Innovated Banana Fiber Nonwoven Reinforced Polymer Composites: Effects of Pre- and Post-treatments on Physical and Mechanical Properties

Four types of nonwovens were prepared from different sections of the banana tree e.g., outer bark (OB), middle bark (MB), inner bark (IB) and midrib of leaf (MR) by wet laid web formation. They were reinforced on two different types of matrices e.g., epoxy (E) and polyester (P) to make eight variants of composites. Different concentration (5–15%) of NaOH and water repellent (WR); and different doses (100-500krd) of gamma radiation were applied in different stages of process. The properties like water absorbency, tensile strength (TS), exural strength (FS) and elongation at break (Eb%) were investigated. OB composites were exhibited higher water absorbency, TS and FS but lower Eb% than other types of composites. Epoxy composites were found to have 16% lower water absorbency, 41.2% higher TS and 39.1% higher FS than polyester composites on an average. Alkali treatment reduced the water absorbency by 32%; improved the TS by 71%; improved the FS by 87% on an average at 15% NaOH. Water repellent treatment (on alkali treated composites) decreased the absorbency by 63% at 10% WR but increased 6.3% at 15% WR. Gamma radiation improved the TS of 30% and FS of 35% on an average at a dose of 100krd for IB and 200krd for other composites. Further increment of dose reduced both the FS and TS.

