Extraction and Characterization of Novel Natural Fiber from Cryptostegia Grandiflora as a Potential Reinforcement in Biocomposites

ABSTRACT The significant environmental pollution caused by synthetic fibers drew researchers’ attention to the development of eco-friendly reinforcement for composite products. This study seeks to identify an alternative novel natural fiber from the Cryptostegia Grandiflora (CG) plant as a reinforcement material for bio composites. The fiber chemical compositions, X-ray diffraction, Fourier Transform Infrared spectroscopy (FTIR), Scanning Electron Microscopy, Thermo Gravimetric Analysis, and tensile test for single fiber are all examined. The fiber had a cellulose content of 79.20% and a crystallinity index of 62%. Thermo Gravimetric Analysis confirms that Cryptostegia Grandiflora fiber (CGF) can withstand temperatures as high as 230°C. It has a density of 1.02 g/cc and a tensile strength of 791 MPa on average. This novel Cryptostegia Grandiflora fiber will undoubtedly be used as reinforcement material in bio-composite materials.


Introduction
The last three decades have been the golden era of material development in engineering applications, with the use of synthetic fibers increasing in composite products; it provides good strength and a significant contribution to ancillary products. Now that we know it causes high carbon emissions, we are focusing on developing eco-friendly composite products for engineering applications. As a result, natural fiber has the potential to replace synthetic fiber in composite industries while also being biodegradable (Belaadi et al. 2014;Jawaid et al. 2014;Kommula et al. 2013;Reddy et al. 2014;Sudhakara et al. 2013).
Composites are classified into three types: polymer matrix, metal matrix, and ceramic matrix composites. Due to its advantageous qualities, such as strength, durability, and elasticity, synthetic fiber is reinforced with a matrix in polymer matrix composites. However, synthetic fiber is nonbiodegradable and releases more carbon into the environment. As a result, much research is being conducted on environmentally friendly natural fibers as suitable substitutes for man-made fibers in polymer matrix composites (Jayaramudu et al. 2014;Reddy et al. 2012).
Usually, natural fibers are taken from several parts of the plant including, seeds, stems, and leaves (Thakur, Kumari Thakur, and Kumar Gupta 2014). The geological aspect of the plant determines the chemical composition of the fibers, which influences the plant fiber's properties (Madhu et al. 2019). The percentage of cellulose in natural fiber determines its strength (Kumar and Singha 2010). Natural fiber-reinforced composite properties are based on fiber selection and the matrix utilized during fabrication (Vijay et al. 2022). Surprisingly, the modulus of some natural fibers is higher than that of manmade fibers (Kommula et al. 2013). Many researchers and scientists are working to develop novel fibers with reinforcement polymer matrices that are used in aircraft, automobiles, sports, food packaging, and construction (Reddy et al. 2015).
Natural fibers are hydrophilic because they are made up of cellulose and hemicellulose layers. Natural fibers' inherent hydrophilicity makes it possible for them to absorb moisture. The hydrophilic property reduces the interaction adhesion of reinforcement with resin, lowering composite performance (Asyraf et al. 2022;Bahrain et al. 2022).
In the United States of America, composite construction materials for building construction are made from a straw. Many auto parts are made of natural composites based on fibers like flax, jute, and sisal. The interior door panel of the Mercedes-Benz S-Class was made in Germany in 1999 with 35% Baypreg F semi-rigid (PUR) elastomer and 65% flax, jute, and sisal blend. An epoxy matrix containing hemp was also used in the door panel products of Mercedes-Benz E-Class vehicles.
Toyota Motor Corporation has developed an eco-plastic material made from sugar cane for car interior panels. Audi AG introduced polyurethane-reinforced eco-friendly door panels made of a flax/ sisal composite in 2000. Natural fiber plays an important role in the creation of green composites in the twenty-first century, so researchers must lay a solid foundation in order to create new opportunities for natural fiber composites (Sanjay et al. 2016).
This study aims to extract a novel potential fiber from the stems of the plant Cryptostegia Grandiflora and investigate its properties for reinforcement in biocomposites. Cryptostegia Grandiflora is a rubber vine native to southwest Madagascar that belongs to the Apocynaceae family. As a shrub, a Cryptostegia Grandiflora can grow up to 2 meters (6 feet) tall, but as a vine, it can grow up to 30 meters (100 feet) long with the support of another plant. Cryptostegia Grandiflora plants are predicted to live up to 80 years. It can produce over 8000 seeds in a single reproductive cycle and produce seeds twice every year. It is widespread in worldwide but it is eradicated as it is an invasive species (Bekele, Seifu, and Ayenew 2019;Luizza et al. 2016;Rodríguez-Estrella et al. 2010). The purpose of this study is to identify the fundamental characteristics of Cryptostegia Grandiflora fiber using chemical composition analysis, X-ray diffraction analysis (XRD), Fourier transforms infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM), thermal analysis, and a single fiber tensile test.

