Preparation and Characterization of Carboxymethyl Microcrystalline Cellulose from Pineapple Leaf Fibre

doi:10.21203/rs.3.rs-4009721/v1

Highly functional and robust biobased materials are still in research to produce valuable bio-composites. In the present research, microcrystalline cellulose (MCC) was obtained through an agricultural waste, pineapple leaf fiber (PL) and further functionalized using upscaled chemical approach to carboxymethyl microcrystalline cellulose (CMMMC). To derive CMMCC from PL fiber, monochloroacetic acid, sodium hydroxide, and ethanol were used as solvents in an etherification procedure. FTIR, TGA, SEM, EDX, XRD, and DSC served to characterize the raw material, high crystalline MCC, and modified carboxy methyl MCC. FTIR analysis determined the presence of a different absorbed peak at approximately 1620.2 cm^-1, and at 1423.8 cm^-1, carboxyl groups were assigned to CMMCC. On the other hand, the XRD findings verified that CMMCC's crystalline structure has decreased. Analysis by SEM revealed a damaged surface morphology for CMMCC. Following chemical treatments, the EDX analysis revealed that each fiber sample contained a highly pure cellulose elemental composition. Thus, results explain the utilization of agricultural waste, pineapple leaf fiber to high valuable products like highly crystalline MCC, in addition further modification of MCC could leads to formation of highly functional material that could be used for other applications too in future.

Pineapple leaf

Microcrystalline cellulose

Carboxymethyl microcrystalline cellulose

Morphological properties

Structural properties

The search for robust, functional, high strength, soluble and active biobased materials is still pending in the field of additives manufacturing, composites productions, high strength applications etc. (Sulaiman et al. 2016). The production of biobased functional micro/nano materials could solve this problem and it is the thrust area in the current scenario. Recently, microfibrillated cellulose, cellulose nanocrystals and nanofibers were chemically/mechanically isolated from wood (Karim et al. 2021) and further modified to more superior materials and then used for highly advanced technologies/applications. For example, fully biobased affinity membranes were produced using various functionalized microfibrillated cellulose having active groups of hydroxyls (-OH), carboxylic (-COO), phosphate (PO4²⁻) and methyl (CH₃) (Karim et al. 2021; Karim et al. 2014; 2017; 2020).

Therefore, study of more sustainable biomaterials has grown rapidly in recent years. Indeed, agricultural waste is the most prevalent and limitless crystalline biopolymer that took place naturally in the world, and there is substantial interest in exploiting it as the main source of cellulose. Maize stalks, orange peel, sugarcane bagasse, rice and wheat straw, soybean pods, banana rachis, mulberry bark, and coconut fiber have all been investigated as potential sources to produce cellulose micro/nano (Karim et al. 2020).

Every year, tropical fruit companies generate lignocellulose waste in the form of pineapple leaf fiber (PALF), albeit only a small portion is now used in energy production and as biomass resources (Cherian et a. 2011; Rachtanapun et al. 2012). PALF is hard to decompose because of its high lignin and cellulose content, which contributes to its adverse environmental effects (Cherian et a. 2011; Rachtanapun et al. 2012; Asim et al. 2015). PALF is made up of 70–85% sugar polymer cellulose, the larger part being crystalline. The monomers that make up hemicellulose are arabinose, mannose, galactose, glucose, and xylose, which account for 6–19% of the total composition. Because it has an abundance of cellulose and a sharp microfibrillar angle, it makes microfibrils with a high tensile strength. Lignin accounts for 4–15% of the remainder, followed by wax at 4%, ash at 1–5%, and minerals in very small quantities. On average, it contains 11–15% water vapor (Asim et al. 2015; Pavithran et al. 1987; Mishra et al. 2001). It generates microfibrils with strong tensile strength because it contains a lot of cellulose and has a steep microfibrillar angle (14°C) (Cherian et al. 2011; Asim et al. 2015; Yaacob at al. 2017). The lignin and hemicellulose matrix that encompasses the cellulosic plant fiber, is linked to ncrystalline forms by intramolecular and intermolecular hydrogen bonding and strikes in an amorphous form, explaining the situation rapid heat deterioration. Because of these linkages, CMNF of PALF possesses better mechanical characteristics as well as is considered to have excellent aptitude strengthening in composite elements (Asim et al. 2015; Yaacob et al. 2017; Lopattananon et al. 2006: Threepopnatkul et al. 2009).

