Green composite friction materials: A review of a new generation of eco-friendly brake materials for sustainability

Article information

Environmental Engineering Research. 2024;29(3)

Publication date (electronic) : 2023 October 31

doi : https://doi.org/10.4491/eer.2023.226

¹Laboratory of Electro-Mechanical System (LASEM), National School of Engineers of Sfax (ENIS), University of Sfax, Tunisia

²University of Sousse, Higher Institute of Transport and Logistics of Sousse, University of Sousse, Tunisia

^†Corresponding author, E-mail: riadh.elleuch@gnet.tn, Tel: +21622311511, Fax: +21674830299

Received 2023 April 17; Revised 2023 September 18; Accepted 2023 October 30.

Abstract

Particulate matter (PM) still poses a significant threat leading to air pollution which is responsible for continued damage to human health and the environment. Particulate matter resulting from non-exhaust emissions are considered as viable a source comes mostly from brake pad wear concept. The scientific challenge of this work is to stimulate a new generation of green friction materials to reduce particle emissions having low-environmental impact. The specificity of braking materials, their effects on the environment and human health are studied. To minimize the levels of air pollution, the use of green friction composites collected from natural elements reducing human diseases is discussed. For this purpose, the novel and high-performance friction composite materials synthesized from vegetable and animal waste used as a raw material are reported. The natural powder and fiber treatments, the optimum formulation and the binder materials related to the green friction composites are reviewed. An overview of environmentally ecofriendly green friction materials embedded by reinforcing phases of natural elements exhibiting excellent mechanical and tribological properties are mentioned. Therefore, scientific and industrial efforts should concentrate on the development of green friction materials to minimize the effect of transport related air pollution.

Abstract

Graphical Abstract

Keywords: Brake materials; Environment; Human health; Green friction composite

1. Introduction

Particle matters are generated from exhaust and non-exhaust emissions. Brake wear is thus considered as non-exhaust traffic related particles. Component wear - road transport- is defined as a direct source of airborne particles from exhaust emission. Particulate matters from brakes are defined as the airborne created by wear, abrasion, corrosion, and turbulence. It has been proven that large amounts of brake and tire wear particles are emitted as PM₁₀ [1]. Although the regulations are focused on the quantity emitted of these particles into our air, their composition is also a preoccupation. As regards the chemical composition of PM₁₀ from the brakes, it was reported the presence of high concentrations of heavy metals (Fe, Cu, Zn, Sn, Sb) although for the finer fractions PM_2.5 is characterized by concentrations of organic elements. Other metals such as Ni, Sn, Cd, Cr, Ti and Sb were also detected although in concentrations lower than 0.1 wt.% [2]. Other studies have shown that brake wear emissions show a potentially significant source of Sb in the environment from (Sb2S3) which is used as a lubricant to reduce noise emissions and provide friction stability [3]. Brake wear emissions have been proven that they can integrate physiological fluids and more serious that they contain carcinogenic substance [4].

Nowadays, environmental respect has drawn research focus to use alternative fibers in brake pad applications. In this trend, several researchers have focused their work on replacing asbestos and other carcinogenic materials in the production of green friction materials. The attractive performance / respect for the environment involved in the production of composite materials in the automotive sector from waste inspired the idea of investing in natural waste as reinforcement for the brake lining. The current direction in friction material’s research is the use of animal or agricultural waste as the raw material for high performance friction composites. Therefore, this article presents a comprehensive review of these studies.

2. Specificity of the Brake Materials

Friction materials are mainly composed of several elements about 10 and up to 30 ingredients with a great diversity in terms of chemical composition, morphology, size distribution, and manufacturing process including a succession of steps: mixing, preforming, hot molding and post curing. All these experimental parameters influence microstructure heterogeneity that must ensure several stringent tribological, squeal and thermal performances for friction materials. Constituents can be divided into four groups, namely fillers, friction modifiers, binder, and reinforcement additives [5, 6]. One of the peculiarities of constituents concerns their synergistic / antagonistic effects [7]. Indeed, the synergies between constituents and the complexity of various phenomena of multi-physical couplings operating at different scales have a marked effect on the micrometric scale regarding the wear mechanisms activated on the surface. Under certain conditions, several films of micrometric thickness were highlighted, and their studies prove that the thickness of the tribofilm is generally less than one micron [8]. These latter films were formed from nanoparticles originating from the fragmentation and mixture of disc and brake lining materials, and probably by chemical reactions between ingredients and oxygen coming from atmosphere with the formation of different kinds of oxides [9]. In fact, wear incites the detachment of particles of variable sizes that can reach under certain conditions, depending on the contact pressure and the sliding speed, a few micrometers to tens of nanometers and even down to a few nanometers [10]. The significant presence of fine-grained particles on the surface of the lining, most often around the plates described above can be trapped in the porosities of the material and remain at least temporarily in contact. They can recirculate and agglutinate on the leading edge of the plates. These particles can also be ejected from contact, thus becoming wearing particles thrown off from brakes. When the brake pads and disc wear, a huge amount of wear debris or particles are released into the atmosphere [11] which depend on the characteristics of friction materials (ingredient’s composition, size and shape) and friction layer (wear process) [12]. The particles emitted or even particulate pollution or PM, is a complex mixture of micro/nano particles [13]. Particulate matter is generally size classified according to their aerodynamic diameter i.e. PM₁₀ (ultrafine particles), PM_2.5 (fine particles) and PM_0.1 (coarse particles) for particulates with aerodynamic diameter smaller than, respectively, 10 μm, 2.5 μm and 0.1 μm [14]. Even though brake wear particles are emitted due to a mainly mechanical and tribological process and should be found mainly in the coarse fraction, many studies have shown high concentrations of fine and ultrafine particles as shown in Fig. 1 [15, 16].

