Hydrothermal treatment of sorghum (Sorghum bicolor (L.) Moench) stalks for enhanced microfibrillated cellulose production

Microfibrillated cellulose (MFC) derived from natural fibers has gained significant interest as an environmentally friendly material for economic and ecological reasons. Sorghum (Sorghum bicolor (L.) Moench), a widely cultivated crop that generates waste during bioethanol production, holds the potential for producing MFC and can be used for enhancing polymer’s performance, particularly in terms of crystallinity. The hydrothermal treatments aimed to unbundle lignocellulose networks into MFC with reduced amorphous content and enhanced crystallinity The hydrothermal treatments, necessitating specialized apparatuses and exhibiting limited scalability, can be effectively replaced by the domestic pressure cooker, an alternative intriguing vessel for the simple, cheap, and economical hydrothermal reactor. Hydrothermal treatments using pressurized steaming methods were performed at different durations (5, 25, and 60 min), in which the fibers were positioned above the water level to enable targeted interaction with the steam. Characterization of the treated fibers namely chemical composition, morphology, crystallinity index, and thermal stability were analyzed using FTIR spectroscopy, FE-SEM, XRD, and TGA. The results demonstrate the removal of binding materials, such as amorphous hemicellulose and lignin, from the sorghum fibers, leading to fiber defibrillation and producing MFC size range from 12.2 to 19.4 μm. Hydrothermal treated fiber started to decompose at Tinitial around 275 °C–282 °C higher than fiber untreated Tinitial = 229 °C. The 5 min treatment has generated the highest crystallinity index (52%) and the highest maximum peak temperature (365.26 °C). Additionally, the treatments have increased the fibers’ crystallinity index and thermal stability, highlighting the potential use of sorghum fiber as a reinforcement candidate in natural fiber polymer composites.