Therefore, transforming cellulose onto its derivatives is required prior to its use in the food industry. Carboxymethyl cellulose (CMC), also acknowledged as Na-CMC, is among the most common derivatives and is used for many purposes. CMC is generated through the reaction of monochloroacetic acid and alkali cellulose, and it is a straight-line polymer, long-chain, and excellent affinity with water (Sangseethong et al. 2015;Borsoi et al. 2015; Chen et al. 2018). According to some articles, CMC may be composed from a diverse of cellulosic sources, including natural cellulose, paper sludge, wood waste, cotton liners, and fibers. Finding more affordable alternatives to make CMC has generated a lot of attention (Gulati et al. 2014; Jia et al. Mohkami, 2011; Mondal et al. 2015). but still, it is difficult to find the one step reaction for the isolation of MCC from PALF. Indeed, various recipes in literature are responsible for less yield and less purity of isolated MCC from such high lignin content raw materials. In addition, due to the less solubility of MCC, it is not suitable to use it in fully water-based system (Sangseethong et al. 2015; Chen et al., 2018; Gulati et al. 2014).

Therefore, the goal of this study is to produce highly functional cellulosic micro/nano materials having high functionality, strength, yield, and purity. Furthermore, it should be soluble in water and could be used in a fully water-based system for production of highly valuable materials/products. Thus, pineapple leaf fiber (PL) was used in this study to fulfil these goals. A very easy, reproducible, and scalable chemical procedure was adapted for the isolation of MCC. Furthermore, to make it soluble in water, MCC was chemically modified to carboxymethyl microcrystalline cellulose (CMMCC) via a carboxymethylation reaction with sodium hydroxide using chloroacetic acid. Examples of the obtained CMMCC were shown by means of Fourier Transform Infrared spectroscopy (FTIR), X-ray diffraction (XRD), Thermogravimetric analysis (TGA), and Differential scanning calorimetry (DSC), as well as by means of Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive X-ray Particle Size Analysis (EDX/PSA). In addition, isolated cellulosic functional materials could be used to produce highly valuable products like additives, composites, adsorbents etc.

2.1. Raw material and chemicals preparations

Pineapple leaf (PALF) were sourced from a plantation in Johor, in the southern region of Malaysia. The pineapple varieties being used is Ananas cosomus, which is a member of the Bromeliaceae family (after the Josapine variety). NaClO₂ (80%), NaOH, Na₂CO₃, KBr, H₂SO₄ (95.0–98.0% w/v), and glacial acetic acid (MO, USA) had been provided by Sigma-Aldrich.

2.2. Extraction of PALF Microcrystalline Cellulose

This experimental setup was found to be ideal for generating white pineapple leaf fiber (PL-Bleach) through the greatest elimination of lignin admixture, and this treatment was carried out on a pilot scale using 500 mL of 2% NaClO₂ (acidified with 5 mL C₂H₄O2) over the course of 2 hours at 80°C with continuous stirring. After removing the lignin-containing filtrate, the NaClO₂-treated fiber substance has been retrieved through filtration using filtered water and nylon fabric. The fiber was then subjected to acid hydrolysis for depolymerization, following which the cellulose and hemicellulose components were swollen in 500 mL of 5% NaOH at 80°C for 5 hours. After being treated with NaOH, the recovered fiber residue was neutralized using purified water to a pH of 7 and filtered through nylon cloth until it turned white. Additional acid hydrolysis treatment was carried out at 80°C for 30 minutes applying a 2.5 M HCl solution to depolymerize the fiber into particulates. The mixture was centrifuged to a pH of around 3 after being quenched with 10 times its volume of cold distilled water to neutralize the acidic reaction. After being filtered and dried, the soft pulp-like structure of the acid-treated fiber (PL-MCC) was made.

