Bio‐inspired low dielectric phenol formaldehyde laminates for electrical insulation applications

This paper describes the tensile, impact, flexural properties and aging behavior of short banana fiber reinforced polyester composites with special reference to the effect of fiber length and fiber content. Maximum tensile strength was observed at 30 mm fiber length while impact strength gave the maximum value for 40 mm fiber length. Incorporation of 40% untreated fibers gave a 20% increase in the tensile strength and a 341% increase in impact strength. On treatment with silane coupling agent, composites showed a 28% increase in tensile strength and a 13% increase in flexural strength. Aging studies showed a decrease in tensile strength of the composites. The experimental tensile strength values were compared with theoretical predictions according to Piggot equation. Scanning electron microscopy studies were carried out to understand the morphology of the fiber surface, fiber pullout and interface bonding. Water absorption studies showed an increase in water uptake with increase in fiber content. Finally, the properties of banana fiber reinforced polyester composites have been compared with other natural fiber reinforced composites.

Effect of fiber surface modification on the mechanical and water absorption characteristics of sisal/polyester composites fabricated by resin transfer molding

The influence of lignite fly ash (LFA) on the physical properties of polymer matrix composite (PMC) was studied by comparing the theoretical, experimental, and numerical simulation results. The study was conducted on various compositions of PMCs prepared using epoxy resin amalgamated with LFA and sisal fiber by hand layup process. The two-dimensional approach of testing the tensile strength of PMC consisted of the rule of mixtures and Halpin–Tsai methods. On the other hand, the three-dimensional approach of testing the tensile strength and flexural strength of PMC was based on finite element analysis using ANSYS Workbench. Collectively, it can be deduced that PMC with 10 wt.% LFA has better mechanical properties than PMC samples without it, which is shown by the higher value of tensile strength as 31 MPa. The observed results showed aconsiderable increase in flexural strength to 85.576 MPa for the sample containing 10 wt.% of LFA. Anotable decrease in the wear resistance from 11.5 to 4.7 at 20 N load showed its improved durability. In addition, Ahigh increase in impact strength to 29 J showed its higher mechanical strength.

The fiber architecture can significantly influence the rate of impregnation of a resin in making composites and the load-bearing ability of individual fibers on testing of the loading directions. Moreover, achieving the maximum mechanical performance of a natural fiber composite selection of yarn liner density and optimization of fabric structure and further modification of the composites remains a great challenge for the composite research community. In this study, a number of jute-based woven derivatives (plain, 2/1 twill, 3/1 twill, zigzag based on a 2/2 twill, and diamond based on a 2/2 twill) have been constructed from similar linear densities of yarn. The effect of the fabric architecture and further modification of optimized composites by applying γ-radiation is also explained in this study. The experimental results show a 54% increase in tensile strength, a 75% increase in tensile modulus, a 69% increase in flexural strength, a 124% increase in flexural modulus, and 64% increase in impact strength of twill (3/1) structured jute fiber polyester composites in comparison to other plain and twill structured composites. A further mechanical improvement of around 20–30% is possible for the optimized twill structured composites by applying γ-radiation on the composites. An FTIR, TGA, and SEM study confirms the chemical, thermal, and fractographic changes after applying the modification of composites.

Sisal fiber, available in various semi-arid regions around the world, is the most studied natural fiber for the reinforcement of polymeric and cement-based composites. However, to improve the fiber–matrix interaction and to reduce the hydrophilicity of the fiber, it is necessary to establish surface treatments that employ sustainable materials, unlike conventional surface treatments. In this work, sisal fibers were coated separately with cellulose acetate, hydrophobic starch, and cassava starch biopolymers in order to verify the possibility of reducing the water absorption capacity of the fiber by the use of a biodegradable resin. A combination of Fourier transform infrared spectroscopy, scanning electron microscopy, and water absorption and tensile tests was used to investigate the effects of the surface treatments on the sisal fiber properties. Pullout tests of sisal fibers with embedded lengths of 20 mm and 40 mm were performed to determine the influence of the treatments on the bond stress with cement mortar. Composites with 4 vol % short fiber were produced and tested for flexion. The study results indicated that all treatments reduced the mechanical properties of the fiber; however, the layer of the cellulose acetate biopolymer film formed on the fiber surface was effective in reducing the fiber hydrophilicity. Experimental tests on the composites revealed that the cellulose acetate treatment reduced the bond stress and, to a lesser degree, the flexural toughness of the composite, despite the increase in flexural strength.

