Introduction
Eco-friendly surface modification and multifunctionalization of cellulosic fabrics using various emerging and sustainable technologies [
12,
15,
28,
57] as well as environmentally sound textile chemicals and auxiliaries are the most recent trends in textile finishing processes [
16,
17,
28,
35] for imparting highly demanded, novel and outstanding functional properties such as antibacterial [
2,
14,
44,
47], UV protection, self-cleaning [
36,
46,
47,
49,
52], wrinkle recovery [
9,
27,
38,
51], enhanced fragrance [
17,
20,
25], etc., with high values added, taken into account the ever-growing consumer demands for high product and ecology quality, along with economical social concerns [
48].
Chitosan (CS) and CS derivatives are currently used in textiles modification, coloration and/or functionalization for their cationic active sites, N
+H
2 groups, especially at acidic conditions [
23,
42,
57,
62]. Antimicrobial activity of CS is attributed to the interaction between its positively charged active sites and the negatively charged sites on the microbial surface [
30,
37,
43], which, in turn, results in disruption of the harmful microbial cells, changes in their metabolism and leads to cell death [
37,
61].
On the other hand, ionic gelation method is widely used for obtaining CS nanocomposites via interaction of positively charged Na-tripolyphosphate (TPP) under appropriate conditions, thereby forming coacervates as a direct consequence of electrostatic interaction between the two aqueous phases along with ionic gelation via transition from liquid to gel phase [
5]. The experimental results showed that the antibacterial activity against both Gram-positive and Gram-negative bacteria of CS-TPP NPs suspension was better than that of the CS solution [
5].
Recently, various techniques of ZnONPs such as chemical reduction [
29,
40], plant extract [
1,
3,
45], fungus [
55], electrochemical method [
8], microwave [
58] as well as
in situ preparation [
4] and their potential textile applications to impart multifunctional properties such as antibacterial, self-cleaning, flame retardant and UV protection, taking in consideration both the environmental concerns and the ever-growing consumer demands have been developed and successfully carried out [
6,
7,
10,
39,
47,
50,
56]. ZnONPs have been widely utilized in textile functionalization due to its desirable physical and chemical properties, biocompatibility compared with other metal oxides and its low production cost. ZnONPs finished fabrics showed excellent antibacterial activity due to the ability of ZnONPs to destroy the growth of the microbe [
41]. Moreover, ZnONPs exhibit significant activity even at neutral condition, in the absence of light as well as excellent stability under high temperature and UV. ZnONPs, as an n-type semiconductor, show photocatalytic activity which, in turn, distinguish ZnO with unique multifunctional properties [
31,
32,
53,
59].
Additionally, a green biosynthesis/cost-effective routes for fabrication of metal (M) and metal-oxide (MO) nanoparticles (NPs) using Miswak-rich active phenolic constituents for promoting, reduction, formation and stabilization of the demanded MNPs or MONPs as well as their potential applications have been developed and implemented recently [
33,
54]. It was observed that the antibacterial activity of the biosynthesized nanoparticles using an eco-friendly aqueous solution of Miswak root extract was better than that prepared by non-eco-friendly conventional chemical methods [
54].
To date, there are few studies focused on the positive role of eco-friendly multifunctionalization of cellulosic substrates using, (i) citric acid/NaH2PO2 (CA/SHP) as zero-CH2O ester-crosslinking system along with biosynthesized ZnONPs using Miswak extracts as bio-reductant and ii) CA/SHP CSNPs alone and in combination with L-ascorbic or vanillin as green bioactive functional additives. Herein, we reported biosynthesis and characterization of ZnONPs and CSNPs along with their potential applications in functional finishing of cotton and viscose substrates using a pad-dry-cure process. The effect of finishing bath constituents on the imparted multifunctional properties such as anti-crease, UV protection and antibacterial activity against both Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria was analyzed. Furthermore, the mode of interaction among the finishing bath constituents and the cellulosic substrates was suggested, and extent of fixation was investigated.
Materials and methods
Materials
Mill scoured and bleached cotton (140 g/m2) and viscose (130 g/m2) woven fabrics were used in this study. Miswak (Salvadora persica root) was purchased from the local market. Chitosan (CS, Mol. Wt. 2.4 × 104 Da and 89.2% deacetaylated), Na-tripolyphosphate monohydrate (TPP) and L-ascorbic acid are purchased from Sigma-Aldrich. Citric acid, glacial acetic acid, Na-hypophosphite monohydrate (SHP, NaH2PO2.H2O), vanillin, zinc acetate, (Zn(CH3COO)2) 0.2H2O and sodium hydroxide were of laboratory reagent grade.
Methods
Freshly obtained roots were cut into small pieces, then grounded. Subsequently, 10 g of the powder were immersed in 100 ml of distilled water and refluxed for 5 h. The obtained extract was filtered by using Whatman No. 1 filter paper, then stored in a refrigerator at 4 °C for biosynthesis of ZnONPs.
Biosynthesis of ZnONPs
ZnONPs were fabricated by adding of 4 ml of freshly prepared Miswak aqueous extract to 100 ml of Zn-acetate aqueous solution (0.225 M), stirred for 12 h, and pH was maintained at 12 by adding 0.02 M NaOH solution and mixing for 1 h, after which it was centrifuged at 6000 rpm for 30 min. The obtained precipitate was washed several times with bi-distilled water to get pH 7 dried at 90 °C for 8 h.