2.3. PALF CMC Synthesis

The microcrystalline cellulose (PL-MCC) was transformed to carboxymethyl microcrystalline cellulose (PL-CMMCC) following the modified method (Mohkami M 2011). The microcrystalline cellulose (15 g), isopropanol (IPA) (450 ml), and 40% w/v NaOH (50 ml) were stirred continuously for 1 hour at 50°C while being mixed. The mixture was then mixed with an chloroacetic acid/IPA mixture (18 g/18 ml), agitated for the next 30 minutes, and place in a 55°C oven for 3.5 hours. After that, the mixture's liquid component was removed. After mixing in 225 ml of methanol, the fibre was neutralised with glacial acetic acid. The combination was then cleansed with 225 ml 70% v/v ethanol five times, accompanied by a final rinse with 225 ml 95% v/v methanol. Finally, the attained CMMCC product was dried in a 55°C oven for 12 hours before being stored in a sealed container before use.

2.4. Characterization of materials

Several cutting-edge approaches were employed for the identification of isolated MCC and functionalized CMMCC. The main aim was the understanding the rection conditions in the final properties of isolated cellulosic materials.

2.5. FTIR analysis

The IR spectra of the manufactured MCC and CMMCC samples have been recorded using an FTIR instrument (Model: FTIR-8900, Shimadzu, Japan). The pellets were prepared by crushing approximately 0.2 mg of CMMCC samples with 2 mg of KBr. Wavenumbers between 5000 and 400 cm^-1 were used to evaluate transmission.

2.6. XRD analysis

A Bruker D8 Advanced Germany X-Ray Diffractometer producing CuKα radiation and running at 30 mA and 40 kV X-ray beam with 2°/min step-by-step was used to analyze each sample's diffraction patterns from 10–50°.

Morphology, Particle Size, and Elements

The surface characteristics were studied using a Field Emission Scanning Electron Microscope (FESEM; Zeiss Sigma, Germany) for all raw PALF, MCC, and extracted CMMCCC. Before being examined, the samples were vacuum coated with an Au layer. Energy Dispersive X-ray (EDX) test with a working distance of 14.5–15.5 mm and a voltage of 20 kV was used to look at their elemental configuration. Using a Malvern Mastersizer 2000 device, the samples' particle size was analyzed.

2.7. Thermal Analysis

Each fiber sample's thermal stability was evaluated with a TGA/SDTA 851e model thermogravimetric analyzer (Mettler-Toledo International Inc., Columbus, OH, USA). The thermogravimetric analysis (TGA) was performed at 30–900°C with 10°C/min heating rate in a nitrogen purge environment. In the meantime, differential scanning calorimetry (DSC) was also performed with a DSC 822 analyzer at a rate of heating of 10°C/min between 30 and 600°C (Mettler-Toledo International Inc., USA).

2.8. Calculating the crystallization index and degree of polymerization

In our prior work, we reported an empirical method for calculating the crystallinity index (which expresses the relative degree of crystallinity) from XRD spectra without first subtracting the base line (Chen et al.2018). Crystallite size (L) was determined for the (101), (10i), (002), and (040) crystallographic planes by subtracting the corresponding Bragg angle from the baseline in spectra, as earlier stated by Chen et al., [16]. The degree of substitution (DS) was calculated by dissolving 0.5 g of MCC or CMMCC that had been dried at for 24 hours in 100 ml of purified water. Methyl red was used as an guideline to titrate a 20 ml sample of each solution with 0.1N sulfuric acid. The mixture was boiled and titrated to a second, more precise endpoint after the first one was reached. The DS of both materails was calculated by Eqs. (1) and (2) given below

Where b is the volumn of 0.1 N sulfuric acid used (in ml) and G is the pure mass of MCC and CMMCC (in g).

