Emulsification of castor oil using poly (N-vinyl-2-pyrrolidone) for functional finishing of cotton fabric

Castor oil (CAO)/poly (N-vinyl-2-pyrrolidone) (PVP) hybrid was synthesized at different reaction conditions including PVP/CAO weight ratio, temperature, and time. The results indicated that the optimum conditions to synthesis that hybrid is reacting of PVP having a molecular weight of 40,000 Da with CAO at a weight ratio of 30% and temperature of 150°C for 60 min. The synthesized hybrid was characterized via FTIR. Emulsification of such hybrid in water results in a white stable emulsion. The TEM analysis proved that the prepared emulsion of a particle size ranges from 320 to 370 nm. The technical feasibility to apply the produced emulsion for functional finishing of cotton fabric was studied. The results obtained indicated that treating cotton fabric with easy care finishing bath containing the synthesized emulsion results in enhancement in nitrogen content, tensile strength, whiteness index, stiffness, and antibacterial activities along with a decreasing in resiliency, wettability, and surface roughness properties of treated fabric, compared to the control sample. Moreover, incorporation of zinc oxide nano-particles (ZnO-NPs) or dihydroxybenzophenone (DHBP) in the above mentioned finishing bath enhances the functional properties of the finished fabric. Furthermore, dyeing fabric samples with different reactive and direct dyes followed by finishing using the aforementioned finishing bath, in absence of ZnO-NPs and DHBP, gives rise to an enhancement in the color strength of such samples compared to the dyed samples. The fastness to washing and perspiration of only the direct dye dyed/finished sample was improved. Almost all the dyed/finished samples exhibited an improvement in their fastness to the wet rubbing and alkaline perspiration along with a reduction in fastness to light. In addition, the SEM, as well as EDX analysis of treated fabric, was investigated.


Introduction
Castor oil is produced from the castor seeds of the castor plant (Ricinus communis).It comprises ricinoleic (about 90%) in addition to other fatty acids such as linoleic, oleic, stearic, palmitic, dihydoxystearic, eicosanoic, and linolenic acids (Figure 1). 1 The presence of a double bond, hydroxyl group, carboxylic group as well as a hydrocarbon long chain in the ricinoleic acid of the castor oil, offers many possibilities for transforming it into versatile materials.Due to the unique chemical structure and renewability of castor oil, it is widely used in versatile industrial applications including cosmetics, textile dyes, paints, coatings, varnishes, plastics, inks, soaps, and lubricants.2][3][4] Castor oil can be emulsified using many emulsifying agents.Emulsions are widely used in the cosmetics, pharmaceutical, and food industries.In the pharmaceutical field, emulsions are able to deliver both hydrophilic and lipophilic drugs. 5Many gums such as Arabic gum and Terminalia gum can be used to emulsify castor oil. 6,7Zhang et al. 8 reported that an emulsifier formula containing polyoxyethylene sorbitan monostearate and sorbitan monooleate achieved a stable emulsion of castor oil.Castor oil can be sulfated using sulfuric acid to become an anionic textile softener (Turkey red oil).Increasing the castor oil sulfate groups renders it to have a higher ionicity with lower lubrication and ultimately becomes a self-emulsifier.Sulfated castor is easily removed from treated fiber or fabric without an auxiliary surfactant. 9oly (N-vinyl-2-pyrrolidone) (PVP) is a water-soluble, nontoxic, and biocompatible synthetic polymer.PVP is a suspending agent, a clarifying agent, protective colloid, stabilizer, viscosity modifier, film former, and complexing agent.It has versatile industrial applications including pharmaceutical, biomedical, and textiles applications.PVP can be crosslinked through heating at 150°C in air, ultraviolet and gamma radiation, or in the presence of persulfates. 10,11llulosic fabrics such as cotton, linen, and viscose provide comfort properties such as softness, high absorbency, and breathability for their wearers.Unfortunately, these fabrics are easily wrinkled and soiled, prone to microbial attack, and have low protection against UV radiation.3][14][15][16][17][18] Various bioactive agents can be used to impart textiles with antimicrobial properties such as metal and metal oxide nanoparticles, for example, Ag, ZnO, and TiO 2 nanoparticles (NPs), chitosan, re-generable N-halamine compounds, metal salts, halogenated phenols, for example, triclosan, quaternary ammonium compounds, and immobilized enzymes. 19,20V absorbers are inorganic or organic colorless compounds having high absorption in the range of 290-360 nm of ultraviolet spectra.0][21][22][23] The ZnO-NPs provide excellent UV protection as well as high antibacterial activity. 24owever, the ability of Zn-NPs as a UV protector is due to the band gap absorption and light scattering mechanism. 25The band gap between the valance and conduction electrons of the ZnO-NPs confer the generation of reactive oxygen species giving rise to conformational changes/oxidant injury to the microorganism membrane surface. 24The substituted benzophenones are the most effective organic compounds in protecting against UV radiation.The dihydroxybenzophenone absorbs UV radiations strongly in the UV-A range while benzophenone absorbs in the UV-B range.The strong absorption for UV-A of dihydroxy benzophenone is due to the conjugate chelation between the carbonyl group and the o-hydroxy. 23esides, the benzophenone derivatives generate reactive oxygen species under their exposure to sunlight or UV irradiation, providing antibacterial activity to their loaded fabrics. 26he main goal of that work is to emulsify the castor oil using poly (N-vinyl-2-pyrrolidone) and investigate the technical feasibility to apply the produced emulsion as a textile softener during easy-care finishing of cotton fabric to impart that fabric with multi-functional properties namely softness, anti-crease, antibacterial, and UV protection.In addition, the coloration and fastness properties of dyed/finished cotton fabric samples will be also studied.

