Comprehensive Bibliometric Review on the Sustainability and Environmental Impact of Fiber-Reinforced Polymers

Abstract

Fiber-reinforced polymers (FRPs) are increasingly recognized in sustainable materials research due to their potential environmental advantages. This study presents a focused bibliometric review of the sustainability research on FRPs. An initial search of the Web of Science (WOS) database identified 803 documents, which were refined to 749 relevant articles, reviews, and proceedings. A co-authorship analysis highlights the significant contributions of the USA and India, with European countries forming regional collaborations. The research output has steadily increased since 2011, peaking in 2022 and 2023. The multidisciplinary nature of the research spans materials science, engineering, and environmental sciences, with journals such as *Polymers*, *Sustainability*, and the *Journal of Cleaner Production* emphasizing sustainability themes. This analysis covers key aspects such as keyword co-occurrence, overlay visualizations, co-authorship networks, and the distribution of publications by year, research area, and journal. The findings underscore the evolving research landscape of sustainable FRPs and highlight the ongoing need for life cycle assessments and interdisciplinary collaboration.

1. Introduction

Escalating environmental concerns and a push toward sustainability have driven significant research and innovation in the field of materials science. Among various advanced materials, fiber-reinforced polymers (FRPs) have garnered considerable attention due to their remarkable mechanical properties and versatility [1,2,3,4,5,6,7]. Traditionally, FRPs have been reinforced with synthetic fibers such as glass or carbon, which, while effective, pose substantial environmental challenges, including non-biodegradability and high energy consumption during production [8,9,10,11,12,13,14,15,16]. Sustainable FRPs, particularly those reinforced with natural fibers, offer a promising alternative to conventional materials due to their environmentally friendly characteristics and superior mechanical properties [17,18].

The utilization of fiber-reinforced polymer (FRP) composites in the construction of new structures and the rehabilitation of existing ones has surged significantly in recent decades [19,20]. FRP composites offer several advantages, including lightweight properties, non-corrosiveness, and high specific strength and stiffness [20]. They are also relatively easy to construct and can be customized to meet specific performance requirements [21]. Typically, FRP composites for structural applications are composed of a polymer matrix—such as epoxy, vinylester, or polyester—reinforced with various grades of carbon, glass, and/or aramid fibers [1,22,23]. These materials collectively contribute to their widespread adoption and versatile application in modern engineering projects.

The advantages of fiber-reinforced polymer (FRP) composites are rooted in their exceptional physical properties and their potential to create structural systems with extended service lives compared to traditional materials. The lightweight nature of FRP composites can significantly reduce construction costs and shorten construction times, thereby lowering environmental impacts [19]. Moreover, their high strength and stiffness enable the use of less material to achieve performance levels equivalent to or better than those of conventional materials, which in turn minimizes resource consumption and waste production [24,25]. The true promise of FRP composites lies in their potential to drastically extend the service life of existing structures and facilitate the development of new structures with superior resistance to aging, weathering, and degradation in harsh environments [11,20,26,27]. These benefits underscore the critical role of FRP composites in fostering the development of more durable and sustainable built environments [28]. By leveraging the unique properties of FRPs, it is possible to achieve enhanced durability and performance, ultimately contributing to the creation of resilient and long-lasting infrastructure [21]. By factoring in these benefits, the use of FRP composites can be assessed more comprehensively within the framework of sustainable construction practices [25].

Fiber-reinforced polymer (FRP) composites, while offering numerous advantages in terms of light weight, high strength, and durability, present challenges in terms of recyclability [29]. The sustainability of FRP composites is not only about their performance and lifespan but also about their end-of-life disposal and potential for recycling [30,31,32,33,34].

Traditionally, the recycling of FRP composites has been limited due to the difficulty in separating the fibers from the polymer matrix. Most FRPs are thermosetting plastics, which cannot be remelted and reshaped like thermoplastics, making their recycling process more complex and less economically viable [35]. As a result, end-of-life FRP composites often end up in landfills, posing environmental concerns.

However, advancements in recycling technologies and processes are gradually improving the recyclability of FRP composites. Mechanical recycling methods, such as grinding and milling, can be used to process FRP waste into reusable filler materials, though this often leads to a reduction in material properties [31]. More innovative approaches, like pyrolysis and solvolysis, are being developed to recover fibers from the polymer matrix with minimal degradation of their properties [36]. These methods involve breaking down the polymer matrix through chemical reactions or thermal treatments, allowing the recovery of high-quality fibers that can be reused in new composite materials.

Furthermore, the development of bio-based and biodegradable polymers for FRP composites offers a promising direction for enhancing their sustainability [37,38]. These materials can be designed to degrade under specific environmental conditions, reducing the long-term environmental impact. Additionally, efforts are being made to improve the design for disassembly, making it easier to separate and recycle the components of FRP composites at the end of their service life [39].

Despite these advancements, there is still a significant need for research and development to make FRP recycling more practical and cost-effective. The integration of sustainable practices throughout the lifecycle of FRP composites—from material selection and manufacturing to end-of-life disposal—will be essential in maximizing their environmental benefits and minimizing their impact.

Bibliometric mapping and analysis serve as powerful tools for understanding the evolution, trends, and key players in this rapidly growing field. By examining a vast array of scientific publications, patents, and citations, bibliometric methods can identify influential research articles, prolific authors, leading institutions, and emerging areas of interest. This information is crucial for researchers, policymakers, and industry stakeholders to navigate the landscape of sustainable FRPs effectively.

Bibliometric analysis has been applied in various studies to explore the research trends and developments in FRPs and related fields. For instance, Ferreira et al. [40] conducted a bibliometric analysis of research on natural fiber composites, revealing increasing publications in this field. Leading countries include China (16), USA (14), and Brazil (11). Key terms such as ‘natural fiber’ (61 occurrences), ‘mechanical properties’ (44 occurrences), and ‘composites’ (31 occurrences) dominate the research. Similarly, Baarimah et al. [41] performed a bibliometric analysis of existing literature on kenaf-fiber-reinforced concrete (KFRC) over the past decade, from 2013 to September 2022. The analysis reveals emerging themes such as “Hybrid Composites”, “Impact Strength”, “Water Absorption”, “Scanning Electron Microscopy”, “Polypropylenes”, and “Polymer Composite”, highlighting areas of growing academic interest and potential future research opportunities. Keyword frequency analysis identified three major research domains associated with kenaf fibers in concrete: “Mechanical Properties”, “Fiber Reinforced Plastics”, and “Tensile Strength”.

Related to carbon-reinforced plastics (CRP), the bibliometric analysis [42] revealed that key journals such as Mechanics of Composite Materials and the Journal of Materials Processing Technology serve as prominent platforms for disseminating research within this domain. Notably, Applied Mechanics Reviews emerges as the leading journal in terms of average citation, indicating its widespread influence in the academic community. Geographically, China, Japan, Portugal, and the United Kingdom stand out as the most active countries in CRP research. Leading institutions such as the University of Tokyo (Japan), the Russian Academy of Sciences (Russia), and the Ministry of Education (China) have played pivotal roles in advancing research efforts in this field.

