Comprehensive investigation on mechanical properties of mango seed shell short fiber-reinforced epoxy based polymer composites

This study concerns with investigation and analysis of hugely available, cost effective filler, obtained by grinding the Moringa oleifera leaves and its reinforcement in epoxy composites for semi‐structural applications. In this work, this novel filler is characterized by compositional analysis, FTIR, AFM, SEM, XRD, and TGA, along with the calculation of activation energy from two integral methods. To understand the interfacial surface chemistry of the fiber, X‐ray photoelectron spectroscopy (XPS) is also carried out. The size of filler was kept at 300 to 500 μm, and composites were prepared with five different loadings ranging from 5% to 25% using hand layup method of fabrication. The effect of varying loadings of filler on water uptake, mechanical, morphological, and thermal properties of its epoxy composites has been evaluated. Composites possess improved water resistance, tensile and flexural strengths in comparison with neat epoxy for an optimum loading of 20%, that is, 37 MPa. FWO and KAS methods are used to calculate the apparent activation energy of fillers. The apparent activation energy calculated from these methods comes to be 220 and 222 kJ/mol. The crystallinity index comes to be 55% which is comparable with other fibers. Approximately 12% increment in tensile strength and 10% in flexural strength takes place compared with neat epoxy at optimum fiber loading of 20%.

The impressive mechanical properties of carbon fibre reinforced polymer (CFRP) have stimulated research interest in the application of CFRP for the retrofitting and strengthening of ageing infrastructures. However, some obstacles such as debonding and the low shear strength of the bond, particularly at temperature about the glass transition temperature (Tg) of bond adhesive, limit the use of CFRP with steel structures. Nanofillers such as carbon nanotubes (CNTs) have the potential to improve the mechanical and thermo-mechanical properties of epoxy resin systems for this purpose. The objectives of the present work were thus threefold: (1) to understand the mechanical properties of CNTs via buckling analysis using molecular dynamics simulations, (2) to fabricate and characterize CNT reinforced epoxy composites to improve their mechanical and thermo-mechanical properties, and investigating the effect of ultrasonication energy, CNT geometry, dispersant type, and type of epoxy on the final properties, and (3) to apply CNT reinforced epoxy resins as structural adhesives in CFRP strengthened steel structures subjected to moderately elevated temperatures. The results show that the compression load capacity of short multi-walled CNTs (MWCNTs) was greater than that of long MWCNTs. It was observed that the variation of the buckling strain of short MWCNTs was inversely proportional to the number of nanotube walls. For slender MWCNTs, the buckling strains fluctuated as the number of walls increased. The strain increased for beam-like buckling mode, decreased for shell-like buckling mode and was approximately constant for shell-beam-like buckling mode. Increase in the length of MWCNT also led to a significant decrease of the buckling strain for short MWCNTs. However, chirality had no significant effect on the buckling strain of MWCNTs, nor did it alter the buckling mode of short MWCNTs. To obtain effective dispersion of CNTs in an epoxy matrix, high shear mixing, ultrasonication treatments and surfactants were found to be essential. It was shown that it is important to use a set of compatible key parameters such as sufficient sonication energy, a strong dispersant, together with the appropriate CNTs. The results show that using ductile epoxy with 3 wt.% CNT masterbatch could enhance Young’s modulus by 20%, tensile strength by 30%, flexural strength by 15%, and Tg by 34% of neat epoxy. The degree of CNT dispersion is not only a matter of the copolymer surfactant concentration; the copolymer adsorption morphology on the surface of CNTs also plays a role. Three adsorption morphologies, i.e. random, hemi-micelle, and cylindrical morphology, of BYK 9076 copolymer on the CNT surface were observed at different copolymer/CNT ratios. It was found that hemi-micelle morphology could prevent the agglomeration of CNTs when CNT concentration increased up to 8.7 mg/ml, whereas a cylindrical morphology was more efficient and stable in providing dispersion of a higher concentration of CNTs. It was found that the failure mode in both double strap joints with neat epoxy and/or CNT-epoxy was a combination of steel-adhesive interface failure, cohesive failure, epoxy-CFRP interface failure and CFRP delamination. Joints bonded with CNT-epoxy adhesive possessed an effective bond length of about 60 mm, whereas the effective bond length of joints bonded with neat epoxy was about 70 mm. Increasing the test temperature caused a transition of failure mode from the epoxy-CFRP interface to the steel-epoxy interface and to the cohesive layer in joints with neat epoxy. The cohesive failure could be avoided in the joints with CNT-epoxy. Observations from scanning electron microscopy revealed that CNTs bridge the cracks in epoxy matrix, providing a reinforcing effect. Overall, CNT-epoxy resin systems can provide a significant increase (about two-fold) in bond strength at moderately elevated temperatures compared with neat epoxy.