Introduction
In recent decades, significant advancements have been made in developing fiber-reinforced polymer composites using synthetic fibers to meet the demands of engineering applications. Nonetheless, the increasing environmental consciousness toward attaining sustainability in manufactured goods has created a demand for more environmentally friendly materials emphasizing renewable raw materials in product design [1,2]. The rapid development of natural fiber-reinforced polymer composites is one of the most promising strategies for reducing the use of synthetic fibers as reinforcement and filler materials in polymer composites. The emphasis on new environmental regulations, concepts of sustainability, and the increase of ecological, social, and economic awareness, combined with the high cost of petroleum resources, has increased the significance of optimal utilization of natural resources [3]. Natural fiber-reinforced polymer composites are considered an environmentally friendly alternative to polymer composites reinforced with glass or carbon. In addition to aiding in the reduction of waste disposal, natural fibers utilization contributes to the reduction of environmental contamination. As sustainable materials, natural fibers have gained popularity in various applications, mainly as reinforcements in composite materials. They offer substantial advantages over conventional glass fibers, allowing them to compete in contemporary industrial applications. There are several advantages of natural fiber-reinforced composites over synthetic fiber-reinforced composites, such as renewability, reduced equipment abrasion, biodegradability, high specific strength, cost-effectiveness, non-corrosive, and nonhazardous nature, and manufacturing versatility [4][5][6][7][8].
Currently, the most important industrial source of cellulose is natural fiber. Besides cellulose, natural fiber consists of hemicellulose, lignin, extractives and inorganic compounds [9,10]. Unlike cellulose, hemicelluloses and lignin are amorphous matrix components that do not form fibrils or fibers and are rarely used as reinforcing agent. Consequently, using various treatments to isolate cellulose fibers, hemicelluloses and lignin are typically separated from natural fiber. Cellulose in its crystalline form, namely microfibrillated cellulose (MFC), has been shown to be effective as a reinforcing for producing eco-friendly composites. Their rigidity characteristics and high crystallinity make them potential composite reinforcements [6,11,12]. Sorghum (Sorghum bicolor (L.) Moench) is the fifth most important cereal crop following maize, wheat, rice, and barley in global cultivation. Sorghum plants are composed of 15% sorghum grains, 10% leaves, and 75% stalk by weight [13]. In addition to sugarcane, the glucose content of sorghum stalk has tremendous potential as an alternative feedstock for bioethanol production. Nonetheless, the bioethanol production process generates a lot of bagasse residue. This sorghum bagasse is fibrous and contains a higher concentration of cellulose (21%-49%) than sugarcane bagasse and rice straw, as well as hemicellulose (14%-33%) and lignin (17%-30%) [13][14][15][16]. Due to its high cellulose content, sorghum could be used as a polymer composite reinforcement to improve its efficacy and crystallinity [10,17].
The extraction of MFC from natural fibers, mainly from cellulose which are chemically bonded to hemicellulose and lignin, can be conducted via biological, physical, or chemical treatments. Chemical treatment, especially alkali treatment, is relatively straightforward among the various methods employed to extract MFC [6,18]. However, chemical treatment procedures exhibit several limitations that hamper their industrial application. Notably, these methods are often indicated by extended processing times, higher production costs, and the use of chemicals, posing potential dangers regarding hazardous waste generation and environmental impacts [19][20][21]. On the other hand, hydrothermal treatment is a thermo-mechanical-chemical defibrillation method widely regarded as an environmentally friendly technique for extracting MFC. This technique involves both chemical modification and mechanical defibrillation. By exposing the fibers to elevated temperatures, organic acids are produced, resulting in the decomposition of lignocellulosic structural components. The application of shear forces further contributes to mechanical defibrillation. There are three crucial mechanisms to extract the MFC from lignocellulosic structures, namely hemicellulosic hydrolysis, alteration of the chemical structure of lignin, and modification of the crystallinity index of cellulose. This treatment removes amorphous components such as wax, pectin, hemicellulose, and lignin, thereby increasing fiber's roughness and crystallinity [12,[22][23][24][25]. The hydrothermal treatments, necessitating specialized apparatuses and exhibiting limited scalability, can be effectively replaced by the domestic pressure cooker, an alternative intriguing vessel for the simple, cheap, and economical hydrothermal reactor [26,27]. The extraction of MFC from sorghum fiber was performed through hydrothermal treatment employing pressurized steaming methods with pressure cooker reactor [9,14,28]. Sorghum fibers treated with a 5% NaOH concentration and 3 min of steam pressure generated a cleaner and fibrillated morphology [14]. By altering the heating duration, the treated fibers' crystallinity index increased significantly compared to the untreated fibers [9]. Hydrothermal treatment of sorghum fiber under steam pressure for 5 min effectively removed impurities, reduced amorphous contents (lignin and hemicellulose), increased crystalline content (cellulose), improved hydrophilic properties via wax loss, and successfully defibrillated fiber, thereby providing valuable insights for future research in manufacturing natural fiber composites with synthetic polymer matrices [28]. During the treatment, the sorghum fibers were immersed in a liquid medium within a reactor [9,14,28].
The main objective of this study is to investigate the effect of hydrothermal treatments on the sorghum stalks with hydrothermal treatments using pressurized steaming methods at different durations. The fibers were positioned on a holder slightly above the water level to avoid direct immersion, and to enable targeted interaction with the produced steam during the treatment. The treated fiber was characterized for its chemical compounds, morphology properties, crystallinity index, and thermal properties to investigate the treatment effect.

Materials
The fiber used in this study was the sorghum (Sorghum bicolor (L.) Moench) belongs to the 'Poaceae' family. The sorghum stalk from which the leaves and nodes, had been removed has a density of 1.08 g cm −3 . They were sourced from a traditional market in Bogor, Indonesia. The chemical components of sorghum stalk on a dry weight basis are hemicellulose (30.95%), cellulose (34.87%), lignin (24.90%), extractives (4.75%), and ash (4.51%).

Fiber preparation
The fibers were cut, crushed, then sieved until passing 100 mesh-size screens. The fibers were placed in a pressure cooker reactor with distilled water to be proceeded via hydrothermal treatment at different durations: 5, 25, and 60 min. In the reactor, the fibers were placed using a porous container holder to prevent water contact. The appropriately-sized receptacle was placed inside the pressure cooker before adding the water. The fibers were positioned carefully on the holder slightly above the water level to prevent their direct immersion in water during the procedure. The pressure applied was at 1 atm (1.013 bar) and a temperature of 99.99°C. After the process, the fibers were dried in a vacuum oven at 50°C for 120 min. The designation of Sorghum fiber with different duration of treatment is mentioned in table 1. The pictorial view of chopped sorghum fiber with 20 mm, untreated sorghum fiber with 100 mesh (SV), and hydrothermal treated sorghum fibers in 5 min, 25 min and 60 min are shown in figures 1(a)-(e) respectively.

