Improving dyeability and antibacterial activity of Lawsonia inermis L on jute fabrics by chitosan pretreatment

Experimental

Treatment of jute fiber with chitosan

Extraction of natural dye from henna

Fresh leaves of henna were dried in the sunlight for 1 day and again dried at 80 °C for 1 h in a hot air oven following washing and cleaning with distilled water. Dried leaves were grinded to powder form for getting proper extraction result. The extraction of dye was obtained after immersing 20 g henna powder in 100 mL water–ethanol mixture (90:10 v/v) for 24 h. This dye extract solution was used for the dyeing of both chitosan-treated and untreated jute fabric samples.

Dyeing with henna dyes

The dyeing of treated and untreated jute fiber was carried out using the required amount of extracts in water–ethanol mixture for 45 min at 75 °C temperature with material-to-liquor ratio 1:30 for optimum dye exhaustion. The dyeing was performed in Sandolab infrared lab dyeing machine from Copower Technology Ltd., Taiwan. After dyeing, the dyed fabric samples were rinsed with cold water and washed in a bath with 1 g/L of soaping agent at 60 °C temperature for 10 min and then dried in a dryer.

Measurement of color strength and related parameters

The values of L*, a*, and b* for a given color locate its position in the three-dimensional CIELab color space, and ∆L* = deviation of lightness; ∆a* = deviation of color in green-red axis; and ∆b* = deviation of color in yellow–blue axis. Both the color deviation and depth of shade of dyed fabric was evaluated according to AATCC test method 173-2006 in illuminant D65, large area view, and CIE 10° standard observer. Each sample was folded twice to give an opaque view, and color reflectance was measured four times at different parts of the fabric surface

Determination of color fastness properties

The fastness properties of dyed fabric samples, i.e., color fastness to washing was done according to ISO 105 C03:1989 by wash fastness tester (Gyrowash 415/8 from James H. Heal and Co., UK). The change and staining of color due to washing were assessed by comparing the untreated fabric with the treated fabric samples with respect to the ratings of color change and color staining gray scales. The evaluation of color fastness to rubbing was performed according to ISO 105 X 12: 2001 by rubbing fastness tester (Crockmeter 670 from James H. Heal and Co., UK). All the analyses of test fabric samples were conducted after conditioning the dyed fabrics in testing atmosphere (temperature 27 ± 2 °C and relative humidity 65 ± 2%) for 24 h.

Characterization

The determination of specific functional groups or chemical bonds that formed between chitosan and cellulose polymer of jute fiber after dyeing with henna was carried out by Fourier transform infrared (FTIR) spectrophotometer (Cary 630) from Agilent Technologies, USA. FTIR spectra were taken by absorption mode and measured by using potassium bromide (KBr) pellets made of finely cut and ground jute fibers.

Antibacterial property testing

where A and B are the surviving cells (colony forming units per milliliter (CFU/mL)) for the flasks containing test samples (chitosan-treated and dyed jute) and the control (untreated and undyed jute), respectively, after 1 h contact time.

Measurement of color strength

The depth of color or color strength of dyed fabric samples was analyzed by K/S value through the Kubelka–Munk equation, the most useful and applicable theoretical approach or model for colorants when colorants exhibit properties of light absorbing and scattering. This value numerically represents the nature of the coloring material layer and an easy way to determine a color as a concentration (Nobbs 1985). The function K/S is directly proportional to the concentration of colorant in the substrate, and the values found for all the experimental fabric samples are shown in Fig. 1.

Figure 1 shows the K/S values of dyed fabric samples for different percentages of chitosan treatment. The greater the amount of dyestuff in the fabric, the deeper is the shade, resulting in higher K/S values. The longer bar diagram showed by the fabric samples treated with 1.5% chitosan indicates the greater absorption of dye, whereas fabric without chitosan treatment forms shortest bar due to lower K/S value consequently lower absorption of dye (Fig. 2).

