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Abstract

In the present project sodium alginate-based polyurethane dispersions were synthesized by two shot processes, using isophorone diisocyanate, polyethylene glycol (Mn-300), dimethylol propionic acid as internal emulsifier along with other reagents including triethylamine and dibutyltindilaurate catalyst. Molecular characterization was performed by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy. Physical properties were observed and samples were found to be translucent yellow with a stability of more than one year. Biological properties such as blood hemolytic and antibacterial action were also noted in order to check if the samples can be used inside human body for bandage coatings. Synthesized dispersions were found to have considerable blood hemolytic activity and good antibacterial activity. After the complete characterization, dispersions were applied on polycotton blend fabric (50/50). After the treatment, fabric was analyzed for its tear strength, tensile strength pilling resistance and morphological properties by scanning electron microscopy. Fabric treated with polyurethane dispersions has decreased tear strength, enhanced tensile strength, improved pilling resistance and more intact appearance as compared to the untreated fabric.

Keywords

Polyurethane dispersions sodium alginate blood hemolytic activity antibacterial activity polycotton fabric

Introduction

Polyurethanes are interesting class of compounds with their tailor-made properties [1]. Urethane linkage is the main feature of these polymers, which is formed by the reaction of an isocyanate and polyol. Polyaddition reaction of polyols (containing –OH group) or diamines (containing active –H group) with –NCO group containing isocyanates leads to the formation of a urethane linkage $($ $)$ in their structure [2,3]. There are a number of subclasses of polyurethanes including fibers, plastics, emulsions etc., but the ones having water in their composition are termed as waterborne polyurethanes. As far as their synthesis is concerned, a number of synthesis routes have been designed in order to get specific physical and chemical properties [4 –6]. First step of synthesis is similar in all processes involving the formation of prepolymer by the reaction of a polyol with an isocyanate, and this prepolymer is further reacted with chain extenders. An internal emulsifier is also added in prepolymer synthesis to ease the dispersion of polyurethane in water at the end. These emulsifiers may include ionic (sulphonates, carboxylates and quaternary ammonium salts) or nonionic compounds (polyethylene oxide). Polyurethane dispersions (PUDs) may further be subdivided into cationic, anionic and nonionic dispersions [7 –9] depending upon their structure and the emulsifier used.

Natural material-based dispersions are in demand nowadays due to their non-toxic nature and environment friendly way of synthesis, giving rise to a wide variety of materials with desirable and biocompatible properties via combination of natural and synthetic raw materials. In the same way, blend of natural materials/polymers into the polyurethane backbone makes them more biocompatible, non-toxic, biodegradable and ideal for many biomedical applications. Vegetable oils are most commonly used for the production of such polymers at lab, pilot and industrial scale, after undergoing trans-esterification and other modifications occasionally [10]. Natural polymers such as hemicellulose, hyaluronic acid, alginate, cellulose and guar gums can be obtained from plants, whereas chondroitin chitin and chitosan are of marine origin that may also be used as raw materials for polyurethane synthesis, which are aimed to be used in biomedical field [11]. Alginates are also a class of biological polymers which are being used for biomedical applications [12,13]. Their natural source is brown algae and bacteria. Alginates are being investigated for their interesting and important applications in textile and food industries as stabilizers, thickeners, film formers and gel formers etc. As they are abundant in waterbodies, a variety of alginates are present naturally with excellent chelating ability, low cost, biodegradability and biocompatibility [14].

Antibacterial finishes for textile material are being investigated, as most of the textile materials used in hospitals may cause infection due to the pathogenic bacteria adhered to its surface. Therefore, textile hygiene is utmost important issue to be dealt with [15]. Researchers are investigating certain materials to meet the requirement of antibacterial finishes to be applied on fabric. The material to be applied should adhere firmly to the fiber so that it may not wash out on laundering [16]. PUDs are successful candidates for this application which on combining with natural materials get enhanced biocompatibility and antibacterial action. They are being synthesized using chitosan, cyclodextrin and collagen as chain extender with different compositions. Efforts are being made to enhance the antibacterial properties of these PUDs by incorporation of biocompatible materials. Therefore, in the present study, aliphatic isocyanate-based PUDs using sodium alginate (a natural antibacterial polymer) were synthesized. Dimethylol propionic acid (DMPA) was used as internal emulsifier which gave stability to the dispersion in aqueous media. These alginate-based dispersions were suggested to be good applicants for antibacterial finishing of textile.

