Fibrous Reinforcements for Composites: Overview

The production technology of reinforcement filler for new multifunctional polymer based composites with weft-knitted structure had been proposed. In such reinforcement filler high-strength carbon fibers (CFs) from PAN precursors (wefts) were laid in a knitted fabric as straight continuous yarns, so in such case these CFs were not twisted by knitting machine to form the loops. Various kinds of chemical and inorganic fibers can be used as base yarn in this case, in particular glass, aramid, carbon fibers from hydrate cellulose and etc. Properties of multifunctional polymer-based composite materials with weft-knitted fillers depend upon fiber composition, relative content of weft and base yarns, scheme filler stacking (1D, 2D and 3D composites). The electrical conductivity of weft-knitted fabrics shows the strong anisotropy along high-strength fibers in comparison with looped rows, depending on the direction of high-strength CFs (weft). Investigation of shielding properties of polymer based composites reinforced by carbon weft-knitted fabrics showed the possibility of using them as shielding materials with the ability to absorb electromagnetic radiation.

The use of synthetic fibers as reinforcement for concrete replacing the steel reinforcement has been diffused worldwide in several applications, gaining prominence in the application for industrial floors, tunnel linings, road pavements, etc., i.e., continuous structures in contact with soil that require performance in the elastic medium. The present study investigated the applicability of concrete reinforced with synthetic fibers in the bottom slab of silos supported directly on the ground, being composed of an experimental study and a case study. The experimental study consisted of the analysis of the mechanical behavior of this concrete by testing three concentrations of synthetic fibers (3.0, 4.5 and 6.0 kg m-3) in a conventional simple concrete matrix. The case study consisted of the design of this part in conventional reinforced concrete and concrete reinforced with synthetic fibers with the objective of performing an economic comparison between the two projects. The experimental results showed that the fiber concentration that contributed to a better mechanical performance of the concrete matrix was 3.0 kg m-3. The case study showed that the most economical design was the one made with fiber-reinforced concrete.

Geotextile tubes have been widely used for the dewatering of high water content fine sediments. Fine sediments include lake sediments, organic soils and coal combustion products, which generally have low shear strength. Several researchers have emphasized the effect of the retained sediment (filter cake) properties on dewatering performance and stability of the geotextile tubes. Maintaining retained sediment properties, in particular permeability and shear strength, allows for faster dewatering time, better retention of sediments and improved stability of the geotextile tubes during multiple filling stages and during the tube stacking process. Several studies have shown that the use of synthetic fibers can increase the shear strength of sand, silt and clays. However, the use of fibers to improve the strength of retained sediments in geotextile tubes has not been explored. In this study, three synthetic fibers varying in length and diameter were used to evaluate the effect of fibers on the dewatering performance and shear strength of the fine sediments. A cationic polyacrylamide flocculant was used as an optimum conditioner for the selected sediment. The fibers were mixed with the flocculant conditioned slurry at 0.25, 0.5, 1 and 2% fiber concentration by mass of the dry solids. The effect of fibers on the undrained shear strength of the dewatered sediments was evaluated using a lab vane test, fall cone test and undrained unconsolidated triaxial test. Jar tests and pressure filtration tests were also conducted to evaluate the effect of fiber on the required flocculant dosage and on the dewatering performance. Based on the results of this study, 0.5% of F1 fiber type was found to be the optimum fiber concentration, yielding an approximately 100% increase in undrained shear strength. It was also found that the diameter and length of the fibers play a significant role in altering the undrained shear strength of the tested sediments. The relatively short (6 mm) and thick (38 μm) fiber did not yield an increase in shear strength for all the tested fiber concentrations, whereas thin fibers (9 μm) of similar length increased the shear strength by 100%. Furthermore, it was found that the use of fibers at any concentration decreases the required optimum doses of flocculant by about 15%, and increases the dewatering rate of the effluents by about 50%.

The use of synthetic fibers in composite materials has a negative impact on the environment. One way to reduce this impact is to replace synthetic fibers with natural fibers. A natural fiber that has the potential as a mixed material in the manufacture of composite materials is citronella (Cymbopogon nardus) fiber. This study aims to determine the effect of volume fractions 40%, 50%, 60%, and 70% of citronella fiber with polyester resin matrix BQTN 157 on tensile strength. The process of making composites used the hand lay-up method. The specimen was formed according to the ASTM D3039 standard and the tensile strength of the specimen was tested by using a Universal Testing Machine (UTM). From the results of the study, the maximum tensile strength was found in the fiber volume fraction 70% of 77.35 MPa, the strain is 6.57%, and the modulus of elasticity is 1.177 GPa. This study indicates that fiber volume fraction affects the tensile strength of composite materials. Hence, the manufacture of composite materials which have good strength is influenced by many things such as raw materials, matrices, mixture composition, and methods.

