Method of producing polymer-cellulose whisker composites

Abstract

The present invention relates to a method of producing a polymer-cellulose whisker composite comprising a polymer and cellulose whiskers synthesized from cotton waste materials using more sustainable and higher yield processes, as a nanofiller. The polymer-cellulose whisker composite produced from the method of the present invention may be used as energy materials, such as membranes in fuel cell applications.

Description

[0001] METHOD OF PRODUCING POLYMER-CELLULOSE WHISKER COMPOSITES

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention relates to a method of producing a polymer-cellulose whisker composite comprising a polymer and cellulose whiskers synthesized from cotton waste materials using greener and high yield processes, as a nanofiller

[0004] BACKGROUND OF THE INVENTION

[0005] Improvements in fuel cell technology are significantly correlated with the development of protonconducting membranes. The main considerations for properties of membrane material for protonexchange membrane fuel cell (PEMFC) are proton conductivity, durability, and thermal stability. Hybrid composites where a polymer matrix is combined with various fillers is a recent research direction for membrane materials (Teixeira et al., 2019). It is assumed that functionalized nano-structured fillers form ionic conduction channels when mixed with polymer matrix, which aids in transport properties and electrochemical reactions through clusters that are interconnected with narrow channels resulting from morphology and microstructure off the hybrid composite (Prykhodko et al., 2021). Nanofillers with hydrophilic natures and surface properties that can maintain water could result to higher performance at higher temperature and low relative humidity of membranes during fuel cell operation (Prykhodko et al., 2021).

[0006] With the recent advances in technology and materials, recent research on designing membrane materials focus on cost-reduction and durability / performance enhancement (Wang et al., 2020). There is a current trend to use renewable biomass, agricultural and industrial wastes as starting materials for nanomaterials — given their sustainability, eco-friendliness, and cost-effectiveness. For example, nano whiskers with thermal and morphological properties were produced from coconut fibers (Rosa et al., 2010) and carbon nanotubes were produced using activated carbon from herbaceous biomass (Osman et al., 2020). The method of the present invention involves selecting and utilizing renewable biomass- derived materials considered as wastes by transforming these materials into more sustainable, higher- value nanomaterials for energy applications. The use of starting materials derived from renewable biomass improves the sustainability outlook and environmental benefit compared to synthetic materials.

[0007] Common biomass materials in the Philippines were profiled and analyzed for use as starting materials for cellulose whiskers. Specifically, cellulose, lignin, and moisture content were determined for coconut fiber, saw dust, cotton lint, and cotton linter samples. Among those tested samples, the cellulose content of the cotton seed fibers showed the highest cellulose content of around 95-98% and cotton lint and linters showed no lignin content. As such, cellulose extraction and purification was determined to be easier and simpler for cotton wastes.

[0008] Cellulose whisker is a type of nano-scaled material produced from biomass-derived cellulose which have found high-performance applications in energy and environmental fields. Due to its many applications, different synthesis methods for different raw materials were utilized to produce cellulose whiskers with desired functional properties for specific applications. One of the many applications for cellulose whiskers is for composite membrane fabrication due to the enhancement effect on functional properties required for fuel cells.

[0009] Using cotton production by-product wastes, such as cotton linter, through the application of more eco- friendly procedures, it is possible to convert the cellulose materials into cellulose whiskers. This waste from cotton seeds comprises of shorter fibers and remains underutilized. However, the shorter fiber length and the absence of lignin are desired physical characteristics for the synthesis of cellulose whiskers using greener processing techniques.

[0010] The combination of cellulose whisker nanofillers with a polymer matrix to produce a hybrid composite may possess the desired surface-modified property to benefit the proton transfer mechanism for membranes in fuel cell applications.