3.1. Isolation of MCC and surface functionalization to CMMCC

The isolation of MCC from high lignin pineapple raw leaf fibers was explored in very detail, indeed, the chemical reaction was followed to produce MCC, the high crystallinity (crystallinity index 95.2%) was an indication of high purity and high yield of isolated MCC. The yield of MCC was about 32% as calculated manually after dry weight. In our previous study, cellulose nanocrystals were isolated from industrial waste (cellulose sludge) and very low (14%) yield was reported (Karim et al. 2014; Chen et al. 1753; Vasconcelos et al. 2017). Furthermore, the chemical reaction used for the isolation of MCC is reproducible and could be used for pilot scale production (Table 1).

The modification of MCC to CMMCC was performed using chemical reaction with some modification, isolated CMMCC was less crystalline, decrease in the crystallinity was recorded from 95.2–69.4%, this indicates the further breakdown of crystalline structure of cellulose. Furthermore, it has also been indicated that the produced CMMCC was more soluble in water compared to MCC. Furthermore, the degree of substitution (DS) was also increased from 0.4 to 0.45 from MCC to CMMCC. In an article, degree of substitution was calculated for the surface functionalization of MCC to carboxymethyl cellulose and the obtained results were in the agreement of our studies (Wang et al. 2007).

Table 1

Detailed characterization of isolated MCC and modified CMMCC
Types of cellulose	Crystallinity index (%)	Degree of Substitution	Yield (%)
MCC	95.2%	0.4	32
CMMCC	69.4%	0.45	NA

3.2. Microstructure, Particle Size, and Elements

Morphology of PL-Raw, PL-Bleach, PL-MCC, and PL-CMMCC were investigated through FESEM examination (Fig. 1a-d). The raw PL-Raw sample (Fig. 1a) exhibited a flawless surface with no holes or else fractures and a solid structure; nonetheless, the cellulose exhibited the presence of tiny fibre structures. The microstructure of the samples changed as the concentration of NaOH was expanded. The treated fibres of PL-Bleach (Fig. 1b) and PL-MCC (Fig. 1c) have turned into tiny fibre with smooth surface morphology (Fig. 3d). When the CMMCC underwent treatment with 40% NaOH, its polymer chain began to degrade, causing PL-CMMCC's structure to crack and deform (Fig. 1d). Defibrillation of cellulose powder was aided by the presence of a high concentration of NaOH, indicating that CMMCC could only have been formed under those conditions. This result was consistent with that observed with carboxymethyl cellulose derived from rice and cassava starch .

Figure 2 depicts the distribution of particle sizes of fibre samples, and Table 2 lists the analysed data. The sample of PL-Raw has the highest size distribution of 564.78 µm. Meanwhile, the size was reducing from PL-Raw to PL-Bleach due to the disintegration of cellulose fibril and removal of lignin and hemicellulose. Despite both PL-MCC and PL-CMMCC have the relatively same size distibution around 200 µm, the PL-CMMCC (196.7 µm) sample has slightly smaller size comparing with PL-MCC (205.6 µm) (Mohkami et al. 2011).

Table 2

Elemental and particle size of PL-Raw, PL-Bleach, PL-MCC, and PL-CMMCC samples
Samples	C (%)^a	O (%)^b	Mg (%)^c	K (%)^d	Ca (%)^e	Na (%)^f	VWMD (µm) ^g
PL-Raw	40.69	56.80	0.29	1.32	0.89	-	564.78
PL-Bleach	61.00	38.84	-	-	0.17	-	412.3
PL-MCC	54.86	45.14	-	-	-	-	205.6
PL-CMMCC	55.64	40.71	-	-	-	3.65	196.7
^a Carbon; ^b Oxygen; ^c Magnesium; ^d Potassium; ^e Calcium; ^f Sodium; ^g Volume weighted mean diameter

Figure 3 shows EDX spectra of samples of PL-Raw, PL-Bleach, PL-MCC, and PL-CMMCC. Each fibre clearly had oxygen and carbon peaks as its primary elements, which is what cellulose is composed of. Also, the EDX test showed that all fibre samples had pure cellulose after being treated with alkali, bleaching, acid, or carboxymethylation [20,24,25].