Banana ber contains 71.08% of cellulose, 12.61% of hemicellulose and 7.67% of lignin in their chemical composition with a diameter of 138 µm and density of 1.28 g/cm 3 (Kenned et al. 2020a). In a tropical country like Bangladesh, banana plants are considered as agricultural crops, growing abundantly due to favorable climate conditions. After harvesting fruits, banana plants are cut at their lower section and the whole cutting portions are considered as a complete waste including pseudo stem and leaf those can be utilized as a source of natural bers for the manufacturing of NFRCs, textiles, nonwoven, packaging materials, wiping materials and so on (Adeniyi et al. 2019). Therefore, the bers can be used in the industry without any additional expenses for the cultivation ). Moreover, banana bers exhibit good mechanical properties competently with other cellulosic bers that makes them a potential reinforcing material for varieties of engineering applications ( However, the performance of the NFRCs depends on ber orientation, ber content, length, shape and their interfacial bonding with the matrix (Al-Oqla and Salit 2017). Fiber orientations are also varied with different forms of reinforcement like chopped ber reinforcement, continuous ber ( lament) reinforcement, woven fabric reinforcement and nonwoven reinforcement. Woven fabrics are generally produced by interlacing the yarns usually at the right angles by following a regular pattern. The strength of woven fabrics can be increased by increasing the twist angle of the yarns up to a certain limit. However, this twist angle plays an opposite role in case of composites. Increase of twist angle decreases the permeability of matrix to the ber which results poor ber-matrix adhesion and low mechanical properties (Peças et al. 2018). In case of lament reinforcement, mechanical properties are much lower in transverse direction of bers that is also a limitation for different applications. To avoid these problems, nonwoven reinforcement can be a great option. Nonwovens are prepared in a at structure with different thickness without interloping or interlacing. Fibers are chopped, uniformly distributed, and bonded together by chemical, mechanical or thermal treatment. They don't have preferential strength direction and can produce in large scale due to availability and low cost (Al-Oqla and Sapuan 2014).
Thermosetting resins are most widely used in the composite industry as a polymer matrix. Among them, epoxy and polyester resin are most applied matrix in the composites. Epoxy resin, also known as poly epoxides, have good adhesion properties with natural bers. Other key features are low moisture absorption, high chemical resistance, low shrinkage, and simple processing. These excellent properties make them superior in market with wide range of applications (Oliveira et al. 2019). However, unsaturated polyester resin, also known as polyhydric alcohols, have satisfactory mechanical properties and enough adhesion properties with the natural bers which are reported in several studies. The main advantage of polyester resin is, they are cheaper, available and can be used in wide ranges of applications (Sreekumar and Thomas 2008).
There is no doubt that, natural ber brings a lot of potentiality for their unique properties and environmental friendliness, but they have some drawbacks like high moisture absorption, low compatibility with the commercial resins, poor adhesion between ber and matrix, less homogenous like laments, low resistance to re (Gholampour and Ozbakkaloglu 2020). However, these challenges can be Loading [MathJax]/jax/output/CommonHTML/fonts/TeX/fontdata.js overcome by different types of physical and chemical treatments. Chemical treatments of the bers including alkaline, saline, acetylation, benzoylation and many more can improve the adhesion between ber and matrix (Faruk et al. 2014). Alkali treatment is one of the simplest and cheapest method which is easily applicable to natural bers by immersing them into the solution of NaOH. After the alkali treatment, bers become more uniform by removing all the impurities. Therefore, physical and mechanical properties of the composites are improved consequently ( To overcome the high-water absorbency problem of NFRCs, surface treatment of natural bers with water repellent is a potential way. The water repellent makes a coating on the ber surface and resist the water to penetrate inside. There is no relevant study yet regarding the water repellent treatment on natural bers to improve the hydrophobicity of NFRCs. Physical treatments like x-ray, ultraviolet (UV) ray, gamma ray, plasma, corona are applied to the composites to improve the ber-matrix adhesion. Due to less time consumptions, high productivity, low environmental pollution, structural availability and easy application, gamma radiation becomes popular day by day (Noura et al. 2018). Gamma radiation is a powerful ionizing radiation which can penetrate inside the polymeric structure of the composites and produce reactive sites to make more oriented polymeric structures and improve the mechanical properties of the composites (Masudur Rahman et al. Martínez-Barrera et al. 2020). However, the studies also reported that, gamma radiation improves the mechanical properties up to a certain level of gamma radiation dose after that it alters the properties. Therefore, an optimum dose must be maintained.
Numerous studies have been noted regarding the properties of banana ber reinforced composite materials. Majority of them used banana ber or pseudo stem mat as a reinforcing material (Jordan and Moreover, no study has been found regarding the surface modi cation of such nonwovens and their composites. The aim of this study is to develop an ecofriendly composite material from a natural source to replace the existing environmentally destructing, carcinogenic, synthetic composites materials those are being used Loading [MathJax]/jax/output/CommonHTML/fonts/TeX/fontdata.js vastly in different areas like packaging, households, building materials, automobiles, technical textiles and so on. To ful l the objectives, four types of banana ber nonwovens were developed from different parts of the banana tree e.g., outer bark, middle bark, inner bark of banana stem and mid rib of banana leaf in our previous study (Motaleb et al. 2020). This study is the continuation of the last work. Nonwovens were prepared by following the previously developed wet laid web formation technique from the extracted bers. The prepared four types of nonwovens were reinforced on two different types of matrices e.g., epoxy resin and polyester resin to make eight variants of composites. Surface treatments were applied in three stages, i) ber stage -alkali (NaOH) treatment, to improve the mechanical properties and hydrophobicity, ii) nonwoven stage -water repellent treatment, to improve the hydrophobicity and, iii) composites stage -gamma radiation, treatment to improve the mechanical properties. Water absorbency of the composite samples and the improvement of hydrophobicity by the surface modi cation were inspected. Mechanical properties like tensile and exural strength and the in uence of physical and chemical treatment on those properties were also analyzed in this study. A comparative study between the composites of epoxy matrix and polyester matrix are elaborated in different aspects throughout the study.

Materials
Banana trees were collected from a banana plantation as a waste material (after harvesting banana fruit) in Gazipur, Bangladesh. Epoxy resin, hardener HY-951, polyester resin and methylethylketone peroxide (MEKP) were bought from a European chemical supplier. Caustic soda and water repellent (per uoroalkyl acrylic) were purchased from Archroma International Ltd.

Banana Fiber Extraction
Banana trees were segregated into four different sections such as 1) outer layers of banana bark designated as outer bark (OB), 2) middle layers of banana bark designated as middle bark (MB), 3) inner layers of banana bark designated as inner bark (IB) and 4) middle rib of banana leaves designated as midrib (MR). All the sections are mentioned in Fig. 1. The raw materials of each section were then pressed by a metal tube squeezer for removing the inside water as much as possible. After that, they were dried in sunlight for about 15 days.
The dried materials were scratched by a metal comber to make like ribbon and cut them with a length of 3 cm. For the initial ber extraction, these small pieces were taken in a big metal pot and treated with 5 (w/v) % of NaOH with a temperature of 90ºC for about 30 minutes until they became soft. They were rinsed properly for removing unwanted materials and dried subsequently. Thus, the raw banana bers from different parts of the banana trees were extracted. Loading [MathJax]/jax/output/CommonHTML/fonts/TeX/fontdata.js

Alkali Treatment on Fibers
The extracted raw bers were still contained various impurities like fat, wax, pectens and so on. To clean off these impurities, the bers were immersed into a solution of NaOH at different concentrations i.e., 5, 10 and 15 (w/v) % for 24 hours at a temperature of 23 ± 2ºC. The bers were rinsed and dried again after the treatment.

