Polyurethane dispersions prepared from vegetable oil and their application as textile finishes

Abstract

One of the major challenges facing the polymer industry now is finding sustainable and renewable alternatives to petroleum-based raw materials. To overcome such challenges, these novel water-borne polyurethane dispersions were prepared from bioresources (vegetable oil). Vegetable oil-based polyol is synthesized by epoxidation and hydroxylation methods from vegetable oil. Consequently, polyurethane dispersions are prepared by reacting the vegetable oil-based polyol with isophorone diisocyanate and dimethylol propionic acid to form the polyurethane prepolymer, which further reacts with 1,4-butanediol, and the final product is obtained by the addition of water. Fourier transform infrared analysis is used for the structural confirmation of the prepared vegetable oil-based polyol and polyurethane dispersions. A number of textile tests, including mechanical (tear strength (ASTM 1424) and tensile strength (ASTM D-5034)) and antibacterial, were conducted on poly/cotton plain weave fabrics after applying the synthesized dispersions by pad dry-cure methods. The hemolytic test method was used to check the biocompatibility of the synthesized dispersions. Results reveal that these finishes effectively increase the tensile strength of the treated fabric samples, such as white fabric samples, which show tensile strength values of (248, 255, 268 and 325 N from untreated 240 N) in the warp direction. The biological outcomes show the antibacterial and hemolytic activity of the dispersions are influenced by the presence of natural polyols in the dispersions. These results indicate that covering poly/cotton fabrics with vegetable oil-based polyurethane dispersions improve their tensile strength and antibacterial properties and they can replace petroleum-based polyurethane finishes.

Keywords

Vegetable oil polyurethane dispersion mechanical properties antibacterial activity

Fabric finishes can alter the physical and esthetic characteristics of fabrics. Therefore, different finishes are employed to enhance the functionality of the fabric surface.¹ Most commonly crosslinking agents used in textiles include formaldehyde-based products and formaldehyde-free products.² Several formaldehyde-based cross-linking agents have been used to reduce creases in cellulose, including dimethylol urea, dimethylol ethylene urea, and dimethylol dihydroxy ethylene urea.³ In the finishing and wearing processes, coated fabrics emit formaldehyde, which is hazardous to human health.⁴ However, the development of formaldehyde-free crosslinking agents includes reactive organic silicon, epoxy resins, ion crosslinkers, polycarboxylic acids, dialdehyde, and modified chitosan.^5–10 There has to be a need for alternative crosslinking agents. Therefore, the use of aqueous polyurethane dispersions (PUDs) has also expanded to textiles as a finishing agent to improve textile properties, such as durability and aesthetics, as well as to provide breathable and formaldehyde-free coatings.^11–13 Many PUDs have been formed which are used as textile finishes due to their performance profile. The literature reveals that shape memory polyurethanes were utilized as a finishing agent on cotton, which increases the durable anti-creasing as well as washing fastness of the cotton.¹⁴ In coatings of leather, textiles, wood, and plastics, water-dispersible polyurethanes provide exceptional versatility.¹⁵ Polyols and diisocyanates are the main building blocks of PUDs.¹⁶ Now mostly nonrenewable (petroleum) source-based polyols are prepared for the preparation of aqueous PUDs. Customers are shifting their concern towards bio-based goods, as they are well aware of environmental problems. As the expense of crude oil is usually rising, people in the industry persistently seem to be seeking their substitutes.¹⁷ The rising cost of fossil oil and climate-friendly strategies have encouraged the advancement of polymers from sustainable supplies as substitutes for petrochemicals.^18,19

Currently, with the help of chemical modification, polyols are prepared from renewable resources such as vegetable oils to substitute petroleum-based polyester and polyether polyols.^20,21 Many other renewable compounds such as protein, cellulose, starch, lignin, sugar, and natural oil have been utilized in different studies as substitutes for petroleum-based resources, among which natural oils are the most beneficial because they are sustainable, readily available, budget and environment friendly.^22,23

Generally, vegetable oils consist of triglycerides that are composed of different fatty acids such as oleic, stearic, palmitic, linolenic, and linoleic acids.²⁴ Some of the plant oils tend to react with the isocyanate and synthesize the polyurethane without any chemical modifications because of the presence of reactive sites such as the hydroxyl groups present in castor oil. However, other vegetable oils comprise reactive positions such as acrylic carbon and C=C bonds, esters, and α-carbon of ester groups, which are transformed into hydroxyl groups by different chemical processes.^25–27