The systematic literature review [43] was conducted on the development of manufacturing, enhancement, and sustainability of fiber-reinforced polymer composites from 1998 to 2020. Utilizing the Web of Science (WOS) database, relevant articles were gathered based on specific keywords related to the aforementioned themes. A total of 151 articles were selected and subjected to citation network analysis to identify key clusters and trends. The analysis revealed seven principal clusters, with emphasis on topics such as fabrication methods, properties of multiscale composites, impact response, natural fibers, rapid curing, nanofillers, and hydrothermal aging.

This study aims to conduct a simplified bibliometric analysis of sustainable FRPs, with a focus on those reinforced with natural fibers. By analyzing articles published from 2000 to 2024 in the Web of Science (WOS) database, this study seeks to uncover significant trends and clusters in the research, thereby providing valuable insights for future research and development efforts.

2. Methodology

A bibliometric study is an essential tool for obtaining a comprehensive overview of various knowledge domains. By employing its two main approaches—performance analysis and mapping—it can thoroughly examine scientific output. Performance analysis involves a quantitative evaluation of publications, assessing data like authors, affiliations, and keywords. Conversely, mapping concentrates on the interconnections within these data, structuring them into networks to reveal relationships and trends within the scientific community [44]. Among the data from publications, an in-depth analysis of keywords is particularly important when the goal is to verify the current scenario and its evolution, providing a comprehensive overview of the field.

A WOS search was conducted on May 2024, using the keywords (sustainability) AND (FRP OR Fiber Reinforced Polymers). From WOS, the bibliographic data were exported into .csv and .txt files that were used for bibliometric mapping and analysis with the VOSviewer version 1.6.20 software program. The methodology flowchart is presented in Figure 1.

The initial Web of Science (WOS) search yielded 803 documents from 2000 up to the search date, as seen

Table 1. Types of identified documents.

Document Type	Record Count
Article	528
Review article	136
Proceedings paper	85
Early access	36
Book chapters	14
Retracted publication	2
Book review	1
Data paper	1

. To refine the analysis, two inclusion criteria were applied: (1) type of document, selecting articles, reviews, and proceedings papers, and (2) language, focusing on documents written in English. After applying these criteria, the total number of documents was reduced to 749, comprising 528 articles, 136 reviews and 85 proceedings papers, as depicted in Figure 1.

To ensure a more comprehensive coverage, the Scopus database was also used for analysis. Using the same words for searching, 1098 sources were found in the Scopus database.

3. Results and Discussion

3.1. VOSViewer Analysis

3.1.1. Keywords Analysis

The visualization from Figure 2 shows various key terms and their relationships within the context of research on the sustainability of fiber-reinforced polymers (FRPs). The VOSviewer software utilized a clustering algorithm to group keywords with strong co-occurrence links, displaying them in various colors to denote thematic clusters. The layout was automatically generated by VOSviewer, which spatially arranges nodes based on the strength of their connections. The proximity and links between nodes indicate how closely related certain concepts are within the dataset. It is observed that the keyword ‘Sustainability’ is positioned centrally in the network, indicating it is a core focus in the research on fiber-reinforced polymers. Many other terms are connected to it, suggesting its integral role in this field. Four clusters were identified:

✓

Red Cluster: Polymer Composites and Related Topics. Polymer composites are essential in the study of sustainable materials. This term is closely linked to other terms such as ‘natural fiber’ and ‘life cycle assessment’, indicating that these aspects are often studied together. The term ‘life cycle assessment’ reflects the importance of evaluating the environmental impact of polymer composites from production to disposal.

✓

Green Cluster: Mechanical Properties and Composites. The term ‘mechanical properties’ is significant, showing that the mechanical performance of sustainable FRPs is a major area of research.

✓

Blue Cluster: Concrete and Durability show that the durability of sustainable materials, especially when used in construction (e.g., concrete), is essential. The term ‘concrete’ is linked with sustainability and durability, indicating research interest in sustainable concrete composites.

✓

Yellow Cluster: Recycling and Circular Economy. ‘Recycling’ is a key aspect of sustainability, emphasizing the importance of reusing materials to reduce waste. The term ‘circular economy’ indicates a focus on sustainable practices that promote the reuse and recycling of materials, aligning with broader environmental goals.

The interconnections between terms such as ‘natural fibers’, ‘biocomposites’, ‘composite’, and ‘sustainability’ highlight a multidisciplinary approach. Researchers are exploring how natural and bio-based materials can enhance the sustainability of polymer composites. Terms like ‘recycling’ and ‘circular economy’ connected to ‘sustainability’ indicate a significant interest in the lifecycle management and environmental impact of these materials. The presence of terms like ‘frp’ (fiber-reinforced polymers) and their connections to ‘concrete’ and ‘durability’ suggest that sustainable FRPs are considered for enhancing the durability and sustainability of construction materials.

Table 2. Keyword occurrences and total link strength.

Keyword	Occurrences	Percentage Contribution (%)	Total Link Strength
Sustainability	195	34.27	125
Recycling	44	7.73	62
Mechanical properties	84	14.76	47
Natural fibers	38	6.68	36
Circular economy	22	3.87	34
Composites	37	6.50	30
Polymer composites	19	3.34	20
Biocomposites	25	4.39	19
Natural fiber	35	6.15	18
Durability	22	3.87	17
FRP	16	2.81	12
Concrete	16	2.81	11
Life cycle assessment	16	2.81	9

provides detailed quantitative data for each keyword presented in Figure 2, showcasing both the occurrences and total link strength of these terms, to illustrate the significance and interconnectedness of specific themes in the study. Also, the percentage contribution of each keyword to the overall discussion was calculated, based on the total number of occurrences (sum of all keyword occurrences = 569), showing not just how often a theme is mentioned but also how integral it is to the overall study.

‘Sustainability’ is the most frequently occurring keyword, with 195 occurrences and the highest total link strength of 125. This indicates a strong emphasis on sustainability within the context of fiber-reinforced polymers (FRPs). ‘Recycling’ is another prominent keyword, with 44 occurrences and a total link strength of 62, suggesting a significant focus on recycling processes and their relationship to sustainability in the research. ‘Mechanical properties’ (84 occurrences, 47 total link strength) and ‘natural fibers’ (38 occurrences, 36 total link strength) are also frequently discussed topics, indicating their importance in the study and application of FRPs. The relatively low frequency and link strength indicate that ‘life cycle assessment’ is not a primary focus in the current body of research on fiber-reinforced polymers (FRPs). This suggests that fewer studies have examined the environmental impacts of FRPs throughout their entire lifecycle, from raw material extraction through production, use, and disposal. The underrepresentation of ‘life cycle assessment’ in the current literature on FRPs presents a significant opportunity for future research to explore this area. By addressing this gap, researchers can contribute to the development of more sustainable FRP materials and practices, ultimately enhancing the overall sustainability of this field.

Table 3 categorizes research into distinct clusters based on their primary focus, each identified by specific keywords. For each cluster, significant papers are highlighted, along with their respective purposes and findings.

Table 3. Cluster analysis.