Experimental

Materials

All the chemicals used were of analytical grade and the materials such as polyethylene glycol (PEG Mn = 300 g/mol), Isophorone diisocyanate (IPDI), sodium alginate (SA Mn = 216.12), dimethylol propionic acid (DMPA), dimethyl sulfoxide (DMSO), methyl ethyl ketone (MEK), triethyl amine (TEA), dibutyltin dilaurate (DBTDL) catalyst (95%) were purchased from Sigma Aldrich Co., USA, and used without further purification. DMPA was dried at 40℃ in oven for 2 h to remove entrapped moisture that may react with isocyanate during prepolymer formation and destroy the reaction chemistry. Phosphate buffer saline (PBS), ethylenediamine tetraacetic acid (EDTA), nutrient agar (media for bacterial growth), bacterial strains (Escherichia coli and Bacillus subtilis) were used for biological analysis. For the application of PUDs polyester-cotton or polycotton (PC) blend (50/50) was used.

Methodology

Aliphatic isocyanate-based PUDs (hereafter named as SA@PUDs_Ali) were synthesized using SA as chain extender following the method in literature [17] with slight modification. In brief, initially, a prepolymer was prepared by reacting PEG, IPDI and DMPA, which was further extended with SA. A series consisting of five samples was prepared by varying the amount of SA and PEG, keeping the ratios of other reactants constant (Table 1) [18].

Table 1.

Sample codes and composition for the preparation of sodium alginate-based polyurethane dispersions (SA@PUDs_Ali).

Serial No.	Sample code	IPDI (moles)	PEG (moles)	DMPA (moles)	SA (moles)	TEA (moles)
1	SA_0.05@PUD_Ali	2.0	1.00	0.95	0.05	1.0
2	SA_0.10@PUD_Ali	2.0	0.95	0.95	0.10	1.0
3	SA_0.15@PUD_Ali	2.0	0.90	0.95	0.15	1.0
4	SA_0.20@PUD_Ali	2.0	0.85	0.95	0.20	1.0
5	SA_0.25@PUD_Ali	2.0	0.80	0.95	0.25	1.0

IDPI: Isophorone diisocyanate; PEG: Polyethylene glycol; DMPA: Dimethylol propionic acid; SA: Sodium alginate; TEA: Triethyl amine.

Synthesis of NCO terminated polyurethane prepolymer

Reaction assembly for the synthesis of PUDs consisted of four-necked round bottom flask fitted with a mechanical stirrer, a reflux condenser, nitrogen inlet and outlet (for inert environment) and a dropping funnel (for adding reactants). The reaction assembly was kept in an oil bath for constant heating during reaction. Weighed amount of DMPA (0.95 mol) and PEG (1 mol for sample 1) were charged into the four-neck flask and heated in oil bath until it reached a temperature of 60℃ (for melting and complete mixing). After 30 min, IPDI (2 mol) (a cycloaliphatic isocyanate) was added dropwise with constant stirring along with 1–2 drops of DBTDL catalyst and the temperature of the reaction mixture was raised to 90℃. The stirring was carried out for 1 h to obtain NCO-terminated polyurethane (PU) prepolymer. Before adding the next reactant, to adjust the viscosity of prepolymer, 5–6 mL of MEK was added. In the meantime, temperature was also lowered to 55℃ and TEA (1 mol) was added to neutralize the acidic groups (–COOH) of DMPA keeping the stirring on for 45 min. At the end a neutralized PU prepolymer was obtained with NCO terminated ends (Figure 1).

Figure 1.

Synthesis of sodium alginate-based polyurethane dispersion using cycloaliphatic isocyanate (IPDI) (SA@PUDs_Ali).

Addition of SA as chain extender and preparation of PUDs

Neutralized PU prepolymer was further reacted with SA (0.05 mol for sample 1) (chain extender). Calculated amount of SA was slowly added into the reaction flask in order to avoid the formation of gel at a temperature of 65–70℃. Stirring was continued to 2 h to ensure the completion of reaction. In the final step, measured volume of distilled water was added into the reaction mixture with constant vigorous stirring for 3 h at 25℃, in order to get a uniform PUD. Figure 1 represents the schematic pathway for the formation of PUD. The other entire samples were prepared following the same methodology by reacting the stoichiometric amounts as given in Table 1.

Physical and structural characterization

Structural characterization of prepared SA@PUDs_Ali was performed by Fourier transform infrared (FTIR) spectroscopy and proton nuclear magnetic resonance spectroscopy. Moreover, synthesized polyurethanes were physically examined for their appearance, stability and color [18].