Natural fibers are replacing synthetic fibers and are used to develop different useful composite products due to their environmental advantages. To fabricate high-performance composites, high-quality natural fibers are essential. Fiber quality largely depends on the extraction method and subsequent treatment. In this study, fibers were extracted using both machine and manual methods, treated with 5% NaOH, and used at a 30:70 fiber-to-matrix volume ratio to fabricate composite laminates. Key properties such as tensile, flexural, and impact strength, water absorption, elemental composition, and morphological structure were analyzed. When comparing the untreated fiber composites, the machine-extracted samples exhibited a 6.7% increase in tensile strength and a 7.06% increase in flexural strength over those extracted manually. For treated fiber composites, the machine-extracted samples showed improvements in tensile, flexural, and impact strengths of 19.82%, 19.38%, and 26.59%, respectively, compared to those extracted manually. These enhancements indicate that machine extraction provides fibers with better structural integrity and consistency, contributing to stronger fiber–matrix bonding. The machine-extracted treated composites showed reduced water absorption and smaller fiber diameters, indicating that machine extraction was more effective in removing impurities from the fibers. Scanning electron microscopy (SEM) confirmed improved fiber–matrix interfacial bonding in the machine-extracted composites, which also exhibited better water resistance. This study highlights that fiber extraction and treatment significantly influence the mechanical, physical, and morphological properties of natural fiber composites, as verified through SEM, EDS, and universal testing machine (UTM) analysis.

The mechanical properties of fiber‐reinforced polymer composites strongly depend on its interfacial bond strength and fiber content, and their further lightweight is the current urgent demands for industry. Basalt fiber (BF), as an emerging natural and environmental‐friendly material, possess a broad application prospect as it can replace glass fiber. Herein, strong PP/BF composites with excellent heat deflection temperature and enhanced impact performance were successfully prepared, which augmented with the increase of BF content. The effect of PP grafted with maleic anhydride (PP‐g‐MAH) on the interfacial bonding properties between BF and PP was investigated based on the PP/20BF composite system, which was significantly improved due to the reaction of maleic anhydride polar groups with the hydroxyl groups on the BF surface. The incorporation of PP‐g‐MAH led to 24.7%, 46.9%, and 77.2% increase in tensile strength, flexural strength and impact strength of PP/20BF composites, respectively. Moreover, the crystallization properties, rheological behavior and thermal stability of the composites were significantly enhanced, which all contributed to the refinement and densification of cellular structure. The cell size was reduced from 36.38 to 13.41 μm after the addition of PP‐g‐MAH with an opening distance of 2 mm, and the cell density was enhanced by nearly one order of magnitude to 6.43 × 107 cells/cm3. The cellular structure further lightens the weight of product and promotes the lightweight development of PP/BF composites.

The potentials of natural fibre encourage researchers to shift their interest from synthetic fibre. Numerous works have been done on the effective use of several natural fibres in manufacturing composites for automotive and structural applications. In the current investigation, effort has been made to evaluate the effect of the addition of glass fibre and influence of stacking sequence on mechanical properties of kenaf-/glass-reinforced hybrid composite laminates. Hybrid laminates with five different stacking sequences were fabricated by using hand layup technique. After curing, the fabricated composite laminates were cut to the dimension as per ASTM standard. Different tests have been carried out to determine tensile strength, flexural strength, and micro-hardness of fabricated laminates. Based on the findings, a sharp increase in mechanical properties is observed due to addition of glass fibre. Laminate with four layers of kenaf fibre shows minimum values of tensile strength, flexural strength and micro-hardness values. On subsequent addition of glass layer to the laminates, an increase in tensile strength from 35.78 to 166.38 MPa, flexural strength from 42.91 MPa to 155.83 MPa and micro-hardness value from 11.51 to 20.84 HV are reflected. To validate the experimental findings, numerical analysis has been made by using ANSYS R19.0 software. On comparison of experimental and numerical values, the deviation of the result is limited to 3%–12%. The morphology of fracture surfaces is also studied by using scanning electron microscope.