Fiber extraction
The CG plant stems are obtained in the Virudhunagar District of Tamil Nadu, India. The CG plant stem has a length of 6-10 feet. The stems are cut to the desired length with a knife before being manually peeled for fiber extraction. These peeled parts are immersed in water at room temperature for 7-10 days. The peeling parts become wet during the water-retting process. Since gum is present in the extracted fibers, they are roughly washed to eliminate unwanted particles. The bundles of dried fibers are collected for further research after they are dried in sunlight for at least 2-4 days to reduce the moisture content. The extracted processes of CG fibers are shown in Figure 1.

Physical and chemical analysis
This study evaluates the percentage values of hemicellulose, cellulose, wax, ash, moisture content, pectin, lignin, density, and diameter. The weight percentage of cellulose is calculated using Kurcshner and Hoffer's method, while the percentage of hemicellulose is measured using the NFT 12-008 standard. CGF's lignin content is calculated using the APPITA P11s-78 method. The ash and moisture content is determined using the IS 199 method. The Conrad method is used to determine the wax percentage. The fiber density of Cryptostegia Grandiflora is calculated using the ASTM D 2320-98 (2003) standard (Manimaran et al. 2018). The apparent fiber diameter is measured using a Leica DM750 M optical microscope. A total of 30 specimens are used to account for natural fiber variability, and an average value is reported.

X-ray diffraction analysis (XRD)
To determine the CGF's phase identification, an X-Ray diffraction analyzer with a monochromatic intensity of CuKα radiation is used. The crystallinity index (CI) is calculated using equation 1. In equation (1), H 22.6 and H 16.61 represent the values of the height of the peaks at 2θ = 22.6 and 2θ = 16.61. Scherrer's formula is used to calculate the crystallinity size (CS).

Fourier Transform Infrared Spectrometry (FTIR)
FTIR spectroscopy is performed to determine the functional groups in the chemical composition of the fiber. The spectrometer is kept at 30 degrees Celsius and 65% relative humidity. The spectrum is scanned at 32 scans per minute in the range of 4000-400 cm −1 with a resolution of 2 cm −1 .

Surface morphological analysis
A Scanning electron microscope (SEM) test is performed by the Carl Zeiss model to study the surface morphology, surface roughness, cell wall structure, and other constituents of the Cryptostegia Grandiflora fiber. SEM images with different magnifications are useful in analyzing the surface morphology of fibers.

Thermal Analysis (TA)
Thermo Gravimetric analyzer is used to calculate the thermal stability of the Cryptostegia Grandiflora fiber on Perkin Elmer (STA 8000). The requisite amount of CGF is weighted and kept in an alumina crucible within a heating chamber. The temperature maintained for the fiber at a constant rate of 5°C/ min from 30°C to 700°C in an inert atmosphere. Nitrogen gas is used as an inert environment. The weight loss in the fiber was observed when the temperature is raised (Narayanasamy et al. 2020).