Nonwoven Formation
Firstly, the alkali treated banana bers were blended with water to make a uniform pulp mixture. Then, they were rinsed properly to remove the leftover of NaOH and dried once again. The prepared banana pulp was taken in the blender again with the ber (pulp)/water ratio of 1:50. After blending, the mixture was poured in a mold prepared with wooden frame and mesh fabric. The bers were distributed uniformly by immersing the complete mold on a tab of water to make a sheet from the ber webs according to the wet laid web formation technique. The sheet, usually known as nonwoven, was then moved to a plastic plate, and pressed with wiping paper to remove extra water. Finally, they were dried in sunlight and straighten with an electrical iron in case of rough surface. Similar procedure was followed to make all types of banana ber nonwovens. The average thickness of the nonwovens were found 0.75 ± 0.05 mm.

Water Repellent Treatment on Nonwovens
Before making composites by reinforcing the nonwovens, some of them were treated with a water repellent (WR) chemical ( per uoroalkyl acrylic) to improve the hydrophobicity of the composites. WR was applied at three different concentrations i.e., 5%, 10% and 15% to nd out the appropriate dose to decrease the water absorbency by keeping up the strength. The nonwovens were immersed into the solution of WR and kept for couple of minutes. The wet nonwovens were then squeezed by a padding roller to remove excess solution. They were dried and cured in an oven with a temperature of 160-170ºC for 30 minutes.

Composite Formation
The composites were prepared with hand layup technique. The already prepared nonwoven from four different section of banana tree i.e., OB, MB, IB, MR were used as reinforcing material and two types of resin i.e., epoxy (E) and polyester (P) were used as matrix. In total, eight variants of composites were prepared, which are designated as OB/E, MB/E, IB/E, MR/E, OB/P, MB/P, IB/P and MR/P with all possible combination of nonwovens and resins. Two metal plates were used as top and bottom surface of the mold with a size of 35×35 cm. The metal plates were wrapped with Te on (PTFE) paper to avoid the sticking di culties during the composite peel off. Three layers of nonwovens were reinforced for all types of composites. At rst, the nonwovens were cut with a size of 30×30 cm. Three pieces of nonwoven sheets were weighted together by a precise scale. According to the weight of nonwovens, a certain amount of resin mixture was prepared with the addition of appropriate catalyst by maintaining a Loading [MathJax]/jax/output/CommonHTML/fonts/TeX/fontdata.js constant ber/resin weight ratio of 30:70 for all the composites. 10% HY951was used for epoxy resin and 2% MEKP was used for polyester resin as a hardener. The bottom metal plate was placed in a suitable at surface. To begin the fabrication of composite, ¼ of the resin mixture was poured on the bottom metal plate and spread them uniformly with a brush according to the size of the nonwovens. Then the rst nonwoven layer was placed on them and pressed with a hand roller in such a way that the resin penetrated throughout the nonwoven. Again, ¼ of the resin mixture was poured on the rst nonwoven layer and repeated the same process to reinforce second and third nonwoven layer. The rest ¼ of the resin mixture was poured on the third nonwoven layer, the top metal plate was placed on them to make a complete sandwich structure. A dead weight of 20kg was laid on the top metal plate and kept them 24 hours for curing. Finally, the dead weight was removed, and the composite was separated from metal plates. Similar procedure was followed for making all the composites. The overall thickness of the composites was found 3 ± 0.5 mm.

Sampling
In total eight types of composites were prepared. Samples for each treatment or test were prepared separately according to the prescribed standards. All types of samples are described in Table 1. Some prepared samples for the tensile tests are presented in Fig. 2. The composite samples were irradiated with different doses of gamma radiation. A capsule type of gamma irradiator Co-60 was used which has remote controlled electromechanical system with a capacity of 65Kci. Five different doses of gamma radiation i.e., 100krd, 200krd, 300krd, 400krd and 500krd were applied for each type of sample.

