Introduction

Hybrid FRP (fiber-reinforced polymer) composites are now a popular concept in the field of composites where more than one fiber, either natural or synthetic, is combined with a polymer matrix which results in higher mechanical properties than that of single fiber–type FRPs (Swolfs et al. 2019; Mochane et al. 2019; Das et al. 2021). The demand for natural fibers is increasing day by day due to environmental concerns all over the globe. Natural fibers such as flax, jute, sisal, hemp, banana, coir, pineapple, silk, and bamboo are largely biodegradable, renewable, available, and eco-friendly as compared to synthetic fibers (Das et al. 2022a, b). However, these fiber reinforcements exhibit lower mechanical properties compared to synthetic ones, such as those of glass (Das et al. 2021, 2023a, b; Cicala et al. 2009; Mahmud et al. 2023). Natural fiber reinforcements have some limitations, such as relatively low strength, poor dimensional stability, poor fiber-matrix interfacial adhesion, and high moisture absorption properties, which lead to quick degradation of the materials (Das et al. 2020, 2023a, b; Akter et al. 2020; Akter et al. 2018; Radoor et al. 2022). On the other hand, synthetic fibers exhibit high mechanical properties and increased durability, but are not biodegradable and sustainable (Das et al. 2021, 2023a, b; Mahmud et al. 2023). Given the above, one can combine natural and synthetic fiber reinforcements together in a hybrid form to develop case-tailored FRPs with desired properties, exploiting the benefits of each reinforcement type (Das et al. 2021). With regard to polymers, among various thermosetting polymer matrices, unsaturated polyester resin is a versatile and widely used polymer matrix for composite production in reinforcement with both natural and synthetic fiber reinforcements (Das et al. 2021; Mahmud et al. 2023; Grammatikos et al. 2016).

Many research works have already studied on natural/synthetic fiber–reinforced hybrid composites. It is reported from the literature that the addition of synthetic fibers in the natural fiber–reinforced hybrid composites increased the mechanical performance as a function of synthetic fiber hybridization (Das et al. 2021; Jawaid and Khalil 2011; Suriani et al. 2021). Das et al. (2021) studied the jute/glass fiber–reinforced polyester hybrid composites; glass fiber content (%) and position of glass reinforcements in the stacking sequence exhibited improved mechanical and viscoelastic performance in the hybrid composites than the neat jute fiber composites. Natural sisal fiber–based glass fiber–reinforced epoxy and polyester composites were developed by Ramesh et al., where tensile strength (TS) was found to be 68.6 MPa and 176.2 MPa for epoxy and polyester matrix–based composites, respectively (Ramesh et al. 2013a, 2013b). Flax/glass/PP (polypropylene) composites with 50% fiber loading and hemp/glass/PP composites with 40% fiber loading were manufactured, and impact strength was found to be 43.2 and 75 kJ/m2, respectively (Santulli 2007). Sreekala et al. (2002) studied the hybridization effect of glass fiber with oil palm fiber–reinforced composites. A significant increase in the mechanical properties was revealed for sisal/glass/LDPE (low density polyethylene) hybrid composites (Kalaprasad et al. 1996; Kalaprasad et al. 1997). The analysis of lignocellulosic fibers proved that the properties of fibers can be effectively employed in hybrid composites (Athijayamani et al. 2009). Glass fibers increased the mechanical attributes by their addition in polyester matrix–based PALF (pineapple leaf fiber) and sisal fiber composites (Mishra et al. 2003). Polyaniline effects were experimented on LDPE/natural rubber/water hyacinth composites which resulted in improved mechanical performance, melting point, and electrical conductivity (Supri et al. 2014). Water hyacinth/polyester composites were prepared by 5–20 wt.% fiber content, where best performances were revealed for 5–10 wt.% fiber loading on the composites (Ramirez et al. 2015). Silk fiber–based eco-friendly composites were also reported by Eshkoor et al. (2015) and Ho et al. (2011), while the hybridization of using silk fiber is reported in Noorunnisa Khanam et al. (2010) for coir/silk/polyester and in Noorunnisa Khanam et al. (2007) for sisal/silk/polyester hybrid composites.