Various methods are used for chemical modification of the vegetable oils into polyols, which include splitting of triglyceride linkages,^28,29 others include transformation of unsaturated double bonds by ozonolysis reduction,³⁰ microbial transformation,³¹ hydroformylation reduction,^32,33 and epoxidation oxirane ring opening.³⁴ Vegetable oils can be effectively converted into polyols with favorable properties by epoxidation and the oxirane ring opening method with the help of the different reagents, and their PUDs exhibit good performance.^35,36 Moreover, among other procedures, epoxidation-oxirane ring opening is preferable as compared to the others because this method has lower cost and has commercial applications.³⁷

Waterborne PUDs synthesized from vegetable oils such as castor oil, soybean oil, and jatropha oil have been well documented in recent times.^38–41 Yet, to the best of our knowledge, limited research work has been published about the waterborne PUDs prepared from the vegetable oils that are used for green textile finishes. No work has been reported on the cottonseed oil-based waterborne PUDs that are utilized as textile finishes.

Regarding the sorts of PUDs obtained from sustainable sources, this research effort deals with the preparation of innovative waterborne PUDs synthesized from polyol obtained from vegetable oil (cottonseed). First, polyol was prepared from vegetable oil by the epoxidation and ring opening methods. Then PUDs were prepared by changing the vegetable oil-based polyol content concerning the 1,4-butanediol (BDO). Then these dispersion samples were characterized with the help of Fourier transform infrared (FTIR) spectroscopy. After the confirmation of the synthesis of the dispersions by FTIR, they were applied as a finishing agent to the polycotton fabrics. The mechanical properties of the treated polycotton fabrics were checked by the estimation of textile tests such as tear strength and tensile strength. In addition, biological parameters such as antibacterial activity and cytotoxicity of the prepared samples were also examined. This research work is the continuation of our published article. All of these properties (tear strength, tensile strength, and antibacterial activity) of the coated fabric samples and the biocompatibility of the PUDs were not estimated in our previous publication.

Experimental

Materials

Chemicals

Analytical grade chemicals were used in the entire research work and used as received. Vegetable oil (cottonseed) was bought from Faisalabad’s local market in Pakistan. Formic acid, ethyl acetate, hydrogen peroxide, sodium bicarbonate, acetic acid, magnesium sulphate, isophorone diisocyanate (IPDI) (98%), dimethylol propionic acid (DMPA), dibutyltin dilaurate, methyl ethyl ketone, BDO (99%), triethylamine and nutrient agar were purchased from Sigma Aldrich Chemical Co. (USA). Sodium carbonate, sodium chloride, and Triton X-100 were obtained from Merck Chemicals (Darmstadt, Germany). Before the synthesis of aqueous PUDs; chemicals were dried in an oven at 80°C such as DMPA, polyol, and BDO for 24 h to remove moisture and air contents, which can interrupt the diisocyanate during a reaction. Pure distilled water was used during the complete research work.

Polycotton fabric as substrate

Plain weaved mill de-sized, scoured polycotton white, printed and dyed fabrics were provided by Arzoo Textiles Mills Ltd. (Faisalabad, Pakistan). Fabric contained an almost 50:50 blend ratio of polyester and cotton as shown in Table 1. The physical characteristics of textile fabrics are shown in Table 1.

Table 1.

Properties of textile fabrics

Fabric specification	Quality	Blend ratio cotton/polyester	Construction/count
White	Plain weave polycotton	48/52	76 × 54/30 × 30
Dyed with reactive dye	Plain weave polycotton	48/52	76 × 54/30 × 30
Pigment printed	Plain weave polycotton	48/52	76 × 54/30 × 30

Polyol synthesis from vegetable oil

Synthesis of polyol from vegetable oil was carried out by using the previously reported procedure,²¹ while the details of the procedure are described in our previous work.⁴² Two steps were involved in the polyol preparation, which included epoxidation and hydroxylation.

For the epoxidation process, the round bottomed flask was charged with 250 g of cottonseed oil, 100 g of hydrogen peroxide, and 38 g of formic acid. Then, the contents were stirred with the help of a mechanical stirrer for 21 h at 25°C in a water bath. The obtained epoxidized vegetable oil (EVO) was washed with a solution of sodium chloride and ethyl acetate, and then EVO was neutralized to pH 7 by using sodium bicarbonate and dried using anhydrous magnesium sulphate, and subjected to a rotary evaporator for one hour at 38°C for vacuum filtration. For complete drying the epoxidized vegetable oil was placed in a drying oven at 70°C overnight.

