1 Introduction

The global surge in interest for natural fibers over recent decades underscores a collective recognition of their unique benefits and the urgent need for sustainable alternatives [1, 2]. Natural fibers have multiple advantages over their synthetic counterparts [3]. Emanating from renewable sources, natural fibers are cost-effective, lightweight, and address both material shortages and environmental challenges [4, 5]. These characteristics make them an appealing choice in the present era of environmental concerns [6]. As materials science evolves, the emphasis on sustainable solutions is growing, propelling natural fiber reinforced composites into the limelight [7]. These composites have intrinsic properties, such as high strength and specific stiffness, which make them attractive in diverse industries [8]. Importantly, these fibers are not just about addressing today’s challenges but also signify a shift towards future-proofing industries against resource shortages and ecological degradation [9, 10]. In addition, the application of agricultural by-products in the composite sector aligns with global sustainability objectives and offers both eco-benefits and economic advantages [11, 12]. The shift towards natural fibers represents a strategic and responsible response to the dual demands of functionality and sustainability [13, 14].

Bamboo fiber has lately been seen as of significant interest in the development of composite materials [15, 16]. Bamboo boasts exceptional tensile strength and modulus as a substitute for synthetic fibers [17]. This natural plant fiber has earned the title of “nature’s glass fiber” because of its unique mechanical attributes, such as with a low density (1.4 g/cm3), specific stiffness, and bending load strength [18]. Historically, the robustness of bamboo was utilized for the construction of light structures such as grid platforms [19]. However, with technological advancements, the scope has expanded to include modern applications such as decking boards, automotive interiors, and protective helmets [20,21,22]. Especially, a noteworthy application is the development of innovative composites that merge bamboo fiber with various polymers [18]. Beyond these attributes, bamboo’s rapid growth cycle, high CO2 sequestration capability, and widespread availability highlight its environmental and economic benefits [23,24,25]. As the world is shifting towards greener solutions, bamboo fiber-reinforced composites offer a sustainable, cost-effective, and performance-oriented alternative.

Hybrid composites are materials composed of two or more different types of reinforcing or filler elements incorporated within a polymer matrix [26, 27]. These composites leverage the strengths of individual fibers, addressing the limitations of each to achieve enhanced properties [28, 29]. The relevance of hybrid composites in modern applications is continually growing [30]. Their advantage lies in achieving a balance between performance and cost through deliberate material design [26]. These composites present enhanced mechanical, thermal, and moisture absorption properties over single fiber-reinforced counterparts, making them suitable for diverse applications, from automotive components to bone implants [26, 31]. In particular, hybrid composites reinforced solely with natural fibers underscore ecological benefits [32]. The rise of hybrid composites signifies a transformative approach in material science, harmonizing strength, sustainability, and cost-effectiveness [33]. Devarshi et al. [34] discussed overview of the advantages and applications of natural-fiber-reinforced hybrid composites, particularly focusing on bamboo. However, this study does not delve deeply into the specifics of bamboo composite preparation techniques or recent studies in detail. Therefore, detailed discussions on preparation techniques, recent advancements, and specific applications of bamboo hybrid composites are imperative. This comprehensive approach will not only address the existing challenges but also paves the way for future innovations in the use of bamboo fiber-reinforced hybrid polymer composites across various industries.

This review aims to fill the existing knowledge gap by offering a comprehensive overview of recent studies in bamboo fiber-reinforced hybrid polymer composites. The novelty of this study lies in its in-depth examination of the fabrication, properties, potential applications, and challenges associated with bamboo hybrid composites. This systematic review will provide crucial insights, setting the stage for future research and industrial applications across several sections. Section 1 introduces the focus of the review. Section 2 provides an overview of the bamboo plant, including its anatomy and chemical composition. Later, Sect. 3 delves into the analysis of fiber/polymer configurations, fiber orientation, and structural configurations in fabrication of bamboo hybrid composites. The effects of hybridization on the mechanical properties, thermal properties, and biodegradability of bamboo hybrid composites are discussed in Sects. 4, 5, and 6, respectively. Section 7 explores the influence of various additives in bamboo hybrid composites. Potential applications of the reviewed studies are discussed in Sect. 8. Section 9 discusses advantages and disadvantages of bamboo composites. Finally, Sect. 9 concludes with results and insights into the future prospects of bamboo hybrid composites.

2 Bamboo plant: an overview

Bamboo, which was initially termed by Carl von Linné in 1753, is more than just another grass [35]. Indeed, it shares kinship with everyday plants like rice and corn in terms of producing organic lignocellulosic matter [36]. However, bamboo has a unique aspect in that its tissues harden over time, making it comparable to wood while retaining an enviable lightness and flexibility [37]. This remarkable plant has an impressive global reach, from the northern latitudes to the tropics, with the exception of Europe [38]. The bamboo grows rapidly, whether in the humid cloud forests of Colombia or the semi-arid areas of India [35]. With around 1500 identified species, Asia and America are home to the majority, with countries like China, Japan, and Brazil showcasing a rich diversity of bamboo [38]. Globally, bamboo forests stretch across 37 million hectares, highlighting its dominance in various ecosystems [39]. Historically, humanity has turned to bamboo as an invaluable resource. Bamboo has been an integral part of cultural progression in Asia and America and has been used as a construction mainstay for centuries [40]. In terms of construction, bamboo types like Bambusa and Dendrocalamus are favored in tropical zones, while Phyllostachys finds its niche in warmer climates [41, 42]. Figure 1 shows these species of bamboo plants.

Fig. 1
figure 1

Various species of bamboo plant: a Bambusa bambos, b Dendrocalamus giganteus, c Phyllostachys bambusoides, and (d) Bambusa vulgaris [43]

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Bamboo’s applications are not limited to construction sector [44, 45]. Early in its growth cycle, it can be a delectable edible food [46]. As it matures, its sturdy rhizome makes it a natural landslide deterrent [47]. Once harvested, its applications range from building components to crafts, thanks to its versatility and malleability [48]. Bamboo, with its hollow structure interspersed with nodes, provides strength and elasticity that many traditional woods lack [49]. Yet, the story of bamboo isn’t just about its physical and practical attributes. The shift from petroleum-based products to sustainable options has cast a spotlight on bamboo once again [50]. As an eco-friendly, biodegradable alternative, bamboo has garnered attention from industries globally [51, 52]. Research indicates that, with its composition of cellulose within a lignin matrix, bamboo can be viewed as a natural composite material [53]. This structure, coupled with its inherent growth advantages, makes bamboo an enticing solution for a sustainable future [54]. Owing to the structural features, bamboo possesses high tensile strength to substitute steel reinforcement in the construction industry and save costs by as much as three times [55]. Moreover, the outstanding seismic resilience, ease of assembly, and comfort help to broaden the application in engineering and construction projects [56].

2.1 Anatomy of bamboo

Bamboo, an incredibly diverse and fast-growing grass, possesses a distinct structure that has intrigued scientists and engineers alike. At a macroscopic level, bamboo culms are typically hollow, segmented structures characterized by nodes and internodes [57]. The internodes are fundamentally hollow tubes with axially oriented cells, while nodes possess a diaphragm-like formation that aids in lateral transport of nutrients and water [58]. These nodes are critical as they also aid in enhancing mechanical strength and preventing crack propagation [59, 60]. Microscopically, bamboo’s anatomy is even more fascinating. The bamboo fibers, consisting of multilayered cell wall, are key contributors to its mechanical strength [61]. Bamboo’s cell wall is predominantly made up of cellulose, hemicellulose, and lignin [36, 62]. This wall exhibits an intricate arrangement of alternating thin and thick layers, each with distinct microfibril orientations. The vascular bundles, which are responsible for nutrient transport, are denser towards the exterior and become larger and sparser towards the interior [63]. This distribution is deliberate, making bamboo a functionally graded material optimized to withstand forces like wind [64]. Numerous studies have proposed various models to describe this cell wall, considering the micro-scale structure and the orientation of microfibrils [65, 66]. The microfibril angle, which relates to the orientation of these cellulose microfibrils, plays a pivotal role in the mechanical properties of bamboo [67, 68]. The precise structure and arrangement of these components, combined with bamboo's unique anatomy, bestow upon its superior strength, toughness, and ductility. In essence, bamboo’s anatomy, both at the macroscopic and microscopic levels, is a testament to nature’s engineering prowess. Figure 2 shows the anatomical structure of a bamboo culm.

Fig. 2
figure 2

Anatomy of a bamboo culm adapted from [69]

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2.2 Bamboo culm structure

Bamboo’s culm, the upper ground section representing the majority of its woody material, is a marvel of natural engineering [40]. Externally, it manifests as a straight, cylindrical entity, distinctly segmented by nodes and internodes. These internodes are hollow, forming cavities within the bamboo [70]. Such a design provides advantages in traditional construction, enabling the formation of unique joints based on bamboo’s shape [71, 72]. Bamboo culms are especially noteworthy for their lack of secondary growth typical of trees [73]. They emerge with a set diameter and grow vertically, but do not expand outward over time [49]. The culm’s wall has a rich composition, and it includes a hard, shiny outer skin layer, a soft matrix material known as parenchyma, and darker, stronger vascular bundles [74]. Figure 3 visually illustrates the dense arrangement of vascular bundles towards the exterior and their sparser distribution inwards.

