Introduction

Blends of polyester and cotton are becoming more and more popular because of their practicality, attractiveness, and simplicity of use1. These blends give the wearer a suitable level of comfort by combining the special qualities of both fibers. Nonetheless, there are a lot of difficulties in the dyeing process for blends of polyester and cotton2. Cotton fibers have a high capacity for water absorption, a property that might cause issues while dying. Cotton may expand when wet, allowing the dye molecules that were initially deposited on the surface to enter the core of the fiber. The dye and the cotton’s cellulose may develop bonding contacts as a result of this penetration3,4. Achieving consistent color and tone throughout the fabric might be more challenging when there are interactions like these throughout the dyeing process.

In contrast, polyester swells less in water and is hydrophobic, which makes it difficult for dye molecules to enter the fiber’s interior structure5. Polyester’s hydrophobic properties and the absence of active chemical groups in its macromolecular structure restrict the kinds of dyes that can attach to it. Due to these qualities, the majority of dye classes, aside from dispersion dyes are inappropriate for use in polyester5,6. The necessity for particular types of dyes highlights the distinct difficulties associated with dealing with polyester in contrast to other fibers7,8.

Traditionally, two-bath dyeing or a one-bath two-step approach has been used to dye polyester/cotton blend fabric. Both techniques call for certain dyes and auxiliaries that are designed for the various fiber types9. These techniques not only take a long time, usually 12 to 14 h on average, but they also come with a lot of complexity and difficulties. They utilize a lot of energy and have problems with different dye classes in the dye bath not working together. To make matters more complicated, reactive dyes may also show weak resistance to later polyester reduction washing10. These drawbacks draw attention to the necessity for more effective and efficient dying methods that can enhance the procedure and the finished quality of the dyed textiles11,12.

Several prior attempts have attempted to simplify dyeing processes into one-bath, one-step approaches to address production issues and growing environmental concerns13. Different dye combinations, like disperse/direct and disperse/vat, can be used in single-bath dyeing; however, color constancy can be challenging to achieve14,15. Eliminating the requirement for reduction cleaning of dyed polyester samples is the main objective of the “rapid dyeing” technique, which greatly increases productivity8,16. Furthermore, by using less water and chemicals, this method not only increases efficiency but also lowers the amount of wastewater produced17. These developments show a dedication to enhancing the sustainability of the dyeing process while meeting the practical needs of contemporary textile production.

The one-bath two-step dyeing method includes a separate phase for reactive fixing to reduce the high rate of hydrolysis that both disperse and reactive dyes may encounter in high-temperature or high-pH dyeing settings. After the initial disperse dyeing, which was carried out at high temperatures and low pH, this phase operates at high pH and low temperature18. While this technique is quicker than the conventional two-bath dyeing procedure, it has some disadvantages as well, such as decreased dyeability and inconsistent repeatability19. On the other hand, the polyester/cotton blend one-bath, one-step dyeing procedure offers various benefits over traditional techniques. In the end, expenses are decreased because it uses less energy, shortens the dyeing cycle, and streamlines the entire procedure. Furthermore, this method does away with the requirement for sodium hydrosulfite, a coloring chemical whose environmental effects are dubious1,20. These advantages draw attention to the possibility of more effective and environmentally friendly dying techniques in the textile sector.

Numerous research studies are presently being carried out on the one-bath step dyeing technique, investigating various dyes on polyester/cotton blends at different temperatures and under acidic or neutral circumstances15,21. Scholars have examined the impact of preheating, under both dry and wet circumstances, on the amorphous structure of polyester and the absorption and behavior of dyes in the micro-voids inside the fiber22. Developing dyes with distinctive coloristic qualities, especially suited for one-bath, one-step dyeing procedures, is another crucial tactic for improving the dyeability of polyester/cotton blends23. To minimize the dyeing cycle and lower energy usage, a one-bath, one-step method of dying polyester/cotton blends utilizing disperse dye after cotton has been acetylated was investigated24. The technique has several benefits when it comes to dying polyester/cotton blends since it facilitates the penetration of dispersed colors into cellulose fibers, which are then fixed by hydrogen bonding and van der Waals forces13,18.