The aim of the article is to analyze the influence of short coir, glass and carbon fiber admixture on the mechanical properties of fly ash-based geopolymer, such as: flexural and compressive strength. Glass fiber and carbon fibers have been chosen due to their high mechanical properties. Natural fibers have been chosen because of their mechanical properties as well as for the sake of comparison between their properties and the properties of the artificial ones. Fourth series of fly ash-based geopolymers for each fiber was cast: 1, 2, and 5% by weight of fly ash and one control series without any fibers. Each series of samples were tested on flexural and compressive strength after 7, 14, and 28 days. Additionally, microstructural analysis was carried out after 28 days. The results have shown an increase in compressive strength for composites with fibers—an improvement in properties between 25.0% and 56.5% depending on the type and amount of fiber added. For bending strength, a clear increase in the strength value is visible for composites with 1 and 2% carbon fibers (62.4% and 115.6%). A slight increase in flexural strength also occurred for 1% addition of glass fiber (4.5%) and 2% addition of coconut fibers (5.4%). For the 2% addition of glass fibers, the flexural strength value did not change compared to the value obtained for the matrix material. For the remaining fiber additions, i.e., 5% glass fiber as well as 1 and 5% coconut fibers, the flexural strength values deteriorated. The results of the research are discussed in a comparative context and the properties of the obtained composites are juxtaposed with the properties of the standard materials used in the construction industry.

This study investigates the development of sustainable flax/Diglycidyl ether Bisphenol-A (DGEBA) composite enhanced through cryogenic surface treatment of flax fibers and the dispersion of Multi-walled carbon nanotubes (MWCNT) in the polymer matrix. The methodology involves modifying flax fibers via cryogenic treatment to improve surface topology and thermal stability, alongside incorporating MWCNT into the DGEBA polymer to enhance composite properties. The effects of these modifications were evaluated through mechanical and thermal testing, focusing on tensile and flexural strengths, and degradation temperature. Results show that cryogenic treatment increases the thermal stability of flax fibers, raising degradation temperature by 10°C, attributed to an increase in hemicellulose composition. Mechanically, cryogenic-treated flax fiber composites without MWCNT demonstrated a 7.3% increase in tensile strength and a 28% increase in flexural strength. The dispersion of MWCNT in DGEBA improved tensile and flexural strength by 8.3% and 29%, respectively, in untreated flax fiber composites. When both cryogenic treatment and MWCNT dispersion were applied, tensile strength improved by 17.2% and flexural strength by 36.6%, attributed to enhanced interfacial bonding between the fiber and matrix. These findings illustrate the synergistic effects of cryogenic treatment and MWCNT dispersion, demonstrating their potential to optimize the thermal and mechanical performance of sustainable polymer composites.

To investigate the toughening mechanisms and key influencing factors of sisal fiber reinforcement in activated magnesia oxide carbonized raw soil materials, splitting tensile and compressive tests were conducted on blocks of activated magnesia oxide carbonized soil incorporating different lengths and contents of sisal fibers. A stage‐wise analysis was performed to elucidate the constitutive relationships of the reinforced activated magnesia oxide carbonized raw soil, specifically highlighting the enhancing effects of different fiber lengths and contents on the material properties. Furthermore, a gray relational analysis was conducted to identify the strength of relationships among various influencing factors on the material’s toughening effects. Results revealed that the splitting tensile strength of the activated magnesia oxide carbonized raw soil fluctuated with increasing sisal fiber content and length. Specifically, the relationship between sisal content and tensile strength exhibited a “double‐peaked” pattern, with peaks at 1% and 3% fiber content. After 9 days of carbonation, blocks with 3% sisal fibers showed an impressive 186.08% increase in tensile strength compared with carbonized samples without fibers. In contrast, the relationship between sisal length and tensile strength appeared as a “triple‐peaked” curve, with peaks at 5, 15, and 30 mm. When 1% of 30 mm sisal fibers were used, the tensile strength increased by 154.21% compared with the fiber‐free variant and by 732.8% compared with conventional raw soil. These trends were not significantly affected by material specifications or carbonation time. The influence of sisal fiber content on toughening was greater than that of fiber length, which was in turn greater than that of carbonation time. Thus, managing sisal fiber content may be the most effective strategy for enhancing material toughness. Overall, the increased strength of activated magnesia oxide carbonized raw soil with sisal fiber reinforcement reveals its stability and potential for sustainable applications, particularly in ecofriendly construction.