[0011] It is known that nanocrystalline cellulose-polymer composites have improved hydrophilicity, mechanical properties, and thermal stability — making these composites good materials for protonexchange membranes (PEMs) for fuel cells and other higher performance applications. A study entitled “Modified Cellulose Proton-Exchange Membranes for Direct Methanol Fuel Cells” by Palanisamy, et al. discusses the developments on cellulose nanomaterial composites, polymers, and derivatives in direct methanol fuel cell applications as PEMs.

[0012] Commercially, cellulose nanomaterials have been widely known as a suitable filler for many composite materials for various applications. For example, W02020050286A1 discloses multiple methods of producing thermoplastic resin-fine cellulose (fine cellulose includes cellulose whiskers; fine cellulose used as a filler) composite particles and producing articles from thereof for various applications, including fuel cell applications, citing enhanced mechanical and thermal properties. There is also patent literature on the use of biomass materials as sources for cellulose nanomaterials, including cotton wastes. For example, EP3202978A1 discloses green cellulose whisker / nanocrystalline cellulose synthesis steps (alkali treatment using NaOH, acid hydrolysis with sulfuric acid, and pH neutralization) for cotton linter as a starting material. SUMMARY OF THE INVENTION

[0013] It is an object of the present invention to develop a method of producing a polymer-cellulose whisker composite comprising a polymer and cellulose whiskers more sustainably synthesized from cotton waste materials, such as cotton linter, as a nanofiller. Said polymer-cellulose whisker composite is suitable for various applications, such as fuel cell applications. It is also an object of the present invention to develop a facile process to tailor properties of synthesized cellulose whiskers.

[0014] Accordingly, the present invention provides method for producing a polymer-cellulose whisker composite, comprising the steps of: a. performing alkali treatment of a cotton waste material, further comprising the steps of: i. adding the cotton waste material in an alkali solution in a 1:33 ratio (solid / liquid) to create a first mixture, wherein the alkali solution is a 5-15% v / v sodium hydroxide solution; and ii. stirring the first mixture to extract a cellulose material; b. filtering the stirred first mixture to obtain the extracted cellulose material; c. neutralizing the pH of the filtered cellulose material by washing with distilled water; d. drying the pH -neutral cellulose material; e. hydrolyzing the dried cellulose material in an acid solution in a 1 : 10 ratio (solid / liquid) for 45-60 minutes to obtain a second mixture, wherein the acid solution is 55-60% v / v sulfuric acid (H2SO4) solution; f. filtering the second mixture to obtain hydrolyzed solids, wherein the hydrolyzed solids comprise cellulose whiskers; g. neutralizing the pH of the filtered hydrolyzed solids via repeated washing with deionized water using a centrifuge, to suspend the cellulose whiskers; h. homogenizing the suspended cellulose whiskers via ultrasonication; i. drying the homogenized cellulose whiskers; j . preparing a first solution comprising the dried cellulose whiskers and a solvent; k. ultrasonicating the first solution; l. dissolving an at least one polymer in the ultrasonicated first solution under continuous stirring to prepare a polymer-cellulose whisker solution at 20% w / w polymer concentration; m. casting the polymer-cellulose whisker solution in an at least one mold to obtain the polymer-cellulose whisker composite; and n. drying the polymer-cellulose whisker composite. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which are included to provide a further understanding of the present invention, are incorporated herein to illustrate embodiments of the present invention. Along with the description, they also explain the principle of the present invention and are not intended to be limiting.

[0016] FIG. 1 shows the FT-IR spectra of cotton linter samples compared to extracted cellulose samples from NaOH alkali treatment, using the method of the present invention.

[0017] FIG. 2 shows the FT-IR spectra extracted cellulose samples at varying %NaOH treatment at a different spectral range, using the method of the present invention.

[0018] FIG. 3 shows the FT-IR spectra of synthesized cellulose whiskers at different treatment conditions, using the method of the present invention.

[0019] FIG. 4 show an SEM image of synthesized cellulose whiskers using the method of the present invention.

[0020] FIG. 5 shows the XRD diffractograms of synthesized cellulose whiskers at different treatment combinations, using the method of the present invention.

