A Review on Cellulose Fibers from Eichornia Crassipes: Synthesis, Modification, Properties and Their Composites

ABSTRACT Eichornia crassipes, ECs is an abundant source of natural fiber, environmentally friendly, and has a great potential to be used as filler in polymer composites. This literature review aims to provide the latest information on ECs synthesis, properties, and ECs-reinforced composites. Modification of the properties of ECs using alkaline chemicals is also discussed in detail through changes in physical, chemical, thermal, and mechanical properties, as well as fiber morphology. After being modified by alkaline chemistry, the fiber density of ECs can be reduced by around 20.69%, and the cellulose content of ECs can reach 90.24%. This literature review also discusses the physical, mechanical, and thermal properties of ECs-filled polymer composites from the results of the latest research and innovations. Polyester reinforced ECs with a length of 10 cm have modulus of elasticity and tensile strength of 11,023.33 N/m2 and 648 N/m2, respectively. Potential applications of ECs composites for product development; cost-effective and efficient replacement of inorganic fillers such as; gypsum, cooling pad, and pulp and paper. This study is expected to be a reference for the development of Eichornia crassipes fiber-filled composite technology for both industry and scientists.


Introduction
The shift toward a bio-based economy and sustainable development because of developing countries on greenhouse gas reduction and CO 2 neutral production offers a high perspective for the natural fiber market. Indonesia country as one of the countries producing natural fiber commodities is very numerous and varied (see in Figure 1). Natural fibers from plants can be obtained from plant parts carbon fiber manufacture, etc. (Asrofi et al. 2017;Chonsakorn, Srivorradatpaisan, and Mongkholrattanasit 2019).
In this review, we provide a more detailed overview of EC synthesis and modification with various chemical solutions such as HCL and NaClO-NaOH-NaClO. Chemical abilities, thermal characteristics, tensile and bending properties, and their composites and applications in the industrial sector are all characteristics of Eichornia Crassipes fibers (ECs).

Plant of Eichornia Crassipes
Eichhornia Crassipes plants are found in almost all countries in the world such as Indonesia, India, Japan, China, Burma, Mexico, etc. This plant (see Figure 2) is known to grow rapidly in water that is high in nutrients, containing nitrogen, potassium and phosphate. Eichhornia Crassipes plant is often considered a weed because it easily spreads through waterways to other water bodies (Davies and Mohammed 2011). The length, width and thickness of the leaves of ECs averaged 4-16 cm, 4-12 cm and 0.43 mm, respectively (AL-Hadeethi et al. 2017;Davies and Mohammed 2011), while the upper, middle and lower diameters were significantly different at 5% probability (Davies and Mohammed 2011).
The dimensions of the Eichhornia C. section are very important for the size and sorting equipment (see in Table

Extraction of Eichhornia Crassipes fiber (ECs)
The Eichhornia C. stem parts that have been separated from the leaves and ECs are shown in Figs. 3. Eichhornia Crassipes is known to contain a lot of cellulose fiber and is elastic (Ajithram, Jappes, and Brintha 2021;Nugroho and Ismail 2020;Tan et al. 2008). Sources of fiber from ECs can be obtained from the stems, leaves, and roots of the Eichhornia C. plant but the most abundant source of fiber found in the stem is about 60%. Fiber extraction from Eichhornia C. as shown in Figure 4. In this process, plant parts are extracted by pouring a 15%-25% NaOH solution into boiling water. Then the Eichhornia C. stems are put into the solution for 5 minutes (Wolok et al. 2018). However, this process is rarely used because it is harmful to humans and the environment. Several other researchers have also used the retting process for plant extraction followed by drying and combing for uniform fiber extraction. Extraction of Eichhornia C. using the retting process as shown in Figure 4.

Hydrochloric acid (HCl)
Modification of ECs properties can be done by giving an alkaline chemical treatment on the surface of the ECs. Chemical treatment of ECs in a solution of HCl is known to remove non-cellulose compounds from the fiber; so that the mass lost is 20.69% of the ECs. HCl is known to be able to react with xylose in hemicellulose but is unable to break benzene bonds in lignin. HCl solvent can penetrate the wax wall and react with organic compounds in ECs. The reaction between non-cellulose  compounds and HCl is known to not occur if ECs are immersed in a solvent of 400 mL of HCl solution (1 M) for 2 hours without heating (Spiridon, Teacă, and Bodîrlău 2011).