Previously, a unique method of dying polyester fabric has been proposed, which entails applying basic dyes after using the enzymes, lipase, and hydrolase2,25. Nevertheless, there is still a dearth of research on this subject, and it hasn’t been investigated yet how to modify the surface of polyester/cotton blend fabrics with protease enzyme to assess how reactive dyes react with them. In this work, a similar strategy was used to improve the dyeability of polyester/cotton mix fabrics using reactive dyes by using the papain enzyme produced from Carica Papaya. The efficacy of the one-bath, one-step dyeing process was evaluated by subjecting the materials to dyeing trials with various reactive dye concentrations, dyeing times, and temperatures. Several variables, such as the degree of reactive dye fixation, dye absorption, color fastness, and color intensity, were examined to assess the dyeing process’s quality. These metrics demonstrated the possible advantages of applying lipase enzyme treatment during the dyeing process and offered insights into the overall performance and aesthetic quality of the colored polyester/cotton blends.

Methods and materials

Materials

Half-bleached polyester/cotton blend fabric was sourced from the EITEX textile chemistry laboratory. The fabric had a blend ratio of 65% polyester to 35% cotton and was characterized by a specification of 85 picks per inch and 160 ends per inch, featuring a 2/2 twill warp face. The warp count was measured at 30 tex, and the weft count was 36 tex, resulting in a fabric weight of 220 g per square meter (GSM). This specific combination of specifications makes the fabric suitable for further dyeing and finishing processes.

The following materials were sourced from the EiTEX textile chemistry laboratory and used without any further purification: C.I. Reactive Dye Red S-8G (reagent grade), sodium hydroxide (NaOH, 99% purity), sodium chloride (NaCl, 99% purity), sodium sulfate (Na₂SO₄, 98% purity), and standard soap. These chemicals were selected for their quality and suitability for the dyeing processes under investigation. The enzyme used was a cysteine type protease, Papain (EC 3.4.22.2), which is derived from Carica papaya latex, supplied by Sachem Chemicals (Addis Ababa, Ethiopia). It was selected for its broad specificity and well-characterized activity in hydrolysis.

Methods

Surface modification methods

The ideal papain treatment parameters for polyester/cotton blend materials were a pH of 7.5, 30 °C, 14% (w/v) papain concentration, and 50 min of treatment time, as shown in Table 1. Following the treatment, all leftover enzymes and residues were removed from the samples by giving them a thorough washing with water at a liquor ratio of 1:50. To prepare them for the ensuing dying procedures, they were then dried at room temperature. The goal of this meticulous treatment process was to improve the materials’ dyeability without sacrificing their integrity.

Table 1 Papain enzyme specifications and conditions.
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Dyeing methods

After the papain enzyme surface modification, the polyester/cotton blend fabric was dyed. A one-bath, one-step dyeing technique was used to find the ideal dyeing conditions under various parameters. To perform this procedure, 1.5% to 4% (w/v) concentrations of C.I. Reactive Dye Red S-8G were added to the dye bath along with 1.5 g of Na₂CO₃ and 3 g of NaCl, resulting in a bath ratio of 1:20 as shown in Table 2. After that, the dyeing mixture was incubated in a Jigger dyeing machine that ran at 50 rpm for 50 to 70 min at temperatures between 60 and 80 °C. Following dyeing, the samples were repeatedly washed in distilled water and then again in normal liquid soap for 15 to 30 min at 80 °C. After several additional rinses in distilled water, they were allowed to air-dry at room temperature. The Box-Behnken design of experiment software (Design-Expert StatEase, Version 11.1.2, developed by Stat-Ease, Inc.) was utilized to conduct 17 experimental runs for the reactive dyeing of polyester/cotton blends, methodically assessing the dyeing process. With this method, the dyeing parameters were optimized for improved quality and performance.

Table 2 Dyeing conditions.
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Color strength measurements Using the Gretag Macbeth Color Eye 3100 spectrophotometer, the color strength of the dyed cloth samples was evaluated. The steps described in the AATCC 6-2003 test standard methodologies were adhered to in this measurement. To determine the color strength, the reflectance values at the maximum wavelength had to be recorded. The K/S value was then utilized to get the surface color strength. The K/S value, which indicates color depth, is derived from the Kubelka–Munk equation, a well-established formula in color science that relates the absorption and scattering of light by the fabric. This systematic approach allowed for a precise quantification of the color strength of the dyed samples, providing valuable insights into the effectiveness of the dyeing process.

$$\frac{K}{S} = \frac{{\left( {1 - R^{2} } \right)}}{2R}$$
(1)

where R represents the fraction of light reflected from the fabric, while K quantifies how much light is absorbed by the dye, and S accounts for how much light is scattered by the fabric.