3.3. FTIR Analysis

The fiber characteristics of each sample were examined using FTIR spectroscopy. In figure. 4, the differences between the FTIR spectra of PL-Raw, PL-Bleach, PL-MCC, and PL-CMMCC are shown. The main differences were observed between 1000 cm^-1 and 1900 cm^-1. The peak intensities of the absorption bands at 1514.2, 1605.2, 1638.5, and 1740.1 cm^-1 decreased from PL-Raw to PL-CMMCC samples.

A wide retention band at 3350 cm^-1 was caused by the stretching of -OH, that was instantaneously linked to hydrogen bonds within and between molecules. Furthermore, structural vibrations and C = O stretching of carbonyl groups were responsible for the maximum intensity at 1514 cm^-1, proving the involvement of MCC. In addition, a prominent peak at 1249 cm-1 was assigned to C-O-C stretching at β-glycosidic bonds. These structural alterations and peak shifting proved the formation of CMC (Mondal et al. 2015; Beck et al. 2015).

The band at 2924.1 cm^-1 is associated with the C-H bending vibration, and both the PL-MCC and PL-CMMCC samples exhibited a large absorption band at 3434.9 cm^-1 due to the stretching vibration of the OH group. A significant and intriguing absorption peak at 1620.2 cm^-1 is consistent with COO-group bending vibrations, and the absorption maximum at 1423.8 cm^-1 is attributed to COO-salts. The bands that are located at 1329.3 cm^-1 and 1112.7 cm^-1 are thought to be caused by C-O-C bending vibrations and OH stretching, respectively. The 1,4- glycoside of cellulose was found and comprehensible when the wavelength was 894 cm^-1 (Karim et al. 2020; Zhang et al. 2017).

3.4. XRD Analysis

XRD analysis is employed to analyze the amount of crystallinity present, such as cellulose, by attributing it to its semi-crystalline structure in origins. The scattering arrangements of PL-Raw, PL-Bleach, PL-MCC, and PL-CMMCC samples are displayed in Fig. 5. Crystalline phases are represented by the peaks, while amorphous phases are shown by the baseline. The XRD approach forecasts that the peaks will be large due to the tiny crystallites in cellulose granules. This idea says that very small crystals with flaws cause more diffraction. The PL-CMMCC diffraction arrangements showed that the crystal structures of the novel cellulose were breaking down (Fig. 5). All the distinct peaks of cellulose have just about vanished and been replaced by an amorphous region. Thus, PL-CMMCC has superior solubility, since decreased crystallinity corresponds to super solubility. Alkaline solution is added to the cellulose molecules during the carboxymethylation reaction. When cellulose granules grow in size, they exert a force on neighboring crystalline cellulose molecules, distorting their shape. Swelling causes their double-helical area to uncoil or detach, as well as the disintegration of their crystal structures (Karim et al. 2020).

3.5. Thermal Stability

Figure 6 depicts the TGA curves of the respective samples. All samples lost mass during the 50–132°C temperature range due to evaporation of remaining hydrate and volatile compounds (Fig. 6a). Above 200℃, the early degradation temperature of PL-Bleach and PL-MCC was higher than that of PL-Raw. The remarkable heat resistance of PL-Bleach and PL-MCC was likely due to their high cellulose content. PL-CMMCC showed a lower early degradation temperature than PL-MCC, which might be attributed to its softer structure (Jia et al. 2016).

