Introduction

Biodegradability, low weight, and affordability have propelled natural fiber-reinforced composites (NFRC) to the forefront of the sustainable materials movement, challenging the dominance of synthetics1,2. Fibers from plants like banana, roselle, Indian mallow, and sisal have great qualities, including a high strength-to-weight ratio, pliability, and the capacity to be renewed3. These fibers, when mixed in a hybrid form, increase the composites’ toughness, rigidity, and durability, which are mechanical qualities4. As a matrix material, vinyl ester resin finds extensive usage because of its high chemical resistance, minimal water absorption, and good adherence to natural fibers5. A wide range of structural applications can benefit from hybrid fiber-reinforced vinyl ester composites due to their enhanced tensile, flexural, and impact strengths6. Lightweight building materials, maritime applications, aircraft constructions, and automobile components all make use of these composites. In addition to that, you may find them in biodegradable packaging, sports gear, and furnishings7.

Woven natural fiber fabric reinforcements in polymer composites increase impact resistance and stiffness by distributing loads more uniformly8. Their structure minimises cracking and improves durability. Strong interfacial bonding between the fibers and the polymer matrix enhances performance, and further improvements in adhesion are achieved through fiber orientation and surface modifications, resulting in superior mechanical properties for a variety of applications9. For example, Oksman investigated the mechanical properties of natural fiber mat reinforced thermoplastic (NMT) composites and compared them with glass fiber mat reinforced thermoplastics (GMT) and pure polypropylene (PP). The study showed that NMT composites have higher stiffness than pure PP, and those with 50% fiber content surpass GMT in stiffness10. However, GMT composites showed superior strength and impact resistance, possibly due to the lower strength of natural fibers and suboptimal fiber-matrix adhesion. In addition, NMT composites exhibited significant anisotropy, with up to 45% variation in properties depending on fiber orientation. These results highlight the potential of NMT composites in applications where high stiffness is a priority11. In another study, Czigány et al. investigated the mechanical and failure behaviour of basalt fiber mat reinforced composites with vinyl ester (VE) and hybrid vinyl ester/epoxy (VE/EP) resins. Results were evaluated by analyzing the effects of resin type and surface treatment with vinyl or epoxy functionalized organosilanes on fiber performance. The findings demonstrated that treated basalt fibers considerably enhanced mechanical characteristics by enhancing adhesion between surfaces12. Researchers Heijenrath et al. looked into NMTs, or natural fiber mat reinforced thermoplastics, by combining flax fibers with a film-stacked polypropylene (PP) matrix. For the sake of comparison, they also created flax mat epoxy composites that were either oriented in one way or randomly. Due to its low cost and high stiffness-to-weight ratio, NMTs were determined to be an ideal material for their technical applications. According to the research, unidirectional composites have better stiffness, and fiber orientation significantly affects mechanical performance. Based on these findings, NMTs may one day replace traditional synthetic fiber composites in uses calling for eco-friendly, lightweight materials13. The mechanical characteristics of hybrid composites reinforced with banana and vetiver fiber mats were examined in a separate investigation. Compared to banana and hybrid fiber mat composites, the impact strength of double-layer vetiver fiber mat composites oriented at 90° was found to be better14.

The mechanical, thermal, and structural properties of composites reinforced with natural fiber mats have been the subject of much research. Researchers have examined a range of synthetic and natural fiber mats in thermoset and thermoplastic matrices, including basalt, flax, glass, and carbon. Fiber matting enhances strength, stiffness, and impact resistance through better load distribution and interfacial bonding, according to studies. Mechanical qualities can be further optimized by surface treatments and hybridization with nanofillers15. Furthermore, anisotropy impacts composite performance and is affected by fiber orientation. As a result of their eco-friendliness and lightweight nature, these materials show great promise as high-performance composite solutions in a variety of engineering domains, including transportation, aerospace, and structural design16,17. Vinyl ester composites reinforced with synthetic and natural fibers are the subject of Salman’s investigation on the effects of fiber hybridization on void content and moisture absorption. This research looks at the effects of fiber type, stacking order, and environmental factors on these characteristics. The findings demonstrate that hybridization influences water absorption and void distribution, which therefore impact the performance and longevity of composites. The research shows that choosing the right fibers and arranging them properly can reduce moisture-induced deterioration. Composites are better suited for structural applications that are susceptible to moisture exposure if these characteristics are optimized to increase their lifespan18. Ahmad et al. also made hybrid composites from jute and cotton fiber. This research looked at the mechanical characteristics of jute and cotton fiber reinforced composites made with epoxy-polyester and hybrid epoxy-vinyl ester matrices. Hybridization boosted strength and durability, according to the data. The research emphasizes eco-friendly materials that can replace synthetic composites in structural applications without sacrificing mechanical performance19.