Cluster	Keyword	Significant Paper	Article Type	Purpose	Findings
Red	sustainability	[12]	Review	➢ Explores environmental benefits and challenges associated with FRP composite products. It emphasizes the advantages of FRPs such as light weight, superior mechanical properties, extended service life, low maintenance, and corrosion resistance. ➢ Addresses sustainability concerns related to material comparison, production processes, waste generation during manufacturing, and end-of-life disposal. ➢ Focuses on current recycling and remanufacturing techniques for FRP composites and outlines future prospects for sustainable applications in both academic research and industrial settings.	➢ FRP composites offer environmental advantages but face challenges in comparing sustainability metrics and managing waste. ➢ Recycling and remanufacturing efforts aim to reduce raw material costs and environmental impact. ➢ There is ongoing research to improve sustainability through advanced recycling technologies and lifecycle assessments.
	Natural fibers	[45]	Review	➢ Assesses suitability and applications of natural fiber-reinforced polymer composites (NFPCs), focusing on their eco-friendly characteristics and sustainability. ➢ Provides insights into various surface treatments used on natural fibers and their impact on NFPC properties.	➢ NFPC properties vary based on fiber type, source, and structure. ➢ Chemical treatments significantly enhance mechanical and thermal properties by improving fiber–matrix adhesion. ➢ NFPCs exhibit drawbacks like water absorption, inferior fire resistance, and lower mechanical strength. ➢ Chemical treatments affect water absorption, tribology, viscoelastic behavior, flame retardancy, and biodegradability of NFPCs. ➢ Applications include automotive and construction industries due to improved properties post-treatment.
		[46]	Review	➢ Explores the development and utilization of natural fiber-reinforced polymer composites (NFPCs) as eco-friendly alternatives to synthetic materials. ➢ Highlights their potential to improve environmental quality by reducing pollution and waste in product manufacturing, particularly in construction applications. ➢ Discusses fabrication techniques and characterizes NFPCs through various analytical methods.	➢ NFPCs offer a sustainable solution by replacing synthetic materials, thereby reducing environmental impact and controlling pollution. ➢ These composites are cost-effective due to the abundance of natural fibers and require lower production energy consumption compared to synthetic counterparts. ➢ NFPCs demonstrate superior mechanical properties, such as strength and durability, compared to traditional materials. ➢ Using NFPCs in construction can enhance sustainability by minimizing waste and improving material efficiency.
		[47]	Review	➢ Focuses on the development and utilization of natural fiber-based composites as eco-friendly alternatives to synthetic materials. ➢ Highlights the increasing demand for these composites across various industrial sectors due to their sustainability, low-cost, lightweight nature, renewability, biodegradability, and high specific properties. ➢ Covers different sources of natural fibers, their properties, methods of fiber modification, the effects of treatments on fiber properties, and explores major applications of natural fibers as reinforcements in polymer composite materials.	➢ Natural fiber-based composites offer sustainability advantages over synthetic materials, contributing to reduced environmental impact and improved ecological balance. ➢ Natural fibers are easily accessible, possess properties like low-cost production, lightweight characteristics, renewability, biodegradability, and high specific properties. ➢ These composites find extensive applications across various manufacturing sectors due to their enhanced mechanical properties and compatibility with polymer matrices. ➢ Chemical treatments enhance fiber–matrix adhesion, improving mechanical properties and overcoming inherent disadvantages such as poor moisture resistance and compatibility issues.
	Polymer composites	[48]	Review	➢ Reviews the utilization of FRP composites in engineering infrastructures, particularly focusing on their role in addressing challenges related to the restoration of existing and deteriorating structures. ➢ Examines the growing interest in both synthetic and natural FRP composites due to their mechanical strength, durability, eco-friendliness, lightweight nature, lifecycle superiority, biodegradability, and cost-effectiveness. ➢ Conducts a comprehensive assessment of the mechanical properties, fire resistance, durability, and sustainability of synthetic and natural FRP composites in civil infrastructure applications.	➢ FRP composites, including both synthetic and natural variants, offer significant benefits in civil infrastructure by improving structural integrity, fire resistance, durability, and sustainability. ➢ Natural FRP shows promise due to its eco-friendly properties but faces limitations in application due to performance uncertainties. ➢ Hybrid FRP composites represent a revolutionary advancement, combining the strengths of synthetic and natural fibers to enhance overall performance in infrastructure applications. ➢ Sustainability is a key driver, with hybrid FRP emerging as a preferred option for improving structural performance while meeting environmental goals.
	Life cycle assessment (LCA)	[49]	Book section	➢ Explores the application of LCA in developing polymer composites, emphasizing its role in promoting sustainable production. ➢ Compares green composites made from natural fibers and bio-derived matrices favorably to traditional composites. ➢ Discusses the emerging impact of nanotechnology in enhancing composite performance.	➢ Green composites show superior environmental benefits over traditional materials. ➢ LCA guides cleaner production processes, efficient energy use, and effective waste management. ➢ Challenges include data uncertainty in composite databases and regional variations affecting LCA outcomes.
Green	Mechanical properties	[50]	Review	➢ Explores the mechanical properties of fiber-reinforced polymer (FRP) composites and their significance in various engineering applications. ➢ Focuses on understanding how these properties influence material selection, design, and performance in sectors like aerospace, automotive, and construction.	➢ FRP composites exhibit directional stiffness and strength variations, known as anisotropic properties, crucial for engineering applications. ➢ They are extensively used in structural components due to their high tensile, compressive, and shear strengths, tailored to specific load conditions. ➢ CFRP offers high tensile strength and weight reduction benefits, while GFRP excels in applications requiring corrosion resistance and durability. ➢ FRP’s performance in various environmental conditions, such as humidity, seawater, and temperature, influences material durability and service life.
		[51]	Review	➢ Investigates the environmental impact of FRP by using FRP composites in structural elements instead of traditional materials.	➢ Carbon, glass, basalt and aramid are reinforcing fibers that are combined with a matrix to produce FRP composite systems, with FRP composites gaining a great reputation. ➢ Although the improvement of the rigidity and capacity of the structural elements can be achieved by replacing conventional steel reinforcing bars with FRP bars as partial reinforcement, in order to provide ductility to the structure and inhibit corrosion problems, a hybrid system is preferred. ➢ During the production stage, FRP materials cause higher carbon emissions compared to conventional materials, but during the maintenance, construction or disposal phases, the high carbon emissions are compensated for by the low weight of FRP decks.
	Composites	[8]	Review	➢ Examines the transformative impact of composite materials in modern engineering, focusing on their classification, manufacturing processes, and widespread applications across industries like automotive, aerospace, and construction.	➢ Composites reduce costs, improve efficiency, and offer environmental benefits like carbon sequestration and energy efficiency. ➢ They are increasingly used in demanding industries due to their light weight, strength, and design flexibility. ➢ Current research focuses on enhancing natural fiber composites and exploring new manufacturing techniques for sustainability and performance improvements.
	Natural Fibers	[52]	Review	➢ Investigates the mechanical behavior of natural fiber composites. ➢ Highlights their appeal as alternative reinforcements in engineering. ➢ Focuses on fibers like abaca, jute, and sisal, renowned for properties such as high specific strength, low weight, cost-effectiveness, eco-friendliness, and biodegradability.	➢ Abaca, jute, and sisal exhibit varied mechanical and physical properties suitable for different engineering applications. ➢ Natural fibers offer high specific strength and are non-abrasive, making them valuable in engineering. ➢ Abaca excels in overall mechanical properties, jute in flexural strength, and sisal in hardness. ➢ These fibers contribute to sustainable practices due to their eco-friendly and biodegradable nature.
	Biocomposites	[53]	Review	➢ Examines the growing interest in biocomposites, focusing on their development from natural resources and their potential applications across various industries. ➢ Highlights the synthesis of biodegradable polymers, natural fibers, manufacturing techniques, and surface modification methods aimed at improving mechanical properties.	➢ Biodegradable polymers derived from natural resources offer sustainable alternatives with enhanced mechanical properties. ➢ Techniques to enhance fiber–matrix adhesion significantly improve biocomposite strength and durability. ➢ Biocomposites show promise in automotive and construction industries due to their eco-friendly nature and diverse application potential.
