Material development science in the construction industry is saddled with the responsibility of seeking alternative materials that can alleviate the reliance on virgin resources, reduce the energy use associated with building material production, mitigate the pollution associated with the disposal of building materials, and ultimately foster a more sustainable environment. In recent years, fibre-reinforced polymer composites have garnered attention across diverse sectors like automobiles, consumer products, transportation, packaging, and construction. However, bio-based alternatives to these composites offer a promising avenue towards creating more environment-friendly building materials. This paper explores the practical applications of bio-based polymer composites in non-structural contexts, such as building panels, partitions, facades, and structural applications, including internal and external reinforcement. It examines the benefits and challenges inherent in these applications, drawing insights from a comprehensive review of research in the field. Through this review, the paper sheds light on the potential of bio-based polymer composites in developing more sustainable construction materials, providing a pathway towards a greener and more sustainable built environment.
1 Introduction
The building/construction industry significantly contributes to resource depletion and environmental pollution [1]. Twenty per cent of the environmental impact stems from processes associated with buildings, encompassing the manufacturing and disposal of building materials [2]. The industry contributed 38% of all energy-related carbon dioxide (CO2) emissions in 2020 [3] and is also one of the largest consumers of virgin materials. In terms of environmental impact, construction and demolition (C&D) wastes make up a large percentage of materials that end up in landfills. For example, 40% of the landfill volume in the USA is from C&D wastes, mainly wood, drywall, and plastic [4]. A fibre-reinforced polymer (FRP) material is typically a composite of synthetic fibres, particularly carbon, glass, or aramid, and a polymer matrix, typically polyester, vinyl ester, or epoxy resins [5]. Owing to its high strength, corrosion resistance, and lightweight nature, the popularity of this material has surged in the construction industry. Specifically, they have been used to develop structural shapes that could be used in various building and bridge applications, sandwich construction, and as internal and external reinforcement for structural elements [6]. Since FRP composites are commonly made with synthetic materials, rising environmental concerns are associated with their production and disposal. These concerns fuel the development of bio-based composites, which describe composites made from natural sources that can invariably reduce the consumption of virgin materials and are more eco-friendly. These bio-based polymer composites, or biocomposites, are poised to be non-abrasive and reduce CO2 emissions and dependence on petroleum products [7]. Given the recycling challenges and toxic emissions associated with synthetic FRPs [8], biocomposites present a promising avenue for embracing the principles of the circular economy, particularly if they exhibit biodegradability [9]. A variety of natural fibres sourced from plants and animals have been utilised to create functional biocomposites. These biocomposites, in comparison to synthetic fibres, exhibit lower density, are biodegradable, potentially more accessible, and are less abrasive [10]. Consequently, they present a promising alternative to reinforcement material for FRP composites.
Biocomposites are becoming increasingly attractive, and their manufacture and supply in recent years have been accompanied by political incentives and tax reductions in some countries [11, 12]. Natural fibres are now used instead of synthetic fibres to create biocomposites across the automobile, sports, aerospace, and other industries. The automobile industry has embraced the use of natural fibre biocomposites to achieve weight reductions and improved mechanical properties of automobile components like door panels, interior carpets, boot lining, dashboards, bumpers, and so on [13, 14]. Specific policies like those established by the European Union and Japan that required 85% (95% for Japan) of a vehicle to be either recycled or reused as of 2015 have encouraged the research and development of biocomposites [15]. Cost is also a crucial factor that encourages the use of natural fibres over synthetic fibres. Natural fibres are cheap compared to their synthetic counterparts, increasing their commercial and research potential [12].