Materials
Mill-scoured and bleached cotton fabric of weave structure, weight of 128 g/m 2 and count (Ne) of 40/1 was supplied by Misr Spinning and Weaving Co., Mahalla El-Kobra, Egypt.Castor oil (CAO) from India, supplied by Iso-Chem.Company was used.Durapret LF (DMDHEU), a low formaldehyde resin of concentration 70%, was used as a crosslinker for easy care finishing of cotton fabric.Poly (N-vinyl-2-pyrrolidone) (PVP) of molecular weight 40,000 Da was supplied by Alpha Chemika.Zinc oxide nanoparticles (ZnO-NPs) and 2,4-dihydroxy benzophenone (DHBP) were supplied by Aldrich.Ammonium sulfate of laboratory-grade chemical was used as a catalyst.

Methods
Preparation of CAO/PVP hybrid emulsion.The CAO/PVP hybrid emulsion was prepared as follows: 5 g of CAO and different weights of PVP (0-4 g) were mixed together in a 150 mL beaker with stirring at different temperatures (100°C-160°C) for a period of time (0-75 min).After a certain time, the reaction medium was left to cool at room temperature followed by the addition of a specific volume of hot distilled water at 70°C and stirring using a strong homogenizer for 3 min to form a stable CAO/PVP hybrid emulsion. 14