UV–VIS spectroscopy measurements A UV–visible spectroscopy device (UV1800) was used to measure the absorbance of dye solutions both before and after the dyeing process26. The conjugation of C.I. Reactive Dye Red S-8G (at a concentration of 1 g/L, with a maximum absorbance range of 400–500 nm) in solutions applied to the modified polyester/cotton blend fabric was analyzed using the absorbance against wavelength curves produced by this device. This research assisted in illuminating how the reactive dye interacted at particular temperatures27. Additionally, using adsorption isotherms obtained from the UV–visible spectroscopy measurements, the mechanism by which the reactive dye interacts with the polyester/cotton mix fabric was examined. Models that explain how the dye molecules adsorb onto the fabric surface, such as Nernst, Freundlich, or Langmuir, were used to examine the isotherms28. A deeper comprehension of the dyeing process and the dye’s efficacy on the altered fabric was made possible by this thorough approach.

Fourier Transform Infrared Spectroscopy (FTIR) analysis Using a Perkin Elmer FTIR instrument and following ASTM 7575 test standard methods, Fourier Transform Infrared Spectroscopy (FTIR) was used to assess the surface chemistry of both control and enzymatically transformed polyester/cotton mix fabrics. To guarantee precision and dependability, the spectral data were gathered in the frequency range of 4000–400 cm1. Each sample was examined through 20 scans. A 500 ml laboratory beaker (Model No. P230, 115-V) was used for the lipase surface modification procedures applied to the polyester fabric. This arrangement made it possible to precisely regulate the modification conditions and allowed for a detailed analysis of the chemical alterations brought about by the enzymatic treatment of the fabric’s surface. This thorough investigation yielded insightful information about the changes in surface chemistry brought about by enzyme application.

Differential scanning calorimetry (DSC) A Perkin Elmer Pyris Series-DSC 7 was used to perform crystallinity tests, and standard aluminum pans were used for the study. The temperature range of 0–300 °C was reached by heating the papain-treated and control samples (10 mg for film samples and 20.70 mg for GPET) at a rate of 20 °C/min. Carefully examining the initial heating run allowed us to pinpoint the areas that matched the melting and cold crystallization peaks. Equation 2 was applied to determine the crystallinity of the samples based on these peak locations. To shed light on the material’s behavior and thermal characteristics, this investigation sought to ascertain how the polyester/cotton blend’s crystalline structures were impacted by the papain treatment.

$${\text{crystallinity}} = \frac{{\Delta {\text{Hm}} - \Delta {\text{Hc}}) }}{{\Delta H0{\text{m }}}}*100{\text{\% }}$$
(2)

where, ∆Hm, ∆ Hc, and ∆H0m are heats of melting, crystallization, and melting of 100% crystalline PET (140.1 J/g), respectively.

Tensile strength measurements

The ASTM D5034 method was used to conduct the tensile strength test on the blended fabric made of esterified polyester and cotton. Tensolab 100 equipment was used to conduct this testing, both before and after the treatment. Measurements were made during the process to document the amount of force needed to shatter the specimen and the extent of fabric elongation29. Understanding the mechanical characteristics of the fabric and how the treatment process affects them requires this assessment.

Fastness properties

Colorfastness to rubbing The AATCC Test Method 8-2013 was used to assess the dyed samples’ wet and dry colorfastness against rubbing. This uniform process gauges how well a fabric’s color resists abrasion under rubbing in both wet and dry environments. The purpose of these tests was to evaluate the fabric’s dye’s durability and make sure that the color would hold up after washing and wear. Understanding the dyed polyester/cotton blend fabrics’ useful performance in practical applications depends on the results of this evaluation.

Colorfastness to washing The colorfastness to washing of the dyed samples was assessed by AATCC Test Method 61-1996, utilizing a Launder-Ometer for the procedure. This test evaluates how well the colors of the fabric withstand repeated laundering. The results were analyzed using the Grey Scale for color change, which provides a standardized reference for evaluating any color shifts that may occur during the washing process. This assessment is essential for determining the longevity and durability of the dye on the polyester/cotton blend fabrics, ensuring they maintain their appearance after multiple washes.