Fig. 1

PM mass concentration in function of particles size distribution [16]

3. Environmental Health Effect of Braking Systems

Sanders estimate PM emission and airborne particles fraction as 50% of the total wear brake [17]. The study of the city of London concerning PM emissions show that non exhausted particulate matter size ranges from coarse, fine to extend ultrafine particles [18]. Specifically, brake wear particles are generated in a wide range of sizes, including PM₁₀, PM_2.5 and PM_0.1. Certainly, particle size determines are an important parameter for the human health consequences. In fact, Particles represent a great danger to human health. Indeed, for coarse particles, we are exposed to diseases in the respiratory system. In the less coarse case, we are faced with bronchial and lung diseases. On the other hand, fine particles can easily enter the lungs and can cause diseases related to vascular inflammation and possibly lung cancer. Furthermore, concerning PM_2.5, the sedimentation of these ultra-fine particles is very slow and when released to air, particles propagate through the atmosphere along kilometers [19]. These nanoparticles are even more dangerous for human health since they have a high capability to absorb organic molecules and can penetrate more deeply into lung [20] and reach the intimate structure of tissues and organs and thus induce cancer and serious pathologies. They can reach the deepest part of the lungs, such as alveoli, and enter the bloodstream [21, 22]. In fact, High concentration of airborne particles has adverse health effects including, respiratory, skin and cardiovascular diseases [23, 24] which can cause lung cancer in the worst case [25]. Other authors focused their studies on PM_2.5 effects on human health. Kim presents two types of effects: moderate health effects such as lacrimation, eye pain, impaired vision and hazardous effects such as pneumonia and diseases of the respiratory system [26, 27]. In addition, nanoparticles can also spread through the blood and move to other vital organs such as the liver and the kidneys [28]. In fact, several research studies the effect of the size of PM on human health as shown in Table 1.

Table 1

Effect of the size of PM on human health

4. Legislations

Nowadays, for environmental concerns, new legislations have forced brake pad industries to produce environmentally friendly materials for their products. Toxicologists classify particulate pollutants as ultrafine, fine and coarse, although regulators, namely World Health Organization (WHO) [35], the United States Environmental Protection Agency (USEPA) and the European Union (EU) describe polluting particulates as particulate matter (PM) classified based on the aerodynamic diameter of the particles. Each class has its own composition, properties, and very specific effects on the environment and human health [36]. Several researcher include brake wear in their Particulate Emission Models and both utilize a 13 mg/mile emission factor for PM₁₀ brake wear debris [37]. The World Health Organization (WHO) studies the effects of particulate matter on human health. It is estimated that PM harmful air quality that effects on human health. In fact, it consists of the most frequent causes of death for around 2 million people every year [38]. The World Health Organization has described the unhealthy effects of PM regardless of short-term and long-term exposure and includes breathing difficulties which in some cases cause asthma, heart disease, high blood pressure and lung cancer and can some cases have caused death [39]. In fact, the chemical composition of the particles is responsible for a number of potential harmful effects on human health. Although there is insufficient information regarding the effects of PM on human health. The World Health Organization agrees that the chemical composition of PM presents several carcinogenic elements classified according to the aerodynamic diameter of the particles. Indeed, PM_2.5 formed by carbon black and certain metals such as Fe, Cu, Ni are currently considered to be responsible for several diseases [40]. American Conference of Governmental Industrial Hygienists [41] assumed that refractory ceramic fibers may causes cancers to humans by the IARC [42] and can induce lung diseases. The WHO assessed the harmful effects of various particulate generated by brake pad wear, including carbon elements [38]. The National Institute for Occupational Safety and Health has recently presented research on mineral elements and asbestos fiber impacts on both human health and air quality [43]. Legislations are usually interested in the particulate brake wear emission since their harmful impact on human health. Therefore, the improvement of human consciousness about environmental concern has led to consider natural fibers as eco-friendly attractive reinforcement for green friction material.

5. Concept of Green Friction Materials

By dint of the wear mechanisms occurring in the Brake system, abrasive particles are released into the environment. Recently, studies proved that some of the commonly used essential ingredients for brake pad materials have started raising environmental concerns that endanger the wellbeing of humans and air quality [44]. In the context of reducing the PM coming from brake wear, many issues have been satisfactorily addressed for the friction material in order to find optimal formulation for ecological brake systems. Significant improvements must be considered such as the respect of different criterion in the selection of constituent of the friction material. These criteria must be aligned with the regulations on environmental and ecological risk. To meet these criteria different environment and healthy friendly alternative materials for brake pad must be considered [45]. Furthermore, numerous efforts were deployed by scientific researchers to address environmental issues and the need to protect human health using natural fibers in brake pad formulation.

5.1. Sustainable Design of Friction Composite Materials from Vegetable Waste

Most green materials are based on fibers derived from agricultural waste since their economic importance and significant environmental challenge. These agricultural fibers have shown their efficiencies for the manufacture of composite materials in the brake pads industries, and this through several properties, namely their low cost, their availability, their high resistance, their nature respectful of the environment and their durability [46]. This has led to a lot of research concerning their treatments for extracting fiber from natural resources profitably employed in environmental and health monitoring. Several plants have shown great potential in the exploitation of fibers as alternative raw materials for industrial uses (banana, corn, pineapple, hazelnut, coir, corn stalk, bamboo, etc.) [47]. Recently, plenty of research focused on the potential of vegetable waste reinforced brake material with restrictions coming from environment. Their scientific studies were focused on physical, mechanical and tribological properties of brake pad alternative materials, which could be very important because of their allied nature to the structure of fibers as shown in Table 2.

Table 2

Physical, mechanical and tribological properties of brake pad using alternative materials

5.2. Sustainable Design of Friction Materials from Animal Resource

Development of innovative friction materials via utilization of marine resources could be part of the solutions to reducing environmental pollution. In this context, many scientific researchers are still on the quest to find suitable green material from animal resource for brake materials to guarantee environmental respects. Bala uses in their contribution Cow hooves as reinforcing components in brake pad material. In this study, the cow hooves were washed and properly sun-dried. The cow hooves can also be dried in an electric vacuum oven for three hours at 250°C to remove contaminating oil, crushed using pestle and mortar then grounded into powder and finally sieved using mesh size of 710 μm. After several test, results show that composite with 15% pulverized cow hooves, 35% epoxy resin present good properties such as wear resistance, water and oil absorption and friction material with 10% cow hoof and 7% epoxy resin gave the better properties for hardness and friction coefficient [64]. Other studies were based on the use of cow dung as a natural ingredient for industrial application [65] as shown in Fig. 2. To be used as reinforcing material, cow dung was dried for 30 min in 1% NaOH solution and washed with distilled water then dried for 7 days in the air. Finally, it was screened with a sieve of 40–60 mesh size and dried again at 70°C. Tribological performance showed that 6 wt.% cow dung fibers are the optimum mass ratio providing best performing [66].

