International audienceThis paper focuses on the study of the effect of chemical treatments of fibers by alkalization on the flexural properties of polyester matrix composite reinforced with natural fibers. The used reinforcement consists of Alfa fiber, extracted from the plant Stippa tenacissima from Hodna Region (Algeria). Alfa fibers are subjected to alkali treatments with NaOH at 1, 5 and 10% for a period of 0, 24, and 48 h to 28 °C. The composites reinforced with layers of Alfa random costituente a rate of 40% by weight. Influence of alkaline treatments on the flexural properties is studied to determine the optimum conditions of alkaline treatment. The experimental results show that the bending behavior of composites made from alkali treated fibers are better compared to the untreated fiber composite, For a fiber processing Alfa 10% NaOH in 24 h, the flexural strength and flexural modulus improved by 23 MPa to 57 MPa and from 1.16 to 3.04 GPa. However, the flexural properties of composites decreased after alkali treatment with 5% NaOH for 48 h. This is mainly due to the reduction of lignin that binds the cellulose fibrils together

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In this paper, composites based on unsaturated polyester resin reinforced with short Alfa fibers are studied in detail. Alfa fibers have been previously treated with various concentrations NaOH (1, 3, 5, 7%) during 24 h. The influence of alkali treatment on fiber morphology is analyzed. Analysis by FTIR and X-ray diffraction showed physico-chemical changes in Alfa fiber treated surfaces. SEM observations also helped to highlight these changes. The results of static tests on composites showed improvements in tensile and flexural strengths of composites reinforced with the treated fibers, particularly the composite with treated fibers at 7% NaOH. These improvements were about 30% and 50%, respectively, compared to untreated fiber reinforced composite.

Purpose The literature reveals there is a limited knowledge regarding the extraction of long natural fibers, in particular those extracted from leaves. This investigation aims to present the extraction process and the characterization of long natural cellulose fibers from doum palm leaves (Hyphaene thebaica L.), with properties suitable for polymeric composite materials and textile applications. Design/methodology/approach The resulting H. thebaica L. fibers were identified using Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The physical properties of the extracted fibers were measured to estimate the reliability of extraction conditions. Mechanical properties were evaluated to determine ultimate strength, Young’s modulus and strain-at-failure of the fibers of the doum leaves. Findings The following properties of the doum palm are listed in this paper: physical properties of doum palm fibers (H. thebaica L.), TGA, XRD of doum palm fibers, tensile properties of doum palm fibers and surface morphology of doum palm fibers. Research limitations/implications Like synthetic fibers, the inclusion of short or long natural fibers into the polymer matrix can increase tensile, flexural and compressive strengths of these matrixes. Compared to the short-length natural fibers, longer-length fibers provide better reinforcements and therefore accord higher performances to the composites. Long fibers can also provide exceptional opportunities to develop a new class of advanced lightweight composites and have the potential to rival glass fiber in the manufacture of composite materials, using matrix materials, such as polypropylene, epoxy and phenolic resins. Originality/value The following values are presented in this paper: density of doum palm fibers = 1.14-1.40 g/cm², linear density (Tex) = 33.10 ±11.5, equivalent diameter (µm) = 178.72 ± 41.7, diameter (µm) = 137.02-220.42, tensile strength (MPa) = 124.84-448.10, Young’s modulus (GPa) = 8.06-19.59, strain-at-failure (%) = 0.81-2.86.

The purpose of this study is to evaluate in detail the usability of new cellulosic fibers extracted from the stem of the plant Strelitzia reginae, as a potential reinforcement for polymer composites. The morphological, physical, thermal, and mechanical properties of fibers were addressed for the first time in this paper. Both untreated and alkali-treated fibers were characterized, using scanning electron microscopy (SEM), Fourier-transform infrared, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), optical microscope, and X-ray diffraction (XRD) and applying tensile test for determining the mechanical behavior. For both fiber treated at one hour (T1H) and at four hours (T4H), the stem anatomy and fiber SEM micrographs showed a strong presence of fiber cells. Thermogravimetry and DSC showed that the fiber was thermally stable up to 233°C for untreated fiber, 254 and 240°C, respectively, In single-fiber tensile tests, it was observed that the fibers extracted from the stem of Strelitzia reginae were strong. The mean values of Young’s modulus exhibited by untreated fibers and treated (T1H) and (T4H) are, respectively, 9.89 GPa, 12.08, and 18.39 GPa. Also mean values of tensile strength are 271.79, 306.23, and 421.39 MPa. The XRD reveals the presence of cellulose with a Crystallinity Index of 70% for raw fiber and 72% for the treated one. Fourier-transform infrared analysis well demonstrated the effect of chemical treatment. It can be concluded from the results of all above experiments that the Strelitzia reginae fibers (SR) could serve as a possible reinforcement in composite materials.

In recent years, natural fibres have been experimented to replace glass fibres in reinforcing thermosetting polymer. Since the interfacial adhesion between the raw natural fibres and the polymer matrix are often not adapted to the intended applications, the fibre surface most often requires a preliminary chemical modification. The fibres which were extracted from the Arundo donax L. Plant (called cane fibres), are little studied in the literature of fibre/polymer composites. In the present work, the cane fibres have been treated at constant soaking time with 2-8% NaOH aqueous solutions for 24 h. The composite reinforced by 6% NaOH-treated cane fibres, exhibited maximum improvements in tensile and flexural strength by 57% and 45% respectively. A combination of Fourier transform infrared, scanning electron microscopy, X-ray diffraction and moisture absorption techniques has been used for material characterisation. The crystallinity index yields information about fibre modification by NaOH. Such cane fibre composites could become an alternative to existing materials, with interesting tensile and flexural strengths, low cost and less ecological impact.

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The present investigation aimed to understand the physicochemical properties of the new cellulosic fiber extracted from the bark of Silybum marianum (SM), in view of using it as a potential reinforcement for polymer composites. The morphological and anatomy, physical, thermal and mechanical properties of fibers were firstly discussed in this paper. The Silybum marianum fibers (SMF) were characterized by scanning electron microscopy, Fourier transform infrared, thermogravimetric analysis (TGA), optical microscope, X-ray diffraction (XRD), and single fiber tensile test. The average Young’s modulus and the breaking stress data presented by the fibers are 15.97 GPa and 201.16 MPa, respectively. XRD reveals the presence of cellulose with a crystallinity index of 45%. Thermal stability (250°C) and maximum degradation temperature (357.72°C) of the SMF are established by the thermogravimetric analysis. An analysis of the mechanical properties was carried out on a population of 35 samples using Weibull statistics with two and three parameters.