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Nov 14, 2024

Effects of cashew nutshell biofillers on the mechanical and thermal behaviour of Basalt/Hibiscus vitifolius hybrid fabrics reinforced polymer biocomposites | Scientific Reports

Scientific Reports volume 14, Article number: 27636 (2024) Cite this article Metrics details Basalt-based natural fiber hybrid composites with fillers are always the most anticipated composite

Scientific Reports volume 14, Article number: 27636 (2024) Cite this article

Metrics details

Basalt-based natural fiber hybrid composites with fillers are always the most anticipated composite material candidates for lightweight structural applications. Current work focusses on the preparation, characterization and testing of Basalt (B)/Hibiscus vitifolius (HV) based epoxy biocomposites with and without cashew nutshell fillers. Individual fiber reinforced composites (with 40 vol% of fibers) and hybrid composites (with 40 vol% of fibers in the ratio 1:1) filled with 10–30 vol% of fillers were manufactured using compression moulding techniques. The X-ray diffraction spectrum showed the crystal size and crystallinity index for all biocomposites. It showed a monoclinic crystal structure with an irregular surface of the fiber and filler. The FTIR spectrum showed the chemical composition presented in the biocomposites. The presence of filler and fibers was confirmed by different spectral peaks. Hybrid biocomposites were then subjected to mechanical and thermal investigations. The mechanical properties of the biocomposites showed that the tensile, flexural, and impact strength of the biocomposites varies with the concentration of the cashew nutshell filler. The surface morphology of the fractured sample showed the presence of fabric layer, fiber fracture and pull out, and homogenous dispersion of the fillers in the biocomposites. Thermal degradation curves showed that the thermal stability of biocomposites is improved by adding filler up to 20 vol% because the filler acted as a barrier element for the thermal degradation of biocomposites. From the results, it could be understood that these biocomposites find their applications probably in lightweight structures.

Natural fiber-based polymer biocomposites have been used very commonly in automobile, construction, and aerospace fields for the last three decades1,2. For increasing the mechanical properties of biocomposites, natural fiber along with synthetic and basalt fibers are used to develop the biocomposites and study the various characteristics. The properties of biocomposites are based on the fiber orientation, fiber weight or volume content, stacking method, etc3,4,5. The stacking of the pure jute biocomposite had shown more impact strength than the hybrid fiber-reinforced biocomposites. The tensile strength of pure basalt fiber biocomposite was 16% more than when compared to hybrid biocomposites6. Jute and basalt fiber hybrid biocomposites were prepared by hand layup method and the stacking thickness was varying the impact energy of the biocomposites. Mechanical tests show results were in line with predictions, revealing a high coefficient of variation due to resin transfer moulding production issues, which was confirmed by microscopic analysis. Here the modulus of elasticity in the compression is 24% more than that of the modulus of elasticity in bending7. Basalt fibers exhibit amorphous structures, with ‘microcrystal’ size impacting mechanical strength. Adhesion is superior to sized glass fibers, comparable to carbon fibers, and can be enhanced by increasing polymer matrix polarity8. The highlights of the fabrication, mechanical properties, process parameters, and applications of hybrid polymeric biocomposites. Manufacturing through hand layup enhances mechanical properties until agglomerates form, limiting volume fraction9.

The impact properties of biocomposites comprising eight plies of basalt with jute fibers polyester exhibit superior performance compared to those containing 4 plies of jute and basalt fiber with a 2 mm thickness10. The four layers of basalt fiber at the center and also the placement of the fibers at the extreme in a stacking sequence showed maximum tensile strength11,12,13,14. Using the injection moulded Polypropylene biocomposites with short glass and basalt fibers, the polymer biocomposites were manufactured with low fiber length and high volume fraction of fibers15. The synergies between glass and basalt fibers in enhancing strength were further confirmed through Charpy impact tests. The addition of basalt fibers to carbon fiber laminates not only elevated the strength but also enhanced the absorption of impact energy, particularly improving fracture propagation components16,17. Basalt and glass fiber-reinforced polypropylene biocomposites were immersed in seawater and experienced mass gain from water absorption and soluble material extraction. Over time, tensile and bending strengths decreased due to physical damage and chemical degradation. Chemical stability in seawater is comparable for both, with potential improvement suggested by reducing Fe2 + content in basalt fibers18.