Fig. 2

Cow dung fiber a) Morphology b) SEM) image of a vertical cross section [65]

Eggshells are also used as reinforcement material to produce ecological friction material since they are composed of 95% calcium carbonate in the form of calcite [67]. Edokpia developed biodegradable material with eggshell and Arabic gum as binder. To remove its membrane, egg was washed, and sun dried then milled and finally sieved and retained on a 125 μm sieve. The investigated combination of eggshell and Arabic gum shows that 18 wt.% of Arabic gum exhibits good physical, thermal and wear properties [68]. Periwinkle shell is a marine waste product produced from the consumption of a greenish-blue marine periwinkle [69]. The ecofriendly utilization of periwinkle shell is considered as a challenge for scientific [70]. In the study, periwinkles shell was grounded and sieved into fine particles (Fig. 3). The composite composed of 35% phenolic resin and shell [71] with different sieve was characterized. The best results of compressive strength, hardness and density is obtained for periwinkle shell particles of 100 μm size compared with 125 μm size propounded by Yawas [72]. Inversely getter oil soak, water soak and wear rate are reached with 350 μm particle’s size by Elakhame compared with 710 μm confirmed by Yawas.

Fig. 3

Periwinkle shell [73]

Aquatic waste from the sea is a major threat to the coastal areas that lead to accumulation causing difficulties in living there. The crab shells, the major solid waste in coastal areas, can be treated properly and used as filler in brake friction composites since they are mainly constituted by calcium carbonate and chitin biopolymer (Fig. 4). The Crab shells were washed with distilled water, grounded then sieved in the range of 210–250 BSS (British Sieve Size). The sieved powder was soaked in a solution of CHCl₃ and CH3OH for 1h to remove the fat. Further, the crab shell powder was immersed in 5 wt.% of NaOH solution for twenty-four hours for deproteination. Then, the powder was treated in 4 wt.% of HCl solution for 1h for decarbonation, filtrated and finally dried at room temperature. Thus, the crab shell powder was successfully processed without any organic compounds, with the help of chemical reagents [74]. Singaravelu research proves that crab shell powder content (12 wt.%) composite showed good thermal stability, friction characteristics and wear resistance. In fact, the higher bonding characteristics of the crab shell with resin enhance the transferring of the heat to surrounding thereby reducing the frictional heat generated in the interface [75].

Fig. 4

Blue crab a) shell b) powder [75]

6. Challenge of Green Friction Materials

Natural fibers are made from a variety of renewable plant and animal resources. Considering their chemical composition rich in cellulose, which is hydrophilic in nature, inducing an affinity for water that limits its use as a reinforcement for friction materials [76]. Green composite swells when it absorbs the water, and after subsequent drying, the shrinking of the fiber occurs causing the separation of the fibers from the matrix decreasing the strength of friction materials [77]. Therefore, the natural fibers do not meet the reinforcement function decreases. Kabir also proves that these hydrophilic fibers are incompatible with some resins of hydrophobic nature [78]. Thus, it is fundamental to improve the interfacial adhesion between the resin and the fibers during water absorption. Several scientific researchers have exploited a powerful method for the application of green friction materials to improve the interfacial adhesion between the resin and the natural fibers. Silane treatment is widely used for friction composite. It consists of a silane surface treatment based on coupling agent (mostly trialkoxysilanes) as a bonding aid to form a bridge of chemical bonds between the natural fiber and the binder [79]. M. Asim proves that applying silane treatment for pineapple leaf fiber (PLF) and Kenaf Fiber (KF)/phenolic formaldehyde (PF) composites showed very good fiber/matrix bonding and lesser fiber peeling off. By dint of good interfacial bonding, it was speculated that the silane treatment of 50 wt.% fiber loading KF and PLF/phenolic composites enhance their mechanical properties [80]. The other treatment was applied to natural fiber, which is an alkaline treatment. This method consists of treatment with 5 wt.% NaOH in order to improve the fiber to matrix adhesion and thus enhance the compatibility of the natural fibers to the polymer matrix accompanied with removal of large amounts of lignin and hemicelluloses [81]. Rajan demonstrated that alkaline and silane treatment induces the removal of hemicellulose, lignin and impurities from the Prosopis Juliflora fiber (PJF). The Silane-treatment increases shear strength and fiber degradation temperature by 10°C to reach 346°C, which are an essential requirement for friction composite. Obviously, results reveal that composite based on silane treated prosopis juliflora fiber exhibit better properties than that based on alkaline treated fiber and raw composite [82]. Recently, alkaline and silane treated Prosopis Juliflora (PJ) bark fiber in the epoxy modified Phenolic composite was subjected to tribological characterization by Rajan [83]. Results have demonstrated that Silane treatment for composite based on Prosopis Juliflora fibers are most suitable for the brake pad materials where frictional heat can exceed 250°C. Rajan has also applied the silane fiber treatment to shell more specifically scallop shell and periwinkle shell powder. It was concluded that treated shell powder could be an alternative for brake pad materials especially for heavy vehicles [84]. Javeed studied the tribological effect of alkaline treatment of friction composite reinforcement with Alkaline Treated Areva Javanica Fiber. It was found that after an alkaline treatment, the impurities were removed so that the NaOH penetrated the surface, which made the surface rougher [85]. The alkaline-treated Areva Javanica fiber has an increase in cellulose content, the fiber is more fibrillated, the thermal stability is increased from 298°C to 310°C and the tribological performances of the green friction composite are higher and more stable [86].

Atiqah investigated the impact of alkaline treatment, silane treatment and alkaline-silane treatment on Sugar palm fiber. The results revealed that silane treated fiber exhibits the best interfacial stress strength and thus better mechanical properties. It has been shown also that fiber treatments, especially silane treatment help to develop high performance sugar palm fibers reinforced thermoplastic polyurethane matrix [87]. Several studies are concerning the choice of the adequate matrix used with natural fiber. In this trend, investigation was carried out with an epoxy-modified phenolic novolac binder that has been shown to be thermally more stable than straight phenolic novolac. S. Rajan confirms that 12 wt.% of phenolic resin modified by epoxy in the friction composite formulation offer better tribological properties [88]. Y. Liu confirms these results by proving that friction material based on modified phenolic resin acquire good thermal properties and good friction and wear performance than those using straight phenolic resin as binder [89]. Similarly, alkylbenzene-modified Phenolic presents good thermal properties than the straight Phenolic resin [90]. Another study shows that boron-modified Phenolic resin exhibits better mechanical properties than conventional one [91].