Characterization
The samples were characterized using FTIR Perkin Elmer 90 325 at the wavenumber range of 4000-800 cm −1 with a scanning resolution of 2 cm −1 to study the functional groups of molecules in the fibers and their interactions. X-ray diffraction (XRD) was used to determine the crystallinity of the treated and untreated sorghum fiber. The samples were also characterized using Philips XRD with Cu K-α radiation at 1.5418 Å; 40 kV, 40 mA, and a step-size of 0.02°/20 s from 2Ɵ = 5 to 50°. The crystallinity index (CrI) was determined based on reflected intensity data following the Segal equation [29]. To obtain the microstructure image of the fiber, the samples were characterized using SEM FEI Quanta F50 EDAX EDS Analyzer and gold coating of the samples was carried out using a sputtering instrument. The thermal properties were determined using a thermal gravimetric analyzer (TGA 4000 Perkin Elmer) from 25°C to 600°C at a heating rate of 10°C min −1 under nitrogen atmosphere (20 ml min −1 ).

Results and discussion
Compound in sorghum Hydrothermal treatment by steaming and boiling is one of the physical methods to modify fiber's surfaces. Steaming involves heating fibers placed in a porous container above the boiling water. Hydrothermal treatment is carried out by steaming (without contact between fibers and boiling water) using a pressure cooker reactor. The heat is generated from boiling water vapor, and during the heating process, the water vapor (as the main medium) is absorbed by natural fibers due to their hydrophilic properties. During the absorption process, the mechanical degradation and thermal instability will occur, which in turns will affect the morphology, molecular configuration, chemical components, and constituent contents of the fibers [30] Figure 2 showed the FTIR spectrum of untreated sorghum fiber (SV) and hydrothermal-treated fibers with steam pressure (KP) at various durations: 5, 25 and 60 min. The peak at wavenumber 1242 cm −1 represents the stretching vibrations of the C-O bond of the acetyl group. The peak at wavenumber 1512 cm −1 represents the stretching vibrations of the C-C bond of the methyl, methylene, and methoxyl groups. The peak at wavenumber 1604 cm −1 represents the stretching vibrations of the C=C bond of the benzene ring and the aromatic C=C bond and conjugated C-C bond in lignin compounds [31][32][33][34]. The peak at wavenumber 1735 cm −1 represents the stretching vibrations of the C=O bond and the C-O bond in lignin and hemicellulose compounds, while the peaks at wavenumbers 2850 and 2918 cm −1 indicate the asymmetric vibrations of the -CH 2 bond in hemicellulose, cellulose compounds, and the presence of wax substances [35][36][37]. The peak at wavenumber 897 cm −1 represents the β-glycosidic bond between monosaccharides and the C-H bond bending, while the peak at 1035 cm −1 represents the stretching mode of the C-O bond of the hydroxyl and ether groups. The peak at 1325 cm −1 represents the -OH bond, the peak at 1373 cm −1 represents the bending vibration of the −OH bond and asymmetric deformation of the C-H bond, and the peak at 1425 cm −1 represents the symmetric bending and scissoring of the -CH 2 bond in cellulose compounds [38,39]. The FTIR test was performed to observe changes in compound composition that occurred during the hydrothermal treatment process. The changes in absorbance peaks at defined wavenumbers between untreated sorghum fiber (SV) and fiber after hydrothermal treatment are shown in figure 3. Higher absorbance values  indicate a more significant presence of molecular bond groups at the corresponding wavenumber. Changes in absorbance peaks were observed at wavenumbers 1242, 1512, and 1604 cm −1 . It respectively represents the stretching of C-O bonds in the acetyl group, the stretching of aromatic ring C-C bonds in the methyl, methylene, and methoxyl groups, and stretching of C=C bonds in the benzene ring, and the stretching of aromatic C=C and conjugated C-C bonds in lignin compounds [9,10]. The absorbance percentage at these wavenumbers decreases after the SV fibers were treated using steam pressure treatment, as shown in figure 3. This indicates that all of these treatments were able to break the bonds between lignin and cellulose, resulting in a reduction of lignin content in the sorghum fiber [14,30].
The peak at 1735 cm −1 represents stretching vibrations of C=O and C-O bonds in lignin and hemicellulose, while the peaks at 2850 and 2918 cm −1 indicate asymmetric stretching vibrations of -CH 2 bonds in hemicellulose, cellulose, and the presence of wax [9,10]. The absorbance values at these wavenumbers decreased after the SV fibers underwent hydrothermal treatment via steam pressure, as shown in figure 3. The decrease in absorbance values suggests a reduction in the number of molecular bonds present at those wavenumbers, indicating that hydrothermal treatment was able to break the bonds between lignin and cellulose and several molecular bonds in hemicellulose compounds [14,30].
The absorbance at wavenumber 897 cm −1 represents the β-glycosidic linkage between monosaccharides and C-H bending group, while the absorbance at 1035 cm −1 represents the stretching mode of the C-O bond from hydroxyl and ether groups. The absorbance at 1325 cm −1 represents the -OH bond, the absorbance at 1373 cm −1 represents the bending vibration of the -OH bond and asymmetric deformation of the C-H bond, and the peak at 1425 cm −1 represents the symmetric bending and scissoring of the -CH 2 bond [9,10,28]. These molecular groups are present in cellulose compounds. The changes in these groups are presented in figure 3. The molecular groups in cellulose compounds decreased after the SV fiber was subjected to hydrothermal treatment using steam pressure. The decrease in these groups is likely occurred due to the breakage of the bonds during the hydrothermal treatment process [9,14,30].
The steam pressure treatment on natural fibers aims to generate cellulose microfibrils. During the steaming process, the heat energy applied to the water in the reactor caused it to boil and generated steam. The steam then heated and pressed the surface of the fibers that were placed on top of the boiling water in a porous container. The absorbed steam diffused into the fibers, causing swelling. Furthermore, the ions from the water molecules reacted with the constituents in the natural fiber and broke the bonds in the fiber compounds, causing mechanical degradation. In addition, during the steaming process, the softening temperature of the fiber compounds (lignin, hemicellulose, and cellulose) was reached. The combination of these phenomena caused alteration in the molecular configuration and composition of the natural fiber compounds [23,30,40,41].

