Synthesis of Novel Bio-Composite Material for Functional Finishing of Cellulosic Textile Substrate

ABSTRACT

Development and useful utilization of materials from agricultural wastes and biomass feedstock for the textile-finishing industry is of great significance to the research community worldwide. In this work, a sustainable and green chitosan and waste onion peel extract (CS-OS) composite material is prepared by the co-precipitation method and applied onto cotton fabrics for the development of antibacterial and radical-scavenging textiles. The composite was loaded onto cotton with and without citric acid as a cross-linker to obtain final textile substrate with durable functions. The composite formation and the coated cotton fabrics were examined using SEM, FT-IR, and TGA techniques. Antioxidant activity of the finished fabrics was evaluated using the DPPH assay, and antibacterial tests were performed using the colony counting method. The results revealed that composite-treated cotton showed good radical-scavenging and antibacterial activities. It was found that citric acid-cross-linked cotton fabrics displayed enhanced antibacterial and antioxidant properties.

摘要

农业废弃物和生物质原料材料的开发和有效利用对世界各地的研究界具有重要意义. 本工作采用共沉淀法制备了一种可持续的绿色壳聚糖和废弃洋葱皮提取物（CS-OS）复合材料，并将其应用于棉织物上，用于开发抗菌和清除自由基的纺织品. 将复合材料负载到含有和不含有柠檬酸作为交联剂的棉花上，以获得具有耐久功能的最终织物基材. 利用扫描电镜、红外光谱和热重分析技术对复合材料的形成和涂层棉织物进行了研究. 采用DPPH法对成品织物的抗氧化活性进行了评价，并采用菌落计数法进行了抗菌试验. 结果表明，复合处理棉具有良好的清除自由基和抗菌活性.研究发现，柠檬酸交联棉织物具有增强的抗菌和抗氧化性能.

KEYWORDS:

• Natural fiber
• plant extract
• chitosan
• finishing agents

关键词:

• 天然纤维
• 植物提取物
• 壳聚糖
• 整理剂

Introduction

Functional textiles, particularly antibacterial fabrics, exhibit diverse applications and are rapidly becoming very popular for use in different sectors, including apparel, healthcare and medical, aerospace, agricultural, and food (Adeel et al. 2018). Given their growing importance, the application of various chemicals such as organic metal complexes, organometallics, heterocyclics, heavy metal ions, formaldehyde derivatives, amines, and synthetic dyes to fabricate antimicrobial textiles has been well documented (Haji 2020). Despite their potential antibacterial nature, some of the synthetic agents have some serious drawbacks, mainly toxicity to humans and disturbing the eco-balance of nature (Khan et al. 2015). To overcome these problems, scientists have recently focused research activities toward developing variously sustainable and green finishing agents (Alebeid et al. 2019; Haji et al. 2020). Chitosan is one such inexpensive, nontoxic, and biodegradable agent that has been extensively studied due to its unique biological properties (Roy et al. 2017). It is a polysaccharide composed of glucosamine and N-acetylglucosamine units and has reactive functional sites that are readily subject to chemical modifications for the development of potential antimicrobial derivatives (Abdul Khalil et al. 2016; Shirvan, Shakeri, and Bashari 2019). Chitosan is a particularly attractive candidate due to its antibacterial properties, which are advantageous for the development of medical and healthcare products (Li et al. 2021). It is gaining popularity in the textile sector as an eco-friendly finishing material and has been widely used on different textile substrates to produce antimicrobial, antistatic, wrinkle-resistant, and UV protection properties (Li et al. 2023; Yavaş and Atav 2022).