Biological analysis of the synthesized PUDs

Antibacterial analysis

Two dilutions of synthesized PUDs were prepared, i.e. 5% and 10%. They were analyzed for their antibacterial activity by agar diffusion method against common human pathogenic bacteria including Bacillus subtilis (B. Subtilis) and Escherichia Coli (E. Coli) according to standard method [19]. Bacteria were grown on agar nutrient media in Petri plates which were then divided in suitable wells into which sample was placed. These plates were incubated at 37℃ for 24 h and the zone of bacterial growth inhibition was estimated in millimeters (mm) [20].

Blood hemolytic analysis

In order to investigate whether the samples are safe for applications inside human body, blood hemolytic analysis was performed using standard method American Society for Testing and Materials (ASTM) standards/ ISO 13485:2003 certified. All the samples were analyzed for their hemolytic activity using the method reported by Choi et al. [21] with a little modification. In short, fresh blood sample was taken in EDTA tube and centrifuged after adding PBS thrice to collect RBCs. After this 10 microliter of each sample was mixed with 90 microliter RBCs, centrifuged and absorbance of the supernatant was recorded in well-plate at 560 nm [21]. Blood hemolytic activity was calculated using formula as given below (equation (1))

\begin{matrix} PercentHemolysis \\ = 100 \times [(Absorbanceofsample - Absorbanceofnegativecontrol) \\ \div (Absorbanceofpositivecontrol - Absorbanceofnegativecontrol)] \end{matrix}

(1)

Application of optimized sample on polycotton fabric

Polycotton blend (50/50) was used for dispersion application. Fabric was soaked in warm water (100℃) containing detergent for 30 min and then washed thoroughly with clean water in order to get rid of any impurity or dust particles. These fabrics were dried at ambient temperature before being coated with PUDs. Two dilutions (5% and 10%) of each sample were prepared and applied onto the fabric by pad dry cure method [18]. Drying of fabric after the application of PUDs was conducted at 80℃ for 30 min followed by curing for 5 min at 140℃, to achieve a uniform and firm coating on the fabric surface.

Analysis of treated polycotton fabric

Fabric sample after treatment with PUDs was analyzed by scanning electron microscopy (SEM) for morphological study and evaluated for tear strength, tensile strength and pilling resistance. Standard methods of tear strength (ASTM D- 1424/BS EN ISO 13937-2) [22], tensile strength (ASTM D-ISO 13934-2) [18] and pilling resistance (ASTM D-3514-02) [23] were used.

Results and discussions

Molecular characterization

FTIR Analysis of SA@PUDs_Ali

Spectrum of SA-based PUDs are shown in Figure 2 demonstrating major corresponding peaks of groups present in PUDs samples. While observing the FTIR spectra for six PUDs samples, a very weak peak (a slight bulging) of –NH stretching vibrations was observed in the range 3375.43 cm⁻¹ to 3500 cm⁻¹ as the urethane. Peak at 2850 cm⁻¹ to 3000 cm⁻¹ was attributed to the C–H stretching of –CH₂ group. Absence of peak in the region 2200 to 2300 cm⁻¹ indicated that all the –NCO groups have reacted. Band present around 1639.49–1637.56 cm⁻¹ was an evidence of carbonyl C=O stretching of urethane (–NHCOO–) linkage [24]. Absorption peak in the range of 1462.04 cm⁻¹ to 1458.18 cm⁻¹ appeared due to C–H bending vibrations in –CH₂ group. Stretching vibrations of C–C bond of –C(CH₃)₂ groups in IPDI exhibited peak in the range 1354.03 cm⁻¹ to 1352.10 cm⁻¹. Peak visible at 1052 cm⁻¹ was allocated to the C–O–C group symmetric stretch in final PUDs samples (Figure 2).

Figure 2.

FTIR spectra of PUDs samples (a) SA_0.05@PUD_Ali (b) SA_0.10@PUD_Ali (c) SA_0.15@PUD_Ali (d) SA_0.20@PUD_Ali (e) SA_0.25@PUD_Ali. SA: sodium alginate, PUDs: polyurethane dispersions.

NMR spectroscopic analysis

Figure 3 represents the NMR spectrum of the polyurethanes synthesized using SA as chain extender. As the chemical composition of all the five compounds is similar having varying amount of SA and PEG, only one spectrum has been given to represent their structural character, assuming that concentration has no effect on signals (ppm values) in NMR spectrum. As shown by the Figure 3, proton labeled as H5-H9 (SA chain extender) exhibit signals in the range of 3.7–5.2 ppm [25]. Solvent peak (water) was observed near 4.7 ppm. Protons H1, H10 and H2 gave prominent signal at 3.5, 3.3 and 3.2 ppm, respectively, being deshielded due to the attachment of highly electronegative element (oxygen) in the immediate neighboring. The signals go on the upfield area, as the signaling group becomes less deshielded as in case of H4 (2.9 ppm) and H14 (2.1 ppm). Protons, H3, H12, H13 and H11 exhibited signals at 1.1, 1.0, 0.9 and 0.8 ppm, respectively, owing to the presence of least electron withdrawing groups in the neighborhood.