Fabric treatment
Soft finishing of cotton fabric.Cotton fabric samples of 30 × 30 cm 2 were padded twice in finishing bathes containing 80 g/L of DMDHEU, ammonium sulfate as a catalyst, and different concentrations of CAO/PVP hybrid emulsion (0-40 g/L), to a wet pick up of 100%.The padded samples were dried at 100°C/3 min in Wenner Mathis AGCH-8155 oven and then cured at 150°C/3 min.The finished fabrics were then washed with distilled water at 50°C for 10 min, thoroughly rinsed, and finally dried for testing.
Dyeing of cotton fabric.Dyeing of cotton fabric with the above-mentioned reactive dyes was performed by dissolving 1% of any of such dyes (owf) in distilled water at 40°C then 30 g/L Na 2 SO 4 was added to the dye bath followed by the addition of the fabric samples using a material to liquor ratio 1:50.After 30 min, the dye bath temperature was raised to 60 °C in case of the C.I. Reactive Blue 19 and C.I. Reactive Black 5 dyes but to 90°C for the C.I. Reactive Red 141, followed that by addition of 15 g/L sodium carbonate dropwise and then the dyeing process was left to proceed for 60 min.At the end, the dyed samples were soaped with 3% nonionic detergent, rinsed with tap water, and finally dried at room temperature.On the other hand, cotton fabric samples were dyed with the nominated direct dye by dissolving 1% of that dye (owf) in distilled water at room temperature and then 30 g/L Na 2 SO 4 was added followed by the addition of the fabric samples to dye bath using a material to liquor ratio 1:50.The dye bath temperature was then raised to 90°C and the dyeing process was preceded for 60 min.At the end, the dyed samples were soaped with 3% nonionic detergent, rinsed with tap, water and finally dried at room temperature.

Tentative mechanism
Previous literature reported that PVP can be crosslinked under heating in air at 150°C through a chain scission mechanism. 10,11,29,30Thus, it is expected that heating a CAO/PVP mixture at the conditions employed will give rise to a formation of crosslinked PVP as well as CAO grafted with PVP.1][32][33] The PVP grafted oil may serve as a self-emulsifiable for the remaining CAO beside the crosslinked PVP that stabilizes the resulting emulsion. 33For simplicity, the reaction product will be pointed out as "CAO/PVP hybrid."The following mechanism may investigate the grafting of the CAO with PVP: (a) Formation of PVP macroradicals (2) Formation of castor oil radicals (3) Formation of crosslinked PVP and castor oil grafted with PVP

Factors affecting the CAO/PVP hybrid emulsion formation
Effect of temperature.Table 1 shows the impact of the reaction medium temperature on CAO/PVP hybrid emulsion state.It is clear that raising the reaction temperature from 100°C to 150°C is accompanied by a gradual improvement in the CAO/PVP hybrid emulsion state.
The matter that can be associated with the positive impact of temperature, in addition to air oxygen, to form PVP macroradicals that in turn enhance the formation of grafted castor oil as well as crosslinked PVP and hence the upgrading in the hybrid emulsion sate. 30Increasing the reaction temperature beyond 150°C and up to 160°C has no effect on the emulsion state of the prepared hybrid.
Effect of time.Table 2 illustrates the effect of the reaction time on the CAO/PVP hybrid emulsion state.It is obvious that prolonging the reaction time from 15 to 60 min gives rise to a gradual enhancement in the emulsion state of the CAO/PVP hybrid to be a stable emulsion.This can be attributed to increasing the extent of formation of the PVP grafted castor as well as crosslinked PVP over time.
The longer reaction time, up to 75 min, does not affect the hybrid emulsion state. 30VP/castor oil weight ratio.Table 3 shows the effect of PVP/ castor oil weight ratio on the emulsion state of the CAO/PVP hybrid.It is well seen that increasing that ratio up to 30% brings about a progressive upgrading in the hybrid emulsion state which can be ascribed to increasing of the extent of formation of both the grafted castor oil and the crosslinked PVP species. 30Beyond the ratio of 30%, within the range studied, plenty of the aforementioned species is present in the reaction medium that keeps the stability of the hybrid emulsion.It seems that the PVP/CAO weight ratio of 30% is the appropriate ratio to achieve a stable CAO/PVP hybrid emulsion.Figure 2 represents a visual appearance of the CAO/PVP hybrid emulsion at the optimum conditions of synthesis.