The better absorption of henna dye by jute fiber due to chitosan treatment has not been investigated extensively so far. However, chitosan has been proved to increase the rate of dye uptake and dye exhaustion of cellulosic fibers in case of reactive dyes (Kitkulnumchai et al. 2008; Bhuiyan et al. 2013). It may be suggested that the introduction of amino groups in the fiber structure due to chitosan treatment offers an additional affinity (Dev et al. 2009). The cationization of cellulose for the formation of ammonium ion (NH₄ ⁺) of chitosan (Bashar and Khan 2013) caused by treatment with jute fiber in acid medium may attract the acidic hydroxylated structure of the coloring component lawsone (2-hydroxy-1,4-naphthoquinone) of henna dye (Ali et al. 2009) resulting in higher absorption of dye by the fiber.

Color difference and relative color strength

The evaluation of the color parameter and the color difference of dyed fabric samples was performed by using CIELab system. The lightness value of color (from 100 to 0) is represented by L*; a higher lightness value indicates a lower color yield by the dyed fabric. Again, a* and b* values characterize the tone of the color; positive values of a* and b* stand for redder and yellower tones, while negative values show greener and bluer tones (Kuehni 2003).

The color difference (ΔE) values are also given in Table 2 and it is clearly demonstrated that there is a significant color difference between the untreated and chitosan-treated dyed samples. The color difference is more prominent in the case of fabric samples treated with 1.5% chitosan solution, and it decreases steadily with the reduction in chitosan concentration. The larger color difference with the increment of chitosan concentration is due to the greater absorption of dye by the fiber and accordingly leads to a higher K/S value with chitosan concentration.

Color fastness properties of dyed fabric

The wash fastness ratings in Table 3 show that chitosan-treated and untreated jute fabrics dyed with henna dye have almost identical fastness ratings of “good” to “excellent” (within numerical grades 4–5) with very little variation. Again, the staining of color to adjacent multifiber fabric has been found higher for chitosan-treated dyed samples (D, E) particularly in cotton and wool fiber (3–4 and 3). Moreover, in case of dry rubbing (Table 4), all types of dyed samples have shown almost similar ratings; however, chitosan-treated samples with higher concentrations represent a lower rating (3–4) compared to untreated samples (4–5) for wet rubbing. In general, deeper shade shows inferior fastness to washing and rubbing than a lighter one on a similar type of fabric for the same dyestuff (Bhuiyan et al. 2013), because in case of deep shade, dye molecules are more saturated and tend to move out from the interior of the fiber due to washing. As discussed earlier, the chitosan present in the fabric enhances the dyesite causing higher absorption of dye resulting in a higher depth of shade. Hence, as a general consequence of achieving deeper shade, the chitosan-treated fabric samples have shown a slightly lower fastness rating in comparison to lighter, untreated fabric.

Characterization of dyed fabric samples

FTIR spectroscopic analysis

The structural properties of chitosan-treated and untreated jute fiber after dyeing with henna dyes were investigated by FTIR spectroscopy. This analytical technique provides information about the chemical bonds and molecular structure of a material. The existence of a specific chemical bond in any material is indicative of the presence of a peak at a specific wavenumber being revealed through scanning the test samples in the infrared light source.

The chemical interaction between chitosan and jute fiber polymer is investigated by the change of the peaks from the characteristic spectra as shown in Fig. 3. In general, no significant changes were observed in bands or their intensities in case of all test fabrics. The broad absorption band which appears in the range of 3500–3100 cm⁻¹ indicates the presence of –OH groups in the cellulose polymer (Agarwal and Bhattacharya 2010). However, the strong absorption in the region 3500–3100 cm⁻¹ in case of chitosan-treated fiber signifies the strong hydrogen bonded chitosan and jute fiber and also the existence of primary –NH₂ and secondary –NH groups (Bhuiyan et al. 2016c). The presence of –NH₂ group in the treated fabric is responsible for introducing a cationic site in jute polymer resulting in improved dye exhaustion and also interaction with microorganisms for antibacterial properties. Again, the spectrum near 2900 cm⁻¹ corresponding to the symmetric stretching of methylene (–CH₂–) groups (Davulcu et al. 2014) and 1735 cm⁻¹ related to the C=O stretch of esters were found to be similar in all the tested samples. The absorption peak that appeared at 1640 cm⁻¹ for chitosan-treated jute suggested the formation of Schiff base (C=N double bond) between aldehydic carbonyl group of cellulose and amino group of chitosan. All three samples showed peaks near 1430 and 1325 cm⁻¹, being related to –OH bending of C–O–H alcohol groups and 1060 cm⁻¹ corresponding to C–O mainly of C₃–O₃H secondary alcohol. Moreover, the peak at 898 cm⁻¹ corresponding to asymmetric out-of-phase ring stretching of C1–O–C4 β–glucosidic bonds (Chung et al. 2004) was increased after the dyeing process.

