Isosorbide-based microcapsules for cosmeto-textiles

Industrial Crops and Products 52 (2014) 150–157

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Isosorbide-based microcapsules for cosmeto-textiles Nedra Azizi a,∗ , Yves Chevalier b , Mustapha Majdoub a a Laboratoire des Interfaces et Matériaux Avancés (LIMA), Faculté des Sciences de Monastir, Université de Monastir, bd de l’Environnement, 5019 Monastir, Tunisia b Laboratoire d’Automatique et de Génie des Procédés (LGEP), Université Claude Bernard Lyon 1, UMR-CNRS 5007, 43 bd du 11 Novembre 1918, 69622 Villeurbanne Cedex, France

a r t i c l e

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Article history: Received 26 June 2013 Received in revised form 12 October 2013 Accepted 14 October 2013 Keywords: Microcapsule Isosorbide Neroline Textile Impregnation Fastness

a b s t r a c t New microcapsules based on renewable materials and containing perfume were designed for cosmetotextile application. Such microcapsules contained the neroline fragrance as core material and a bio-based polyurethane as wall material. The polymer wall was synthesized by interfacial polycondensation of isosorbide and methylene bis(phenyl isocyanate). The chemical structure of the microcapsules was confirmed by IR and 1 H NMR spectroscopies. The encapsulation efficiency of perfume was determined using 1 H NMR analysis technique accounts for 30%. Microcapsules of spherical shape and 27 ␮m diameter consisted of a liquid core and a polymer wall, as revealed by means of small-angle light scattering measurements and scanning electron microscopy (SEM) observations. Neroline-loaded microcapsules were impregnated on polyamide textile substrate. The impregnation yield was about 80%. The presence of microencapsulated perfume and the durability of the impregnation effect were tested by SEM, UV–visible spectroscopy and gas chromatography. The polyamide knitting finished with microcapsules slowly released its microcapsule content and the neroline remained until twentieth washing cycles. © 2013 Elsevier B.V. All rights reserved.

1. Introduction

Ichikawa, 2002; Suryanarayana et al., 2008; Tseng et al., 2005; Whateley, 1992).

Microencapsulation of various materials is an effective method that aims at two major purposes:

(i) the control over the delivery rates into the surroundings leading to sustained release properties; (ii) the stabilization of functional agents by their protection against reactions with moisture, light and oxygen (Benita, 1996; Mercadé-Prieto and Zhang, 2012; Park et al., 2001; Vandamme et al., 2007). Microencapsulation of solid, liquid or gaseous materials results in a solid powder form that is advantageous in many applications. In particular, immobilization of liquid compounds onto solid supports often requires their encapsulation as prerequisite to their deposition onto solid surface as an adhesive and durable coating. This technique has been early applied to carbonless copy paper (Green, 1957; White, 1992) and it has currently found applications in many technical domains such as, food, adhesives, cosmetics, pharmaceutics, phytosanitary products, medicine, liquid crystals labels, phase-change materials (Bouchemal et al., 2004; Glenn et al., 2010; Matsunami and

∗ Corresponding author. Tel.: +216 52083376. E-mail address: [email protected] (N. Azizi). 0926-6690/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.indcrop.2013.10.027

Encapsulation processes have been introduced in the textile industry for the implementation of specific properties to textile materials by coating them with various active substances (Monllor et al., 2007). Such application takes advantage of the solid powdered form of microencapsulated liquids for an easy deposition onto the textile fibers. Fabrics having long-lasting fragrance release properties are manufactured by coating fibers with microcapsules loaded with perfumes (Delaye, 2004; Madene et al., 2006; Monllor et al., 2007; Nelson, 2001; Pena et al., 2012; Rodrigues et al., 2009; Specos et al., 2010a,b; Tzhayik et al., 2012; Zhang and Rochefort, 2012). The microcapsules can be applied by stamping works, exhaustion dyeing, impregnation, spraying and coating. Besides, microcapsules can be incorporated in the fiber directly without modifying its touch and color (Monllor et al., 2007; Nelson, 2002; Roxana et al., 2008). Polyurethane is an appropriate candidate for microcapsule-shell in textile application owing to its good adhesive properties and compatibility with skin (Cordeiro et al., 1997; Dieterich, 1981; Fenouillot et al., 2010; Gaudina and Sintes-Zydowicz, 2008; Saihi et al., 2006; Shuklay et al., 2002; Varke and Sreekumar, 2010). Microencapsulation processes rely on several chemical methods such as in situ polymerization, coacervation (Jyothi et al., 2010).