Water Absorbency
Samples were prepared and tested according to the standard ASTM D570-98. Before immersing into the water, they were conditioned in an oven for 24 hours at 50°C, cooled in a desiccator, and weighted immediately to have the dry weight of each sample. The conditioned samples were then put in a beaker of water, maintained the temperature of 23 ± 2°C. The samples were taken out for maximum 2 minutes for measuring weight after every hour for the rst four hours and then after every 4 hours over the 24 hours. Before measuring weight, the samples were wiped off every time to remove surface water. The water absorbency by weight percentage was calculated by the following Eq. (1).
Where W w is wet weight after water immersion and W c is conditioned weight.

Mechanical Tests
Tensile properties like tensile strength (TS) and elongation at break percentage (Eb%) were tested according to the standard ASTM D638-14. A universal testing machine (UTM) from the brand Zwick was used for testing the samples at Laboratory of Materials Engineering, Kaunas University of Technology (KTU), Kaunas, Lithuania. Samples were prepared with according to the standard size of 165mm×13mm. A gauge length of 50mm was maintained. Load was applied at a constant rate of motion 10 mm/min of grips. The tensile strength and elongation at break were calculated by the following equations (2) and (3) respectively.

A (2)
Where F max is maximum load and A is cross-sectional area of the sample.
Where Δ l b is elongation at breaking point and l 0 is initial length of the sample. Flexural property was tested with the same UTM according to the standard ASTM D790-03 to determine the exural strength (FS) of the composites. Samples were prepared according to the standard and placed on the two supports with a span length of 16 times the thickness of the samples. Load was applied on the midspan with a constant de ection speed of 0.10 mm/mm/min until breaking. The exural strength was calculated by the Eq. (4).

FS = 3FL
2bd 2 (4) Where F is breaking load, L is length of support span, b is width and d is thickness of the sample. Which results better covering of hydrophilic bers by the hydrophobic resins and make them more watertight. Better adhesion also leads to remove the amorphous regions and porosity in the ber-matrix interface thus, water absorbency reduces.
Loading [MathJax]/jax/output/CommonHTML/fonts/TeX/fontdata.js Alkali treatment improves the hydrophobicity of the composite samples which are clearly visible in Fig. 3 (b Water absorbency ows described in Fig. 4, shows that water absorbency rate is very fast in rst couple of hours. It was observed that, approximately 40-50% water was absorbed in rst two hours of 24 hours of complete observation. The rate can be considered medium during the time of 3-8 hours. Near about 80% water is absorbed after 8 hours of 24 hours. Then all the ows were become slow up to 20 hours and very slow up to 24 hours.

Effect of Water Repellent Treatment on Water Absorbency
The water absorbency of untreated (0% WR + 15% NaOH) composites after 24 hours of immersion into water is presented in Fig. 5  For the further improvement of hydrophobicity, alkali treated nonwovens were treated again with water repellent chemical. Figure 5. (b) details the effects of WR on the water absorbency of the composites. It is evident that, water absorbency is decreased remarkably by the WR treatment for all types of composites. For instance, only at 5% concentration of WR treatment, water absorbency is reduced by 45 42.4% for OB/P, MB/P, IB/P, MR/P composites respectively in compared to untreated composites. Water absorbency was continued to decrease at 10% WR application. An overall 60-70% decrease of water absorbency was found at 10% WR in compared to untreated composites. However, from the 2nd order polynomial curves, the in uence is lower at 10% WR when compared to 5% WR.
WR treatment improves the hydrophobicity of the composites dramatically to a certain level of concentration. The WR chemical which was used in this study is per uoroalkyl acrylic. This WR create a surface coating on the materials and consequently resist water molecules to enter inside of the material. WR may also cross-links with the cellulose to make them harder and rougher the surface. This rougher surface of the ber creates air trap on the surface that makes them more hydrophobic (Bae et al. 2009;Chowdhury 2018). However, at 15% WR, the water absorbency started to increase which is due to the thicker coating of the ber surface. That weaken the interfacial ber-matrix bonding and creates porosity between them. Therefore, water can penetrate on those perforated structures easily.
From the absorbency ows over the soaking times presented in Fig. 6, water absorbency was very fast in rst couple of hours like the absorbency ows of alkali treated composites. About 50-60% of water was absorbed in rst two hours and about 75-85% was in rst eight hours. After that all the ows were become very slow. Moreover, at 24 hours, they seemed quite stable and absorbed the maximum amount of water. The main difference between the ows after alkali treatment (Fig. 2) and after WR treatment ( Fig. 4) is, the curves look more stable after WR treatment than after alkali treatment at 24 hours. That gives an assumption of further water absorbency of the composites after the period of 24 hours. The composites after alkali treatment will have the possibility to take water over a long period of time whereas, the composites after WR treatment will have the possibility to stop taking water in a short time after the period of 24 hours.