Tensile test
To test the tensile strength of CGF, a 100 g load cell ZwickRoell Universal Testing Machine is used undergoing the ASTM D 3822-07 standards (Baskaran et al. 2018). The test is carried out at a temperature of 21°C and relative humidity of approximately 63%. A gauge length of 50 mm and a crosshead speed of 1 mm/min are used to test 30 single fibers and the average value is reported.

Physical and chemical analysis
It is preferable to have a smaller diameter of fiber in order to get better mechanical properties (Ganapathy et al. 2019). The CGF's diameter is 117 µm. The diameter of the fiber is mainly controlled by soil conditions, regional climatic conditions, plant age, and extraction methods (Premalatha et al. 2021;Vinod et al. 2020). The CGF's diameter is measured using an optical microscope as shown in Figure 2.

XRD analysis
The crystalline peak is identified for CGF, the highest peak is found at 2θ = 22.6° whereas the lowest is at 2θ = 16.61°. As per the high peak, the fiber has a crystallographic plane of cellulose -I and the lower intensity proves the fiber contains a more amorphous region which includes amorphous cellulose, lignin, hemicellulose, and pectin (Mayandi et al. 2016). CGF has a calculated crystallinity index of 62%, which is higher than the crystallinity indexes of other natural fibers such as Calotropis gigantea (56.08%), Coir (57%), and Dracaena reflexa (57.32%). Also lower than Banyan tree aerial root (72.47%) and Hemp (87.87%). A high crystallinity index indicates crystalline nature, which is advantageous for using fiber as potential reinforcement in composites (Ganapathy et al. 2019;Raja et al. 2021;Vinod et al. 2020). The calculated crystallite size of Cryptostegia Grandiflora fiber is 20.6 nm.

FTIR analysis
In the FTIR analysis, the chemical functional group observed in the FTIR peak once again confirms the existence of cellulose, wax, hemicellulose and lignin. The peak intensities in the region of 613,667,896,1061,1161,1240,1371,1431,1647,1742,2887,2940 and 3416 cm −1 are associated with the different significant modifications, according to this analysis. CGF's, FTIR peaks are shown in Figure 4. The OH bonding of cellulose is attributed to the broad absorption peak at 613 cm −1 (Ramasamy, Obi Reddy, and Varada Rajulu 2018). The large absorption peak at 667 cm −1 is attributed to cellulose bonding due to out-of-plane COH bonding. Hemicellulose is found to have characteristic peaks at 896 cm −1 , which correspond to CCH, COC, and CCO stretching vibration and deformation of cellulose (Senthilkumar et al. 2019). The lignin's symmetric COH stretching is represented by the observable  peak at 1061 cm −1 (Hyness et al. 2018). The CO stretching vibration of an acetyl group in lignin is accountable for the absorbance peak at 1240 cm −1 (Sumrith et al. 2020). The wide and intense absorption peaks seen at 1647 cm −1 represent the CO stretching vibration of lignin composition (Manimaran et al. 2018). The occurrence of the CO group in hemicelluloses is shown by the highest concentration at 1742 cm −1 (Sumrith et al. 2020). The CH bonding vibrations from CH 2 group cellulose and hemicellulose correlate to the peak at 2887 cm −1 (Atiqah et al. 2018). The CH stretching vibrations in cellulose and hemicellulose recorded the largest proportion at 2940 cm −1 ; whereas OH stretching vibrations of cellulose's hydrogen bond of hydroxyl groups produced the highest proportion at 3416 cm −1 (Kumar et al. 2018). Figure 5 shows the irregular surface of the fiber, and the impurities and organic ingredients found on it.

Surface morphological analysis
The hemicellulose and lignin influence the uneven surface caused by the extraction process and the impurities present on the surface of the fiber (Narayanasamy et al. 2020). FTIR and XRD analysis show that hemicellulose and lignin are present on the fiber surface. Hence, chemical treatment is required to remove these fiber impurities and improve interfacial adhesion with the polymer matrix before the preparation of polymer matrix composites.