A few studies were carried out on Tindora and Calotropius gigantea fiber reinforced epoxy composites filled with Haritaki powder (HP) in various weight fractions. Mechanical and absorption property results suggested that the composites filled with HP exhibited better properties than the unfilled hybrid composites19. A few experiments were carried out on jute and hemp hybrid fiber composites filled with tamarind seed filler (TSF) in various proportions. Results portrayed that the biocomposites with 50% TSF powder exhibited better mechanical properties when the hybridization ratio of the composites was 1:120. The addition of fillers (cork powder and nano clays) significantly increased the maximum impact load, with nano clays exhibiting the best elastic recuperation performance. The fillers improved residual strength, with nanoclays yielding the best results. The enhanced properties with the incorporation of natural fibers, and hybridization of the composites with biofillers were extensively studied, and concluded that the incorporation of biofillers had positive effects on mechanical and thermal properties of the hybrid composites21,22,23,24.

Anisotropy is influenced by the properties of reinforcing fibers, with basalt and hemp fibers showing limited direction dependence, while carbon and glass fibers exhibit significant anisotropy. Static mechanical tests reveal improved strength properties compared to the pure PP matrix, with the degree of improvement linked to fiber properties and cost25,26,27. The utilization of basalt fiber in biocomposites, initially for military and industrial purposes. Basalt, found to outperform asbestos and glass fibers, is highlighted for its eco-friendliness, chemical inertness, and promising mechanical properties28,29. The jute, basalt and E-glass fiber-reinforced plastic laminates revealed that basalt biocomposites outperformed in terms of Young’s modulus, compressive strength, and flexural behaviour. However, glass exhibited higher tensile strength while jute and basalt hybrid exhibited appreciable characteristics30. Basalt biocomposites and BG-HI hybrids demonstrated superior energy absorption compared to glass and BG-HS laminates. Glass laminates exhibited poor damage resistance, improved by hybridization with the basalt layer31. Hence, the hybridization of basalt and glass fiber with any natural fiber had synergistic effects. For instance, in a study conducted using basalt and glass fiber hybrid composites reinforced with flax fibers in different layering sequences, all the compositions attained better mechanical properties due to the presence of flax fibers in each of its composite configurations32. From all the above discussions, it was understood that the hybridization of basalt fibers with natural fibers resulted in enhanced mechanical properties and thermal stability. Additionally, when biofillers were used to increase the density of the biocomposites, the mechanical properties were improved further. However, a minimal literature background is available for hybridizing basalt and HV fibers filled with cashew nutshell powders. The evidence for the properties improvement were also very less which would be the novelty of the current experimental work. Accordingly, the current experimental works focussed on hybridizing basalt fibers with Hibiscus Vitifolius (HV) fibers and Cashew nutshell powder (C) and evaluating the mechanical and thermal properties of the hybrid biocomposites. The thermal stability of the biocomposites was determined using thermogravimetric analysis and the biocomposites were characterized using X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR).

Figure 1a shows bi-directional plain basalt fiber fabric that was purchased from Go Green Products, Chennai, and Fig. 1b plain Hibiscus vitifolius fiber fabric (HV) was prepared using handloom machine by manual process in Department of Mechanical Engineering, Kongu Engineering College, Erode, Tamil Nadu.

(a) Basalt fiber fabric, (b) Hibiscus vitifolius fabric.

Epoxy resin of laboratory grade LY556 epoxy and hardener of grade HY951 was purchased from Covai Seenu industry (Resin supplier) in Coimbatore, Tamil Nadu. The viscosity of resin and hardener is around 12,000 MPa and 250 Cps. The density of epoxy resin is 1.20 g/cm2 and density of hardener is 0.98 g/cm2. The thermal resistance of epoxy resin is 315 ºC. Table 1 shows the physical and mechanical properties of the materials.

The basalt and HV fiber biocomposite were fabricated using the compression molding method. The basalt and HV fiber were cut according to the size of the mold 240 mm × 200 mm. Then to achieve the mixture the resin and hardener were poured into a cup and stirred for some time. The basalt and HV fibers were then layered and the mixture of resin and hardener was mixed with the cashew nutshell powder fillers at a volume fraction of 10, 20, and 30 vol% separately. After placing the laminates of basalt and HV fibers in the mould, the mixture of resin, hardener, and filler was poured into the mould. The process was repeated until the required number of layers were placed into the mould to achieve the desired biocomposite thickness. Totally five layers of basalt and HV fiber were used to prepare the biocomposite plate and the obtained thickness is around 3 mm. The samples were then kept in the compression moulding machine at a temperature of 160 ℃ and a pressure of 35 MPa for 4 h. Then the fabricated composite laminates were allowed to cure for 24 h at room temperature. The biocomposite plates were taken out for post curing and the test specimens were cut out of them for further testing and characterization. Table 2 shows the designation of the fabricated composites.