Figure 3.

¹H NMR spectrum of sodium alginate-based polyurethane dispersions using cycloaliphatic isocyanate (SA@PUDs_Ali).

Physical characterization of SA@PUDs_Ali

Certain tests of physical properties such as appearance, stability and solid contents are of significance to check the quality of polymeric dispersions. The data obtained after careful investigation of these parameters for the synthesized material has been given in Table 2. The solid contents continue to increase from 38.3% to 40%. This increment might be due to the increased contents of SA used for synthesis of dispersions [23].

Table 2.

Physical characteristics and sample codes of SA@PUDs_Ali with varying molar ratios of sodium alginate.

Serial No.	Sample codes	Sample appearance	Sample stability (months)	Solid contents (%)
1	SA_0.05@PUDs_Ali	Translucent yellow	12	38.3
2	SA_0.10@PUDs_Ali	Translucent yellow	12	38.3
3	SA_0.15@PUDs_Ali	Translucent yellow	12	38.7
4	SA_0.20@PUDs_Ali	Translucent yellow	13	39.0
5	SA_0.25@PUDs_Ali	Translucent darker yellow	13	40.0

SA@PUDs_Ali: sodium alginate-based polyurethane dispersions using cycloaliphatic isocyanate.

While observing the appearance of PUDs, the samples were noted to be translucent and none of the samples was totally clear. There was a visual color variation of translucent yellow to a darker tinge as the SA contents changed from minimum (0.05 M) to maximum (0.25 M). It is due to the increased concentration of SA which imparted a darker tinge to the samples.

The stability investigations of the synthesized samples revealed them to be stable as they contain DMPA and TEA. DMPA is an internal emulsifier and helps in the uniform dispersion formation in aqueous media due to incorporated –COOH groups. These carboxylic groups are neutralized by TEA which further aided in the dispersion stability. PEG is also another stabilizing factor that was used as polyol, similar to the findings of in literature [26], where it was reported that using alkylene oxide polyol may enhance the shelf stability by reducing the interfacial tension of PUDs in water. In present study, PEG with molecular weigh 300 was used which resulted in small particle size in dispersion giving rise to high stability factor [27]. Studies have been reported to describe that macro diol affect the dispersion stability creating an impact of hydrophilicity [28].

Synthesized polyurethanes were kept for long time without disturbing at STP in order to check their stability period. It was noted that dispersions were stable for a maximum of 1 year (12 months). There was slight variation in stability of the samples, i.e. some of the samples were stable for more time span than 12 months but overall they followed the same trend of stability. The stability of PUDs owes to the presence of ionic units in the structural backbone imparted by carboxylic group in DMPA used as emulsifier and amino group of TEA used as neutralizing agent [7,29].

Biological analysis of synthesized SA@PUDs_Ali

Blood hemolytic activity of SA@PUDs_Ali

For a material to be applied in biomedical applications, blood hemolytic/ hemocompatibility assay is performed that gives tolerance of body fluid/blood towards any material that come in contact with it, without getting ruptured [30]. In order to test the impact of synthesized dispersions when applied on wound dressing inside body cuts, blood hemolytic test was performed for all the samples (in dilutions to be applied on fabric i.e. 5% and 10%). Blood hemolytic activity values of control (sample with no SA), positive control (Triton X-100) and negative control (PBS) were found to be 27.31443%, 81.40117% and 0, respectively. The blood hemolytic values for the PUDs formulated using aliphatic isocyanate and SA chain extender were observed to be in the range 22% to 29% approximately. The samples having less concentration of SA exhibited greater hemolytic activity up to 22% both for 5% and 10% dilutions. Increment in the SA contents resulted in marked decrease in blood hemolytic activity and it was lessened up to 10.59% for 0.25 M SA-incorporated samples (Table 3). It was inferred that SA is a good essence in creating blood hemocompatibility/biocompatibility [31] and lowered the percentage rupturing of red blood cells (RBCs); however, this was not enough for a sample to fall under non-hemolytic category according to ASTM standards/ ISO 13485:2003. A sample to be considered as non-hemolytic should have a blood hemolytic value in the range 0–2% and none of the synthesized samples dilutions reflected such a low value, although a visual decrease in hemolytic activity was observed by increasing concentration of SA. Keeping in view the present findings, it is therefore inferred that an application interior to human body, of such a sample coating/wound dressing, may not be recommended as it can cause lysis of RBCs, resulting in serious inflammation.