After that, polyol was synthesized by adding the 1:3 ratio of the EVO and acetic acid to a two-neck round bottomed flask equipped with a reflux condenser and mechanical stirrer. The reaction was carried out at 80°C for 8 h. The same procedure was used for cleaning the polyol as was followed in epoxidized oil. Figure 1 shows the chemical reaction for the synthesis of the polyol.

Figure 1.

Schematic diagram of the synthesis of polyol from vegetable oil.

Synthesis of the vegetable oil-based PUDs

PUDs were synthesized from vegetable oil-based polyol by following the formerly reported procedure¹⁷ as described in detail in our previous work.⁴²

First, the measured amount of cottonseed oil-based polyol was mixed with the DMPA and homogenized in four-neck flask equipped with a mechanical stirrer, reflux condenser, nitrogen inlet, and thermometer. The reaction was carried out at 80°C for 30 min then IPDI was added within the next 30 min, and at the same time dibutyltin dilaurate was also added and preceded the reaction for 3 h. The viscosity of the reaction was controlled by the addition of methyl ethyl ketone. After the completion of 3 h, a prepolymer was formed, and a measured amount of chain extender (BDO) was added to extend the polymer chain. Then the mixture was neutralized by adding triethylamine. After that, distilled water was added with high-speed mechanical stirring for the final waterborne PUD. A series of PUDs were prepared by changing the polyol and 1,4-butanediol contents. A schematic diagram of the reaction is shown in Figure 2, and a detailed formulation of the synthesized dispersions is presented in Table 2.

Figure 2.

Schematic diagram of the synthesis of polyurethane dispersion (PUD).

Table 2.

Composition of the synthesized PUDs

Sample code	Polyol^a	DMPA	IPDI	BDO
Weight (g)
COT-PUD-1	3.54	2.4	11.12	2.25	2.53
COT-PUD-2	7.08	2.4	11.12	1.50	2.53
COT-PUD-3	10.62	2.4	11.12	0.75	2.53
COT-PUD-4	12.39	2.4	11.12	0.38	2.53

^aVegetable oil-based polyol.

BDO: 1,4-butanediol; DMPA: dimethylol propanoic acid; IPDI: isophorone diisocyanate; PUDs: polyurethane dispersions; TEA: triethylamine.

FTIR analysis

FTIR spectroscopy was used for the structural confirmation of the vegetable oil-based polyol and the dispersions prepared from this polyol. For this purpose, we used the Bruker-IFS 48 FTIR spectrometer (Ettlingen, Germany). Spectra were recorded in the frequency range of 400–4000 cm⁻¹ and the scanner had a resolution of 4 cm⁻¹ with numerous scans.

Application of the PUDs to the fabrics

Two dilutions of the prepared dispersions (30 g/l and 50 g/l) were obtained using distilled water (stirred continuously for 4–5 min) and subsequently applied by the pad dry-cure process to the poly/cotton (24 cm (L) ×12 cm (W)) fabrics. A Padder machine was then used to process these fabrics. Afterwards, each fabric was dipped into these solutions and finished through the Padder machine. Next, samples were dried for 3 min at 80°C in an electric oven, followed by 5 min of curing at 140°C.

Mechanical properties of the PUDs applied fabrics

After the application of the different dilutions of the dispersions to the plain weaved poly/cotton fabrics, their mechanical properties were determined by evaluating the tear and tensile strength.

Tear strength

In selecting textiles for a variety of applications, tear strength is another important factor to consider. The force needed to separate fabric held between two parallel clamping jaws in the direction of the applied force is termed ‘tear strength’. The tear strength of the PUDs applied to finished and unfinished fabric samples was evaluated by using the ASTM 1424 standard test method.⁴³ In practice, with the help of the tear strength tester, rectangular fabric samples being evaluated are cut into the centre between two clamps and torn over a predetermined distance using force. As the sample is torn, the tear force is directly shown on the screen of the equipment.

