Effective waste water management in colouration of polyester using Bio-shell microcapsules

doi:10.21203/rs.3.rs-1641694/v1

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Effective waste water management in colouration of polyester using Bio-shell microcapsules

https://doi.org/10.21203/rs.3.rs-1641694/v1

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The present work aimed at efficient utilization of resources viz., water, dyes and chemicals (without using any supportive chemical) for colouration of polyester. Disperse dye microcapsules were prepared using the method of complex coacervation. Bio-shell coated microcapsules of disperse dyes were analyzed for their resource efficient auxiliary chemicals free colouration on polyester (PET) over conventionally dyed one. The remnant liquor recovered from colouration of polyester was recycled for subsequent four colouration cycles (without treatment) showing acceptable shade difference. The remnant liquor obtained from fourth colouration cycles treated with basic primary water treatments and was found to be translucent, neutral in pH and low effluent load (TDS > 231 ppm, BOD > 114 mg/l, and COD > 469 mg/l). The solids recovered from bath were analyzed and found to be nontoxic (LD₅₀,> 8000) as well. Cost involved in microencapsulated colouration (USD $ 6.48) is lower than that of conventional process of colouration (USD $ 8.40). Thus, microencapsulated colouration is easily adoptable in existing process line of polyester colouration, which leads to small liquid discharge of low.

Bio-shell

Colouration

Disperse dye

Microcapsules

Polyester

Recycling

Polyester or polyethylene terephthalate (PET) has been accepted as the most desired fibre in both technical and apparel applications of textiles. The fibre has many advantageous properties for apparel uses, viz., low price, easy care and endurance properties, but complicated colouration process using disperse dyes, based on anthraquinone or substituted benzenoid mono- or diazo- compounds, along with number of chemical additives, certainly raise the question against its acceptance in future. Although, the disperse dyes are completely entrapped by the polyester micro molecular system, so, colouration technique facilitating higher uptake of the dyes inside the fibre leading to low residual dye on cloth as well as in the remnant liquor can greatly mitigate the threat raise to the textile industry in this direction. Further, the textile wet processing necessitates huge water consumption (1.6 million l) (Kant 2012) [9] and has a high environmental impact in terms of its remnant disposal. Thus, resource efficient process leading to maximum utilization of input materials (chemicals) towards low solid as well as minimum liquid discharge are the major concerns of present textile industry (Sandin and Peters 2018) [3].

Conventional colouration of polyester shows 60–90% uptake of dye particles (exhaustion) using disperse class of dyes depending on their shade depth/intensity (Blackburn and Gallaghe 2008). The major problem of conventional polyester colouration is inadequate dispersibility and consequent random adsorption of dye particles to the substrate (polyester cloth) causing uneven dyeing. Thus, colouration process are essentially carried out adding auxiliary/supportive chemicals viz., dispersing agent, cationic type retarding/leveling agent (Xu et al. 2016) at acidic pH with a slow rate of heating to synergize the dye uptake, and as well as improve the evenness of dyeing. It is noteworthy that, all commercial disperse dyes inherited to contain high quantity of dispersants (40–60%) (Chakraborty 2010). Even on using different additives, during colouration dye molecules move in aggregates in the bath liquor; create bottleneck at the entrance of pores and resulted in poor absorption and ultimately causes wastage of substantial quantity of dye particles.

