Polysulfone/Vanillin Microcapsules for Antibacterial and Aromatic Finishing of Fabrics

Polysulfone/Vanillin Microcapsules for Antibacterial and AromaticFinishing of FabricsCinta Panisello, Brisa Pena, Guillem Gilabert Oriol, Magda Constantí, Tania Gumí,and Ricard Garcia-Valls*

Departament d’Enginyeria Química, Universitat Rovira i Virgili, Av. Països Catalans, 26, 43007 Tarragona, Spain

*S Supporting Information

ABSTRACT: Microencapsulation technology is being more and more applied in the textile industry because microcapsules canconfer additional properties to conventional fabrics. In this context, polysulfone microcapsules containing vanillin were prepared,and their morphology, thermal stability, and antibacterial properties against Staphylococcus aureus were assessed. Themicrocapsules were fabricated onto 100% cotton fabrics by a coating technique. The resistance of the coating to several washingcycles was studied, and the durability of the aromatic finishing was determined. Capsules were stable in the range between 20 and100 °C, and they inhibited the growth of the bacteria at 37 °C for, at least, one week. Most of the capsules added to the fabricwere flushed away between the first and second washing cycle; however, some capsules were still observed after the fifth washing.Finally, a survey was conducted in order to know how consumers perceived the aroma, before and after several washings. Surveydata was statistically analyzed, and a model was built, which allowed the probability of maintained aromatic finishing for specificwashing cycles to be predicted. Thus, this work sets the basis for further development of fabrics with antimicrobial activity andpleasant aromatic finishing based on polysulfone/vanillin capsules.

1. INTRODUCTION

Innovation is a key factor for the competitiveness of industries;thus, the development of high value-added products is anespecially interesting topic. In this context, microencapsulationtechnology is a growing area in many fields,1 among which wehighlight the textile industry. Fabrics with microcapsules notonly behave like conventional fabrics, but also have someadditional features, which depend on the encapsulated (core)material.2 Among the most promising applications we find theencapsulation of phase change materials (PCM) for providingclothes with thermo-regulating properties,3−14 perfumes forproducing clothes with long-lasting fragrance benefits,15−24

antibacterial agents,25−29 animal repellents,30,31 cosmetics,2,32

and others.33−36

Our research group has experience in microencapsulation. Inprevious works, we encapsulated vanillin inside polysulfone(PSf) microcapsules prepared by phase inversion precipitation,which is a method widely used for the preparation of capsulesby using this polymer.37−43 In addition, the products showedpromising results in terms of stability and encapsulationcapacity.37,44,45 The interest of these capsules lies on thespecial characteristics of both the wall and the core material.Polysulfone is one of the most used polymers for preparingmembranes and microcapsules because of its good mechanical,thermal and chemical properties.43,46 Vanillin is an importantaromatic aldehyde, in fact, it is considered to be one of the mostwidely appreciated flavor compounds. Furthermore, it exhibitsseveral bioactive properties47 such as antioxidant48,49 andantimicrobial activities against yeasts, molds50 and bacteria.51,52

In particular, we would like to emphasize the inhibitory effect ofvanillin against the growth of Staphylococcus aureus (S. aureus)53

which is one of the most common bacteria that often provoke

postsurgical wound infections.54 S. aureus may induce a varietyof diseases ranging from mild to severe illness.Thus, incorporating PSf/vanillin capsules to fabrics may

provide interesting properties to the textile. However, not onlyare the characteristics of the microcapsules are important butalso the way in which they are added to the fabrics is crucial.For this purpose several methods have been proposed andused,55,56 such as integration of the capsules into a coat-ing,3,8,10,57 printing,58 impregnation, padding or exhaustingbath,4,5,15,18,22,33,55 and grafting of the microcapsules to thefabrics with chemical links25,35,36 among others.19,26−28,59

The prepared polysulfone capsules are used for providingantibacterial and aromatic properties to fabrics. This area ofresearch is extremelly interesting for medical applications,because there are some infections, such as S. aureus, that can bespread through contact with fabrics used by an infectedperson.60 Thus, it is important to develop fabrics that inhibitthe growth of this bacterium. In addition, the aromatic finishingmay provide additional pleasant effects to the users.In this work, a simple method is proposed for providing

antibacterial properties and aromatic finishing to 100% cottonfabric, which could be used for medical applications. Theproperties are provided by incorporating polysulfone/vanillincapsules to the fabrics. For this purpose, capsules are producedand their morphological characteristics are investigated byscanning electron microscopy (SEM). In order to determinethermal effects on capsule stability differential scanningcalorimetry (DSC) is used. The inhibitory activity of

Received: December 27, 2012Revised: June 21, 2013Accepted: June 28, 2013Published: June 28, 2013

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encapsulated vanillin against S. aureus is determined bymodified agar-well diffusion technique.61 Capsules are adheredto fabrics by coating and their resistance to several washingcycles is studied. In addition, the durability of the aromaticfinishing is determined by means of an aroma perception testwhich data is statistically analyzed.

2. EXPERIMENTAL SECTION2.1. Materials. For microcapsules preparation the following

materials were used: Polysulfone (PSf, Sigma−Aldrich, Spain,transparent pellets of Mw = 16 000) was used as polymer.Solvent and nonsolvent were dimethylformamide (DMF,Scharlab, reagent grade ACS-ISO) and distilled waterrespectively. Vanillin (Acros organics, 99% pure) was used ascore material.For the antimicrobial test, S. aureus (CECT 794) was used as

the bacteria strain. Nutrient agar was prepared by mixing 15 gof agar−agar (powder for bacteriology, Scharlab), 5 g of beefextract (Scharlab), 10 g of meat peptone (Scharlab), and 5 g ofNaCl (Sodium chloride, reagent grade ACS-ISO, Scharlab) in 1L of distilled water.For the fixation of microcapsules on the fabrics (100%

cotton) a commercial coating, seitex100, was used. Laundrycycles were performed by using a commercial detergent (15−30% zeolites, 5−15% anionic, or non ionic surfactants).2.2. Microcapsules Preparation. An air atomizing nozzle

(nozzle diameter = 0.7 mm) was installed over a beakercontaining the precipitation bath. Air pressure was set to 2 barand the air flow at this pressure was 800 L/h. Figure 1 showsthe schematic diagram of the setup.