Due to the highly hydrophilic characteristics of natural fibers, their performance degraded in different outdoor environmental conditions. Recently, Das et al. (2023a, b) studied the weathering and hygrothermal aging of natural and synthetic fiber–reinforced composites. The study reveals the significant degradation of mechanical and viscoelastic properties in the case of natural fiber composites (NFCs) than their synthetic fiber counterparts. The aging tests of bamboo/glass-reinforced polymer matrix hybrid composites disclosed that the decline in TS and tensile modulus (TM) for the hybrid composites was nearly half of the unhybridized ones (Thwe and Liao 2002, 2003). Amaro et al. (2013) observed the effects of alkaline (NaOH) and acid (HCl) solutions on glass/epoxy composites and reported a decline of flexural properties (bending strength (BS) and bending modulus (BM)) with the exposure time. However, the alkaline solution promoted a higher decrease in the flexural properties than the acid solution aging, and a similar tendency was observed for the performance of impact strength. The effect of water aging on water hyacinth/polyester composites was also experimented by Abral et al. (2014), and the outcome of water uptake on the mechanical performance of randomly oriented natural fiber/polyester hybrid composites was demonstrated by Athijayamani et al. (2009). Grammatikos et al. (2016) also studied the hygrothermal aging of GFRPs in a water medium for up to 224 days for civil engineering application purposes.

In this work, incorporating the higher mechanical properties of short E-glass fibers with three biomass-derived available and cheap fibers (jute, silk, and water hyacinth) to produce hybrid composites can be a sustainable solution towards circularity. Basically, water hyacinth (Eichhornia crassipes) is a waste material with no value-added applications, so these waste materials can be utilized to produce sustainable composite materials. Randomly oriented short fibers are used in this work, so waste jute and silk fibers from textile mills can be utilized to fabricate composites. Incorporating glass fibers may impart desired properties (relatively higher mechanical performance). Hence, the present work mainly focuses on developing hybrid composites by mixing randomly oriented short jute, silk, and water hyacinth with glass fibers. The matrix material is also a low-cost unsaturated polyester resin. The characterization of the hybrid composites was performed by mechanical and water uptake testing. Further, aging studies of the composite samples were performed under the soil and chemical solutions to assess their durability under these two aging conditions. The primary aim of this study is to develop low-cost, sustainable hybrid composite materials with multiple natural fibers.

Materials and Methods

Materials

Jute fiber was collected from Bangladesh Jute Research Institute (BJRI), Dhaka; silk fibers (Bombyx mori) from Sopura Silk Mills Ltd., Rajshahi, Bangladesh; and water hyacinth (Eichhornia crassipes) from a local pool. E-glass fiber (non-woven, 400 GSM) was procured from SHCP, Singapore. Unsaturated polyester resin and hardener (MEKP) were collected from Polynt Composite Malaysia. Other chemicals such as NaOH, HCl, H2SO4, and CuSO4 were collected from BASF, Germany.

Methods

Fabrication of the Hybrid Composites

At first, the fiber web was formed with different compositions of fibers, as shown in Table 1. The fibers were cut to the desired length (approximately 1 in.), then all the fibers were mixed, blended, and formed a fiber web of the desired size by pressing with a dead weight. In the web, fiber orientation was randomly scattered. The matrix material was prepared by mixing unsaturated polyester resin and MEKP hardener (1–2 wt.%) thoroughly before applying them to the fibers. The composite samples were fabricated by the simple hand lay-up method, using two aluminum plates, and then placed under a dead weight (approximately 40 kg) at room temperature for at least 24 h for better curing and interfacial adhesion between fibers and polyester matrix. Five composites (S1, S2, S3, S4, and S5) were prepared with different fiber compositions with polyester resin according to Table 1, and the experimental design of the work is presented in Fig. 1. A fabricated hybrid composite is shown in Fig. 2. The average thickness of the hybrid composites was approximately 4.5 mm.

