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Influence of water on liquid ammonia-based sustainable dyeing of ramie fiber
⁎Corresponding authors at: Hubei Provincial Engineering Laboratory for Clean Production and High Value Utilisation of Bio-based Textile Materials, Wuhan Textile University, Wuhan 430200, China (Y. Cai and L. Lin) and Sanitary Environmental Engineering Division (SEED), Department of Civil Engineering, University of Salerno, Via Giovanni Paolo II #132, 84084 Fisciano, SA, Italy (V. Naddeo). linalin@wtu.edu.cn (Lina Lin), yingjiecai@wtu.edu.cn (Yingjie Cai), vnaddeo@unisa.it (Vincenzo Naddeo)
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Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Liquid ammonia dyeing emerges as an environmentally benign and sustainable option for the textile industry, characterized by a minimal ecological impact. However, its adoption is hampered by certain limitations, such as suboptimal dye exhaustion and issues with color uniformity, which present significant hurdles to its widespread industrial application. Building on the premise that the addition of water to an ethanol solvent can enhance reactive dye exhaustion in cotton fiber dyeing, this study delves into the dyeing behavior of ramie fiber using a water-liquid ammonia mixture with Reactive Red 195. The incorporation of water into the liquid ammonia solution was observed to marginally decrease the color strength (K/S value) of the dyed ramie fiber, compared to the dyeing with anhydrous liquid ammonia. This reduction is likely due to the diminished expansion of the amorphous regions within the fiber. However, the color levelness of the dyed ramie fiber was enhanced by the addition of water to the liquid ammonia. To decipher the influences on the dyeing process, the Taguchi method, utilizing an orthogonal array (L16), was applied. The analysis revealed that the dye mass factor was the predominant influencer (79.08 %), followed by the liquor ratio factor (18.53 %), with both factors demonstrating statistically significant effects (p < 0.05). A multifaceted analysis of the samples was conducted using advanced techniques such as XRD (X-ray diffraction), FTIR (Fourier transform infrared), TGA (thermogravimetric analysis), and SEM (scanning electron microscopy). These analyses confirmed that the water-liquid ammonia treatment induced changes in the samples’ properties. The treated samples exhibited lower barium activity numbers and breaking force values, indicating structural alterations. Furthermore, the molecular structure of Reactive Red 195 remained intact throughout the dyeing process in the water-liquid ammonia mixture, thereby affirming its viability for practical applications in the textile industry.
Keywords
Liquid ammonia
Sustainable dyeing
Ramie
Taguchi
Color strength
1 Introduction
The textile dyeing and finishing industries release a significant amount of wastewater containing toxic dyes that harm humans and the environment, making them among the most polluting sectors globally (Gürses et al., 2021). In recent years, various technologies like adsorption, Fenton catalytic systems, membranes, and others have been employed to treat these complex wastewater effluents (Hossain et al., 2022, Pervez et al., 2023). However, the sustainability of these approaches in the textile sector remains debatable. Sustainable (i.e., waterless) dyeing methods, such as supercritical fluid, silicone oil, liquid paraffin oil, plant oil, and organic solvent mixtures, have been explored to reduce water pollution from textile industries (Cai et al., 2024, De Oliveira et al., 2024, Hossain et al., 2021b, Jorge et al., 2024, Ramalingam et al., 2024, Wang et al., 2024).
Liquid ammonia, a colorless solvent with a boiling point of −33.4 °C at atmospheric pressure (Gezerman, 2016), is commonly used in the textile industry to mercerize cotton fibers (Greenwood, 1987, Manian et al., 2024) due to its low environmental impact and ability to enhance tactile touch, abrasion resistance, and anti-wrinkle properties (Chen et al., 2023). Reactive dyes are soluble in liquid ammonia; thus, liquid ammonia can serve as a dyeing medium (Cai et al., 2014). Liquid ammonia dyeing presents an alternative, cleaner, and sustainable dyeing technology where cellulosic fibers are dyed in a liquid ammonia dyebath at a constant temperature of approximately −34 °C, followed by a dye fixation process with resin treatment (Cai et al., 2014) or cationic fixation treatment (Cai et al., 2020). During liquid ammonia dyeing, liquid ammonia immediately wets and swells the cellulosic fiber due to its low surface tension, which removes the air and moisture adsorbed in the fiber. At the same time, the reactive dyes dissolved in liquid ammonia are quickly adsorbed onto the fiber and migrate into the interior of the fiber with liquid ammonia. After the evaporation of liquid ammonia in the dyed fibers, the adsorbed reactive dyes are retained in the fiber (Cai et al., 2014). Notably, the dichlorotriazinyl category of reactive dyes is unstable in liquid ammonia because the dichlorotriazinyl reactive group is easily destroyed. In contrast, bifunctional reactive dyes with one monochlortriazinyl reactive group and one vinyl sulfone sulfate reactive group are reliable for dyeing cellulosic fiber in liquid ammonia (Su et al., 2019).