[0021] FIG. 6 shows images of the produced polymer-cellulose whisker composite, wherein the polymer matrix comprises PSU, at different loading levels using the method of the present invention.

[0022] FIG. 7 shows the water contact angle (WCA) measurement of a produced polymer-cellulose whisker composite sample, according to the method of the present invention.

[0023] DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention discloses a method of producing a polymer-cellulose whisker composite comprising a polymer and cellulose whiskers synthesized from cotton waste materials, such as cotton linter, using more eco-friendly and higher yield processes. The polymer-cellulose whisker composite produced using the method of the present invention demonstrates enhanced properties for fuel cell application.

[0025] “Cotton waste material” as used herein refers to cotton waste by-products from cotton production, such as cotton lint and cotton linter. “Cellulose whisker” as used herein refers to cellulose nanocrystals (CNCs) or cellulose nanowhiskers produced by acid hydrolysis or temperature-controlled methods.

[0026] “Alkali treatment” as used herein refers to treatment of biomass using alkali solutions wherein the hydrogen bonds between -OH groups of cellulose, hemicellulose, and lignin are broken, leading to the breakdown of fibers into smaller fibers.

[0027] “Composite” as used herein refers to a material produced from two or more components with differing chemical and physical properties to produce a new material with a tailored set of properties. The composite referred to in this disclosure consists of a polymer matrix and a filler (cellulose whisker nanofiller).

[0028] The present invention relates to a method for producing a polymer-cellulose whisker composite, using cellulose whiskers synthesized from cotton waste material as a filler, comprising the steps of: a) performing alkali treatment of a cotton waste material, further comprising the steps of i) adding the cotton waste material in an alkali solution in a 1 :33 ratio (solid / liquid) to create a first mixture, wherein the alkali solution is a 5-15% volume / volume (v / v) sodium hydroxide (NaOH) solution and ii) stirring the first mixture to extract a cellulose material; b) filtering the stirred first mixture to obtain the extracted cellulose material; c) neutralizing the pH of the filtered cellulose material by washing with distilled water; d) drying the pH -neutral cellulose material; e) hydrolyzing the dried cellulose material in an acid solution in a 1:10 ratio (solid / liquid) for 45-60 minutes to obtain a second mixture, wherein the acid solution is 55-60% v / v sulfuric acid (H2SO4) solution; f) filtering the second mixture to obtain hydrolyzed solids, wherein the hydrolyzed solids comprise cellulose whiskers; g) neutralizing pH of the filtered hydrolyzed solids via repeated washing with deionized water using a centrifuge, to suspend the cellulose whiskers; h) homogenizing the suspended cellulose whiskers via ultrasonication; i) drying the homogenized cellulose whiskers; j) preparing a first solution comprising the dried cellulose whiskers and a solvent; k) ultrasonicating the first solution; 1) dissolving an at least one polymer in the ultrasonicated first solution under continuous stirring to prepare a polymer-cellulose whisker solution at 20% weight / weight polymer concentration; m) casting the polymer-cellulose whisker solution in an at least one mold to obtain the polymer-cellulose whisker composite; and n) drying the casted polymer- cellulose whisker composite, using one or more drying methods.

[0029] In a preferred embodiment of the present invention, the steps of the method will be elaborated herein:

[0030] First, alkali treatment of a cotton waste material is performed — which further comprises the steps of: i) adding the cotton waste material in an alkali solution in a 1 :33 solid / liquid ratio to create a first mixture; and ii) stirring the first mixture to extract a cellulose material. The alkali solution used in alkali treatment of the cotton waste material is a 5-15% v / v NaOH solution. The cotton waste material used may be cotton linter, cotton lint, or a combination of both. Preferably, the stirring step ii) is performed under constant stirring at 250 rpm and 60 °C for 6 hours. Then, the first mixture is filtered to obtain the extracted cellulose material, which is pH-neutralized after by repeatedly washing with distilled water until the pH is neutral (pH = 7). Filtration can be done by filter paper, mesh filter, vacuum filtration, or any combination thereof. The pH-neutral cellulose material is then dried until weight becomes constant. Preferably, the drying is done using an oven at 60 °C. The dried cellulose material is then collected, stored, and characterized.