Improvement of antimicrobial properties

The antibacterial activity of chitosan-treated and untreated dyed jute fabric samples were carried out against S. aureus (gram-positive) and K. pneumoniae (gram-negative) bacteria. The pathogenic gram-positive bacterium S. aureus is the most frequently evaluated species, commonly found in the nose, respiratory tract, and on the skin, the major cause of cross-infection in hospitals as well as in commercial and home laundry practices (Kluytmans et al. 1997). It causes skin and tissue infections, respiratory infections, and food poisoning (Weese and van Duijkeren 2010). Again, the gram-negative bacterium K. pneumonia, which is a popular test organism, is found in the normal flora of the mouth, skin, and intestines and can cause severe bacterial infections leading to pneumonia, bloodstream infections, wound infections, urinary tract infections, and meningitis (Eliopoulos et al. 2008).

The reduction of microorganisms (S. aureus and K. pneumoniae) on chitosan-treated dyed jute fabrics are shown in Table 5 respectively. In case of untreated and undyed fabric samples, no antibacterial activity was observed against S. aureus and K. pneumoniae. However, jute fabrics dyed with henna dye following the treatment with chitosan demonstrated a significant improvement of antibacterial property against both organisms (Figs. 4 and 5) which revealed a wide spectrum activity and a high killing rate of chitosan against gram-positive and gram-negative bacteria. Furthermore, the microbial inhibition was found to be increased with the increase in chitosan concentration. The most accepted mechanism for the microbial reduction by chitosan is its polycationic structure which causes death of the cell by interacting with anionic proteins of microorganisms (Lim and Hudson, 2004). Moreover, the strong electrostatic interaction which is caused by higher positive charge density adsorbs the electronegative substance in the cell and disturbs the physiological activities of the microorganism (Bhuiyan et al. 2016c; Zheng and Zhu 2003). There are several intrinsic and extrinsic factors, such as pH, microorganism species, positive charge density, molecular weight (MW), and the degree of deacetylation (DD) of chitosan can influence the antimicrobial activity (Zivanovic et al. 2004), while the density of cations depends on the concentration of chitosan and its degree of substitution resulting in a greater reduction of microorganism with the increment of chitosan concentration.

Organism→	S. aureus		K. pneumoniae
Fabric samples↓	Surviving cells (CFU/mL)	Reduction (%)	Surviving cells (CFU/mL)	Reduction (%)
U	2.55 × 105 [B]		2.80 × 105 [B]
A	1.32 × 105 [A]	48.2	1.94 × 105 [A]	30.7
B	28.0 × 103 [A]	89.0	50.0 × 103 [A]	82.1
C	22.0 × 103 [A]	91.4	21.0 × 103 [A]	92.5
D	15.0 × 103 [A]	94.1	17.0 × 103 [A]	93.9
E	11.0 × 103 [A]	95.8	15.0 × 103 [A]	94.6

CFU/ml: Colony Forming Units per milliliter which is mentioned in the experimental section

On the other hand, fabrics dyed with henna alone without chitosan application also exhibit antimicrobial activity especially in case of S. aureus bacteria in Table 5. Moreover, the presence of residual ethanol influences the antibacterial property of henna dye due to ethanolic extraction. Several studies showed that the ethanolic extraction of L. inermis is the most active against all the bacteria in the test system compared to aqueous extraction of henna dye (Sukanya et al. 2009; Ali et al. 2001). In addition, the presence of colored pigment lawsone (2-hydroxy-1,4-naphthoquinone) is also responsible for the inherent antimicrobial activity of henna dye. The highly reactive nature of ketone groups (˃C=O) in the aromatic ring of quinones of lawsone exhibits the antimicrobial property by forming a complex irreversibly with nucleophilic amino acids in proteins and leading to inactivation of the protein and loss of function (Dev et al. 2009). Hence, the natural antimicrobial efficacy of henna dye can be enhanced considerably by coupling with chitosan for the application on textile materials to protect the clothes against common infections.