NaClo-NaOH-NaClo
400 mL of NaClO (0.5N) and 2 mL of the glacial acetic acid solution for 1 hour (NaClO-NaOH-NaClO) were known to remove more non-cellulosic compounds from ECs than other solvents. Noncellulose compounds such as lignin, pectin, and hemicellulose are degraded and separated from the fiber as a result the mass of ECs also decreases very much. T6e cellulose content of ECs after soaking in NaClO-NaOH-NaClO is known to be 90.24% (Spiridon, Teacă, and Bodîrlău 2011). The comparison of the mass loss of each solvent is shown in Figure 5. The alkalization and oxidation processes are able to break the C=O ester bonds in non-cellulose compounds, even the oxidation solution which in this case is NaClO is able to break the benzene bonds in lignin.

Chemical composition of ECs
Like other natural fibers, ECs is known to contain cellulose, hemicellulose, lignin, ash, and small amounts of Calcium (Ca), Sodium (Na), Magnesium (Mg), Ferrous (Fe), Copper (Cu), etc. as shown in Tables 2 and 3. The cellulose content in roots was found to be the highest at 16% wt) and the lowest found in stems at 8.4% by weight. Other literature states that the cellulose content in ECs can reach 18.2%, and can also reach 63.75-64.51 (wt. %) (Nugroho and Ismail 2020). The hemicellulose content of the ECs is in the range of 3-49.3% wt) (Nugroho and Ismail 2020;Spiridon, Teacă, and Bodîrlău 2011). Various values of the chemical content of the fiber indicate that the amount of chemical content of ECs is influenced by the habitat and environment in which the ECs. plant grows. Cellulose is a structural polysaccharide that is responsible for providing protection, shape, and support to cells and tissues. Cellulose molecules are arranged in the form of fibers because composed of several parallel molecules linked by glycosidic bonds.
Hemicellulose is related to water absorption properties, and lignin is related to fiber stiffness.

Fourier transfer Infra-red (FT-IR) Spectroscopy of ECs
FT-IR spectroscopy of ECs (shown in Figure 6) is known to have bands at 1033.85 cm −1 and 1242.16 cm −1 corresponding to the strong intensity of the CO strain which indicates the presence of cellulose,  (Cerchiara et al. 2010). Figure 7 shows that the Differential Scanning Calorimetry of the ECs. From Figure 7 it is known that the glass transition (Tg) of ECs is known to be in the range of 72.7°C. The fiber persists up to 498.3°C and is left as a residual mass without breaking down.

Physical and mechanical properties of ECs
ECs obtained by extraction are known to have a fineness of 7 tex (the smallest fiber) with a moisture content of 15% − 17.64%, while the density of leaf, stem, and root fibers is 0.048-0.074 g/cm 3 , 0.217-  0.303 g/cm 3 and 0.070-0.096 g/cm 3 respectively (Adeleke et al. 2020). This value is lower than that of sugarcane fiber and coconut fiber with densities of 0.36 g/cm 3 and 1.36 g/cm 3 , respectively. Furthermore, the tensile strength of this fiber was found in the range of 45.5 gf − 384 gf with an elongation of 2.5% ± 1.1%. The physical and mechanical properties of ECs are detailed in Table 4.

Morphology of ECs
The morphology of ECs under scanning electronic microscopy (SEM) showed the presence of some layers of lignin and hemicellulose (Cerchiara et al. 2010), as shown in Figure 8. The structure of the ECs surface is shallow which indicates that there are cavities in the ECs bundle called lumens and also indicates that the fiber has good absorption. The presence of some lumens in the ECs bundle is known to affect the density of the fiber (Purboputro 2017), it can be utilized as a composite sound-dampening filler material .

Tensile strength and modulus of elasticity
One of the parameters that have an important role in determining the mechanical properties of the composite is the length of the ECs, fiber content, and the orientation of the fibers in the composite.
Conforming to the ASTMD 3039 standard, polyester composites reinforced with ECs with a length of 10 cm are known to have a maximum modulus of elasticity of around 11,023.33 N/m 2 than fibers with a length of 2 cm, as shown in Figure 9a (Purboputro 2017).  Furthermore, as a reinforcing material for polymer composites, several ECs content can provide different mechanical strengths to polyester composite materials. When the ECs content is 10% (% vol.) in the composite, the tensile strength of this composite can reach about 27.27 Mpa (see Figure 9a). The tensile strength properties of the composite will tend to decrease when the fiber content increases; it is due to the bond strength between the fiber and resin in the polyester composite (Ajithram, Jappes, and Brintha 2021) because the amount of matrix decreases. The resin does not completely wet the fiber causing the force to not be distributed optimally because the bonds between the fibers are weak so that the strength tends to decrease. Figure 9b shows that the strain value of the composite fluctuated with increasing ECs. The strain value of the composite is known to be high when the ECs content is 20% (9.29%), and above 20% the strain value can decrease by about 7.52% − 7.66% (Yudo and Kiryanto 2012). The maximum modulus of elasticity of the composite can be obtained when the fiber content of 10% is 318.3 MPa and this value will tend to decrease when the ECs content is >20%; because the composite tends to be elastic (see Figure 9c).