Table 3.

Blood hemolytic values of SA@PUDs_Ali.

Serial No.	Sample code	Blood hemolytic activity (%)
		Sample dilution
		5%	10%
1	SA_0.05@PUDs_Ali	22.97 ± 0.02	20.72 ± 0.04
2	SA_0.10@PUDs_Ali	19.89 ± 0.03	16.97 ± 0.02
3	SA_0.15@PUDs_Ali	15.13 ± 0.03	14.80 ± 0.03
4	SA_0.20@PUDs_Ali	12.88 ± 0.01	11.21 ± 0.03
5	SA_0.25@PUDs_Ali	10.88 ± 0.01	10.59 ± 0.04

SA@PUDs_Ali: sodium alginate-based polyurethane dispersions using cycloaliphatic isocyanate.

Antibacterial activity of SA@PUDs_Ali

In this project antibacterial PUDs were prepared and their antibacterial properties were evaluated making two dilutions, i.e. 5% and 10%, which were later on applied on fabric as antibacterial finish. Antibacterial activity of SA-based polyurethanes using aliphatic isocyanates was estimated by agar diffusion method against gram positive (B. subtilis) and gram-negative bacteria (E. coli) using standard method protocol [23]. The results obtained are presented in Table 4.

Table 4.

Bacterial inhibition zone values of SA@PUDs_Ali.

Serial No.	Sample code	Antibacterial activity (mm)
		5% dilution		10% dilution
		Escherichia coli	Bacillus Subtilis	Escherichia coli	Bacillus Subtilis
1	SA_0.05@PUDs_Ali	28	29	31	30
2	SA_0.10@PUDs_Ali	28	30	33	31
3	SA_0.15@PUDs_Ali	30	33	33	34
4	SA_0.20@PUDs_Ali	32	33	34	34
5	SA_0.25@PUDs_Ali	32	34	34	35

SA@PUDs_Ali: sodium alginate-based polyurethane dispersions using cycloaliphatic isocyanate.

Distinguished antibacterial activity was exhibited by all the polyurethanes against both gram-positive (S. subtilis) and gram-negative bacteria (E. coli) as reported by Yagci et al. [32]. First sample SA_0.05@PUDs_Ali gave minimum inhibitory effect with an inhibition zone of 28 mm (E. coli), 29 mm (S. subtilis) for 5% dilution and 31 mm (E. coli), 30 mm (S. subtilis) for 10% dilution. Sample SA_0.10@PUDs_Ali had somewhat similar trend and represented inhibition up to 28 mm (E. coli), 30 mm (S. subtilis), 33 mm (E. coli) and 31 mm (S. subtilis) for 5 and 10% dilutions, respectively. The inhibition zone was almost in the similar range for the next three samples also as shown by data; in Table 4 increment in antibacterial activity at each step was due to the increasing SA contents that combat with microbes.

Mechanistically it can be said that presence of hydroxyl groups in SA might be responsible for the possible antimicrobial action. Maximum killing activity was observed when 0.25 moles SA was incorporated to the PU backbone and bacterial growth was inhibited in the vicinity of wells made for sample introduction to agar media [33]. The possible cause of antibacterial action might be due to the bacterial cell adhesion and ultimately entrapment by sticky SA incorporated PUDs, like being engulfed by it leaving no way for the passage of nutrients required for growth [34]. It is therefore inferred that the synthesized PUDs have very good antibacterial property and are promising candidates for antibacterial coating application.