Fig. 3
figure 3

Cross-sectional views of bamboo culm: a overall view and (b) microscopic detail [75]

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Further intricacies arise in the culm’s diaphragms, present at the nodes. These wooden partitions are paramount for horizontal nutrient and water transport within the bamboo [76]. The culms, in addition to their physical robustness, also demonstrate remarkable growth rates, with some species growing up to 1 m per day [77]. This rapid growth, combined with their ability to reach full height and girth in a single season, marks bamboo as one of the world’s fastest-growing plants [78]. However, this growth rate can be influenced by bamboo species and surrounding climatic conditions [79]. Additionally, bamboo’s culm wall exhibits varying characteristics along its length. For instance, the internode length increases from the base, peaks at the middle, and decreases towards the top. Meanwhile, the culm diameter and wall thickness consistently decrease from the base to the apex [80, 81]. These structural variations play a pivotal role in bamboo’s processing and its subsequent utilization in various applications. Table 1 shows the physical and mechanical properties of bamboo culms from various species (Dendrocalamus asper, Dendrocalamus sericeus, Dendrocalamus membranaceus, Thyrsostachys oliveri, and Phyllostachys makinoi). In essence, the culm’s unique structure and characteristics underscore bamboo’s remarkable versatility and strength, making it an invaluable resource across various industries and traditional applications.

Table 1 Physical and mechanical properties of bamboo culms of various species [70]
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2.3 Chemical composition of bamboo

The chemical composition of bamboo is intricate and plays a fundamental role in determining its structural and functional properties. The major chemical components are cellulose, hemicellulose, and lignin as depicted [82]. Cellulose is the primary structural skeleton of the bamboo cell wall, accounting for approximately 74% of the total composition as depicted in Fig. 4 [43]. The rest of the components are approximately 12% hemicellulose, 10% lignin, 3% moisture, and 0.4% wax.

Fig. 4
figure 4

Chemical composition of bamboo fiber [43]

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Figure 5 details the chemical structures of three major components of bamboo fiber: cellulose, hemicellulose, and lignin. Cellulose is formed of extensive, unbranched chains of anhydro-D-glucose units linked by β-1,4 glycosidic bonds [83]. This structure leads to tightly packed and high molecular weight fibers resistant to dissolution in alkaline and water environments. Hemicellulose has a branched structure with a mix of five-carbon and six-carbon sugars, excluding glucose, which contributes to an amorphous matrix interwoven with lignin and cellulose [84]. Lignin, a complex phenolic compound, consists of three types of phenylpropanoid units. Lignin is vital for providing rigidity, a yellowish color to bamboo, and strengthening the overall structural integrity of the cell wall [85].

Fig. 5
figure 5

Chemical structures of various components of bamboo fiber [86]

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The crystallinity index (CRI) of bamboo, determined through X-ray diffraction analysis, represents the proportion of crystalline cellulose to approximately 65% (Fig. 6). The crystalline region in conjunction with the microfibril angle (MFA) affects bamboo’s mechanical properties such as tensile strength and elastic modulus [87]. The calculation of the CRI for bamboo cellulose takes into account the distinct peaks (1–10/110), (200), and (004). Interestingly, CRI values can vary depending on the method used; the peak area method tends to yield values approximately 20% higher than the peak height method. This variance aligns with discrepancies from the different mathematical functions applied in the peak fitting process. In Fig. 6b, the transverse crystallite size (D200) of the parenchyma cells varied within a range, which was narrower than that of the fibers. This data suggests that the microfibrils in parenchyma cells, while still robust, are packed differently from those in the fibers, possibly leading to differences in the mechanical behavior of the two cell types. Ren et al. [88] showed that the d-spacing in parenchyma cells was larger than in fibers, suggesting a looser arrangement of cellulose chains. This looser structure could enhance the accessibility of chemical agents, potentially easing the degradation process. By considering the crystallite size and d-spacing, the study reveals that parenchyma cells may provide the bamboo with a unique combination of strength and flexibility, which could be pivotal for certain applications where the mechanical properties of bamboo are utilized properties like rigidity and impermeability to water are provided by lignin, which typically comprises roughly 21 to 32% [89]. In between the cellulose and lignin, hemicellulose acts as a filler, playing a crucial role in the bamboo’s flexibility [90]. Apart from these primary components, bamboo also contains a minute quantity of ash, silicon dioxide, and less than 1% nitrogen [91]. Furthermore, the external culm wall is characterized by an epidermal layer covered in wax, which influences the culm’s wettability properties, impacting its ability to bond and adhere with other materials [92]. The internal composition and the interaction of the chemicals grant bamboo its characteristic strength, flexibility, and resilience [93]. In summary, the chemical composition of bamboo is a complex blend of organic compounds that sets it apart from many other natural materials.

Fig. 6
figure 6

a XRD profile of two components: bamboo fiber and parenchyma cell, b curve fitting highlighting diffraction peaks at specific angles: 14.64°, 16.05°, 22.05°, and 35.14°, along with a hypothetical amorphous peak [88]

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3 Hybridization in bamboo fiber-reinforced composites

3.1 Fiber/polymer configurations

Recent works in bamboo fiber (BF)-reinforced hybrid polymer composites showcase various configurations of fiber as displayed in Table 2. Epoxy was predominantly used as a matrix with diverse fiber combinations such as BF-date palm [94, 95], BF-kenaf [96, 97], and BF-glass fiber [98,99,100]. Although epoxy resin poses environmental concerns due to its non-biodegradability, its popularity stems from its exceptional adhesion properties, high mechanical strength, dimensional stability, and resistance to moisture and chemicals [101,102,103]. Notably, additives such as nanoclay [97], ethylene‐co‐glycidyl methacrylate (EMGA) [99], TiO2, and ZrO2 were incorporated in some studies to enhance the properties of composites [104]. The fiber loading ranged from 10 to 70 wt%, with a corresponding adjustment in polymer content. While there’s a range in fiber loading percentages across the studies, it’s imperative to note that there is not a fixed or standard fiber loading percentage ensuring optimal performance. This variability hinges on the diverse types of fibers and the intricate interplay of processing parameters. It underscores the notion that achieving the highest performance is rather subjective and depends heavily on the specifics of each composite’s configuration. Interestingly, the hand lay-up technique emerged as the favored fabrication approach. This preference is attributed to its suitability for lab-scale research, offering simplicity and cost-effectiveness [94,95,96,97,98,99, 105]. However, other methods like compression molding and the hot press were also employed [106,107,108]. These myriad configurations underline the versatility of BF in composite applications.

Table 2 Various fiber configurations used in recent studies on bamboo hybrid composites
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3.2 Fiber orientation

Composite materials have significantly evolved, integrating both synthetic and natural fibers to exploit their synergistic properties [113]. Among the multitude of factors influencing composite performance, fiber orientation stands out as a paramount parameter [114,115,116]. Venkatesha et al. [117] detailed the influence of orientation on bamboo-glass fiber-reinforced epoxy composites, noting that a 45° orientation offered maximum weight gain and thickness swelling, while the values decrease in the case of a 60° orientation. Further investigations by Sathish et al. [118] highlighted the merits of the 45° orientation in terms of mechanical characteristics for banana-kenaf epoxy hybrid composites. However, the current body of research has merely scratched the surface of understanding these orientation effects, especially in hybrid composites. A substantial research gap, underscoring the need for intensified exploration into fiber orientations in hybrid composites to ensure optimal material performance tailored to specific applications.

3.3 Structure of composites

Hybrid composites comprising two fibers can be fabricated using three main configurations: interlayer or layer-by-layer, intralayer or yarn by-yarn, and intra-yarn or fiber-by-fiber [119, 120]. The interlayer method is the simplest and cheapest way for producing hybrid composites [96]. However, the layering sequence has great influence on the final performance of the composites [121]. In recent investigations into bamboo hybrid composites, a predominant emphasis has been placed on configurations that optimize the synergistic properties of the constituting fibers and fillers. A prevalent configuration observed in several studies is the “layer-by-layer” structure. For instance, studies conducted by Supian et al. [94], Refaai et al. [95], Chee et al. [96], Latha and Rao [99], Venkatesha et al. [117], and Chandramohan et al. [122] employed this configuration, exploring combinations of fibers such as date-palm with bamboo, bamboo with kenaf, and bamboo with glass, among others. Zhang et al. [123] reported several advantages of layer-by-layer assembly in the development of multilayered polymer composites. One of the primary benefits is the ability to control sample thickness at the nanometer scale, which is pivotal for tailoring optical and mechanical properties. Precision in thickness allows broad applicability of the composites across packaging, optical films, and coatings application. Moreover, layer-by-layer method allows for the engineering of composites with specific functionalities and responsiveness. The ability of multilayered interfaces to regulate stress distribution and crack propagation further underscores the potential for enhancing material durability. Another noteworthy configuration is the sandwich layout, where the reinforcing fibers are embedded between two external layers, often for enhanced stiffness and interlaminar shear properties [124]. This configuration, either explicitly termed or inferred based on described methodologies, was prominently featured in studies by Nor et al. [98], Shah et al. [100], Liew et al. [104], and Liew et al. [125]. Uniquely, Tran et al. [108] adopted a unidirectional configuration for coir, bamboo, and polypropylene composites, offering potential benefits in terms of specific directional strength and modularity. As the field progresses, the choice of configuration becomes a pivotal determinant in achieving desired composite properties and, in turn, application potentials. Table 3 presents a summary of the various composite structures of the bamboo hybrid composites.