[0031] Acid hydrolysis is performed to synthesize cellulose whiskers from cellulose. Acid hydrolysis was selected, as it is known as the simplest approach to highly effective cellulose whisker preparation using cellulose, given its mechanism of hydrolytic cleavage of glycosidic bonds of the disordered regions in the polymer (Teo and Wahab, 2020). Treatment methods used to synthesize cellulose whiskers influence their crystallinity, thermal stability, and aspect ratio (Teo and Wahab, 2020). Key parameters that were optimized in acid hydrolysis treatment included: acid concentration, reaction time, and temperature.

[0032] The dried cellulose material, extracted from the cotton waste material, is then hydrolyzed in an acid solution using a 1:10 solid / liquid ratio for 45-60 minutes to obtain a second mixture. The acid solution used in hydrolysis is 55-60% v / v H2SO4 solution. Preferably, hydrolysis is performed under constant stirring at 250 rpm and 45 °C. The second mixture is then filtered to obtain hydrolyzed solids, wherein the hydrolyzed solids comprise cellulose whiskers. The filtered hydrolyzed solids’ pH is then neutralized via repeated washing with deionized water using a centrifuge, to suspend the cellulose whiskers. In a preferred embodiment, the centrifugation is conducted at 10,000 rpm, 10 °C for at least 5 minutes. The suspended cellulose whiskers were then homogenized via ultrasonication. Preferably, the ultrasonication of the suspended cellulose whiskers is performed at 10,000 rpm for at least 30 minutes. The homogenized cellulose whiskers are then dried — preferably, using an oven at 60 °C for 6-8 hours until weight becomes constant.

[0033] Then, a first solution is prepared, comprising the dried cellulose whiskers and a solvent. In a preferred embodiment of the present invention, the solvent used in the first solution is a binary solvent of dimethylsulfoxide (DMSO) and tetrahydrofuran (THF). The prepared first solution is then ultrasonicated — preferably, performed at room temperature (or about 25 °C) and 10,000 rpm for at least 10 minutes. An at least one polymer is then dissolved in the ultrasonicated first solution under continuous stirring to prepare a polymer-cellulose whisker solution at 20% weight / weight polymer concentration. The at least one polymer may be chosen from perfluorinated polymers (e.g. perfluorosulfonic acid, perfluorocarboxylic acid), partially fluorinated polymers (e.g. poly vinylidene fluoride, polystyrene sulfonic acid), non-fluorinated hydrocarbons (e.g. polyether ether ketone, polybenzimidazole, polysulfone), or any combination thereof. In a preferred embodiment, the polymer dissolved in the first solution is polysulfone (PSU).

[0034] The prepared polymer-cellulose whisker solution is then cast in at least one mold to obtain the polymercellulose whisker composite and then dried using one or more drying methods. The composite comprises a polymer matrix and the cellulose whiskers as filler / nanofiller. Preferably, the casted polymercellulose whisker composite is dried using air-drying, oven-drying, or a combination of both. In a preferred embodiment of the present invention, air-drying is performed at room temperature (about 25 °C) for at least 24 hours to remove residual solvents, then placed in the oven at 60 °C to further cure and dry the composite completely.

[0035] In a preferred embodiment of the present invention, the produced polymer-cellulose whisker composite has suitable properties as membrane for fuel cells.

[0036] To demonstrate the chemical and physical properties of the extracted cellulose from cotton waste material, the synthesized cellulose whiskers, and the produced polymer-cellulose whisker composite using the method of the invention, Fourier Transform Infrared (FT-IR) spectra, XRD diffractograms, and images of the aforementioned are disclosed herein.