Analysis of fabric after application of SA@PUDs_Ali

Tear strength analysis of fabric/ treated with SA@PUDs_Ali

Diluted solutions (5% and 10%) of the PUDs samples were applied separately on plain PC fabric and it was tested for its quality parameters including tear strength. The results obtained after the careful investigations are presented in Table 5. As a general estimation, tear strength was observed to be decreased with increasing chain extender contents. The finished fabric treated with the PUDs having lowest concentration of SA exhibited greatest tear strength of all the other samples. For the sample SA_0.05@PUDs_Ali tear strength was observed to be 8.91 ± 0.03 in warp and 4.88 ± 0.02 in weft ways for 5% solution application, whereas it was noted to have a value of 8.40 ± 0.01(warp) and 4.67 ± 0.02 (weft) when 10% solution of this samples was applied. In case of second sample i.e. SA_0.10@PUDs_Ali decreased values of tear strength were noted i.e. 8.87 ± 0.02 (warp) and 4.72 ± 0.01(weft) for 5% solution whereas 8.40 ± 0.02 (warp ways) and 4.55 ± 0.01 (weft ways) when a 10% diluted solution was applied. Similarly, a decreasing trend of tear strength was observed for sample application of SA_0.15@PUDs_Ali where it was 8.64 ± 0.02 (warp) and 4.57 ± 0.02 (weft) for 5% sample dilution application and 8.33 ± 0.03 (warp) and 4.20 ± 0.01(weft) for 10% dilution application. For samples application of SA_0.20@PUDs_Ali and SA_0.25@PUDs_Ali tear strength values were found to be in the range 8.33 to 7.99 (warp) and 4.30 to 4.01 (weft). All the fabric samples treated with various dispersion dilution exhibited less tear strength as compared to untreated fabric which had a value of 9.03 ± 0.01 (warp) and 4.90 ± 0.02 (weft). The decreasing trend of tear strength with the sample application having higher content of chain extender might be due to the interaction developed between fibers and dispersion coating. The dispersion sample bind to the yarns of fabric via various interactions such as Van der Waals force of attraction, hydrogen bonding or other polarity-based interaction which hinder the movement of yarns and does not let them slide pass each other [35]. As for the sample to be strong tear wise, it should possess flexibility in yarns of fabric, enabling them to move across each other easily, so factor decreasing this character results in decreased tear strength. In this way treated fabric could not withstand load for so long and tore away more easily as compared to untreated fabric and exhibited less tear strength. The sliding movement of yarns goes on decreasing with increasing contents of SA in sample enhancing their entanglement and ultimately decreasing the fabric tear strength [36].

Table 5.

Tear strength of PC fabric before and after the treatment with dispersions/ SA@PUDs_Ali.

Serial No.	Sample code	Tear strength (1bf/in)
		5% dilution		10% dilution
		Warp	Weft	Warp	Weft
1	SA_0.05@PUDs_Ali	8.91 ± 0.03	4.88 ± 0.02	8.40 ± 0.01	4.67 ± 0.02
2	SA_0.10@PUDs_Ali	8.87 ± 0.02	4.72 ± 0.01	8.40 ± 0.02	4.55 ± 0.01
3	SA_0.15@PUDs_Ali	8.64 ± 0.02	4.57 ± 0.02	8.33 ± 0.03	4.20 ± 0.01
4	SA_0.20@PUDs_Ali	8.33 ± 0.01	4.30 ± 0.01	8.17 ± 0.02	4.05 ± 0.02
5	SA_0.25@PUDs_Ali	8.00 ± 0.02	4.01 ± 0.01	7.99 ± 0.02	4.01 ± 0.01
6	Untreated Fabric	9.03 ± 0.01	4.90 ± 0.02

SA@PUDs_Ali: sodium alginate-based polyurethane dispersions using cycloaliphatic isocyanate.

Tensile strength analysis of fabric/ treated with SA@PUDs_Ali

Tensile strength values of the fabric treated with SA@PUDs_Ali were noted and presented in Table 6, which was noted by using standard method BS EN ISO 13934-1. It was observed that irrespective of the tear strength, tensile strength values were found to be enhanced with the increasing concentration of SA in the sample. Tensile strength values for fabric treated with sample SA_0.05@PUDs_Ali were noted to be 699.30 ± 0.02 (warp) and 400.55 ± 0.02 (weft) and 733.00 ± 0.03 (warp) and 422.21 ± 0.04 (weft) for a 5% and 10 dilution, respectively. In the next run, when SA_0.10@PUDs_Ali was applied on the fabric, it showed the same trend with tensile strength values varying from less to high as 707.50 ± 0.02 (warp) and 420.31 ± 0.02 (weft) for 5% dilution application and 756.01 ± 0.02 (weft) and 431.34 ± 0.03 (weft) for 10% dilution application of the same sample. In the similar manner SA_0.15@PUDs_Ali was also used for fabric treatment and in turn fabric generated tensile strength values as 719.40 ± 0.01(warp) and 422.55 ± 0.01 (weft) when treated with 5% dilution and 776.30 ± 0.02 (warp) and 442.54 ± 0.02 (weft) when treated with 10% dilution of sample. Fourth sample of the series i.e. SA_0.20@PUDs_Ali was also diluted to 5% and 10% in order to check its efficiency when used for finishing the fabric. It was noted that fabric has developed some more good characteristics from tensile strength point of view exhibiting the tensile strength as 728.11 ± 0.03 (warp) and 430.45 ± 0.02 (weft) for 5% dilution whereas 781.54 ± 0.02 (warp) and 459.35 ± 0.02 (weft) for 10% dilution. Sample SA_0.25@PUDs_Ali was then diluted up to 5% and 10% and applied on fabric and tested for its tensile strength as all of the previous samples. Tensile strength was observed to be greater than all other samples of the same series as 732.33 ± 0.02 (warp) and 444.23 ± 0.01 (weft) (with 5% dilution) and 783.11 ± 0.03 (warp) and 460.79 ± 0.02 (weft) (with 10% dilution). Control fabric with no sample application was observed to have tensile strength of 653.58 ± 0.01 (warp) and 388.02 ± 0.01 (weft), which was less than all samples application.

