A Study on Improving Dyeability of Polyester Fabric Using Lipase Enzyme

1.1 Aminolysis

Several studies have assessed the effects of amine interaction with polyester. Early studies assessed the aminolysis of polyester as a means of examining fiber structure without maintaining the integrity of the polymer. The degradation effects on polyester of a monofunctional amine versus alkaline hydrolysis have been studied. These studies, which again involved high levels of fiber degradation, demonstrated that alkaline hydrolysis has a more substantial effect on fiber weight without extensive strength loss. In contrast, aminolysis had less effect on fiber weight but decreased fiber strength, indicative of a reaction within the polymer structure rather than simply at the surface. It was later demonstrated that bifunctional amine compounds could be reacted with the polymer with minimal loss in strength while generating amine groups at the fiber surface. The early stages of the reaction were largely confined to the fiber surface and the resulting fiber had modified wetting properties and improved adhesion with the matrix when used in composites [18].

2.1 Pretreatment of polyester fabric

Polyester fabric was immersed in 10 gpl HCl at 40°C and treated for 1 hour at the same temperature with material to liquor ratio of 1:50, to get rid of the added impurities [19].

2.2 Sodium hydroxide treatment

The pretreated PET fabrics were subjected to various concentrations of sodium hydroxide treatment at boil for 1 hour and 2 hours of treatment time.

2.3 Lipase enzyme treatment

Each fabric sample was cut into specific dimensions and weighed ~1 g. Depending on pH, temperature, concentration, and treatment time, the PET fabrics were treated with lipase in Tris buffer solution, using a liquor ratio of 80:1. All the lipase treatments were performed at 150 rpm using a shaking water bath. The enzyme inactivation was performed at 80°C for 10 minutes. The lipase-treated samples were thoroughly washed with water and dried at room temperature. Then, weight loss, scanning electron microscope (SEM) micrographs, water vapor permeability, Fourier transform infrared spectroscopy (FTIR), Color analysis, and low-stress mechanical properties of lipase-treated PET fabrics were measured.

2.4 Dyeing

Enzyme-treated as well as sodium hydroxide–treated polyester fabrics were dyed using 0.5% (owf) dianix navy S2G (disperse dye), C.I. Disperse Blue 284 and 1 g/L dispersing agent in a HTHP dyeing machine. The dyeing was carried out at a temperature of 130°C and at pH 5 (adjusted by acetic acid). The dyed samples were washed with hot water, soaped, and dried.

3.1 Weight loss evaluation

The weight loss (WL) is expressed as relative WL according to the equation:

where W1 and W2 are the weights of the samples before and after treatment, respectively.

3.2 Wicking height measurement

The wicking heights of the treated fabrics are tested as per AATCC Test Method 197 to evaluate the specimens to transport liquid along them. The distance at a given time is measured.

3.3 Absorbency measurement

The water absorbency of treated fabrics is tested as per AATCC Test Method 79 to know the time taken by a drop of water placed on the fabric surface to completely absorb.

3.4 SEM analysis

The enzyme-treated polyester and blended samples are analyzed through SEM to know the effect of enzyme treatment on surface etching. The surface morphology of polyester fabrics was observed in SEM (JOEL JSM-6360).

3.5 FTIR analysis

FTIR tests were carried out to reveal the additional functional groups present due to alkaline and enzymatic hydrolysis. The attenuated total reflectance–Fourier transform infrared spectroscopy (ATR–FTIR) measurements were carried out on polyester fabrics (control and treated) using an infrared spectroscopy. Nicolet IR200 FT-IR system with a single-reflection attenuated total reflectance attachment was used. Solid samples are prepared by shaving material off of the part that is thin enough to obtain a good FTIR spectrum. The x-axis is wavenumber (cm⁻¹), which is the inverse of wavelength (cm). The y-axis is absorbance normalized on a scale of 0 to 1, where 0 denotes no absorption and 1 denotes maximum absorption.

3.6 Water vapor permeability measurement

The water vapor transmission rates of treated fabrics are tested as per ASTM D6701-16 using water vapor permeability tester.

3.7 Color measurements

The relative color strength (K/S) of dyed fabrics was measured using SS5100A spectrophotometer premier color scan by the light reflectance technique at a wave length 400–700 nm. Reflectance values were measured and the relative color strength (K/S) was calculated using Kubelka–Munk equation. K/S defines a relationship between spectral reflectance I of sample and its absorption (K) and scattering (S) characteristics.