[0037] The extracted cellulose and the synthesized cellulose whiskers (CW) were characterized for their structural compositions using FT-IR spectrometer with Attenuated Total Reflectance (ATR) to determine the functional groups and correlate peaks associated with amorphous and crystalline structures to the total crystallinity index (TCI) of the materials. The crystallinity index (CrI) is further validated by performing X-ray Diffraction (XRD) analysis on the extracted cellulose and cellulose whiskers samples.

[0038] FIG. 1 shows the FT-IR spectra of cotton linter sample compared to extracted cellulose samples from varying NaOH alkali treatment (at 5%, 10%, and 15% NaOH concentrations). The broad band at 3200- 3500 cm'1confirms the O-H group of the extracted cellulose — thus, the broadening O-H band with increasing %NaOH alkali treatment shows increasing presence of O-H functional groups, likely from increasing cellulose extraction. All spectra exhibited peaks at 2800-3000 cm'1, which indicated the characteristic of C-H stretching vibration in cellulose, interrelated to lignin molecules. The reduction of intensity at 2850 cm'1peak compared to the cotton linter sample shows that the 10% and 15% NaOH treatment was very effective in eliminating undesired impurities and unwanted non-cellulosic components.

[0039] FIG. 2 shows the FT-IR spectra extracted cellulose samples at 5%, 10%, and 15% NaOH treatment at a different spectral range. The peak at 1429 cm'1is related to stretching the C-H group and bending of the 0-H or C-H group of hemicellulose. The C-0 stretching at 1050-1120 cm'1confirms the presence of hemicellulose and lignin, while the peaks at 1032-1167 cm'1are amorphous regions. It can be observed that the spectra of the 15% NaOH extracted cellulose sample shows that the peaks for lignin, hemicellulose and amorphous functional groups have disappeared, while the peaks for the cellulose functional groups became more evident. Thus, the spectra confirmed the desired composition of the extracted material from cotton linter as cellulose.

[0040] FIG. 3 shows the FT-IR spectra of synthesized cellulose whiskers (CWs) at different treatment conditions. The structural composition of the synthesized cellulose whiskers was confirmed using FT- IR. The spectra show the presence of characteristic peaks attributed to SO2 symmetric and asymmetric stretching at 1163 cm'1and 1036 cm'1. The presence of these SO2 peaks are primary indicators of cellulose conversion into cellulose whiskers. The peak at 2892 cm'1is associated with cellulose II from the glycosidic linkages. Other prominent peaks in the spectra at 1429 cm'1, 1366 cm'1, and 898 cm'1are associated to CH2rocking, CO stretching, and CH bending, respectively.

[0041] FIG. 4 shows an scanning electron microscope (SEM) image of synthesized cellulose whiskers from the method, at 80pm and lOOOx magnification. The morphology and microstructure of the cellulose whiskers and functionalized cellulose whiskers were analyzed for their geometric aspect ratio based on the SEM images using Image J software (version 7.0.0). FIG. 4 shows a significant difference in structural appearance and morphology. Further analyzing the SEM images using Image J software shows that the average fiber diameter is 6.16 pm and the average fiber length is 2977 pm. The aspect ratio (L / D) was calculated as 483.27, which is higher than the usual range of 5-50 aspect ratio. The higher aspect ratio presents potential for creating new materials and suitable for facilitating chemical processes, such as functionalization due to the surface energy and potentially lowers agglomeration level than unmodified cellulose.

[0042] FIG. 5 shows the XRD diffractograms of synthesized cellulose whiskers at different treatment combinations. The XRD analysis of the synthesized cellulose whiskers was performed to compare and determine the crystallinity of the synthesized cellulose whiskers. The XRD diffractograms show a sharp peak at 20° between 22-23 degrees — which confirms the cellulose type II crystals present in cellulose whiskers.

