Conversion of sugarcane biomass into sustainable fabrics: softening of fibers using alkali and silicone softener treatment

This study addresses environmental concerns related to sugarcane biomass as an industrial fuel source by exploring its potential for textile applications. Bagasse undergoes sequential alkali-H2O2 treatment, followed by varying concentrations of silicone softener (50 g l−1 − 100 g l−1 − 150g l−1). The goal is to enhance fiber fineness and softness. Comprehensive physical and chemical characterization reveals significant alterations in treated fibers, impacting surface morphology, crystallinity, linear density, and moisture regain. Results indicate a decline in fiber linear density from 59.47tex to 48.84tex, thus improved fineness, moisture regain initial from 6.9% to 4.7%, reduced crystallinity, and enhanced mechanical strength with silicone softener treatment. Treated fibers show promise as a sustainable alternative to conventional cotton, emphasizing the importance of sugarcane biomass for eco-friendly textile manufacturing.


Introduction
Saccharum officinarum, most commonly known as sugarcane, is a plant that holds significant importance as a sugar crop globally [1].The crushing of sugarcane produces a residue called 'bagasse' which accounts for over 30%.A large quantity of this is being used as animal feed and as a source of fuel in the industrial sector [2][3][4][5].On the contrary, the value addition of by-products has long been neglected and not given much importance [6][7][8].The transformation of plant-based natural resources to bio-based products like biocomposites or geotextiles has proved to be more environmentally friendly and sustainable [9][10][11][12][13].Research has been made into the characterization of biochars resulting from the pyrolysis of biomass and calcium oxide mixtures, offering insights into their potential applications [14].Simultaneously, composite bioplastics derived from tapioca starch and sugarcane bagasse fiber has emphasized on the impact of ultrasonication duration on the final bioplastic properties, contributing to the understanding of sustainable materials production [15].However, the fibre extraction methodology and the post-treatment play an important role in achieving viable textile fibres.The literature has cited alkali treatment to be a frequently used method to modify and enhance the characteristics of natural fibres.This treatment is often termed 'Mercerization' which employs the use of sodium hydroxide with varying solution concentrations under some load to treat natural fibres [16].The following treatment shows some significant improvements, like better sheen and dying properties with enhanced strength [17].
Although, the natural fibre's alkali treatment enhances the intrinsic properties of fibers but has also reported to increase stiffness [18][19][20][21].In addition to alkali treatment, hydrogen peroxide (H 2 O 2 ) is used to assist in removing lignin and hemicellulose content from the treated fiber, resulting in a larger surface area and more reactive hydroxyl groups on the fiber's surface [22].The variation in treatment time and concentration of NaOH employed is critical in modifying the properties of natural fibers [23].In general, the concept of dissolution of amorphous segments (reduced hemicellulose, lignin content) is perceived.However, this concept has been opposed by a small number of researchers who believe that the lignin content remains unchanged [18].
Nevertheless, the increased stiffness due to alkali treatment makes it essential to post-treat the fibers with different softeners to get the required softness to make a fabric.A number of enzymatic and silicone-based softeners are employed to enhance the feel of fibers by softening the fiber strands [24].
Furthermore, both softeners (enzymatic and silicone) are easily available and don't adversely affect health.Amrita [25] used four different enzymes (cellulase, hemicellulase, pectinase, and lacase) to enhance the fineness of banana fibers.A drastic decrease in strength was observed as the conc. of enzyme-based softeners increased due to the removal of cellulose and hemicellulose, whereas the fiber's surface felt smoother [25].Similar to some other softeners available commercially, silicone softener is also essential and widely used to achieve the required fineness and softness in textile yarns and fabrics [24].It offers better mobility, tear strength, crease recovery, and abrasion resistance to the fibers.Silicone softeners also enhance durability and makes the treated fibers thermally stable, which is beneficial for the fiber's conversion to a value-added product [26][27][28].
Herein, the proposed study presents an eco-friendly value addition to sugarcane bagasse, which previously have been only used as industrial fuel and feedstock by converting it to fibers and then improve the fiber fineness and softness and other properties like moisture regain, mechanical behavior, etc. Fibers were extracted from sugarcane bagasse through NaOH and H 2 O 2 pretreatment, and silicone softener was used to optimize the softness of fibers.The various prepared samples were tested to obtain the tensile strength, torsional-flexural rigidity, fiber fineness, moisture regain, fiber's crystallinity, and morphological properties.

Materials and methods
Sugarcanes were obtained from local fields and were crushed on a crusher to produce bagasse.
Sodium hydroxide (NaOH) and Hydrogen peroxide (H 2 O 2 ) were used to extract fibres and purchased from Sigma Aldrich.Silicon softener was also purchased from Sigma Aldrich which was employed to enhance the fineness of extracted sugarcane fibres.