		[54]	Review	➢ Studies the construction of biocomposites, their applications and life cycle assessment (LCA), highlighting the benefits of biocomposites in cost reduction and environmental protection.	➢ The use of natural fibers as reinforcement in concrete is the most well-known application of natural fibers. There is great interest in the study regarding the surface treatment method, the optimal fiber content as well as the fiber length. ➢ Research directions on natural FRPs are in the sense of their long-term durability. ➢ Compared to materials on the market, biocomposite insulations offer thermal performance and comfort. ➢ Due to their natural origin, biocomposite materials promise to be an economical and environmentally friendly construction.
Blue	Durability	[55]	Review	➢ Reviews findings on the durability and performance of fiber-reinforced polymer (FRP) composites, emphasizing their response to moisture and humidity. ➢ Highlights significant impacts on mechanical properties, including strength and interlayer shear strength, and discusses the influence on FRP/steel joint performance. ➢ Underscores the need for predictive models to estimate long-term mechanical behavior.	➢ Moisture effects: Moisture and humidity cause notable reductions in the strength and interlayer shear strength of FRP composites. ➢ Durability challenges: Factors like moisture absorption, chemical reactions, and microstructural changes contribute to the deterioration of FRP composite properties over time. ➢ FRP/steel joints: Moisture initially strengthens FRP/steel joints but can lead to long-term strength degradation.
	Concrete	[56]	Review	➢ Systematically reviews 158 research articles published between 2000 and 2021 on natural fiber-reinforced concrete (NFRC), highlighting its role in enhancing mechanical properties and addressing sustainability challenges in construction materials.	➢ A notable increase in research activity since 2015 reflects heightened interest in NFRC. ➢ Identified prominent natural fibers (e.g., basalt, sisal), their combinations, and synergistic effects with synthetic fibers like polypropylene. ➢ NFRC improves tensile, flexural, compressive strength, impact resistance, and thermal properties. ➢ Network analysis reveals influential journals, prolific authors, and prevalent keywords, offering a comprehensive view of the field’s development.
Yelow	Recycling	[29]	Review	➢ Reviews various waste disposal methods for FRP materials, including minimization, repurposing, reuse, recycling, incineration, co-processing in cement plants, and landfilling. It critically examines the strengths, limitations, and energy demands of these methods for both glass (GFRP) and carbon fiber (CFRP)-reinforced polymers.	➢ Landfilling and co-incineration are the most common and cheapest disposal methods. ➢ Mechanical recycling is suitable for GFRP and used industrially; thermal and chemical recycling are more suited for CFRP due to higher reclaimed fiber value despite higher costs and energy demands. ➢ Chemical recycling is the most energy-intensive and costly. ➢ Sustainable FRP waste disposal is crucial, with recycling, reusing, and repurposing becoming more important due to strict environmental regulations.
		[57]	Review	➢ Investigates the mechanical recycling of carbon fiber-reinforced polymer composites (CFRPCs) and highlights their significance for sustainable material management.	➢ Mechanical recycling is noted for its low energy consumption and minimal environmental impact. ➢ Reviews existing mechanical recycling techniques, emphasizing energy efficiency and material recovery. Identifies challenges such as fiber damage leading to degraded mechanical properties and difficulties in achieving strong interfacial adhesion in recycled composites. ➢ Introduces the use of FEA to predict the behavior of recycled CFRPCs, demonstrating potential for maintaining structural integrity and performance. ➢ Emphasizes the necessity for more research to develop standardized recycling protocols that enhance material properties and optimize processes.
		[58]	Research	➢ Explores the additive re-manufacturing of end-of-life glass fiber composites, aiming to achieve mechanical performances comparable to virgin glass fiber-reinforced materials. The paper investigates the potential of using recycled composites in additive manufacturing to enhance circular economy models, especially in the wind energy sector.	➢ Additive manufacturing using recycled glass fiber-reinforced polymers is emerging, though the mechanical properties of recycled materials are still not on par with pristine materials. ➢ Systematic characterization of recycled materials identified filler requirements for the liquid deposition modeling process. Printability and material surface quality were analyzed using a low-cost modified 3D printer. ➢ Two hypothetical design concepts were manufactured to validate practical applications. ➢ Tensile tests showed that mechanically recycled glass fibers could potentially substitute pristine fillers, demonstrating comparable mechanical behavior to virgin materials.
		[59]	Review	➢ Reviews the recycling of carbon fiber-reinforced composite (CFRC) and glass fiber-reinforced composite (GFRC) using pyrolysis, highlighting technical challenges, re-use possibilities in high-performance composites, and commercialization prospects.	➢ CFRC and GFRC are widely used but pose challenges in end-of-life (EoL) waste management. ➢ Pyrolysis shows promise for recovering valuable materials and producing fuel and chemicals from composite waste. ➢ Technical challenges include optimizing energy efficiency and maintaining acceptable mechanical properties. ➢ Discusses challenges and market potential for pyrolysis-recycled composites. ➢ Highlights the role of recycling in promoting a circular economy and cradle-to-cradle approach.
	Circular economy	[60]	Review	➢ Addresses the urgent need for recycling glass fiber-reinforced polymer (GFRP) and carbon fiber-reinforced polymer (CFRP) composites. ➢ Provides an overview of the latest knowledge on recycling techniques for these composites. ➢ Highlights the limitations of recycled fibers in high-value applications due to the depreciation of mechanical properties. ➢ Discusses the present challenges and modern trends in fiber-reinforced composite recycling.	➢ The review summarizes various recycling methods for GFRP and CFRP composites, noting the progress and limitations of each technique. ➢ It is observed that recycled fibers suffer a significant reduction in mechanical properties, which restricts their applications. ➢ Despite the mechanical depreciation, the review identifies potential high-value applications for composites made from recycled fibers. ➢ Current challenges in recycling processes and the emerging trends in technology are discussed, indicating areas where further innovation is needed.
		[61]	Review	➢ Focuses on the sustainability, waste reduction, and cost savings of using recycled milled fibers in aerospace applications. ➢ Discusses the industrialization and potential uses of recycled fiber-reinforced plastics (FRP), cutting-edge recycling and re-manufacturing processes, and the mechanical properties of milled fiber composites for sustainable applications.	➢ Emphasizes the importance of transforming composites to reduce waste and promote sustainability, supporting a circular economy. ➢ Highlights the need for innovative recycling methods to maintain high performance and environmental friendliness in FRPs. ➢ Reviews the mechanical properties of milled fiber composites, noting their relegation to low-value applications due to performance impacts. ➢ Discusses the necessity for rigorous testing and qualification to ensure confidence in these materials, addressing the lack of centralized knowledge and providing an overview of R&D efforts, as well as financial and logistical considerations.
		[62]	Review	➢ Addresses the urgent need for a circular economy strategy in fiber-reinforced polymer (FRP) recycling by evaluating current recycling technologies and assessing the potential of microwave-assisted heating as an energy-efficient, selective, and fast processing method.	➢ Overview of estimated FRP production and waste generation per sector over the next decades. ➢ Analysis of existing FRP recycling methods, including their strengths, weaknesses, readiness levels, and environmental impacts, specifically in terms of CO2 emissions. ➢ Evaluation of emerging microwave-assisted FRP recycling technology, highlighting its potential benefits and challenges. ➢ Review of current and future international legislation on managing end-of-life FRP. ➢ Summary of existing prototypes, microwave-assisted waste-to-value processes, and their reported energy demands.
		[63]	Research (conference paper)	➢ Explores innovative solutions for re-using end-of-life fiber-reinforced polymer (FRP) structures, particularly wind turbine blades and glass fiber-reinforced polymer (GFRP) pipes, as structural elements in new bicycle and pedestrian bridges. ➢ Contributes to a sustainable and cost-effective use of GFRP waste.	➢ Highlights the potential to re-use decommissioned FRP structures for new applications in the building and infrastructure sectors due to their lightweight, strong, stiff, and durable properties. ➢ Develops and discusses a concept design for a decking system made of GFRP pipes for pedestrian bridges. ➢ Considers main design requirements for pedestrian bridges and addresses assumptions about the quality and mechanical properties of end-of-life GFRP. ➢ Emphasizes the economically profitable potential of recovering and reusing/re-manufacturing end-of-life GFRP composites.