Recently, Printed circuit board development is one area where natural fiber reinforced composites have recently been noticeable20. For instance, Thanikodi et al. developed and studied eco-friendly printed circuit boards by replacing traditional E-glass fibers with natural fibers like banana and rice husk in epoxy resin. Through the flammability studies, they found that the optimum parameters—16 mm flame gap, 45 mm flame travel in 15 s—minimised weight loss. The composites with 60% fiber content, 12 MPa compression pressure and 36 h immersion showed reduced moisture absorption21. In another study, Jayaseelan et al. investigated de-oiled palm cake cellulose (PKC) and palm sprout fiber (PSF)-reinforced vinyl ester composites and evaluated their mechanical, fatigue and dynamic mechanical properties. They extracted cellulose using a modified chemical process and produced composites by hand lay-up. Their results showed improved properties with fiber addition, achieving a tensile strength of 155 MPa, flexural strength of 178 MPa and impact toughness of 5.13 J. The V5 composite exhibited a storage modulus 104.5% higher than plain resin. These composites demonstrated potential applications in the commercial, residential and automotive sectors due to their improved durability22. Rajesh kumar et al. studied that chemical surface treatment was applied to the fibres so that the Epoxy matrix and Bauhinia Purpurea L fibres (BPFs) can interface more strongly with one another. Mechanical parameters such as tensile, flexural, impact, shore-D hardness, and vibration were improved in the NaOH-treated purple Bauhinia Purpurea L Fiber/Epoxy (BPFE) composites compared to the untreated ones. Composites made of BPFE followed a predictable pattern: their characteristics improved as the percentage of fibres treated with NaOH increased up to 15%, and then they degraded as the percentage of fibres treated with NaOH increased beyond 20%23. Balaji et al. explored that fabrics were made using Agave vera-cruz fibre rope, Agave vera-cruz fibre that had been purposefully twisted, and Agave vera-cruz fibre that had been irregularly orientated. Fabrics made with Agave vera-cruz fibres reinforcing polyester produced higher-quality, more cost-effective materials with improved heat resistance, according to the results. For instance, in comparison to the other three types of fibers—fiber random, fibre rope random, and horizontal direction fabric—polyester composites reinforced with Agave vera-cruz fibre rope (vertical fabric) on the vertical direction exhibited superior mechanical properties, including higher tensile strength (54.7 MPa), flexural strength (316.6 MPa), impact strength (109.6 kJ/m2), and barcol hardness (40). Along with that, out of the four types of polyester composite, the Agave vera-cruz fibre rope vertical fabric had the lowest thermal conductivity (0.138 Wm−1 K−1) and the maximum heat deflection temperature (77 °C)24. Manikandan et al. explored that the hand layup method was used to create the composites, which had a filler content of 0 to 15 wt% PLSF and 0 to 9 wt% graphite. Finding out how the hybrid filler affected the composites’ mechanical properties was the main goal. Synthesis of composites using P. longifolia seeds and graphite powder was investigated experimentally for their mechanical characteristics. Hardness, impact resistance, flexural strength, and tensile strength were some of these characteristics. The highest tensile strength and tensile modulus of the hybrid composite were 48.4 MPa and 1.66 GPa, respectively. The flexural strength, which is approximately 148 MPa, is best in the hybrid filler that contains 15% wt% PLSF and 6% graphite. With the addition of 15 wt% of hybrid filler, the maximum impact strength was found to be 41.3 kJ/m2, and the hardness was 44.525.