7. Conclusion

From these overviews, it is concluded that scientific efforts are geared towards using natural fiber as reinforcement for environmental and health related concerns. Currently, novel composite material formulations ensuring required performance of standard brake pads are studied for environmental concerns in order to reduce the particulate matter in the air. A comprehensive review of application of natural elements from vegetable and animal waste as possible reinforcement for green composite friction materials has been highlighted in this study. The physical, mechanical and tribological properties of these ecofriendly brake pads were compared favorably with standard brake pads. Physical and chemical treatments were applied to overcome the poor adhesion fiber/matrix, low thermal stability, and incompatibility of natural fibers with organic matrix. The agro and animal waste can be strongly used as a replacement for toxic ingredients in the formulation of brake pad materials when added with other elements to guarantee good combination of performances. It is expected that this purpose-built innovation in friction material will complement future formulations to reduce particulate emissions needed to meet environmental regulations.

Acknowledgments

The authors gratefully acknowledge the Tunisian Ministry of Higher Education and Scientific Research for their continuous support of research at the Laboratory of Electro-Mechanical Systems of Sfax.

Notes

Author Contributions

S.A. (Associate professor) wrote the article. E.R. (Professor) revised the article.

Conflict of Interest Statement

The authors declare that they have no conflict of interest.

References

1. Beddows D, Harrison R, Gonet T, Maher BA, Odling N. Measurement of road traffic brake and tyre dust emissions using both particle composition and size distribution data. Environ Pollut 2023;331:1–20. https://doi.org/10.1016/j.envpol.2023.121830 .

2. Kukutschová J, Moravec P, Tomášek V, et al. On airborne nano/micro-sized wear particles released from low-metallic automotive brakes. Environ. Pollut 2011;159:998–1006. https://doi.org/10.1016/j.envpol.2010.11.036 .

3. Uexküll O, Skerfving S, Doyle R, Braungart M. Antimony in brake pads: a carcinogenic component. J. Clean. Prod 2005;13:19–31. https://doi.org/10.1016/j.jclepro.2003.10.008 .

4. Varrica D, Bardelli F, Dongarrà G, Tamburo E. Speciation of Sb in airborne particulate matter, vehicle brake linings, and brake pad wear residues. Atmos. Environ 2013;64:18–24. https://doi.org/10.1016/j.atmosenv.2012.08.067 .

5. Grigoratos T, Martini G. Brake wear particle emissions: A review. Environ. Sci. Pollut. Res. Int 2015;22:2491–2504. https://doi.org/10.1007/s11356-014-3696-8 .

6. Kukutschová J, Moravec P, Tomášek V, et al. On airborne nano/micro-sized wear particles released from low-metallic automotive brakes. Environ. Pollut 2011;159:998–1006. https://doi.org/10.1016/j.envpol.2010.11.036 .

7. Chavez D, Jang H. Synergistic effects of the ingredients of brake friction materials on friction and wear: A case study on phenolic resin and potassium titanate. Wear 2019;15:222–232. https://doi.org/10.1016/j.wear.2019.05.011 .

8. Österle W, Dmitriev AI. Functionality of conventional brake friction materials, Preceptions from findings observed at different length scales. Wear 2011;271:2198–2207. https://doi.org/10.1016/j.wear.2010.11.035 .

9. Karlsson HL, Gustafsson J, Cronholm P, Möller L. Size-dependent toxicity of metal oxide particles – a comparison between nano- and S micrometer size. Toxicol. Lett 2009;188:112–118. https://doi.org/10.1016/j.toxlet.2009.03.014 .

10. Sellami A, Hentati N, Kchaou M, Asaduzzaman CM, Elleuch R. Effect of Size and Shape of Copper Alloys Particles on the Mechanical and Tribological behavior of Friction Materials. Mech. Ind 2020;21:613–616. https://doi.org/10.1051/meca/2020079 https://doi.org/10.1016/j.toxlet.2009.03.014 .

11. Hagino H, Oyama M, Sasaki S. Laboratory testing of airborne brake wear particle emissions using adynamometer system under urban city driving cycles. Atmos. Environ 2016;131:269–278. https://doi.org/10.1016/j.atmosenv.2016.02.014 .

12. Sellami A, Kchaou M, Elleuch R, Cristol AL, Desplanques Y. Study of the interaction between microstructure, mechanical and tribo-performance of a commercial brake lining material. Mater. Des 2014;59:84–93. https://doi.org/10.1016/j.matdes.2014.02.025 .

13. Ciudin R, Verma P, Gialanella C, Straffelini G. Wear debris materials from brake systems: environmental and health issues. WIT. Trans. Ecol. Enviro 2014;2:1423–1434. https://doi.org/10.2495/SC141202 .

14. Lee H. Generation characteristics of the airborne wear particles emitted from the wheel–rail contact for various train velocities and their generation relation with the train velocity. Atmos. Environ 2020;5:68. https://doi.org/10.1016/j.aeaoa.2020.100068 .

15. Kawamoto AM, Pardini LC, Diniz MF, Lourenço VL, Takahashi MFK. Synthesis of a boron modified phenolic resin. Aerosp Technol. Manag 2010;2:169–182. https://doi.org/10.5028/JATM.2010.02027610 .

16. Slezakova K, Morais S, Pereira M. Atmospheric Nanoparticles and Their Impacts on Public Health. Current Topics in Public Health 2013;:3–4.

17. Sanders PG, Xu N, Dalka TM, Maricq M. Airborne brake wear debris, size distributions, composition, and a comparison of dynamometer and vehicle tests. Environ. Sci. Technol 2003;37:4060–4069. https://doi.org/10.1021/es034145s .

18. Grag BD, Cadle SH, Mulawa PA, Groblicki P, Laroo C, Parr GA. Brake Wear Particulate Matter Emissions. Environ. Sci Technol 2000;34:4463–4469. https://doi.org/10.1021/es001108 .