Table 6.

Tensile strength of PC fabric before and after the treatment with dispersions/ SA@PUDs_Ali.

Serial No.	Sample code	Tensile strength (N/m)
		5% dilution		10% dilution
		Warp	Weft	Warp	Weft
1	SA_0.05@PUDs_Ali	699.30 ± 0.02	400.55 ± 0.02	733.00 ± 0.03	422.21 ± 0.04
2	SA_0.10@PUDs_Ali	707.50 ± 0.02	420.31 ± 0.02	756.01 ± 0.02	431.34 ± 0.03
3	SA_0.15@PUDs_Ali	719.40 ± 0.01	422.55 ± 0.01	776.30 ± 0.02	442.54 ± 0.02
4	SA_0.20@PUDs_Ali	728.11 ± 0.03	430.45 ± 0.02	781.54 ± 0.02	459.35 ± 0.02
5	SA_0.25@PUDs_Ali	732.33 ± 0.02	444.23 ± 0.01	783.11 ± 0.03	460.79 ± 0.02
6	Untreated Fabric	653.58 ± 0.01	388.02 ± 0.01

SA@PUDs_Ali: sodium alginate-based polyurethane dispersions using cycloaliphatic isocyanate.

There are so many factors that may affect the tensile strength of the fabric including extent of crosslinking, attachment to the fabric, soft and hard segment contents in the dispersion applied on it [37]. All of these factors go on increasing as the amount of SA increases in the samples making the dispersion coating more entangled to the yarns by Van der Waals forces and hydrogen bonding formation [35]. These forces enable the formation of crosslinking of dispersion with fabric and make them stick together to bear more load and exhibit good to excellent tensile strength. On fabric treatment greater tensile strength of fabric coated with 10% dilution as compared to the 5% dilution is due to the more extent of penetration of sample in the yarns of fabric and strong film formation over the fabric surface [38].

Pilling resistance analysis of fabric/ treated with SA@PUDs_Ali

Pilling is an important factor in indicating the fabric quality and a point of interest to users. It badly disturbs the fabric quality and decreases the value of textile material in industry. This factor has forced the manufacturer to pay a keen attention to the factors that may reduce the pilling tendency of the fabric. More the pilling on fabric, the more it looks fuzzy having a rough surface with fibers protruding out. Pilling occurs as a combined event of formation and disappearance of pills at various levels [39]. All the treated samples along with control were tested for pilling and results were tabulated as in Table 7.

Table 7.

Pilling resistance of PC fabric before and after the treatment with dispersions/ SA@PUDs_Ali.

Serial No.	Sample code	Pilling resistance
Serial No.	Sample code	5% dilution	10% dilution
1	SA_0.05@PUDs_Ali	4	4
2	SA_0.10@PUDs_Ali	4–5	4–5
3	SA_0.15@PUDs_Ali	4–5	4–5
4	SA_0.20@PUDs_Ali	5	5
5	SA_0.25@PUDs_Ali	5	5
6	Untreated Fabric	3–4

SA@PUDs_Ali: sodium alginate-based polyurethane dispersions using cycloaliphatic isocyanate.

Fabric after SA@PUDs_Ali treatment was more resistant towards pilling as compared to the control (untreated fabric). Fabric sample treated with SA_0.05@PUDs_Ali had pilling resistance up to 4. It was further improved on increasing SA contents and reached a value of 4–5 for SA_0.10@PUDs_Ali and SA_0.15@PUDs_Ali applied fabric. Maximum value of pilling resistance was found to be 5 on application of samples SA_0.20@PUDs_Ali and SA_0.25@PUDs_Ali on PC fabric.

The enhancement in the pilling resistance on application of PUDs to the fabric was most probably due to the presence of dispersion layer on fabric surface which resisted in protruding out of yarns. Dispersion film on fabric was formed by polar interactions or hydrogen bonding resulting in more intact and smooth surface. Yarns were stuck together tightly and did not contribute in pilling by rupturing and this effect became more pronounced as the chain extender concentration, i.e. SA increased and reached a maximum pilling resistance value of 5 [35].