Table 3 Summary of the bamboo hybrid composites structures
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The study of bamboo fiber (BF)-reinforced hybrid polymer composites has evolved, revealing a variety of configurations, fiber orientations, and structures tailored for enhanced performance. Epoxy, favored for its adhesion and mechanical properties, often serves as the matrix, combined with fibers like date palm, kenaf, and glass. Additives such as nanoclay and EMGA are incorporated to improve composite characteristics. The fiber loading varies, highlighting the lack of a standard for optimal performance, dependent on the specific composite configuration. The hand lay-up technique is preferred for its simplicity, although other methods like compression molding are also utilized. The orientation of fibers, particularly at a 45° angle, has been shown to significantly influence mechanical properties and durability, pointing to the need for further research in this area. The structural configurations, including layer-by-layer and sandwich layouts, allow for precise control over properties such as thickness, optimizing the composites for various applications. This burgeoning field, with its focus on optimizing the synergy between different materials, underscores the potential for innovative composite applications, albeit with a recognition of the need for continued exploration into the effects of fiber orientation and composite structure.

4 Impact of hybridization in mechanical properties

The mechanical properties of BF hybrid composites have been investigated by numerous authors [94,95,96,97, 100]. The development of bamboo fiber (BF) hybrid composites has been propelled by the need for materials that balance mechanical performance with environmental sustainability. Recent investigations have revealed that bamboo, along with other natural fibers, when reinforced within polymer matrices, significantly improves the mechanical properties of the resulting composites. The addition of bamboo and coconut fibers to epoxy composites, for example, has been shown to result in composites with a tensile strength reaching up to 62.42 MPa, highlighting the fiber’s reinforcing capability [105]. In the hybrid combination of bamboo with other natural fibers like kenaf and coir, the mechanical properties vary based on the fiber ratios, matrix selection, and manufacturing process. When combined with polylactic acid (PLA) polymer, such hybrid composites show a linear increase in tensile strength and modulus up to 158 MPa and 7 GPa, respectively, with optimal fiber content [112]. Supian et al. [94] highlighted the importance of fiber/matrix interfacial bonding, fiber proportions, content/volume fraction, and fiber length and thickness in determining the tensile modulus of bamboo hybrid composites. Strategic fiber placement has been demonstrated by the inclusion of kenaf and coir in different layering sequences alongside bamboo fibers. The strategic fiber placement has been proven to impact both tensile and flexural properties [127, 128]. Apart from this, the treatment of natural fibers with NaOH has been reported to enhance the interfacial bonding between the fibers and the matrix, leading to improved mechanical properties [129, 130]. The alkaline treatment actually removes impurities from the fiber surfaces, thereby improving the fiber-matrix adhesion and contributes to the composites’ increased tensile strength [105].

Flexural properties are notably enhanced in bamboo hybrid composites as well due to hybridization. The addition of palm fibers to bamboo in an epoxy matrix has led to an increase in flexural strength by up to 49%, compared with composites with low modulus and ductile (LMD) fibers [122]. This increase is attributed to the higher stiffness and density of bamboo fibers, which contribute significantly to the load-bearing capacity of the composites. Supian et al. [94] demonstrated substantial improvement in flexural strength (ranging from 60.56 to 61.10 MPa) and flexural modulus (ranging from 5.52 to 6.04 GPa), with a notable increase of 17% in flexural strength of date palm-bamboo compared with date palm fiber composites. The impact strength of BF composites is also significant. While the presence of palm fibers can reduce the impact strength of BF hybrid composites, a balanced hybridization with other natural fibers can mitigate this effect. A composite with a 50:50 ratio of bamboo to other natural fibers such as sugarcane bagasse has been shown to possess improved impact strength, indicating superior energy absorption and making it suitable for applications where resistance to impact is crucial [109]. In addition to mechanical properties, the durability of BF composites under environmental stressors is also critical. Accelerated weathering tests have shown that while all composites exhibit a decline in tensile and impact strengths post-weathering, BF hybrids display a lesser drop, suggesting a protective effect imparted by the natural fiber layers [111].

In summary, BF hybrid composites exhibit a complex interrelation of mechanical properties that can be optimized through fiber treatment, hybridization, and proper composite formulation as displayed in Fig. 7. These composites offer a compelling combination of high mechanical strength, flexibility, and environmental benefits, making them attractive for various industrial applications, including the automotive and construction sectors. The research underscores the potential of BF hybrid composites to replace traditional synthetic materials, contributing to the advancement of green composite materials.

Fig. 7
figure 7

Important aspects to consider for the mechanical performance of bamboo hybrid composites

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5 Impact of hybridization in thermal stability

The investigation into the thermal stability of bamboo hybrid composites has yielded promising results for their application across various industries. Research conducted by Jawaid et al. [131] revealed that the integration of date palm and bamboo fibers into an epoxy resin markedly improves thermal stability, seen in higher decomposition temperatures (max 382 °C) and increased glass transition temperatures (Tg = 79.46 °C), indicating the materials’ ability to maintain structural integrity across a wide temperature spectrum. Complementing these findings, Chee et al. [96] determined that a 50:50 bamboo to kenaf fiber weight ratio optimizes the thermal expansion properties. This hybrid composite displayed the lowest coefficient of thermal expansion (CTE) of 118.2 ppm/°C, total expansion of 1.14%, and superior dynamic mechanical properties. Such advancements suggest that these composites are not only stable but also maintain their shape effectively under thermal stress. Further research by Abedom et al. [109] demonstrated the exceptional thermal insulation properties of composites made from bamboo charcoal and bagasse fiber, particularly with a 30:70 ratio, exhibiting high thermal resistance suitable for automotive interiors. Similarly, Liew et al. [104] have shown that treatments like silane coupling agents, copolymers, and hexamethylene diisocyanate can significantly enhance the thermal stability of jute-bamboo/polyethylene composites up to 310 °C (Fig. 8), although certain additives such as nanoclay or tin (IV) oxide nanopowder may have complex effects on thermal stability.

Fig. 8
figure 8

Thermogravimetric analysis graph of (A) treated jute-bamboo/polyethylene composite; (B) treated jute-bamboo/EGMA/polyethylene composite, (C) untreated jute-bamboo/EGMA/polyethylene composite and (D) untreated jute-bamboo/polyethylene composite [104]

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Moreover, Yorseng et al. [111] confirmed that bioepoxy composites reinforced with bamboo, basalt, and carbon fabrics retain their thermal stability even after accelerated weathering tests (Fig. 9), highlighting their suitability for long-term use in sectors such as automotive, aerospace, and construction. These studies provide a comprehensive understanding of the potential of bamboo hybrid composites as environmentally friendly alternatives to traditional materials. These composites offer a blend of high thermal stability, low thermal expansion, and excellent insulation properties. However, optimizing fiber treatments and carefully selecting hybridization strategies are vital for maximizing performance, ensuring the viability of materials capable of withstanding diverse thermal environments.

Fig. 9
figure 9

TGA and DTG graphs of the composite samples (bamboo, BB; basalt, BS; and carbon, CB) pre-weathering (a, b) and post-weathering (c, d) [111]

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6 Impact of hybridization in biodegradability

Chee et al. [132], Liu et al. [133], and Hasan et al. [134] collectively emphasize the potential of bamboo as a sustainable and biodegradable material for developing hybrid composites aimed at a variety of applications. Chee et al. [132] investigated the effects of environmental stressors on the biodegradability and other properties of bamboo/kenaf fiber reinforced epoxy composites. The study discovered that the hybrid composites with a higher ratio of kenaf fibers showed greater biodegradability after prolonged soil exposure. This can be attributed to kenaf’s higher hemicellulose content, which is more amenable to microbial degradation [135, 136]. As depicted in Fig. 10, a balanced 50% bamboo and 50% kenaf composition (B:K:50:50) offers better biodegradability, making it ideal for outdoor structural applications where environmental degradation is desired at the end of the product’s lifecycle.