Incorporating graphene into epoxy composites is a facile strategy to improve their mechanical performances. However, the uniform and reliable dispersion of graphene within epoxy matrix remains a large challenge owing to the intrinsic difference in chemical properties. Here, pyrene‐functionalized polyethylene glycol (Py‐PEG‐Py) was easily synthesized and utilized as a dispersant to homogenize graphene. The effect of graphene loading on mechanical performances of reinforced epoxy composites was also investigated. As 0.01 to 0.05 wt% of graphene were incorporated in epoxy resin, the resulted composites exhibited excellent improvement in flexural strength and fracture toughness compared with neat epoxy. Typically, the flexural strength increased from 63.57 ± 1.5 MPa for neat epoxy to 108.36 ± 1.9 MPa (about 70.5%) for composite, and the fracture toughness (KIC) increased from 1.25 MPa m1/2 for neat epoxy to 2.15 MPa m1/2 (around 72%) for composite modified with only 0.04 wt% of graphene and 4 wt% of Py‐PEG‐Py. Crack pinning caused by well dispersed graphene was contributed to enhancement of the fracture toughness. This work reveals a tiny amount graphene can also largely improve the mechanical properties of composites, providing a feasible approach to disperse graphene and fabricate high performance graphene composites.

Mechanical behavior of unsaturated polyester toughened epoxy hybrid polymer network reinforced with glass fibre

In the present work, Eulaliopsis binata, a natural fiber collected from the eastern part of India is taken as a reinforcement with epoxy resin to develop a new class of polymer composite material, which has been unexplored till date for tribological applications in the composite industry. Different characterization studies of the fiber such as SEM, EDS, XRD are carried out to astern its potential to be used as a fiber in composite. Short Eulaliopsis binata fiber of different weight percent (10, 20, 30, and 40) is incorporated in neat epoxy and polymer composites are fabricated using the hand lay-up method. Solid particle erosion behavior of the fabricated composites is studied with four different impact velocities (48, 72, 82, 116 m/s) and impinging angles (30°, 45°, 60°, 90°). Improved erosion wear resistance is exhibited by the composites after the addition of Eulaliopsis binata fiber to neat epoxy. In addition, the inclusion of fiber altered the erosion behavior of neat epoxy from brittle to semi ductile nature. The impact velocity of the erodent particles also shows significant effect on the erosion behavior of the developed composites. The eroded surfaces of the worn samples are analyzed with SEM to ascertain the failure mechanism of the developed composites.

Fabrication of geopolymer composites using egg-shell and fly-ash: Comparison between the strength and stability, physio-chemical and mechanical properties

A basic characterization of novel epoxy matrix composites incorporated with up to 40 vol% of processed leaf fibers from the Copernicia prunifera palm tree, known as carnauba fibers, was performed. The tensile properties for the composite reinforced with 40 vol% of carnauba fibers showed an increase (40%) in the tensile strength and (69%) for the elastic modulus. All composites presented superior elongation values in comparison to neat epoxy. Izod impact tests complemented by fibers/matrix interfacial strength evaluation by pullout test and Fourier transformed infrared (FTIR) analysis revealed for the first time a significant reinforcement effect (> 9 times) caused by the carnauba fiber to polymer matrix. Additional thermogravimetric analysis (TG/DTG) showed the onset of thermal degradation for the composites (326 ~ 306 °C), which represents a better thermal stability than the plain carnauba fiber (267 °C) but slightly lower than that of the neat epoxy (342 °C). Differential scanning calorimetry (DSC) disclosed an endothermic peak at 63 °C for the neat epoxy associated with the glass transition temperature (Tg). DSC endothermic peaks for the composites, between 73 to 103 °C, and for the plain carnauba fibers, 107 °C, are attributed to moisture release. Dynamic mechanical analysis confirms Tg of 64 °C for the neat epoxy and slightly higher composite values (82–84 °C) due to the carnauba fiber interference with the epoxy macromolecular chain mobility. Both by its higher impact resistance and thermal behavior, the novel carnauba fibers epoxy composites might be considered a viable substitute for commonly used glass fiber composites.