Likewise, different plant extracts or compounds derived from natural products, endowed intrinsically with antioxidant and antibacterial properties are considered safer and more effective functional agents for different textile modifications (Shabbir et al. 2017). Among various plant extracts, Allium cepa is a well-known medicinally rich crop that has been successfully grown in all parts of the world (Jin et al. 2011). The phytochemicals isolated from all parts of the onion plant have been well documented in the literature to have a myriad of medicinal properties such as antibacterial, antioxidant, anti-carcinogenic, anti-platelet, antibiotic, and anti-asthmatic properties (Venkatasubramanian et al. 2020). The outer dry layers of onions, which are discarded as waste, provide ample opportunity to be used as a rich source of natural dye that imparts a yellowish-brown color to fabrics (Uddin 2014). Onion peels despite rich in polyphenols remain underutilized natural products worldwide. Therefore, it is necessary to explore their use in different industrial sectors as green and ecofriendly functional materials. In the textile sector, several research studies have demonstrated the potential of onion extracts in the dyeing and finishing of different textile substrates. It is pertinent to mention that the dyeing and antimicrobial properties of onion extracts have been attributed to the presence of flavonoid compounds (Rehman et al. 2013). Figueroa et al. (Figueroa et al. 2022) investigated the coloration and fastness of wool and cotton using aqueous extracts of three natural dyes, including purple onion peel, and observed good dyeing results. Joshi et al. (Joshi et al. 2022) prepared onion peel-based emulsions and reported their use in the development of antibacterial and UV-protective cotton fabrics. It is important to mention that natural dyeing with onion extracts, like other natural colorants, requires the use of metallic salts as mordants for fixation and improved dye performance (Rather et al. 2020). The application of metallic mordant may pose health and environmental risks. To avoid this, more recently, Rahman and his coworkers noticed that the extracts of onion peel exhibited better dyeing performance after mixing with other natural dyes (Rahman, Koh, and Hong 2022). To date, there have been little efforts made in the synthesis and application of natural product-based bio-composites for the development of functional finishes on textile surfaces. Because natural polymers are biodegradable and renewable, they can easily interact via electrostatic interactions and hydrogen bonding, resulting in an eco-friendly and green finishing formulation. Keeping these facts in view, it is important to investigate the functional effects imparted to textiles by the synergistic use of chitosan and onion peel extracts without using any toxic metallic mordants. Therefore, this study is focused on synthesizing chitosan-onion shell (CS-OS) composite and investigating its effectiveness in the development of bioactive cotton for various healthcare uses. The incorporation of aqueous onion shell extract into synergistic chitosan polysaccharide allows the formation of a CS-OS composite material, which was characterized using a variety of analytical techniques. In this work, citric acid was cross-linked to cotton before composite material treatment and evaluated for antibacterial and antioxidant actions.

Material and methods

Materials

The plain-woven cotton fabric (plain weave-2/1 twill, ends per inch = 128, and picks per inch = 66, areal density = 126 gm⁻² and cover = 94%) used for the lab-scale experiment was purchased from Vardhman fabrics, India. Chitosan was supplied by Sigma-Aldrich. Onion peels were obtained from a local vendor of IIT, Delhi. Citric acid and methanol were procured from Merck, Germany.

Onion peel extract

For aqueous extraction, 3 g of onion peel powder was placed in 100 mL DI water and sonicated for 3 h at 90°C. The solution obtained was passed through Whatman’s filter paper and used in subsequent experiments.

Synthesis of composite

For the synthesis of chitosan onion shell extract composite, 0.3 gm of CS, dissolved in 25 mL of 2% CH₃COOH was transferred in a round bottle flask followed by sonication for half an hour using ultra-sonic cleaner bath as per the method reported by Revathi and Thambiduri (Revathi and Thambidurai 2017). Onion peel extract (25 ml) was added dropwise to the prepared solution, and the mixture was stirred for 3 h. During this process, 30–40 mL of 1 M aqueous NaOH solution was added slowly until a precipitate was formed. The reaction was allowed to stand for the next 24 h to obtain the final product. Afterward, the obtained precipitate was washed several times with distilled water. The final filtrate was dried at 100^◦C for 5 h in a hot air oven and powdered well with mortar.

Coating of chitosan-onion peel composite on cotton fabric

The synthesized composite was applied onto cotton and citric acid cross-linked cotton following the recommended procedure reported by Revathi and Thambiduri (Revathi and Thambidurai 2017). The cross-linking of cotton was done by immersing cotton fabrics in 1.25 mL of citric acid (25%) for half an hour at room temperature. After half an hour, the treated cotton fabrics were padded on padding mangle and cured at 120°C for 5 min in a hot oven (Scheme 1).

Scheme 1. Schematic view of the formation of composite agent between onion skin extract and chitosan.

Scheme 1

Spectroscopic characterizations

The FTIR instrument (Nicolet Magna 550 spectrometer) with a resolution of 8 cm⁻¹ was used to characterize samples in the spectral range of 4000 cm⁻¹-500 cm⁻¹. For understanding surface changes, a scanning electron microscope JEOL JSM-6300 was used.

Thermal characterization of samples was carried out on Perkin Elmer DTA/TGA, model STA 449 in the presence of high-purity N₂ gas in the range of 50–800°C temperature.

Functional properties

The radical scavenging activity of the synthesized composites and treated cotton was evaluated by DPPH assay as per a well-established essay (Islam et al., 2018). DPPH radical scavenging activity was measured using the following equation.

(1) $Antioxidantactivity\left(\mathrm{\%}\right)=\frac{C-S}{C}\times 100$(1)

Where S and C represent the absorbance of the treated sample and control, respectively.

Likewise, the antibacterial activity of the composite material and treated cotton was analyzed AATCC 100:1998 test standard. The decrease in the bacterial population was calculated using the following formula.