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Properties of biocomposites, such as their lightweight, high strength-to-weight ratio, corrosion resistance, and thermal insulation properties, make them suitable building materials, and their adoption in the industry offers several benefits. From an environmental perspective, biocomposites reduce reliance on fossil fuels and mitigate greenhouse gas emissions throughout the product lifecycle [16, 17]. Biocomposites are often biodegradable or recyclable, minimising waste generation and contributing to a circular economy. Economically, bio-based composites can reduce material costs and create new opportunities for rural development and job creation in agricultural communities. The potential for biocomposites in the construction industry lies in the current applications of conventional synthetic FRPs. Bakis et al. [6] outlined the specific applications of FRP composites for construction, including bridge decks, sandwich construction, internal reinforcement, and externally bonded reinforcement. Biocomposites have also found their place in the building industry, where they have been developed for non-structural applications such as furniture, insulation boards, and partitions. This study explores the various practical applications of biocomposites in the construction industry as available in existing literature. Biocomposites, though promising, still have their limitations; standardisation, durability, and strength concerns have widely limited their acceptance for their practical usage in the construction industry. This paper also seeks to examine the challenges limiting their use in the building industry.
2 Bio-Based Polymer Composites
An FRP composite comprises a matrix material and a reinforcement material. The matrix defines the shape of the material and guards against chemical and mechanical damage, while the fibres provide the strength and stiffness of the composite [12, 18]. Biocomposites can be a blend of organic and inorganic components [16], i.e. natural fibres with a synthetic polymer, synthetic fibres with a bio-based polymer, a hybrid of natural and synthetic polymers, or a pure biocomposite with all organic components. Natural fibres can be sourced from plant sources like leaves (sisal, pineapple, banana), bast (jute, flax, hemp, kenaf, ramie), seed/fruit (cotton, coir), stalk (rice, wheat), cane (bamboo), wood, animal (wool, silk), and mineral sources (basalt, asbestos) [19]. For the polymer matrix, thermosets or thermoplastics like polyester, vinyl ester, and epoxy, polypropylene, low-density polyethene, high-density polyethene, and nylon serve as the matrix. Typical thermosets and thermoplastics are not biodegradable, so the ideal polymers for the sustainable development of FRP products would be biodegradable bio-based polymers, also known as bioplastics or biopolymers. Bioplastics are crop-derived renewable resources, such as cellulose plastics, polylactides, starch plastic, soy-based plastic, and polyhydroxyalkanoate polymers [20].
3 Biocomposites in the Building Industry
Biocomposites can be used for non-structural (non-load-bearing) and structural (load-bearing) applications in the building industry. These applications are presented in Fig. 1 and will be examined in this section.
Fig. 1
Classification of biocomposites for building
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3.1 Non-Structural Applications
Building Insulation Material
Energy consumption in the building industry is responsible for 40% of global CO2 emissions [21], and this can be reduced with building thermal insulation. The commonly used materials for thermal insulation in buildings are fibreglass, mineral wool, polymers, aerogels, etc. [22]. More eco-friendly materials like primarily sourced plant fibres or agricultural wastes, can be used to develop more sustainable building thermal insulators [23]. These fibres have lower density and heat retardant properties, which make them suitable insulators [24]. Several authors have developed biocomposites for specific use as thermal insulation materials. Madival et al. [22] developed rice straw/furcraea foetida boards with an epoxy matrix for thermal insulation. They evaluated the fabricated composite’s thermal stability, conductivity, transmittance, resistance, specific heat capacity, and flammability properties. The authors were able to create a composite that was thermally stable up to 272 °C. Le and Pásztory [24] developed boards with rice straw and reed/phenol formaldehyde, coir fibre/phenol formaldehyde, and a binder-less coir fibre panel that can be used as thermal insulating material. Though the thermal resistance of the developed material was evaluated and found to be suitable, no comparisons were made with existing commercial thermal insulation boards. Bhuiyan et al. [21] fabricated jute/polypropylene biocomposite boards and established that the porous morphology and low thermal conductivity of cellulose fibres make them good heat insulators. The developed biocomposite’s water absorption and mechanical properties were then compared to those of a commercial gypsum/polyvinyl chloride plasterboard and found to be superior. The biocomposite had superior thermal resistance to the commercial board, but the commercial board had higher thermal stability at higher temperatures. Low thermal conductive fillers in the biocomposites were proposed to improve the heat barrier performance.