Tensile strength

Tensile strength represents the maximum force that a textile material can withstand before it breaks or ruptures. The samples were placed in the jaws of the tensile strength tester and tested for tensile strength. Unfinished and PUDs applied to finished swatches of poly/cotton fabrics were broken in parallel with the warp and weft directions. The tensile strength of the PUDs applied finished and unfinished textile fabrics was evaluated by the ASTM D-5034 standard test method.⁴⁴

Biological parameters of the synthesized PUDs

Antibacterial activity

The biological potential in terms of antibacterial activity of PUD samples was assessed after applying 50 g/l dilutions of these dispersions to the fabric swatches. The disc diffusion method was used to investigate the antibacterial activity of the fabric samples.¹³ Freshly grown bacterial cells were used for the bacterial inhibition determination. First of all, nutrient agar media was prepared in a 1000 ml flask and transferred into100 ml flasks and autoclaved at 120°C for 15 min. Then these flasks were allowed to cool. Then 100 µl Bacillus subtilus and Escherichia coli were poured separately into different flasks. After that, about 20 ml of agar media was added to each sterilized petri plate and allowed to cool at room temperature. Fabric samples were placed on the agar medium and incubated for 24 h at 37°C, and inhibition zones were measured in mm after 24 h.

Hemolytic assay

Hemolytic assay of dispersions was evaluated by following a previously reported hemolytic assay test method.⁴⁵ Freshly obtained heparinized human blood was lightly mixed and centrifuged for 5 min after being transferred into a sterilized falcon tube. After that, the plasma layer was discarded and the thick pellet was washed with the help of a cool isotonic phosphate-buffered saline (PBS) solution, then the same washing procedure was repeated three times. Then the samples were again centrifuged after the addition of 20 µl PUD sample, 180 µl blood cell suspensions in 2 ml Eppendorf tube. The upper layer of 100 µl was collected from the Eppendorf tube and 900 µl PBS was added to dilute it. Consequently, 100 µl was transferred into 96 well plates. PBS was used as a negative control while Triton X-100 (0.1%) was used as a positive control. The sample’s absorbance was measured using an enzyme-linked immunosorbent assay (ELISA) reader at 576 nm. The hemolysis percentage was determined by using the following formula:

Hemolysis (%)= \frac{Absorbance of sample}{Absorbance of control} \times 100

(1)

Results and discussion

FTIR spectral analysis

Relative FTIR spectra of vegetable oil (cottonseed), epoxidized vegetable oil and polyol are demonstrated in Figure 3. Cottonseed oil spectrum (Figure 3(a)) shows the characteristic stretching band of unsaturation at 3007 cm^–1, which disappeared in the infrared spectra of the epoxidized oil (Figure 3(b)) and a new peak appeared at 842 cm^–1, which shows the formation of the epoxidized group by complete utilization of the olefinic group. Then the cottonseed oil-based polyol was synthesized by the ring opening reaction of the epoxidized cottonseed oil with acetic acid. In the infrared spectra of the polyol as shown in Figure 3(c) the epoxy ring at 842 cm^–1 vanished and the new broad symmetrical stretching peak of the hydroxyl group was observed at 3467 cm^–1, asymmetric stretching vibrations of the ether linkage appeared at 1162 cm^–1 and stretching signals of the carbonyl group appeared at 1738 cm^–1. However, the peaks seemed within the range of 2800–3000 cm^–1 in all spectra, which are due to the stretching vibrations of the C–H bond.^46,47

Figure 3.

Fourier transform infrared (FTIR) spectra of (a) vegetable oil, (b) epoxidized vegetable oil, and (c) vegetable oil-based polyol.

Then this synthesized polyol reacts with other monomers to form the final product. Figure 4 displays the important functional groups present in these monomers and in the final product of the PUDs, which have already been comprehensively discussed in our previous work.⁴²

Figure 4.

Fourier transform infrared (FTIR) spectra of (a) isophorone diisocyanate (IPDI), (b) dimethylol propionic acid (DMPA), (c) 1,4-butanediol (BDO) and (d) final polyurethane dispersion (PUD).

