Performance enhancement of water and energy efficient foam dyeing and finishing through different foaming agents

ABSTRACT Foam dyeing and finishing is an ecofriendly alternative to conventional padding in textile processing. However, the generation and application of foam is a challenging task especially for wide range of dyes and chemicals due to technical and compatibility issues. In the foam dyeing and finishing process, foaming agent plays a central role. However, there is a lack of research on the compatibility of range of foaming agents with the range of different dyes and finishes. Therefore, in this research, foam was generated and optimized for seven different colorants including three reactive dyes, two direct dyes, and two pigments, and three different finishes including softener, oil and water repellent, and fire retardant using three different foaming agents separately. These foaming agents are alkyl dimethyl amine oxide, alkane sulfonate sodium salt, and ethoxylated decanol. Foam was successfully generated, optimized, and applied on the cotton fabric. Performance of the fabric samples treated with padding and three foaming agents for each dye and finish was evaluated. In most of the foam dyeing and foam finishing recipes, alkane sulfonate sodium salt-based foaming agent indicated the best dyeing and finishing properties and its performance was comparable with conventional padding in addition to significant savings of water, chemicals, and energy.


Introduction
The traditional textile processing techniques consume the substantial water, energy, and chemicals leading to resource depletion and pollution (Bhavsar et al. 2017;Tecer et al. 2020). For instance, the global processing of 60 billion kg fabric requires nine trillion liters of water leading to one trillion kilowatt hour energy consumption along with substantial chemical consumption and wastewater Amphoteric (Yu et al. 2014) sodium dodecylbenzene sulfonate, cetyl trimethyl ammonium bromide, Tween 80, glycine betaine) using Reactive Red 120 in the cotton fabric dyeing. It was concluded that the sodium dodecyl sulfate provided the superior foamability. They added different stabilizers in sodium dodecyl sulfate and found that the addition of one or more stabilizers increased the half-life. Protein-based biodegradable surfactant namely keratin hydrolyzate was also reported as a foaming agent which exhibited the good foam stability in the fabric dyeing using a reactive dye (Levafix Navy CA) and an acid dye (Nylosan Navy S-3 G SGR) (Bhavsar et al. 2017). Foam-dyed fabric exhibited the satisfactory shade depth, and good fastness properties. Mohsin and Sardar (2019) compared padding, foam dyeing, and finishing using three primary colors for direct dyes and three primary colors for reactive dyes, while Unifroth 450 was used as foaming agent. Substantial cost savings were achieved related to chemical, energy, water, and production time. Two new foaming agents cetyltrimethylammonium glycine (CTAG) and octadecyltrimethylammonium glycine (OTAG) using cetyltrimethylammonium chloride (CTAC), octadecyltrimethylammonium chloride (OTAC) were also developed (Chen et al. 2019). It was concluded that the new foaming agents have better foamability and other properties compared with original surfactants. However, the halogen was used in the formulation and the developed foaming agents were not applied on the textile materials. Some other papers studied the foam properties of different foaming agents in the applications other than the textile processing. For instance, Sheng et al. (2016) mixed the foaming agent "silicone surfactant of polyoxyethylene trisiloxane" with hydrocarbon surfactants of sodium dodecyl sulfate, BAC-12 (Dodecyl dimethyl benzyl ammonium chloride) and Brij30 (Polyoxyethylene lauryl ether). It was concluded that the mixture of silicone and hydrocarbon surfactants resulted in the synergistic effects. The foamability of sodium dodecyl sulfate can be enhanced through mixing of trisiloxane surfactant. Sodium dodecyl sulfate and hexadecyltrimethyl ammonium bromide were also compared as foaming agents (Tiong, Tan, and Foo 2019). Sodium dodecyl sulfate generated foam of 21% longer half-life and 17% better foamability as compared to other foaming agent. From the existing literature, it can be concluded that a number of scientists have reported the various foaming agents (Chen et al. 2020;Dawson 1981;Kinnunen-Raudaskoski et al. 2014) but mostly single foaming agent or with either one or limited dyes and/or finishes. The optimization of various foaming agents for range of dyes and finishes for textile is mostly lacking. The comprehensive research is required to evaluate the impact of the different foaming agent on performance properties. The present paper presents the three foaming agents; ethoxylated decanol (Unifroth 520), alkyl dimethyl amine oxide (Genaminox CSL), and alkane sulfonate sodium salt (SAS 60) for foam dyeing with seven colorants of direct, reactive and pigments as well as with three finishing agents for cotton fabric.