In addition, PL-MCC exhibited remarkably high peak degradation temperature, which reflected its highly crystalline cellulose structure (Fig. 6b). The decreased peak degradation temperatures of PL-CMMCC may be attributable to the presence of amorphous constituents. In addition, the peak degradation grew more pronounced from PL-Raw to PL-CMMCC, indicating that the PL-CMMCC sample contained purer cellulose compartment. Meanwhile, lower weight loss was revealed by PL-MCC as compared with PL-CMMCC. This was due to flame retard behavior of cellulose crystals within PL-MCC sample. The relatively high peak degradation temperature of PL-CMMCC at around 352.7°C also proved that it has great capability to resist high temperature (Chen et al. 2018).

The thermal property of PL-Raw, PL-Bleach, PL-MCC, and PL-CMMCC samples were evaluated with DSC, while the DSC thermograms are presented in Fig. 7. The crystallizing temperature (T_c) of PL-Raw was 227.5°C, PL-Bleach was 215.1°C, PL-MCC was 241.2°C, and PL-CMMCC was 243.9°C, respectively. This shift in melting point is caused by the carboxymethyl side group's abnormalities, which interfere with crystallisation and raise the melting point (Karim et al. 2020; Mihra et al. 2001; Wang et al. 2007; Zhang et al. 2017).

In this study, we report the key results of an etherification reaction involving monochloroacetic acid, sodium hydroxide, and ethanol to produce CMMCC from pineapple leaf fibre. In the FTIR spectrum, a new absorbed peak appeared at 1620.2 cm^-1, which corresponds to the vibrational stretch of carboxyl groups (COO), and a second peak at 1423.8 cm^-1 was attributed to the carboxyl group salts in CMMCC. The XRD results showed that the structure of PL-CMMCC was less crystalline after the synthesis process. Since the native cellulose peaks changed into an amorphous structure, they are now almost impossible to observe. The SEM evaluation revealed disintegrated individual structure of PL-CMMCC powder. When the samples were exposed to 40% NaOH, the MCC polymer chain violated, which caused the surface of the PL-CMMCC powder to be cracked and deformed. The EDX analysis justified that each fiber sample composed highly plain cellulose elemental composition after respective chemical treatment process. In addition, the DSC curves for both PL-MCC and PL-CMMCC powders were fairly flat, indicating a stable thermal behaviour. Consequently, the attained PL-CMMCC output has conceivable practiced for pharmaceutical and food additives application industry in the forthcoming. Furthermore, these functional material scould be easily used for some valuable product developments in future.

Ethical approval - No ethical clearance is required.
Human and animal rights - We declare that there are no animal studies or human participant involvement in the study.
Conflict of interest - The authors declare no competing interests.

Availability of data and materials - The data that support the findings of this study are available from the corresponding author, (Jawaid, M.), upon reasonable request.

Competing Interest-The authors declare that they have no competing interest.

Funding

The authors would like to extend their gratitude to King Saud University (Riyadh, Saudi Arabia) for funding this research through Researchers Supporting Project number (RSP2023R117).

Author’s contribution

Data curation, H.F. A.M. and M.J.; Formal analysis, H.F. and M.J.; Funding acquisition, H.F., M.J., M.H. and M.M.N. Project administration, H.F., M.J., Z.K., M.H. and A.M.; Writing—original draft, H.F., Z.K. and M.J.; Writing—review & editing, S.N.S, M.J., Z.K., M.H., M.M.N. and A.M. All authors have read and agreed to the published version of the manuscript.

Acknowledgements

The authors would like to extend their gratitude to King Saud University (Riyadh, Saudi Arabia) for funding this research through Researchers Supporting Project number (RSP2024R117).

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No competing interests reported.

Preparation and Characterization of Carboxymethyl Microcrystalline Cellulose from Pineapple Leaf Fibre

Status:

Version 1

Abstract

Figures

1. Introduction

2. Materials and Method