Colorfastness to perspirationAATCC Standard Test Method 15-1997 was used to assess the dyed samples’ colorfastness to sweat. This test simulates real-world scenarios in which the fabric may come into contact with sweat and assesses how resistant the fabric’s color is to fading or bleeding when exposed to perspiration. This evaluation is essential to make sure that, especially in warm or muggy settings, the dyed polyester/cotton blend textiles keep their aesthetic and color integrity while being worn.

Results and discussion

Optimization of dyeing polyester/cotton blend fabric

After refining the papain enzyme surface modification, the polyester/cotton blend fabric was dyed using reactive dyes in a one-bath, one-step process. The dyeing procedure involved the examination of several parameters, with particular emphasis on dye concentration, dyeing time, and dyeing temperature. In the meantime, the material liquor ratio (M.L.R.) and pH levels were kept constant. The polyester/cotton blend was dyed using both conventional dyeing techniques and the novel one-bath, one-step procedure for comparison’s sake. The main parameter used to assess the fabric’s dyeability with reactive dyes was the resultant color strength. To investigate the correlations between the variables of dye content, dyeing time, and dyeing temperature, an experimental design was utilized. Analysis of Variance (ANOVA) was performed to ascertain the relevance of these variables on the reaction color strength, as shown in Table 3. The goal of this thorough investigation was to pinpoint the ideal circumstances for getting successful dyeing outcomes.

Table 3 Experimental design dyeing papain-modified fabric.
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The effect of independent factors on the response color strength was assessed using the Analysis of Variance (ANOVA) for the quadratic model. The findings showed that the F-value was 26.98 and the P value was 0.0001, with a 95% confidence interval. It is clear that 0.05 > 0.0001 0 when comparing the alpha level of 0.05 with the P value of 0.0001, indicating that the model is statistically significant. This suggests that, as shown in Table 4, the independent factors probably have a significant impact on the response.

Table 4 ANOVA and fit statistics table for color strength.
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The results for all factors, factor A (dye concentration), factor B (dyeing time), and factor C (dyeing temperature) indicated F-values of 105.32, 30.08, and 54.75, respectively. Corresponding P values were found to be < 0.0001 for dye concentration, 0.0009 for dyeing time, and 0.0001 for dyeing temperature. At a 95% confidence interval, with an alpha value of 0.05, the significance level of 0.05 is greater than all calculated P values. This confirms that each factor has a statistically significant effect on the response color strength, demonstrating their real impact on the dyeing process. The interaction effects of factors AB (dye concentration and dyeing time) and BC (dyeing time and dyeing temperature) were found to be non-significant. This is evidenced by the F-values of 0.3252 for AB and 0.9399 for BC, with corresponding P values of 0.5863 and 0.3646, respectively. At a 95% confidence interval, using an alpha value of 0.05, the significance levels of 0.05 are less than both P values (0.5863 and 0.3646).

This indicates that the interaction between these factors does not have a meaningful impact on the response color strength. The results indicate that the lack of fit had an F-value of 1.57 and a P value of 0.3288. At a 95% confidence interval, with an alpha value of 0.05, the comparison shows that the alpha value is greater than the P value (0.05 < 0.3288). This suggests that the lack of fit is not significant, meaning that the model can effectively predict the response color strength based on the data. Furthermore, Adjusted and predicted R2 implies that the data are a suitable fit for the selected model, reinforcing its validity for making predictions.

Effects of dye concentration on color strength

The modified dyed material’s K/S value is significantly influenced by dye concentration. A comparable rise in color strength occurs when the dye concentration is increased, as seen in Fig. 1. Table 3 illustrates how increasing the dye concentration from 1.5 to 4% produced the greatest color strength ever measured, which was 4.6. This rise is explained by the fact that more dye diffuses into the fibers from the dye bath at higher concentrations. Furthermore, there’s a greater chance that more dye molecules will stick to the fibers if there are more of them in the dye bath. Thus, a higher K/S value results from this improved dye molecule attachment30. The significance of dye concentration in attaining the ideal color strength in dyed materials is highlighted by this relationship.

Fig. 1
figure 1

Dye concentration Vs color strength.