Fig. 10
figure 10

Soil burial test results of the weight loss of the composites after 3, 6, and 12 months [132]

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Liu et al. [133] focused on creating biodegradable tableware from a mix of bamboo and sugarcane bagasse fibers. The resulting product provided a viable alternative to synthetic plastics, offering rapid biodegradation in soil and superior mechanical properties like tensile strength and hydrophobicity. The study demonstrated that the tableware degrades substantially within 2 months in soil, with the degradation process beginning as early as 20 days with the growth of fungi, highlighting its environmental friendliness and suitability as a sustainable option for food packaging (Fig. 11). Hasan et al. [134] fabricated sustainable packaging materials by reinforcing seaweed films with bamboo-derived microcrystalline cellulose (MCC). The incorporation of MCC improved the tensile strength and reduced the permeability to water vapor, essential for packaging applications. The biodegradability assessment showed that these composites began to lose weight within the first week of soil burial, with significant degradation observed by the end of one month. The results indicate the composites’ ability to break down in a natural environment. This characteristic makes them suitable for applications where quick biodegradation is beneficial, such as packaging for dry goods.

Fig. 11
figure 11

Examination of molded fiber tableware’s morphology and biodegradation: A, B optical microscope images of bamboo and bagasse fibers, C–E SEM views of molded cup surfaces at different magnifications, F–H SEM of fiber cross-sections in cups (F) and photos comparing biodegradation of molded cups (G) to a plastic lunchbox (H) [133]

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7 Role of additives in bamboo hybrid composites

7.1 Nanoclay

This section discusses the impact of nanoclay additives in bamboo hybrid composite materials. Chee et al. [97] provide a detailed analysis of how nanoclay, particularly organically modified montmorillonite (OMMT), enhances the mechanical robustness of bamboo-/kenaf-reinforced epoxy hybrid composites. The findings indicate a notable increase in tensile strength and Young’s modulus, highlighting the improved rigidity and structural integrity imparted by nanoclay. This enhancement in mechanical properties can be attributed to the expansive aspect ratio of nanoclay [137]. The nanoclay actually acts as a filler within the fibrous matrix, effectively diminishing void content and bolstering flexural tenacity [138]. Figure 12 shows that the composite samples having OMMT (BK/E-OMMT) offer the lowest void content (1.28%). Furthermore, this study emphasizes the role of OMMT in augmenting interfacial adhesion strength. OMMT plays a critical factor in composite resilience, by impeding polymer chain mobility [139]. This results in improved load-bearing capacity and energy dissipation capabilities. This is demonstrated by the higher impact strength and superior storage modulus in OMMT-infused composites.

Fig. 12
figure 12

FESEM images of tensile-fractured samples: a bamboo-kenaf/epoxy; b bamboo-kenaf/epoxy-montmorillonite; c bamboo-kenaf/epoxy-halloysite nanotube; d bamboo-kenaf/epoxy-OMMT; e agglomeration observed in bamboo-kenaf/epoxy-montmorillonite; f agglomeration observed in bamboo-kenaf/epoxy-halloysite nanotube [97]

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Conversely, Liew et al. [125] explore the broader implications of incorporating nanoclay, along with tin(IV) oxide and hexamethylene diisocyanate (HDI), in jute/bamboo/polyethylene hybrid composites. Their research underscores the complex interplay between these materials, particularly noting how nanoclay improves adhesion by filling voids between fibers and the matrix, as indicated by the shift in hydroxyl peaks in Fourier transform infrared spectroscopy (FTIR) analysis in Fig. 13. However, they highlight drawbacks, including the tendency of nanoclay to agglomerate and its hydrophilic nature, which leads to increased water absorption and can negatively impact the composite’s thermal–mechanical properties.

Fig. 13
figure 13

FTIR analysis of different composites: untreated jute-bamboo/polyethylene (UJBC), HDI-treated jute-bamboo/polyethylene (HJBC), HDI-treated jute-bamboo/MMT 1.31PS/polyethylene (HMJBC), and HDI-treated jute-bamboo/SnO2/polyethylene (HSJBC) [125]

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A recent review reported significant potential of kaolinite to enhance bamboo fiber-reinforced composites by improving their mechanical and thermal properties [140]. Through effective intercalation techniques using molecules like dimethylsulfoxide (DMSO) and N-methylformamide (NMF), kaolinite becomes compatible with polymer matrices, resulting in superior nanocomposite formation. Methods such as in situ polymerization and melt blending can ensure uniform dispersion and integration of kaolinite within the composites. Additionally, thermal characterizations indicate that kaolinite can increase the thermal stability of the polymeric matrix, making the composites more suitable for high-temperature applications. Overall, kaolinite can provide substantial mechanical reinforcement and improved thermal performance, contributing to the development of advanced, sustainable bamboo composites.

Synthesizing these insights, it becomes evident that while nanoclay, especially OMMT, offers substantial mechanical property enhancement to bamboo hybrid composites, there are also negative impacts. Liew et al. [125] demonstrated the potential negative impacts of nanoclay on other properties of the composites such as thermal stability and moisture resistance. Therefore, the utilization of nanoclay in bamboo hybrid composites requires a balanced approach. Researchers should consider both the advantages in enhancement of mechanical performance and the trade-offs in terms of thermal and moisture-related properties. The decision to incorporate nanoclay, including the variance and concentration, must align with the specific requirements of the intended application. This approach would ensure that the benefits are maximized while mitigating the adverse effects.

7.2 Carbon nanotubes (CNT)

The studies on multi-walled carbon nanotubes (MWCNTs) as additives in bamboo/glass fiber hybrid composites, explored by Nor et al. [98] and Nor et al. [141], offer a comprehensive view of the crucial balance between enhanced mechanical properties and the potential drawbacks of excessive MWCNT concentration. Nor et al. [141] identified a critical threshold value for MWCNT incorporation, where up to 0.5 wt.% of MWCNT modestly increases tensile strength by 7.7%. However, a higher concentration of 1.0 wt.% of MWCNT leads to a significant 36.8% reduction in tensile strength and a marked decrease in flexural properties. This highlights the delicate balance between MWCNT concentration and composites’ performance. Therefore, while the optimal dispersion of MWCNT yields mechanical enhancements, excessive amounts result in brittleness and reduced flexural integrity. The field emission electron microscope (FESEM) findings become particularly relevant in this scenario. FESEM analysis provides crucial insights into the nanostructural arrangement of MWCNTs within the composites. The findings show that the uniform dispersion and interfacial bonding of MWCNTs are integral to their performance at the macroscopic level. The nanoscale observations of FESEM from Fig. 14 show that 0.5 wt.% of CNTs achieved better dispersion while the higher content of CNTs resulted in agglomeration.

Fig. 14
figure 14

FESEM images of tensile fracture samples having (a) 0.5wt.% CNTs and (b) 1.0 wt.% CNTs [141]

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Another study by Nor et al. [98] focuses on the benefits of MWCNTs in enhancing impact resistance and flexibility of the composites. It reports that a 0.5% weight fraction of MWCNTs not only improves the composite’s low-velocity impact (LVI) resistance, reducing energy absorption by 9.21% and increasing peak force by 36.23%, but also enhances deflection capabilities and compression after impact (CAI) strength. This study emphasizes the importance of material engineering and preparation techniques, such as homogenization and the use of acetone, to ensure even distribution of MWCNTs within the epoxy matrix and overcome natural agglomeration tendencies.

Thakur et al. [142] found that CNTs in epoxy-bamboo composites notably improved tensile and flexural strengths, although increased brittleness was a drawback. Prabhudass et al. [143] also noted enhanced tensile strength and thermal stability in bamboo/kenaf hybrid polymer nanocomposites filled with MWCNTs. Yang et al. [144] developed a composite for electromagnetic interference (EMI) shielding by mixing CNTs with bamboo fiber and high density polyethylene (HDPE), revealing improved shielding effectiveness and thermal stability. Lastly, Zheng et al. [145] presented an application of CNTs in energy storage by incorporating them into composite phase change materials (PCMs). CNTs were highlighted for their contribution to the thermal conductivity and photo-thermal conversion efficiency of PCMs, demonstrating their utility in creating efficient, sustainable energy storage solutions. Despite these advancements, challenges persist in uniformly dispersing CNTs, mitigating increased brittleness, and optimizing thermal stability. Thakur et al. [142] tackled dispersion issues using sonication and acetone, whereas Prabhudass et al. [143] focused on improving interfacial bonding through fiber treatments. The balance of CNT content is vital for maximizing benefits without compromising other material properties or incurring high costs. These challenges call for precise process control and careful consideration of manufacturing techniques to fully leverage CNTs in composite materials for industrial and technological applications. These studies discussed the key challenges associated with CNTs in composite materials, such as poor dispersion and brittleness. Research conducted by Wang et al. [146] not only addressed these key challenges but also reported significant enhancement in interfacial bonding, tensile, and wear properties with a uniform dispersion of carboxylated CNTs on basalt fibers. This innovative approach, achieved through carboxylated CNTs and environmentally friendly sizing methods, holds substantial potential for broader industrial applications. This innovation led to a 17.5% increase in tensile strength, a 36.0% increase in flexural strength, and a 40.5% improvement in wear resistance. Moreover, the promising results suggest that similar methodologies could be explored and adapted for bamboo fiber composites, potentially leading to further advancements in sustainable, high-performance composite materials tailored for diverse applications.