Fiber extraction from sugarcane
Sugarcane stalks were thoroughly rinsed to remove any foreign material, and sugarcane bagasse was obtained by crushing the stalks in a crusher, after which the bagasse was thoroughly washed to remove any foreign substance.The outer rind part was separated to extract fibres and further processed and cut (1-2 mm wide, 20 cm long).
The cut sample of cane bagasse was treated with hot water for 60 min so that the sugar traces and coloring matter were removed.Afterward, samples were treated with NaOH and H 2 O 2 at 90 °C for 4 h and were finally washed and sun-dried.

Treatment of sugar cane fibers
The extracted sugar cane fibres were treated with different concentrations of silicon softener (50, 100, 150 g l −1 ) to enhance the softness of the fibres.Moreover, raw fibres were also treated directly with H 2 O 2 and silicone softener, having ratios of 12 g l −1 and 50 g l −1 , respectively.The silicone softener treatment was done by dipping the previously alkali-treated fibres in a silicone softener solution for 5 min along with continuous stirring.The alkali-treated raw fibres were immersed for 5 min in a solution of silicon softener while stirring continuously.The moisture was then removed from the fibres by drying them at 100 °C in an oven and curing them at 150 °C for improved adhesion and softener penetration into the fibres.
Likewise, 12 g l −1 H 2 O 2 treatment was carried out by boiling raw fibers in an aqueous solution for 1 h at 80 °C.Afterwards, the fibers were washed and then dried at 100 °C in an oven.Different fiber samples were given a name in relation to the different treatments implied: RF -Raw fibers, NH-50S - The whole process of fuber's extraction and treatments is given in fgure 1.

Mechanical testing
The mechanical behaviour of a single fibre (tenacity, elongation at break, and force at break) was evaluated with a Lloyd LRX tensile tester (USA) in accordance with ASTM D-3822.The gauge length was set to be 10 mm long so that the fibre easily clamps in between the testing assembly.
A pendulum assembly consisting of a bar suspended by fiber was used to measure the torsional rigidity (based on the oscillations of the pendulum) of various fibers.The time of 4 torsional oscillations (negligible damping) for fiber samples was observed and calculated by the following formula: where I is the moment of inertia of the rod Peirce method (deformation of loop under applied load) was employed to determine the flexural rigidity of fibers.The deformation (increased diameter) of the circular fiber ring loaded with the rider based as compared to its original length was determined using the formula: where mg represented the rider weight and r is the radius (0.9 cm) of the ring.

Moisture regain
To calculate the moisture regains of various fibre samples, ASTM D-2495 was followed.This was accomplished by drying the fibre in an oven and then exposing it to standard atmospheric conditions, allowing the moisture to penetrate.The difference in weight before and after moisture absorption was calculated analytically for various fibre samples.

Fiber linear density
The fibre linear density (fibre fineness) was evaluated using the ASTM D-1577 protocol.Five random fibres were selected from each type of treated fibres and the length was measured on a knitmeter, electronic balance was utilized to find the weight of the samples, and subsequently, the fibre linear density was calculated.
2.6.Characterization of pre-and post-treatment samples Fiber samples were evaluated to obtain crystalline behaviour according to ASTM D-2809 through x-ray diffraction.Cu radiation was set at 40 kV, 35 mA and anode excitation were set in the 2θ range 1-70°whereas powder samples were used to record traces.On the other hand, Quanta 250-FEG (ELECMI, Spain) scanning electron microscope was used to obtain the morphological results of fibres at 5 kV following ASTM E-2809-13.Gold sputtering was done to make the fibre samples conductive, and were taped to aluminium studs.The results were produced at a magnification between 300-550 μm figure 1.