Mechanical properties of all the composite configurations as shown in Table 2 were evaluated. The tensile and flexural tests were performed in a UTM (DTRX model machine made by Deepak Poly Plastics, India) with a loading capacity of 5 kN and a crosshead speed of 1 mm/min. The hybrid biocomposite samples were cut into 165 mm × 13 mm x 3 mm according to ASTM D638 and ASTM D790 for tensile tests and flexural tests respectively. An axial load was applied to the specimens to measure their tensile behaviour while three-point bending was used to test the flexural characteristics of the samples. The load versus deflection curve of all specimens was recorded from the output of the load cell and encoder. These data were used to plot the tensile and flexural stress versus strain curves and calculate the tensile properties. Impact tests were carried out using the Izod-Chappy impact testing machine. Five specimens of dimensions 64 mm × 13 mm × 3 mm, as per ASTM D256 standards, were prepared without notch and subjected to an impact load using a pendulum hammer with 2.57 J of potential energy. The impact energy of the composite samples was taken directly from the machine’s digital display. To measure the interlaminar shear strength of the material, the composite specimens of size 35 mm × 13 mm × 3 mm, as per ASTM D2344 standards, were subjected to three-point bending tests, and the shear stress and strain curves were plotted. Five samples in each composition were taken for testing and the average of the obtained values was taken for further analysis in the case of all the mechanical tests.

FTIR was used to obtain the chemical constituents and bonds present in the biocomposites. FTIR spectra of the biocomposites were obtained using a Shimadzu spectrometer (Model: 8400 S). The samples were powdered, mixed with potassium bromide, and pelletized using a compact hydraulic machine before placing them in the spectrometer. Infrared radiation at a wavelength range of 4000 cm− 1 to 500 cm− 1 was passed into the sample with a scan rate of 32 scans/min at a resolution of 4 cm− 1.

X-ray diffraction analysis was used to obtain the structure, crystallinity, and crystallite size of the hybrid biocomposites. XRD analysis was carried out in an X-pert Pro PAN analytical diffractometer with a monochromatic beam of CuKα radiation over a Bragg’s angle between 10° and 80° with a 0.05° step and 30 mA and 45 kV machine settings.

The fracture surface morphology, fiber-matrix interfacial bonding, and microstructural failure modes of hybrid biocomposites were examined on fractured samples. The JOEL model SEM machine was used for scanning the image resolution of 3.0 nm, and the Electron gun accelerating voltage of 0.5 to 30 kV.

The thermal degradation behavior of the hybrid biocomposites with biofiller was studied using a thermogravimetric analyzer. The Jupiter simultaneous thermal analyzer (JSTA) was used to heat the powdered biocomposite sample from room temperature to 600 °C at a heating rate of 10 °C/min in a nitrogen atmosphere to avoid the effects of oxidation. The flow rate of nitrogen gas was maintained at 20 ml/min.

Figure 2 shows the FTIR spectrum of basalt, HVC, HY, and HYC biocomposites. The peak intensity at 3745.76 cm− 1 is observed only in the natural fiber. The peak at 3745.76–3045.60 cm− 1 is associated with the stretching vibrations of hydroxyl (–OH) functional groups (Fig. 2a,d). This peak shows the existence of hydroxyl groups in the molecule. The peak at 2962.66–2873.94 cm− 1 corresponds to the stretching vibrations of C–H (carbon-hydrogen) bonds in aliphatic hydrocarbons. The absorption peak at 2962.66 cm− 1 shows the presence of C–H stretching vibration which are the aliphatic functional groups that are commonly encountered in hydrocarbon molecules. The intensity peak at 1741.72 cm− 1 is observed only in the presence of the natural fibers (Fig. 2a and d). The peak at 1741.72 cm− 1 typically corresponds to the stretching vibration of the carbonyl group (C=O). The peak at 1610.56 and 1510.26 cm− 1 is typically associated with the C=C stretching vibration in alkenes. Whereas the 1460.11 cm− 1lies in the (CH2) group. The peak at 1363.67 cm− 1 falls in the (CH3) group. The peak range of 1300.02 cm− 1 lies in the (C–H) group. The peak at 1242.16 cm− 1 corresponds to the stretching vibration of C–O bonds, specifically observed in esters. The peak from 1180.44 to 1029.99 cm− 1 corresponds to the (C–O) bonds. The peaks at 910.40 and 829.39 cm− 1 lie in the (C–H) bonds. The peak range of 563.21 cm− 1 lies in the (C-CL) bond and is commonly present in natural and artificial biocomposites. Here the peak of 3745.76 cm− 1 is present only in the natural fibers (Fig. 2a,d). The intensity peak of 3429.43, 829.39, 1242.16, and 1510.26 cm− 1 are commonly present in both natural and artificial fibers (figure a, b, c, d) are of the Hydroxyl (–OH) functional groups. The peak of 459.06 cm− 1 (Fig. 2d) is present in the group of the Alkyl Halides.