19. Oberdörster G, Oberdörster E, Oberdörster J. Nanotoxicology: an emerging discipline evolving from studies of ultrafine particles. Environ. Health Perspect 2005;113:823–839. https://doi.org/10.1289/ehp.7339 .

20. Labiris NR, Dolovich MB. Pulmonary drug delivery. Part I: Physiological factors affecting therapeutic effectiveness of aerosolized medications. Br. J. Clin. Pharmacol 2000;56:588–599. https://doi.org/10.1046/j.1365-2125.2003.01892.x .

21. Oberdörster G. Pulmonary effects of inhaled ultrafine particles. Int. Arch. Occup. Environ. Health 2001;74:1–8. https://doi.org/10.1007/s004200000185 .

22. Brunekreef B, Holgate ST. Air pollution and health. Lancet 2002;360:1233–1242. https://doi.org/10.1016/S0140-6736(02)11274-8 .

23. Chen J, Hoek G. Long-term exposure to PM and all-cause and cause-specific mortality: A systematic review and meta-analysis. Environ. Int 2020;143:1–23. https://doi.org/10.1016/j.envint.2020.105974 .

24. Gasser M, Riediker M, Mueller L, et al. Toxic effects of brake wear particles on epithelial lung cells in vitro. Part. Fibre Toxicol 2009;6:30. https://doi.org/10.1186/1743-8977-6-30 .

25. Nel A, Xia T, Madler L, Li N. Toxic potential of materials at the nanolevel. Science 2006;311:622–627. https://doi.org/10.1126/science.1114397 .

26. Kim T, Kim H, Yi SM, Cheong JP, Heo J. Short-term Effects of Ambient PM2.5 and PM2.5–10 on Mortality in Major Cities of Korea. Aerosol. Air. Qual. Res 2018;18:1853–1862. https://doi.org/10.4209/aaqr.2017.11.0490 .

27. Dai L, Zanobetti A, Koutrakis , Pand P, Schwartz JD. Associations of fine particulate matter species with mortality in the United States: A multicity time series analysis. Environ. Health Perspect 2014;122:837–842. https://doi.org/10.1289/ehp.1307568 .

28. Helland A, Wick P, Koehler A, Schmid K, Som C. Reviewing the environmental and human health knowledge base of carbon nanotubes. Environ. Health. Perspect 2007;8:1125–1131. https://doi.org/10.1289/ehp.9652 .

29. Buseck PR, Adachi K. Nanogeoscience: nanoparticles in the atmosphere. Elements 2008;6:389–394. https://doi.org/10.2113/gselements.4.6.389 .

30. Riediker M, Devlin R, Griggs T, Herbst M, Bromberg P, Williams R. Cardiovascular effects in patrol officers are associated with Fine particulate matter from brake wear and engine emissions. Part. Fibre. Toxicol 2004;1:2–12. https://doi.org/10.17615/0fjxae47 .

31. Kukutschova J, Roubíceka V, Malachovab K, et al. Wear mechanism in automotive brake materials, wear debris and its potential environmental impact. Wear 2009;267:807–817. https://doi.org/10.1016/j.wear.2009.01.034 .

32. Ghio AJ, Cohen MD. Disruption of iron homeostasis as a mechanism of biologic effect by ambient air pollution particles. Inhal Toxicol 2005;17:709–716. https://doi.org/10.1080/08958370500224482 .

33. Geiger A, Cooper J. Overview of Airborne Metals Regulations, Exposure Limits, Health Effects, and Contemporary Research Cooper Environmental Services; 2010. p. 1–50.

34. Velasco RP, Jarosińska D. Update of the WHO global air quality guidelines: Systematic reviews – An introduction. Environ. Int 2022;170:556. :568. https://doi.org/10.1016/j.envint.2022.107556 .

35. WHO, World Health Organization. Report of the World Health Organization. Conference on mechanisms of fibre carcinogenesis and assessment of chrysotile asbestos substitutes 8–12. November. 2005. Lyon, France:

36. Li C, Yu L, He W, Cheng Y, Song G. Development of Local Emissions Rate Model for Light-Duty Gasoline Vehicles: Beijing Field Data and Patterns of Emissions Rates in EPA Simulator. Transp. Res. Rec 2017;2627:67–76. https://doi.org/10.3141/2627-08 .

37. USEPA. Brake and Tire Wear Emissions from On-road Vehicles in MOVES2014. [Internet]. Assessment and Standards Division Office of Transportation and Air Quality U.S. Environmental Protection Agency[Internet]. EPA; c2014. Available from https://www.epa.gov/transportation-air-pollution-and-climatechange .

38. World Health Organization. Asbestos: Elimination of asbestos-related diseases. [Internet]. WHO Fact sheet no 343 c2010. Available from https://www.who.int/news-room/fact-sheets/detail/asbestos-elimination-of-asbestos-related-diseases .

39. World Health Organization. Particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide [Internet] c2012. Available from https://www.who.int/publications/i/item/9789240034228 .

40. Kosowska GA, Dajda J, Adamiec E, et al. Human Health Risk Assessment of Air Pollution in the Regions of Unsustainable Heating Sources. Case Study—The Tourist Areas of Southern Poland. Atmos 2021;12:615–631. https://doi.org/10.3390/atmos12050615 .

41. Smith CJ, Perfetti TA. 142 ACGIH Threshold Limit Values established from 2008–2018 lack consistency and transparency. Toxicol Res 2019;3:1–9. https://doi:10.1177/2397847318822137 .

42. International Agency for Research on Cancer (IARC). IARC Monographs on the evaluation of carcinogenic risk to humans: Arsenic, metals, fibers, and dusts 2012. p. 40–85.

43. Nelson AR, Catharyn T, Liverman CT, Elizabeth , Eide EA, Eileen Abt. Review of the NIOSH Research Roadmap on Asbestos Fibers and Other Elongate Mineral Particles National Academies Press; 2009. p. 20–33.

44. Liatia A, Schreibera D, Lugovyyb D, Gramstatc , Dimopoulos P, Eggenschwiler P. Airborne particulate matter emissions from vehicle brakes in micro- and nano-scales: Morphology and chemistry by electron microscopy. Atmos. Envi 2019;212:281–289. https://doi.org/10.1016/j.atmosenv.2019.05.037 .