(2) $Antibacterialactivity\mathrm{\%}=\left(A-B\right)/A100$(2)

A= number of E. coli colonies on control and B= number of E. coli colonies formed on the sample

Results & discussion

Characterizations

FT-IR analysis was done to observe the role of chitosan and chemical compounds present in the onion skin extract that were used in the synthesis of the composite functional agent. Figure 1a displays the FTIR spectra of chitosan and onion peel extract. A broad peak at 3435 cm⁻¹ is ascribed to the O-H group, and peaks at 1649 and 1427 cm⁻¹ are due to Amide I and II present in the backbone of chitosan. A peak at 3427 cm⁻¹ represents vibrational O-H stretch of polyphenolic compounds in the onion peel extract. Moreover, the presence of the intense peak at 1634 cm⁻¹ represents the carbonyl stretching vibrations, confirming the existence of quercetin molecules as reported by previous researchers (Rehman et al. 2013). Other characteristic peaks were observed from C-H and C-OH stretching at 2912 cm⁻¹ and 1235 cm⁻¹, respectively. The FTIR spectra of the CS-OS composite are presented in Figure 1b. Characteristic bands found in the FT-IR spectra of CS-OS composite include peaks due to O-H (3327 cm⁻¹) and amide I – III arising due to stretching vibrations of chitosan. The amide I at 1648 cm⁻¹ and the amide III at 1425 cm⁻¹ are ascribed to stretching vibrations. The FT-IR spectra of untreated cotton and after treatment with CS-OS composite in the absence and presence of crosslinking agent are also shown in Figures 1c. From Figure 1c, the peaks for untreated cotton at 3300 cm⁻¹ are due to O-H stretching and N-H vibrations (Caiqin et al. 2002). The bands around 1428 cm⁻¹ (C-H scissoring motion) and the peak at 1153 cm⁻¹ could be assigned to stretching vibration of the C-O-C anti-symmetric bridge (Shariatinia and Fazli 2015). It is noteworthy that the FTIR spectrum of CS-OS composite-coated cotton fabric shown in Figure 1c shows the slight shifting of some peaks along with the appearance of a new peak at 1648 cm⁻¹ which is assigned to C=O stretching vibration. The new band at 1648 cm⁻¹ in the spectrum confirms the presence of carbonyl groups present in the synthesized composite agents on the cotton surface (Lu et al. 2011). The FTIR spectrum (Figure 1c) for cross-linked cotton appears similar to that of CS-OS composite-coated cotton with some bands slightly shifted to higher wavenumbers. This slight variation in bands confirms the bonding of composite onto cross-linked cotton and further proves that this treatment causes only slight changes in the chemical structure of the cotton. The tensile strength of neat cotton fabric was found to be 815 ± 1.11, which slightly decreased to 782 ± 1.76 after exposure to citric acid as a cross-linking agent. On the contrary, direct application of composite material did not alter the chemical nature of cotton with a tensile strength of 803 ± 1.97. The areal density of the cotton after the treatment was also found to 132 gm⁻².

Figure 1. FT-IR analysis of a. chitosan and onion extract b. composite powder c. untreated cotton, composite-coated cotton and composite-coated cotton fabric with citric acid.

To examine the morphological characterization of cotton fabrics before and after treatment, SEM analysis was performed. Figure 2 represents the SEM micrographs for synthesized composite and the treated cotton. The SEM micrographs revealed that the composite surface was multilayered and rough. Raw cotton fabric displays a smooth surface opposite to the cotton coated with composite material. The surface of composite-coated cotton in the presence of citric acid seems rougher with spots spreading over the surface reflecting more deposition of composite.

Figure 2. SEM micrographs of composite (a), untreated cotton fabric (b), composite-coated cotton fabric (c), composite-coated cotton fabric with citric acid (d).

The thermal stability of the synthesized composite powder was confirmed by TGA analysis in a nitrogen atmosphere with a temperature range from 50 to 800°C. Figure 3a, b displays TGA of chitosan, onion extract, and the derivative of the weight loss of composite. The first decomposition at around 100°C in both chitosan and onion extract is generally associated with physically associated water molecules. At temperature above 250°C, the weight loss occurred probably by the decomposition of chitosan and secondary metabolites in onion extract. From the results, it can be noticed that the rate of weight loss is slow initially till 240°C. After this temperature, sharp weight loss occurs at around 300°C (Corazzari et al. 2015). Likewise, the untreated cotton fabrics exhibit small weight loss at around 100°C due to adsorbed water molecules. The weight loss at 240°C and 350°C correspond to de-polymerization of the cellulosic structure (Basak and Wazed Ali, 2018). On the other hand, composite-treated cotton shows a lower weight loss rate. The weight loss in the case of composite-coated cotton at about 250–450°C may be caused by the decomposition of the pyranose ring in the chitosan skeleton. The composite-coated cotton with citric acid exhibits slightly higher thermal stability (Figure 4).