Liquid ammonia dyeing is an anhydrous technology that reduces water consumption (Gao et al., 2022) and allows the recycling of liquid ammonia from evaporation and residual dyebath. This method eliminates the need for salt compared to traditional reactive dyeing, addressing the issue of excessive salt in wastewater. The dyeing process is efficient, completed quickly, and does not require temperature adjustments. Commercial reactive dyes can be used directly without purification, simplifying operations and reducing costs while enhancing product value (Cai et al., 2020, Gao et al., 2022). However, challenges like low dye exhaustion and fixation, color unevenness, and poor color fastness to washing hinder the widespread application of liquid ammonia dyeing technology. Research focuses on improving dye exhaustion, with modifications like cationic treatment enhancing dye fixation and color fastness (Cai et al., 2014). Additionally, post-treatments using micro-emulsion systems for dye fixation have shown promising results (Cai et al., 2020).
In the realm of cellulosic dyeing, binary solvent mixtures, including water–ethanol miscible systems (Xia et al., 2018), water-D5 micro-emulsion systems (Hossain et al., 2021a, Pei et al., 2019), and water–oil systems (Lin et al., 2022b, Liu et al., 2021), have proven to be highly effective in augmenting dye exhaustion. The presence of water contributes to fiber swelling and modifies dye solubility within the medium, which may enhance dye exhaustion by diminishing dye solubility in the dyebath (Dong et al., 2019). On the other hand, addition of the water content in liquid ammonia solutions reduces the adsorption of reactive dyes in ramie fibers, contrary to the desired outcome. Nevertheless, the dyeing of ramie fibers in a medium combining water and liquid ammonia yielded an enhanced color levelness, surpassing the results of employing liquid ammonia alone.
2 Experimental
2.1 Materials
Loose ramie fibers (scoured and bleached) were purchased from Hunan Huasheng Zhuzhou Cedar Company, China. Liquid ammonia (99.999 %) was obtained from the Wuhan Niuruide Gas Company, China. Industrial alcohol (ethanol, 95 %) was used as a refrigerant and supported by Wuhan Dianda Chemical Company, China. C. I. Reactive Red 195 (commercial grade) was purchased from Shanghai Jiaying Chemical Company, China. C. I. Reactive Red 195 (high purity, 100 % strength) was purchased from the Shanghai Macklin Biochemical. Non-ionic detergent (Luton 500) was obtained from Dalton UK Company (Shanghai, China). Barium hydroxide (Ba(OH)2·8H2O, ≥97 %) and ammonia solution (25 %) were bought from China National Pharmaceutical Group Corporation, China. Tetrabutylammonium bromide (≥99.0 %) and ammonium acetate (≥99.0 %) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Acetonitrile (HPLC/Spectro) was bought from TEDIA Company, Inc., USA.
2.2 Dyeing process of ramie fiber
Liquid ammonia was carefully introduced into a glass tube, after which a drop-by-drop addition of ammonia solution was performed onto the inner surface of the glass tube to mix with the liquid ammonia. The resulting mixture was slowly stirred with a glass rod to achieve a water-liquid ammonia solvent mixture. Subsequently, Reactive Red 195 dye was incorporated into this solvent mixture to prepare the dyebath. The glass tube containing the dyebath was submerged in a refrigeration tank (FP40, JULABO Labortechnik GmbH) containing an ethanol solvent to maintain an ultra-low temperature of −40°C, thereby preventing evaporation. Short immersion dyeing was applied to the loose ramie fibers in the dye bath, as detailed in Table 1. After dyeing, the excess dyebath on the dyed ramie fibers was removed using a laboratory-scale centrifugal dehydrator, followed by drying in an oven set at 60°C.
Factor
Unit
Range
Water concentration
% (V/V)
0–10
Liquor ratio (LR)
/
20:1–50:1
Dyeing time
Second
10–600
Dye mass usage
% o.m.f
1–50
2.3 Performance characteristics
2.3.1 Measurement of dye solubility
To measure the solubility of Reactive Red 195 (commercial grade), varying amounts were added to 40 mL of pure liquid ammonia, water-liquid ammonia mixture, or distilled water to prepare the dye solutions. These solutions were then frozen at −40°C within a refrigeration tank (FP40, JULABO Labortechnik GmbH), which was filled with ethanol solvent. The dye solutions were gently stirred with a glass rod. After a 5-minute stand time, a 2 mL glass bottle was used to collect the clear dye solution, which was then diluted to a total volume of 100 mL with distilled water. The diluted solution's light absorbance was measured using a UV–Vis spectrophotometer (Cary 300, Agilent Technologies, Australia), and the average value of 20 repeated samples was used. The standard curve of Reactive Red 195 aqueous solutions was prepared with the high purity grade of Reactive Red 195.
2.3.2 Color strength of dyed ramie fiber
The color strength of dyed loose ramie fiber was evaluated using a K/S value, which was randomly measured at 20 positions using a spectrophotometer (CHN-Spec CS-650A, Hangzhou Color Spectrum Technology Company, China), and the average value was used.