Table 1 Fiber percentage (%) in different hybrid composites
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Fig. 1
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Experimental design

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Fig. 2
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Photograph of a hybrid composite sample

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Fig. 3
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a Universal testing machine and b impact testing machine.

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Fig. 4
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Mechanical properties of hybrid composites: a tensile strength (TS), b tensile modulus (TM), c bending strength (BS), d bending modulus (BM), and e impact strength

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Fig. 5
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Water uptake (%) of the hybrid composites

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Fig. 6
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Water uptake mechanism of natural fiber composites or composite materials (reused from Azwa et al. (2013) with permission from Elsevier)

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Fig. 7
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Effect of biodegradation on tensile strength (TS) of the hybrid composites

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Fig. 8
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Effect of biodegradation on tensile modulus (TM) of the hybrid composites

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Fig. 9
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Percentage (%) loss of TS and TM as a function of biodegradation in soil of the hybrid composites

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Fig. 10
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Degradation of a TS and b TM of the hybrid composites after aging in alkali solution

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Fig. 11
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Degradation of a TS and b TM of the hybrid composites after aging in HCl acid solution

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Fig. 12
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Degradation of a TS and b TM of the hybrid composites after aging in H2SO4 acid solution

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Fig. 13
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Degradation of a TS and b TM of the hybrid composites after aging in salt solution

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Fig. 14
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Percentage (%) loss of TS of hybrid composites after aging in different chemical solutions

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Fig. 15
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Percentage (%) loss of TM of hybrid composites after aging in different chemical solutions

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Characterization

Mechanical Testing

Mechanical characterization of the hybrid composites was conducted via tensile, flexural, and impact testing. The tensile, flexural, and impact testing was performed according to ASTM D3039, ISO 14125, and ASTM D256 standards, respectively. A universal testing machine (UTM) (model: H50KS-0404, Hounsfield Series S, UK) (Fig. 3a) was used for the tensile and flexural testing, while a universal impact tester (Hung Ta Instrument CO. LTD, Taiwan) (Fig. 3b) was used for the impact testing. The hammer mass was 2.63 kg, the gravity distance was 30.68 mm, and the lift angle was 150° for the impact testing machine. For the case of tensile testing in UTM, the crosshead speed was 10 mm/min, and the span distance was 50 mm. For the flexural testing, the crosshead speed was 60 mm/min, and the span distance was 25 mm.

Water Uptake

The water uptake characteristics of composites were studied as per ASTM D 570 by immersion in distilled water at room temperature. Before starting the water uptake test, the composite samples were oven-dried, and then the weight of the samples was recorded. After that, the composite samples were immersed in a static water bath at room temperature for a time interval of 6 h (up to 48 h). After 6 h, the samples were taken out from the water bath, wiped using tissue paper, and then weighed. The water uptake (%) was calculated according to the following equation:

\(\text{Water uptake }\left(\%\right)\text{=}\left[\frac{{W}_{f}-{W}_{i}}{{W}_{f}}\right]\times 100\%\)

where Wi and Wf are the weights of the oven-dried samples and wet samples after immersion in water at a certain period, respectively.

Biodegradation

Composite samples were buried in soil (having at least 25% moisture) for 25 days. After 25 days, the composite samples were withdrawn from the soil, cleaned, and washed carefully with distilled water. The excess water from the sample surface was removed by tissue paper. These samples were kept at room temperature for 24 h, and then mechanical testing was performed (Khan et al. 2011; Zaman et al. 2012).