45. Ogah AO, James TU. Mechanical Behavior of Agricultural Waste Fibers Reinforced Vinyl Ester Bio-composites. Asian J. Phys Chem. Sci 2018;5:1–10. https://doi.org/10.9734/AJOPACS/2018/35841 .

46. Jawaid M, Khalil HA. Effect of layering pattern on the dynamic mechanical properties and thermal degradation of oil palm-jute fibers reinforced epoxy hybrid composite. Bioresources 2011;6:2309–2322. https://doi.org/10.15376/biores.6.3.2309-2322 .

47. Hamatschek C, Augsburg K, Schobel D, et al. Comparative Study on the Friction Behaviour and the Particle Formation Process between a Laser Cladded Brake Disc and a Conventional Grey Cast Iron Disc. Metals 2023;13:300–320. https://doi.org/10.3390/met13020300 .

48. Zhen-yu W, Jie W, Feng-hong C, Yun-hai M, Singh T, Fekete G. Influence of banana fiber on physic mechanical and tribological properties of phenolic based friction composites. Mater Res. Express 2019;:6–21. https://doi.org/10.1088/2053-1591/ab160a .

49. Zhen-yu W, Jie W, Yun-hai Ma. The Evaluation of Physicomechanical and Tribological Properties of Corn Straw Fibre Reinforced Environment-Friendly Friction Composites. Adv. Mater. Sci. Eng 2019;4:1–9. https://doi.org/10.1155/2019/1562363 .

50. Nayak S, Heckadka SS, Thomas LG. Evaluation of physico-mechanical characteristics of cashew nut shell liquid-epoxy composites with Borassus and Tamarind fruit fibres as reinforcements. J. Nat. Fibers 2019;16:328–341. https://doi.org/10.1080/15440478.2017.1423254 .

51. Akıncıoğlu G, Öktem H, Uygur I, Akıncıoglu S. Determination of Friction-Wear Performance and Properties of Eco-Friendly Brake Pads Reinforced with Hazelnut Shell and Boron Dusts. Arab. J. Sci. Eng 2018;43:4727–4737. https://doi.org/10.1007/s13369-018-3067-8 .

52. Irawan AP, Fitriyana DF, Tezara C, et al. Overview of the Important Factors Influencing the Performance of Eco-Friendly Brake Pads. Polymers 2022;14:1180. https://doi.org/10.3390/polym14061180 .

53. Maleque MA, Atiqah A. Development and characterization of coir fiber reinforced composite brake friction materials. Arab J. Sci. Eng 2013;38:3191–3199. https://doi.org/10.1007/s13369-012-0454-4 .

54. Yunhai M, Siyang W, Jin T, et al. Tribological and Mechanical Behaviours of Rattan-Fibre-Reinforced Friction Materials under Dry Sliding Conditions. Mater. Res. Express 2018;5:3. https://doi.org/10.1088/2053-1591/aab4a7 .

55. Yucheng L, Yunhai M, Che J, Duanmu L, Zhuang J, Tong J. Natural fibre reinforced non-asbestos organic non-metallic friction composites: Effect of abaca fibre on mechanical and tribological behavior. Mater. Res. Express 2018;5:5. https://doi.org/10.1088/2053-1591/aac1e0 .

56. Lertwassana W, Parnklang T, Mora P, Jubsilp C, Rimdusit S. A High performance aramid pulp/carbon fiber-reinforced polybenzoxazine composites as friction materials. Compos. B. Eng 2019;177 https://doi.org/10.1016/j.compositesb.2019.107280 .

57. Kumar N, Singh T, Grewal JS, Patnaik A, Fekete G. Experimental investigation on the physical, mechanical and tribological properties of hemp fiber-based non-asbestos organic brake friction composites. Mater. Res. Express 2019;6:8–29. https://doi.org/10.1088/2053-1591/ab2399 .

58. Ilanko AK, Vijayaraghavan S. Wear mechanism of flax/basalt fiber-reinforced ecofriendly brake friction materials. Tribology - Materials, Surfaces & Interfaces 2017;11:47–53. https://doi.org/10.1080/17515831.2017.1299323 .

59. Shalwan A, Yousif A. In State of Art: Mechanical and tribological behaviour of polymeric composites based on natural fibres. Mater. Des 2013;48:14–24. https://doi.org/10.1016/j.matdes.2012.07.014 .

60. Singh T, Pruncu CI, Gangil B, Singhe V, Fekete G. Comparative performance assessment of pineapple and Kevlar fibers based friction composites. Mater. Res. Technol 2020;9:1491–1499. https://doi.org/10.1016/j.jmrt.2019.11.074 .

61. Amirjan M. Microstructure, wear and friction behavior of nanocomposite materials with natural ingredients. Tribol. Int 2019;131:184–190. https://doi.org/10.1016/j.triboint.2018.10.040 .

62. Ikpambese KK, Gundu DT, Tuleun LT. Evaluation of palm kernel fibers (PKFs) for production of asbestos-free automotive brake pads. J. King. Saud. Univ. Eng. Sci 2016;28:110–118. https://doi.org/0.1016/j.jksues.2014.02.001 .

63. Yigrem M, Fatoba O, Tensay S. Tribological and mechanical properties of banana peel hybrid composite for brake-pad application. Mater. Today 2022;62:2829–2838. https://doi.org/10.1016/j.matpr.2022.02.381 .

64. Bala KC, Lawal SS, Ademoh NA, Abdulrahman AS, Adedıpe O. Effects of Nigerian Plant Gum Binder in the Optimized Multi-response Performance of Cashew Nut Shells Based Composites for Automobile Brake Pads. Eurasia. Proc. Sci Technol. Eng. Math 2021;12:17–27. https://doi.org/10.55549/epstem.991311 .

65. Fasake V, Dashora K. Characterization and Morphology of Natural Dung Polymer for Potential Industrial Application as Bio-Based Fillers. Polymers 2020;12:3030. https://doi.org/10.3390/polym12123030 .

66. Yunhai M, Wub S, Zhuangb J, Tong J, Hongyan Q. Tribological and physio-mechanical characterization of cow dung fibers reinforced friction composites: An effective utilization of cow dung waste. Tribol. Int 2019;131:200–211. https://doi.org/10.1016/J.TRIBOINT.2018.10.026 .

67. Dolińska B, Jelińska M, Szulc-Musioł B, Ryszka F. Use of Eggshells as a Raw Material for Production of Calcium Preparations. Czech J. Food Sci 2016;34:313–317. https://doi.org/10.17221/59/2016-CJFS .