[0043] FIG. 6 shows images of the produced polymer-cellulose whisker composite samples, wherein the polymer matrix comprises PSU, at different loading levels of cellulose whiskers (0%, 3%, 5%, and 8%), using the method of the present invention. The polymer-cellulose whisker composite samples in FIG. 6 showed no separation and agglomeration of the cellulose whiskers. However, the polymer-cellulose whisker composite samples, which underwent air-drying and oven-drying at 60 °C, showed warping of the membrane, likely due to the effect of temperature or air moisture. This example, however, does not limit other drying and curing methods for the polymer-cellulose whisker composite produced using the method of the invention.

[0044] FIG. 7 shows the WCA measurement of a polymer-cellulose whisker composite sample, produced according to the method of the present invention. The resulting WCA showed complete wettability of the polymer-cellulose whisker composite — thus. showing the highly hydrophilic nature of the composite surface. This hydrophilicity is a suitable property for membranes in fuel cell applications, given its ability to retain water and conduction properties.

[0045] EXAMPLES

[0046] Example 1 : Biomass waste material profiling and selection

[0047] The characterization of different biomass materials was conducted by determining cellulose, lignin, and moisture content via TAPPI Useful Method 249: Sulfite Method, TAPPI T 222 om-02, and TAPPI T 264 cm-97, respectively. Table 1 below tabulates these composition values.

[0048] Table 1. Chemical composition of common biomass waste materials

[0049] Among the characterized biomaterials, cotton seed fibers showed the highest total cellulose content at around 95-97%. Cotton lint and linter samples also showed no lignin content and lower moisture content.

[0050] Example 2: Extraction of cellulose from cotton waste material

[0051] Experiments were performed to determine the better alkali treatment conditions that will give higher yield of extracted cellulose from cotton waste material, specifically, cotton linter. Yield was calculated as the weight ratio of the dried extracted cellulose and the starting cotton material, as a percentage.

[0052] Table 2 summarizes the yield results for different runs and %NaOH concentration used in alkali treatment.

[0053] Table 2. Chemical composition of common biomass waste materials

[0054] One-way ANOVA performed on the Table 2 data showed that there was a significant effect of the NaOH concentration on the yield. For the cellulose whiskers, yield was calculated as the weight ratio of the dried cellulose whiskers and the extracted cellulose material used for each mn, as a percentage. The higher NaOH concentration at 15% showed an average yield of 90.97%, which was lower compared to runs using 5% NaOH and 10% NaOH — which showed average yields of 92.74% and 92.61%, respectively. At 15% NaOH concentration with lower yield compared to 5% and 10% NaOH concentration, it showed that more impurities and unwanted components were removed. Thus, based on these results, the higher NaOH concentration used in alkali treatment, the more purified the extracted cellulose materials are after alkali treatment.

[0055] Example 3 : Synthesis of cellulose whiskers from extracted cellulose

[0056] Experiments were performed to determine the optimized acid hydrolysis parameters that will give higher yield of synthesized cellulose whiskers, from the extracted cellulose from cotton linter. Table 3 below summarizes these runs using different treatment parameters and their total crystallinity index (TCI) and response yield results. Table 3. Results of acid hydrolysis experiments

[0057] Two-way ANOVA was used to determine if there are significant effects of the individual parameters (acid concentration and reaction time). Based on the ANOVA results (with replicates), acid concentration was found to be a significant factor in the yield, while reaction time had no significant effect.

[0058] The increase in acid concentration from 55% to 60% showed a sharp decrease in yield from 77-92% to 31-43%. In comparison to EP3202978A1, which discloses a similar method of synthesizing cellulose whiskers / nanocrystals that produces 75-80% efficiency / yield, the method of the invention shows a higher yield (highest at 92%) for acid hydrolysis of cotton linter celluose at 55% acid concentration and 60 minutes reaction time.

[0059] Forthe reaction time of 45 to 60 mins., there was no significant change in yield from 30.5% to 39% and from 82% to 88%, for runs with 60% acid concentration and 55% acid concentration respectively. Thus, using 55% acid concentration in acid hydrolysis treatment showed the highest % yield of cellulose whisker synthesis in the experiment, while the reaction time was statistically insignificant.