Acoustic insulation is also an essential aspect of the service life of a building. Insulating materials are sometimes developed to have both thermal and acoustic insulation properties. Vasconcelos et al. [25] developed green high-density polyethylene composites with natural powdered cork to have thermal and acoustic insulation properties. It was found that the acoustic absorption coefficient was dependent on the reinforcement ratio within the composite. Urdanpilleta et al. [26] used the wool fibres of the Latxa sheep breed combined with a soy protein isolate matrix to develop a sound-insulating biocomposite material. It was found that the fibrillary microstructure in natural fibres and the presence of empty cells ensure high porosity and absorption properties, making them have good sound absorption coefficients at medium and high frequencies. Alencar et al. [27] proposed using expanded natural rubber as the polymer matrix reinforced with a wood filler (eucalyptus) in developing biocomposites with acoustic insulation. The developed material had three times the acoustic insulation capacity of polyurethane foam, a commercially available acoustic absorbent.
The use of waste in developing biocomposites is also a significant circular economy consideration. Polyethylene (PE) and polypropylene (PP) are projected to account for over 60% of global plastic production by 2050 and are projected to account for 20% of global petroleum consumption by 2050 [28]. The construction industry is responsible for 19% of the world’s consumption of plastics and is the second largest stack globally [25]. Waste plastics can also be repurposed to reduce the environmental pollution associated with their disposal [28].
Sandwich Composite Panels
A sandwich composite is a type of material typically consisting of two outer stiff layers called the face sheets bonded to an inner core material sandwiched between them [6]. The face sheets are usually made of strong and stiff materials, while the core material is often considerably thicker and lighter and can use foam [17], honeycomb [29], or wood design. This design provides high strength and stiffness while keeping the structure’s overall weight relatively low. The facing typically provides the bending resistance, while the core provides shear resistance and insulation [30, 31]. This type of material has applications in the aerospace, marine, and automotive industries, and in the building industry, it has found its place. Chomachayi et al. developed a sandwich structure from polyhydroxyalkanoate, polylactic acid, and cellulose microfibres to act as a building envelope vapour retarder, reducing mould growth and providing proper building insulation. The developed composite had a water vapour permeance value within the limits set in the national building code of Canada. Fu and Sadeghian [30] developed sandwich composite beams with flax/bio-based epoxy facing and a paper honeycomb core that could be used as building and cladding systems.
Sandwich panels can also be made to be prefabricated building modules that can be assembled off-site to ensure fast assembly and construction. Laraba et al. [32] developed a sandwich panel with an alfa fibre/epoxy core and jute/metallic mesh sheets to be potentially used as building partitions or roof panels. Conventional fabrication techniques such as manual lay-up, vacuum moulding and resin transfer moulding were used. Recently, 3D printing technology has also been used to fabricate sandwich composites with more intricate geometry [29]. Dweib et al. [17] developed a structural sandwich panel for potential residential building applications such as roof, wall, or floor material. The authors made sandwich beams with different face sheets made of flax fibre, chicken feathers, and cellulose from recycled paper with a soybean oil-based resin as the matrix. The sandwich beams were designed to have vertical webs and a structural polyurethane foam core that provided both acoustic and thermal insulation. The manufactured samples, except those made of flax fibre, had comparable strength and flexural rigidity to the available lumber sections. Their further work in [33] saw the successful development of the recycled paper composite into a prototype roof structure.