To evade the problem, continuous efforts have been made in textile wet processing for colouration of polyester fibre using several methods, viz., supercritical carbon dioxide (Hou 2010), liquid paraffin (Xu 2016), and microcapsules (Zhong et al. 2006). The non aqueous media (carbon dioxide, liquid paraffin), which carry the dyes effectively to the micro corners of polyester matrix, needed much big scale processing facility thus lack in cost competitiveness for their commercial adoption. The contemporary approach of colouration of polyester using microcapsules was aqueous based and almost similar to its conventional one. The microcapsules have a unique property of sustained release of entrapped dye from capsules without any assistance of auxiliary chemicals for the entire colour treatment cycle (Zhong et al. 2006, Mishra et al. 2012). Zhong et al. (2006) reported colouration of polyester fibre by microencapsulated disperse dyes formed by interfacial polymerization using synthetic shell material, diphenylmethane-4,4‐di-isocyanate. Mishra et al. (2012) [6] reported a much simpler methods ((i) simple coacervation, (ii) complex coacervation, and (iii) spray drying) of microencapsulation of disperse dye using bio-shell materials (gelatin and gum acacia) along with the structure (shape, size and its distribution), properties (sustained rate of release and temperature stability) and colouration performance on polyester. Both the work suggested microencapsulated colouration resulted in improved surface colour strength (11%-16%) along with uniform dye absorption and equivalent fastness properties without use of auxiliary chemicals and post treatment over the conventionally dyed one. But, the authors did not discuss the effective waste water management systems and how this may be achieved as economically as possible. Thus, the novelty of the work was to explore the reusability and its recycling possibilities of the remnant liquor, for efficient utilization of its resources to reduce effluent load.

2.1. Materials

The fabric used was plain weave polyester (PET) having areal density 61 g/m² and Bio-shell coated disper dyes Microcapsule. Materials used for preparation of shell were gelatin-A (alkali extracted high IEP 8.7), and gum acacia (Acacia Senegal) supplied by Aragum Flavor, India. Disperse dyes CBENE Yellow SGL (C.I. Disperse Yellow 114, λ_max, 410 nm) (Fig. 1) was supplied by Colorbrand Dyestuff (P) Ltd., India. Other chemicals used acetic acid, di-methyl formamide, sodium hydroxide, sodium dithionite dispersing agent (SPAN 20) and nonionic surfactant (Auxipon NP) was supplied by S.D. Fine Chemicals, India for preparation and analysis of microcapsules. All the above chemicals were of laboratory regent grade.

2.1.1. Details of complex coacervate Bio-shell Microcapsule

The work (Mishra et al. 2012) reported that, disperse dye microcapsules formed by complex coacervation had been superior (efficiency of microencapsulation, size distribution, release rate and thermal stability) than the microcapsules obtained from simple coacervation and spray drying. Complex coacervation microcapsules were obtained by a simple physico-chemical batch type method maintaining ratio of core (disperse dye) to shell (gelatin and gum acacia) at 1:2. The characterization of the microcapsule is given in Table 1 (Mishra et al. 2012).

Table 1

Characterization of microcapsules
Parameters	Microencapsulated
Size, µ	16.375
Shape	Spherical in collapsed form with smooth surface
Size distribution, µ	3.6- 36.35 (0.12) (Binomial distribution)
Thermal stability, ° C	≥ 300
Dye release rate, min	≥ 150
Efficiency of microencapsulation, %	74.13

2.2. Methods

2.2.2. Method of colouration

Colouration was carried out using control and microencapsulated disperse dye (2%) on weight of Fabric (OWF) separately. The appropriate concentration of microcapsulated dye for producing 2% shade depth as similar as control (disperse dye) was estimated. For this, 0.0025% of control dye solution was prepared with DMF (solvent) and its absorbance was determined. Different concentration of microencapsulated dye solution was prepared with DMF (dipping the microcapsules for 12 h) to match with the absorbance of control dye. From the reported study, it was observed that, to obtain same shade and depth, the weight of microcapsules had to be 4.7 times of control dye. Colouration was carried out in a closed exhaust bath (pressure 1.8 kg/cm2) maintaining material to liquor ratio, 1:15.

Conventional colouration of polyester fabrics was carried out with essential chemicals viz., dispersing agent (2%) and acetic acid (1%). The dyeing temperature was raised slowly to 130° C at the rate of 2°C/min having 1 h holding time at 130°C (Waheed and Ashraf 2000). The dyed samples were further treated with reducing agent (3 g/l sodium hydro sulphite) and alkali (2.5 g/l sodium hydroxide) for 30 min at 70–80° C having material to liquor ratio, 1:15 to remove the unfixed dyes and additives. Control samples were then given a hot wash, neutralized with acetic acid followed by further wash before air drying.