The use of synthetic fibres as reinforcement to stabilise expansive soils is gaining momentum. As a contribution towards this growing field of research two different types of synthetic fibres, Fiber Mesh® and Fiber Cast®, were evaluated as a stabilisation alternative for expansive soils in the presence of lime. California bearing ratio (CBR) is chosen as a performance indicator as it is a good pointer towards pavement effectiveness. Variables such as length and amount of the fibres as well as curing period were studied. Both deterministic and probabilistic (or reliability) analyses is presented in this paper. While the deterministic analysis helps in understanding the measured experimental data, the probabilistic approach accounts for the stochastic nature of the experimental data and provides a better rationale for the design methods. The deterministic approach showed that the improvement in CBR increased with higher fibre contents and longer lengths and the effect was prominent when lime was used as a s...

The use of synthetic fibers as reinforcement in composites has disadvantage which are unsustainable and an adverse impact on the environment. An alternative reinforcement for composites is natural fiber. Polypropylene and Sumberejo kenaf fibers were used respectively as the matrix and reinforcement. The aim of this research was to obtain the optimum tensile properties and deflection temperature with the variation of kenaf fiber fractions. Polypropylene/kenaf fiber composites were fabricated by hot press method. The kenaf fiber was soaked in NaOH solution before being used as the reinforcement and polypropylene was extruded before being used as the matrix. The weight fractions were varied to produce composites and pristine polypropylene samples were also prepared for comparison. The optimum tensile strength, modulus and deflection temperature were found in the composites with the 40 wt% kenaf fiber fraction with an increase up to 80% and 170% compared to the pristine polypropylene with the values of (60.3 ± 4,3) MPa and (159.1 ± 1,8) °C respectively. The Scanning Electron Microscope observation results in the fracture surface of the composites with the 40 wt% fiber fraction showed a relatively good bonding interface between fibers and the matrix and the failure modes were fiber breakage and matrix failures.

Natural fibre-reinforced composites have been developed by researchers and industries as a solution to reduce the use of synthetic fibres. Kenaf fibre is one of the most abundant natural fibres in Indonesia. This study aimed to obtain the mechanical and thermal properties of kenaf fibre-reinforced epoxy laminated composites fabricated using a vacuum-assisted resin infusion method. The alkaline-treated fibres were arranged in the orientations 0°/0°/0°/0° and 0°/90°/0°/90°. Density measurements, mechanical tests, and thermogravimetric analysis were carried out on the epoxy and the composites. The results of the mechanical testing showed that the tensile, flexural, and compression strengths of the kenaf fibre-reinforced epoxy composites with a 0°/0°/0°/0° fibre orientation were higher than those of the composites with a 0°/90°/0°/90° fibre orientation, with values of (96.61 ± 10.18) MPa, (131.01 ± 6.60) MPa, and (71.96 ± 5.50) MPa, respectively. Scanning electron microscope observations showed that the composites had good fibre-matrix adhesion. The thermal stability of the epoxy was enhanced from 557 °C to 571 °C by incorporating kenaf fibre with 0°/0°/0°/0° orientation. With reference to the Indonesian National Standard 01-4449–2006, the two composites could be classified as T2 45 High Density Fibreboard.

The use of synthetic fibers as reinforcement in fiber-reinforced cementitious composites (FRCC) demonstrates a combination of better ductile response vis-à-vis metallic ones, enhanced durability in a high pH environment, and resistance to corrosion as well as self-healing capabilities. This study explores the effect of macro- and micro-scale polypropylene (PP) fibers on post-crack energy, ductility, and the self-healing potential of FRCC. Laboratory results indicate a significant change in fracture response, i.e., loss in ductility as curing time increases. PP fiber samples cured for 2 days demonstrated ductile fracture behavior, controllable crack growth during tensile testing, post-cracking behavior, and a regain in strength owing to FRCC’s self-healing mechanism. Different mixes of FRCC suggest an economical mixing methodology, where the strong bond between the PP fibers and cementitious matrix plays a key role in improving the tensile strength of the mortar. Additionally, the micro PP fiber samples demonstrate resistance to micro-crack propagation, observed as an increase in peak load value and shape deformation during compression and tensile tests. Notably, low volume fraction of macro-scale PP fibers in FRCC revealed higher post-crack energy than the higher dosage of micro-scale PP fibers. Lastly, few samples with a crack of < 0.5 mm exhibited a self-healing mechanism, and upon testing, the healed specimens illustrated higher strain values.