Synthesizing these findings, MWCNTs emerge as a significant additive for bamboo hybrid composites, capable of improving both strength and impact resistance. However, the success in harnessing the benefits of MWCNTs lies in meticulous material engineering to achieve effective stress transfer and homogeneous distribution within the composite matrix. This balance is crucial in advancing composite material technology, especially for applications demanding exceptional mechanical properties.

7.3 TiO2 and ZrO2

The study of Latha and Rao [99] investigated the influence of TiO2 and ZrO2 ceramic fillers on bamboo-glass hybrid polymer composites. This study provides valuable insights into how these fillers enhance the composites’ mechanical and wear characteristics. The research reveals that addition of these fillers in varying concentrations (3%, 6%, and 9%) significantly improves the composites’ tensile strength, particularly with the inclusion of ZrO2. Notably, the tensile strength increases as long as the concentration of ZrO2 is up to 9% as depicted in Fig. 15. The glass-bamboo-bamboo-glass (GBBG) sequence of composites containing 9% ZrO2 filler achieved tensile strength close to pure glass fiber composites. This indicates a substantial enhancement in the material’s strength and suggests its potential application in high strength materials. Additionally, the flexural strength of the composites also improved with the addition of these fillers, especially in the glass-bamboo-bamboo-glass (GBBG) composites with a 6% filler concentration. The wear properties of the composites are positively influenced by the addition of ZrO2, which significantly enhances wear resistance, peaking in performance with 6% ZrO2 filler in GBBG composites. However, it’s observed from Fig. 16 that beyond a 6% filler concentration, wear resistance tends to decrease, likely due to issues with filler-matrix bonding.

Fig. 15
figure 15

Tensile strength data of glass (G) and bamboo (B) hybrid composites with varying percentages of ZrO2 [99]

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Fig. 16
figure 16

Flexural strength data of glass (G) and bamboo (B) hybrid composites with varying percentages of ZrO2 [99]

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The study conclusively determines that ZrO2 filler, in comparison to TiO2, is more effective in improving both strength and wear properties of the hybrid composites. The optimal filler concentration of ZrO2 is 9% for strength and 6% for wear resistance. These findings are crucial for the development and optimization of bamboo-glass hybrid polymer composites. This study underscores the critical role of filler type and concentration in enhancing the properties of hybrid composites.

7.4 Graphene nanoplates

The study by Gouda et al. [147] demonstrated that the incorporation of graphene nanoplatelets (GNPs) in bamboo micro filler-epoxy hybrid composites significantly enhances the mechanical and thermal properties. GNPs have improved both the tensile and flexural strength, as well as the loss and storage moduli. However, when GNPs are added more than 0.8 wt%, the mechanical properties decreased due to filler agglomeration. The addition of GNPs also markedly increases the composite’s thermal conductivity, almost quadrupling that of neat epoxy. Morphologically, the even distribution of GNPs within the epoxy matrix enhances the interfacial bonding and structural integrity as shown in Fig. 17. However, this enhancement comes with a slight increase in corrosion rates, attributed to increased voids and chemical interactions. Overall, GNPs have greatly contributed to the robustness and application potential of the hybrid composites, balancing improved properties with considerations for optimal filler content and corrosion resistance.

Fig. 17
figure 17

Even distribution of GNP within the bamboo micro filler-epoxy hybrid composites [147]

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8 Applications of bamboo composites

8.1 Aerospace applications

Aerospace-grade composites must be lightweight yet robust, with a high strength-to-weight ratio essential for fuel efficiency and maneuverability [148, 149]. They require exceptional mechanical properties to endure the extreme stresses of flight and thermal stability to withstand varied temperature extremes, particularly in engine and atmospheric re-entry applications [150]. Resistance to microcracking and low water absorption is critical to maintain structural integrity [151]. Moreover, aerospace materials need to be cost-effective and eco-friendly, with the adaptability for various manufacturing processes [152]. Bamboo hybrid composites, as described in this review, exhibit noteworthy mechanical properties, thermal stability, and eco-friendly characteristics. They display promising tensile strength, flexural strength, and impact strength, making them suitable for various applications. However, when evaluated against the demanding criteria of aerospace-grade composites, certain areas require further improvement. The mechanical properties mentioned, while impressive, may not match up with the extreme stresses of aerospace applications. One of the main reasons for fuselage cracking is cyclic stress, resulting from numerous cycles of pressurization and depressurization [153]. Additionally, the thermal stability needs to withstand even higher temperature extremes, particularly in engine components. For instance, in a gas turbine engine, the temperatures can reach up to 1600 °C [154]. Therefore, the materials being used need to be capable of enduring such extreme heat. The incorporation of nanoclay [97] and carbon nanotubes (CNTs) [98, 141] into bamboo composites, as discussed in the paper, significantly enhances their mechanical strength and thermal stability. These improvements are pivotal for aerospace applications, where materials must endure extreme stresses and temperature variations. For example, the enhanced tensile strength and reduced thermal expansion coefficient due to nanoclay addition make the bamboo hybrid composites suitable for aerospace components that demand lightweight materials with high structural integrity. Moreover, bamboo composites hold significant potential for space exploration due to their inherent strength, lightweight nature, and cost-effectiveness. When engineered with advanced materials like carbon nanotubes or kaolinite, bamboo composites can meet the demanding requirements of space applications, such as resistance to micro-meteorites, extreme temperatures, and electromagnetic interference (EMI) [155]. Their biodegradability and renewability also contribute to sustainable space missions. By enhancing bamboo composites with properties like fire resistance, thermal stability, and EMI shielding, they can improve the safety, functionality, and feasibility of spacecraft and inter-planetary colonies, making them a promising alternative to traditional synthetic materials in space technology. Hence, further research, testing, and engineering are required to optimize these composites for aerospace-grade applications while maintaining their eco-friendly advantages. Bamboo composite-based potential application is shown in Fig. 18.

Fig. 18
figure 18

Bamboo composite-based overhead compartment door for airplanes [156]

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8.2 Ballistic applications

In the context of ballistic applications, the role of multi-walled carbon nanotubes (MWCNTs) and graphene nanoplates in bamboo composites is of particular interest. The improved impact resistance and energy dissipation capabilities, resulting from the homogeneous dispersion of MWCNTs, make these composites ideal candidates for personal protective gear and vehicle armor [98, 141]. The high toughness and flexural strength, accentuated by graphene nanoplates, ensure that bamboo composites can effectively absorb and distribute the force of ballistic impacts, providing enhanced protection while maintaining lightweight characteristics [147]. Moreover, the study of Ali et al. [157] explored laminated woven bamboo and E-glass fiber composites in ballistic applications. The findings reveal a promising potential for these materials in defense and personal protective equipment. These hybrid composites blend the lightweight, high tensile strength of bamboo fibers with the rigidity and durability of E-glass fibers in an unsaturated polyester matrix, resulting in materials that offer superior protection without excessive weight. This synergy not only enhances impact resistance but also brings sustainability into the equation, as bamboo is a renewable resource. The V50 ballistic limit tests indicate that these composites can withstand high-velocity impacts, making them suitable for body armor and other protective gear. The potential for optimization is significant, suggesting that further exploration into layering techniques, fiber orientation, and matrix materials could yield even more effective ballistic-resistant materials. Moreover, the ecological aspect of using bamboo, coupled with the performance benefits, aligns with the growing emphasis on sustainable practices in material engineering. These insights point towards a broader applicability of such composites, extending beyond ballistic uses to areas like aerospace, automotive, and sports equipment, where strength, lightness, and durability are crucial. Figure 19 showcases the composite’s structural response to ballistic impacts, which would further elucidate their protective capabilities.

Fig. 19
figure 19

Damages occurred by ballistic projectile: a fiber breakage, b matrix breakage, c delamination between composites layers, and (d) shear plug area [157]

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8.3 Automotive applications

Historically, a lack of communication between vehicle designers and composite manufacturers led to inefficiencies and underutilization of materials [158]. Therefore, bridging the knowledge gap between design requirements and manufacturing capabilities is crucial for optimizing the use of composites in vehicle design [159]. The design criteria for automotive structures are centered around achieving cost-efficiency, sustainability, and safety [160]. Automotive parts need to be stable and lightweight for enhanced performance and fuel efficiency, as well as durable to withstand various stresses [161]. Studies suggest that natural fiber-reinforced composites can lead to a cost reduction of 20% and a weight reduction of 30% in vehicle components [162]. Lightweight automotive parts contribute to lower fuel consumption, enhanced recycling potential, and reduced noise levels. Safety is also a key aspect, with materials chosen for non-toxicity and the ability to absorb energy in crashes [163].