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Effects of dyeing time on color strength

The influence of dyeing time on the color strength of the dyed fabric is illustrated in Fig. 2. The graph demonstrates a clear trend: as the dyeing time increases, the color strength also rises, reaching a peak until the dye exhaustion stabilizes. The maximum color strength recorded was 4.6, achieved by extending the dyeing time from 50 to 70 min, as detailed in Table 3. The longer dyeing period allows more dye to permeate from the dye bath to the surface of the fibers and then penetrate deeper into the fiber structure, which explains the increase in color strength. More dye molecules become available for absorption as the dyeing period increases, which promotes improved dye exhaustion31. As a result, the increased dye concentration within the fibers as well as on the surface greatly enhances the fabric’s overall color strength. This relationship emphasizes how crucial it is to maximize dyeing time in textile applications to attain desired color outputs.

Fig. 2
figure 2

Dyeing time Vs color strength.

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Effect of dyeing temperature on color strength

The color strength of the dyed modified polyester/cotton blend is comparatively poor at lower temperatures, 60 °C. It can be difficult to dye polyester at these low temperatures because the material’s crystalline structure might not open up enough to allow the dye to diffuse into the fiber matrix. A notable improvement in color strength is observed when the dyeing temperature is raised, as shown in Fig. 3. Increased temperature causes the molecular chains in the fibers to become more mobile, which improves dye dispersion through the material’s more accessible structure32. The decrease in the polyester component’s glass transition temperature is responsible for the enhanced color strength at higher temperatures. Reactive dyes can enter fibers more readily as a result of the relaxation and opening of the fiber structure brought on by this decrease33. A stronger color is produced as a result of improved dye molecule fixation within the fibers. This demonstrates how important temperature is for maximizing dye absorption and producing vibrant color outcomes throughout the dying procedures for blends of polyester and cotton.

Fig. 3
figure 3

Dyeing temperature Vs color strength.

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According to the output data, the ideal circumstances were attained by carefully regulating the temperature, reaction time, and dye concentration to reduce the expenses of both time and dye and to preserve the energy needed for heating. Maximizing color strength was the aim because it improves dyeability and fabric quality in general. With the aid of Design Expert 11 software, 32 possible solutions in all were produced. A few of these choices were chosen to apply the ideal dyeing conditions. To provide the greatest outcomes for the dyeing process, our selection method concentrated on striking the perfect balance between cost-efficiency and the required color strength. The optimal condition gives a low to medium color strength of 2.8 when there is a 2.48% dye concentration, 50 min dyeing time, and 67 °C. These conditions are selected because they give a desirability value of 0.56. This newly developed optimum condition was then used for dyeing polyester/cotton blend fabric and testing color fastness properties and for further evaluations.

Colorfastness properties for dyed papain-treated Fabric

Table 5 shows how washing fastness affects the dyed samples by presenting the ratings for colorfastness to washing (more especially, staining). The findings show that the polyester/cotton blend fabric dyed in one bath using reactive dye after surface modification has colorfastness that is roughly equivalent to samples of traditional two-bath, two-step dyed fabric. The reason for this resemblance is that reactive dyes are hydrophilic, which improves the dyed fabric’s wash-fastness characteristics. These dyes are durable throughout laundry because of their capacity to create strong chemical connections with the fibers, which reduces stains and color loss. All things considered, the results indicate that the enhanced dyeing process keeps good color retention, much like conventional dyeing methods.

Table 5 Wash fastness of papain-treated and conventional two-bath method.
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The color fastness to washing, in particular the color change, of the polyester/cotton blend dyed in one bath and one stage is almost equal to that of the traditional two-bath, two-step dyed samples, as Table 5 shows. This suggests that the improved dying procedure performed comparably to the more conventional techniques in terms of preserving color fidelity throughout washing. These findings demonstrate how well the one-bath, one-step method works to produce long-lasting dyeing effects while also perhaps providing advantages in terms of efficiency and cost-effectiveness.

Table 6 shows that samples colored with reactive dyes in a one-bath, one-step approach after the cotton component’s surface was modified have better dry and wet rubbing fastness than samples dyed using conventional two-bath methods. These results imply that the one-bath dyeing method enhances the overall performance of the dyed fabric while preserving good color persistence. Thus, this suggests that using this effective technique to dye polyester/cotton blends can lead to practical breakthroughs in this area.