Mechanical Properties
Mechanical properties like Tensile Strength (TS), Flexural Strength (FS) and Elongation at Break (Eb%) were analyzed in this study. The effects of alkali treatment, water repellent treatment and gamma radiation on these mechanical properties were also investigated for all the composites. There is apparent in uence of alkali treatment on the tensile strength of the composites which is presented in Fig. 7 Fig. 8  Elongation properties of the composites shows exactly opposite trend of TS and FS which is presented in Fig. 9 (a). The highest Eb% was found from IB/P and lowest was from OB/E. In comparison of different nonwoven reinforcements, OB always showed lowest and IB always showed highest Eb% where MB and MR exhibited medium Eb% for both polyester and epoxy matrix composites. The composite with polyester matrix showed higher Eb% than epoxy matrix. Study found that, OB/P, MB/P, IB/P and MR/P demonstrated 11.8%, 32.1%, 25.8% and 29.5% of higher Eb% than OB/E, MB/E, IB/E and MR/E composites respectively.

Effects of Alkali Treatment
The effects of NaOH on Eb% of the composites are illustrated in Fig. 9  percentages of cellulose that leads them to achieve better mechanical properties. The cellulose percentage may gradually decrease from the outer bark (OB) to the inner bark (IB) of the banana tree. As a result, lower cellulose content makes the IB bers weaker and consequently lower mechanical properties in composites. Also, outer bark of the banana tree is found harder as a raw material that can make stronger materials than other layers of the banana stem. The midrib also found harder but surprisingly became soft after chemical extraction. The previous study also proved the higher mechanical properties of OB as a nonwoven material (Motaleb et al. 2020). Epoxy composite always found higher mechanical properties i.e., higher value of TS and FS but lower Eb% than polyester composites. This because of better interfacial bonding between ber and epoxy that leads very good adhesion between them. As a result, the applied load can be distributed properly though the ber and matrix which leads to bear higher loads. Similar results were found in some earlier studies ( The alkali treatment demonstrated the improvement of mechanical properties like TS and FS but decrease the Eb%. As discussed above, alkali treatment eliminates some unwanted materials including lignin and hemicellulose. This elimination creates rough ber surface that helps better mechanical interlocking among the bers. By cleaning the impurities, the cellulose content of the bers is increased which may increase the reactive sites and create strong bonding with the matrix. Therefore, the mechanical properties like TS and FS were improved. Due to the same reason, Eb% of the composites were decreased. As better as the adhesion between the ber and matrix, the material become more solid .0% and 6.2% where, the TS of OB/P, MB/P, IB/P and MR/P composites were decreased by 6.7%, 6.0%, 12.9% and 13.2% respectively at a concentration of 5% WR. At 10% WR, the TS of epoxy composites were reduced by approx. 10% where the TS of polyester composites were reduced by approx. 34% in an average. Likewise, at 15% WR, polyester composites were also showed higher reduction (approx. 65%) than epoxy composites (approx. 27%) in an average.

Effects of Water Repellent Treatment on Flexural Strength
Effect of WR on the exural properties are evident in Fig. 11. Similar negative trend was found for all the composites like TS as it declined the FS to a large extent of about 40-50% (in an average) after treating with 15% WR in compared to untreated composites. But the effect was much lower at 5% and 10% WR.
For examples, the FS of OB/E, MB/E, IB/E and MR/E composites were declined by 4.4%, 3.9%, 7.5% and 6.0% while, the FS of OB/P, MB/P, IB/P and MR/P composites were declined by 4.1%, 2.6%, 11.0% and 8.8% respectively at 5% WR in compared to untreated composites.