The synthesis of recent research in automotive composite materials reveals a significant trend towards the use of sustainable, cost-effective, and performance-oriented materials, with a focus on natural fibers. Studies by Supian et al. [94], Refaai et al. [95], Chee et al. [96], Abedom et al. [109], Sakhtivel et al. [110], and Yorseng et al. [111] have provided valuable contributions to this field. Supian et al. [94] and Refaai et al. [95] have highlighted that date palm and bamboo fiber hybrid composites possess impressive mechanical properties such as tensile strength (39.16 MPa), flexural strength (61.10 MPa), and impact toughness (12.70 J/m2). These properties underscore the suitability of these composites for lightweight yet durable automotive parts. Chee et al. [96] demonstrated that a 50:50 weight ratio of bamboo-kenaf hybrid composites showed the lowest coefficient of thermal expansion and the highest dynamic mechanical properties. This finding is very crucial for maintaining the stability and the integrity of automotive parts under varying conditions. Additionally, for automotive applications, the addition of nanoparticles like TiO2, ZrO2, and carbon-based additives to bamboo composites translates into materials with superior wear resistance, thermal stability, and mechanical strength [99]. The improved wear properties due to ZrO2 addition can significantly extend the lifespan of automotive components subjected to frictional forces. Figure 20 illustrates the application of bamboo fiber composites in the design and construction of car chassis, highlighting their lightweight, durability, and impact resistance, which are essential for modern automotive engineering.

Fig. 20
figure 20

Bamboo composite-based car chassis [164]

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The study by Abedom et al. [109] on bagasse fiber/bamboo charcoal composites revealed that a 30% bagasse-70% bamboo composition displayed higher thermal insulation, superior impact, and flexural strength, indicating potential for automotive interior applications. The tensile strength of these composites reached 255.80 MPa, closely matching the strength (260.10 MPa) of artificial fiber composites. Sakhtivel et al. [110] enhanced sound absorption properties in composite samples, achieving sound absorption coefficients of 0.0230, 0.033, 0.061, 0.065, and 0.113 at a frequency of 4000 Hz. This improvement in sound absorption across a wide frequency range is crucial for enhancing passenger comfort and safety in automotive applications. Yorseng et al. [111] exploration into replacing synthetic epoxy with bioepoxy resin in bamboo, basalt, and carbon hybrid composites also aligns with the industry’s sustainability goals. Their composites demonstrated excellent mechanical property retention, even under accelerated weathering conditions, suggesting their viability as substitutes for traditional materials in automotive applications.

The research on hybrid biocomposites using lignocellulosic fillers from Chamaerops humilis and Posidonia oceanica offers valuable strategies that can be applied to bamboo composites for automotive applications [165]. The use of a balanced hybrid network to create a strong interphase region between the fibers and the PLA matrix is particularly notable. This strategy involves optimizing the morphological features and physicochemical characteristics of the components to achieve significant enhancements in mechanical properties and thermal stability such as a 120% increase in mechanical strength and a 50% increase in stiffness. By employing similar techniques, bamboo composites can be developed with improved strength, durability, and thermal performance, making them suitable for various automotive applications.

In summary, these studies collectively underscore the potential of natural fiber composites in the automotive industry. They highlight not only the importance of sustainability and cost-efficiency but also the need for materials that provide the necessary mechanical strength, durability, and safety. The incorporation of natural fibers, such as date palm, bamboo, kenaf, and bagasse along with the development of bioepoxy resin, represents a significant stride towards more environmentally responsible and high-performing automotive materials.

8.4 Structural applications

Biocomposites, known for their eco-friendly design and energy efficiency, are gaining popularity in architecture and structural design [166]. They offer a sustainable alternative to traditional materials like cement and steel, reducing material and energy consumption [167]. Their key benefits include recycled content, use of renewable materials, and enhanced earthquake resistance [168, 169]. These materials are used in various applications, from roof panels to window lineals, and contribute to achieving green certifications like Leadership in Energy and Environmental Design (LEED) [170]. The shift towards biocomposites signifies progress towards sustainable and eco-friendly building practices [171]. Recent studies on biocomposites provide compelling evidence for their suitability in structural applications. These studies demonstrate advancements in material science that align well with the growing demand for sustainable and efficient building materials. For instance, a recent review on renewable wood-based composites is highly significant for bamboo composites research [172]. The review highlights innovative approaches to enhance mechanical properties, flame retardancy, hydrophobicity, frost resistance, and transparency in wood-based composites, which can be directly applicable to bamboo composites. By adapting similar fabrication methods and mechanisms, such as using all-green structural blocks and biomimetic techniques, bamboo composites can be improved to meet the high-performance demands of smart homes and industrial applications. Furthermore, the review focuses on sustainable manufacturing methods which align well with the eco-friendly nature of bamboo, offering insights that can help advance the development and application of bamboo composites in structural applications. Another research on functionally graded hybrid composites (FGHC) fabricated from natural fibers like banana stem and fly ash demonstrates significant improvements in mechanical properties, thermal stability, and interfacial bonding, making them viable alternatives to conventional materials in structural applications [173].

Jawaid et al. [131] developed date palm fiber (DPF)- and bamboo fiber (BF)-reinforced epoxy composites. The study showed notable improvements in thermal stability, a crucial attribute for materials used in varied thermal environments typically in the construction sector. The hybrid composites displayed a higher glass transition temperature (Tg), indicating a broader range of temperature stability. This is crucial for materials exposed to environmental temperature fluctuations. Additionally, the thermogravimetric analysis (TGA) revealed superior thermal decomposition temperatures and residual mass percentages in the hybrid composites. This finding suggests enhanced durability and stability. The dynamic mechanical analysis (DMA) findings indicate an increased storage modulus, representing material stiffness, which is key in construction materials to withstand mechanical stresses while maintaining shape and integrity. The study on bamboo and kenaf fiber-reinforced epoxy composites by Chee et al. [96] further supported these findings. The thermomechanical analysis (TMA) of these composites highlighted the significant influence of fiber orientation on material behavior, with a noted reduction in the coefficient of thermal expansion (CTE) in a 50:50 bamboo to kenaf ratio. This finding indicates enhanced dimensional stability. In terms of stiffness and structural integrity, bamboo/epoxy composites exhibited a higher complex modulus (E*) of 4016 MPa, compared with 3568 MPa for kenaf/epoxy composites. This greater stiffness and load-bearing capacity make these highly suitable for structural applications. Moreover, enhanced interfacial bonding and reduced void content improve the load-bearing capacity of bamboo composites which can be achieved by the incorporation of nanoclay, CNTs, and graphene nanoplates as discussed earlier.

A study by Chee et al. [97] on bamboo/kenaf/epoxy hybrid composites with nanoclay infusion, particularly organically modified montmorillonite (OMMT), brought a significant improvement in mechanical properties. The composites showed tensile strength of 55.82 MPa, with a flexural strength of 105 MPa and an impact strength of 65.68 J/m. These findings are attributed to the improved interlayer spacing and dispersion of OMMT. The dynamic mechanical analysis (DMA) results showed an increased storage modulus in these composites, suggesting superior stiffness and load-bearing capacity, which is critical for structural applications.

Wang et al. [174] developed transparent bamboo composites through lignin modification method in order to replace conventional glass in structural applications. Traditional delignification processes, while aimed at creating transparency, often compromise structural integrity and mechanical properties, leading to low transmittance. The study proposes a novel strategy that modifies lignin to preserve its aromatic structure while removing light-absorbing chromophores. The process of lignin removal involves treating bamboo with a concoction of sodium hydroxide, sodium silicate, magnesium sulfate, DTPA, and hydrogen peroxide. This innovative approach not only decolorizes bamboo but does so without fully removing lignin or damaging its aromatic structure, preserving a significant 78% of the lignin content. This method is pivotal in maintaining bamboo’s robustness for subsequent epoxy infiltration, crucial for achieving the desired high optical transparency while retaining excellent mechanical properties. The impact of this lignin removal technique is profound, yielding a bamboo composite with remarkable optical transparency of 87%, alongside enhanced whiteness and reduced light absorbance (Fig. 21). Additionally, the composite showcases superior mechanical strengths, such as high tensile strength and toughness, coupled with beneficial properties like low density, thermal conductivity, and excellent thermal insulation. These results underscore the composite’s potential as a viable, eco-friendly alternative to traditional glass, particularly in the context of energy-efficient building construction, thereby highlighting the significance of lignin modification in advancing bamboo-based sustainable materials. In a separate study, Wang et al. [175] developed bamboo steel through the removal of lignin and hemicellulose contents from bamboo. Lignin and hemicellulose were removed through a chemical treatment process involving sodium hydroxide (NaOH), sodium sulfite (Na2SO3), and hydrogen peroxide (H2O2). The process increased the porosity of the bamboo, making it more receptive to the epoxy resin infiltration and allowed better impregnation and adhesion between the bamboo fibers and the resin. This adhesion is crucial for transferring stress effectively, and it helps in preserving the bamboo scaffold’s integrity while facilitating densification under high pressure. The removal of lignin and hemicellulose had a profound impact on the bamboo. The treated bamboo demonstrated a high specific tensile strength (302 MPa g−1 cm3), surpassing that of conventional high specific strength steel. The bamboo steel also showed a tensile strength of 407.6 MPa, a record flexural strength of 513.8 MPa, and a high toughness of 14.08 MJ/m3, which are improvements of 360%, 290%, and 380% over natural bamboo, respectively.