Table 3. Cluster analysis.

Cluster	Keyword	Significant Paper	Article Type	Purpose	Findings
Red	sustainability	[12]	Review	➢ Explores environmental benefits and challenges associated with FRP composite products. It emphasizes the advantages of FRPs such as light weight, superior mechanical properties, extended service life, low maintenance, and corrosion resistance. ➢ Addresses sustainability concerns related to material comparison, production processes, waste generation during manufacturing, and end-of-life disposal. ➢ Focuses on current recycling and remanufacturing techniques for FRP composites and outlines future prospects for sustainable applications in both academic research and industrial settings.	➢ FRP composites offer environmental advantages but face challenges in comparing sustainability metrics and managing waste. ➢ Recycling and remanufacturing efforts aim to reduce raw material costs and environmental impact. ➢ There is ongoing research to improve sustainability through advanced recycling technologies and lifecycle assessments.
	Natural fibers	[45]	Review	➢ Assesses suitability and applications of natural fiber-reinforced polymer composites (NFPCs), focusing on their eco-friendly characteristics and sustainability. ➢ Provides insights into various surface treatments used on natural fibers and their impact on NFPC properties.	➢ NFPC properties vary based on fiber type, source, and structure. ➢ Chemical treatments significantly enhance mechanical and thermal properties by improving fiber–matrix adhesion. ➢ NFPCs exhibit drawbacks like water absorption, inferior fire resistance, and lower mechanical strength. ➢ Chemical treatments affect water absorption, tribology, viscoelastic behavior, flame retardancy, and biodegradability of NFPCs. ➢ Applications include automotive and construction industries due to improved properties post-treatment.
		[46]	Review	➢ Explores the development and utilization of natural fiber-reinforced polymer composites (NFPCs) as eco-friendly alternatives to synthetic materials. ➢ Highlights their potential to improve environmental quality by reducing pollution and waste in product manufacturing, particularly in construction applications. ➢ Discusses fabrication techniques and characterizes NFPCs through various analytical methods.	➢ NFPCs offer a sustainable solution by replacing synthetic materials, thereby reducing environmental impact and controlling pollution. ➢ These composites are cost-effective due to the abundance of natural fibers and require lower production energy consumption compared to synthetic counterparts. ➢ NFPCs demonstrate superior mechanical properties, such as strength and durability, compared to traditional materials. ➢ Using NFPCs in construction can enhance sustainability by minimizing waste and improving material efficiency.
		[47]	Review	➢ Focuses on the development and utilization of natural fiber-based composites as eco-friendly alternatives to synthetic materials. ➢ Highlights the increasing demand for these composites across various industrial sectors due to their sustainability, low-cost, lightweight nature, renewability, biodegradability, and high specific properties. ➢ Covers different sources of natural fibers, their properties, methods of fiber modification, the effects of treatments on fiber properties, and explores major applications of natural fibers as reinforcements in polymer composite materials.	➢ Natural fiber-based composites offer sustainability advantages over synthetic materials, contributing to reduced environmental impact and improved ecological balance. ➢ Natural fibers are easily accessible, possess properties like low-cost production, lightweight characteristics, renewability, biodegradability, and high specific properties. ➢ These composites find extensive applications across various manufacturing sectors due to their enhanced mechanical properties and compatibility with polymer matrices. ➢ Chemical treatments enhance fiber–matrix adhesion, improving mechanical properties and overcoming inherent disadvantages such as poor moisture resistance and compatibility issues.
	Polymer composites	[48]	Review	➢ Reviews the utilization of FRP composites in engineering infrastructures, particularly focusing on their role in addressing challenges related to the restoration of existing and deteriorating structures. ➢ Examines the growing interest in both synthetic and natural FRP composites due to their mechanical strength, durability, eco-friendliness, lightweight nature, lifecycle superiority, biodegradability, and cost-effectiveness. ➢ Conducts a comprehensive assessment of the mechanical properties, fire resistance, durability, and sustainability of synthetic and natural FRP composites in civil infrastructure applications.	➢ FRP composites, including both synthetic and natural variants, offer significant benefits in civil infrastructure by improving structural integrity, fire resistance, durability, and sustainability. ➢ Natural FRP shows promise due to its eco-friendly properties but faces limitations in application due to performance uncertainties. ➢ Hybrid FRP composites represent a revolutionary advancement, combining the strengths of synthetic and natural fibers to enhance overall performance in infrastructure applications. ➢ Sustainability is a key driver, with hybrid FRP emerging as a preferred option for improving structural performance while meeting environmental goals.
	Life cycle assessment (LCA)	[49]	Book section	➢ Explores the application of LCA in developing polymer composites, emphasizing its role in promoting sustainable production. ➢ Compares green composites made from natural fibers and bio-derived matrices favorably to traditional composites. ➢ Discusses the emerging impact of nanotechnology in enhancing composite performance.	➢ Green composites show superior environmental benefits over traditional materials. ➢ LCA guides cleaner production processes, efficient energy use, and effective waste management. ➢ Challenges include data uncertainty in composite databases and regional variations affecting LCA outcomes.
Green	Mechanical properties	[50]	Review	➢ Explores the mechanical properties of fiber-reinforced polymer (FRP) composites and their significance in various engineering applications. ➢ Focuses on understanding how these properties influence material selection, design, and performance in sectors like aerospace, automotive, and construction.	➢ FRP composites exhibit directional stiffness and strength variations, known as anisotropic properties, crucial for engineering applications. ➢ They are extensively used in structural components due to their high tensile, compressive, and shear strengths, tailored to specific load conditions. ➢ CFRP offers high tensile strength and weight reduction benefits, while GFRP excels in applications requiring corrosion resistance and durability. ➢ FRP’s performance in various environmental conditions, such as humidity, seawater, and temperature, influences material durability and service life.
		[51]	Review	➢ Investigates the environmental impact of FRP by using FRP composites in structural elements instead of traditional materials.	➢ Carbon, glass, basalt and aramid are reinforcing fibers that are combined with a matrix to produce FRP composite systems, with FRP composites gaining a great reputation. ➢ Although the improvement of the rigidity and capacity of the structural elements can be achieved by replacing conventional steel reinforcing bars with FRP bars as partial reinforcement, in order to provide ductility to the structure and inhibit corrosion problems, a hybrid system is preferred. ➢ During the production stage, FRP materials cause higher carbon emissions compared to conventional materials, but during the maintenance, construction or disposal phases, the high carbon emissions are compensated for by the low weight of FRP decks.
	Composites	[8]	Review	➢ Examines the transformative impact of composite materials in modern engineering, focusing on their classification, manufacturing processes, and widespread applications across industries like automotive, aerospace, and construction.	➢ Composites reduce costs, improve efficiency, and offer environmental benefits like carbon sequestration and energy efficiency. ➢ They are increasingly used in demanding industries due to their light weight, strength, and design flexibility. ➢ Current research focuses on enhancing natural fiber composites and exploring new manufacturing techniques for sustainability and performance improvements.
	Natural Fibers	[52]	Review	➢ Investigates the mechanical behavior of natural fiber composites. ➢ Highlights their appeal as alternative reinforcements in engineering. ➢ Focuses on fibers like abaca, jute, and sisal, renowned for properties such as high specific strength, low weight, cost-effectiveness, eco-friendliness, and biodegradability.	➢ Abaca, jute, and sisal exhibit varied mechanical and physical properties suitable for different engineering applications. ➢ Natural fibers offer high specific strength and are non-abrasive, making them valuable in engineering. ➢ Abaca excels in overall mechanical properties, jute in flexural strength, and sisal in hardness. ➢ These fibers contribute to sustainable practices due to their eco-friendly and biodegradable nature.
	Biocomposites	[53]	Review	➢ Examines the growing interest in biocomposites, focusing on their development from natural resources and their potential applications across various industries. ➢ Highlights the synthesis of biodegradable polymers, natural fibers, manufacturing techniques, and surface modification methods aimed at improving mechanical properties.	➢ Biodegradable polymers derived from natural resources offer sustainable alternatives with enhanced mechanical properties. ➢ Techniques to enhance fiber–matrix adhesion significantly improve biocomposite strength and durability. ➢ Biocomposites show promise in automotive and construction industries due to their eco-friendly nature and diverse application potential.