FTIR spectrum of composites (a) Basalt fiber composite, (b) HV fiber composite, (c) HY fiber composite and (d) HYC composite.

XRD analysis was used to find the crystallinity index (CI) of the biocomposites with and without the biofillers and to ascertain the influence of the CI on the mechanical behaviour of the biocomposites. To determine the value of CI, the following Eq. (1) was used in which Icr and Iam denote the intensity of the crystalline and amorphous peaks respectively.

The spectrum shows different peak intensities with diffraction angles. The presence of HV fiber in epoxy biocomposites showed less intensity compared with HV fiber33,34. The presence of HV in epoxy biocomposites is proven by shifting of angle from 15.76º to 23.56°. It was also observed from the peaks that the crystalline peaks were present in between 19.35 ° and 22.17 ° for the composite samples while the amorphous peaks were present between 35.02 ° and 39.87°. The following Table 3 enlists the crystalline peaks and the CI values for various composite samples.

The additional crystalline peaks in hybrid biocomposites results from the effective hybridization of biocomposite materials. Generally, increased crystallinity enhances the hardness and other mechanical properties of biocomposites. It could be observed from the values that the addition of cashew nut biofiller enhanced the crystallinity of the composites. A similar observation was made in some of the early research works36,37. As HYC 20% higher, crystallinity, their mechanical behaviour was expected to be better comparatively. Figure 3 shows the XRD spectrum of HV, B, HY and HYC biocomposites.

XRD spectrum of composites.

The tensile stress versus strain curve of basalt (PB), HY, and HV with basalt and biocomposite of cashew net shell filler is shown in Fig. 4. The stress increases gradually with strain in all cases. When the tensile strength of individual basalt, HV fibers and their hybrid composites were compared, pure basalt exhibited higher tensile stress than the other composites because of hybridization effect and due to the better properties of synthetic fibers. The lowest value of tensile strength was obtained for the unfilled hybrid composites. In the addition of cashew nutshell to the biocomposites (10%), the strength of HV with basalt is way lower than HY in comparison. In 20% of basalt, HY, and HV with basalt the tensile stress in basalt has the maximum stress value compared to HY and HV with basalt. In 30% the tensile stress and strain of basalt is higher and in HY, HV with basalt the tensile stress is lesser. It could be understood from the results that the stress transfer between the basalt and HV fibers were greatly facilitated by the addition of cashew nutshell fillers. Due to this reason, the addition of cashew nutshell fillers to any of the composites enhanced their stress values when compared with the unfilled ones. Overall, the tensile stress and strain in 20% of hybrid filled biocomposite has the highest value.

Tensile stress versus strain of bio-composites.

Figure 5 shows the SEM morphology of the tensile fracture of the hybrid fiber biocomposite. Figure 5a and b show the unfilled hybrid biocomposites while Fig. 5c and d show the image of a pure HV biocomposite layer and pure basalt fiber layer in the fractured area respectively. It could be understood from morphologies that the interfacial interaction between the hybrid composites was better when compared with the individual composites, resulting in better mechanical strength. Voids are commonly present in the hybrid composites and in the basalt and HV fabric composites which retarded the composites from obtaining higher mechanical properties. Matrix cracks and ridges were observed in the failure morphology depicting the relatively lesser compatibility with the composite constituents. The failure crack would have commenced from the matrix crack resulting in relatively lesser mechanical properties. It can be observed from Fig. 5 and b that the interfacial adhesion between the hybrid fibers and the matrix was not very good which has to be eradicated by the usage of fillers. Though the properties of the hybrid composites are better than the individual fiber composites, the need for the filler to bridge the compatibility issues is imminent.