Table 6 Rubbing fastness of papain-treated and conventional two-bath method.
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The degree to which a cloth will not fade or discolor when exposed to perspiration is known as its colorfastness to perspiration. Large local discoloration can occur in garments that come into contact with body parts that sweat a lot. This test evaluates the dye’s resilience to sweat that is both acidic and alkaline. Table 7 indicates that the samples dyed using the one-bath, one-step method with reactive dyes after the surface modification of the polyester component exhibit commendable fastness to alkaline perspiration when compared to those dyed using the traditional two-bath method. While the differences in colorfastness to perspiration between these two dyeing techniques are relatively minor, the one-bath method demonstrates effective performance, suggesting its viability for producing durable and high-quality dyed textiles.

Table 7 Perspiration fastness of papain-treated and conventional two-bath method.
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UV–VIS spectroscopy measurements

The UV–Vis spectra of C.I. Reactive Dye Red S-8G (at a concentration of 1 g/L, with a maximum absorption range of 486–495 nm) were recorded before and after dyeing papain-treated polyester/cotton blend fabric (also at 1 g/L) at different temperatures for an hour using a jigger dyeing machine to demonstrate the formation of reactive dye. Figure 4 displays their spectra. The statistics presented in Fig. 4 demonstrate that the wavelength at which 6.02233 exhibits maximum absorption is 486–492 nm. This suggests a notable alteration in absorption as the temperature rises from room temperature to 80 °C. On the other hand, the absorption peak significantly drops at greater dye solution concentrations at the indicated temperatures, indicating a significant change in the color of C.I. Reactive Dye Red S-8G. Changes in the dye’s conjugation structure can be the cause of this occurrence. Additionally, a multilayer adsorption process on the fabric surface was indicated by the identification of the reactive dye’s dye adsorption mechanism on the treated polyester/cotton blend as following the Freundlich adsorption isotherm.

Fig. 4
figure 4

UV–VIS spectroscopy measurement.

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Fourier Transform Infrared Spectroscopy (FTIR) analysis

The observed higher absorption peaks suggest that polar functional groups have been added to the surface of the polyester/cotton (p/c) blend textiles, along with extra oxygen (O). These results are consistent with the enhanced hydrophilicity noted in the cloth optimized for papain treatment. The FT-IR spectra of polyester/cotton blend fabrics treated with papain and those that are not are shown in Fig. 5. Strong absorption peaks can be seen in the spectra of both samples at 3317, 2920, 2854, 2109, 1715, 1309, 1242, 1106, 1016, and 724 cm⁻1. Compared to the untreated sample, the absorption peaks in the fabric modified by the papain enzyme had a noticeable increase in amplitude. This suggests that the fabric’s chemical and physical qualities are effectively enhanced by the treatment, which improves the fabric’s performance. The existence of aliphatic O–H groups linked to the glycosidic ring is shown by the peak at 3317 cm1, which correlates to broad and strong O–H stretching. O–H stretching is also linked to the peak at 2854 cm1, which shows up as a very broad signal.

Fig. 5
figure 5

FTIR of papain-treated fabric.

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Furthermore, the stretching vibration of the O-C = O bond in carboxylic acid groups (–COOH) is responsible for the peak at 2109 cm⁻1. The coupling frequencies of O–H and C–O bonds are associated with the peaks at 1715, 1309, and 1242 cm⁻1. The 724 cm⁻1 peak is linked to the out-of-plane bending vibration of C–H (more precisely, CH₂) in benzene, whereas the 1080 cm⁻1 peak is related to C–O trans-vibrations. Moreover, the papain-modified polyester/cotton blend fabrics spectra show faint absorption peaks at 1016 and 864 cm1, which correspond to the C–H and = C–O vibrations in benzene, respectively. The lipase-modified fabric’s spectrum showed the appearance of a new, weak absorption peak at 724 cm⁻1. This peak is indicative of the out-of-plane deformation vibration of O–H…H interactions, which most likely involve the hydrogen atoms of the two polycarboxylic acid groups seen in the fabrics transformed by papain. This draws attention to the substantial chemical alterations brought about by the treatment, which improve the fabric’s qualities.