Effects of Water Repellent Treatment on Elongation at Break
Elongation of the composites were increased with the increase of WR% that is clearly de ned in Fig. 12.
The maximum increases of Eb% were found at 15% WR. For example, OB/E, MB/E, IB/E and MR/E composite exhibited 63.8%, 66.7%, 62.0% and 61.3% of increment at 15% WR than untreated composites.
At 10% WR, the effect was lower, Eb% were increased by 25% (approx.) on an average considering all types of composites. Furthermore, at 5%WR, the effect was very low as Eb% was increased by about 10% maximum from the untreated composites. The 2nd order polynomial curves also prove this trend. to penetrate inside the ber thus improve the hydrophobicity. However, because of this coating or polymer blockage, mechanical properties can be reduced. The ber-matrix interface can be disrupted by this type of coating that results poor adhesion between the ber and matrix thus the poor mechanical properties of the composites. The good thing is, this effect is negligible at lower concentration like 5% WR. Study revealed that the deterioration of TS and FS in about 10% maximum for all types of composites at a concentration of 5% WR. Whereas the hydrophobicity was increased by 40-50% (in an average) at the same concentration of WR. Therefore, it is recommended to apply the WR with a concentration of 5% to balance the water absorbency and mechanical properties.

Effects of Gamma Radiation
Effects of gamma radiation on mechanical properties like tensile strength, exural strength and elongation at break were investigated in this study. The results are described in 2nd order polynomial curves because the mechanical properties were in uenced by gamma radiation in two opposite factors. Figure 13 depicts the in uence of gamma radiation on tensile properties of the composites. All the curves demonstrate that, gamma radiation improves the mechanical properties signi cantly to a certain level of .9% for IB/P composite at 100krd but after that the TS was decreased with the increase of radiation dose. At higher dose like 500krd, TS was drastically by 60% in an average for all types of composites from the maximum value of TS, which is even less than half of the TS of nonirradiated composites. Both the polyester and epoxy composites were in uenced by the gamma radiation in the same ways though the TS of epoxy composites were improved slightly higher in percentage than polyester composites.

Effect of Gamma Radiation on Flexural Strength
The effect of gamma radiation on the exural strength of the composites are presented in Fig. 14

Effect of Gamma Radiation Treatment on Elongation at Break
Effect of gamma radiation on Eb% of the composites are revealed in Fig. 15. The Eb% was reduced by the gamma radiation to a small amount up to a certain level of irradiation then increased gradually.

Conclusions
The current study reveals the developments of an innovative natural composite materials by reinforcing different banana ber nonwovens which were developed by a special manual technique of wet laid web formation. The outcome of this study can be summarized by the following points.
1. OB composites showed higher mechanical properties (TS and FS) and higher water absorbency than other nonwoven composites. Between the two matrices, polyester composites exhibited higher absorbency and lower mechanical properties than epoxy composites. 2. The hydrophobicity and mechanical properties of the composites were improved signi cantly by the alkali treatment due to the better ber-matrix adhesion which is achieved by removing unwanted materials from the bers through this treatment. For instance, about 32% decrease of water absorbency, 71% increase of TS and 87% increase of FS was found on an average at a concentration of 15% NaOH. 3. The hydrophobicity was continued to improve remarkably by the water repellent treatment on the nonwovens by creating a surface coating on the materials. On the other hand, the mechanical properties were decreased by disrupting the ber matrix bonding through this treatment. But the good thing is, this declination is less than 10% approximately at a concentration of 5% WR with the signi cant improvement of hydrophobicity by 47.5% on an average. Therefore, this study recommends applying the WR with the maximum concentration of 5% to balance the water absorbency and mechanical properties. 4. Gamma Radiation improved the mechanical properties like TS, FS and decreased Eb% due to more oriented polymeric structure achieved by this radiation. Maximum 30% of TS and 35% of FS were increased at a radiation dose of 200krd but further increasing of dose decreased the properties due to breaking of main polymeric chains at higher radiation. Thus, this study recommends gamma radiation dose of maximum 200krd.
Based on the achieved results, it is evident that, banana ber nonwoven reinforced composites are well developed by different physical and chemical treatments on their pre and post manufacturing stages. The developed material demonstrates excellent hydrophobicity and comparable mechanical properties which can replace the existing non-biodegradable, carcinogenic and synthetic materials on the market.

Declarations
Funding Not applicable.
Con icts of interest The authors declare that they have no con icts of interest.
Ethics approval Not applicable.

Figure 6
Water absorbency ows of 10% WR treated composite samples by the soaking time up to 24 hours.