Materials and methods
This study performed padding, foam dyeing, and foam finishing on the scoured and bleached fabric with 100% cotton, 260 GSM (gram per square meter), and 3/1 S-Twill weave. Fabric ends per inch was 120, picks per inch was 71, warp count was 30, and weft count was 10. The padding was performed at 70% pickup on the lab scale padding machine. Padder was horizontal type, having model no. PAD VH350 GD from color smith, UK. The fabric samples dyed and finished with padding were kept as reference samples for comparison with foam treated samples. The foam dyeing and foam finishing recipe optimization were performed on the lab-coating machine, Model MU572C, by Fanyuan Instrument. In this machine, the foam is applied on the fabric through a roller on blade technique. Before applying the foam on the fabric, the foam was generated with mechanical agitation and optimized quantity of each foaming agent was determined through numerous trials. This paper uses 1:8 foaming ratio which interprets that 1 L liquid generates 8 L foam. The foam half-life was calculated for each foaming agent. Foam half-life is the time in which the solution remains one-half of the original volume. The dyeing/finishing of the textile fabrics requires minimum half-life of 1.5 minutes (Mohsin and Sardar 2019).
Three lab grade foaming agents were purchased from Sigma Aldrich and used in this research, which include ethoxylated decanol (Unifroth 520), alkyl dimethyl amine oxide (Genaminox CSL), and alkane sulfonate sodium salt (SAS 60). Alkyl dimethyl amine oxide (Genaminox CSL) is an anionic surfactant and its composition is alkyl dimethyl amine (R = C 12 ). The chemical structure of alkyl dimethyl amine oxide with 12 carbon items of alkyl chain is given in Figure 1.
The numerous trials were performed with varying quantities of a foaming agent, RPM, and stirring time. In these trials, the different amounts of the foaming agents were prepared in water. Then, the foam was generated at different stirring speed and time. At this stage, any dye or finish was not added. For ethoxylated decanol (Unifroth 520), the stable foam with half-life of 337 seconds was achieved when the foaming agent quantity was 2.5%, RPM 900 for the stirring time of 300 seconds. Increasing RPM from 900 to 1000 and 1200 resulted in better half-life but the foam became unstable. For alkyl dimethyl amine oxide (Genaminox CSL), the stable foam with half-life of 320 seconds was achieved when the foaming agent quantity was 3.5%, RPM 1000, and stirring time 360 seconds. For alkane sulfonate sodium salt (SAS 60), the stable foam with half-life 396 seconds was achieved when the foaming agent quantity was 3%, RPM 900, at the stirring time of 300 seconds. Foam half-life is the time in which the foam volume becomes half (Mohsin and Sardar 2019). The optimal foam generation recipe for each foaming agent is given in Figure 3. The optimized foam quantity was used in the foam production for different dyes and finishes.
Following is the step-by-step general experimentation process for foam finishing and foam dyeing.
Step 1: Mixing of the specific foaming agent into the desired amount of water and its rotation at specific speed for specific time.
Step 2: Addition of dye or finish and any other ingredient like binder, salt or alkali if required into the recipe of step 1 and its rotation for further 30 seconds.
Step 3: Final foam recipe is applied onto the fabric through foam coating machine.