Fiber morphology
Hydrothermal treatment of natural fibers using the steam pressure treatment will change their surface morphology. Changes in morphology that occur in sorghum fibers during the hydrothermal treatment process compared to untreated sorghum fibers were observed using FE-SEM. Figure 4 displays the surface morphology of untreated sorghum fibers and hydrothermal-treated fibers using steam pressure treatment at heating durations of 5, 25, and 60 min. Figure 4(a) shows a rough surface appearance, indicating the peeled sections on the fibers' surface. The peeling of several fibers' surface was caused by the cutting and crushing forces of the machine during the comminution process into smaller sizes (100 mesh). In addition, the morphology of the SV fibers is still bundled or fused as a single fiber. The morphology of hydrothermal-treated fibers using steam pressure treatment is shown in figures 4(b)-(d). The figure depicts the surface of steamed fibers, which appear as a continuous bundle of cellulose microfibrils that run along the fiber axis. Several partition patterns were formed between the microfibril bundles, indicated by the smoother and cleaner fibers' surface, which are not present in untreated sorghum fibers (SV).
During the steaming and boiling process using a pressure cooker reactor, the water vaporized and was absorbed by the sorghum fibers. The absorption of water molecules into the fiber caused swelling and, under certain conditions, the breaking of compound chains within the fiber due to water vapor molecules [23,42]. This is shown in figures 4(b)-(d), where the fiber bundles fray into single fiber elements (defibrillation). The diameter of the fiber bundle increases in steam pressure treatment for 5 min (KP5). The increased fiber diameter was caused by water vapor absorption on the fiber surface and diffusion into the fiber, resulting in swelling. Excessive water vapor molecules caused the breaking of the bonding between lignin and cellulose in the fiber. The breaking of binding materials in the fiber caused fibrillation into fiber elements, and cellulose compounds were exposed to the fiber surface [12,[22][23][24][25]. This is shown in figure 4(a), where micro-pores are visible on the fiber surface, and there is a visible separation line parallel to the length of the fiber. The longer the treatment duration, the more the molecular diffusion of water molecules continues, resulting in an increasing number of degraded binding materials. In conclusion, defibrillation of sorghum fibers due to hydrothermal treatment using steam pressure was able to break the bonds between lignin and cellulose and increases the exposure of cellulose compounds to the fiber surface, thereby increasing absorbance peak when analyzed using FTIR.
Hydrothermal treatment using pressurized steaming method has generated the fibrillated bundles of sorghum fiber (MFC). Table 2 compares bundle and MFC sizes between untreated fibers (SV) and fibers subjected to all hydrothermal treatment processes. The table shows the increased bundle size after hydrothermal treatment, particularly at 5 and 25 min. This increase in size is due to fiber swelling during the hydrothermal treatment. In addition, hydrothermal treatment has resulted in MFC sizes ranging from 12.2 to 19.4 μm.