[0060] Example 4; Crystallinity of cellulose whiskers

[0061] In addition to the FT-IR spectra and XRD diffractograms obtained for the extracted cellulose and cellulose whiskers, crystallinity indicators were also estimated and examined for the synthesized cellulose whiskers to gauge the samples’ physical properties. The total crystallinity index (TCI) can be calculated using Segal’s method from the FIG. 3 FT-IR spectra peaks associated with the crystalline components of the synthesized cellulose whiskers. After performing TCI estimation for the different cellulose whisker samples (treatment conditions in Table 3), the estimated TCI values ranged from 65.67% to 77.61%. The highest TCI (77.61%) was reported for the cellulose whisker sample treated with 60% acid concentration and 60 minutes reaction time. The lowest TCI value (65.67%) was recorded for the sample treated with 55% acid concentration and 45 minutes of reaction time. Crystallinity index (CrI) was estimated using the XRD analysis and the XRD diffractograms in FIG. 5. TCI and CrI values for the different cellulose whisker samples are tabulated below in Table 4.

[0062] Table 4. TCI and CrI values for cellulose whisker samples

[0063] CrI estimated from the same samples using were statistically the same with TCI values, ranging from 69.5%-72.4%. These crystallinity values show the presence of high-crystallinity regions in the tested samples — which is a characteristic of cellulose whiskers.

[0064] Example 5: Fabrication and characterization of PSU -cellulose whisker composite

[0065] In fabricating the polymer-cellulose whisker composite of the present invention, the cellulose whisker filler is considered an energy material (EM), in view of fuel cell membrane applications, due to its surface and functional properties. Energy materials are advanced high-performance materials with capacity to react and release energy — and have many applications in energy conversion such as in photovoltaic solar cells, energy storage, bioenergy, renewable fuels, batteries, and fuel cells. PSU- cellulose whisker composite samples were produced with 20% PSU concentration in DMSO / THF binary solvent with varying EM %loading (as weight percentage of the total polymer), specifically, at 0%, 3%, 5%, and 8% loading. Ultrasonication of the cellulose whiskers in the binary solvent, prior to blending with PSU, was found to be effective in dispersing the cellulose whiskers in the solvent and homogenizing the solution with PSU.

[0066] Electrochemical capacity in relation to the ion exchange capacity (1EC) was also determined. IEC measures the capacity of insoluble functional groups within the membrane to undergo displacement of ions incorporated into its structure. In the preferred embodiment of the present invention, wherein the polymer-cellulose whisker composite comprises a PSU matrix, the sulfonate groups present in the polymer are relevant to the electrochemical capacity for proton transport during reactions. The PSU- cellulose whisker composite sample had an IEC value of 0.314 meq / g — which is reasonably good, compared to Nafion 117, a commercial ionic polymer, with an IEC value of 0.93 meq / g.

[0067] REFERENCES

[0068] The detailed description refers to several documents, the content of which is herein incorporated by reference in their entirety. These documents include, but are not limited to, the following:

[0069] Osman, A. I., Farrell, C., Al-Muhtaseb, A. H., Harrison, J., & Rooney, D. W. 2020. The production and application of carbon nanomaterials from high alkali silicate herbaceous biomass. Scientific Reports, 10(1), 1-13.

[0070] Palanisamy, G., Oh, T.H., & Sadhasivam Thangarasu. 2023. Modified Cellulose Proton-Exchange Membranes for Direct Methanol Fuel Cells. Polymers 2023, 15(3), 659.

[0071] Prykhodko, Y., Fatyeyeva, K., Hespel, L., & Marais, S. 2021. Progress in hybrid composite Nafion®- based membranes for proton exchange fuel cell application. Chemical Engineering Journal, 409.