2.3.3 Fourier transformation infrared (FT-IR) analysis of ramie fiber
The loose ramie fiber underwent treatment in a mixture of water and liquid ammonia at −40°C for 180 s, followed by drying in an oven at 60 °C. The dried ramie fiber was then cut into powder and then mixed with KBr powder (Zare, 2023). The FT-IR spectrum of the loose ramie fiber's powder was recorded using a spectrophotometer (Bruker Optik EQUINOX 55, Ettlingen, Germany).
2.3.4 X-ray diffraction (XRD) analysis of ramie fiber
The XRD of loose ramie fiber’s powder was carried out using an X-ray diffractometer (Rigaku Ultima III, Tokyo, Japan) under CuK α radiation (λ = 1.54056 Å) in a range of 5–40° of 2 θ with a step size of 0.02°. The XRD curve was deconvoluted using the FitYK 1.3.1 software to obtain the characteristic peaks. The crystalline index (CI, %) of the ramie fiber was calculated by Eq. 1 (Xia et al., 2021). Meanwhile, based on the deconvoluted results, the ratio of Cellulose III (RⅢ) in the crystalline region was calculated by Eq. 2.
where Ac and Aa refer to the area of crystalline peaks and the area of amorphous peaks, respectively.
where AⅢ and AⅠ refer to the area of the crystalline peak at c.a. 21.0° (Cellulose III) and the area of the crystalline peak at c.a. 22.5° (Cellulose I), respectively.
2.3.5 Thermogravimetric analysis (TGA) of ramie fiber
The thermal properties of the ramie fiber were examined using a thermogravimetric analyzer (TGA/DSC1, Mettler-Toledo, LLC, Shanghai, China) in a range of 30–800°C with a heating rate of 10°C/min under a nitrogen flow rate of 50 mL/min. The first derivative of the TG curve, known as DTG, was calculated to represent the rate of change of mass over time dependent on temperature.
2.3.6 Scanning electron microscope (SEM) of ramie fiber
The morphological structure of loose ramie fiber was analyzed using a field-emission scanning electron microscope (Philips SEM 515, Germany) at 10 kV accelerated voltage. The loose ramie fiber was gold sputter-coated using a sputtering instrument (JSM-560, Rigaku, Japan).
2.3.7 Barium activity number of ramie fiber
The barium activity number of the treated loose ramie fiber was determined according to AATCC 89–2012 (Mercerization in cotton).
2.3.8 Breaking force of ramie fiber
The breaking force of both original and treated ramie fibers was measured following the standard GB/T 5886–1986 (Testing method of single fiber breaking tenacity of ramie) using an electronic strength tester for a single fiber (LLY-06E/PC, Laizhou Electron Instrument Co., Ltd, China). A random selection of 50 fibers from each sample was tested to average the values.
2.3.9 High-performance liquid chromatography (HPLC) analysis of Reactive Red 195
The impact of the liquid ammonia medium on the molecular structure of Reactive Red 195 during dyeing conditions was assessed using an HPLC system (L-3000, RIGOL, China). To prepare a hydrolyzed Reactive Red 195 sample, the high-purity Reactive Red 195 was dissolved in a 2 g/L NaOH solution (using distilled water) to create a 1 g/L dye solution, which was then heated to 80°C in a water bath. The sample for analysis was prepared as described in a previous study (Su et al., 2019). The HPLC analysis of Reactive Red 195 was conducted on a C18 column (250 mm × 4.6 mm, Rigol, 5 µm) maintained at a temperature of 30°C. The mobile phase consisted of solvent A (0.002 mol/L tetrabutylammonium bromide and 0.05 mol/L ammonium acetate) and solvent B (acetonitrile), with a gradient method employing different proportions of the mobile phase as specified in Table 2. A 20 µL dye solution was injected with a flow rate of 1.0 mL/min for analysis. The detection wavelength was set to the maximum absorbance wavelength of 542 nm for Reactive Red 195.
Time (min)
Solvent A (%)
Solvent B (%)
0
72
28
10
68
32
25
68
32
30
72
28
3 Results and discussion
3.1 Solubility of Reactive Red 195
The UV–Vis spectrophotometer (Cary 300, Agilent Technologies, Australia) determined that the maximum light absorbance of Reactive Red 195 occurred at 542 nm. Fig. 1 presents the standard curve for Reactive Red 195 (high purity) in water, covering a concentration range of 10–50 mg/L, including the regression equation and coefficient (R2). The regression coefficient 0.9998 (Fig. 1a) signifies a strong linear correlation between light absorbance and dye concentration. This equation was employed to calculate dye solubility in the dyebath based on its light absorbance. Fig. 1b shows the relationship between dye concentration in the dyebath and dye mass usage, with an R2 value approaching 1, indicating a high linear correlation.