Fiber crystalline fraction
Natural fibers generally consist of three main components that bind together: lignin, hemicellulose, and cellulose. Lignin and hemicellulose contain an amorphous structure, while cellulose contains a semi-crystalline structure (composed of both amorphous and crystalline structures). As explained earlier, fiber crystallinity is an important parameter that affects its mechanical properties. The higher the crystalline fraction in the fiber, the higher the fiber's strength. This is particularly important when natural fibers are used as reinforcement in polymer matrices. The crystallinity index is the parameter used to describe the crystalline fraction in the fiber. The crystallinity index was calculated using the approach proposed by Segal. In addition, this section also discusses the effect of hydrothermal treatment on the size of resulted crystallites and the type of cellulose following the procedure by Nam et al [29].
The comparison of x-ray diffraction spectra and crystallinity index between untreated sorghum fibers (SV) and fibers treated with steam pressure cooking (KP) is shown in figure 5. Compared to SV fibers, the x-ray diffraction spectra of thermally modified fibers at 5, 25, and 60 min heating durations show nearly identical patterns. The figure exhibits the same peak shapes between untreated and modified sorghum fibers (SV) fibers. The difference lies in the intensity and width of the peaks generated. The difference can be seen in the peaks at 15.7°-16.3°, which represent the (110) plane, and at 21.9-22.1°, which represent the crystallographic (200)  plane of cellulose [43][44][45]. The crystallographic plane is labeled according to the original cellulose structure, as explained by Wada and Okano [45]. Table 3 shows a comparison of crystallite size, crystallinity index, and discriminant Z values between untreated sorghum fiber (SV) and hydrothermal treated fibers using steam pressure (KP) at different heating durations (5, 25, and 60 min). The crystallinity index decreases with increasing heating duration compared to SV fibers. The 5 min duration of hydrothermal treatment has generated a higher crystallinity index that of 25 and 60 min, as prolonged heating duration can lead to the degradation of cellulose fibers due to the generated thermal energy, same result showed by Ismojo [28]. Thus, the highest crystallinity index was resulted from sorghum fibers treated with the steam boiling method for 5 min. It can also be seen in table 3 that both untreated sorghum fiber and hydrothermal treated fiber exhibit negative Z values. This indicates that all fibers contain cellulose with dominant type of I β . This is consistent with the explanation given by Kim, et al [46] and Poletto, et al [47], who stated that there are naturally two types of cellulose in nature: I α and I β . In general, type I β is commonly found in plants, while I α cellulose is commonly found in bacteria and alga.
In addition, table 3 also shows the crystallinity index values of SV fibers and treated fibers. The sorghum fibers treated by steam pressure showed an increase in crystallinity index compared to untreated fibers, indicating that hydrothermal treatment was able to increase the crystalline fraction in the fibers. The increase in crystalline fraction also indicates a decrease in amorphous fraction in the fibers. An increase in crystallinity index is followed by an increase in crystal size in modified fibers. A larger crystal size also indicates an increase in crystalline fraction in the fibers. These results are consistent with the data generated from FTIR and FESEM analysis.