[0072] Rosa, M. F., Medeiros, E. S., Malmonge, J. A., Gregorski, K. S., Wood, D. F., Mattoso, L. H. C.. Glenn, G., Orts, W. J., & Imam, S. H. 2010. Cellulose nanowhiskers from coconut husk fibers: Effect of preparation conditions on their thermal and morphological behavior. Carbohydrate Polymers. 81(1), 83- 92.

[0073] Teo, H.L, Wahab., R.A. 2020. International Journal of Biological Macromolecules. 16, 11414-1430.

[0074] Teixeira, F. C., de Sa, A. I., Teixeira, A. P. S., & Rangel, C. M. 2019. Nafion phosphonic acid composite membranes for proton exchange membranes fuel cells. Applied Surface Science, 487 (April), 889-897.

[0075] Wang, Y., Seo, B., Wang, B., Zamel, N., Jiao, K., & Adroher, X. C. 2020. Fundamentals, materials, and machine learning of polymer electrolyte membrane fuel cell technology. Energy andAI, 1, 100014.

Claims

CLAIMS1. A method for producing a polymer-cellulose whisker composite, comprising the steps of: a. performing alkali treatment of a cotton waste material, further comprising the steps of: i. adding the cotton waste material in an alkali solution in a 1 :33 ratio (solid / liquid) to create a first mixture, wherein the alkali solution is a 5-15% v / v sodium hydroxide solution; and ii. stirring the first mixture to extract a cellulose material; b. filtering the stirred first mixture to obtain the extracted cellulose material; c. neutralizing the pH of the filtered cellulose material by washing with distilled water; d. drying the pH-neutral cellulose material; e. hydrolyzing the dried cellulose material in an acid solution in a 1 : 10 ratio (solid / liquid) for 45- 60 minutes to obtain a second mixture, wherein the acid solution is 55-60% v / v sulfuric acid (H2SO4) solution; f. filtering the second mixture to obtain hydrolyzed solids, wherein the hydrolyzed solids comprise cellulose whiskers; g. neutralizing the pH of the filtered hydrolyzed solids via repeated washing with deionized water using a centrifuge, to suspend the cellulose whiskers; h. homogenizing the suspended cellulose whiskers via ultrasonication; i. drying the homogenized cellulose whiskers; j. preparing a first solution comprising the dried cellulose whiskers and a solvent; k. ultrasonicating the first solution; l. dissolving an at least one polymer in the ultrasonicated first solution under continuous stirring to prepare a polymer-cellulose whisker solution at 20% w / w polymer concentration; m. casting the polymer-cellulose whisker solution in an at least one mold to obtain the polymer- cellulose whisker composite; and n. drying the polymer-cellulose whisker composite.

2. The method of claim 1, wherein the cotton waste material is selected from the group consisting of cotton linter, cotton lint, and a combination thereof.

3. The method of claim 1, wherein the stirring of the first mixture in step a) is performed at 250 rpm and 60 °C for 6 hours.

4. The method of claim 1, wherein the hydrolysis in step e) is performed under constant stirring at 250 rpm and 45 °C.

5. The method of claim 1, wherein the centrifugation in step g) is conducted at 10,000 rpm, 10 °C for at least 5 minutes.

6. The method of claim 1, wherein the ultrasonication of the suspended cellulose whiskers in step h) is performed at 10,000 rpm for at least 30 minutes.

7. The method of claim 1, wherein the solvent in step j) is a binary solvent of dimethylsulfoxide (DMSO) and tetrahydrofuran (THF).

8. The method of claim 1, wherein the ultrasonication of the first solution in step k) is performed at room temperature and 10,000 rpm for at least 10 minutes.

9. The method of claim 1, wherein the at least one polymer in step 1) comprises polysulfone.

10. The method of claim 1, wherein the concentration of the dried cellulose whiskers in the first solution is 3-8% (solid / liquid).

11. The method of claim 1, wherein the casting in step m) is one of solution casting and die casting.

12. The method of claim 1, wherein the drying in step n) comprises air-drying and oven drying.

13. A polymer-cellulose whisker composite obtained by the method of claim 1.

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