Characterization of CAO/PVP hybrid and its emulsion
FTIR of the CAO/PVP hybrid.The FTIR spectra of CAO/ PVP hybrid, PVP, and castor oil are represented by Figure 3(a) to (c) respectively.It is clear that Figure 3(a) includes: (1) Peaks resemble that of PVP spectrum Figure 3(b) that are 16,30,34,35  TEM image of the CAO/PVP hybrid emulsion.The CAO/PVP hybrid emulsion was characterized using the TEM analysis.The TEM image (Figure 4) shows that such emulsion particles are in a size ranges between 320 and 370 nm.

Inclusion of the CAO/PVP hybrid emulsion in easy-care finishing of cotton fabric
The performance properties of the finished fabric.The performance properties of cotton fabric samples treated   with easy-care finishing formulations containing different concentrations of the prepared CAO/PVP hybrid emulsion is illustrated in Table 4.It is well seen that: (i) finishing of fabric samples in absence of the nominated emulsion, results in an enhancement in nitrogen content, resiliency, stiffness, and surface roughness along with a decrease in tensile strength, wettability, and whiteness index properties of the treated fabric, compared to the untreated sample.The matter that can be attributed to crosslinking of hydroxyl groups of cotton cellulose with DMDHEU is represented by the following equation 1,12,17 : (ii) Incorporation of the prepared hybrid emulsion in the above-mentioned finishing bath gives rise to an enhancement in nitrogen content, tensile strength, whiteness index, and stiffness accompanied by a decrease in resiliency, wettability, and surface roughness properties of the treated fabric, compared to the control sample.The matter that can be associated with the fixation and deposition of such hybrid ingredients onto/within the fabric structure is shown by the following equations 1,12,17 : (a) Fixation of the hybrid emulsion ingredients onto/ within cotton cellulose (b) Deposition of the hybrid emulsion ingredients onto/within cotton cellulose And, (iii) increasing such emulsion concentration in the finishing bath from 20 to 40 g/L is accompanied by an increase in the extent of nitrogen content, tensile strength, and stiffness along with a reduction in resiliency, whiteness index, wettability, and surface roughness properties of treated fabric reflecting of increasing of the extent of fixation of such hybrid ingredients onto/within treated fabric structure. 1,12,17e functional properties of the finished fabric.Table 5 signifies the functional properties of cotton fabric samples treated with easy care finishing formulations containing the CAO/PVP hybrid emulsion individually or in combinations with ZnO-NPs or DHBP.It is obvious that treating fabric sample with the hybrid emulsion acquires the treated fabric with antibacterial activities against the pathogenic Gramnegative (E.coli) and Gram-positive (S. aureus) bacteria, reflecting the antibacterial properties of castor oil. 40Combining the hybrid emulsion with the Zn-NPs or DHBP, regardless of their concentration, in different easy-care finishing formulations gives rise to an enhancement in the antibacterial properties as well as UV-blocking ability.The extent of improvement in such functional properties reflects the differences between such bio-additives in their chemical structure, functional groups, molecular size, the extent of fixation, mode of interaction, anti-bacterial activity, and ability to reflect or absorb harmful UV radiation. 41,42The upgrading in the antibacterial activity of ZnO-NPs treated fabric is attributed to a generation of reactive oxygen species such as HO • , O 2 • , and H 2 O 2 and their subsequent damaging effect on the bacterial cells. 41,43The promotion in the antibacterial activities of DHBP finished fabric can be associated with the impact of exiting the benzophenone chromophoric groups to active radicals under UV light on destroying of the pathogenic bacteria. 44,45The improvement in UPF values of DHBP-loaded fabric is a direct consequence for the change in the benzophenone structure from keto to enol form, the matter that enhances the absorption of the harmful UVB radiation and prevents it to penetrate the fabric structure. 46The higher the prepared hybrid, ZnO-NPs, or DHBP concentration in the finishing bath, the higher is the resistance against such bacterial strains.On the other hand, increasing the laundering of the treated fabric from 5 to 20 cycles gives rise to a reasonable decrease in extents of the functional properties of the treated fabric, irrespective of the bio-active type and concentration.However, the functional properties of the DHBP-loaded fabric are more durable to washing compared to the other treated fabric samples, the matter which can be attributed to the binding of DHBP molecules chemically, in addition to castor oil, to the cellulose structure through their hydroxyl groups during easy-care finishing of the treated fabric as represented by equation ( 7) 47 : In contrast, Zn-NPs are not firmly attached to the cellulose structure as they lack reactive groups capable to bind to the cellulose structure, the matter which indeed lowers the durability of the finished to laundering.