Colouration with microcapsules was carried out similar to the conventional one other than the comparatively faster (5° C/min) rate of heating without any essential auxiliary chemicals. The microencapsulated dyed samples were simply washed in water before drying in air.

2.2.3. Recycling possibility

Microencapsulated colouration on Polyester fabrics dyed in fresh water and in remnant water (from consecutive dyeing baths) was carried out using similar amount of microencapsulated dyes (2%, OWF) in each cycle separately. The difference in surface colour uptake (K/S) of the dyed fabrics was evaluated up to four dyeing cycles.

2.2.4. Colour yield measurement

Dyed samples were evaluated for tone and depth of the colour using a spectrophotometer (Data Colour Spectraflash® SF 300, USA) using CIE Standard Illuminant D65 and 10° observer. Tone of the colour was measured in terms of CIE L* (lightness or darkness), a* (redness or greenness) and b* (blueness or yellowness) values of the colour. In order to derive the CIE, the parameters L, a, and b color space values (based on the opponent color theory) the following expressions were used.

L ^* = 116 (Y/Y_n)^1/3, a* = 500 [(X/X _n)^1/3 -(Y/Y_n)^1/3], and b* = 200 [(Y/Y_n)^1/3 -(Z/Z_n)^1/3]

where, X, Y, Z and Xn, Yn, Zn, are tristimulus values of the object and the white point of the illuminant respectively.

Depth of the colour of both conventional and microencapsulated dyed samples was evaluated by reflectance values (Data Colour Spectraflash® SF 300, USA). An average of five readings of reflection taken at different places of a sample was used to calculate the surface colour uptake (K/S) and change of colour (ΔE).

(ΔE) = [(l_sam-l_std)² + (a_sam-a_std)² + (b_sam-b_std)²]^1/2

where, l_sam-l_std,a_sam-a_std, b_sam-b_std, is the difference in lightness, redness or blueness and brightness respectively between standard (control) and the sample. The differences in hue and chroma value were determined by h_sam-h_std, c_sam-c_std respectively.

2.2.5. Effect of colouration on migration of dye

The effect of colouration process (conventional and microencapsulation) on migration of dye from bath liquor to polyester was studied. Three cycles of colouration was carried out using fresh cloth in each time. The first dying cycle was carried outsimilar to the chemical recipe and conditions mentioned earlier. However, in subsequent two cycles, colouration was attempted using liquor left from their previous batch of corresponding conventional and microencapsulated colouration cycle without addition of dyes or/and chemicals.

2.2.6. Estimation of quantity of dye particles in remnant bath after microencapsulation and conventional colouration

The residual bath liquors after preparation of microcapsules and colouration cycles were assessed for the residual dye content. For assessment of absorbance, residual bath liquors (5 ml) were mixed with di-methyl formamide (5 ml) to make a solution, which was analyzed against the blank solvent prepared by mixing water and DMF in the ratio of 1:1. The absorbance of the dye present in remnant liquor was measured at their corresponding λ_max using an UV-1201 single beam spectrophotometer (SHIMADZU, Japan) and the concentration of dye particles present in them were determined by using the calibration curve.

To plot the calibration graph, pure dyes were collected by extracting in benzene in a Soxhlet apparatus for 48 h. The removal of impurities from disperse dyes was assessed by Thin Layer Chromatography (TLC) method before and after the soxhlation.

2.2.7. Assessment of colour, pH, TDS, BOD and COD of the remnant liquor

The pH, total dissolved solid (TDS) and conductivity of the effluent at different stages were measured by using a pH electrode (PCS Tester 35, Make-EVTECH). Change in colour of the treated effluent was assessed using UV-1201 single beam spectrophotometer (SHIMADZU, Japan). Chemical oxygen demand (COD) and biological oxygen demand (BOD) of the effluent was analyzed by the open reflux method according to APHA 22nd Edition, 2012-5220B and IS: 3025 (PART – 44) 1993: Reaffirmed 2003 methods respectively.

2.2.8. Toxicity of sludge

Sludge was examined in a double beam FTIR spectrophotometer (ALPHA-Bruker-Germany) using attenuated transmittance resonance (ATR) technique.Toxicity of the sludge was obtained through analysis of lethal dose concentration (LD₅₀).