The increase in global environmental impacts has driven the development of eco-friendly and biodegradable materials for the next product generation. The use of synthetic fibers presents ecological concerns, while natural fiber application as a reinforcing no-material in composite development has stood out as a viable alternative. Natural fibers present attractive properties such as biodegradability, renewability, high specific strength, and specific modulus that make this material suitable for composites development in different areas such as packaging, automotive, sports, aerospace, medical devices, and so on. However, some challenges still limit its broad application, including poor interfacial adhesion between matrix and natural fibers, poor compatibility between non-polar matrix and natural polar fiber, poor moisture absorption, fire resistance, low impact resistance, low thermal stability, and low durability, which need to be addressed before processing. Furthermore, during the manufacture of this type of composite, the processing conditions, fiber loading, and inherent fiber properties must be evaluated, as all these factors affect the properties of the composites and may promote defects in the products. The wide variation in the characteristics of composites based on natural fibers presents a significant challenge to understanding the properties of these systems and ways to optimize them. This review seeks to infer, analyze, and optimize the characteristics of composite materials reinforced with natural fibers in relation to different types and sources of natural fibers, processing, modification techniques, physical, and mechanical behavior toward sustainable products. Therefore, this review aims to better understand the behavior of green composites and promote the increased use of renewable resources in advanced materials.

An experimental laboratory study of fiber-reinforced asphalt mortars with polyolefin-aramid and polyacrylonitrile fibers

The use of synthetic fiber and natural fiber for concrete production has been continuously investigated. Most of the materials have become popular for their higher flexibility, durability, and strength. However, the current study explores the engineering properties of cement concrete reinforced with nylon and jute fibers together. Varying proportions and lengths of nylon and jute fibers were utilized in the concrete mixture. Hence, the combined effects of nylon and jute fibers on workability, density, water absorption, compressive, tensile, flexural strength, and drying shrinkage of concrete were investigated. Results showed that concrete with 1% of nylon and jute fibers together by the volume fraction showed a maximum enhancement of the compressive strength, split tensile strength, and flexural strength by 11.71%, 14.10%, and 11.04%, respectively, compared to the control mix of concrete at 90 days. However, the water absorption of concrete increased with increasing nylon and jute fiber contents. The drying shrinkage of concrete decreased with the addition of nylon and jute fibers together after 90 days. Thus, the sparing application of both nylon and jute fiber as discussed in this study can be adopted for concrete production.

Influence of chemical modifications on water-sorption and mechanical properties of Agave fibres

Modifying buckling behavior of the composite structure has been investigated in the recent few years with different reinforcement fiber and powder materials and nanomaterials. It can be seen from previous studies that the addition of nanomaterials leads to a significant modification in the buckling behavior of structure by using a low mount of nanomaterials. In this work, reinforcement of composite materials using two types of nanomaterials together, SiO2 and Al2O3 nanomaterials, to modify the buckling behavior for plate structure is studied. Therefore, the investigation was done experimentally and numerically. The experimental work is performed by manufacturing composite plates with various weight fractions with the nanoeffect, and then their mechanical properties and buckling characterization were evaluated. The numerical work was done using the finite element method to estimate the plate structure’s buckling behavior with various nanomaterials effects. A comparison between the experimental and the numerical results for plate buckling behavior is expressed, showing that the discrepancy of the results was not more than 12.56%. Finally, the results showed that the buckling behavior for a reinforced plate was improved by 35% when two types of nanomaterials were used together.

Compared with synthetic fibers, natural fibers have shown the most significant promise as reinforcement materials for composites. Because they are derived from plants and animals, natural fibers are widely available and reasonably priced. They are also biodegradable. Date palms contain high dietary fiber, which is extracted via chemical, physical, mechanical, and biological techniques and has been employed in the development of composites. The date palm fiber (DPF) composites are developed through resin transfer molding, hand layup, compression molding, and filament winding. The composites developed with date palm fibers have shown remarkable improvements in mechanical, thermal, and physical properties. These appreciable properties possessed by the DPF composites have demonstrated their applications in the automotive industry, building construction, water treatment, biomedical, and pharmaceutical fields. DPFs are environmentally friendly and substitute materials that help achieve sustainable development goals by lowering excessive reliance on nonrenewable resources. This review offers a systematic and quantitative literature-based comparison of the relationships among extraction, processing, and property-performance in DPF composites, providing a comprehensive synthesis not available in earlier studies.

The emerging “green” economy is based on energy efficiency, renewable food stocks in polymeric products, industrial processes that reduce carbon emissions, and recyclable materials. Natural fiber is a type of renewable source and a new generation of reinforcements and integrators for polymer-based materials. Because of its advantages over synthetic fibers, the use of natural fibers as reinforcements in composite materials has become important in recent years. To meet certain design criteria, natural fiber-reinforced composites impose certain secondary operations during assembly. Limited literature is available only in connection with the processing of natural fiber-reinforced composites. This paper analyzes a comprehensive review of the natural fiber-reinforced composite processing literature along with the challenges during processing.