In summary, NFRCs provide eco-friendly substitutes for synthetic materials since they are biodegradable, lightweight, and inexpensive. A number of studies have demonstrated that mechanical, thermal, and structural characteristics may be affected by changes in fiber type, orientation, and surface treatment. Because of the enhanced strength, stiffness, and impact resistance that results from hybridization, NFRCs find widespread use in the aerospace, automotive, and structural industries. Furthermore, the strengthening of fiber mats enhances both the distribution of loads and their longevity.26. This research delves into the practical and theoretical possibilities of hybridizing sisal fiber with Indian mallow/roselle/banana fiber mat reinforced vinyl ester composites, as well as their mechanical performance and manufactured composites, while tensile, flexural, and impact tests were used to evaluate the mechanical behaviour.

Materials and methods

Materials

The fibers used in this study were sourced locally, treated extensively to remove contaminants, and then dried at room temperature. The fibers included sisal, Indian mallow, roselle, and banana. Before the composite was made, the dried fibers were kept in dry containers so they wouldn’t absorb any moisture. Using the hand lay-up technique and vinyl ester resin, five distinct composite versions were created. The mechanical characteristics were examined by arranging the fiber mats in either a mat or random orientation. To make sure the resin was evenly distributed and bonded well, compression molding was done after impregnation. The cured laminates were then post-cured at room temperature and cut into standardized specimens according to ASTM guidelines. These specimens were then subjected to mechanical and thermal tests to evaluate their performance in structural applications.

Composite preparation

Figure 1 displays the fabrication of the biocomposite plates. The composite panels were produced by compression moulding. To produce five different types of panels, a single layer of sisal mat was kept constant, and a second layer varied with different natural fibers such as randomly oriented sisal, Indian mallow, Roselle and banana mat reinforced vinyl ester in a 200 mm × 200 mm × 3 mm mould. Hardeners were then added to the resin before the mixture was poured into the mould cavity. The mould was sealed at a continuous pressure of 100 kPa for 24 h to allow the composites to cure at ambient temperature. Five different hybrid composite panels made from sisal mats. The five different permutations of hybrid sisal mat reinforced vinyl ester composites are abbreviated in Table 1, and the different shapes of hybrid sisal composite sheets are shown in Fig. 2.

Fig. 1
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The fabrication of the biocomposite plate.

Table 1 Various combinations of hybrid mat reinforced vinyl-ester composites symbols.
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Fig. 2
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Different forms of the hybrid sisal composite plates.

Mechanical properties

Tensile properties

The tensile test was carried out at the National Institute of Technology, Tiruchirappalli, in accordance with ASTM D 638-10 (165 × 13 × 3 mm). A universal testing machine was used to conduct the test after the specimens were prepared according to the necessary dimensions. To make sure the loading was consistent, the strain rate was kept at 1 mm/min. Important mechanical parameters for evaluating the composites’ structural integrity were obtained by the test, including tensile strength, yield strength, and elongation at break27.

Flexural properties

The flexure test was carried out at the National Institute of Technology, Tiruchirappalli, in accordance with ASTM D790-10 (127 × 10 × 3 mm). The samples were cut to size and then put through a series of tests using a Universal Testing Machine with a three-point flexure configuration. The loading conditions were kept consistent by keeping the strain rate at 1 mm/min. Crucial to comprehending the material’s resistance to flexural pressures and overall mechanical capabilities, the test examined crucial metrics such as flexural modulus and flexural strength.28.

Impact strength

The impact test is performed in accordance with ASTM D256-10 (65 × 10 × 3 mm) to evaluate the toughness and resistance to high-speed forces of a composite material. It evaluates energy absorption, brittleness and fracture behavior. This test is essential for natural fiber reinforced polymer composites, which can ensure the reliability of materials used in structural applications where impact resistance is critical to durability29.