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Interfacial polymerization is a widely used method that allows the manufacture of microcapsules from an o/w emulsion by the formation of thick polymer walls around liquid droplets (Arshady, 1992; Frère et al., 1998; Hong and Park, 1999; Jabbari, 2001; Mirabedini et al., 2012; Pearson, 1985; Salaün et al., 2011; Wagh et al., 2009; Yan et al., 1993). Encapsulation methods based on in situ polymerization are open to health concerns coming either from residual monomers in case of their incomplete conversion, or the formation of hazardous degradation products during the life cycle of the materials. A well-known example of such potential health hazard is bisphenol A contained in polycarbonate. In order to remedy such concerns, the substitution of harmful reagents by alternative monomers is a definite progress toward safety. Sustainability of the manufacture processes also requires the utilization of bio-based materials from renewable sources. Attractive diol monomers to be used in polycondensation in place of bisphenol A are dianhydrohexitols such as isosorbide (Fenouillot et al., 2010). The present work aims at the development of microcapsules based on materials taken from sustainable renewable sources. Since polyurethane is widely used as a wall materials of microcapsules prepared by interfacial polycondensation, and considering the large body of work devoted to polyurethane materials using diols from natural sources (Fenouillot et al., 2010), the preparation and properties of isosorbide-based polyurethane microcapsules have been investigated. Microcapsules loaded with the neroline perfume were prepared by interfacial polymerization using the bio-based isosorbide as a diol in place of the conventional diols often used in polycondensation (Rodrigues et al., 2009). The substitution of such diols for isosorbide kept the main favorable characteristics of polyurethane microcapsules. The microcapsules were characterized for their chemical composition and morphology. Finally, the behavior of such microcapsules for polyamide textile finishing was investigated so as to assess them with regards to their application for cosmeto-textiles. 2. Experimental 2.1. Materials and methods 2.1.1. Materials 4,4 -Methylene bis (phenyl isocyanate) (MDI, Aldrich 98%), isosorbide (Acros 98%), Polysorbate 80 (TweenTM 80, Aldrich 98%), dibutyltindilaurate (SnDBDL, Aldrich 95%). In order to bond the microcapsules to the polyamide knitting, an acrylic cross linking agent (RESACRIL BD CONC; supplied by Prochimica Novarese SPA, Italy) was used. 2-Ethoxynaphthalene (neroline) was synthesized by O-ethylation of ␤-naphthol with ethyl bromide (Azizi et al., 2011). Microencapsulation processes were carried out in a thermostated double jacketed 1 L glass reactor, (Sovirel), equipped with an anchor blade mixer, a digital control of stirring rate and an oil thermostat bath. The emulsion was maintained by a homogenizer Ultra-Turrax T 25 Basic equipped with a S25N 25F shaft rotating at 12,000 rpm. 2.1.2. Methods 1 H NMR spectra were recorded on a Bruker AV300 spectrometer. IR analyses were carried out in transmission mode with a Shimadzu FT-IR spectrometer on KBr pellets with sample concentration of 1 wt%. Optical microscopy pictures of microcapsules were taken with a Leica DMLM microscope equipped with Color view camera and soft imaging system. A drop of the aqueous suspension placed between a glass plate and a cover slip was observed in transmission mode. scanning electron microscopy (SEM) analyses of the surface morphology were performed using a Jeol JCM 5000 microscope operating at 10 kV acceleration under moderate