		[54]	Review	➢ Studies the construction of biocomposites, their applications and life cycle assessment (LCA), highlighting the benefits of biocomposites in cost reduction and environmental protection.	➢ The use of natural fibers as reinforcement in concrete is the most well-known application of natural fibers. There is great interest in the study regarding the surface treatment method, the optimal fiber content as well as the fiber length. ➢ Research directions on natural FRPs are in the sense of their long-term durability. ➢ Compared to materials on the market, biocomposite insulations offer thermal performance and comfort. ➢ Due to their natural origin, biocomposite materials promise to be an economical and environmentally friendly construction.
Blue	Durability	[55]	Review	➢ Reviews findings on the durability and performance of fiber-reinforced polymer (FRP) composites, emphasizing their response to moisture and humidity. ➢ Highlights significant impacts on mechanical properties, including strength and interlayer shear strength, and discusses the influence on FRP/steel joint performance. ➢ Underscores the need for predictive models to estimate long-term mechanical behavior.	➢ Moisture effects: Moisture and humidity cause notable reductions in the strength and interlayer shear strength of FRP composites. ➢ Durability challenges: Factors like moisture absorption, chemical reactions, and microstructural changes contribute to the deterioration of FRP composite properties over time. ➢ FRP/steel joints: Moisture initially strengthens FRP/steel joints but can lead to long-term strength degradation.
	Concrete	[56]	Review	➢ Systematically reviews 158 research articles published between 2000 and 2021 on natural fiber-reinforced concrete (NFRC), highlighting its role in enhancing mechanical properties and addressing sustainability challenges in construction materials.	➢ A notable increase in research activity since 2015 reflects heightened interest in NFRC. ➢ Identified prominent natural fibers (e.g., basalt, sisal), their combinations, and synergistic effects with synthetic fibers like polypropylene. ➢ NFRC improves tensile, flexural, compressive strength, impact resistance, and thermal properties. ➢ Network analysis reveals influential journals, prolific authors, and prevalent keywords, offering a comprehensive view of the field’s development.
Yelow	Recycling	[29]	Review	➢ Reviews various waste disposal methods for FRP materials, including minimization, repurposing, reuse, recycling, incineration, co-processing in cement plants, and landfilling. It critically examines the strengths, limitations, and energy demands of these methods for both glass (GFRP) and carbon fiber (CFRP)-reinforced polymers.	➢ Landfilling and co-incineration are the most common and cheapest disposal methods. ➢ Mechanical recycling is suitable for GFRP and used industrially; thermal and chemical recycling are more suited for CFRP due to higher reclaimed fiber value despite higher costs and energy demands. ➢ Chemical recycling is the most energy-intensive and costly. ➢ Sustainable FRP waste disposal is crucial, with recycling, reusing, and repurposing becoming more important due to strict environmental regulations.
		[57]	Review	➢ Investigates the mechanical recycling of carbon fiber-reinforced polymer composites (CFRPCs) and highlights their significance for sustainable material management.	➢ Mechanical recycling is noted for its low energy consumption and minimal environmental impact. ➢ Reviews existing mechanical recycling techniques, emphasizing energy efficiency and material recovery. Identifies challenges such as fiber damage leading to degraded mechanical properties and difficulties in achieving strong interfacial adhesion in recycled composites. ➢ Introduces the use of FEA to predict the behavior of recycled CFRPCs, demonstrating potential for maintaining structural integrity and performance. ➢ Emphasizes the necessity for more research to develop standardized recycling protocols that enhance material properties and optimize processes.
		[58]	Research	➢ Explores the additive re-manufacturing of end-of-life glass fiber composites, aiming to achieve mechanical performances comparable to virgin glass fiber-reinforced materials. The paper investigates the potential of using recycled composites in additive manufacturing to enhance circular economy models, especially in the wind energy sector.	➢ Additive manufacturing using recycled glass fiber-reinforced polymers is emerging, though the mechanical properties of recycled materials are still not on par with pristine materials. ➢ Systematic characterization of recycled materials identified filler requirements for the liquid deposition modeling process. Printability and material surface quality were analyzed using a low-cost modified 3D printer. ➢ Two hypothetical design concepts were manufactured to validate practical applications. ➢ Tensile tests showed that mechanically recycled glass fibers could potentially substitute pristine fillers, demonstrating comparable mechanical behavior to virgin materials.
		[59]	Review	➢ Reviews the recycling of carbon fiber-reinforced composite (CFRC) and glass fiber-reinforced composite (GFRC) using pyrolysis, highlighting technical challenges, re-use possibilities in high-performance composites, and commercialization prospects.	➢ CFRC and GFRC are widely used but pose challenges in end-of-life (EoL) waste management. ➢ Pyrolysis shows promise for recovering valuable materials and producing fuel and chemicals from composite waste. ➢ Technical challenges include optimizing energy efficiency and maintaining acceptable mechanical properties. ➢ Discusses challenges and market potential for pyrolysis-recycled composites. ➢ Highlights the role of recycling in promoting a circular economy and cradle-to-cradle approach.
	Circular economy	[60]	Review	➢ Addresses the urgent need for recycling glass fiber-reinforced polymer (GFRP) and carbon fiber-reinforced polymer (CFRP) composites. ➢ Provides an overview of the latest knowledge on recycling techniques for these composites. ➢ Highlights the limitations of recycled fibers in high-value applications due to the depreciation of mechanical properties. ➢ Discusses the present challenges and modern trends in fiber-reinforced composite recycling.	➢ The review summarizes various recycling methods for GFRP and CFRP composites, noting the progress and limitations of each technique. ➢ It is observed that recycled fibers suffer a significant reduction in mechanical properties, which restricts their applications. ➢ Despite the mechanical depreciation, the review identifies potential high-value applications for composites made from recycled fibers. ➢ Current challenges in recycling processes and the emerging trends in technology are discussed, indicating areas where further innovation is needed.
		[61]	Review	➢ Focuses on the sustainability, waste reduction, and cost savings of using recycled milled fibers in aerospace applications. ➢ Discusses the industrialization and potential uses of recycled fiber-reinforced plastics (FRP), cutting-edge recycling and re-manufacturing processes, and the mechanical properties of milled fiber composites for sustainable applications.	➢ Emphasizes the importance of transforming composites to reduce waste and promote sustainability, supporting a circular economy. ➢ Highlights the need for innovative recycling methods to maintain high performance and environmental friendliness in FRPs. ➢ Reviews the mechanical properties of milled fiber composites, noting their relegation to low-value applications due to performance impacts. ➢ Discusses the necessity for rigorous testing and qualification to ensure confidence in these materials, addressing the lack of centralized knowledge and providing an overview of R&D efforts, as well as financial and logistical considerations.
		[62]	Review	➢ Addresses the urgent need for a circular economy strategy in fiber-reinforced polymer (FRP) recycling by evaluating current recycling technologies and assessing the potential of microwave-assisted heating as an energy-efficient, selective, and fast processing method.	➢ Overview of estimated FRP production and waste generation per sector over the next decades. ➢ Analysis of existing FRP recycling methods, including their strengths, weaknesses, readiness levels, and environmental impacts, specifically in terms of CO2 emissions. ➢ Evaluation of emerging microwave-assisted FRP recycling technology, highlighting its potential benefits and challenges. ➢ Review of current and future international legislation on managing end-of-life FRP. ➢ Summary of existing prototypes, microwave-assisted waste-to-value processes, and their reported energy demands.
		[63]	Research (conference paper)	➢ Explores innovative solutions for re-using end-of-life fiber-reinforced polymer (FRP) structures, particularly wind turbine blades and glass fiber-reinforced polymer (GFRP) pipes, as structural elements in new bicycle and pedestrian bridges. ➢ Contributes to a sustainable and cost-effective use of GFRP waste.	➢ Highlights the potential to re-use decommissioned FRP structures for new applications in the building and infrastructure sectors due to their lightweight, strong, stiff, and durable properties. ➢ Develops and discusses a concept design for a decking system made of GFRP pipes for pedestrian bridges. ➢ Considers main design requirements for pedestrian bridges and addresses assumptions about the quality and mechanical properties of end-of-life GFRP. ➢ Emphasizes the economically profitable potential of recovering and reusing/re-manufacturing end-of-life GFRP composites.