Hardness

The hardness of the polymer material was determined using a Barcol hardness tester (model: VBH2) in accordance with ASTM 2583 (50 × 13 × 3 mm). The sample was placed under the indenter of the Barcol hardness tester and then continuously compressed until the dial indicator reached its maximum. Absolute Barcol values were calculated from the indentation depth. Samples were required to be at least sixteenth of an inch thick. The composite was cut to a thickness of 3 mm for the test specimens29.

Heat deflection temperature

A standard test bar measuring 60 × 12 × 3 mm was deflected at a force of 0.455 MPa as part of the heat deflection temperature test. The specimen was preserved in a silicone oil bath. The temperature at which the bar was deflected was determined as the heat deflection temperature in accordance with ASTM D-64829.

SEM analysis

SEM analysis was used to examine the interfacial bonding between the fiber and matrix of the fracture surfaces of the various composite specimens after mechanical testing. To prepare the surface of the fractured specimens for morphological study, a thin section was cut and coated with gold. SEM micrographs of the fractured specimens were taken using secondary imaging settings with voltages ranging from 10 to 15 kV.

Results and discussion

Tensile properties

In general, the weave, fiber orientation and matrix-fiber bonding determine the strength of woven fiber composites24,25,26. The tensile properties of different combinations of natural woven fibers such as sisal, Indian mallow, roselle and banana of hybrid fabric composites are shown in Fig. 3. It is clear from the Fig. 3. that the breaking load varies from 1.02 to 1.18 KN for the SMSR and DSM reinforced vinyl ester composites. The percentage elongation at break for both SMSR and DSM composites ranges from 3.96 to 7.47%. The tensile strength of the DSM composites is 40 MPa, which is 20% higher than that of the SMSR reinforced vinyl ester composites. An improvement in the load-bearing capacity of the composite is achieved by reinforcing with sisal woven fibers. The tensile strength of the DSM composites is then improved. In contrast to woven composites, random orientated composites are weaker in tension. This may be due to the early failure caused by the amorphous nature resulting from the uneven distribution of fibers in the resin matrix.27.

Fig. 3
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Tensile properties of various combinations of hybrid sisal/Indian mallow/roselle/banana fiber mat composites.

Among the four hybrid DSM, SIM, SRM and SBM reinforced vinyl ester composites, the tensile strength of the hybrid SRM reinforced vinyl ester composite is much higher than that of the Indian mallow, banana and woven sisal reinforced vinyl ester composites. The composite with SRM reinforcement has the maximum tensile strength of 74 MPa as shown in Fig. The tensile strength of the SRM composites increased by 45% compared to the DSM composites, but only by 24% compared to the SIM composites and 35% compared to the SBM composites. From Fig. 3, it is clear that the breaking load varies from 1.02 to 1.45 KN for the double-layer sisal mat (DSM), sisal roselle mat (SRM) and sisal banana mat (SBM) reinforced vinyl ester composites. The percentage of elongation at break between the two DSM, SRM and SBM reinforced vinyl ester composites is 0.51 to 1.01%. Due to the lower load-sharing properties of banana, Indian mallow and sisal fibers, SRM composites show an increase in tensile strength. When stronger fibers are oriented in both directions, they can each carry a better tensile load, increasing the tensile strength of the material28,29,30. With its bidirectional orientation, the stronger and stiffer Roselle fiber may be able to absorb more stress and have more mechanical strength. A comparison of the tensile strength of various natural fiber reinforced polymer composites are given in Table 2. SRM reinforced vinylester composites exhibits 2.34 times greater than the golden cane polyester composites ,1.57 times greater than vetiver/hybrid vinylester composites, 1.54 times greater than Palmyra leaf stalk/polyester composites, 1.23 times greater than Typha Angustata fiber/Vinylester, 1.13 times greater than Indian mallow fiber/polyester composites14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31.