Chemical Aging

To test the chemical aging, the composite samples were immersed in 10% solution of different chemicals such as alkaline (NaOH), acid (HCl and H2SO4), and salt (CuSO4) for 10 days. The pH of these solutions were 13.6 for NaOH, 0.26 for HCl, 0.09 for H2SO4, and 4.06 for CuSO4. After 10 days, the aged samples were withdrawn, and excess water from the sample surface was removed by tissue paper. Prior to mechanical testing, the samples were kept at room temperature for 24 h.

Results and Discussions

Mechanical Properties

The mechanical properties of the hybrid composites, such as tensile strength (TS), tensile modulus (TM), bending strength (BS), bending modulus (BM), and impact strength, are depicted in Fig. 4. As can be seen from Fig. 4a, the value of TS was 45, 47, 54, 33, and 37 MPa for S1, S2, S3, S4, and S5 type composites, respectively, and the value of TM was 0.88, 0.96, 0.97, 0.70, and 0.71 GPa for these composites, respectively, as exhibited in Fig. 4b. On the other hand, the value of BS was 48, 40, 41, 46, and 39 MPa for these composites, respectively, as illustrated in Fig. 4c, while BM was 2.32, 2.38, 2.40, 1.63, and 1.54 GPa for these composites, respectively, as demonstrated in Fig. 4d. It is revealed from the tensile and flexural characterization of the hybrid composites that the S3 type composites exhibited the optimum performance compared to other hybrid composite samples. This may be due to the higher amount of glass fiber content in S3 type composites, i.e., glass fiber content was the maximum (10 wt.%) than other natural fibers such as jute (3.33 wt.%), silk (3.33 wt.%), and water hyacinth (3.33 wt.%) in it. Hence, the presence of glass fibers plays a dominant role in the case of mechanical performance (Das et al. 2021; Jawaid and Khalil 2011). In the case of other hybrids, the tensile and flexural properties did not follow any specific trends; rather, it was random, which may be due to the presence of different types of natural fibers in the hybrid composites. Also, the adhesion between these fibers and polyester resin plays an important role in determining their mechanical performance. Usually, poor interfacial adhesion between fibers and matrix resulted in poor mechanical performance, while the improved mechanical performance indicated better fiber/matrix interfacial adhesion in the composites. Other factors, such as the type of reinforcing fibers, fiber content, manufacturing technique, polymer matrix, and post-curing, may have an influence on the overall mechanical performance of the composites (Das et al. 2021, 2022a, 2023a, b; Pickering et al. 2016).

The impact strength of the hybrid composites was found to be 9.33, 7.56, 6.06, 10.92, and 7.22 kJ/m2 for S1, S2, S3, S4, and S5 type composites, respectively, as manifested in Fig. 4e. The highest value of impact strength was found for S4 type composite, while the lowest value was exhibited for S3 type composites. These results of impact strength were influenced by the interfacial adhesion between the reinforcing fibers and polyester matrix, which seemed to be poor in the case of test specimens used for S3 type composites, while much better interfacial adhesion was revealed for the case of S4 type composites. Generally, the impact strength of the composites may be governed by the type of reinforcing fibers and polymer matrix employed, as well as their interfacial adhesion (reinforcement/polymer matrix) (Das et al. 2021; Mishra et al. 2003).

Water Uptake

Figure 5 shows the water uptake (%) for all hybrid composites up to 48 h. From Fig. 5, it is noticed that the water uptake was initially high; then, it went a steady progression up to the studied period. However, the composite samples did not reach the saturation point in this study, which may take more time (Mahmud et al. 2023). The hydrophilic nature of natural fibers is mainly responsible for the water uptake behavior of their composite samples. The water uptake (%) of the S4 type composites was exhibited much higher than that of the other composite samples due to the higher content of water hyacinth fibers in them (S4 type composite). On the other hand, S3 type composite samples exhibited the lowest water uptake (%) due to the maximum amount of hydrophobic glass fibers present in them (S3 type composite). Here, the water absorption rate is very low in comparison to the study of jute/polyester composites (Mahmud et al. 2023) and jute/PP composites (Das et al. 2018). This may be due to comparatively low fiber content and significantly higher polyester resin matrix content in the composites in the current study.