Thermal properties of fibers
The thermal properties of sorghum fibers were analyzed using TGA. TGA was used to determine the thermal stability of the fibers by measuring weight loss as a function of increasing temperature. The effect of steam pressure treatment on thermal stability compared to untreated sorghum fiber is illustrated in figure 6 and summarized in table 4. Fibers' weight loss occurred due to the decomposition of lignin, hemicellulose, and cellulose. Thermal decomposition of lignocellulosic fibers occurred in three stages [48]. First, data recorded below 100°C indicates the evolution of absorbed moisture. Second, data recorded above 220°C to around 310°C is primarily generated from the thermal decomposition of hemicellulose and several lignin. Third, the highest recorded temperature range (310°C-400°C) is associated with cellulose and lignin degradation. In this temperature range, cellulose components decomposed, while lignin exhibits a wide range of decomposition temperatures from 200°C to 700°C due to phenyl groups that are difficult to degrade in lignin. Higher decomposition temperature components provide more excellent thermal stability [49]. Fiber degradation occurred in four stages: water evaporation, hemicellulose degradation, cellulose degradation, and lignin decomposition. There are two forms of moisture contained in fibers: free water and bound water. Free water is water that adheres to the surface of natural fibers and evaporates at lower temperatures (25°C-150°C), while bound water is water that forms bonds with hydroxyl groups in lignin, hemicellulose, and cellulose and evaporates at higher temperatures. After free water evaporated, the degradation occurred between the temperature range of 150°C-500°C for bound water, lignin, hemicellulose, and cellulose [48].
A relatively low decrease in the weight of MFC occurred in the temperature range of 40°C-260°C, and a constant weight decrease of MFC was observed in the temperature range of 120°C-250°C. The weight decrease in these ranges was 11.5%, 8.95%, 7.50%, and 11.25%, respectively for SV, KP5, KP25, and KP60. A significant weight decreases of MFC occurred in the temperature range of 260°C-380°C, which was 83.01%, 66.01%, 62.11%, and 63.19%, respectively, for SV, KP5, KP25, and KP60. Above 380°C, the weight decrease of MFC returned to a relatively low level. Maheswari et al [48] explained that cellulose, hemicellulose, and lignin degradation occur at temperatures of 320, 200, and 150°C-540°C, respectively. In this case, the weight decrease in the temperature range of 40°C-230°C for SV and 40°C-250°C for MFC is attributed to the loss of free water due to the evaporation process (above 100°C) and partial decomposition of bound water, lignin, and hemicellulose [48]. The weight loss of SV fibers in the temperature range of 230°C-470°C and MFC fibers generated via steaming at the temperature range of 250°C-380°C has caused significant changes in their structure. During this temperature range, the majority of hemicellulose, lignin, and cellulose decomposed with a rapid weight loss due to the breakdown of their molecular structure. Furthermore, the degradation of cellulose's structure also occurred within this temperature range. The degradation temperature range of cellulose (250°C-350°C) is higher than that of hemicellulose (25°C-290°C) and lignin (150°C-420°C). Hemicellulose, lignin, and cellulose degradation continue at above 380°C with less significant weight loss [50]. The thermal stability of a material corresponds to the temperature at which the material begins to decompose. This temperature is determined as the point in the TGA curve where a deflection is first observed from the established baseline before the thermal event, also known as the onset point represented by T initial [51,52]. According to the results, all treated fiber started to decompose at T initial around 275°C-282°C higher than fiber untreated at T initial = 229°C. This mainly occurred due for the removal of hemicellulose, lignin and other compounds, leading to a more thermally stable fiber [53]. The maximum peak (T maximum ) in the DTG indicates the temperature point where the greatest mass loss occurred and their thermal stability was achieved [51,52,54]. In the fibers with 5 min duration of treatment, the highest peak temperature was achieved, namely at 365°C. Based on this result, it is concluded that the sorghum MFC fibers obtained from the steam pressure treatment for 5 min exhibit the better thermal stability compared to the other treated fibers and untreated fiber (SV). This result is consistent with the results of FTIR and XRD analysis, which indicate that the steam pressure treatment for 5 min generates the highest crystallinity index among all treatments.

Conclusions
The hydrothermal treatments, necessitating specialized apparatuses and exhibiting limited scalability, can be effectively replaced by the domestic pressure cooker, an alternative intriguing vessel for the simple, cheap, and economical hydrothermal reactor. Hydrothermal treatments of sorghum stalks using pressurized steaming methods were performed at different durations, in which the fibers were positioned above the water level to  Table 4. Thermal behavior of untreated sorghum fiber (SV) and hydrothermal treated sorghum fibers at different durations: 5 min (KP5), 25 min (KP25) and 60 min (KP60).

Sample
T initial (°C) enable targeted interaction with the steam. Hydrothermal treatments using pressurized steaming methods were employed, with the fibers positioned above the water level to enable targeted interaction with the steam. The treatments aimed to unbundle lignocellulose networks into microfibrillated cellulose with reduced amorphous content and enhanced crystallinity. Characterization of the treated fibers included chemical composition, morphology, crystallinity index, and thermal stability. The results have demonstrated the removal of binding materials, such as amorphous hemicellulose and lignin, from the sorghum fibers, leading to fiber defibrillation and the production of MFC at size range from 12.2 to 19.4 μm. Additionally, the treatments have increased the fibers' crystallinity index and thermal stability. Hydrothermal treated fiber started to decompose at T initial around 275°C-282°C higher than fiber untreated T initial = 229°C. The 5 min duration of treatment has generated the highest crystallinity index (52%) and the highest peak temperature (365.26°C). Future studies can investigate compatibility of sorghum fibers with polymer matrices to further explore its potential as reinforcement in natural fiber polymer composites.