3.8 Evaluation of low-stress mechanical properties

The Kawabata Evaluation System of Fabric (KESF) tester is used to measure the low-stress mechanical properties of alkaline- and lipase-treated fabrics.

3.9 Statistical analysis

To understand the significance of various test results, statistical parameters are analyzed using SYSTAT Software. The statistical parameters like t-test, correlation coefficient, and regression equation were derived.

4.1 Influence of lipase treatment on weight loss of polyester fabrics

It is understood from Tables 4 and 5 that the increase in concentration of enzyme causes increase in weight loss in both the cases. The weight loss is significantly lower for lipase-treated samples than alkaline-treated, in similar concentrations (t value=2.963; p value=0.098).

There is a high degree of positive correlation between enzyme concentration and weight loss in both the cases, but the lipase treatment shows lesser (0.955<0.981). The multiple R of 0.981 indicated in Table 6 shows linear relationship, and F ratio of 25.075 indicate that samples treated at different concentrations have significant weight loss.

4.2 Effect on absorbency

Table 7 values indicate that lipase-treated samples are having higher absorbency characteristics compared with the untreated and alkaline-treated fabrics.

4.3 Effect of lipase treatment on surface characteristics of polyester fabrics

The enzyme-treated polyester and blended samples are analyzed through SEM to know the effect of enzyme treatment on the surface etching. The SEM photographs of the alkaline- and lipase-treated samples are magnified (5000×) to understand the effect of treatments, respectively. The extent of damage is shown in Figure 2.

Figure 2

Scanning electron microscope (SEM) images of A (alkaline-treated) and B (lipase-treated) polyester fabric

4.4 Effect of lipase treatment on moisture regain

FTIR tests reveal the additional functional groups due to alkaline and enzymatic hydrolysis. The addition of hydroxyl groups in polyester is responsible for the hydrophilicity. The following comparative FTIR spectrum reveals the modification in the functional chains, which are responsible for the property changes.

Figures 3–6 and Table 8 indicates that additional groups, such as aromatic rings, alkynes, esters, hydrogen bonds, and carboxylic acids, are present in treated fabrics. The stretching in the region of 3600–3200 is responsible for the hydrophilicity of lipase- and alkaline-hydrolyzed polyester. The high peaks from 1700 cm⁻¹ to 600 cm⁻¹ indicate the original signals, such as characteristic spectra of stretching vibration band of C=O at 1760 cm⁻¹ and C–O–C stretching vibration band at 1097 and 1240 cm⁻¹. All these peaks confirm the existence of ester linkage. This is attributed to the carboxylic group (–COOH) introduced on the surface due to hydrolysis of the ester linkage. The stretching is very high in the case of lipase-hydrolyzed polyester, which makes the enzyme treated more hydrophilic. It is also noted that the presence of basic functional groups inherent in the polyester materials.

Figure 3

FTIR spectra of untreated polyester

Figure 4

FTIR spectra of alkaline-hydrolyzed polyester

Figure 5

FTIR spectra of lipase-hydrolyzed polyester

Figure 6

FTIR comparison spectra of untreated and hydrolyzed polyester

4.5 Effect of lipase treatment on water vapor permeability of polyester fabrics

From Table 9, it is understood that the alkaline- and lipase-treated polyester fabrics are having improved water vapor permeability compared with the untreated polyester fabrics. It is mainly due to the degradation of chain links and the addition of hydroxyl groups.

4.6 Effect of enzyme treatment on dye uptake of polyester fabrics

The alkaline-treated, lipase-treated, and dyed fabrics are tested by reflectance type spectrophotometer to know the K/S values. These values help understand the difference in luster and color values. The treatment offers better dye uptake that enhances the color values.

From Table 10, it is understood that lipase-treated fabrics shows higher reflectance and lower K/S values. Similar trend is observed in dyed fabrics. This clearly shows that treatment enhances the dye uptake of the polyester fabrics.

4.7 Effect of enzyme treatment on the low-stress mechanical properties of polyester

The Kawabata evaluation tests are used for evaluating compression and shear properties in lipase-treated and untreated polyester fabrics, as it reveals the effectiveness of the enzyme treatment.

Table 11 shows that lipase treatment reduces the linearity of compression and compression energy, whereas enhances the compression resilience in polyester fabrics. The enzyme treatment makes the fabric much softer, and it retains its original shape as quickly as possible while applying low stress load. Hence it is possible to infer that lipase treatment makes the polyester fabric with low shear rigidity, which indicates that the fabric will conform to 3-dimensional structures while applying low stress.