Isolation and characterization of banyan tree root filler for polymer composites in light-weight applications

The applicability of bio fillers as reinforcement with polymers is promoted by economic and ecological concerns. Nowadays, a large range of reinforcements are employed for this purpose, including cellulosic fillers and natural fibres owing to the favorable mechanical behavior, cheap price, negligible tool wear, low density, and eco-friendliness etc. The motive of this investigation is to explore the possibilities of utilizing plant sources as reinforcing filler in polymeric matrices. In this study particulate fillers were obtained from banyan tree’s aerial roots and were subjected to various characterization such as physiochemical evaluation, Fourier Transform Infrared Spectroscopy (FTIR), x-ray diffraction (XRD), thermal analysis (TGA), and Scanning Electron Microscopy (SEM). From the physiochemical analysis it was found that the banyan tree aerial root filler (BTAR) contained 40.13% of Cellulose, 15.22% of Hemicellulose, 15.31% of Lignin and 6.86% of Pectin. The density of the BTAR filler was found to be 0.27 gm cc−1 whereas the average particle size was 136.3 μm. The maximum inflection temperature referred to the maximum degradation of the BTAR filler was 295.7 °C. The SEM analysis exposed the rough surface of filler, with micro-structured strands and pores. The rough surface and the pores could help in better bond ability of the matrix and reinforcement when combined. Given the features of the examined BTAR filler, it is suggested as potential reinforcing filler for polymer composites to strengthen material properties for different light weight applications.


Introduction
The need to use renewable resources to tackle the environment pollution has resulted in an increase in the use of plant materials in the polymer sector, as the durability of products during processing and disposal is crucial.Organic fillers are viable and promising reinforcement materials for several polymer matrices in different applications, including vehicles, building, aircraft, retail, defense, leisure products, and technological gadgets [1][2][3].The main motive of using natural fillers in the composite sector is to minimize the costs while improving the processes, characteristics, and sustainability aspects.Many researchers and manufacturers choose natural fillers over synthetic ones due to their eco-friendliness, affordability, reduced tool wear out, lower density, and suitable mechanical characteristics [4,5].Massive quantities of biomass, forestry, and agriculture-based wastes exist naturally and are widely used as a probable resource of materials in various industries.Many plant species, agricultural produce, and seeds are recognized as valuable natural fillers in the polymer composite industry [6,7].Fillers sourced from plants and other agricultural products, contain cellulosic components, lignin, pectin, and wax etc [8].Composites reinforced with natural fillers having higher cellulosic concentration possess better mechanical and thermal behavior.Hence, using cellulosic fillers in polymers is critical for increasing the useful properties of the resultant composite.The major challenges of polymer composites include poor material characteristics, biodegradability, and economic factors.Polymeric materials can be turned into highperformance composites by selecting appropriate fillers, improving filler/matrix interaction, and using modern processes [9][10][11].
Several natural fillers have been isolated and characterized from plant resources and to name a few are Ficus benjamina L. stem, Waltheria indica Linn.Stem, Furcraea selloa K Koch peduncle etc.The characterization of Ficus benjamina L. stem revealed that it contained 68.71% cellulose, 10.15% hemicellulose, 11.31% lignin and 0.91% wax, whereas cellulose content of Waltheria indica Linn.Stem and Furcraea selloa K Koch peduncle were found to be 60.5% and 71.13% respectively [12][13][14].Another study explored the potential of sapodilla seeds as reinforcing filler in polymeric composite applications.The characterization showed that the filler possessed 49.94% of cellulose, 20.93% of hemicellulose and 15.65% of lignin contents.The thermal stability of the sapodilla fillers was found to be 330 °C [8].Microfibrils from Phaseolus lunatus peels (PLP) and Vigna radiata peels (VRP) possessed a cellulose and hemicellulose content of 65.2%, 20.1% and 58.2%, 21.9% respectively.The fibril density has a considerable impact on composite weight, with PLP and VRP fibrils having densities of 0.46 and 0.53 g cm −3 .The TG evaluation showed that both fibrils were thermally stable till 330 °C [7].Mechanical isolation technique was used to extract novel cellulosic fibres from the Calamus manan stem.It was reported that the fibres comprised 42% cellulose, 20% hemicellulose, and 27% lignin.The fibre exhibited a crystalline index of 48.28%, resulting in an ultimate decomposition point of 332.8 °C which demonstrate its employability as strengthening material for polymers within a functional temperature of 300 °C [10].
Although banyan tree aerial roots have been considered as a potential candidate in medicinal applications especially in the health and hygiene products.In their study, Verma et al examined the phytochemical makeup of the banyan tree's aerial roots and discovered that substances including lutein, α-Amyrenyl acetate, γ-Sitosterol, palmitic acid, and luteol predominate.Numerous significant medicinal properties, including antimicrobial, antioxidant, anti-inflammatory, antidiabetic, anti-cancerous, and others, are known to be exhibited by these substances [15].However, its usage as reinforcement material in polymer composites is scanty.Very few reports are available on its application as reinforcing filler in polymer composites.The mechanical properties of epoxyreinforced banyan aerial root filler were assessed at weight proportions of 2%, 4%, 6%, and 8%.The results demonstrated that the addition of filler enhanced the mechanical properties of the composites, as demonstrated by rise in tensile, flexural, and impact strengths.The specimen with 6% filler had the highest impact strength (194.02kJ m −2 ), while the composites with 4% filler exhibited the highest tensile and flexural properties of 407.81 MPa and 339 MPa, respectively.Beyond this level of filler reinforcement there was a down trend in the properties, however, the characteristics remained noticeably superior to those of laminates made with unaltered resin [16].Banyan tree roots have been characterized and utilized in the forms of chopped fibres and particulate fillers.The mechanical performance examination of epoxy composites reinforced with fibers from banyan tree aerial roots and incorporating graphene powder was carried out in a different study.The tensile strength and flexural strength of the composites made using banyan tree fiber were 27.93 MPa and 155.51 MPa, respectively.Conversely, the hybrid composites with the highest flexural strength (163.23 MPa) and tensile strength (40.6 MPa) contained 4% graphene [17].Hence, this study aims to perform a comprehensive analysis of the characteristics of BTAR filler for its potential usage in polymer composites especially in the light weight applications such as the composite filaments for 3D printers, particle boards in semi structural areas etc.The filler was evaluated by physiochemical analysis, FTIR, XRD, particle size evaluation, SEM and TGA.