Figure 3. (A) TGA analysis of the CS and onion extract. (b) TGA analysis of the CS-OS composite.

Figure 4. TGA analysis of untreated cotton fabric, composite-coated cotton fabric, and composite-coated cotton fabric with citric acid.

Antibacterial activity

Antibacterial activity of the untreated cotton, CS-OS composite treated cotton with and without citric acid was examined against E. coli. The results in the form of percentage inhibition are shown in 5.

From the results, it is clear that cotton treated with CS-OS composite possesses antibacterial activity toward E. coli. In particular, cotton fabrics cross-linked with citric acid and coated with CS-OS composite showed much-improved activity than CS-OS coated cotton fabric against E. coli bacterium. The inhibition activity of the CS-OS composite treated fabric in the presence and absence of citric acid was found to be 91.6% and 95.2%, respectively against E. coli. The microbial inhibition mechanism of chitosan relies on the protonated amino groups. It is believed that chitosan-bearing positive charge binds with the negatively charged cell membrane of bacteria, hampering normal metabolic activities, and eventually resulting in bacterial death (Islam et al, 2019; Kong et al. 2010). It is also noteworthy to mention that active biomolecules present in onion shell extract are reported to possess quite good antibacterial activity. This has led to the tentative conclusion that the antibacterial activity of composite-coated cotton is due to synergism between chitosan and onion peel extract. As can be seen in Figure 5, the antibacterial activity is the highest for composite deposited fabrics cross-linked with citric acid. The more deposition of composite on cross-linked fabric could be attributed to the reaction between functional groups of cellulose and amino groups of chitosan through citric acid.

Figure 5. Percentage of antibacterial activity of composite-coated cotton.

Radical-scavenging activity

While much current research focuses on the development of antibacterial clothing, we highlight that antioxidant or radical-scavenging activity of fabrics to protect skin against oxidative damage should also be considered. Chitosan polysaccharide and onion shell extract are commercially abundant and contain useful functional groups, mainly free hydroxyl compounds which are already reported as potent antioxidants (Cao et al. 2013; Sousa, Guebitz, and Kokol 2009).

The radical-scavenging activity of composite-coated cotton was analyzed by DPPH assay. The result for antioxidant activity is displayed in Figure 6. As compared to untreated cotton, the

Figure 6. Antioxidant activity of composite-coated cotton.

composite-coated cotton showed good antioxidant activity of 76.26%, while composite-coated cotton in the presence of citric acid showed much improved antioxidant activity of 83.28%. This enhancement could be attributed to the retention of higher amounts of composite onto citric acid-treated cotton due to chemical linkage between reactive hydroxyl groups of cotton with chitosan and onion shell extract biomolecules. The results displayed in Figure 7a, b demonstrate the retention of anti-bacterial and free-radical scavenging properties after several wash cycles on fabrics coated with composite cotton and composite cotton along with cross-linker. It can be noticed that cross-linked cotton retains a significant percentage of functional properties even after five repeated washing cycles.

Figure 7. The retention of free-radical scavenging and anti-bacterial properties after several wash cycles.

Conclusion

In summary, chitosan, a natural polymer, and onion peel extract were used to produce a novel green composite for the functional finishing of cotton. The composite was prepared using the precipitation method, and various analytical techniques, such as SEM and FT-IR, confirmed the successful synthesis and binding of the composite onto the cotton. The results showed that the chitosan-onion composite exerted interesting antibacterial and antioxidant properties on the cotton surface. The use of citric acid resulted in the highest disposition of the composite onto the cotton. The composite-coated cotton demonstrated antioxidant activity and was quite effective against E. coli, displaying strong antibacterial activity. The synergism between chitosan and active phytochemicals present in the onion extract was identified as responsible for inhibiting bacterial growth. Additionally, the use of citric acid played an important role in imparting functional properties to the cotton by facilitating crosslinking between the composite and reactive sites on the cotton surface. It is believed that the composite-coated cotton may prove to be an excellent candidate for preventing nosocomial infections in the healthcare sector.

Highlights

• Simple one-step facile green synthesis of chitosan-onion peel composite is reported.

• Green composite formulation successfully imparted excellent antibacterial and good antioxidant properties to cotton fabrics.

• Composite material in the presence of citric acid maintained functional properties after several washing cycles

Disclosure statement

No potential conflict of interest was reported by the author(s).