(a) The standard curve of Reactive Red 195 in water and (b) the measured dye concentration of the dyebaths. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
In the range of 1–10 % o.m.f of Reactive Red 195 dye, the experimental dye concentrations of solutions prepared with 0.02–0.20 g in 40 mL of anhydrous liquid ammonia (0 % water), 3 % (V/V) water in liquid ammonia, 10 % (V/V) water in liquid ammonia, and pure water (100 % water) closely matched the theoretical values derived from the standard curve equation. These results suggest that dye dissolution in anhydrous liquid ammonia, water-liquid ammonia mixtures, and water is similar. In other words, the presence of water within the liquid ammonia did not affect the maximum light absorbance of the dyebath. However, as the dye mass increased from 30 to 50 % o.m.f (0.60–1.00 g) in 40 mL of dyebath, the measured dye concentration in water dyebaths was lower compared to anhydrous liquid ammonia and its mixtures. The measured dye concentrations in the water dyebath decreased to 12.3 and 20.2 g/L for the 30 and 50 % o.m.f of dye prepared dyebaths, respectively, while the theoretical values were 15 and 25 g/L, respectively.
The dissolution behavior of Reactive Red 195 in liquid ammonia (Barkhuysen, 1977, Tratnyek, 1972) differs from its behavior in aqueous solutions, displaying better solubility in liquid ammonia and its mixtures than in water. The strong solvating properties and interactions (Lagowski, 1971) of liquid ammonia with the dye's functional groups and molecules contribute to this behavior, resulting in a solvent film around the dye molecules. Moreover, Reactive Red 195, which has a phenolic hydroxyl group, generated ammonium ion pairs in liquid ammonia (Strassberger et al., 2015), potentially promoting dye dissolution.
3.2 Influence of water concentration in liquid ammonia on the K/S value
The loose ramie fiber was dyed with 3 % o.m.f of Reactive Red 195 for 180 s at −40°C and a 20:1 LR ratio using liquid ammonia with varying water concentrations. The K/S values of the dyed ramie fibers after drying are presented in Fig. 2. The K/S values decreased from 4.98 to 3.58 when 3 % of the water concentration was present in the liquid ammonia and then gradually decreased to 3.24 when the water concentration was increased to 10 %. This suggests that 3 % water in the liquid ammonia significantly contributed to reducing dye exhaustion in the ramie fiber, and further increases in water concentration do not effectively lower the K/S values.
K/S and its color uniformity of dyed ramie fibers treated by various water concentrations in water-liquid ammonia dyeing.
Previous studies have identified one of the limitations of liquid ammonia dyeing of ramie fiber as the low dye exhaustion (Cai et al., 2014), which may be attributed to the higher dye solubility in liquid ammonia compared to water. At equilibrium dyeing conditions, the dye concentration of the dye solution within the fiber tends to equilibrate with the concentration in the dyebath, a concentration equilibrium (Dong et al., 2019). Therefore, the addition of a solvent to the dyebath, which decreases dye dissolution, can enhance dye exhaustion. The investigation into dye dissolution in water-liquid ammonia mixture dyebaths revealed that the dissolution of Reactive Red 195 in the presence of 3–10 % water in liquid ammonia is similar.
Moreover, during dyeing, water tends to remain in the dyebath rather than being adsorbed by the fiber due to liquid ammonia's rapid removal of adsorbed water. This means that the assumption of an aqueous wet fiber adsorbing more reactive dyes in liquid ammonia dyeing is incorrect. Consequently, adding water to liquid ammonia dyeing does not increase but rather decreases dye exhaustion. The addition of water to liquid ammonia also diminishes the decrystallization efficiency, as confirmed by XRD analysis, resulting in a reduced amorphous region within the fiber. This likely leads to a slight decrease in dye exhaustion, reducing the K/S value.
Although the K/S values of the dyed loose ramie fibers decreased, the color uniformity improved because the standard deviation (error bars) of the 20 measured K/S values decreased. However, the standard deviation of K/S values for all dyed ramie fibers remains acceptable.
3.3 Influence of dye mass usage on the K/S value
The loose ramie fiber was dyed with various dye masses of Reactive Red 195 for 180 s at −40°C and a 20:1 LR ratio using liquid ammonia with 3 % water concentration. The K/S values of the resulting dyed fibers after drying are depicted in Fig. 3. Generally, an elevation in dye mass usage was accompanied by an increase in K/S values, suggesting that a higher quantity of reactive dyes was adsorbed due to the concentrated dyebath (Mondal et al., 2018). However, the rate of K/S increase within the range of 1–10 % o.m.f surpassed that of the 10–50 % o.m.f range, with respective linear relationship slopes of 1.1732 and 0.3025. This suggests that the dye absorption efficiency was significantly higher during the dyeing process with a reduced dye mass (Al-Ghouti and Al-Absi, 2020, Mondal et al., 2018), presumably because of the enhanced efficiency of dye adsorption within the amorphous regions of the fiber's free volumes (Purkait et al., 2005), ultimately resulting in a considerable increase in the rate of dye uptake. The dye sorption approached saturation levels within the range of 10–50 % o.m.f. Although the sorption of dye mass continued to rise, its efficiency of increase was notably lower than that observed during dyeing with lower dye concentrations. This suggests that the dye bath contained an excessive amount dye. The dye sorption behavior fitted the Freundlich adsorption, which was assistance with the previous studies (Cai et al., 2018b, Zhang et al., 2022a) on the reactive dyeing of cellulosic fibers. Moreover, the dyed loose ramie fibers with robust color strength, as indicated by a high K/S value, exhibited a decreasing trend in color uniformity as the standard deviation of K/S values rose to 1.89 with a 50 % o.m.f of dye usage.