Step 4: Drying and curing of the foam treated fabric. This research used seven colorants and three finishes (Table 2). 100 mL water was used in each dyeing and finishing recipe. For each dye, padding at 1% dye concentration resulted in better shade depth than the foam dyeing at 1% dye concentration as foam recipe is diluted 8 times due to foaming ratio of 1:8. To get the comparable shade depth, the dye quantity was increased to 2% for each foam dyeing recipe. Hence, foam dyeing was performed at 1% and 2% dye concentration for each foam dyeing recipe. The finishes include the polyethylene softener, oil and water repellent finish, and flame-retardant finish. The padding and foam dyeing/finishing recipes for each dye and finish are presented in Table 2.
The dyed and finished samples from padding, foam dyeing, and foam finishing were dried at 100°C and cured at 180°C. All samples were conditioned before testing as per standard. Sample were conditioned at the temperature of 20°C and relative humidity of 65% for 24 hours. Shade depth of  foam dyed fabric was assessed by using spectrophotometer. Shade depth (K/S) was measured by assessing reflectance at diffused illumination 8 degree viewing and specular component included. The reflectance was measured by spectrophotometer model (Konica Minolta 3600a) benchtop which can measure both reflectance and transmittance. Test Method (8-2004) was used to assess the dry and wet rubbing fastness. Colored fabric was rubbed against bleached fabric for 10 cycles and rate of rubbing was one turn per second. Gray scale for color change was used to assign the dry and wet rubbing fastness rating. ISO 105 C06 A1S standard test method was used for washing fastness test. 4 g/L of SDC-ECE detergent (phosphate based) was dissolved in water and its solution was used for washing along with 10 steel balls. Samples were attached with bleached fabric and washed as per standard conditions of 30°C for 45 minutes. Grey scale was used to give the washing fastness rating. Crease recovery angle of fabric was assessed by using standard test method AATCC 66-2003. Total 20 specimens having size of 40 × 15 mm were taken from the sample. Each specimen was kept under weight of 500 g for five minutes and then it was removed from the load and hanged on the crease recovery tester for five minutes as a recovery time. After five minutes crease recovery angle of the specimen was noticed. Water repellency of finished fabric was assessed by using standard test method AATCC-2001. Specimen size was 180 mm × 180 mm. Fabric was clamped in the hoop and distilled water quantity of 250 ml was poured onto the fabric surface through specified fine holes. ISO standard spray chart was used to assign the water repellency rating. Fire Retardancy by char length was assessed by vertical burning test 16 CFR 1610. Flame height was 16 mm and ignition time was 10 seconds. Damaged fabric char length was measured in mm after the test. Air permeability of fabrics was assessed by ASTM D 737. Fabric was clamped on the air permeability machine with specified pressure and area as per requirement and equipment exhibited the air permeability value after the completion of the test. Bending length of the foam finished fabric was assessed by standard test method ASTM D 1388. The cantilever test apparatus was used to measure bending length of fabrics. Tear strength of fabrics was determined by ASTM D1424. Fabric specimen along warp and weft direction were cut into 100 mm × 73 mm from 5 different places and tear strength was measured at the load of 10 N using tear strength testing machine.