Banyan tree aerial root filler
The banyan tree can be found in Southeast Asia, India, and other parts of the Indian subcontinent, as well as in many tropical places around the world.Banyan tree aerial roots are unique roots that emerge from the branches and dangle down into the earth.The aerial roots were collected from a Banyan tree at the Kalasalingam University campus for the extraction of the filler.

Extraction of filler
The aerial root was chopped in to small pieces and dried under sunlight to eradicate the moistness.The aerial root of the banyan tree retains moisture due to its ability to absorb water from the surrounding environment.The root was left in the sun for about eight hours every day for a week in order to remove the moisture content.At that point, the root turned black instead of green, indicating that a majority of moisture had been removed.This can be evidenced from figure 1.The chopped root was ground into a fine powder using a ball mill once it had dried.Repeated sieving was employed to generate a finely powdered filler from the crushed root that resulted.Figure 1 shows the aerial roots, the chopped root after drying and the obtained filler.

Physiochemical evaluation
The physical properties and chemical content of the BTAR filler were determined by physiochemical testing.This analysis was done based on the methods reported in our previous studies [7,8].

FTIR spectroscopy
The FTIR spectra of BTAR filler was acquired by an IR Tracer 100 FTIR Spectrophotometer in the wavelength of 4000 to 500 cm −1 with a scanning speed of 32 scans/min and a resolution of 4 cm −1 in transmission mode.

Particle size (PA) analysis
The particle size of BTAR filler was evaluated by Shimadzu SALD-2300 (V 3.1.1)particle size analyzer.The PS was measured for each 100 particles in various ranges.