Tensile fractured morphology of hybrid fiber composite (a) 30× magnification, (b) 100× magnification, (c) HV fabric composite, (d) Basalt fabric composite.

Figure 6a–d shows the fracture morphology of basalt/HV fabric hybrid composites filled with 20% cashew nutshell powders. It could be clearly understood from the morphology that the presence of voids was meagerly witnessed due to the filling of voids by the cashew nutshell powder fillers. It could also be seen that matrix failures factors like matrix cracks, craters, and matrix bedonding were not observed in the morphology depicting the better compatibility between the composite constituents with the polymer matrix. Most of the failure mechanisms observed were fiber delamination (as shown in Fig. 6a), fiber pullout (as shown in Fig. 6b), interlaminar fiber delamination (as shown in Fig. 6c), and fiber breakage (as shown in Fig. 6d). All these failure mechanisms depict a good interfacial bonding between the hybrid fibers, biofillers, and the polymer matrix. Even though the load transfer has successfully occurred between the fibers and the matrix, the failure occurred only from the fiber side which is evident from the high strength of this composite configuration. Hence it could be concluded that the fiber-matrix interfacial adhesion with less number of voids facilitated the basalt/HV hybrid composites filled with 20% cashew nutshell fillers for obtaining higher tensile properties.

Tensile fractured morphology of hybrid fiber composite with 20% cashew nutshell filler (a) 100× magnification, (b) 250× magnification, (c) 500× magnification, (d) 750× magnification.

Figure 7 shows the various tensile properties of the bio-biocomposites. Figure 7a shows the tensile strength of basalt, HY, and HV for the cashew nutshell-filled and unfilled composites. Results portray that the hybridization effect of the basalt fiber and HV fiber ended positively in the case of tensile strength which was reflected in the strength values. The unfilled hybrid composites exhibited higher tensile strength than the individual fiber-reinforced composites which could also be seen from the morphology of the unfilled composites. The interfacial adhesion between the fibers and matrix was found to be better in hybrid composites which resulted in effective stress transfer. Meanwhile, the tensile strength of filled hybrid composites was also found to be higher than that of filled individual fiber composites. The brittleness of the cashew nutshells facilitated the increase in strength of the hybrid biocomposites and their presence decreased the voids in the filled composites. Besides, the hybrid biocomposites with 20% biofiller exhibited the highest tensile strength owing to the better interfacial bonding between the fibers, fillers and the matrix. Figure 7b,c show the tensile strain and Young’s modulus of all the biocomposite samples respectively. Due to the higher brittleness of the biofillers, the strain value exhibited by the 20% hybrid composites was higher. The Young’s modulus value of all the filled biocomposites is almost equal which depicts the positive effect of biofiller incorporation into the hybrid composites. Composites with 30% filler exhibited relatively lower tensile properties due to the inefficient load handling by the fillers and fibers due to the availability of more amount of filler concentration. Overall, it could be stated that the composites with 20% filler content exhibited better tensile properties.

Tensile properties of bio-composites (a) Tensile stress, (b) Tensile strain, (c) Young’s modulus.

Figure 8 shows the flexural stress versus strain curve of basalt (PB), HY, and HV with basalt and biocomposite of cashew net shell filler. The stress increases gradually for strain in all cases. In pure basalt, HY, HV with basalt the flexural stress of pure basalt is higher than the HY with basalt. Where the HV has the lowest flexural stress value. In the addition of biocomposites (10%) to basalt, HY, and HV with basalt the stress of HV with basalt is way lower than HY in comparison. In 20% of basalt, HY, and HV with basalt the flexural stress in basalt has the maximum stress value compared to HY and HV with basalt. In 30% the flexural stress and strain of basalt is higher and in HY, HV with basalt the flexural stress is lesser. Overall, the flexural stress and strain in 20% of basalt biocomposite has the highest value.

Flexural stress versus strain of bio-composites.