Epoxy composites with biphenyl liquid crystalline polyester (BLCP)-grafted graphene oxides (GO) as inclusions were prepared successfully. The thermal and texture analyses of BLCP were characterized by DSC and POM. The results show that the texture structure of BLCP turned into fan texture from woven texture with increasing temperature and present double texture structure. More importantly, the thermal and mechanical properties of epoxy composites could be improved by incorporating BLCP-grafted GO (BLCP-GO). The epoxy composite with only 0.5 wt% BLCP-GO produced an increase in the initial decomposition temperature (T d) by 28 °C and glass transition temperature (T g) by 17.2 °C when compared with the neat epoxy. Moreover, for the mechanical properties tests, the composites with 1.0 wt% BLCP-GO exhibit an increase in impact strength, tensile strength, flexural strength and flexural modulus by 103, 52, 66, and 56 %, respectively, compared with the neat epoxy resin. These excellent performances of the graphene–epoxy composites have a great potential for applications in aerospace and other electrical devices.

Natural fibers from renewable resources offer a sustainable as well as biodegradable alternative to synthetic reinforcements in polymer composites. This study investigates the thermal and mechanical behavior of Borassus husk fiber-reinforced epoxy composites, fabricated via the hand layup method. The fibers were alkali-treated with 5% sodium hydroxide (NaOH) for varying durations (0.5 to 2 h) to improve interfacial bonding. Thermal and dynamic mechanical properties were analyzed using thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Alkali treatment enhanced thermal stability, as indicated by increased char residue (up to 9.43%) and higher integral process decomposition temperatures (IPDT), with the 1-h treated sample achieving the highest IPDT of 554°C. Compared to neat epoxy and other natural fiber composites, Borassus fiber composites exhibited superior energy dissipation, stiffness, and mechanical strength. Although the glass transition temperature (Tg) decreased from 149°C in neat epoxy to between 122°C and 140°C in treated composites, the values remained competitive. The 0.75TBHFE demonstrated the best overall performance, with optimal storage modulus, improved damping and minimal mass loss. These findings underscore the potential of alkali-treated Borassus husk fiber/epoxy composites for high-performance applications, such as aerospace, while promoting environmental sustainability and supporting net-zero carbon emission goals.

This work outlines the characterization of epoxy resin [Bisphenol A-(epichlorhydrin): epoxy] and hardener [[Formula: see text](3-dimethylaminopropyl)-1,3-propylenediamine] with various inorganic nano-fillers. Dielectric characterizations of epoxy, hardener, neat epoxy (epoxy + hardener) and nano-epoxy (nano-filler + neat epoxy) composites loaded with 1 wt.% of inorganic nano-fillers (SiO2, Al2O3, TiO2 and ZnO) were carried out using precision LCR meter, over the frequency range of 1 kHz–2 MHz at a constant temperature of 300.15 K. The structural information of nano-fillers, neat epoxy and nano-epoxy composites was understood by Fourier transform infrared spectroscopy and by XRD. Moreover, hardness and shear strength (shear punch) were also determined in order to gain additional information about the mechanical properties of epoxy composite. Influence of inorganic nano-fillers on the dielectric properties, structural chemistry and mechanical properties of neat epoxy composite is discussed thoroughly in this study.

The present work deals with the characterization of mango seed shell fiber reinforced epoxy composites by using hand layup method by varying the volume composition of the mango seed shell from 0 vol. % to 60 vol. % (M-0 to M-60). The physical density test, tensile test, flexural test, and water absorption test were conducted as per the American Society for Testing and Materials (ASTM) standards. Results revealed that the tensile strength of M-20 (20 vol. %) is 43% more than a neat epoxy, while the flexural strength of M-50 (50 vol. %) is greater than 10.85% more than a neat epoxy. The water absorption test was conducted by immersing the samples in distilled water at room temperature, and the weight of the specimens was measured and recorded at every 24-hour time interval. For all composite samples, saturation in water absorption and thickness swelling were observed after 432 hours of water immersion. The moisture absorption increases with the inclusion of reinforcements as compared to the neat epoxy samples. However, for the M-50 composite, the water absorption decreases due to the uniform mixing and stronger bonding between the matrix and the reinforcements. The scanning electron microscope (SEM) images of the composite specimens also depicted the particulate fiber distribution and the presence of micro-voids in the epoxy matrix.