68. Edokpia RO, Aigbodion VS, Atuanya CU, et al. Experimental study of the properties of brake pad using egg shell particles-gum Arabic composites. J. Chin. Adv. Mater. Soc 2016;4:172–184. http://doi.org/10.1080/22243682.2015.1100523 .

69. Afolayan J, Wilson U, Zaphaniah B. Effect of Sisal Fibre on Partially Replaced Cement with Periwinkles Shell Ash (PSA) Concrete. J. Appl. Sci. Environ. Manage 2019;23:715–719. http://doi.org/10.4314/jasem.v23i4.22 .

70. Chanadusakorn k, Kaewlob k, Reubroycharoen P. Effect on the Properties of Brake Pads of Recycling Dust as Filler. Key Eng. Mater 2019;824:52–58. http://doi.org/10.4028/www.scientific.net/KEM.824.52 .

71. Amaren GS. Development of automobile disk brake pads using ecofriendly periwinkle shell and fan palm shell materials Nigeria: Univ of Engineering Ahmadou Bell; 2016.

72. Yawas DS, Aku SY, Amaren SG. Morphology and properties of periwinkle shell asbestos-free brake pad. J. King. Saud. Univ Eng. Sci 2013;28:103–109. https://doi.org/10.1016/j.jksues.2013.11.002 .

73. Aimikhe V, Lekia GB. An Overview of the Applications of Periwinkle (Tympanotonus fuscatus) Shells. Curr. J. Appl. Sci Technol 2021;18:31–58. https://doi.org/10.9734/CJAST/2021/v40i1831442 .

74. Hsu HC, Wu SC, Lin CY, Ho WF. Characterization of Hydroxyapatite/Chitosan Composite Coating Obtained from Crab Shells on Low-Modulus Ti–25Nb–8Sn Alloy through Hydrothermal Treatment. Coatings 2023;13:228. https://doi.org/10.3390/coatings13020228 .

75. Singaravelu L, Ragh M, Vijay R, Manoharan S, Kchaou M. Development and Performance Evaluation of Eco-Friendly Crab Shell Powder Based Brake Pads for Automotive Applications. Int. J. Automot. Mech. Eng 2019;4:491–458. https://doi.org/10.15282/IJAME.16.2.2019.4.0491 .

00. Vijay R, Singaravelu DL. Tribological characterization of different mesh-sized natural barite-based copper-free brake friction composites. Tribol. Surf. Eng 2021;2:297–300. https://doi.org/10.1016/B978-0-12-819767-7.00014-1 .

76. Sanjay M, Madhu P, Jawaid M, Senthamaraikannan P, Senthil S, Pradeep S. Characterization and properties of natural fiber polymer composites: A comprehensive review. J. Clean. Prod 2018;172:566–581. https://doi.org/10.1016/j.jclepro.2017.10.101 .

77. Purjari S, Ramakrishna A, Balaram Padal KT. Prediction of Swelling Behaviour of Jute and Banana Fiber Composites by using ANN and Regression Analysis. Mater. Today. Proc 2017;4:8548–8557. https://doi.org/10.1016/j.matpr.2017.07.201 .

78. Kabir M, Wang H, Lau KT, Cardona F. Chemical treatments on plant-based natural fibre reinforced polymer composites: an overview. Compos. B. Eng 2012;43:2883–2892. https://doi.org/10.1016/j.compositesb.2012.04.053 .

79. Sepe R, Bollino F, Boccarusso L, Caputo F. Influence of chemical treatments on mechanical properties of hemp fiber reinforced composites. Compos. B. Eng 2018;133:210–217. https://doi.org/10.1016/j.compositesb.2017.09.030 .

80. Asim M, Jawaid M, Abdan K, Ishak MR. The Effect of Silane Treated Fibre Loading on Mechanical Properties of Pineapple Leaf/Kenaf Fibre Filler Phenolic Composites. J. Bionic. Eng 2018;13:426–435. https://doi.org/10.1016/S1672-6529(16)60315-3 .

81. Cruz J, Fangueiro R. Surface Modification of Natural Fibers: A Review. Procedia. Eng 2013;155:285–288. https://doi.org/10.1016/j.proeng.2016.08.030 .

82. Rajan S, Balaji MAS, Sathickbasha K, Hariharasakthisudan B. Influence of Binder on Thermomechanical and Tribological Performance in Brake Pad. Tribol. Ind 2018;40:654–669. https://doi.org/10.24874/ti.2018.40.04.12 .

83. Rajan S, Balaji MAS, Saravanakumar SS. Effect of chemical treatment and fiber loading on physico-mechanical properties of Prosopis juliflora fiber reinforced hybrid friction composite. Mater. Res. Express 2019;6:5302–5315. https://doi.org/10.1088/2053-1591/aaf3cf .

84. Rajan B, Saibalaji MA, Mohideen R. Tribological performance evaluation of epoxy modified Phenolic FC reinforced with chemically modified Prosopis Juliflora bark fiber. Mater. Res Express 2019;6:5313–5315. https://doi.org/10.1088/2053-1591/ab07e6 .

85. Javeed MA, Saibalaji MA, Rajan B, Yucheng L. Characterization of Alkaline Treated Areva Javanica Fiber and its tribological performance in phenolic friction composites. Mater. Res Express 2019;52:5–34. http://dx.doi.org/10.1088/2053-1591/ab43ad .

86. Sanjay MR, Siengchin S, Parameswaranpillai J, Jawaid M, Pruncu CI, Khan A. A comprehensive review of techniques for natural fibers as reinforcement in composites: Preparation, processing and characterization. Carbohydr. Polym 2019;207:108–121. https://doi.org/10.1016/j.carbpol.2018.11.083 .

87. Atiqah A, Jawaid M, Sapuan S, Ishak M. Effect of Surface Treatment on the Mechanical Properties of Sugar Palm/Glass Fiber-reinforced Thermoplastic Polyurethane Hybrid composites. Bioresources 2017;1:1174–1181. https://doi.org/10.15376/biores.13.1.1174-1188 .