3.1. Analysis of extent of dye migration during microencapsulation

The absorbency values of dye from waste water after successive colouration cycles are shown in Fig. 2. The figure reveals that, much more dye particles are remained (absorbance, 0.263 Au) unused in the residual liquor in first colouration bath in the conventional process of polyester colouration, as compared to microencapsulated process (absorbance, 0.104 Au). Recycling of bath liquor of conventional colouration (second and third trial) was intended to understand the effect of remnant auxiliary chemicals on inducing the migration of the dyes or self-transferability of the disperse dyes present in the bath liquor. The concentration of dyes quantified in terms of absorbance value (0.117 Au) in remnant bath liquor for third cycle of conventional colouration was even higher than the absorbance (0.104 Au) of remnant liquor of first cycle of microencapsulated colouration. This proves that, in the conventional process a lot of dye particles were wasted, which was not self transferable. However, the process of microencapsulation, which consumed no additional chemicals, had much improved dye transfer capacity over conventional colouration. Thus, the surface colour strength (K/S, 12.94) for the microencapsulated coloured polyester fabric was found to be much higher than the surface colour strength (K/S, 10.15) obtained by conventional process (Fig. 2)

3.2. Reuse of remnant bath liquor

Table 2 shows the colour parameters of the microencapsulated dyed polyester fabric up to four dyeing cycles. It is noteworthy that, surface colour strength (K/S) and reflectance values of the fabrics dyed with fresh and remnant liquor are almost similar. The tristimulities colour difference (ΔE, 0.086) up to the fourth dyeing cycles samples was less than 1.0, thus the difference in shades was visually unnoticeable and considered to be similar as reported by Mokrzycki and Tatol (2011) also.

Table 2

Surface colour strength and tone of microencapsulatedcoloured polyester cloth
Colour indices	Dyeing cycle
	Fresh	Remnant liquor
	1st	2nd	3rd	4th
R_max, %	2.93	2.99	2.97	2.95
K/S	12.82	12.75	12.84	12.79
L	82.75	82.68	82.79	82.84
a	-5.87	-6.11	-6.13	-6.06
b	90.65	89.71	89.68	89.79
c	90.84	89.93	89.96	89.91
h	93.70	94.03	94.11	94.08
ΔE ^a	-	0.44	0.054	0.086
^acolour difference calculated from the immediate previous batch

The reflectance curves (Fig. 3) of fabric dyed using the fresh water and remnant liquor of successive microencapsulated dyeing cycles showed much similar reflectance values. So, it may be interpreted that, each dye bath was initiated with similar concentrations of dyes and also, their uptake rate for each cycle were much alike to each other to a large extent so as to have similar residual dye concentration in the dye baths liquor. Hence, we may suggest that; reuse of the remnant liquor needs no additional treatment for successive microencapsulated dyeing. The process, in turn, could save huge quantity of water, and could simultaneously eliminate the problem of effluent treatment/disposal.

3.3. Analysis of remnant solids and wastewater

Table 3

Remnant water quality parameters of having disperse dye CBENE Yellow 114
Parameters	Residual water
	After microencapsulation	After Dyeing
Visual observation	Translucent	Translucent with little turbidity
Dye, % (w/w)	0.0004	0.0011
Absorbance, Au	0.018	0.13
pH	6.8	7.2
TDS, ppm	29	231
BOD, mg/l	56	114
COD, mg/l	149	469
TDS – Total dissolved solid; BOD – Biological oxygen demand; COD – Chemical oxygen demand;

The method for treating the remnant liquor from the microencapsulated formation and colouration process included some simple primary treatments viz., storage of the bath liquor, precipitation for deposition of insoluble solids followed by centrifugation to remove the dissolved solids. The primary treatments took about 6 h storage and separation of solids was carried out through centrifugation at 7000 rpm for 5 min at ambient temperature 30 ± 5° C. The properties of remnant water recovered are given in Table 4. The recovered/treated liquor was found to be translucent and having neutral pH and low effluent load (TDS, > 231 ppm, BOD, > 114 mg/l and COD, > 469 mg/l). The parameters of effluent were well under acceptable limits. Since, recycling of waste water was also possible; hence, it further lessened the load of effluent discharge and provided an alternative approach for water conservation in textile industry. The solid recovered from the remnant liquors were found to have very low toxicity as analyzed from median lethal dose (LD₅₀) values studied on rat. The Ld50 for solids recovered from residual bath of microencapsulation and colouration were 10845 mg/kg and 8968 mg/kg respectively, which is found to be very high, thus confirming the sludge, are nontoxic.