Figure 4(a) and (b) displays the FTIR spectrum of IPDI and DMPA, respectively. First, the polyol and DMPA contents were homogenized in the reaction flask then IPDI was added to the flask and the reaction proceeded for 3 h. The hydroxyl groups of the polyol and DMPA reacted with the NCO group of the IPDI and form the prepolymer. An important and broad peak appeared at 2243 cm^–1 in the FTIR spectrum of IPDI attributed to the stretching vibration of the (NCO) group of the IPDI reacting with the hydroxyl groups of the polyol and DMPA which appeared at 3467 cm^–1 and 3559 cm^–1. All these three monomers reacted and form the isocyanate terminated polyurethane prepolymer which was confirmed by the disappearance of the OH peaks of the poyol and DMPA and formation of the new peak of NH stretching observed at 3355 cm^–1. This NCO terminated polyurethane prepolymer further reacted with the 1,4-butanediol to extend the chain of the polymer. Figure 4(c) displays the prominent band at 3330 cm^–1, which was due to the hydroxyl group moiety in BDO which reacted with the polyurethane prepolymer and formed the final PUDs. The other important peaks in the FTIR spectra of the BDO observed at 2932 cm^–1 and 2873 cm^–1 correspond to the asymmetric and symmetric stretching vibrations of methylene while the peak at 1042 cm^–1 proved the primary alcohol groups.⁴⁸ The hydroxyl peak of the BDO present in the spectra at 3330 cm^–1 also disappeared in the final product of polyurethane dispersions indicating that all the OH groups of the BDO have been joined with the backbone of the polyurethane. The FTIR spectrum of the final PUD prepared from cottonseed oil-based polyol with IPDI is shown in Figure 4(d).

The isocyanate (N=C=O) groups of the IPDI molecule show a characteristic peak at 2243 cm^–1 and the wide peaks of OH groups existing in the preceding spectra of cottonseed oil-based polyol, DMPA and BDO, vanished in the final PUD spectra and urethane stretching peaks at 3355 cm^–1. The characteristic bands appearing at 2927 cm^–1 indicate the asymmetric stretching vibrations of methylene while the peak present at 2855 cm^–1 is ascribed to the symmetric stretching vibrations of methylene. However, other observed peaks appeared at 1696 cm^–1 stretching vibration of both ester and urethane C=O, 1556 cm^–1 –NH deformation, 1237 cm⁻¹ CN stretching and 1181 cm⁻¹ stretching vibrations of C–O–C.^47,49,50

Mechanical properties of the PUDs applied fabrics

In usage, fabrics are subjected to various forces coming from different directions. Fabric’s mechanical properties are determined by its ability to withstand forces such as tensile, compression, bending, shearing, and friction. This mechanical quality is also a key to the processing, garment production, designing, and buying of textiles. We can also estimate the useful life of textile fabrics by looking at their mechanical properties.^51,52 Moreover, the surface treatment affects the mechanical characteristics of the textiles. In our studies, the mechanical properties of the PUD treated fabric samples were determined with the help of tear and tensile strength test methods.

Tear strength

Waterborne PUDs are applied as textile finishes to improve the fabric properties such as breathability, crease recovery, and tear strength.^53,54 Table 3 shows the tear strength of the white, dyed, and printed unfinished and PUD applied poly/cotton fabrics. These outcomes conferred a decrease in the tear strength of the finished fabrics both in warp and weft directions. In contrast, as the concentration of the dispersion increases from 30 g/l to 50 g/l, tear strength decreases from 30 g/l. This may be due to an increase in crosslinking as the concentration of the dispersion increases. These results agree well with the previously reported literature. They prepared the PUDs by using polyethylene glycol as polyol, which reacted with the IPDI, DMPA, and polymer chains were extended with the different contents of the nano chitosan/BDO.⁵⁵ When PUDs are applied to fabrics, they form hydrogen bonding, Van der Waals forces, and polar attraction with the fabric substrate. As cotton fabric contains hydroxyl groups, these groups form hydrogen bonds with PUDs –NH and –C=O groups. In this way, a strong hydrogen bond between the fabric and the polyurethane finish was formed. These dispersions easily penetrate the spaces present between interfibers and swap interfiber hydrogen bonds to an appropriate extent that holds back the movement of fiber under tearing load, which results in a decrease in the tear strength of the treated fabrics as compared to the untreated fabrics. The tough layer on the fabric forms as the polyol concentration in the PUDs increases due to increased interaction with the interfiber links, causing the triggering in the fabric to stiffen. A cross-linked fiber does not move freely to group up to bear the tearing load collectively. As a result, every fiber bears the tearing load independently, so it requires less force to spread and start the tear. All the treated fabrics show significant increases in their properties, such as colorfastness and pilling resistance (as described earlier in previous findings)⁴² except tear strength, which decreases.

Table 3.