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vacuum, thus avoiding the need for metallization of the samples. An aqueous suspension of microcapsules was cast on aluminum stubs and dried before observation by SEM. Particle size distribution was studied by small-angle light scattering using a Coulter 13320 laser-diffraction particle size analyzer. UV–vis absorption spectra were recorded with a Cary 50 Probe spectrophotometer of Hellma quartz cuvettes in 10 mm optical path. 2.2. Microcapsules preparation Isosorbide-based polyurethane microcapsules were prepared by interfacial polycondensation method using the dibutyltindilaurate catalyst according to previous reports (Giraud et al., 2005; Rodrigues et al., 2009). The polyurethane synthesis reaction is shown in Fig. 1. The synthesis process starts with an o/w emulsion involving two phases: a continuous phase containing 225 mL of water and 0.63 mmol of Polysorbate 80 (solution I); and a dispersed phase containing neroline and 7.08 mmol of MDI in 45 mL of cyclohexane (solution II). 7.08 mmol of isosorbide and 0.4 mL of SnDBDL were dissolved in 35 mL of the solution I, to form the solution III. The solution II was stirred with 190 mL of solution I in the reactor at room temperature for 5 min. Agitation was regulated, by a homogenizer Ultra-Turrax T 25, at a speed of 12,000 rpm in order to prepare an o/w emulsion. Then, the solution III was added and the speed was decreased to 500 rpm. The temperature was maintained at 60 ◦ C during 6 h (Azizi et al., 2011). The obtained microcapsules were separated by centrifugation (Gyrozen 416G) at a speed of 3000 rpm for 20 min, rinsed with cyclohexane to eliminate the residual monomer and non-encapsulated neroline and dried under vacuum. In order to study the shell structure, polyurethane microcapsules were prepared following the same procedure, without introducing neroline in organic phase (dispersed phase) and characterized with 1 H NMR and IR spectroscopies. 1 H NMR (300 MHz, DMSO-d6, ı in ppm from TMS): 9.64–9.562 (m, NH urethane); 8.4 (s, NH urée); 7.09–7.39 (m, Ar-H) 5.16–3.6 (H isosorbide + Ar-CH2-Ar). IR (cm-1): 3325 (m, N H asymmetric bending), 3050 (m, aromatic C H stretching); 2872 (s, aliphatic C H stretching); 1720 (m, C O stretching); 1410 (m, C C stretching); 1530 (s, C N bending); 1230 (m, C O stretching). 2.3. Application of microcapsules to textile finishing Impregnation was chosen as the most suitable process to apply neroline-loaded polyurethane microcapsules on textile fibers. Pure polyamide knitting (203 g m−2 ) was impregnated with encapsulated active product (Jing et al., 2011; Rodrigues et al., 2009). Microcapsules were suspended in bath containing acrylic cross-linking agent (RESACRIL BD CONC, 50 g L−1 ). Fabric was impregnated in the bath for 15 min. The impregnated textile was dried for 5 min at 100 ◦ C and thermally fixed at 120 ◦ C during 5 min. 3. Results and discussions 3.1. Preparation of the neroline-loaded microcapsules The preparation process of microcapsules consisted in two steps, as a first step, the organic phase containing the neroline perfume and the hydrophobic monomer (MDI) in cyclohexane was emulsified in water at room temperature. The Polysorbate 80 surfactant added in the aqueous phase is a hydrophilic emulsifier (HLB = 15) that causes the formation of an emulsion of the oil-in-water type (o/w). The full oil phase was stable with respect to coalescence. Creaming was prevented by keeping stirring at a low rotation rate. The second step is the polycondensation reaction that was

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Fig. 1. Synthesis reaction of polyurethane microcapsules shell.

started by addition of an aqueous solution containing the second hydrophilic monomer (isosorbide) in stoichiometric amount with respect to MDI and dibutyltindilaurate (SnDBDL) catalyst and Polysorbate 80, while the temperature was raised to 60 ◦ C. The solution III was homogeneous although SnDBDL is not soluble in water because DBDL was solubilized by the Polysorbate 80 micelles. Indeed the concentration of Polysorbate 80 (2.8 mM) was much larger than its cmc of 0.018–0.028 mM (Patist et al., 2000). Full conversion of the monomers was reached after 6 h polymerization at 60 ◦ C. The aqueous suspension of microcapsules was washed by centrifugation and dry microcapsules were recovered. Microcapsules could easily be re-dispersed in water by gentle mixing. 3.2. Chemical analysis of the neroline-loaded microcapsules Dry microcapsules were analyzed by IR and 1 H NMR spectroscopy in order to check against the polycondensation reaction and to determine the encapsulation rate of neroline. 3.2.1. IR analysis Dry microcapsules were mixed with KBr and pressed as pellets for recording the IR spectrum in transmission mode. Fig. 2 shows the IR spectrum of the loaded polyurethane microcapsules (MPUN), compared to spectra of pure polyurethane (MPU) and neroline. The spectrum of the microcapsules was the sum of subspectra of pure polyurethane and neroline. IR spectra did not show residual bands at 2270 cm−1 characteristic of the isocyanate group, which confirmed the full conversion of MDI monomer. In particular,