3.4. FTIR analysis of remnant solids

Effluent liquor obtained from the microcapsule of colouration found to have 6.8 g solid residues over the weight of total solid added (9.0 g) during formation of microcapsules. The functional group analysis (Fig. 4) through FTIR showed significant traces of residues of gum acacia and gelatin than disperse dyes. Being a protein, gelatin macromolecules characterized to contain polypeptide and amide units Paul et al. 2017). The absorption peaks at 3433 and 3383 cm^− 1 attributed to the presence of hydrogen bond may belong to gelatin and gum acacia both. Peak at 1624 cm^− 1 corresponds to the occurrence of amide-I (C = O stretching/hydrogen bonding coupled with COO), at 1554 cm^− 1 indicates amide-II (vibration of N-H groups and stretching vibrations of C-N groups), peak at 1240 cm^− 1 indicates the amide-III in plane vibrations of C-N and N-H groups. Peaks ranges from 1460 to 1380 cm^− 1 were attributed to the symmetric and asymmetric vibrations of methyl group present in gelatin. Gum acacia has exhibited characteristic peaks at 3420, 2940 and 1419 cm^− 1, which represent the -OH, -CH2, and -CH3 aliphatic groups respectively for its carbohydrate structure (Venkatesham et al. 2012). The peaks at 1618 and 1426 cm^− 1 are due to asymmetric stretching of COO − group of gum acacia. Presence of disperse dyes were associated with the peaks at 2825 cm, 1590, 1040 and 664 cm^− 1, which were also may be associated with peaks of amide-1 at 1586 and 1040 cm^− 1 for saturated or unsaturated bonds of –Nitrogen, where as others are the characteristic presence of aliphatic -CH, -CH3 groups of gum acacia.

3.5. Cost competitiveness

Table 4 shows comparison of cost of colouration involved in conventional as well as microencapsulated colouration methods detailing the quantity and costing for chemicals and energy consumed. A similar breakup for formation of microencapsulated disperse dyes considering its efficiency of microencapsulation (74%) is given in Table 5. Cost of disperse dye microcapsules was calculated to be $ 12.67 USD/kg. In the analysis, cost of civil infrastructure, space, labour, hazards in material handling and consumption of water and its effluent treatments have not been included. Cost involved in microencapsulated colouration (USD $ 6.48) is much lower than that of conventional process of colouration (USD $ 8.40). Low process cost of microencapsulated colouration was due to absence of auxiliary chemicals, and also the quantity of electrical energy consumption is lower than that of conventional coloration technique. The reported microencapsulated method further abstain additional chemical, water and considerable quantity of electrical energy needed in post treatment. In addition, the method is cost effective in terms of infrastructure building, space, labour and requires no effluent management, and thus ensures more user friendliness and industrial viability as compared to the conventional method.

Table 4

Costing (USD $) of high temperature polyester colouration (2% shade) of 5 kg batch
Inputs	Conventional		Microencapsulation
	Quantity	Cost	Quantity*	Cost
During colouration
Dye, g	100	0.09	470	6.25
2% Non ionic detergent, ml	100	2.13
2% Retarding agent, ml	100	1.07
2% Acetic acid, ml	100	0.83
Time of treatment, min	110		70
During post treatment
2%, Sodium dithionite, g	100	1.33
2% Sodium hydroxide, g	100	0.81
2% Acetic acid, ml	100	0.83
Time of treatment, min	30
Electricity consumption (KWH) for heating	3.357	0.50	1.671	0.23
*Quantity of dye for microencapsulation process = 4.7 times of conventional process Rate of electricity/kWh @ 0.14 US$ "Electric Power Monthly – Average Retail Price of Electricity to Ultimate Customers by End-Use Sector, by State" 4 august 2020. Retrieved 14 August 2020).