Mechanical attributes of fibres after extraction
Mechanical strength of a fibre is of prime importance and can be critical in making it viable for the apparel industry [29][30][31][32].The mechanical behaviour of the fibres (tenacity, elongation at break, force at break) was determined as depicted in figures 2(a), (b).Raw fibre sample (RF) shows the lowest tenacity and force at the break.In contrast, the alkali-H 2 O 2 treated fibre samples (NH-50, 100 and 150S) with varying softener ratios result in an increment in the force at break (cN) and tenacity which can be observed.The raw fibre samples (RF) contain a sufficient quantity of lignin and hemicellulose in their fibrillar structure, which binds the cellulosic chains and is primarily responsible for their lower tenacity.As soon as the fibre samples are alkali-H 2 O 2 treated, the hemicellulose and lignin get removed and the cellulosic chains come close which in return enhances the overall mechanical strength of fibres.However, due to compactness of chains the treated fibres becomes hard and brittle [33], a demonstration of which can be seen in figure 2(a) as a reduction in elongation at break of fibres.Furthermore, the treatment with an increasing silicone softener ratio makes the fibre finer and dimensionally stable, positively influences the fibre strength, and exhibits a direct relation to elongation at break of treated fibres [34].The fibres become more and more strengthened as the silicone softener ratio increases resulting in an increased value of elongation at break.Moreover, a slight reduction in tenacity of H 2 O 2 treated sugarcane fibres (figure 2(a) (12HO)) (as compared to raw sample RF) is observed, which can be the result of cellulosic structural damage [35,36].Figure 2(b) illustrates the torsional and flexural rigidity of various samples of sugarcane fiber.The rigidness of extracted fibers is directly influenced by the concentration of alkaline treatment implied.Considering this the treatment of silicone softener was introduced to make the fibers soft and flexible as discussed earlier.The higher concentration of silicone softener results in a significant decline in the rigidness of alkali-H 2 O 2 treated fiber samples.This behavior satisfies the claims made earlier, that the treatment with silicone softener softens the fibers by penetrating in void spaces and covering the outer surface [34].A decline in fiber rigidity was observed as compared to untreated fibers (RF) when fibers were treated with silicone softener only (50S).The H 2 O 2 treatment of raw fibers (12HO) does show a major increment in the flexural and torsional rigidity of fibers.
An increase in the concentration of silicone softener and constant ratio of alkali-H 2 O 2 (Sample NH-50, 100 and 150S) in figure 2(b) results in a decline in the fiber's torsional and flexural rigidity because silicone softener penetrates the space available in between the chain and molecules and results in a reduction in torsional and flexural rigidity [37].However, the flexural and torsional rigidity does increase with the alkali-H 2 O 2 treatment of fibers due to the elimination of hemicellulose and lignin content [33] but the value of rigidity does remain constant for all samples because of the constant ratio of alkali treatment employed.Whereas the increase in the amount of silicone softener treatment reduces the fiber's overall rigidity which is can be critical in the selection of these fibers for woven and non-woven textile applications [38].

Moisture regain of extracted fibers
Comfort in a fabric depends on the yarn formation and its subsequent processing whereas the moisture handling ability of a fibre can definitely enhance the comfort and feel of the fabric [39,40].Due to a large number of void spaces in between fibre bundles, natural fibres have an inherent capacity to hold moisture.Therefore, natural fibres have greater moisture retention than synthetic fibres [41].Sugarcane fibres are such natural fibres that have higher moisture absorbing ability due to the presence hydrolytic hemi cellulosic bonds [42].A comparison of moisture regain (%) of various treated and untreated sugarcane fibres has been drawn in figure 3. The higher amount of lignin and hemicellulose (having hydrolytic nature) present in the untreated fibre sample (RF) exhibits the highest amount of moisture absorption at 6.9% in comparison to all other treated fibre samples [42].Whereas, the treatment with alkali H 2 O 2 destroy the hemicellulose and lignin linkages thus causing a reduction in the natural hydrophilicity of treated fibres as shown in figure 3 (NH-50,100 and 150S) [22,42] Furthermore, the moisture regain values keep on decreasing from 5.8% to 4.7%, which is caused by the increasing concentration of silicone softener (50 g l −1 to 150 g l −1 ) used in the treatment of fibres which is hydrophobic in nature [34].Higher concentration covered more surface area on the fibre, which restricted moisture absorption [43].The treatment of raw fibres with 50 g l −1 silicone softener alone (50S) results in a minor reduction in moisture regain ability, whereas in contrast, H 2 O 2 -treated fibre samples (12HO) show higher decline in moisture regain ability of treated samples due to removal of hemicellulose structure [42].

Fiber linear density
Figure 4 describes the fiber linear density of untreated and treated samples of sugarcane fiber Samples RF, NH-50S, NH-100S, NH-150S, 50S, 12HO exhibit linear densities ranged from 59.47tex to 48.84tex, respectively.
After alkali H 2 O 2 treatment, the fibre linear density lowered from 59.47tex to 56.67tex and continued reducing from 56.67tex to 48.84tex as the silicone softener ratio was raised.When raw fibres are treated with H 2 O 2 and silicone softener alone, there is a modest loss in fibre linear density when compared to untreated raw fibre (RF).Untreated raw fibres had the maximum linear density of 59.47tex.This is owing to the occurrence of more hemicellulose and lignin than in alkali-treated samples, which causes the fibre sample to be coarser [44].After the treatment with alkali and hydrogen peroxide, hemicellulose and lignin are removed, allowing  intramolecular chains to pack closer, decreasing linear density and increasing fiber fineness [33,45].Subsequently, as the ratio of silicone softener increases the fiber linear density decreases which results in an increment of fiber fineness, as shown in figure 4 (NH-50, 100, 150S).Raw fiber treatment with 50 g l −1 of silicone softener (50S) only shows a minor reduction of fiber linear density over untreated raw fibers (RF).Whereas treatment of raw fibers with H 2 O 2 only (12HO) also results in minor fineness improvement because of the degumming process.