K/S and its color uniformity of dyed ramie fibers treated by various dye mass usage in water-liquid ammonia dyeing.
3.4 Influence of dyeing time on the K/S value
The loose ramie fiber was dyed with 3 % o.m.f of Reactive Red 195 for varying dyeing durations at −40°C and a 20:1 LR ratio using liquid ammonia with 3 % water concentration. The K/S values of the dyed ramie fibers after drying are illustrated in Fig. 4. The K/S values exhibited fluctuations within the range of 3.31–3.59 from 10 to 600 s of the dyeing period, which were considered negligible. This suggests that the dye adsorption was rapid due to the low surface tension of the dyeing medium (Stairs and Sienko, 1956), which included liquid ammonia and a water-liquid ammonia mixture attributed to the liquid ammonia solvent. In other words, the presence of 3 % water in liquid ammonia did not significantly impact the surface tension of the liquid ammonia. The swift dye adsorption outcomes align with previous findings (Cai et al., 2014). In the conventional aqueous dyeing of cellulosic fibers with reactive dyes, the dye exhaustion percentage increases upon the addition of alkaline substances due to the disruption of the dye absorption equilibrium by dye fixation (Broadbent, 2001). The marginal differences in K/S values in Fig. 4 may stem from the physical dye adsorption within the fibers during dyeing in liquid ammonia or water-liquid ammonia mixture medium.
K/S and its color uniformity of dyed ramie fibers treated by various dyeing time in water-liquid ammonia dyeing.
Moreover, loose ramie fibers contain approximately 3–6 % (w/w) of non-cellulosic substances (Mao et al., 2019), including ash, lignin, and hemicellulose. During the liquid ammonia dyeing process, it is plausible that the hydrogen bonds linking these non-cellulosic components to the cellulosic fibers were disrupted. This disruption likely led to the creation of additional free volume and the exposure of more hydroxyl groups, thereby enhancing the capacity for dye adsorption and dye fixation.
Concerning color uniformity, the standard deviation of K/S fluctuated within the range of 0.42–0.53, likely influenced by the similar dye adsorption behaviors reflected in the K/S values.
3.5 Influence of liquor ratio on the K/S value
The loose ramie fiber was dyed with 3 % o.m.f of Reactive Red 195 for 180 s at −40 °C and various LR with 3 % water concentration in liquid ammonia. The K/S values of the dyed ramie fibers after drying are presented in Fig. 5. It is evident that the K/S value linearly (R2 = 0.9755) decreased from 3.58 to 1.75 as the LR was increased from 20:1 to 50:1. This decrease is attributable to the reduced dye concentration within the dyebath, which occurred as the LR rose. Concurrently, the reduction in K/S was accompanied by a decrease in the standard deviation of K/S, indicating that the color shade of the dyed samples became more uniform with increasing LR.
K/S and its color uniformity of dyed ramie fibers treated by various liquor ratios in water-liquid ammonia dyeing.
3.6 Taguchi analysis of K/S values of dyed ramie fibers
The experimental factors and their conditions were selected for an orthogonal experimental scheme with an L16 (4^4) array, as shown in Table 3. The orthogonal experimental results were evaluated using K/S values, and their corresponding S/N ratios were calculated using the “larger is better” equation, as shown in Table 4. Based on the Taguchi analysis (Fig. 6), the K/S values showed a decreasing trend with an increase in LR and a rising trend with an increase in dye mass usage across the range of orthogonal experimental conditions. Additionally, the K/S decreased as the water concentration factor increased from 7 to 9 % in liquid ammonia and then leveled off at 10 % water concentration. Lastly, the dyeing time factor showed a fluctuating trend.
Symbol
Factor
Unit
Level 1
Level 2
Level 3
Level 4
A
LR
/
20:1
30:1
40:1
50:1
B
Water concentration
%
7
8
9
10
C
Dye mass
% o.m.f
2
3
4
5
D
Dyeing time
Second
90
120
150
180
Exp. No.
A
B
C
D
K/S
S/N ratio (dB)
1
20:1
7
2
90
1.49
3.3733
2
20:1
8
3
120
2.01
6.0793
3
20:1
9
4
150
2.36
7.1942
4
20:1
10
5
180
2.83
9.3749
5
30:1
7
3
150
1.69
4.8969
6
30:1
8
2
180
1.32
2.1474
7
30:1
9
5
90
2.57
8.2140
8
30:1
10
4
120
2.23
6.8756
9
40:1
7
4
180
2.05
6.2504
10
40:1
8
5
150
2.35
7.3309
11
40:1
9
2
120
1.07
0.9269
12
40:1
10
3
90
1.52
3.3728
13
50:1
7
5
120
2.34
7.1203
14
50:1
8
4
90
1.64
4.6361
15
50:1
9
3
180
1.31
2.2550
16
50:1
10
2
150
0.92
0.7089
Main effects plot for S/N ratios in K/S values of dyed loose ramie fiber.