Tear strength of the untreated and treated textile fabrics with PUDs

Textile test	Sample codes	White fabric
		30 g/l		50 g/l
		Warp	Weft	Warp	Weft
Tear strength (N)	White fabric
	COT-PUD-1	10.84 ± 0.04	7.66 ± 0.05	10.44 ± 0.05	7.34 ± 0.04
	COT-PUD-2	10.72 ± 0.05	7.54 ± 0.03	10.37 ± 0.04	7.23 ± 0.03
	COT-PUD-3	10.65 ± 0.03	7.47 ± 0.02	10.28 ± 0.04	7.15 ± 0.03
	COT-PUD-4	10.49 ± 0.03	7.40 ± 0.03	10.16 ± 0.05	7.07 ± 0.03
	Untreated	11.00 ± 0.05	7.90 ± 0.03
	Dyed fabric
	COT-PUD-1	9.29 ± 0.04	8.97 ± 0.03	9.08 ± 0.02	8.71 ± 0.03
	COT-PUD-2	9.19 ± 0.03	8.83 ± 0.04	9.00 ± 0.04	8.62 ± 0.03
	COT-PUD-3	9.10 ± 0.04	8.67 ± 0.05	8.87 ± 0.05	8.51 ± 0.04
	COT-PUD-4	9.01 ± 0.05	8.50 ± 0.02	8.75 ± 0.04	8.23 ± 0.04
	Untreated	9.55 ± 0.03	9.27 ± 0.04
	Printed fabric
	COT-PUD-1	9.01 ± 0.03	6.78 ± 0.03	8.67 ± 0.04	6.32 ± 0.03
	COT-PUD-2	8.88 ± 0.02	6.56 ± 0.05	8.57 ± 0.02	6.16 ± 0.02
	COT-PUD-3	8.76 ± 0.04	6.30 ± 0.04	8.41 ± 0.02	5.97 ± 0.05
	COT-PUD-4	8.57 ± 0.03	6.11 ± 0.03	7.34 ± 0.03	5.68 ± 0.05
	Untreated	9.18 ± 0.02	7.23 ± 0.03

Values are average ± SD of triplicates.

PUDs: polyurethane dispersions.

Tensile strength of the textile fabrics

A material’s tensile strength relates to its ability to resist stretching forces that are intended to expand it. An object’s tensile strength is defined as the maximum load that the object can withstand before it breaks under a stretching load applied to draw the object apart, and it is measured by the maximum load that an object can withstand before it breaks under such a strain.⁵⁶ The tensile strength of the PUDs applied poly/cotton white, dyed and printed cellulosic fabrics and untreated fabrics was evaluated by the ASTM D-5034 standard test method, and the outcomes are presented in Table 4. All the samples employed by the PUDs showed an increase in tensile strength both in the warp and weft direction. These results are worthy of agreement with previously reported work in the literature by Man and coworkers.⁵⁷ The authors synthesized the waterborne PUD based films by increasing the polyol content prepared from tung oil. Results show that an increase in polyol content results in an increase in the tensile strength of the films.⁵⁷ This increase in the tensile strength of the fabrics may be due to the sticking impact of PUDs that reinforces the threads in the progression of employed tensile pressures, and so the fabric can endure a large employed tensile load. The impact of the tensile strength of PUDs on white and dyed fabric is better to some degree than on printed textiles. This may be due to the involvement of the printing paste applied onto the printed fabric, which leads to a decrease in the penetration of the dispersions into the fabric and the outside surface film formed, which affects the tensile strength. Other properties of the finished fabric swatches also show the improved results (as in tensile strength), which means this finish provides better quality fabric as compared to the unfinished fabric samples.⁴²

Table 4.