Table 2 Comparison of tensile strength of various natural fibre–reinforced polymer composites.
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Flexural properties

A three-point flexural test was used to investigate the flexural properties of the composites. The flexural strength of composites is typically determined by their combined compressive and shear strength26. There was an increasing trend in the flexural load from SMSR to DSM composites, which ranged from 90 to 171 N, and the increased flexural strength varied from 58 to 110 MPa. It is found that the breaking load of the DSM composites is high, proving that the flexural strength of a random composite is influenced by the weave characteristics of the fabric. The low flexural strength associated with short and randomly oriented SMSR composites is caused by the fiber discontinuity. Both the SMSR and DSM composites had elongation at break percentages ranging from 3.7 to 4.7%. The tensile strength of the DSM composite is 110 MPa, which is 47% higher than that of the SMSR composites.

The comparison of the flexural strength of different natural fiber reinforced polymer composites is given in Table 3. Among the four different hybrid woven composites, the breaking load for SRM, SBM, and DSM reinforced vinyl ester composites ranged from 160 to 235 N as shown in Fig. 4. The flexural strength of SBM composites was found to be quite low at around 103 MPa among all the above composites. The maximum flexural load and strength were obtained at 235 N and 152 MPa for SRM composites. The improved compressive strength and shear resistance of the hybrid is the result of the mixed use of sisal and roselle fibers. The key factor determining the flexural strength of the hybrid composites is the placement of high strength fibers on the outer layer. It was about 32.2% higher than that of SBM, 27.6% higher than that of DSM, 17.1% higher than that of SIM reinforced vinyl ester composites. This is due to the fact that the bending force is greatest on the roselle fiber mat and the stretching of the long cellulose structure of the roselle fiber, and the longitudinal load acts perpendicular to the fiber axis during the flexure test28.SRM reinforced vinylester composites exhibits 4.90 times greater than the golden cane polyester composites, 3.61 times greater than the Betal palm/polyester, 2.92 times greater than the Jute/polyester, 2.53 times greater than the Banana/polyester, 2.37 times greater than Palmyra leaf stalk/polyester composites,1.92 times greater than Vetiver/banana fiber/vinylester, 1.76 times greater than Vetiver/banana fiber/vinylester, 1.36 times greater than Indian mallow fiber/polyester composites14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31.

Table 3 Comparison of the flexural strength of various natural fibre–reinforced polymer composites.
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Fig.4
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Flexural properties of various combination of hybrid sisal/Indian mallow/roselle/banana fiber mat composites.

Impact properties

The interfacial and interlaminar adhesion between the matrix and the fiber determines the impact characteristics of composites28. Impact strength of composites varies with reinforcing fiber type, even for the same weaving pattern. Fiber-matrix interface, composite construction, and geometry are not the only determinants of impact strength; the strength and structure of each individual fiber component also play a role28. In the event of random orientation, it is clear that the impact strength is determined completely by the interfacial strength. The impact strength and interfacial strength are both imparted by the effect of inter-laminar delamination in composites reinforced with a weaving pattern30. The different combinations of reinforcement and the impact strength of the composite are shown in Fig. 5. It was clear that the impact properties of composites are strongly influenced by the type of fiber reinforcement used. Compared to the more common short fiber reinforcement, the impact strength of woven fabric reinforced composites is significantly higher. Among the sisal/mat sisal random (SMSR) and double-layer sisal mat (DSM) reinforced vinyl ester composites, the DSM composites have a higher impact strength of 92 kJ/m2 compared to the SMSR composites. This was almost 1.70 times higher than the SMSR composites. This could be due to better alignment of the sisal mat between fiber and matrix, fewer voids, which may improve absorption capacity and better distribution of impact energy29.

Fig. 5
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Impact properties of various combination of hybrid sisal/Indian mallow/roselle/banana fiber mat composites.