The analysis of variance (ANOVA) for the S/N ratios of the K/S values of the dyed loose ramie fiber is detailed in Table 5. The LR and dye mass usage factors are deemed significant, with p-values of 0.010 and 0.001, respectively, both falling below the threshold of 0.05 (Lin et al., 2022a), while the remaining factors are considered insignificant. Furthermore, the contribution percentages (P(%)) reveal that the dye mass factor (C) plays a predominant role (79.08 %), followed by the LR factor (18.53 %). The water concentration factor contributes minimally, with a P(%) of 1.19 %, and the dyeing time factor contributes the least, at only 0.56 %. The relatively low contribution percentages suggest that both the water concentration and dyeing time factors have a negligible impact on dye uptake during the dyeing process. It should be noted that all the analyzed results are based on the orthogonal experimental conditions. Consequently, it indicates that the order of factors influencing K/S is dye mass (C) > LR (A) > water concentration (B) > dyeing time (D).
Source
Variable
DF
SS
MS
F
p-value
Remarks
P (%)
A
LR
3
22.5132
7.5044
29.13
0.010
Significant
18.53
B
Water concentration
3
1.4468
0.4823
1.87
0.310
Insignificant
1.19
C
Dye mass
3
96.0846
32.0282
124.35
0.001
Significant
79.08
D
Dyeing time
3
0.6787
0.2262
0.88
0.541
Insignificant
0.56
Residual Error
3
0.7727
0.2576
Total
15
121.496
The interactions among the four factors during the dyeing process are depicted in Fig. 7. In the dyeing conditions, it is apparent that the interactions between factors A (LR) and C (dye mass usage) are weak, as there are no crossing points in their interaction curves (A vs. C) (Shafiq et al., 2018). According to the ANOVA analysis, both factors significantly contribute to the K/S values, suggesting that even small changes in dyeing conditions can lead to substantial contributions, indicating no interaction between these factors. In contrast, factors B (water concentration) and D (dyeing time) strongly interact due to their intertwined curves.
Interaction plot for S/N ratios in K/S values.
3.7 XRD analysis of ramie fiber
The XRD patterns of the original and treated ramie fibers are presented in Fig. 8. The distinct diffraction peaks associated with Cellulose I at 15.06°, 16.68°, and 20.86° of 2θ for Miller indices (1–10), (110), and (200) (French, 2014) are observed in the original ramie fiber. After liquid ammonia treatment, the cellulosic fiber's crystalline structure transitions from Cellulose I to Cellulose III (Wada et al., 2009), as indicated by the appearance of characteristic diffraction peaks for Cellulose III at 12.06° of 2θ for the (010) plane and 20.98° of 2θ for the (100)/(012)/(1–10) composite plane (Wu et al., 2020a, Wu et al., 2020b) in the pure liquid ammonia-treated ramie fiber (0 % water concentration curve in Fig. 8a). As the water concentration in the liquid ammonia decreased from 20 to 0 %, the characteristic peaks of Cellulose I at 15.06° and 16.68° of 2θ gradually vanished (Fig. 8b), concurrent with a shift of the peak of maximum intensity from 22.30 to 20.98° of 2θ (Fig. 8a), suggesting the formation of a mixed crystal structure (Cai et al., 2018a) of Cellulose I and III, particularly in the water concentration range of 7 to 10 %.
XRD patterns of the ramie fibers, (a) 2 theta from 10 to 40°, and (b) 2 theta from 10 to 20°.
Additionally, the CI of the ramie fiber decreased after the liquid ammonia treatment. The CI and the ratio of Cellulose I to III are detailed in Table 6. The CI of the original ramie fiber is 72.0 %, which decreased to 39.9 % after treatment in pure liquid ammonia. With the introduction of water into the liquid ammonia, the efficiency of crystal collapse reduced as water concentration increased. Moreover, the conversion efficiency from Cellulose I to III diminished as the water concentration in liquid ammonia increased. Notably, when the water content in the liquid ammonia reached 20 %, the crystallinity of Cellulose III was reduced to a mere 4.3 %. When the water concentration in the liquid ammonia was less than 5 %, the structure was composed entirely of Cellulose III (100 % Cellulose III).