Differential scanning calorimetry analysis

A differential scanning calorimeter (DSC) was used to assess the thermo-physical characteristics of polyester/cotton (P/C) blend fabric samples under control and after lipase treatment. Figure 6 displays the melting and glass transition temperatures of the textiles for both the control and lipase enzyme-treated samples. The melting temperature of the materials is indicated by the peak values on these curves. Distinctive Scanning. One useful method for determining the molecular orientation and crystallinity of a polyester/cotton blend is calorimetry. The crystalline structure of the fabric was not considerably altered by the lipase treatment, as seen by the roughly 31.2% percent crystallinity for both the control and lipase-treated samples. The key to this research is the clear distinction in temperatures of fusion between the polymer’s crystalline and non-crystalline forms. By figuring out important variables such as the glass transition temperature (Tg), melting temperature (Tm), and degree of crystallinity (XDSC), DSC thermal analysis can provide insights into the structure and characteristics of the polyester/cotton blend34. By integrating the peak area from the differential scanning calorimetry curve, the degree of crystallinity for the lipase-treated polyester/cotton mix was determined, offering a numerical representation of the crystalline properties of the material.

Fig. 6
figure 6

DSC of papain-treated fabric.

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Effect of papain-treated dyed sample on the physical properties of the fabric

The tear and tensile strength of the dyed fabric samples were examined. The tensile strength of the polyester/cotton blend dyed using the one-bath, one-step method with reactive dyes, following papain enzyme surface modification, was found to be slightly lower than that of the conventional two-bath dyed samples and the control samples, as indicated in Table 8. This suggests that while the one-bath method offers advantages in terms of efficiency, it may have a minor impact on the mechanical strength of the fabric compared to traditional dyeing techniques.

Table 8 Effect of dyeing on tensile strength properties of the fabric.
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In comparison to the control samples, Table 8 shows that the polyester/cotton blend fabric’s tensile strength falls in samples dyed using the one-bath, one-step approach when assessed in both the warp and weft directions. The higher papain concentration during the treatment procedure and the higher dyeing temperature, both of which hurt the fabric’s structural integrity, are to blame for this decrease in tensile strength. Higher lipase concentrations, longer reaction periods, and higher treatment temperatures change the original polyester/cotton blend’s crystalline structure during the surface modification. Furthermore, the dyeing temperature has a major impact on the dyed samples’ crystallinity during the dyeing process. Consequently, the reactive dyed polyester/cotton blend exhibits a decreased tensile strength in comparison to the control samples. On the other hand, when using the two-bath dyeing procedure, the fabric’s tensile strength is mostly determined by the dying temperature. This demonstrates the intricate relationships that exist between the fabric’s mechanical qualities, dyeing techniques, and treatment settings.

The tear strength of polyester/cotton blends dyed with reactive dyes using the one-bath, one-step method is nearly comparable to that of the conventional two-bath dyed samples. However, as shown in Table 9, the tear strength of the lipase-treated polyester/cotton blend in the one-bath, one-step dyed samples is reduced in both the warp and weft directions when compared to the control samples. This decrease in tear strength can be attributed to the treatment conditions and the dyeing temperature, which negatively impact both the tensile strength and tear strength of the polyester/cotton blend fabric.

Table 9 Effect of dyeing on tear strength properties of the fabric.
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Conclusion

This study establishes a sustainable pathway for the one-bath, one-step dyeing of polyester/cotton blend fabrics using reactive dyes, predicated on enzymatic pre-treatment with papain. The research demonstrates that papain treatment effectively modifies the fabric’s surface chemistry, as evidenced by the introduction of hydrophilic functional groups (O–H, C–O, C = O, and COOH). This modification was critical in enhancing the substrate’s affinity for reactive dyes, which are not typically suitable for such blends without complex multi-step processes. The Box-Behnken design was used to optimize both the pre-treatment and dyeing parameters. The optimal enzymatic pre-treatment was achieved using a 14% papain concentration for 50 min at 30 °C. Subsequent dyeing under the optimized conditions 2.48% dye concentration (o.w.f.), 50 min, and 67 °C produced a colour strength (K/S) of 2.8. Furthermore, the dyed fabrics exhibited good functional performance, achieving wash, rubbing, and perspiration, rating 4, which are comparable to, conventional methods. A key limitation of this process is the moderate colour strength value (K/S = 2.8), which suggests that there is potential for further improvement in the degree of dye exhaustion and fixation. Future work should focus on exploring synergistic enzyme systems or post-dyeing chemical treatments to enhance the depth of shade. Notwithstanding this limitation, the research makes a significant contribution by demonstrating that papain pre-treatment efficiently overcomes the fundamental hydrophobicity of the blend, enabling a simplified and more environmentally friendly dyeing process.