the well-resolved bands at 1257 and 1039 cm−1 , in the microcapsule spectrum corresponded, to the neroline C O C asymmetrical and symmetrical stretching vibrations, which confirmed that the perfume was successfully encapsulated. The sub-spectrum of the polymer was identical to that of pure polyurethane prepared by mass polycondensation of isosorbide and MDI. This showed that the amount of polyurea was not significant in the microcapsules. Indeed the presence of water during the interfacial polycondensation process opens the possible hydrolysis of the isocyanate groups into primary amines that form urea bonds upon their condensation with isocyanate. Polyurea is a side-product of polyurethane when water is present in the reaction medium. The formation of polyurea would not be disastrous anyway since the side reaction does not yield pure polyurea homopolymer but a mixed urea/urethane polycondensate by copolymerization of MDI with both isosorbide and the hydrolysis product of MDI. 3.2.2. 1 H NMR analysis Fig. 3 shows the 1 H NMR spectrum of the loaded polyurethane microcapsules, compared to neroline spectrum. The 1 H NMR spectrum of the loaded polyurethane microcapsules shows the characteristic peaks of the neroline: The peaks between 7.8 and 7.1 ppm were assigned to the aromatic protons, the peaks at 4.1 ppm and 1.4 ppm were attributed to the OCH2 and CH3 protons respectively. Quantitative comparison between the integral intensities of the polyurethane shell peaks and those of neroline was used to estimate a neroline encapsulation rate of 30%. 3.3. Morphology of the microcapsules

Fig. 2. IR spectra of the neroline, pure polyurethane (MPU) and loaded microcapsules (MPUN).

3.3.1. Optical microscopy Aqueous suspensions of the microcapsules were observed by optical microscopy at different magnifications. The obtained optical micrograph (Fig. 4) showed that the perfume microcapsules had a spherical shape and different sizes. The microcapsules were well-dispersed without significant agglomeration. The pictures at the highest magnification (100×) definitely revealed the internal structure of the microcapsules with a core-shell morphology. The clear oil droplets were surrounded by a thick layer of material appearing dark in the pictures. The pictures were characteristic of capsules having a shell with optical properties different of the internal oil phase. The edges of droplets of a simple oil-in-water emulsion use to appear as very thin lines separating oil and water in optical microscopy pictures. Even an out-of-focus picture does not show such a well defined shell around the oil droplets. Such layer appeared dark probably because the shell material strongly scattered light. Although the pictures did not allow to state whether the oil core was encapsulated to completion by the polymer shell, the polymer shells appeared as continuous membranes all around the oil droplets. The thickness of the polymer shell was not the same in all droplets: large droplets were encapsulated by a thicker polymer shell. This behavior was expected since the MDI monomer

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Fig. 3.

1

H NMR spectra (DMSO-d6, 300 MHz) of the neroline and loaded microcapsules (MPUN).

Fig. 4. Optical pictures of neroline-loaded microcapsules.

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interval between 1 and 100 ␮m, however in Rodrigues et al. (2008) works, the distribution was bimodal. The microcapsules mean size was 27 ␮m and 75% of the particles had a diameter lower than 34 ␮m. Hence, the PSD was in the range 1–50 ␮m considered as appropriate for the implementation of the microcapsules into a textile impregnation process (Madene et al., 2006). 3.3.3. Scanning electron microscopy (SEM) SEM pictures of the microcapsules clearly demonstrated the core-shell morphology of the particles. Thus, owing to the low boiling temperature of the oil (cyclohexane), both water and oil were evaporated upon drying the suspensions of microcapsules. Therefore, the microcapsules appeared as collapsed empty capsules (Fig. 6). Such observation showed that the mechanical strength of their walls was not enough for they could resist the drying shrinkage stress. Fig. 5. Particle size distribution of polyurethane-based microcapsules.

amount was higher in larger droplets, resulting in a larger amount of polymer material in the shell. 3.3.2. Particle size distribution Particle size distribution (PSD) of the perfume microcapsules was measured by small-angle light scattering (Fig. 5). The volumePSD showed unimodal distributions of particle sizes ranging in the

3.4. Application to microcapsule-impregnated fabrics Microcapsule deposition at the surface of polyamide fibers was performed by means of an impregnation process (Jing et al., 2011; Rodrigues et al., 2009). Adhesion of the microcapsules to the polyamide knitting was ensured by an acrylic cross-linking agent present in the bath and thermal curing at 120 ◦ C for 5 min. The microcapsules remained in the bath after impregnation was separated by centrifugation in order to quantify the non-fixed

Fig. 6. Scanning electron microscopy photographs of the microcapsules.

Fig. 7. Scanning electron microscopy photographs of textile impregnated with microcapsules.