Syntactic foam composite offers versatile application possibilities in marine, structural, aerospace industries due to their good tensile, flexural, and compressive strength, corrosive resistance, high specific strength and modulus, light weight nature. Their porous structure is by mixing hollow particles called microspheres as fillers into matrix materials such as polymer, metal or ceramic etc. In this study, a high-density hollow glass microsphere is used to fabricate syntactic foam by mixing it with epoxy resin. Five different compositions 5, 10, 15, 20 and 25 vol% of hollow glass microspheres were varied in fabricating the syntactic foam. Impact and flexural properties were investigated on the syntactic foam. All the compositions of the volume fraction variations of hollow glass microsphere content in the syntactic foam increased more than the neat epoxy. The highest impact resistance, flexural strength and flexural modulus is at 5 vol%, 113.12 kJ/m2, 86.7 MPa, and 80 GPa respectively with 25.2%, 38.29%, and 33.25% increase respectively more the neat epoxy while the specific impact and flexural strength is at 25 vol% with 53.78% and 57.77% increase respectively more than the neat epoxy.

In this work, the effect of cellulose nanofiber (CNF) on the mechanical properties of long pineapple leaf fiber (PALF)-reinforced epoxy composites was investigated. The content of PALF was fixed at 20 wt.% and the CNF content was varied at 1, 3, and 5 wt.% of the epoxy matrix. The composites were prepared by hand lay-up method. Comparison was conducted between CNF-, PALF- and CNF-PALF-reinforced composites. It was found that the introduction of these small amounts of CNF into epoxy resin caused very small effects on flexural modulus and strength of neat epoxy. However, impact strength of epoxy with 1 wt.% CNF increased to about 115% that of neat epoxy, and, as the content of CNF increased to 3 and 5 wt.%, the impact strength decreased to that of neat epoxy. Observation of the fractured surface under electron microscope revealed the change in failure mechanism from a smooth surface to a much rougher surface. For epoxy containing 20 wt.% PALF, both flexural modulus and strength increased significantly to about 300% and 240% that of neat epoxy. The composite impact strength increased to about 700% that of the neat epoxy. For hybrid systems containing both CNF and PALF, there were few changes observed in both flexural modulus and strength compared to the PALF epoxy system. However, much improvement in impact strength was obtained. By using epoxy containing 1 wt.% CNF as the matrix, the impact strength increased to about 220% that of 20 wt.% PALF epoxy or 1520% that of neat epoxy. It thus could be deduced that the spectacular improvement in impact strength was due to the synergistic effect of CNF and PALF. The failure mechanism leading to the improvement in impact strength will be discussed.

Mechanical and thermal performance of recycled glass fiber reinforced epoxy composites embedded with carbon nanotubes

Growing environmental concerns have heightened the demand for eco‐friendly materials, prompting a shift from carbon fibers and conventional polymers to recyclable biopolymer composites. Natural fibers, such as hemp, are widely incorporated into green epoxy composites to enhance performance, with applications spanning industries including transportation, aerospace, construction, energy, and shipping. The thermal and mechanical properties of hemp fiber‐reinforced green epoxy composites are essential in determining their effectiveness and broader viability. However, challenges such as limited fracture resistance, fragility, low impact strength, and fatigue resistance currently restrict their durability, particularly in demanding applications like automotive engineering. This study investigates the mechanical, thermal, fire, and morphological properties of hemp fiber‐reinforced green epoxy composites through comprehensive mechanical, thermal, and flammability testing, as well as SEM analysis to examine fiber behavior and microstructure. The use of green epoxy is also an area that was not deeply explored by the researchers. Furthermore, hemp fibers are known for their tensile strength and environmental benefits, which result in sustainable material production. Results demonstrated significant improvements in flexural strength, with values increasing from 53.654 MPa in neat epoxy to a minimum of 139.834 MPa in reinforced samples. Impact strength also improved, ranging from 4.04 to 8.26 kJ/m2, along with enhanced flame resistance. In conclusion, hemp fiber‐reinforced green epoxy composites showed overall performance improvements, except in tensile strength, compared to neat green epoxy samples, underscoring their potential in sustainable material applications.Highlights Hemp fiber improves green epoxy's flexural and impact strength. Enhanced flame resistance in green epoxy composites with hemp fiber. SEM analysis reveals improved fiber microstructure in composites. The flexural strength of composites exceeds neat green epoxy by 160%.