XRD
By means of a spectrometer (Eco D8 Advance, Bruker) diffraction data was recorded between 10 to 80°2 theta range at a scanning speed of 4°/min.The crystalline index (CI) and size (CS) were calculated using the equations (1) and (2) [7,8]:  3. Results and discussions

Physiochemical properties
The chemical composition of natural fillers reinforced with the polymer has a significant impact on the structural and mechanical properties of the composites.Hence, to choose a particular filler as strengthening material in composites, it is inevitable to know its chemical composition.Various components of the BTAR filler were analyzed and listed as follows.The BTAR filler possessed 40.13% of cellulose, 15.31% of lignin, 6.86% of pectin, 6.48% of ash, 4.49% of wax and 15.22% of hemicellulose respectively.It is to be noted that higher the cellulose content in the filler, higher will be the hydrogen bonding which eventually enhances the crystallinity and the strength of the resultant composites.The properties of pectin make it to function like a natural glue which has the potential to improve the bonding of fillers with the matrix.Better bonding results in better load transfer in the composites thereby improving mechanical behavior.On other hand, higher hemicellulose and wax contents may degrade the properties which could be attributed to the filler disintegration and weak bonding strength [12,18].The moistness in BTAR filler was about 11.51%.Lesser the moisture content in the filler lesser is the water uptake by the composites and better is their mechanical attributes.The density of BTAR filler was 0.27 g cc −1 .BTAR's low density makes it an appealing choice for usage in light weight composites.The chemical composition of various reinforcing materials is compared with the BTAR filler and present in table 1.It is evident from the table 1 that the density of most reinforcement materials is quite lesser that BTAR filler making it a perfect choice for lightweight materials especially the automotive components [20].

Particle size analysis
The size distribution of the particles in the filler can be figured out by the particle size analysis.Determining the filler's particle size is essential since it affects the composites' characteristics.In this work, the average particle size (APS) of the BTAR filler was evaluated and presented in figure 2. Based on the illustrations in figure 2, the APS of BTAR filler was measured as 136.3 μm.The results indicated that the fillers fall within the micro-range.The smaller particle size could be advantageous in modifying the properties of the polymer matrix when employed as fillers.Larger diameter fillers are not compatible with the matrix; instead, fillers with an intermediate diameter are better suitable as strengthening material.Researchers demonstrated that as particle size drops, crystallinity and melting temperature increase.It has been noted that when particle size reduces, composites' mechanical properties get better.This may be explained by the fact that when particle size increases, the fracture surface area grows and the notched impact energy increases [21].

XRD analysis
X-ray diffractograms (figure 3) were taken to find the crystallinity of BTAR filler under investigation.BTAR filler's diffractograms show four noticeable peaks.A very small peak was found at 2q = 16.1°which could be attributed due to the (1 1 0) plane, a broad and intense peak at 2q = 22°was due to the (2 0 0) plane and another small peak at 2q = 34.7°couldbe ascribed to the (0 0 4) plane.Similar peaks positions were also reported on the Napier grass cellulosic filler [5].These diffraction planes at 2q = 16.1°and at 2q = 22°represent the occurrence of cellulose I and cellulose IV structure in the BTAR filler [18].A strong narrow peak at 2q = 27.5°couldbe ascribed to the organic groups present in the BTAR filler.The CI and CS of BTAR filler was also calculated and found to be 32.3% and 0.5025 nm respectively.Table 2 reports the evaluation of the CI and CS of BTAR filler in comparison to other fillers.

FTIR analysis
The BTAR fillers' functional groups were identified using FTIR spectroscopy.Figure 4 displays the BTAR filler's FTIR spectrum.Different absorption peaks were visible in the spectra, suggesting the existence of distinct components.It could be seen from the FTIR spectrum, the peaks at 3851 and 3641 cm −1 corresponding to the cellulose molecules by OH stretching.The small peak at 3375 cm −1 belongs to the O-H stretching vibrations [23].Further the peaks at 2985 and 2981 cm −1 are allocated to the-CH 2 OH and-CH 2 stretching that projected the presence of cellulose and hemicellulose components [22].The peaks at 2819 cm −1 and 1382cm −1 are ascribed to the C-H stretching and C-H and C-O bending [24].The band at 2376 cm −1 represented the C≡C stretching of wax in the BTA roots [25].The stretching vibration of carbonyl (C=O) group could be ascribed to the peak at 1731 cm −1 [26].The peaks at 1607 cm −1 and 1016 cm −1 could be credited to the existence of O-H bending of hemicellulose components and symmetric C-OH stretching of lignin components [18].Furthermore, the filler's hydrophilic character is confirmed by the peak at 1607 cm −1 [20].Peak at 1517 cm −1 represented the aromatic rings in lignin [27].The peak near 1408 cm −1 indicated the symmetric deformation of CH 2 in cellulose [28].At 1244 cm −1 , an absorbance peak corresponded to the CH stretching vibration of the acetyl group in lignin [29] while the bending vibration of C-H in lignin appeared at 823 cm −1 [30].
Table 1.Comparison of the chemical composition of BTAR filler and other reported materials.