88. Rajan B, Balaji MAS, Noorani MA. Effect of Silane surface treatment on the Physico-mechanical properties of shell powder reinforced Epoxy modified Phenolic Friction composite. Mater Res. Express 2019;6:5315–5325. https://doi.org/10.1088/2053-1591/ab0ca5 .

89. Liu Y, Ma Y, Lv X, Yu J, Zhuang J, Tong J. Mineral fibre reinforced friction composites: effect of rockwool fibre on mechanical and tribological behavior. Mater. Res. Express 2018;5:5308–5322. https://doi.org/10.1088/2053-1591/aad767 .

90. Bijwe J, Nidhi N, Majumdar N, Satapathy BK. Influence of modified phenolic resins on the fade and recovery behavior of friction materials. Wear 2005;259:1068–1078. https://doi.org/10.1016/j.wear.2005.01.011 .

91. Rajan R, Tyagi YK, Pruncu CI, Kulshreshtha S, Ranakoti L, Singh T. Tribological performance evaluation of slag waste filled phenolic composites for automotive braking applications. Polym. Compos 2022;43:7118–7133. https://doi.org/10.1002/pc.26772 .

Article information Continued

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Brake wear Particle matter	Effects	References
PM₁₀	lung cancer, cardiovascular and respiratory problems,	[16]
PM_2.5	Heart rate variability	[16]
< PM_2.5	Translocation of Blood in liver, kidneys and more dangerously brain	[19]
< PM_2.5	cardiovascular diseases and pulmonary inflammation	[29]
PM₁₀; PM_2.5	high blood pressure and provokes inflammatory	[30]
Brake wear rich in copperand iron oxides	Inflammatory reactions in bronchial branch	[31]
Iron	Iron induce conjunctivitis and inflammation of the retina in the eye	[32}
Copper	copper causes irritation of the respiratory tract and eyes and in the worst cases kidney failure	[33]
Nickel	Nickel is a carcinogenic substance, causing cancers of different organ such as prostate, lung and nose.	[34]

Natural fibers	Treatment	Results	References
Banana	soaking 24 h in NaOH solution-Washing with distilled waterdrying in an oven. 60°C for 5h-cutting at 1–5 mm length	Quantity less than 10 wt.% improves friction performance and stability	[48]
Corn stalk fiber	Soaking 24 h in 3% NaOH solution-Washing with distilled water-drying in an oven. 60°C for 5 h-cutting at 4–5 mm length	7 wt.% in the composite exhibited excellent friction and wear performance.	[49]
borassus and tamarind fruit fibers	Washing with distilled water-baking in an oven at 50°C – Soaking 2 h in NaOH solution and neutralization with hydrochloric acid	Increase the hardness of the composites.	[50]
hazelnut shells	Drying - pulverization with a high-speed grinder-sieving (400 μm)	Good compressibility and high level of friction coefficient and good stability	[51]
Sawdust	Drying for about 1 month after collection-milling into powder using a ball milling machine-sieving	The lower the sieve grades of sawdust, the better are mechanical and friction properties.	[52]
Coir fiber (coconut fiber)	Soaking 1h in 5% Na OH solution - washed with distilled water-drying process-cutting to 7 mm of length and storing with silica gel.	Composite with 20 vol % coconut fiber and 46% of epoxy resin show similar frictional properties than commercial brake pad	[53]
Rattan-Fibre	dipping into 2 vol.% of NH₃H₂O and 4 vol.% of CON₂H₄ for 60 min at 100°C - soaking for 40 min at 65°C in 5 vol.% NaOH solution-washing in distilled water-neutralization for 20 min with 2 vol.% H₂SO₄ - drying in an oven at 90°C for 3 h	5% of rattan fiber exhibits better wear resistance	[54]
abaca fibre	Immersion in 3 wt.% NaOH solution for 90 min - soaking 40 min in the H₂SO₄ solution (1 wt.%) - washing in distilled water - drying in an oven at 75°C for 40 min – cutting of different lengths	Short fiber (5mm and 10 mm of lengths) improve the wear resistance of the friction composites	[55]
Aramid pulps	Extraction with acetone for 24 h in a Soxhlet extractor -drying at 70°C for 5 h in an air oven	Optimal aramid: carbon fiber mass ratio is 75:25 which enhance mechanical properties and friction stability of the composites associated with good thermal stability.	[56]
Hemp fiber	Immersion with 2% NaOH solution for 24 h-washing with distilled water fibers - drying for 5 h in an oven at 60°Ccutting into short fiber of 1–5 mm length	5 wt.% of Hemp fiber content enhance the friction and wear performance of the composite	[57]
Flax and basalt fibres	drying at 80°C for 30 min in a hot air oven-soaking 1 h in 5% NaOH solution-washing with distilled water-drying in hot air oven for 5 h at 80°C-soaking - washing with acetone solution-drying in atmospheric air - drying at 80°C for 5 h.	Due to the thermal characteristics of basalt fiber and its bonding nature composite show a good wear resistance.	[58]
Areva javanica fiber	Extraction from its seed-soaking with 3 % alkaline solution for 1 h	-Good physical, chemical, and mechanical properties -Good dispersion od fiber in the matrix -Good wear resistance	[59]
pineapple leaf fiber	Soaking for 24h in 5 wt.% of NaOH - washing with distilled water-drying in oven for 5h at 60°C-cutting to a length of 2–6mm	5 wt.% pineapple fiber content enhance highest friction performance and wear resistance	[60]
Bagasse/ banana peel	Bagasse: Soft milled for 30 min in a ball mill Banana peel: drying in oven at 75°C for 8h-ball milling for 5h	5 wt.% of bagasse content improves hardness value. Composite with 5wt.% of bagasse and 5wt.% of nanoalumina particle show good friction and wear behavior.	[61]
Palm Kernel Shell	Collection-Extraction-suspension in a solution of caustic soda (sodium hydroxide) for 24 h	Composite with 40% epoxy-resin, 10% palm kernel shell presented good properties (physical, mechanical and tribological)	[62]
Durian Fruit Skin and Teak Leaves	Durian fruit skin fiber: cutting into pieces 5×5 cm - drying in the sun for 36 h-stoving 1h at temperature 100°C-cutting Teak leaves: heating with the oven at a lower temperature of 50°C.-cutting	composition 40% of durian fruit skin fiber, 10% magnesium oxide, 40% teak leaf, and 10% polyester resin have identical properties with standard brake pad	[63]