Impact strength
The highest impact strength of the ECs composite is known to achieve 2,344 J/m 2 when utilizing a 5 cm long fiber, according to the ASTMD 256 test technique. For fiber lengths of 2.5 cm and 10 cm, the value of the impact strength of the composite can reach 1.0836 J/m 2 and 1.6115 J/m 2 . Longer fibers are known to decrease the impact strength properties of composites because the uneven distribution of fibers due to the overlapping of fibers causes the absorbed energy to be smaller by forming brittle fractures (Yudo and Kiryanto 2012). The ECs content in the composite is also known to affect the value of the impact strength of the composite (see Figure 10).

Thermal properties of ECs composites
Thermal properties of composites with ECs raw and treated have shown in Figs. 11,Figs. 12. In the raw ECs reinforced composites polypropylene (PP), the initial peak was at temperatures between 260°C and 350°C which was associated with decomposition thermal of hemicellulose, and the glycosidic linkage of cellulose. After this peak, the curve corresponding to the ECs-PP composite treated with Benzenediazonium salt solution (NNDMA)/NaOH showed a single peak at 469°C, while the crude ECs-PP composite showed a peak at 462°C. The DTG curve of Benzenediazonium (Anl)/NaOH treated with ECs-PP composite showed a single decomposition with the highest peak at the decomposition temperature of 478°C. The peak in the range of 400-500°C is caused by the thermal decomposition of lignin and cellulose. The thermal stability of treated ECs-PP composites was higher than that of Benzenediazonium salt, (NNDMA)/NaOH composites, raw ECs-PP composites in terms of the highest value, final decomposition temperature, and the largest amount of residual mass. Raw ECs-PP composites are known to exhibit the lowest thermal stability due to good interfacial adhesion between ECs and PP; as a result of uniform fiber dispersion throughout the PP. The detailed thermomechanical properties of ECs composite are shown in Table 5. The release of volatiles from the composite during thermal degradation is hindered by the dispersal of the filler. It may also be attributed to the adsorption effect of volatile gases on the fiber surface to slow down the decomposition rate of the polymer composite (Prasetyaningrum, Rokhati, and Rahayu 2009).

Flexural properties of ECs composite
The flexural strength of raw ECs-PP composites which refers to the results of the evaluation of the flexural test for the ASTM790 standard is known to be optimal when the fiber content is 25% (see Figure 13), but above this strength will decrease. The flexural strength of these ECs composites will be high when the ECs are chemically treated and optimal strength can be achieved at 35% fiber content.
The stable behavior of the flexural strength of the ECs treated -PP composites indicated that the fiber content could help increase the adhesion of the PP-ECs interface to become stronger. The ECs treated -PP  composites (NNDMA)/NaOH are known to have 10-28% higher flexural strength compared to other ECs-PP composites. And the increase was 4-11% over the treated (Anl)/NaOH ECs-PP composites (see Figure 13). The addition of ECs to PP is known to significantly increase the composite modulus (Putri and Mahyudin 2019). Since ECs have a high modulus, a higher fiber concentration in the composite demands stronger stresses for the same amount of deformation. As a result, the flexural modulus of the composite increases with increasing fiber content. Both flexural strength and modulus were found to be higher for chemically treated ECs, which may be due to better fiber-matrix interface adhesion and effective stress transfer from matrix to fiber (Alzate et al. 2022).

Sound absorption properties of ECs based composite
The sound absorption capabilities of polyurethane foam (PUF) composites are known to be affected by variations in ECs size. Because the presence of ECs in the PUF composite causes high porosity (see Figure 14), which is the dominant factor in absorbing sound, PUF filled with ECs with a mesh size of 80 is known to have a sound absorption coefficient value of 0.92, which is suitable for application as a sound-absorbing material. Sittinun, Pisitsak, and Ummartyotin (2020) found that the existence of porosity in this PUF/water hyacinth (ECs) composite may absorb oil as well. Figure 15 depicts the method of making a PUF composite packed with ECs.

Application of ECs composite
Composite-filled ECs have many usages or applications in industries, for example, gypsum, cooling pad, fiberboard, pulp and paper, supercapacitor applications, and others. The applications are further Table 5. Thermomechanical and morphological properties of Eichhornia C. fiber reinforced polypropylene composites (Prasetyaningrum, Rokhati, and Rahayu 2009  explained in the next section. Some of the potential applications of ECs composite are tabulated in Table 6.