Fiber
CI (%)
Cellulose I (%)
Cellulose III (%)
Original
72.0
100
/
0 % water
39.9
/
100
3 % water
41.2
/
100
5 % water
44.8
/
100
7 % water
43.1
70.8
29.2
10 % water
43.1
80.9
19.1
20 % water
50.1
95.7
4.3
3.8 FT-IR analysis of ramie fiber
The FT-IR spectra of the original and liquid ammonia-treated ramie fibers are depicted in Fig. 9. These spectra display similarities, indicating the absence of any new functional groups. A prominent absorption band in the wavenumber range of 4000–3000 cm−1 corresponds to the stretching of hydrogen-bonded OH groups (Cai et al., 2018a). However, only the original ramie fiber exhibits a sharp peak at 3446 cm−1, which aligns with previous research findings (Manian et al., 2022). The absorbance band observed at 2900 cm−1 in all spectra is attributed to CH stretching vibrations (Hu et al., 2017, Moharram and Mahmoud, 2008). Additionally, the absorbance band at 897 cm−1 can be assigned to the valence vibration of the C–O–C group (Colom and Carrillo, 2002), becoming a more distinct and intense peak in the treated ramie fibers. The absorbance band at 1112 cm−1 corresponds to the asymmetric valence vibration of the ring (Široký et al., 2010), showing a weakened intensity in the treated ramie fibers. The absorbance band at 1159 cm−1 can be attributed to the antisymmetric stretching vibration of the C–O–C group, C–O stretching vibration, or O–H bending vibration (Široký et al., 2010). Other characteristic absorption bands of cellulose (Oh et al., 2005), such as the bending of OH groups in adsorbed water at 1647 cm−1, in-plane bending vibrations of HCH and OCH at 1431 cm−1, CH deformation vibrations at 1373 cm−1, stretching absorption of C–O–C at 1058 cm−1 (Zhang et al., 2006), and out-of-plane bending absorption of C–OH at 669 cm−1 (Schwanninger et al., 2004), are similarly presented in the spectra.
FT-IR spectra of original and treated ramie fibers.
3.9 TGA of ramie fiber
The TGA and DTG curves of the original and treated loose ramie fibers are presented in Fig. 10. Although the thermal behaviors of these samples display similarities, there is a slight difference between the original and treated ramie fibers. However, the variations in thermal stability among the treated fibers were relatively minor. In the TGA curves (Fig. 10a), the initial weight loss observed between 30 and 150 °C could be attributed to moisture evaporation from the fibers. The original ramie fiber experienced a weight loss of 4.7 %, whereas the treated fibers exhibited weight losses ranging from 5.5 to 7.0 %. This moisture evaporation is responsible for the peaks observed in the DTG curves (Fig. 10b). The peaks in the DTG curves for the treated loose ramie fibers appear stronger and broader compared to the original fiber, indicating higher moisture content in the treated fibers due to their more amorphous nature. This observation is consistent with previous findings (Liu et al., 2008).
TGA (a) and DTG (b) of untreated and treated loose ramie fibers.
Subsequently, a primary decomposition occurred between the temperature ranges of 260–390 °C for the original fibers and 260–380 °C for the treated fibers. The temperature at which maximum decomposition occurred, as depicted in Fig. 10b, is 362 °C for the original ramie fiber and decreases to 350 °C for the treated fibers, which could be attributed to the collapse of the crystalline phase (Zhang et al., 2022b), suggesting an accelerated decomposition of the treated ramie fibers. It is conceivable that minute quantities of non-cellulosic substances were dissolved in the liquid ammonia during the treatment. Consequently, the residual char content in the treated ramie fibers is slightly lower than that of the original fiber.
3.10 SEM of ramie fiber
The morphology of the original and treated ramie fibers was examined through SEM micrographs, as displayed in Fig. 11. The original ramie fiber exhibited a flat shape with several grooves on its outer surface (Fig. 11a), whereas the fiber treated with liquid ammonia displayed a uniformly modified topography with smooth rod-like structures, attributed to fiber swelling (Fig. 11b) (Cai et al., 2018a). When ramie fibers were treated in a water-liquid ammonia mixture, traverse striations and surface grooves were observed, albeit with less prominence compared to the original fibers (Fig. 11c-f). This indicates that the swelling capacity of the fibers was diminished by the inclusion of water in the liquid ammonia treatment, potentially due to a lower collapse of the crystalline structure.
SEM images of the morphological ramie surface of (a) original, treated with (b) liquid ammonia, (c) 3 % water in liquid ammonia, (d) 5 % water in liquid ammonia, (e) 7 % water in liquid ammonia, and (f) 10 % water in liquid ammonia.
3.11 Barium activity number of ramie fiber
The barium activity number is a widely used parameter for evaluating the mercerization performance of cellulosic fibers, calculated as the ratio of barium hydroxide (Ba(OH)2) adsorption in a mercerized cellulosic fiber to that of the untreated fiber. A barium activity number of 150 or higher generally indicates complete mercerization performance (Cheek and Roussel, 1989). The pure liquid ammonia-treated ramie fiber exhibited a barium activity number of 160, indicating a successful mercerization process. However, the ramie fibers treated with a mixture of water and liquid ammonia exhibited lower barium activity numbers, approximately 145 (Fig. 12), attributed to the lesser collapse of the crystallinity. This conclusion is supported by the crystallinity index (CI) results (section 3.7).
Barium activity number of ramie fibers treated with various water concentrations.