SEM analysis of fabric treated with SA@PUDs_Ali

SEM is used to view the surface morphology of sample using a focused beam of electrons. It is therefore performed in present study to check the surface features of fabric before and treatment with polyurethane dispersions under “field emission scanning electron microscopy” (FE-SEM). Figure 4 represents the SEM images of fabric samples treated with the 10% solution of each of the polyurethane dispersion synthesized using aliphatic isocyanates. Figure 4(a) shows the image of untreated fabric revealing that the surface does not have coating of any material and appear to be rough as compared to the other samples. Figure 4(b) to (f) represents the fabric sample finished with dispersion solutions and it is evident from the images that dispersion has been applied in an even manner and pressed firmly to the fabric surface making it smooth. This increased the tensile strength and reduced the chances of pilling formation as fibers now have very little tendency to protrude to make pilling.

Figure 4.

SEM images of (a) untreated fabric and fabric samples treated with 10% solution of (b) SA_0.05@PUDs_Ali (c) SA_0.10@PUDs_Ali (d) SA_0.15@PUDs_Ali (e) SA_0.20@PUDs_Ali (f) SA_0.25@PUDs_Ali. SA@PUDs_Ali: sodium alginate-based polyurethane dispersions using cycloaliphatic isocyanate.

Conclusions

Herein SA-based polyurethane dispersions with excellent antibacterial activity were synthesized. Antibacterial potential dispersions were synthesized by using varied concentration of SA from 0.05 M to 0.25 M. Other basic monomers used in the synthesis were IPDI, TDI, PEG and DMPA. After synthesis, biological testing of these materials was conducted. Blood hemolytic analysis data made it evident that the synthesized materials were not safe to apply as wound dressing coating inside human body and further investigation is needed to reach a non-hemolytic value. Strong antibacterial activity of synthesized dispersions make them potential materials to be applied in textile as antibacterial finishing. After morphological and biological characterization, dispersions were applied on polycotton blend fabric (50/50). Later on the treated fabric was tested for tear strength, tensile strength and pilling resistance to investigate the effect of dispersions over the finished fabric. Dispersion not only improved the tensile strength and pilling resistance but also affected the morphology of the fabric which was confirmed by SEM. On the other hand, a decline in tear strength of fabric was observed. While studying the physical parameters of the synthesized materials, it was observed that they were transparent yellow. Solid contents were estimated to be in the range of 37–41% and stability was found to be 1 year on average. It was therefore inferred that the synthesized PUDs were good candidate to be applied as antibacterial coating for textile materials.

Footnotes

Acknowledgement

Authors are thankful to Department of Chemistry, UAF, Pakistan and Higher Education Commission (HEC), Pakistan for providing facilities to accomplish the present project successfully.

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Synthesis,biological efficiency evaluation and application of sodium alginate-based polyurethane dispersions using cycloaliphatic isocyanate,as antibacterial textile coating

Abstract

Keywords

Introduction

Experimental

Materials

Methodology

Synthesis of NCO terminated polyurethane prepolymer

Addition of SA as chain extender and preparation of PUDs

Physical and structural characterization

Biological analysis of the synthesized PUDs

Antibacterial analysis

Blood hemolytic analysis

Application of optimized sample on polycotton fabric

Analysis of treated polycotton fabric

Results and discussions

Molecular characterization

FTIR Analysis of SA@PUDsAli

NMR spectroscopic analysis

Physical characterization of SA@PUDsAli

Biological analysis of synthesized SA@PUDsAli

Blood hemolytic activity of SA@PUDsAli

Antibacterial activity of SA@PUDsAli

Analysis of fabric after application of SA@PUDsAli

Tear strength analysis of fabric/ treated with SA@PUDsAli

Tensile strength analysis of fabric/ treated with SA@PUDsAli

Pilling resistance analysis of fabric/ treated with SA@PUDsAli

SEM analysis of fabric treated with SA@PUDsAli

Conclusions

Footnotes

Acknowledgement

References

FTIR Analysis of SA@PUDs_Ali

Physical characterization of SA@PUDs_Ali

Biological analysis of synthesized SA@PUDs_Ali

Blood hemolytic activity of SA@PUDs_Ali

Antibacterial activity of SA@PUDs_Ali

Analysis of fabric after application of SA@PUDs_Ali

Tear strength analysis of fabric/ treated with SA@PUDs_Ali

Tensile strength analysis of fabric/ treated with SA@PUDs_Ali

Pilling resistance analysis of fabric/ treated with SA@PUDs_Ali

SEM analysis of fabric treated with SA@PUDs_Ali