Gypsum
Gypsum board made from 20% by weight of chopped ECs with castable flour matrix is known to have a tensile strength, compressive strength of moisture content, a water absorption capacity, and a thickness expansion of 4.17% of 19 N/m 2 , 18.44 N/m 2 , 5.96%, 57.1%, respectively. The density of ECs filled into PUF composites (c) 3% ECs filled into PUF composites (d) 5% ECs filled into PUF composites (e) 7 % ECs filled into PUF composites (Sittinun, Pisitsak, and Ummartyotin 2020). this gypsum is in the range of 1248 Kg/m3-1782 Kg/m 3 , where this density value meets the JIS A 5908-2003 standard (Alzate et al. 2022). Furthermore, increasing ECs in the gypsum composite is known to tend to decrease the properties associated with large pores of ECs. In addition, the unevenness of the gypsum constituents causes the density value to be below. The morphology of the gypsum composite surface showed the presence of a white color (gypsum flour and castable flour), and black color was ECs, as shown in Figure 16.

Cooling pad
ECs have also been known to replace carbon fiber in the manufacture of cooling pads with a composition of 10 g of ECs and 20 g of flour (Yudo and Kiryanto 2012).
Fiberboard (MDF) ECs can be used as raw materials for making fiberboard. MDF can be an inexpensive, durable, and sustainable material that can replace wood. MDF from a mixture of ECs 20 (wt%) with ureaformaldehyde (UF) resin can be produced using the hot press technique. The physical and mechanical properties of this board are known to meet the American standard for Medium Density fiberboard (ANSI), Indian Standard (IS), and Australian/New Zealand Standard (AS/NZS). Eichornia C. fiberboard can be a cheap, sustainable, and durable material that can replace wood and reveal new ways to wisely use this aggressive weed. The modulus of elasticity and the modulus of rupture of the boards are known to be 3135 MPa and 31.25 MPa, respectively. This board has an expansion of board thickness and water absorption properties of 48.41% and 71.03%, respectively (Davies and Mohammed 2011).

Pulp and Paper
ECs biomass can also be used as an alternative raw material in the process of making pulp and handmade paper using the KOH pulping method at alkali concentrations (8-12%) with a liquor to   (Sittinun, Pisitsak, and Ummartyotin 2020) solid ratio of 7:1 at 145°C for 2 h. While a by-product of the process can be used to improve the nutritional quality of compost. Such cottage-industry production of EC green products could be developed to control EC infestation in water bodies (Islam et al. 2021). The pulp of this ECs is known to have light properties and is wear-resistant (Alzate et al. 2022).

Electrode material
Ananas comosus blend Eichornia C. in polyester composite coated with polypyron was reported to have a high areal capacitance value of 104.31 mF.cm −2 , good volumetric power of 0.1362 Wh. L −1 and an energy density of 16.03 WL −1 at 1 mA.cm −2 , which is promising as electrode material for supercapacitor applications (Alzate et al. 2022;Jirawattanasomkul et al. 2021). Compared with polyester composites, these electrode composites also have higher electroactivity properties, good tensile strength, and electrochemical performance.

Concrete reinforcement
The development and utilization of Eichornia C waste as reinforcement of polymer composites for reinforced concrete has been reported by Jirawattanasomkul et al. (2021). The presence of EC in polyester composites is known to increase strength and ductility performance, are acceptable for concrete reinforcement purposes compared to conventional fiber-reinforced polymer composites. More importantly, the use of ECs-reinforced polymer composites is rewarded by their environmental friendliness, as evidenced by less water consumption during production and a reduction in natural waste.

Conclusions
Eichornia C. (ECs) is an excellent filler polymer composite material choice. A fantastic potential for the industrial industry to develop goods built from abundant and sustainable natural fibers. The cellulose content may be increased by 90.24% after soaking in a solution of NaClO-NaOH-NaClO, and the ECs fiber can endure a temperature of 498.3°C. The fiber's tensile strength ranges from 45.5 gf to 384 gf. Furthermore, when the fiber content is 10%, the composite's maximum modulus of elasticity may reach 318.3 MPa, and when the fibers are arranged in a unidirectional orientation, the composite's tensile strength and modulus of elasticity can reach 648 N/m 2 and 472.46 N/m 2 , respectively. Because of the good interfacial adhesion between ECs and PP, raw-PP composite ECs are known to have poor thermal stability. Because of their superior physical, mechanical, thermal, and structural properties, ECs are now employed in a broader range of applications such as gypsum, cooling pads, supercapacitors, and others. The morphology of ECs under SEM showed the presence of shallow and there are lumens; indicates that the fiber has good absorption. We can design desired composite qualities and enhance the role of plant fibers by combining ECs mixed polymer composites with various other fibers. More emphasis should be paid to the function of reinforcing fibers in future research on composites constructed from ECs. Experimenting with different fiber characteristics can be used to design composite properties.