Based on Table 3, the analysis of relevant papers for different FRP composite clusters highlights key insights into their sustainability, mechanical properties, applications, and challenges. Sustainability is a central theme, with FRP composites offering benefits like light weight, durability, and corrosion resistance, but challenges such as production waste and disposal issues remain. Recycling and remanufacturing efforts are essential to reducing environmental impact, with ongoing research into advanced recycling technologies. On the other hand, NFPCs are emerging as sustainable alternatives, enhanced by chemical treatments that improve mechanical and thermal properties. These materials are cost-effective and energy-efficient, making them suitable for automotive and construction sectors. Hybrid composites, combining synthetic and natural fibers, also offer improved performance and environmental benefits.

Life cycle assessments of composites emphasize the advantages of green materials made from natural fibers, while mechanical properties, such as anisotropic stiffness, are critical for industries like aerospace and construction. Recycling methods for FRP, including mechanical and chemical approaches, are being refined, with emerging technologies like additive manufacturing showing promise, though challenges in fiber quality persist.

Biocomposites are gaining attention for their eco-friendly nature, with surface modifications enhancing their strength and durability. Durability concerns, particularly regarding moisture and humidity effects, remain a challenge for FRP composites, requiring predictive models for long-term performance.

Overall, these findings collectively illustrate the multifaceted research on composite materials, emphasizing their potential for sustainability, mechanical performance, and innovative recycling practices.

In order to ensure a comprehensive and validated understanding of sustainability research by capturing diverse trends and perspectives across databases, a cluster analysis was performed also for the Scopus database search. The co-occurrence network is presented in Figure 3.

The network visualization from VOSviewer shows clusters related to the central concept of “sustainability”, distinguished by different color groupings. One prominent cluster, represented in green, focuses on materials such as biocomposites and natural fibers. This group includes terms like “biocomposites”, “natural fibers”, “additive manufacturing”, and “mechanical properties”, highlighting research that emphasizes eco-friendly and natural materials, their mechanical properties, and their contribution to sustainability.

Another cluster, shown in yellow, centers around the concept of “life cycle assessment (LCA)” and includes related terms like “composite materials”.

A significant cluster in red covers aspects related to construction and reinforced materials, with terms such as “durability”, “reinforced concrete”, “GFRP”, “CFRP”, and “geopolymer”. This cluster points to sustainability considerations in the context of construction materials, particularly focusing on the strength and durability of reinforced composites.

The blue cluster emphasizes themes like “recycling”, “circular economy”, and “polymer composites”, representing sustainable approaches that incorporate recycling and the broader concept of a circular economy.

The common elements between the Scopus and WOS figures include central themes such as “sustainability”, “mechanical properties”, “natural fibers”, and “recycling”, indicating a shared focus on eco-friendly materials and sustainable practices. Both highlight connections to “biocomposites” and “composites”, suggesting widespread interest in sustainable material development.

The overlay visualization from VOSviewer is shown in Figure 4. This visualization maps key terms in the context of research on sustainable fiber-reinforced polymers over a period from 2015 to 2023.

The color spectrum represents the average publication year of documents linked to each keyword, ranging from blue to red. Blue indicates keywords associated with older publications, around 2016, green represents keywords linked to publications around 2018, while yellow/orange signifies keywords associated with more recent publications, up to 2022.