This study includes untreated sisal fibers, fibers that had been mercerized using 0.06 M NaOH and fibers cornified at 100°C in different volume fractions used as reinforcement into a general purpose unsaturated polyester resin matrix. Untreated sisal fiber-reinforced polyester resin displayed the most significant gain in flexural strength with a Modulus of Rupture of 79.32 Mpa at 2% fiber volume fraction, which represented a 296.65% increase compared to unreinforced polyester resin. Cornified sisal fiber-reinforced polyester resin had the least significant gain in flexural strength with a maximum Modulus of Rupture of 49.71 Mpa at a 1.2% fiber volume fraction, which represented a 142.8% increase in flexural strength compared to the unreinforced polyester resin specimen. These results show that the untreated sisal fiber reinforcement could withstand the thermal effect of the exothermic curing of unsaturated polyester resin better than the surface-modified sisal fibers.

Traditional concrete, made from binding material, fine aggregate, coarse aggregate, and water, often suffers from low tensile strength and susceptibility to cracking. Microscopic cracks can develop before any significant load is applied, making the structure vulnerable to damage. Fiber reinforced concrete (FRC) tackles these issues by adding different types of fibers, like steel, glass, and polypropylene, to enhance strength and flexibility. This study aims to find the best mix for Steel Fiber Reinforced Concrete (SFRC) and Hybrid Fiber Reinforced Concrete (HFRC) of M25 grade. Compressive strength, split tensile strength, flexural strength, Young's modulus, and ultrasonic pulse velocity tests are conducted to see how well the fibers work to prevent cracks and boost strength. Results have showed that SFRC with 1.5% steel fiber content significantly improve compressive strength, split tensile strength, and flexural strength compared to normal concrete. Similarly, HFRC mix of steel, glass, and polypropylene fibers, performs well, showing a notable increase in split tensile and flexural strength. The percentage increase in strength highlights how effective fiber reinforcement can be, with HFRC showing better results in some aspects compared to SFRC. Furthermore, both SFRC and HFRC are stiffer than normal concrete, indicating better overall structural integrity. Our comparison suggests that incorporating a blend of fibers, as seen in HFRC, can provide even better results, particularly in enhancing split tensile and flexural strength, showing promise for future reinforced concrete applications.

Surface modification of graphene oxide (GO) is one of the most important issues to produce high performance GO/epoxy composites. In this paper, the imidazole ionic liquid (IMD-Si) was introduced onto the surface of GO sheets by a cheap and simple method, to prepare a reinforcing filler, as well as a catalyst in epoxy resin. The interlayer spacing of GO sheets was obviously increased by the intercalation of IMD-Si, which strongly facilitated the dispersibility of graphene oxide in organic solvents and epoxy matrix. The addition of 0.4 wt % imidazolium ionic liquid modified graphene oxide (IMD-Si@GO), yielded a 12% increase in flexural strength (141.3 MPa), a 26% increase in flexural modulus (4.69 GPa), and a 52% increase in impact strength (18.7 kJ/m2), compared to the neat epoxy. Additionally the IMD-Si@GO sheets could catalyze the curing reaction of epoxy resin-anhydride system significantly. Moreover, the improved thermal conductivities and thermal stabilities of epoxy composites filled with IMD-Si@GO were also demonstrated.

Investigation of the effect of bagasse ash, hooked steel fibers and glass fibers on the mechanical properties of concrete