The water uptake mainly depends on the nature of the constituent materials in a composite. In hybrid composites, the natural fibers are hydrophilic in nature, which is the major contributor to water uptake performance. Moisture is mainly penetrated inside the composites by diffusion process via the micro gaps, pores, or cavities in the matrix surfaces of the composites; thus, the fibers swell and plasticize (soften). Swelling may also cause dimensional changes in the hybrid composites. The existing defects produced during composite production, such as micro-cracks, pores, or voids in the composites, also increase the moisture absorption rate (Fiore et al. 2022; Azwa et al. 2013).

The swelling of natural fibers can induce swelling stresses inside the composites, resulting in micro-cracks and dimensional changes inside the composites. It is also well-known that the interface between natural fibers and polymer matrices is poor compared to the interface of synthetic fiber/polymers, which is also affected during moisture absorptions. The absorbed natural fibers by water molecules may damage the secondary bonds among cellulose macromolecules, which can also be the reason for the destruction of natural fibers, thus facilitating more moisture uptake (Fiore et al. 2022; Azwa et al. 2013; Stamboulis et al. 2001). Figure 6 represents the water uptake mechanism of natural fiber composites (Azwa et al. 2013). Natural fibers usually contain numerous –OH and carboxyl groups that may interact with water molecules via H-bonding (Das et al. 2022a; Yan et al. 2014). The innumerable –OH groups in the cellulose and hemicellulose lead to poor interface and poor resistance of the fibers to moisture absorption, which promote the water gain of the natural fiber–based hybrid composites. In addition, the cell cavities (i.e., hollow core) in the natural fibers may provide extra spaces for moisture while soaked in the water solution (Azwa et al. 2013; Yan and Chouw 2015).

In the case of polyester matrix, the unreacted hydrophilic and polar groups of the resin (e.g., hydroxyl or amine) can interact with water molecules. These phenomena can be facilitated by the water diffusion process in the composites. All these phenomena may contribute to the higher rate of moisture uptake in natural fiber–based hybrid composites (Azwa et al. 2013).

Effect of Aging

To study the durability of the hybrid composite materials, they were exposed to a soil medium for biodegradation and different chemical solutions for a certain period. After the aging test, the durability of the composite samples was assessed by tensile testing. The effects of biodegradation and chemical aging on the tensile properties of the hybrid composites are discussed in the following sections.

Effect of Biodegradation

The effect of biodegradation in soil medium on tensile strength (TS) and tensile modulus (TM) of the hybrid composite samples is presented in Figs. 7 and 8, respectively. After 25 days of biodegradation in soil, the TS of the exposed composites were 23, 20, 21, 17, and 23 MPa for S1, S2, S3, S4, and S5 type composite samples, respectively. Hence, the reduction of TS found to be 49, 57, 61, 48, and 38%, respectively, for S1, S2, S3, S4, and S5 type composites than their reference (unaged) composite cases (Fig. 9). On the other hand, TM was found to be 0.30, 0.27, 0.32, 0.31, and 0.30 GPa for S1, S2, S3, S4, and S5 type composites, respectively, which demonstrated the loss of TM as 66, 72, 67, 56, and 58%, respectively, for these composites, as shown in Fig. 9. The degradation of TS and TM did not follow any specific trend; instead, it was random which was due to the presence of different types of natural fibers in the composites. Jute and water hyacinth are naturally degradable fibers because these fibers are cellulose-based, and they absorb the water immediately after immersion into water, exposing their highly hydrophilic nature and causing them to become saturated with water. After the saturation point, moisture exists as free water in the void structure, which leads to delamination and void formation (Azwa et al. 2013; Mavani et al. 2007). Usually, cellulose has a strong trait to destroy when buried in soil. Water also enters from the cutting edges of the composite samples, and the damage process of cellulose being accelerated in jute and water hyacinth fibers in the composite samples during the soil burial period. Thus, the tensile properties of the composites dropped remarkably (Akter et al. 2018; Azwa et al. 2013; Masudul Hassan et al. 2003). Silk fibers also take moisture and readily decompose during soil burial biodegradation testing, resulting in the poor tensile performance of the composites. In addition, microbial degradation took place in the soil medium, which also accelerated the degradation process of the natural fibers as well as their hybrid composites (Khan et al. 2010).