Results and discussion
This section discusses the results based on experimentation performed in the previous section. The   Table 3 presents the shade depth comparison for padding and foaming agents on cotton fabric. It can be observed that padding with 1% dye concentration exhibited superior shade depth than all the foaming agents. It is not surprising as foam recipe is diluted eight times as compared to padding. However, increasing the dye concentration has improved the results. Therefore, raising the dye amount to only 2% in foam dyeing has given the shade depth near to padding recipes. Furthermore, more dyes exhibited good shade depth for alkane sulfonate sodium salt (SAS 60). It may be due to the reason that other two foaming agent involve comparatively more reactive amine oxide group (Genaminox CSL) and ethylene oxide group (Unifroth 520) as compared to simple carbon chain for SAS 60 foaming agent, which may cause slight interference with the dyes and chemicals in the recipe.

Fastness properties with reactive dyes
The dyeing with 1% reactive dye, in case of all three reactive dyes of reactive red, reactive, yellow and reactive blue, indicates equivalent and excellent dry rubbing fastness rating for padding and foam dyeing/finishing recipes. Only ethoxylated decanol (Unifroth 520) has exhibited half a rating lower dry rubbing in case of reactive yellow as compared to all other recipes. However, in case of reactive yellow and reactive red, the dyeing at 2% dye concentration shows half grade inferior dry rubbing fastness than dyeing at 1% dye concentration. This decrease in rating is due to the fact that certain dyes exhibit lower fastness in the presence of the higher amount of color on the fabric surface. It was also observed that wet rubbing fastness of all three reactive dyes at 1% with either padding or foaming was one rating lower than the dry rubbing fastness. Such trend is typical in nature in dyeing because the wet rubbing involves the rubbing action in addition to the help of water that removes more color. Similar trend of decrease in washing fastness was observed due to the same reason.
Only ethoxylated decanol (Unifroth 520) has exhibited slightly (half a rating) low rating in certain cases like in case of washing fastness of 1% reactive blue and wet rubbing fastness of 1% reactive yellow as compared to other foam dyeing. In addition, alkane sulfonate sodium salt (SAS 60) has exhibited either similar or sometime better fastness properties (in case of 2% reactive yellow wet rubbing fastness, 1% and 2% reactive yellow washing fastness, 1% reactive red wet rubbing fastness and washing fastness). The same foaming agent, alkane sulfonate sodium salt (SAS 60), has exhibited better shade depth as mentioned in earlier section. This behavior could be attributed to the presence of the non-active group of methyl. Consequently, there is a less chance of interference with the dyeing recipe as compared to other two foaming agents where amine oxide group (Genaminox CSL) and ethylene oxide group (Unifroth 520) are present in the foaming agent.

Fastness properties with pigment colorants
The coloration with 1% pigment red and 1% pigment blue indicates equivalent dry rubbing fastness for padding recipe as well as for foam coloration for all three foaming agents ( Figure 5). Foaming agent based on ethoxylated decanol (Unifroth 520) for 1% pigment red indicated half grade poor wet rubbing fastness than the padding, Genaminox CSL, and SAS 60. Similarly, at 2% pigment blue coloration with ethoxylated decanol (Unifroth 520), there was decrease of half a rating in case of washing fastness. While alkyl dimethyl amine oxide (Genaminox CSL) based foaming agent exhibited washing fastness rating decrease of half a rating when it was used with 1% pigment red as compared to padding and other foaming agents. Nevertheless, foaming agent based on alkane sulfonate sodium salt (SAS 60) exhibited the highest fastness rating for both pigments and it was comparable with padding.
In addition, the non-reactive nature of the SAS 60 proved best for the pigment coloration as well.

Fastness properties with direct dyes
The dyeing with both 1% and 2% direct yellow dye indicates equivalent dry rubbing fastness for all the four recipes of padding and three foaming agents ( Figure 6). SAS 60 with Direct pink dyeing exhibited half a rating superior fastness in all fastness as compared to other two foaming agents. Ethoxylated decanol (Unifroth 520) based foaming agent exhibited half a rating lower fastness in case of wet rubbing fastness at 2% direct yellow as well as 1% and 2% washing fastness. It can be observed that foam dyeing with reactive dyes exhibited the overall highest fastness as compared to pigment and direct dyes and this trend is in line with normal dyeing without foaming agents. It is mainly due to the reason that reactive dyes have reactive groups which exhibit the better bonding with fabric. Consequently, the superior fastness was achieved as compared to the pigment and direct dyes that do not have the reactive groups. Table 4 presents the finishing results for polyethylene softener, oil and water repellent, and flame retardant with padding and all three foaming agents. Bending length can be used to assess the softness as higher bending length reflects greater softness. The bending length, air permeability, and tear strength of the fabric samples were superior for the treated recipe with foaming agent alkane sulfonate sodium salt (SAS 60) as compared to other two foaming agent. Similar to the better dyeing performance, SAS 60 foaming agent exhibited the best softener finishing performance due to its better compatibility as compared to other foaming agents.