Thermal analysis
The TGA curve of the CG fiber and its DTG derivative showed in Figures 6 and Figure 7.
Thermal stability is an important factor to determine the use of natural fiber as reinforcement in biocomposites (Fiore, Scalici, and Valenza 2014). The hydrophilic nature of natural fibers has been noted by several authors as an initial mass loss (6.65%) between 30°C and 110°C due to the evaporation of moisture content from the fiber (Belouadah, Ati, and Rokbi 2015;Fiore, Scalici, and Valenza  2014). Then, the thermal stability of Cryptostegia Grandiflora fiber observed up to 230°C is evidenced by the DTG curve. Thermal degradation begins with a higher degree of chain branching and a more diverse set of polysaccharides in hemicellulose, which leads to a lower degree of polymerization, causing hemicellulose to degrade and the linear polymeric chain of cellulose to degrade (Nurazzi et al. 2021). The second mass loss of 62% is discovered between 230°C and 340°C, indicating the start of CGF degradation. This is due to the degradation of hemicelluloses, pectin, and cellulose's glycoside bonds. The peak found at about 300°C suggests that cellulose I and α -cellulose may have decomposed. Similar peaks for jute, bamboo, hemp and kenaf fibers have been recorded in the literature at 298.2, 321, 308, and 307.2°C, respectively (Indran, Edwin Raj, and Sreenivasan 2014). At 455°C decomposition of lignin occurs (Maache et al. 2017). According to TGA and DTG studies, it is concluded that Cryptostegia Grandiflora fibers are suitable for low-temperature composite applications.

Tensile test
The tensile properties of raw CGF are reported in Table 2.
When subjected to a tensile load, the fibers of Cryptostegia Grandiflora exhibit nonlinear deformation after linear deformation. This nonlinear deformation is caused by a weakened primary cell wall and delamination between fiber cells (Belouadah, Ati, and Rokbi 2015). CGF has a tensile strength of 791 MPa, which is greater than sugar palm (156.96 MPa), jute (690 MPa), pineapple (627 MPa), and sisal (535 MPa), but less than flax (1035 MPa) (Nurazzi et al. 2021). Various combinations of cellulose with other constituents in fibers factor in variations in the mechanical properties of natural fibers (Ding et al. 2022).
The mechanical properties of natural fibers are determined by the cellulose percentage, microfibril angle, and degree of polymerization (Santhanam et al. 2016). When the fiber attained ultimate tensile strength, failure occurs immediately due to the presence of lignin in the fibers, resulting in brittle fracture (Vijay et al. 2022). The elongation at break of Cryptostegia Grandiflora fiber is 3.1%, comparable to flax (3.2%), ramie (3.8%), and Hemp (1.6-4%) (Nurazzi et al. 2021). Hence, Cryptostegia Grandiflora fiber can be used as a potential reinforcement in composites. Figure 8 illustrates the tensile properties of the CG fiber.

Conclusion
A new natural cellulosic fiber from the plant Cryptostegia Grandiflora is extracted and its properties are studied. Chemical analysis showed the cellulose and density content of Cryptostegia Grandiflora fiber to be 79.20% and 1.02 g/cc respectively. XRD and FTIR studies confirm the chemical functional groups and semi-crystalline structure of CGF. Also, the calculated crystallinity index from the X-ray diffraction pattern is 62%. Uneven and rough surfaces of CGF were observed in SEM images, indicating improved mechanical bonding with the matrix in the composite. The fibers can withstand up to 230°C, making them suitable for composite reinforcements. Cryptostegia Grandiflora fiber has a tensile strength of 791 MPa. The detailed characterization studies on Cryptostegia Grandiflora fiber conclude that it is desirable for the development of lightweight composites for automobile interiors and packaging applications due to its significant mechanical, thermal, physical, and chemical properties.

Highlights of this article works
(1) A novel natural fiber extracted from Cryptostegia Grandiflora for reinforcement of polymer materials.