3.12 Breaking force of ramie fiber
The breaking forces of the original and treated loose ramie fibers are depicted in Fig. 13. The original loose ramie fiber exhibited a breaking force of 28.20 cN. As the water concentration in the liquid ammonia treatment decreased from 10 to 0 %, the breaking force gradually declined. The loose ramie fiber treated with anhydrous liquid ammonia (0 % water) demonstrated a reduced breaking force of 19.72 cN, which could be attributed to potential damage to the crystalline structure (Cai et al., 2018a). Additionally, it is likely that the bonds connecting the non-cellulosic components to the cellulosic fibers were disrupted in the liquid ammonia. This disruption could have potentially contributed to a reduction in the breaking force of the treated ramie fibers.
Breaking forces of untreated and treated loose ramie fibers.
3.13 HPLC analysis of Reactive Red 195
The HPLC chromatograms of Reactive Red 195 in the residual dyebath following dyeing and its fresh and hydrolyzed states are depicted in Fig. 14. Reactive Red 195 is a bifunctional reactive dye, composed of a monochlorotriazinyl group and a vinyl sulfone sulfate group, with the latter being more reactive and thus more prone to hydrolysis. The hydrolysis pathway of Reactive Red 195 is illustrated in Fig. 15. The two major peaks observed at retention time (Rt) of 12.9 and 17.2 min correspond to compounds 1 and 2 in Fig. 15, indicative of the increased polarity and earlier detection on a C18 column. The peak at Rt 15.8 min represents compound 3, which arises from the vinyl sulfone group's instability and susceptibility to hydrolysis. This is also why reactive dyes are commonly sold in the vinyl sulfone sulfate form, as it is more stable than the vinyl sulfone group. Furthermore, after 10 min of hydrolysis, a new peak at Rt 15.5 min appears, corresponding to compound 4, likely due to similarities in polarity to compound 3. After 30 min of hydrolysis, the peaks from the fresh sample are no longer detectable, and the peak at Rt 9.9 min is attributed to the completely hydrolyzed form, compound 5. Notably, minor peaks at Rt 4.3 min are likely the ionized derivatives of compound 5, which are not present in the fresh sample curve. Therefore, the HPLC chromatogram provides a sensitive means to analyze the molecular structural transformations of Reactive Red 195.
HPLC chromatograms of Reactive Red 195 in the residual dyebaths contained 3–10 % water concentration in liquid ammonia and its fresh and hydrolyzed forms. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Hydrolyzed route of Reactive Red 195 in water. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
In previous literature (Su et al., 2019), Reactive Red 195 was found to be stable in the residual dyebath when used in pure liquid ammonia. However, in the current study, water was added to the liquid ammonia dyebath, which introduced more hydroxide (OH−) groups and could potentially react with or hydrolyze the reactive groups of Reactive Red 195. The HPLC chromatograms indicate that the molecular structure of Reactive Red 195 remained unchanged during dyeing in the liquid ammonia bath containing water concentrations ranging from 3 to 10 %. Temperature and pH are key factors influencing the hydrolysis of reactive dyes. Although the dyebath was strongly alkaline, the ultra-low temperature retarded the hydrolysis process.
4 Conclusions
In this study, following an industrial dyeing protocol, we investigated the dyeing behavior of ramie fiber using a water-liquid ammonia mixture as a dyeing medium. The results demonstrate that the dye dissolution in anhydrous liquid ammonia, a mixture of water and liquid ammonia, and water were not significantly different, and the standard deviation of K/S values for all dyed ramie fibers fell within an acceptable range. It was noticed that the presence of 3 % water in the liquid ammonia significantly contributed to reducing dye exhaustion in the ramie fiber, and further increases in water concentration do not effectively lower the K/S values. XRD analysis revealed the presence of mixed crystal forms of Cellulose I and III resulting from treatment in a water-liquid ammonia mixture, consistent with the findings from FTIR spectra. The differences in thermal stability among the treated fibers were relatively subtle, as confirmed by the TGA. SEM images exhibited a weakened swelling performance of the fibers when water was added during the liquid ammonia treatment, potentially due to minimal disruption of the crystalline structure. These observations align with the decrease in barium activity number (approx. 145) and breaking force measurements (19.72 cN). Importantly, the molecular structure of Reactive Red 195 remained unchanged following the water-liquid ammonia dyeing process.
CRediT authorship contribution statement
Shaochen Li: Writing – original draft, Methodology, Formal analysis, Data curation. Qingyong Zhao: Methodology, Formal analysis, Data curation. Jianhua Xiong: Methodology, Formal analysis, Data curation. Nahid Pervez: . Lina Lin: Writing – review & editing, Writing – original draft, Supervision, Project administration, Conceptualization. Yingjie Cai: Writing – review & editing, Writing – original draft, Supervision, Project administration, Conceptualization. Vincenzo Naddeo: Writing – review & editing, Supervision, Funding acquisition.
Acknowledgment
This work was financially supported by the National Innovation Center of Advanced Dyeing & Finishing Technology (Grant Number: 2022GCJJ24). Besides, this work was supported by the Italian Ministry of Foreign Affairs and International Cooperation through the project coordinated by prof. V. Naddeo (grant number: KR23GR05).
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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