Figure 9 shows the various flexural properties of the biocomposites. Figure 9a shows the flexural stress of basalt, HY, and HV-filled and unfilled composites. It could be understood from the figure that the flexural strength of unfilled hybrid composites was slightly less than basalt fiber composites but higher than HV composites. This could be due to the reduced synergy between the basalt and HV fibers. To improve this, the composites were filled with cashew nutshell biofillers. It was also seen from the figure that the filled composites exhibited better flexural strength than unfilled composites. The hybrid biocomposites with 20% filler exhibited the highest value of flexural stress, strain, and modulus owing to the better interfacial compatibility between the fibers, fillers, and polymer and the high bending stiffness exhibited by the basalt fibers and the biofillers. Figure 9b and c show the variation of flexural strain and modulus of all the biocomposite samples which also followed the same trend. The strain value of the biocomposites was higher for 20% hybrid composites owing to the better dimensional stability and their higher resistance towards flexural loads.

Flexural properties of bio-composites (a) Flexural stress, (b) Young’s modulus, (c) Flexural strain.

Figure 10 shows the interlaminar stress versus strain curve of basalt (PB), HY and HV with basalt and biocomposite of cashew net shell filler. The stress increases gradually for strain in all cases. In pure basalt, HY, and HV with basalt the interlaminar stress of HY is higher than basalt. Where the HV with basalt has the lowest interlaminar stress value. In the addition of biocomposites (10%) to basalt, HY, and HV with basalt the stress of HV with basalt is way lower than HY in comparison. In 20% of basalt, HY, and HV with basalt the interlaminar stress in basalt has the maximum stress value compared to HY, and HV with basalt has the lowest value. In 30% the interlaminar stress and strain of basalt are higher and in HY, HV with basalt the interlaminar stress is lesser. Overall, the interlaminar stress and strain in 20% of basalt biocomposite has the highest value.

Interlaminar stress versus strain of bio-composites.

Figure 11 shows the various interlaminar properties of the biocomposites. Figure 11a shows the interlaminar stress of basalt, HY, HV both filled and unfilled composites. More like other mechanical property results, interlaminar properties for the hybrid composites were found to be higher than or on par with the basalt fiber composites due to the better interaction between the basalt fiber and HV fiber laminates. HV fiber composites exhibited lower interlaminar properties than the basalt and hybrid composites owing to their brittle nature. In the case of filled biocomposites, hybrid biocomposites with cashew nutshell fillers exhibited higher values since the biofiller promoted an effective interlaminar stress transfer. The shear loading applied to the filled biocomposite laminates was evenly distributed among the fillers and the fibers which increased their load-bearing capacity resulting in higher stress values. It could also be understood from the results that the stress value of any composition of the filled biocomposites was higher than all of its counterparts. This could be attributed to the positive synergy of the cashew nutshell biofillers with the basalt and HV fibers. Due to the agglomeration of biofillers and the poor binding ability of the polymer, the stress values of the 30% filler composites were reduced drastically. Figure 11b and c show the interlaminar strain and shear modulus variation for each of the composites. These properties also follow the same trend as discussed above. Basalt fiber composites exhibited higher interlaminar strain owing to their ductility while the shear modulus of biocomposites with 20% biofiller was relatively higher owing to the layer-by-layer resistance offered by the biocomposites at this composition.

Interlaminar shear properties of bio-composites (a) Interlaminar stress, (b) Shear modulus, (c) Interlaminar strain.

Figure 12 shows the various impact properties of the biocomposites of basalt, HY, HV filled and unfilled composites. It could be understood from the figure that impact strength of hybrid composites is higher than the individual fiber reinforced composites owing to the better synergy between the basalt and HV fibers. In the case of the filled composites, hybrid composites filled with cashew nutshell biofillers exhibited higher value owing to the better energy absorption capability of the biofillers. Additionally, the voids present in the composites were filled by the biofillers which also promoted the toughness of the composites. In all the composites, 20% biofillers rendered better properties and the highest value of impact strength was exhibited by hybrid filled biocomposites. Owing to the presence of more amount of biofillers in 30% composites, and due to the poor wettability of the fibers and fillers at this composition, the impact strength decreased at this proportion of the cashew nutshell filler.

Impact properties of the composite.

Figure 13 shows the TGA of basalt composites, HV composites, hybrid composites and the hybrid biocomposites filled with cashew nutshell powders. The TGA curves for all samples exhibit a declining trend attributed to the loss of weight. The TGA curve of the HV fiber shows a gradual weight loss with increasing temperature which starts around 300 ℃. When compared to HV fiber, the basalt fiber weight loss was around 350 ℃ due fiber hardness and strength. The residual mass of the hybrid fibers was less than the individual basalt and HV fiber composites due to the synergistic effects between the fibers. The thermograms of the hybrid composites filled with the biofillers exhibited a behaviour like the mechanical behaviour. The degradation of the HYC20% was found to be better than its counterparts at 355 ℃ exhibiting a better thermal stability than all other composite specimen. This could be due to the restrictions offered by the cashew nutshell fillers towards the polymeric chain mobility of the matrix material during the temperature gradients. As HYC10% could not resist the chain mobility due to lesser amount of biofillers and due to agglomeration in HYC30%, their thermal stability was not as good as HYC20%. The residual mass of the HYC 20% was found to be lower than its counterparts, indicating a better thermal degradation. Hence, it could be concluded that HYC 20% outperformed all other composites in terms of thermal stability.