Effect of Chemical Aging

The chemical aging of the hybrid composite samples was carried out on different chemical solutions such as an alkali (NaOH) solution, two acidic solutions, HCl and H2SO4 acid solutions, and a salt (CuSO4) solution. The effect of aging in alkali solutions, i.e., the degradation of tensile properties (TS and TM) after 10 days for S1, S2, S3, S4, and S5 types of composites, is demonstrated in Fig. 10. The chemical aging effects in acidic solutions are presented in Fig. 11 for the case of HCl acid solution, and in Fig. 12 for the case of H2SO4 acid solution. On the other hand, Fig. 13 demonstrates the effect of salt solution aging in the hybrid composites. The percentage (%) loss of TS and TM of the aged hybrid composites due to chemical aging is depicted in Figs 14 and 15, respectively.

After 10 days aging in alkali solution, the TS and TM found for S1, S2, S3, S4, and S5 composite samples were 23, 19, 21, 16, and 9 MPa and 0.37, 0.34, 0.39, 0.34, and 0.32 GPa, respectively. The loss of TS and TM found for S1, S2, S3, S4, and S5 composites in alkali aging was 49, 60, 60, 51, and 76% (Fig. 14) and 58, 65, 60, 51, and 55% (Fig. 15), respectively. In the case of aging in HCl acid solution, the TS decreased by approximately 67, 44, 53, 61, and 42% for S1, S2, S3, S4, and S5 samples, respectively. At the same time, the TM dropped to about 69, 74, 73, 29, and 51%, respectively, for the composite samples. On the other hand, in the case of H2SO4 acid aging, the composites exhibited a random fall of their TS and TM in comparison to the prior acid solution–aged hybrid composites, as illustrated in Figs. 14 and 15, respectively. Similarly, in the case of salt solution aging, the degradation of TS was found to be 43, 53, 59, 59, and 55% (Fig. 14), while the degradation of TM was displayed to be 60, 56, 65, 51, and 56% (Fig. 15) after 10 days aging at the salt solution for all the exposed composites, respectively. In all the chemical aging, the drop of tensile properties was random, i.e., no specific degradation trend was observed. This may be due to the use of different types and content of natural fibers in the hybrid composites.

In general, several phenomena may be responsible for the significant reduction of tensile strength and modulus of the exposed composites as a function of chemical aging; these may include the hydrophilic character of natural fibers, swelling, plasticization, degradation of both natural fibers and polyester matrix, debonding, and the damage of their interface (fiber/matrix) (Das et al. 2022a, 2023a, b; Azwa et al. 2013; Yan and Chouw 2015). Natural fibers are composed of cellulose and hemicelluloses, which contain numerous –OH and acetyl groups. These are mainly responsible for the hydrophilic character of natural fibers. In natural fibers, cellulose is the stiffest component, which is responsible for their tensile properties. Cellulose is embedded in hemicellulose matrices. Hence, after exposure to the chemical aging environments, the fiber/matrix interfacial damage occurred due to the breakdown of cellulose and hemicellulose (Azwa et al. 2013; Yan and Chouw 2015). Due to aging, the other hydrophobic ingredients in natural fibers (e.g., hydrocarbons, lignin, wax) are also removed, facilitating the damage of fiber/matrix interface. As a consequence, the mechanical properties of the composites decreased (Das et al. 2023b; Azwa et al. 2013; Yan and Chouw 2015).

