).

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Abstract

This study's main goal was to make an eco-friendly composite from palm petiole fibers that could be used as fillers in a linear low-density polyethylene (LLDPE) matrix with a loading of 15–25 wt% and to look into how the composites age naturally. To achieve this main objective, lignocellulosic fibers were prepared using successive treatments on the fiber surface (NaOH, hydrogen peroxide, and acetic anhydride). The NaOH pretreatment aimed to overcome the recalcitrance of lignocellulosic biomass. FTIR showed that pretreatment with NaOH helped the peroxide hydrogen treatment of NaOH-petiole fibers to break down biomass without separating it into different parts. This made it possible to get micrometric-sized lignocellulosic fibers. These lignocellulosic fibers that have been extracted are hydrophilic, which means that the hydroxyl groups in the fibers interact with water molecules. The hydrophilic nature of these lignocellulosic fibers often results in poor compatibility with hydrophobic polymeric matrices. Surface modification is therefore necessary to make them more hydrophobic and compatible with the hydrophobic matrices. For this reason, we treated the lignocellulosic fibers with acetic anhydride, which is used to modify the surface of the fibers and make them more hydrophobic. The scanning electron microscopy (SEM) results showed that the enhanced interfacial adhesion between the fibers and the matrix makes treated composites more rigid and more homogeneous, which means that the fibers are distributed more uniformly. The tensile modulus and flexural strength were all enhanced by adding 15-25% of untreated palm petiole fibers, while the tensile strength was decreased. Palm-petiole fiber composites' storage modulus increased, and the acetylated-alkali fiber (FNA) reinforced LLDPE composite showed the highest storage modulus. Loss modulus increased when palm petiole fibers were strengthened. The Tan delta of composites made from palm petiole fibers was low initially but expanded with fiber addition. After exposing the LLDPE/PPF composites to natural aging, we observed, by IRTF, the formation of several oxidation products, an increase in the crystallinity rate, and Young's modulus. Furthermore, the SEM images clearly show that the degradation is severe with aging. We concluded that successive treatments improve the performance of the palm petiole fiber and have the potential to create a new type of sustainable and eco-friendly material for various applications.

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