The impact strength of the four reinforced vinyl ester composite samples (DSM, SIM, SRM, and SBM) was 92, 213, 104, and 66 kJ/m2, respectively. According to the results, the SIM reinforced vinyl ester composite samples achieved a higher impact strength of 213 kJ/m2 compared to the other composites. It was almost 3.22, 2.31 and 2.04 times higher than that achieved by SRM, DSM and SBM composites, respectively. This is due to the impact of the hybrid natural fiber, which combines the best properties of two different types of natural fiber, in this case, Indian mallow and sisal, with a matrix to produce a material with increased strength and durability. The comparison of the impact strength of different natural fiber reinforced polymer composites is given in Table 4. A strong absorption capacity with evenly distributed impact energy was also helped by it. SIM reinforced vinylester composites exhibits 59.49 times higher than the golden cane polyester composites, 27.48 times higher than the Betal palm/polyester, 22.53 times higher than the cylindrica/polyester, 16.38 times higher than the Coconut sheath –polyester, 22.53 times higher than the Banana/polyester, 14.75 times higher than Indian mallow fiber/polyester composites, 1.33× higher than Vetiver/banana fiber/vinylester, 2.69× higher than Vetiver/banana fiber/vinylester, 1.33 times higher than Vetiver/banana fiber/vinylester.

Table 4 Comparison of impact strength of various natural fibre–reinforced polymer composites.
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Hardness

The hardness of the five stacked sequenced composite samples is shown in Fig. 6. The DSM composite recorded a Barcol hardness value of 52, a significant increase compared to the SMSR composite with a hardness value of 44. This can be attributed to a more uniform and strong composite structure with a more evenly distributed fiber within the matrix, which improved its hardness quality. The effect of the fiber was to ensure that the matrix could withstand higher loads without significant deformation35.

Fig. 6
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Hardness properties of various combination of hybrid sisal/Indian mallow/roselle/banana fiber mat composites.

The SIM composite showed the maximum Barcol hardness value of 72, which was approximately 1.63× higher than SMSR, 1.38× higher than DSM, 1.24× higher than SRM and 1.33× higher than the SBM composite samples. A strong network of evenly distributed fibers provides excellent resistance to wear and indentation. The optimum composite has good resistance to localised deformation and improved hardness, which can be attributed to the fiber synergy that distributes stress uniformly36,37,38.

Heat deflection temperature (HDT) test

The results of an HDT test conducted on a reinforced vinyl ester composite with the effect of sisal fiber mat are shown in Fig. 7. From the results obtained, the SMSR composite recorded an HDT value up to 40 °C. Significantly, the HDT was further slightly increased up to 60 °C when sisal fiber mat was added instead of sisal random. This was about 1.5 times higher than that of the DSM composite. In addition, the HDT values of four combinations of hybrid mat composites (DSM, SIM, SRM and SBM) were recorded from 60 to 80 °C. The SRM composite showed a maximum HDT value of 80 °C, which was approximately 1.33 times higher than the DSM composite, 1.17× higher than the SIM composite and 1.42 times higher than the SBM composite.

Fig. 7
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Heat deflection temperature properties of various combination of hybrid sisal/Indian mallow/roselle/banana fiber mat composites.

The advance from 40 °C in SMSR to nearly 60 °C with mat-based reinforcement, and further up to 80 °C in hybrid configurations, indicates that fibre orientation and hybridisation play a critical role in resisting thermal distortion. In particular, the SRM composite revealed the highest HDT of 80 °C, highlighting its superior ability to retain mechanical integrity under elevated temperatures.

These increments make mat-reinforced hybrid composites promising candidates for civil structures such as roofing sheets, panels, and structural laminates exposed to heat. In sports equipment, the improved HDT ensures improved performance and durability under repeated thermal and mechanical loading. Similarly, in industrial sectors, particularly in automotive and lightweight structural components, the greater thermal resistance extends service life and reliability. As a whole, the results confirm that integrating sisal and other natural fibre mats into vinyl ester matrices offers a sustainable pathway to develop cost-effective composites with improved thermal stability for diverse engineering applications39,40,41,42,43.

SEM analysis

The SEM topography of a tensile fractured sample of the hybrid composites is shown in Fig. 8. From the picture shows the results it is clearly evident that reveals matrix enrichment and natural fiber bending.

Fig. 8
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SEM topography of fractured surface of the hybrid fiber mat composites specimen after the tensile test.