Fig. 21
figure 21

a Depicts a diagram showing how lignin alteration occurs and the subsequent changes in the structure of lignin. (b) Outlines the steps involved in creating a transparent bamboo composite, along with images of raw bamboo, bamboo treated to modify its lignin, and the final transparent bamboo composite [174]

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The reported studies collectively justify the potential of biocomposites in the structural sector. They highlight the significant improvements in mechanical and thermal properties, aligning with the current trends towards sustainable, eco-friendly building practices. Figure 22 shows two such example of sustainable bamboo-based composite materials for structural applications. The enhanced performance metrics, particularly in terms of thermal stability, stiffness, and load-bearing capacity, underscore the viability of biocomposites in modern construction. The integration of natural fibers like bamboo and kenaf, along with innovative approaches like nanoclay infusion, marks a significant stride in developing materials that are not only environmentally responsible but also meet the rigorous demands of structural applications.

Fig. 22
figure 22

Bamboo composite-based (a) profiling and (b) roof materials [176]

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8.5 Filtration applications

The innovative use of bamboo in air filtration technologies represents a promising advancement in environmental science, as illustrated by the studies conducted by Zhao et al. [177] and Narakaew et al. [178]. Both research efforts highlight the effectiveness of bamboo activated charcoal in enhancing air purification systems, albeit through distinct methodologies and composite material formulations. Zhao et al. [177] developed a cellulose nanofibril/poly(vinyl alcohol)/bamboo activated charcoal (CNF/PVA/BAC) aerogel sheet, achieving an impressive 99.69% efficiency in capturing PM2.5 particles (Fig. 23). This study underscores the synergistic effect of combining bamboo activated charcoal with CNF and PVA, where the bamboo component plays a critical role in boosting electrostatic adsorption, thereby significantly improving filtration performance. In contrast, Narakaew et al. [178] explored the creation of a silver-nanowire/bamboo-charcoal composite on a nylon sheet, which also demonstrated superior filtration efficiency (> 99.9%), but through the incorporation of silver nanowires to enhance electrostatic forces alongside the adsorptive properties of bamboo charcoal. Both studies reveal the bamboo activated charcoal’s pivotal contribution to developing high-efficiency, low-energy air filtration systems capable of high thermal stability and reusability. However, the addition of silver nanowires by Narakaew et al. [178] introduces an interesting comparative aspect regarding the use of metallic components to augment the electrostatic capture capabilities of filters. This approach not only achieves comparable filtration efficiencies but also emphasizes low power consumption and operational efficiency at lower voltages, a significant advantage in applications where energy conservation is crucial. Despite their shared focus on bamboo's utility in air purification, the studies differ in their composite material strategies and the implications for practical application. Zhao et al. [177] use of a biopolymer matrix (CNF and PVA) alongside bamboo activated charcoal reflects a strong emphasis on environmental sustainability and material reusability, with significant attention to maintaining filtration efficiency after multiple cleaning cycles. Meanwhile, Narakaew et al. [178] incorporation of silver nanowires presents a novel method of leveraging bamboo charcoal’s adsorptive capacity, potentially offering enhanced performance in electronic or powered air filtration systems, albeit with considerations for the cost and environmental impact of silver usage. Similarly, research on bio-enzyme pretreatment and PDADMAC-assisted alkali impregnation for wood fibers in water filtration underscores the importance of chemical treatments to enhance material performance. This technology can be further researched for its application in bamboo composites as well [179].

Fig. 23
figure 23

a Preparation, b sample, c hydrophobicity, and (d) filtration mechanism of CNF/PVA/BAC aerogel sheet [177]

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The role of bamboo in advancing sustainable environmental technologies, particularly in the context of water purification and membrane fabrication, has been notably explored in recent studies by Phuong et al. [180], Xiao et al. [181], and Esfahani et al. [182]. These investigations collectively illustrate the innovative use of bamboo, offering insights into its potential as a versatile and eco-friendly material. Phuong et al. [180] development of bamboo fiber-reinforced poly(lactic acid) (PLA) composites for membrane supports (Fig. 24) and Esfahani et al. [182] fabrication of bamboo-based membranes from waste fibers both emphasize bamboo’s applicability in creating sustainable alternatives to conventional, non-degradable materials. In contrast, Xiao et al. [181] introduce a unique application of bamboo in water purification through the development of hierarchical bamboo/silver nanoparticle composites, showcasing bamboo’s effectiveness in pollutant degradation when combined with silver nanoparticles. A comparative analysis reveals shared themes of sustainability and innovation, yet distinct methodologies and applications. Phuong et al. [180] and Esfahani et al. [182] focus on the structural and mechanical benefits of bamboo in membrane technology, highlighting its role in enhancing mechanical stability, reducing swelling, and improving permeance. Both studies underline bamboo’s potential to replace petroleum-based polymers with biodegradable alternatives, thus contributing to the sustainability of membrane fabrication. However, while Phuong et al. [180] incorporate bamboo fibers directly into PLA composites, Esfahani et al. [182] utilize waste bamboo fibers, regenerated into cellulose-based membranes, emphasizing waste revalorization and the use of green solvents in the process. Xiao et al. [181] work, while also centered on sustainability, diverges by leveraging bamboo’s natural structure enhanced with silver nanoparticles for efficient water purification, indicating a different aspect of bamboo’s utility. This approach not only underscores bamboo’s adaptability in environmental technologies but also its potential in synergistic applications with nanomaterials for catalytic degradation of pollutants.

Fig. 24
figure 24

Illustration of the production process for bamboo-PLA membrane support [180]

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8.6 Electrode and EMW absorption applications

Research across various studies indicates that bamboo composites are becoming an increasingly important material in the field of energy storage, specifically for developing electrodes in supercapacitors and batteries. The high surface area, porosity, and carbon content of bamboo are being leveraged to enhance the electrochemical performance and sustainability of these devices. Notable, Gong et al. [183] prepared Co/P co-doped bamboo-based electrodes with a specific capacitance of 453.72 Fg−1, highlighting the role of bamboo’s natural structure in supporting advanced electrode designs. Bamboo also serves as a structural material in wearables with high areal capacitance (2032 mF cm−2) and as a support for advanced electrode designs with significant specific capacitance [184]. Furthermore, bamboo’s structure is exploited to create porous carbon materials for lithium-sulfur batteries, improving energy storage capacity and addressing the shuttle effect [185]. Various studies also emphasize bamboo’s role in boosting electrochemical performance and cyclic stability in supercapacitor applications as shown in Table 4. These studies collectively underscore the potential of bamboo-based materials to push forward the development of flexible, high-performance, and sustainable energy storage solutions. Across these studies, the common theme is the utilization of bamboo’s inherent properties to improve the functionality of electrode materials, whether through its carbon structure, hierarchical porosity, or ability to be doped with other elements. Despite the promising results, challenges such as scalability, uniformity in material properties, and the optimization of bamboo’s integration with other materials remain areas for further research.

Table 4 Summary of bamboo-based composites application in electrodes
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Lou et al. [186] underline the critical importance of lignin modification in bamboo for the advancement of biochar composites with enhanced electromagnetic wave (EMW) absorption capabilities. Through a meticulous process of delignification, involving the treatment of bamboo chips with a sodium chlorite solution and subsequent incubation at elevated temperatures, lignin content is significantly reduced, paving the way for the in-situ decoration of the biomass with magnetic inorganic materials like Fe3O4. This process not only preserves the structural integrity of bamboo but also optimizes its chemical composition for the loading of magnetic phases and the promotion of graphitization upon carbonization. The profound impact of lignin removal is manifested in the resultant biochar composites’ superior EMW absorption performance, boasting exceptionally low reflection loss values and a broad maximal absorption region, alongside remarkable thermal stability. These findings underscore the transformative potential of lignin modification in bamboo, opening new avenues for its application in energy conversion, electromagnetic pollution mitigation, and beyond, thereby highlighting the synergy between biomass treatment techniques and advanced functional material development.