The polyester matrix also degraded physically and chemically as a function of chemical aging. These may include hydrolysis of polymer chains and damage in interfacial bonding. The presence of voids, micro-cracks, cavities, or holes in the surfaces of the polymer matrix may accelerate the damage to the chemical structure of the matrix resin (Das et al. 2023a, b; Azwa et al. 2013; Yan and Chouw 2015). Finally, all these phenomena may reduce the tensile properties of the aged composite materials.

Zhu et al. (2011) explained that due to the immersion of composites in an alkaline solution, numerous free –OH ions are found in the epoxy polymer matrix, which is thereafter hydrolyzed. The hydrolysis of the ester group–containing epoxy polymer may induce chain scission and microcracking of matrices and generate soft dissolvable products. Thus, the mechanical properties of the aged composites degraded significantly in alkali solution. In the case of aging in acid solution, the acid solution penetrates the polyester matrix’s free space or macromolecules, generating more cracks and cavities. These may damage the fibers, matrix, and fiber/matrix interfaces (Das et al. 2023b; Bagherpour et al. 2011; Huang and Sun 2007). The more extended period of aging and heating may accelerate the rate of degradation in composites, as well as swelling and discoloration may be observed. As a result, mechanical properties such as TS and TM are decreased (Das et al. 2018, 2023a, b; Bagherpour et al. 2011; Huang and Sun 2007). Hydrolysis of ester groups of the polyester resin can be occurred by acid solution aging. As these groups are situated in the chain backbone of the polymer, chain scission may occur. The molecular weight of the composite also decreases due to this chain scission, which also results in degradation of the mechanical properties (Grammatikos et al. 2016; Das et al. 2018; Bagherpour et al. 2011; Hammami and Al-Ghuilani 2004). Nair et al. (2018) state that mechanical properties reduced due to the presence of alkali metal oxides in salt water (seawater) may facilitate the acceleration of the penetration of water molecules inside the composites; thus, fiber/matrix interface is damaged and deboned. Yan and Chouw (2015) reported that salts generate cations and anions in seawater, which penetrate the composites along with water, then degrade the fibers, matrix, and interface between fibers and matrix. Physical damage also occurred, which included swelling, plasticization, and relaxation of matrix polymer. In the case of salt water or seawater aging, Hammami and Al-Ghuilani (2004) claimed that “the main failure mechanism is caused by water absorption and diffusion.”

Conclusion

In this study, the unsaturated polyester matrix was incorporated with short natural fibers (jute, silk, and water hyacinth) and a high-strength synthetic fiber (E-glass) to fabricate natural/synthetic fiber–reinforced hybrid composites. The fibers were randomly oriented, and a hand lay-up technique was employed to fabricate the hybrid composites. The performance of the fabricated composites was assessed by mechanical testing such as tensile, bending, and impact strength. Synthetic glass fiber contents in the composites played an important role in the mechanical performance of the hybrid composites, and maximum glass fiber content hybrid composites exhibited the optimum mechanical performance in most cases. However, the interfacial adhesion between fibers and polymer matrix materials also played a dominant role in imparting the optimum mechanical performance in hybrid composites. That is why the mechanical performance was random in some cases due to the presence of different fiber materials and their content (wt.%) in the hybrid composites, their wettability with polyester resin, and fiber/resin interfacial adhesion. The aging study in soil and chemical solution reveals significant deterioration of tensile properties for all the exposed hybrid composites since they are composed of natural fibers that are highly susceptible to degradation in moist outdoor environments. From the overall study, the optimum result was obtained for S3 hybrids which were composed of a maximum amount of glass fibers (10 wt.%) and three natural fibers (3.33 wt.% jute, 3.33 wt.% silk, and 3.33 wt.% water hyacinth). However, further studies, such as fiber surface modification and employment of fillers, are recommended to improve the interfacial properties and mechanical performance of the hybrid composites. The developed hybrid composites can be used for low-strength and non-load-bearing indoor applications.