The SEM analysis shows how the polymer matrix is distributed around the natural fibers, demonstrating that the matrix has been effectively enriched. This is important because it allows for strong adhesion between the surfaces and load transfer within the composite. The image shows that the matrix covers the fibers evenly, with few gaps or voids, an indication of strong wettability and adhesion. The SEM images clearly showed the bending of the natural fibers, shedding light on the pliability and torque-induced stress response of the fibers and at micro-cracks, deformation patterns in the bending zones, failure mechanisms and fiber-matrix interaction can be better understood44,45.

The fracture surface of the specimen after the bending test is shown in Fig. 9. The SEM micrograph shows the microstructural formation of voids in polymer composites. Particularly, the aggregation of natural fibers and densely packed fibers indicated that the composite had an uneven load distribution. In addition, the micrographs revealed some defects such as small micro gaps between the fibers and the matrix and microbubbles caused by moisture, which could reduce the mechanical strength of the composite. These micro gaps can be caused by poor matrix wetting of the fibers and low interfacial bond between matrix and reinforcement46,47.

Fig. 9
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SEM image of fractured surface of typical test specimen after the flexural test.

The fracture in the specimen of the samples after the impact test using SEM analysis is presented in Fig. 10, which revealed how polymer composites experience matrix fracture and natural fiber pull-out. Different areas of broken polymer matrix can be seen in the micrograph, indicating localized stress concentrations and possible weak spots in the composite. Failure of a matrix can be caused by fracture propagation, excessive mechanical stress or insufficient adhesion between surfaces. The image also shows natural fiber pull-out, which occurs when fibers separate from the matrix, leaving holes. Inadequate stress transfer or weak fiber-matrix bonding48,49,50.

Fig. 10
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SEM image of fractured surface of typical test specimen after the impact test.

Applications

Vinyl ester polymer composites reinforced with hybrid matting of sisal, Indian mallow, roselle, and banana fibres provide an eco-friendly solution to enhance mechanical and thermal performance while decreasing dependence on synthetic reinforcements. Reducing the total carbon footprint of composite manufacture, these natural fibres are plentiful, biodegradable, and process far more efficiently than glass or carbon fibres. Hybrid systems boost durability and heat resistance, which means they last longer in service, and they also help with end-of-life strategies like recycling, energy recovery, or the safe biodegradation of fibre fractions. Composites like this have the potential to replace traditional FRPs in car parts, including dashboard components, door trims, and interior panels, resulting in lighter vehicles with better crash protection. They have similar applications in the construction industry as claddings for walls, sheets for roofs, and boards for dividing rooms; these materials save embodied energy while providing thermal insulation and mechanical dependability. Since these hybrid natural fibres with vinyl ester combine performance, eco-efficiency, and practical application relevance, they match with global sustainability goals51,52,53.

Conclusions

Five sequential hybrid sisal/Indian mallow/roselle/banana fiber mat reinforced vinyl ester bio composites were innovatively prepared and analysed by mechanical testing and SEM analysis. From the results obtained, it was evident that the sisal mat/roselle mat reinforced vinyl ester composite sample exhibited the optimum mechanical properties and heat distortion temperature resistance up to 80 ºC. In addition, the sisal mat/Indian mallow mat reinforced vinyl ester composite exhibited maximum impact strength and hardness values of 213 kJ/m2 and 72, respectively. The SEM study of the fracture specimens confirmed a good interfacial adhesion between the hybrid sisal mat and the vinyl ester matrix surface. Considering the obtained mechanical properties, several products such as engine bonnets, motorcycle mudguards, helmets, bicycle seats, fan blades, fiber doors, fiber window, civil pipes, switch boxes, automotive side mirror housings, lathe guards, engine guards, vehicle interiors, and table tennis rackets can be manufactured using the optimum SRM reinforced vinyl ester composite samples. Future research can concentrate on incorporating fire-retardant additives or nanofillers with the hybrid fibre mats to improve safety and thermal stability even more. These environmentally friendly composites may also be widely adopted in the industrial, sports, and civil sectors with the help of sophisticated modelling and life-cycle analysis.