Tensile strength of the untreated and treated textile fabrics with PUDs

Textile test	Sample codes	White fabric
		30 g/l		50 g/l
		Warp	Weft	Warp	Weft
Tensile strength (N)	COT-PUD-1	248.40 ± 0.03	199.61 ± 0.04	258.11 ± 0.05	206.42 ± 0.03
	COT-PUD-2	255.32 ± 0.04	203.55 ± 0.04	263.54 ± 0.05	210.64 ± 0.05
	COT-PUD-3	268.54 ± 0.05	207.23 ± 0.05	279.93 ± 0.04	216.84 ± 0.05
	COT-PUD-4	325.55 ± 0.04	218.39 ± 0.05	330.71 ± 0.03	228.42 ± 0.03
	Untreated	240.51 ± 0.04	187.66 ± 0.05
	Dyed fabric
	COT-PUD-1	440.90 ± 0.05	254.3 ± 0.05	455.51 ± 0.03	260.11 ± 0.04
	COT-PUD-2	448.63 ± 0.04	261.34 ± 0.03	461.71 ± 0.04	266.71 ± 0.03
	COT-PUD-3	459.70 ± 0.04	266.86 ± 0.04	465.84 ± 0.03	270.45 ± 0.05
	COT-PUD-4	474.13 ± 0.04	271.2 ± 0.04	478.34 ± 0.02	280.12 ± 0.03
	Untreated	198.25 ± 0.03	246.42 ± 0.03
	Printed fabric
	COT-PUD-1	437.46 ± 0.03	229.91 ± 0.04	442.16 ± 0.04	235.43 ± 0.04
	COT-PUD-2	444.40 ± 0.05	231.54 ± 0.02	449.43 ± 0.05	238.32 ± 0.02
	COT-PUD-3	448.68 ± 0.04	235.31 ± 0.04	451.62 ± 0.03	242.16 ± 0.05
	COT-PUD-4	450.20 ± 0.04	245.63 ± 0.03	456.32 ± 0.02	249.18 ± 0.05
	Untreated	379.8 ± 0.05	227.60 ± 0.03

Values are average ± SD of triplicates.

PUDs: polyurethane dispersions.

Biological parameters of the synthesized PUDs

A great deal of what chemical finishes do for end-users depends on biological parameters. As textiles are used and stored, microbes may develop on them, which negatively impact the user as well as the textile.⁵⁸ They can infect fabrics, causing fiber damage, emitting foul odors, and leaving a slick, slimy appearance.⁵⁹ Antibacterial textile finishing was thought to be the best solution for protecting humans and products from bacteria. There are some factors that should be considered when treating textiles with an antimicrobial agent to achieve optimal results.^60,61 First, it must be effective against a large range of bacterial and fungal species. In addition, a textile treated with an antimicrobial finish must undergo compatibility testing (toxicity, skin reaction) before it can be marketed. Therefore, the biological potential of the synthesized dispersion samples was determined by finding their antibacterial activity as well as biocompatibility tests.

Antibacterial activity

In this research work, novel vegetable oil-based PUDs were prepared and used as textile finishes on the poly/cotton fabric. The antimicrobial activity of the fabrics applied by the water-borne PUDs was conducted by the inhibition zone method. Detailed data of antibacterial activity is listed in Table 5. As anticipated, all the treated fabric samples show well-intentioned antibacterial activity against both bacterial strains (E. coli and B. subtilus). Both printed and dyed fabrics showed significant inhibition zones for E. coli and B. subtilus. The antibacterial activity increases first by an increase in the polyol content (COT-PUD-1–COT-PUD-3) but decreases at maximum concentration (COT-PUD-4), which is due to the fractional accumulation of the hydrophobic part of the samples of PUDs which may interact with the bacterial action and reduce the antibacterial action.⁶² The sample COT-PUD-3 has superior antibacterial performance as compared to the other treated fabric samples. Here is an interesting illustration of how the structure is correlated with the property. Samples with a greater polyol concentration have more functionality in their backbones, which will allow for more contact of the polymer with the substrate, leading to improved antibacterial, as well as washing and rubbing resistance. This could be due to the fact that as the polyol content increases, the crosslinking density of these polyurethane molecules increases with the fabric, which results in creating a network structure with the cellulosic fabric through different physical interactions. So these treated fabric samples easily cling to the bacterial cell membrane by the electrostatic interaction and enhance their performance. Overall, fabric samples show better results with E. coli than with B. subtilus, this may be because of the difference in the composition of the cell wall structures. The resultant antibacterial mechanism has been confirmed by earlier work.⁵⁷ Previously, castor oil-based polyurethanes incorporated with natural and synthetic rubber supported these antibacterial findings.⁶³ Collectively, good bactericidal properties were shown by all the samples of fabrics. Outcomes explained that the antibacterial activity of the samples depends on the bacterial strain being used. Printed fabric samples have shown good results as compared to dyed fabric samples. The reason behind this behavior might be because of the presence of the binder layer on the exterior side of the printed fabric. While in the case of the dyed fabric samples, the antibacterial activity of the fabric samples was less as compared to the printed fabric samples, it may be due to the development of temporary links between the dyed fabric and PUDs that result in cytotoxicity, which reduces the antibacterial activity of the dyed fabrics.