Morphological analysis
It is a well-known fact that the surface morphology of fillers influences the functional load carrying capability of the filler reinforced composites.Hence it becomes inevitable to examine the surface morphology of the fillers [31].In this aspect, the morphological analysis of the BTAR filler was performed.It is evident from the SEM characterization of the BTAR filler that the filler's surface was uneven and rough (figure 5(b)).It is to be noted that rough surface of the filler can aid in resisting the pullout phenomenon in the composites [32].Further, the SEM image confirms the BTAR filler had irregular shape and size (figure 5(c)).It is also evident that the fillers possessed many micro-voids and lateral pores (figures 5(a), (d)) which allows the matrix material to penetrate in to it thereby promoting better matrix-filler adhesion.The pore diameters within the filler ranged approximately from 5.274 to 6.029 μm, respectively (figure 5(e)).The resultant surface properties suggests that the BTAR filler could possibly be implemented as a reinforcing filler in polymer composites and also as fillers for making composite filaments for 3D printers.3.6.Thermogravimetric analysis Reinforcement materials with excellent thermal stability are deemed essential for use in high-temperature applications [33].TGA was used to examine the BTAR filler's temperature-dependent degrading behavior.Figure 6 shows the thermograms of the BTAR filler.Figure 6 makes it clear that there were several stages to the BTAR filler's thermal deterioration.The material experiences a number of thermal transitions as the sample temperature rises, including oxidation, breakdown, and evaporation.The mass of sample varies with respect to temperature as a result of these transitions [34].During the first weight loss phase, moisture and other unstable substances were eliminated from the BTAR filler which took place around 70 °C.Further, at temperature below 150 °C, a slight decrease in weight was seen due to the materials' low molecular weight compounds.The weight loss at this phase was 9.42%.Volatile compounds in the BTAR filler degraded between the range of 100 °C-240 °C with a weight loss of about 4.69% [35].
In the next stage a maximum degradation was noticed known as the maximum inflection temperature which could be evidently seen in the derivative thermograms.In this stage a maximum weight loss of about 43.86% was noticed which could be credited to the decay of the cellulosic compounds [23].The material that is hardest to disintegrate is the lignin and this degraded in a broad temperature range when related to the cellulose i.e., between 200 °C to 650 °C.The weight loss was found to be 31.11%.During this stage the breakdown of lignin, wax and other materials were witnessed.In the last stage of the degradation process the carbon or char residues were noticed having occurred beyond the temperature of 500 °C making a weight loss % of 6.38.

Conclusions
The BTAR filler was successfully extracted and characterized for its applicability as a strengthening material in polymers to use in different applications.The physiochemical evaluation of BTAR filler revealed that the filler possessed 40.13% of cellulose, 15.22% of hemicellulose and other components.The density was recorded as 0.27 g cc −1 which makes BTAR filler a potential reinforcing candidate in light weight polymer composites.The filler's average particle size was 136.3 μm.Still, the bulk of the particles were within the 100-200 μm range.The filler's rough surface and some micropores, as revealed by the morphological study, help to improve the bonding between the filler and the polymer matrix.The filler's outstanding thermal stability was demonstrated by the thermograms obtained from the thermogravimetric study of the material.The analysis led to the conclusion that the BTAR filler, particularly for future lightweight applications including those for the composite filament making for 3D printers and might be employed successfully as a reinforcing filler in polymer composites.

Table 2 .
CI and CS of BTAR filler with other reported materials.