Characterization analysis
X-ray diffraction pattern of different sugarcane fibre samples can be seen in figure 4 at room temperature.Sharp peaks at around 20.81°are observable in figure 5, which determine the crystalline regions in alkali-H 2 O 2 treated fibre samples (NH50, 100, 150S, and 12HO).In contrast, position 22.57°exhibit a visible amorphous region for all fibre samples.The crystalline region for untreated fibre samples (RF) is not sharp as compared to alkali treated samples which is due to the presence of hemicellulose and lignin in the interfibrillar region of the fibre that limits chain compactness.Fibres treated with alkali-H 2 O 2 have higher crystallinity because the interfibrillar chains are more compact and packed closely after the removal of lignin and hemicellulose [33].As the alkali H 2 O 2 pretreated fibres are post-treated with an increasing silicone softener ratio; 50 g g −1 l −1 , 10 0 g g −1 l −1 , 15 0 g g −1 l −1 , (figure 5, Samples NH50, 100 and 150S), a decline in sharp peaks (crystallinity) at 29.81 o position was observed.The decrease in crystallinity upon increasing the silicone softener ratio is due to the incorporation of silicone softener in the void spaces which results in weakening the van der waals force and hydrogen bonding creating flexibility and ductility in response ultimately reducing the fibres crystallinity [46][47][48].In contrast, when raw fibres were H 2 O 2 treated (12HO) an increase in the crystallinity of the fibres can be observed in figure 5 because of the degumming and compact rearrangement of molecular chains [36].
Figure 6 shows the SEM results of various fibre samples.The morphology of the untreated raw fibre (RF) has a plain surface with a well-ordered fibre structure which depicts a multicellular nature due to the dispersion of hemicellulose and lignin.In contrast, alkaline H 2 O 2 pre-treated fibre samples with varying concentration of silicone softener treatment as shown in figure 6 (NH-50, 100, and 150S), demonstrate a rather rough and cracked fibre surface (blue arrow in figure 6) [49,50].This is due to alkali-H 2 O 2 pre-treatment which results in the destruction of linkages containing lignin and hemicellulose [33,45].The increase in conc. of silicone softener treatment from 50 g g −1 l −1 to 150 g g −1 l −1 resulted in increased fibre fineness and formed a layer of grease along the edges [51] as observed in figure 6 (NH 50, 100, 150S and 50S), which is more prominent in figure 6 (NH-100S; 50S) and the fibre edges seem to be lustrous (orange arrow in figure 6).The use of H 2 O 2 treatment on raw sugarcane bagasse damaged the surface of the fibres (figure 6 (12HO)), possibly due to the higher conc of H 2 O 2 [36].

Conclusions
The alkali-H 2 O 2 pre-treatment was employed for the extraction of sugarcane fibres from biomass and then the fibres were post-treated with silicone softener having various concentrations.The direct separate treatment of raw fibres with alkali-H 2 O 2 and silicone softener was also done for characteristic evaluation and comparison purposes.All the treated and untreated samples' mechanical and analytical characteristics were examined.The physical morphology of various extracted fibre samples was affected through alkali treatment due to the removal of lignin and hemicellulose.The mechanical strength of alkali-treated fibres increased but the fibres seemed rigid and stiff.Treatment with silicone softener reduced the linear density and made the fibres overall finer and softer.A slight reduction in the mechanical strength of fibres was evaluated upon H 2 O 2 treatment possibly due to higher concentration used.Upon increasing the conc of silicone softener, a major decline in fiber moisture regain ability was observed; as well as the torsional and flexural rigidity was significantly reduced.An increase in fibre crystallinity was observed after alkali treatment, but the crystallinity was disturbed as the silicone softener conc.was increased, but an overall enhanced fibber's fineness, mechanical strength and optimum rigidity are enough characteristics to prove the fibres viability for textile applications.

Figure 1 .
Figure 1.Pictorial representation of fiber extraction from sugarcane and post treatment process.

Figure 2 .
Figure 2. (a) The comparison of different fibre samples (a) elongation at break, tenacity, and Force at break (b) torsional and flexural rigidity.

Figure 4 .
Figure 4. Fiber linear density values of various treated and untreated fibre samples.

Figure 3 .
Figure 3. Moisture regain % of various treated and untreated fibre samples.

Figure 5 .
Figure 5. X-ray diffraction peaks of pre-and post-treated sugarcane fibres.