Finishing with polyethylene softener, water repellent, and flame retardant
In case of special performance finishes like oil and water repellent finishes and flame retardant finishes, it was not easy to obtain the performance for foam technology similar to the conventional padding technology. It is mainly due to the reason that the foam finishing recipe is diluted many times as compared to padding. In addition, compatibility of the various chemical properties of finishes against the different ingredients and especially foaming agents is a great challenge. Water repellent finish with two foaming agents; ethoxylated decanol (Unifroth 520) and alkyl dimethyl amine oxide (Genaminox CSL) exhibited one scale lower water repellency as compared to padding. However, water repellency (shower test AATCC 22 spray test) of the foaming recipe with alkane sulfonate sodium salt (SAS 60) was one grade higher than the recipes with foaming agents ethoxylated decanol (Unifroth 520) and alkyl dimethyl amine oxide (Genaminox CSL). Above trend was mainly due to the unavailability of the reactive group, and consequently no interference was observed in case of the SAS 60 foaming agent as compared to other two foaming agent. Similar trend was observed for the crease recovery angle performance of the fabric treated with SAS because it was better than the recipes with ethoxylated decanol (Unifroth 520) and alkyl dimethyl amine oxide (Genaminox CSL) foaming agents. Non finished cotton fabric exhibits no fire retardancy as cotton is inherently non fire retardant. Typically, higher dosage of fire retardant (10% or higher) is required to obtain certain level of fire retardancy. Generation of foam for higher chemical dosage of 10% is much more challenging as compared to padding. Typically, halogen-based flame retardants are used for cotton but they are toxic, therefore, halogen free flame retardant of diammonium hydrogen phosphate is used in this research. It is well reported in literature that halogen free flame retardants are less effective but environment friendly option. Nevertheless, all three foaming agents exhibited the certain flame retardancy as exhibited by char length. Alkane sulfonate sodium salt (SAS 60) with fire retardant finish exhibited the superior char length as compared to other finishing agents exhibiting the effectiveness of the SAS 60 foaming agents over other two foaming agents. It was mainly due to the absence of the reactive groups, and subsequently no hindrance was observed in the case of SAS 60 as compared to other two foaming agents.

Conclusion
All the seven dyes and three finishes were successfully applied with three foaming agents: alkane sulfonate sodium salt, ethoxylated decanol and alkyl dimethyl amine oxide. Optimization of the foaming agent dosage and rpm was critical in the successful formation of foam for all three foaming agents. It was noticed that in case of dyeing, padding exhibited superior shade depth as compared to foam dyeing with any foaming agent and it is mainly due to the reason that foam recipe is diluted 8 times due to blow ratio of 1:8. Nevertheless, just increasing the dye % from 1% to 2% in foam dyeing similar results of 1% padding was achieved. Among the three foaming agents for dyeing, simple carbon chain-based alkane sulfonate sodium salt in SAS 60 exhibited superior performance than the comparatively more reactive amine oxide group in Genaminox CSL and ethylene oxide group in Unifroth 520. Foam finishing whether with softener, oil and water repellent, and fire retardant, exhibited good performance properties but retention of superior physical properties like tensile strength, air permeability and bending length as compared to padding due to less application of the chemical on the treated fabric surface. Concerning the finishing with polyethylene softener, oil and water repellent and fire retardant, the foaming agent alkane sulfonate sodium salt (SAS 60) exhibited better bending length, air permeability, and tear strength as compared with other foaming agents. It can be concluded from this research that foaming agent and its chemistry will play important role in the performance of the foam dyeing and finishing of the textile and selecting the appropriate foaming agent can enhance the performance of the foam dyeing and finishing. Textile industry is under severe pressure to adopt water and energy efficient dyeing and finishing techniques, while currently optimized foam dyeing and finishing processes can be a good alternative option.

Highlights
• Foam dyeing and finishing is an ecofriendly alternative to conventional padding in textile processing.
• Generation and application of foam is a challenging task especially for wide range of dyes and chemicals due to technical and compatibility issues. • In this research, foam was generated and optimized for seven different colorants and three different finishes using three different foaming agents separately. • In most of the foam dyeing and foam finishing recipes, alkane sulfonate sodium salt-based foaming agent indicated the best dyeing and finishing properties.