Coloration properties and fastness properties of the dyed and dyed/finished cotton fabric
Wavelength and coloration properties of the dyed and dyed/finished cotton fabric.Table 6 shows the wavelength (λ max ), color strength (K/S), and colorimetric data (L*, a*, and b*) values of the dyed samples before and after treatment with easy care finishing bath containing the prepared CAO/PVP hybrid emulsion.It is clear that the variation in  dye type results in dyed samples having different wavelengths, color strength as well as colorimetric data, which can be associated with the alteration in affinity, molecular size, functionality, as well as the mode of interaction of that dyes. 18,20,48,49In addition, treating the dyed samples with the aforementioned emulsion, irrespective of dye type, brings about an enhancement in K/S of the treated samples, which may be attributed to the color-deepening effect of the CAO/PVP hybrid emulsion as a textile softener. 50e fastness properties dyed/finished fabric.Table 7 shows the fastness properties of the dyed and dyed/finished fabric samples.It is clear that finishing of the dyed samples results in: (i) an enhancement in the washing and perspiration fastness of only the sample dyed with the direct dye, (ii) an improvement in the wet rubbing fastness as well as the alkaline perspiration fastness of almost all the dyed/finished samples, and (iii) a lowering in the lightfastness of all the dyed/finished fabric samples.The variation in such fastness properties reflects the impact of the prepared CAO/PVP hybrid ingredients deposition as a film onto the dyed cotton fabric structure.
SEM and EDX images of the treated fabric.Figure 5 shows SEM images of (a) untreated cotton fabric and (b) cotton fabric treated with a finishing bath containing 60 g/L of DMDHEU, 6 g/L of ammonium sulfate, 30 g/L of the prepared emulsion, and 2 g/L of ZnO-NPs.It is clearly seen that the SEM image of fabric sample (b) shows a homogenous deposited film of the hybrid ingredients onto the surface of that sample, compared to that of the untreated sample.On the other hand, Figure 6 shows EDX analysis of the above-mentioned fabric samples.It is clear that, EDX image of the untreated sample contains only the elements of C and O whereas the EDX image of the sample (b) contains the elements of C, O, N, and Zn.

Storage stability of the CAO/PVP hybrid emulsion
Upon storage of the CAO/PVP hybrid emulsion for one month, tinny oil drops appeared on the emulsion surface after 1 week that continued for a month without almost any change, and then disappeared upon shaking and a stable emulsion was formed again.

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.

Figure 2 .
Figure 2. A visual appearance of the CAO/PVP hybrid emulsion.

Figure 4 .
Figure 4. TEM image of the CAO/PVP hybrid emulsion.

Table 1 .
Effect of reaction temperature on CAO/PVP hybrid emulsion state.

Table 2 .
Effect of reaction time on CAO/PVP hybrid emulsion state.

Table 3 .
Effect of PVP/castor oil weight ratio on CAO/PVP hybrid emulsion state.

Table 4 .
Effect of the CAO/PVP hybrid emulsion concentration on performance properties of treated fabric.

Table 5 .
The functional properties of the CAO/PVP hybrid emulsion treated fabric.

Table 6 .
Effect of the dye type on wavelength and coloration properties of the dyed and dyed/finished cotton fabric.

Table 7 .
The effect of finishing of the dyed fabric with the CAO/PVP hybrid on the fastness properties of that fabric.