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Fig. 8. SEM photographs of textile impregnated with microcapsules after washing cycles.

microcapsules. The impregnation yield was determined by the ratio of the fixed microcapsules and the initial quantity introduced in impregnation bath. So it was about 80% and this result was in the same range as found in literature (Monllor et al., 2007). The extent of microcapsules deposition was assessed by means of scanning electron microscopy observations. The presence of microcapsules adhering on impregnated textile was obvious. SEM micrographs showed the favorable adhesion of microcapsules to the fabrics and also confirmed the spherical morphology of the microcapsules (Fig. 7). However, during the impregnation process microcapsules tended to agglomerate and the microcapsules shape changed in comparison to their original shape in the dispersed state. The effect of cleaning cycles on impregnated textile substrates was studied, according to the ISO 105-C10 standard of 2010, in order to improve the lifetime of scent textiles. The washing time was for 15 min and the final rinse was for 5 min. A decrease of the amount of the microcapsules on the fabric after cleaning was observed. Nevertheless, microcapsules still remained on the textile substrate, even after 15 washing cycles. It was noted also that some microcapsules were broken and empty but still remained on the fabric as they were protected by neighboring fibers (Fig. 8). The amount of neroline in the impregnated textile was determined by gas chromatography confirming that the microcapsules remained loaded with perfume after washing cycles (Fig. 9). The neroline peak appears at 25 min. The resistance of microcapsules to washing has been evaluated by means of titrations of the neroline remaining on the textile

fibers upon application of repeated washing cycles (Fouda and Fahmy, 2011; Jabbari and Khakpour, 2000). The effect of the number of washing cycles on the concentration of fragrance inside the microcapsules in the impregnated textile substrate was assessed by UV–visible absorbance. After every washing cycle we used an adequate solvent for solubilize the remained encapsulated active product (neroline) in the textile substrate, and we study the result by UV visible, to make sure of the existence of neroline. In solution, the spectrum shows two absorption maxima at 262 and 272 nm which are characteristic of the neroline reference as shown in Fig. 10. The UV–vis absorbance spectra (Fig. 10) decreased in intensity as repeated washing cycles have been applied. The spectra were identical throughout the whole washing process, which showed that neroline and polyurethane were washed off simultaneously. This is again a strong indication of an efficient encapsulation of neroline inside the microcapsules. Fig. 11 shows the absorbance ratio variation (Ai /A0 ) at 272 ppm which is function of the number of washing cycles. Where A0 and Ai are respectively the absorbance of the extracted encapsulated neroline solution before washing and after i washing cycles. A slow decrease of neroline amount with respect to the number of washing cycles was observed (Fouda and Fahmy, 2011). The impregnated textile fabrics with perfume microcapsules showed high resistance to washing cycles compared with Rodrigues et al. (2008, 2009) works, where the resistance to dry cleaning was five cycles. A neroline loss of 10% was found after the first washing cycle. The loss of neroline was 40% after the fifth cycle and 70% after the twentieth cycle. This agreed with the characterizations

Fig. 9. Chromatograms obtained by gas chromatography of: (a) neroline and (b) textile substrates impregnated with microcapsules and subject to twentieth cleaning cycle.

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was only 10% after the first washing cycle and up to 30% of neroline remained on the fabrics after the twentieth washing cycle.

References

Fig. 10. UV–vis absorbance spectra of encapsulated neroline at different washing cycles.

Fig. 11. Amount of neroline present in textiles substrate according to the number of washing cycles.

of microcapsules by SEM that showed nice core-shell morphology of the microcapsules and an efficient encapsulation of neroline. 4. Conclusions Encapsulation is a good way to control fragrance release and to make more durable perfumed textiles. Isosorbide-based polyurethane microcapsules were produced by interfacial polymerization technique. Such microcapsules make use of the bio-sourced isosorbide in place of the conventional diols often used in polycondensation. The substitution of such diols for isosorbide kept the main favorable characteristics of polyurethane microcapsules manufactured by interfacial polycondensation. The particle size distribution of microcapsules showed a unimodal size distribution in volume, with an average particle size of 27 ␮m. The observation of microcapsules by optical microscopy showed the spherical morphology and the absence of agglomerates. The impregnation of textile fabrics with microencapsulated the odorant entity neroline was successful. SEM photographs confirmed the spherical shape of microcapsules and also an effective adhesion between microcapsules and textile fibers. The amount of neroline component decreased slowly when the impregnated textile substrates were subjected to washing cycles since the loss of neroline

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