Table 5.

Antibacterial activity of the untreated and treated fabric samples with PUDs (50 g/l)

Sample code	Zone of inhibition (mm)		Zone of inhibition (mm)
Sample code	Dyed fabric		Printed fabric
Species of bacteria	Escherichia coli	Bacillus subtilis	Escherichia coli	Bacillus subtilis
COT-PUD-1	11 ± 0.56	10 ± 1.30	12 ± 1.21	11 ± 0.65
COT-PUD-2	13 ± 1.0	11 ± 1.10	13 ± 0.53	12 ± 0.83
COT-PUD-3	14 ± 0.77	12 ± 0.79	15 ± 0.74	12 ± 0.44
COT-PUD-4	10 ± 0.89	09 ± 0.91	11 ± 0.96	10 ± 0.51
Untreated sample	–	–	–	–

Values are average ± SD of triplicates.

PUDs: polyurethane dispersions.

Hemolytic assay

To evaluate the biocompatibility of PUDs, human red blood cells were used in the hemolytic assay. Further results were compared with negative and positive control PBS and Triton X-100, respectively. Results of the positive control, negative control, as well as (%) hemolysis of PUDs are shown in Table 6.

Table 6.

Hemolytic activity of the synthesized PUDs

Sample code	Hemolytic activity (%)	Result
COT-PUD-1	5.55 ± 2.05	Nontoxic
COT-PUD-2	4.41 ± 2.11	Nontoxic
COT-PUD-3	3.39 ± 1.33	Nontoxic
COT-PUD-4	2.89 ± 2.30	Nontoxic
PBS^a	0.08 ± 1.22	Nontoxic
Triton-X-100^b	100 ± 1.19	Extremely toxic

Values are average ± SD of triplicates.

^aNegative control.

^bPositive control.

PBS: phosphate-buffered saline; PUDs: polyurethane dispersions.

Positive control Triton X-100 has shown 100% hemolysis, while negative control PBS has shown percentage hemolysis of 0.08. Synthesized PUD samples displayed 5.55, 4.41, 3.39, and 2.89% hemolysis for COT-PUD-1, COT-PUD-2, COT-PUD-3, and COT-PUD-4, respectively. All the samples showed nontoxic behavior towards the living cells because the percentage of hemolysis of all the samples was within the limit of nontoxicity. This sophisticated biocompatibility of the samples was due to the bio-based polyol content in the polyurethane backbone. However, polyurethane itself also displayed biocompatible behavior. The results showed that COT-PUD-4 had the least toxic behavior due to its higher polyol content, indicating that more polyol content (bio-based content) in PUDs results in a decrease in cytotoxicity.⁴⁹ While all the values of PUDs samples stayed in the border of nontoxicity, the scale was as follows: nontoxic, 1–10; slightly toxic, 11–25; moderately toxic, 26–50; and highly toxic, 50–100.

Conclusions

In brief, innovative multifunctional aqueous PUDs were successfully prepared from cottonseed oil. The dispersions were applied to the textile fabrics, and different quality tests of the treated and untreated fabrics were evaluated. The tear strength of the fabric decreases as the polyol concentration increases in the polyurethane backbone. However, the tensile strength of the fabric increases as the polyol concentration increases, which shows the dependence of tensile strength on the polyol concentration. The biological behavior of the samples was also analyzed in terms of antibacterial activity and biocompatibility. Although coated fabric samples showed favorable antibacterial activity against the E. coli and B. subtilis strains as compared to the fabric samples without coatings. Reported outcomes showed that these PUDs as a textile finish improved the fabric quality as well as antibacterial activity. Cytotoxicity of the synthesized samples is within the range of nontoxicity, which is enhanced as the bio-based polyol content increases. These finishes can replace petroleum-driven PUD finishes with renewable resource (vegetable oil) based PUD finishes. In the future, this research can be extended to silk, woollen, and cotton fabrics.

Footnotes

Acknowledgements

Financial support from the Higher Education Commission (HEC), Government of Pakistan, is highly acknowledged and appreciated for this experimental work. It is part of the NRPU project no. 5575/Punjab/NRPU/R&D/HEC/2016 awarded by the HEC.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Khalid Mahmood Zia

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