Façade and Partitions
Biocomposites can be developed for their specific use as vertical wall panels. Ks et al. [34] developed a sandwich composite with a flax/epoxy sheet and coir/polyurethane foam core as an alternative to conventional building partitions. The light weight of biocomposites and their insulation properties make them suitable alternatives. Astudillo et al. [35] set out to develop four different biocomposite products: an interior partition system with 40% bio-content, a multi-layered wall system with 70% bio-content, and a curtain wall with 30% bio-content. The products were designed according to the European Building Code and tested for structural performance, fire performance, air quality, thermal insulation, and durability. The developed biocomposites also underwent a monitoring phase where full-scale prototypes were found to have comparable performance to commercially available alternatives. A green vertical system is an innovative solution to introduce green areas directly in urban cities by having vertical gardens either supported by the façade or incorporated directly into the façade [36]. This green wall has been shown to improve air quality and the thermal and acoustic performance of a building. Cork agglomerate boards produced from waste from cork oak agglomerated with natural resins are one such nature-based solution in the building system [37].
Given their natural source, biocomposites have been shown to have less environmental impact when used as partition and façade systems. Morganti et al. [16] examined the global warming potential of three prefabricated façade system modules made with bio-based resin reinforced with basalt fibres and wooden particles. The biocomposite modules, through the product lifecycle from cradle to practical completion, reduced associated CO2 emissions across all the categories considered compared to a conventional alternative.
3.2 Structural Applications
External Reinforcement
Among the different structural retrofitting techniques, using FRP sheets, which are typically bonded to concrete members, is one of the least disruptive. In recent years, natural fibre composites have been developed to be a more sustainable alternative to the popularly used carbon and glass fibre FRP sheets used as external reinforcement to retrofit structural members. A holistic review of their use was done in [38], which saw the strengthening of beams, columns, walls, and slabs across concrete, masonry, and wooden structural elements. Structural elements were strengthened with biocomposites made with different natural fibres, including bamboo [39], hemp [40], kenaf [41], pineapple leaf [42], sisal [43], flax and jute [44], and so on. Bio-based polymers have also been used in this regard to develop completely green biocomposites [40, 45], or to make partial biocomposites when in conjunction with synthetic fibres [46]. In instances where the biocomposite was designed and the thickness increased to compensate for the lower strengths of natural fibres as compared to their synthetic counterparts, the RC beam strengthened with the biocomposite had a comparable load-carrying capacity with those strengthened with carbon FRP [41, 44].
The advantage of biocomposites as an external reinforcing material lies in their eco-friendliness, cost, and lower strength. Since they are developed from bio-based materials, the composite could be biodegradable. Composites could also be cheaper since they are produced from locally available materials. The high strength and stiffness of synthetic FRPs have resulted in more abrupt debonding failures [19], but natural FRPs have lower strengths that are more compatible with concrete.
Internal Reinforcement
Due to durability considerations, FRP rods have been developed as a non-corrosive alternative to conventional steel rebars. Its advantage lies in its non-reactive nature, which makes properties unchanged in aggressive environments where steel rebars would corrode [47]. Attai et al. fabricated 12 mm diameter glass FRP and jute FRP reinforcement bars with the hand lay-up technique. Though the glass FRP had much superior performance, the developed jute FRP rebars had tensile strength and elastic modulus up to 178.42 MPa and 12.15 GPa, respectively. Though these strength values are lower than the steel alternative, they can be used in low-loading structural applications. It was also established that the fibre volume fraction greatly influences the strength of the developed composite rebars. Sharkawi et al. [48] used an infusion technique to make reinforcement bars with jute and flax yarn fibres. Though the bars had modest strength, they still enhanced the strength of a normal-weight concrete slab and that of a lightweight concrete slab by 175% and 56%, respectively. Elbehiry et al. [49] made banana fibre/polyester as reinforcement bars in a concrete beam. Though the natural FRP rebars had a much lower strengthening effect than conventional steel bars, they enhanced the beam’s flexural strength by up to 25% more than the plain concrete beam. The natural FRP bar can be a low-cost alternative in low-strength applications. Joyklad et al. [50] used sisal fibre rope embedded in epoxy as post-installed shear reinforcement in flat concrete slabs. The natural sisal fibre performed better than the carbon and aramid FRPs, although it had the lowest strength.