8.7 Sensor applications

The exploration of bamboo composites in sensor technology is gaining significant attention, evidenced by the pioneering work of Guo et al. [194] and Kulkarni et al. [195]. These studies demonstrated bamboo’s natural qualities to boost sensor functionality in diverse areas like energy conversion and environmental monitoring. Guo et al. [194] utilized bamboo pulp to create origami-like pressure sensors that offer impressive sensitivity and a wide detection range, suitable for interactive technologies. Kulkarni et al. [195] embedded bamboo micro particles in polymer films, significantly increasing energy harvesting efficacy, pointing to bamboo’s utility in green energy solutions. Significant research has been done in the field of wearable technology by Zhu et al. [196], Dai et al. [197], and Liu et al. [198]. Zhu et al. [196] crafted a strain sensor from carbonized bamboo aerogel that exhibits high conductivity and flexibility, making it an excellent fit for wearable tech. Dai et al. [197] took inspiration from bamboo to design highly sensitive pressure sensors capable of capturing delicate movements (~ 0.6 kPa−1 at 0–1 kPa), which could revolutionize human motion detection (Fig. 25). Through the application of bamboo leaves, Liu et al. [198] created flexible pressure sensors that not only demonstrate bamboo’s adaptability in achieving variable sensitivity but also its cost-effectiveness.

Fig. 25
figure 25

Bamboo-inspired cellulose nanofiber/polydimethylsiloxane (CNF/PDMS) foam composites’ flexible pressure sensor [197]

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8.8 Infrared shielding applications

In a recent study, sustainable wearable infrared shielding based on bamboo fiber fabrics loaded with antimony-doped tin oxide/silver binary nanoparticles has been explored [199]. Hybridization, through the incorporation of materials such as antimony-doped tin oxide (ATO) and silver nanoparticles, has enhanced the functionality of bamboo fiber composites. The integration of these nanoparticles not only improves the mechanical properties of the composites but also imparts multifunctional characteristics such as infrared shielding, hydrophobicity, and antibacterial activity (Fig. 26). The formation of a Schottky junction between Ag and ATO nanoparticles, for instance, enables plasmon resonance absorption of near-infrared light, thereby reducing the infrared emissivity to as low as 0.68 in the 8–14 μm thermal imaging band. This is particularly advantageous for applications requiring thermal insulation and stealth capabilities. Moreover, the chemical deposition and hot press processes used in fabricating these composites ensure uniform distribution of nanoparticles, leading to consistent performance across the material. The hydrophobic properties, achieved through treatment with n-hexadecyl mercaptan, enhance the durability of the composites by providing a water contact angle (WCA) of 147.7°, an increase of 273.9% compared with untreated fabrics. Additionally, the antibacterial properties endowed by Ag nanoparticles offer significant benefits, achieving 100% inhibition of both Escherichia coli and Staphylococcus aureus. Thus, the hybridization of bamboo fibers with advanced nanoparticles not only leverages the inherent sustainability of bamboo but also elevates the performance of polymer composites, positioning them as promising candidates for a wide range of high-performance and eco-friendly applications. Future research should focus on addressing several key challenges to fully realize the potential of these innovative materials. Scalability remains a critical issue, and efforts should be directed toward developing cost-effective and efficient production methods for mass manufacturing. The long-term durability and performance of these composites under various environmental conditions need comprehensive evaluation to ensure their reliability in real-world applications. Additionally, extensive field testing in diverse operational scenarios is essential to validate the effectiveness of these materials.

Fig. 26
figure 26

Diverse application of sustainable wearable infrared shielding based on bamboo fiber fabrics loaded with antimony-doped tin oxide/silver binary nanoparticles [199]

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9 Advantages and disadvantages of bamboo composites

Bamboo composites provide multifaceted benefits starting with natural abundance and remarkable mechanical properties of bamboo fiber. Therefore, it emerges as a prime candidate for eco-friendly and cost-effective composite materials [200]. Another key feature is high strength-to-weight ratio akin to natural glass fiber, making it a superior alternative for tensile-loading applications [201]. Bamboo’s sustainability is underscored by its rapid growth rate and capacity to absorb atmospheric CO2. The promotion of a sustainable future through bamboo usage aligns with environmental sustainability goals, with advancements in fiber characterization and analysis ensuring high-quality performance. Bamboo’s production is markedly more energy-efficient compared with steel, emphasizing its role in sustainable development [202]. Bamboo stands out in its effectiveness against natural disasters like earthquakes, making it a reliable material for structural applications. As delineated in this article, bamboo fiber-reinforced composites have demonstrated significant promise in structural applications that demand high strength and flexibility. Additionally, functional high-performance composites can be developed with combination of other natural fibers and nanoparticle additives.

While bamboo’s potential as a sustainable material is recognized, several studies have illuminated a spectrum of challenges and disadvantages across different applications and processing methods. Initially, the hydrophobic nature of bamboo’s surface layers impedes effective bond formation in composites [203]. Surface modification methods unfortunately lower the fiber recovery rate and highlight a tension between natural material properties and composite performance demands. Specifically, laminated bamboo exhibits a mere 35% fiber recovery, underscoring the inefficiency of processing methods [204]. Moreover, the mechanical processing aimed at enhancing interfacial bonding often introduces damage, necessitating substantial resin use and compaction to mend, thereby raising concerns about the environmental and economic impacts of high-density, high-consumption production processes. Concurrently, the diversity and thermal sensitivity of bamboo fibers present formidable obstacles in harvesting uniform, high-quality fibers for industrial use, further compounded by the material’s brittleness due to high lignin content and the variable mechanical properties attributable to the extensive range of bamboo species [205]. In structural applications, bamboo’s advantages are tempered by propensity for water absorption that compromises mechanical properties and necessitates sophisticated seasoning techniques to mitigate [206]. Additionally, the variability in bamboo’s structural integrity over time, alongside its lower durability compared with conventional materials like steel, raises concerns about its reliability and the need for enhanced treatment methods to ensure longevity and performance.

Despite the challenges, the pursuit of bamboo as a reinforcement material reflects a broader ambition to reconcile material innovation with environmental stewardship, underscoring the need for continued research, development, and innovation in bamboo processing and application techniques. The convergence of these studies delineates a critical path forward: to harness bamboo’s inherent strengths while methodically addressing its weaknesses, thereby advancing its role as a cornerstone of sustainable material science.

10 Conclusions and future prospects

This article reviewed the crucial aspects of developing bamboo hybrid polymer composites as environmentally friendly materials. Primarily, the focus was on the fabrication of bamboo and other natural fiber composites. Additionally, the review delves into recent studies involving mechanical properties, thermal properties, biodegradability, and the use of various fillers or additives in bamboo hybrid composites. The reported studies highlighted that epoxy matrix is the preferred choice for composite development despite its environmental concerns. However, the application of green epoxy as a substitute for traditional epoxy matrix is being suggested. The selection of composites structure is also pivotal in terms of performances. As evidenced by the reported studies, a layer-by-layer structure has been utilized in most studies. A significant problem with layer-by-layer construction is the potential for layers to separate, a process known as delamination. This fault occurs when the layers are not adequately bonded or adhered to each other. This fault enforces the layers to split apart under stress or impact. Such an event can greatly undermine the composite’s structural strength. A probable solution can be continuum-based cohesive elements, which can simulate the initiation and progression of cracks or delamination at the fiber-matrix interfaces. This can provide valuable insights into the failure mechanisms of the composites.

As evidenced by the reviewed studies, the mechanical properties such as tensile and flexural strength, vary depending on factors like the type and ratio of fibers, the choice of matrix, and the manufacturing process. This implies that a level of customization and optimization is a crucial factor in composites design. In terms of thermal performance, bamboo hybrid composites have emerged as environmentally friendly alternatives to traditional materials, offering a combination of high thermal stability, low thermal expansion, and excellent insulation properties. Additives including nanoclay, CNTs, TiO2, ZrO2, and GNPs have been shown to play a significant role in enhancing the mechanical and thermal properties. However, the concentration and distribution of these additives is crucial in balancing the improvement in properties with potential drawbacks such as increased brittleness, moisture absorption, or corrosion. Lastly, in terms of biodegradation, bamboo hybrid composites are a key sustainable resource. These composites are suitable for diverse applications ranging from structural components to food packaging and other consumer products where biodegradability after the product’s lifecycle is a key factor.

The future of bamboo hybrid composites holds immense potential across various industries, owing to their biodegradability and mechanical strength. These composites have potential for wider usage in industries such as automotive, aerospace, and construction, providing eco-friendly substitutes to conventional materials. Innovations are expected to enhance their biodegradability while maintaining structural integrity. This potential in particular can revolutionize the food packaging industry. The fusion of these composites with cutting-edge technologies such as smart sensors could pave the way for innovative uses, in line with waste minimization. Customization for specific industrial requirements will lead to specialized materials, and as the market grows, the development of industry standards and regulations will become crucial. Increased environmental concerns are expected to fuel the market expansion and stimulate the ongoing innovation and exploration in this field. This combination of elements establishes bamboo hybrid composites as a significant contributor to the progress of eco-friendly material technology.