Preparation of CS/TPP NPs suspension
Preparation of CS/TPP NPs was carried out successfully according to the method given by Bangun et al. [
5] with some modifications. Briefly, 3 g of CS were dissolved in 600 ml of 1% acetic acid and stirred continuously for 30 min. Subsequently, an aqueous solution of TPP (1.4 g/600 ml) was then slowly added and stirred for 2 h at room temperature and sonicated for 1 h.
Functional finishing of cellulosic fabrics
Cotton and viscose fabric samples were padded twice in various functional finishing formulations containing:
(i)
Citric acid (30 g/L), as ester-cross linker, and SHP (15 g/L), as a catalyst, CS-TPP NP (2.5 g/L), as a polycationic agent, and ZnONPs (0–15 g/L), as a multifunctional agent, or
(ii)
CA/SHP (30 g/L/15 g/L), CS-TPP NPs (2.5 g/L) and L-ascorbic acid (0–20 g/L) or vanillin (0–20 g/L), as environmentally sound functional additive, to give wet pick-up of 85%, followed by drying at 100 °C/3 min and curing at 150 °C/3 min, thoroughly washed to remove unfixed/non-reacted constituents and finally dried and conditioned before evaluation.
Testing and analysis
Fourier transform infrared (FTIR) spectroscopy was carried out using a Nicolet 380 spectrophotometer (Thermo Scientific), and the IR spectra were scanned 32 times over the wavenumber range of 4000–400 cm−1. The sample (0.002 g) was mixed with KBr to reach (0.2 g) to form around disk suitable for measurements.
Transmission electron microscopy (TEM)
TEM images of the samples were obtained using a JEOL (JEM-1400 TEM, Japan), with an accelerating voltage of 100 kV. The CSNPs and ZnONPs suspension sample was ultrasonically dispersed in deionized water. Then, a small droplet of the diluted CSNPs and ZnONPs suspension was deposited on a 300-mesh copper grid coated with holey carbon film.
Particle size analysis
The average size and size distribution of the CSNPs and ZnONPs were estimated by dynamic light scattering (DLS) using a Malvern Zetasizer Nano ZS (Malvern Instruments Ltd., UK) equipped with a He–Ne laser (0.4 m W; 633 nm) and a temperature-controlled cell holder. The mean intensity weighted diameter was recorded as the average of three measurements.
Scanning electron microscopy (SEM)
SEM images for surface morphology of the samples were taken using SEM Model Quanta 250 FEG (Field Emission Gun) attached with EDX Unit (Energy-Dispersive X-ray Analyses), with accelerating voltage 30 KV, magnification 14 × up to 1,000,000 and resolution for Gun.1n. The surfaces of all the samples were coated with a gold thin layer under vacuum before SEM studies.
Textile testing
The amount of metal content in the post-treated fabric samples was determined by a flame atomic absorption spectrophotometer (GBC-Avanta, Australia).
Nitrogen content of fixed finished fabric was estimated as per a standard Kjeldahl method [
60] using instrument model DNP-3000 (Raypa-SPAIN) using standard reference materials [
60].
UPF was determined according to the Australian/New Zealand Standard (AS/NZS 4399-1996). Fabric can be rated as providing good, very good and excellent protection if their UPF values range 15–24, 25–39 and above 40, respectively.
The antimicrobial activity assessment against Gram-positive, Staphylococcus aureus (S. aureus) and Gram-negative, Escherichia coli (E. coli) bacteria was determined quantitatively according to AATCC 100 test method. The reduction of colonies was calculated using the following equation: R = 100 (B−A)/B, where R: % reduction, A: the number of bacterial colonies survived after contacting with treated sample and B: the number of colonies present in untreated control sample (blank).
Dry wrinkle recovery was determined according to AATCC Test Method 66-2008 using iron recovery apparatus type FF-07 (Metrimpex).
Conclusion
The main task of the present research work is to a develop a single-stage multifunctional treatment of cotton and viscose cellulosic substrates to impart anti-crease, UV blocking and antibacterial functions using environmentally sound and sustainable finishing formulations. Green synthesis of ZnONPs and CSNPs and their positive role in the development of multifunctionalized cotton and viscose fabrics using CA/SHP as ester-crosslinking system and pad-dry-cure thermofixation method are reported. Inclusion of ZnONPs (15 g/L) or a synergistic constitutions of CSNPs (2.5 g/L)/L-ascorbic acid (20 g/L) or CSNPs (2.5 g/L)/vanillin (20 g/L) in the ester-crosslinking formulations resulted in a remarkable improvement in the imparted anti-crease, UV protection and antibacterial efficacy of the finished fabrics, irrespective of the treated substrate.
The extent of improvement in the imparted functional properties is determined by the kind of cellulosic substrate as well as type of finishing formulation constituents. Moreover, FTIR, SEM and EDX analysis confirm surface modification and functionalization of the treated fabric samples. The results obtained further signify that increasing washing cycles up to 10 cycles resulted in a slight decrease in the imparted functional properties. Thus, it can be concluded that developing of durable multifunctionalized textile products using an eco-friendly, and facile single-step finishing regime greatly supports the possibility of a wide range of potential and practical applications.
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