TGA curve of composites.

The mechanical and thermal properties of HVF and Basalt fiber fabric-reinforced epoxy biocomposites with and without cashew nutshell fillers were extensively investigated. The FTIR spectrum showed the presence of various chemical groups in HV, Basalt, and hybrid fiber epoxy biocomposites with and without filler. The spectrums confirm the presence of elements in biocomposites. XRD spectrum showed the increase in crystallinity of the samples upon the addition of cashew nutshell biofillers which in turn enhanced the mechanical properties. The maximum tensile, flexural, and impact strength of HV fiber, basalt fiber fabric, and hybrid fiber epoxy biocomposites were obtained for a 20% weight fraction of filler reinforcements because the filler played a major role in transferring load between fiber and matrix. The fractured images showed that the filler present around the fiber was tightly packed which increased the mechanical properties. This led to fiber fracture rather than fiber pullouts. Flexural, interlaminar, and impact properties were also found to be higher for hybrid basalt/HV fabric fiber composites filled with 20% cashew nutshell powder fillers. Beyond that fraction, due to the presence of more constituents and poor wettability of the matrix, all the properties decreased. Thermal stability of hybrid biocomposites was improved by increasing the filler content and maximum stability was obtained for hybrid biocomposites with 20% biofiller at 355 ℃. Hybridization of HV and Basalt fiber fabric biocomposites showed better characteristics than individual HV and basalt fiber composites. Hence the hybrid biocomposites filled with cashew nutshell biofiller resulted in better performance in all the tests which may be used as lightweight materials in the automobile and aerospace industry.

All data generated or analysed during this study are included in this article.

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We sincerely acknowledge the support rendered by our students M. Nithiya Shree, C. M. Parimalacharyan, and S. Rahul for the material preparation and experimentation.

Department of Mechanical Engineering, Kongu Engineering College, Erode, 638052, Tamil Nadu, India

T. P. Sathishkumar & S. Santhoshkumar

AU-Sophisticated Testing and Instrumentation Centre (STIC), Department of Mechanical Engineering, Alliance School of Applied Engineering, Alliance University, Bengaluru, 562106, India

L. Rajeshkumar

Department of Mechanical Engineering, Kalasalingam University, Srivilliputhur, 626126, Tamil Nadu, India

N. Rajini

Department of Mechanical Engineering, JJ College of Engineering and Technology, Tiruchirapalli, 620009, Tamil Nadu, India

S. Sivalingam

Department of Civil Engineering, University College of Engineering, Tindivanam, 604001, Tamil Nadu, India

R. Gopinath

Department of Mechanical Engineering, Amrita School of Engineering, Amrita Vishwa Vidyapeetham, Chennai, 601103, India

M. Sathishkumar

Department of Mechanical Engineering, Sri Ramakrishna Engineering College, Coimbatore, 641022, Tamil Nadu, India

M. Ramesh

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T.P.S. and L.R.—Writing: original and revised draft; N.R. and S.S.—Investigation and methodology; R.G. and S.S.K.—Conducted the experiments; T.P.S. and M.R.—Conducted the experimentation and validated the results; L.R. and M.S.K.—Arranged funding. All the authors reviewed and proofread the manuscript for technicality and language.

Correspondence to L. Rajeshkumar or M. Sathishkumar.

The authors declare no competing interests.

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Sathishkumar, T.P., Rajeshkumar, L., Rajini, N. et al. Effects of cashew nutshell biofillers on the mechanical and thermal behaviour of Basalt/Hibiscus vitifolius hybrid fabrics reinforced polymer biocomposites. Sci Rep 14, 27636 (2024). https://doi.org/10.1038/s41598-024-79515-8

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Received: 09 August 2024

Accepted: 11 November 2024

Published: 12 November 2024

DOI: https://doi.org/10.1038/s41598-024-79515-8

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