4 Challenges and Future Directions
There are associated challenges with adopting biocomposites in the building industry, some of which are discussed in this section.
1.
Natural fibre viability: The mechanical properties of natural fibres are not consistent and predictable; they depend on the age of the plant, plant species, plant origin, and the soil and weather conditions in which the plant was cultivated [51]. This viability can affect the consistent and predictable material performance of biocomposites.
2.
Processing technique: Various techniques, such as wet lay-up, compression moulding, resin transfer moulding, and vacuum infusion, have been used to make biocomposites. Sophisticated apparatus is hardly needed to make samples for laboratory testing and prototyping. However, in developing larger sizes and amounts, some of the techniques used become labour-intensive, and the quality of the manufactured composite becomes challenging to ensure as there could be inconsistencies within the produced samples [18]. The specific process used to manufacture biocomposites affects the quality of the composite produced. As long as the manufacturing process remains unstandardised and has no specific methodology, the quality of biocomposites with natural fibres will remain uncertain [52].
3.
Water absorption: Polymers are hydrophobic, while lignocellulosic natural fibres absorb moisture. The increase in fibre content in biocomposites directly increases the moisture absorption capabilities of natural fibre composites. When biocomposites absorb moisture, they swell and return to their original state after drying; this causes the fibres to lose their bond with the matrix material [53] and consequently reduces the mechanical performance of the developed biocomposite.
4.
Thermal performance: When there is a fire outbreak in a building, elements within should be able to maintain their intensity for particular durations. Natural fibres are organic materials that degrade at high temperatures. The initial degradation of natural fibres, which results in the breakdown of hemicellulose, occurs between 220 °C and 280 °C, while a second and much faster degradation, involving the breakdown of lignin, occurs between 280 °C and 300 °C [54]. If biocomposites are to be used as a building material, their fire performance must be ensured.
5.
Degradation behaviour: Degradation behaviour: The biodegradability of biocomposites is essential in advocating for their adoption. Natural fibres are often paired with resins that are not eco-friendly or degradable.
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The methodology for material development, from the initiation of an idea to product testing in a laboratory to final integration into a building as a usable product, was outlined in [35]. A semi-industrial-scale sample prototype development should be done after material development and laboratory testing. A life cycle cost analysis and monitoring should then follow the prototype development. As researchers continue to develop biocomposites for use in the building industry, more prototype development should be done, and the abovementioned issues should be addressed further. Standardisation is encouraged within the industry to create more consistent composites. The durability of biocomposites given actual service life loads should be considered, and pure biocomposites with bio-based polymers should be developed.
5 Conclusion
Biocomposites have great potential for creating a more sustainable built environment. Natural fibres sourced directly from plants or indirectly from waste materials and bio-based polymers hold potential as raw materials in creating more eco-friendly building materials that can reduce the buildings industry’s associated CO2 emissions, reduce the non-biodegradable waste that ends up in landfills, reduce the dependence on virgin materials, and reduce building costs by utilising locally available materials while empowering local communities. Researchers have made substantial efforts to develop biocomposites that can be used within the building industry for structural and non-structural applications. The weight, strength, and insulation properties of specific biocomposite modules in the form of panels, sandwich composites, partitions, or building facades make them suitable building materials. This review also saw the development of natural fibre reinforcement rebars for concrete and bio-based structural retrofitting materials. Though the potential for the increased adoption of biocomposites within the building industry exists, associated stakeholders, from researchers to manufacturers should address making the industry more standardised and making more durable biocomposites.
Acknowledgements
This research is funded by the Intra-Africa Mobility Scheme of the European Union in partnership with the African Union under the Africa Sustainable Infrastructure Mobility (ASIM) scheme (624204-PANAF-1-2020-1-ZA-PANAF-MOBAF). Opinions and conclusions are those of the authors and are not necessarily attributable to ASIM. The work is supported and part of collaborative research at the Centre of Applied Research and Innovation in the Built Environment (CARINBE).
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