This analysis offers a comprehensive view of the changing landscape of FRP (fiber-reinforced polymer) research, particularly regarding sustainability and environmental concerns. It highlights a noticeable shift towards prioritizing sustainable practices, as evidenced by the keyword ‘sustainability’ transitioning to a yellow color, indicating increased attention in recent years. This reflects a growing commitment within the research community to address the environmental challenges associated with FRPs. Another significant trend is the emergence of bio-based materials, as seen in the attention given to ‘natural fibers’ and ‘biocomposites’. This trend signifies a broader movement towards utilizing renewable and biodegradable materials in FRP production, aligning with global sustainability objectives. However, the analysis also identifies a notable gap in the integration of life cycle assessment (LCA) within FRP research. While LCA is recognized as important, its underrepresentation in recent studies suggests an area for improvement. Incorporating LCA into future research endeavors is crucial for obtaining a comprehensive understanding of the environmental impacts of FRPs throughout their entire lifecycle. Moving forward, the recommendations for future research focus on addressing this gap by actively integrating LCA methodologies. Additionally, exploring circular economy principles within FRP research can lead to more sustainable production and recycling practices. Furthermore, continued investigation into sustainable material innovations, such as natural fibers and biocomposites, can drive further advancements in developing environmentally friendly FRPs.

3.1.2. Co-Authorship Analysis

The visualization from Figure 5 depicts the collaboration/co-authorship network among different countries in the context of research on the sustainability of fiber-reinforced polymers.

The central position of the USA and India indicates their pivotal roles in driving research and fostering international collaborations in the field of sustainable fiber-reinforced polymers. European countries (primarily Italy, Spain, Portugal, France, Poland) form a compact group, indicating regional collaborations. There is a notable link between ‘Australia’ and Middle Eastern countries (Egypt, Iran), suggesting targeted regional collaborations. South Africa’s position shows some degree of isolation but still maintains connections to the broader network.

3.2. Distribution of Articles

3.2.1. Distribution of Articles by Publication Year

Figure 6 illustrates the distribution of articles published each year from 2000 to 2024.

It can be observed that in early years (2000–2010), the research in this field began with minimal activity, with only one publication per year. The interest started to grow slowly, with a gradual increase in publications. By 2009, there were three publications, indicating the beginning of a more focused research effort. In the period 2011–2015, there was a significant increase in research output. The number of publications rose from 6 in 2011 to 25 in 2015. This phase marks the period when the research community began to recognize the importance and potential of sustainable fiber-reinforced polymers. The period 2019–2021 shows a sharp increase in the number of publications. The count grew from 28 in 2016 to 84 in 2021. The rapid expansion indicates that sustainable fiber-reinforced polymers became a major research focus, likely driven by increased awareness of environmental sustainability and advancements in material science. The highest number of publications were recorded in 2022 (137) and 2023 (144), indicating a peak in research activity. This suggests that the field has reached a high level of maturity and widespread interest among researchers.

3.2.2. Distribution of Articles by Geographical Location

Figure 7 presents the distribution of articles by geographical locations and indicates that India (146 publications) leads the research output in this field, indicating a strong focus on sustainable fiber-reinforced polymers. This aligns with its central position and extensive connections in network visualization. The USA is another major contributor, with significant research activity and collaboration. Its central position in the visualizations also reflects its importance.

Figure 8 illustrates the geographic distribution of articles by continent, highlighting the research output from different regions. This visualization provides insight into the global focus of the study, with Asia leading in article contributions, followed by Europe and North America.

3.2.3. Distribution of Articles by Research Area

The provided data in Figure 9 list the number of records (publications) across various research areas related to the sustainability of fiber-reinforced polymers, in order to help in understanding the multidisciplinary nature and the primary focus areas within this field. The publication data across research areas reveal the multidisciplinary and evolving nature of research on the sustainability of fiber-reinforced polymers. Materials science, engineering, and polymer science are the core areas driving this field, supported by significant contributions from construction building technology and environmental sciences and ecology. The data also highlight the broad and diverse applications, ranging from energy and fuels to agriculture and automation. This comprehensive view of research areas, combined with network and overlay visualizations, underscores the dynamic and interconnected research landscape dedicated to advancing sustainable fiber-reinforced polymers.

3.2.4. Distribution of Articles by Publication Title

Figure 10 presents the number of records (publications) across various journals related to the sustainability of fiber-reinforced polymers, for understanding the key publication venues and the focus areas within this research field.

The publication data across journals reveal the multidisciplinary nature and key focus areas within the research on sustainable fiber-reinforced polymers. ‘Polymers’ is the leading journal, reflecting the core focus on polymer science. ‘Sustainability’ and ‘Journal of cleaner production’ highlight the strong emphasis on sustainability. ‘Construction and building materials’ underscores the practical applications in construction. Specialized journals like ‘Composites part B engineering’ and ‘Engineering structures’ cover specific aspects of composites and structural applications. The diverse range of journals, from materials science to environmental sciences, showcases the wide-ranging interest and collaborative efforts in advancing sustainable fiber-reinforced polymers. This comprehensive view of publication venues, combined with network and overlay visualizations, provides a detailed understanding of the research landscape and key themes driving this field.

4. Conclusions

This comprehensive bibliometric analysis provides a nuanced understanding of the research landscape surrounding the sustainability of fiber-reinforced polymers (FRPs). By delving into co-occurrence patterns of keywords, overlay visualizations, co-authorship networks among countries, and distribution of articles across various dimensions, this study presents critical trends and areas of focus within the field.

The prominence of sustainability-related keywords highlights the increasing attention on environmental considerations within the field. However, the limited focus on LCA suggests a critical gap in the current research that warrants further investigation. LCA, as a tool for evaluating the environmental impact of FRPs, could provide a more comprehensive understanding of their sustainability throughout the product lifecycle.

The analysis of key papers, as shown in Table 3, reveals important insights into the sustainability, mechanical properties, applications, and challenges of various FRP composite clusters. Sustainability remains a prominent focus, with FRP composites offering advantages such as light weight, durability, and corrosion resistance. However, challenges persist, particularly in relation to production waste and disposal, underscoring the need for further advances in recycling and remanufacturing technologies. In contrast, NFPCs have emerged as promising sustainable alternatives. These composites, especially when enhanced with chemical treatments, demonstrate improved mechanical and thermal properties, making them cost-effective and energy-efficient choices for industries such as automotive and construction. Hybrid composites, which combine synthetic and natural fibers, also show considerable promise, offering a balance of enhanced performance and environmental benefits. Life cycle assessments of composite materials highlight the advantages of bio-based composites made from natural fibers. Recycling techniques, including both mechanical and chemical methods, are being refined to improve the sustainability of FRP composites, and emerging technologies such as additive manufacturing hold great potential for enhancing recycling processes. However, challenges remain in terms of fiber quality and performance when recycled fibers are used.

Furthermore, the co-authorship analysis highlights the significant roles of the USA and India in advancing research, alongside strong collaborative networks among European countries and focused regional partnerships, underscoring the global scope of FRP research. This interconnectedness fosters knowledge exchange and accelerates advancements in sustainable materials science.

The upward trajectory of research output over the years, coupled with the multidisciplinary nature of research areas, reflects a maturing field with diverse applications and growing recognition. This evolution underscores the collective commitment to addressing environmental challenges and advancing sustainable FRP solutions.

Also, the performed investigation highlights that future research on FRP sustainability should focus on more specific and interdisciplinary approaches. Collaboration between experts in materials science, environmental engineering, and economics is essential to address the challenges of FRP composites. Additionally, incorporating LCA in future studies will help better understand the environmental impacts of FRPs throughout their life, from production to disposal.