3.6. Novelty of the Microencapsulated Dyes

The conventional colouration of polyester has its limitations in regard to heat of dyeing, controlled migration and diffusion of dyes. For this, it is essential to employ many auxiliary chemicals in the conventional dye bath, and still, the process leads to faulty dyeing, poor washing/sublimation fastness and huge effluent generation with high COD, BOD load. Polyester colouration depends on three dynamic energy levels (dispersion, migration, diffusion) of dye particles, which are mainly based on the size of the dyes. Thus, disperse dyes are milled into very fine size up to1 µm but their small size causes them to agglomerate in aqueous bath due to high surface energy (Yang et al. 2008, Waheed and Ashraf 2000). The larger the structure of dye molecule, more dispersing agent is required to maintain homogeneous existence in the bath and at the same time requires more heat energy to migrate them. High temperature of dyeing is required to obtain larger swelling of surface also to make fibre pores sufficiently large to diffuse large dye molecules. Since, process of microencapsulation reduced the size of dyes by breaking their agglomeration through sonication, which leads to formation of micron size capsules as tiny vessels for dye molecules. The comparatively larger (16.37 µm) microcapsules were less tends to agglomerate and the hydrophilic coating helps them to remain dispersed in aqueous bath. Thus, all disperse dyes exhaust well at or below 130°C. Further, the sustained release of capsulated dyes overcomes the need of controlled rate of heating particularly at high temperature, which in turn avoids the use of sophisticated high temperature high pressure machine, which is an existing limitation associated with polyester colouration. Thus avoids the use of many auxiliary chemicals (dispersing agent, retarding/levelling agent, buffering agent), energy and reduce the total time from 110 to 70 min.

The encapsulated disperse dyes formed using bio based shells (gelatin and gum acacia) would advance the process of polyester dyeing due to its (i) much even/regular dyeing with notably higher colour strength (K/S increased by 28%), (ii) much cost effective as no auxiliary chemicals and post treatments are required, (iii) generates substantially less effluent due to maximum use of dye molecules as well recoverable bio based shell of the capsules. In addition, less requirement of water makes the process industry friendly. The fabrics dyed in normal and remnant liquors up to certain multiple cycles were of similar shade with negligible differences in total colour values. The effluents are reusable without any additional treatment and sludge obtained was proven to be nontoxic. So, adoption of the microencapsulation colouration would not only help towards resource efficient production of polyester processing without much change in its existing industrial practice but also serve to clean the soil and water bodies and reclaimed the useable water effortlessly.

Funding

“This work was supported by institute internal fund. No special Funds/grants have been issued to carry out the work. Thus, “The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.”

Competing Interests

The authors have no relevant financial or non-financial interests to disclose.”

Author Contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by [full name], [full name] and [full name]. The first draft of the manuscript was written by [full name] and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

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Effective waste water management in colouration of polyester using Bio-shell microcapsules

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Abstract

Figures

1. Introduction

2. Materials And Methods

2.1. Materials

2.1.1. Details of complex coacervate Bio-shell Microcapsule

2.2. Methods

2.2.2. Method of colouration

2.2.3. Recycling possibility

2.2.4. Colour yield measurement

2.2.5. Effect of colouration on migration of dye

2.2.6. Estimation of quantity of dye particles in remnant bath after microencapsulation and conventional colouration

2.2.7. Assessment of colour, pH, TDS, BOD and COD of the remnant liquor

2.2.8. Toxicity of sludge

3. Result And Discussion

3.1. Analysis of extent of dye migration during microencapsulation

3.2. Reuse of remnant bath liquor

3.3. Analysis of remnant solids and wastewater

3.4. FTIR analysis of remnant solids

3.5. Cost competitiveness

3.6. Novelty of the Microencapsulated Dyes

4. Conclusion

Statements & Declarations

References

Table 5

Supplementary Files

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