Polymeric solution was prepared 24 h before microcapsulesproduction, for ensuring complete dissolution of the polymer,and it was kept in a closed bottle in order to avoid their contactwith humid atmospheric air, which could cause polymerprecipitation. The polymeric solution microdroplets wereprojected into the precipitation bath, producing immediatelythe microcapsules. Finally, the product was collected byfiltration and kept into a desiccator for one day.2.3. Removal of Residual Solvent. Polysulfone/vanillin

capsules are contained a certain amount of residual solvent,DMF, which is toxic and thus, it needs to be removed. Previousinvestigations proposed a method for removing it withoutlosing vanillin.37 The method consisted of immersing thecapsules in an aqueous solution saturated with vanillin. Avanillin saturated solution was prepared by adding 2.5 g of

vanillin per every 100 mL of distilled water. A total of 1 g ofcapsules was added per every 100 mL of vanillin saturatedsolution, and the preparations were kept under stirring for 4days. Afterward, the product was collected by filtration, rinsed,and kept into a desiccator.37

2.4. Microcapsules Characterization. SEM was con-ducted by using a Jeol JSM-6400 Scanning Microscope workingwith a voltage between 15 and 20 kV. Samples of capsules weresputtered with gold, at 30 mA for 180 s, and afterward, theirsurface features were investigated. Moreover, some sampleswere cut by cryogenic breaking and their cross sections wereobserved by SEM.62,63

In order to determine thermal influence on microencapsu-lated products, calorimetric curves were obtained by using aMettler-Toledo 822 DSC (Mettler-Toledo Inc., Schwerzen-bach, Switzerland). DSC curves were obtained at 10 °C/minheating rate in a nitrogen atmosphere. The pan type used was astandard aluminum crucible with a 40 μL volume and sealcapacity to avoid loss of material. The weight of the sampleswas approximately 8 mg. Capsules behavior in the rangebetween 20 and 100 °C was assessed (standard laundrytemperature range). In addition, pure vanillin and polysulfonewere analyzed separately for comparison.

2.5. Antibacterial Activity. The aim of this study was toasses if polysulfone/vanillin microcapsules can inhibit thegrowth of the bacteria, although the active ingredient isentrapped in a polysulfone capsule.Study of the inhibitory activity of vanillin against S. aureus

was carried out by modified agar-well diffusion technique.60

Petri dishes were filled with a mixture of 100 μL of standard 108

Colony Forming Unit (CFU)/mL of S. aureus and 15 mL ofnutrient agar. Once the medium was solidified, holes withdiameters of 5 mm were made using a sterile Pasteur pipet.After that they were filled either with 45 μL of vanillin in

solution (1.25, 2.5, 5, and 10 wt % vanillin/ethanol) or 0.1 g ofsolid vanillin or 0.1 g of PSf/Vanillin capsules. Milli-Q waterand ethanol were used as control solutions. Vanillin/ethanolsolutions with different concentrations were used to determinethe minimum amount of vanillin necessary to detect a clearzone around the hole, and according to preliminary results onthis work, it was determined that 0.1 g of capsules, whichcontains 8 mg of vanillin, was an adequate amount of productfor the analysis. Pure solid vanillin was assessed as reference,only to determine if vanillin inhibited the growth even being ina solid state; thus, the total amount of vanillin is not important.The plates were incubated at 37 °C for 1 week. The

inhibitory activity of vanillin against S. aureus was detected asclear zones around the holes, which were measured daily for 1week. It is important to point out that the main goal of theseexperiments was not to compare, neither quantify, theinhibitory activity among the different preparations. Inhibitiondiameters were measured in order to check if the inhibitoryeffect was sustained on time. However, any comparison was notpretended. Thus, we did not consider necessary to use the sameamount of vanillin in the tests as far as our aim was, solely, toassess if polysulfone/vanillin capsules, even being vanillinencapsulated, can effectively inhibit the growth of the bacteriafor a determined period of time.

2.6. Adhesion of Microcapsules to Fabrics. Cottonfabric samples were cut in pieces of (160 ± 2) × (190 ± 2)mm2. The method which was used for attaching themicrocapsules to the fabric was an adaptation of a previouslydescribed coating technique.10 Nevertheless, some modifica-

Figure 1. Schematic diagram of the atomization setup.

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tions in the described technique were performed, in order toavoid blocking the microcapsules pores with the coating agent.Thus, in order to stick the capsules to the fabrics the procedurebelow was followed. First, the fabrics were coated withseitex100, by using a casting knife providing 50 μm thickfilms, which was pushed by an applicator (K-Pain applicator,United Kingdom). Second, a layer of capsules was placed on atray. Finally, every fabric was introduced in the tray whichcontained the capsules. Fabrics were deposited allowing itscoated side to be in contact with the layer of capsules. Slightpressure was exerted in order to facilitate the adhesion of thecapsules to the coating. This procedure ensured that themaximum number of capsules per area of fabric was attached.2.7. Resistance of Coating to Washings. The resistance

of the coating of capsules was determined by exposure of thefabric samples to repeated washing cycles, which wereconducted in a commercial washing machine (Bosch maxxWFO-2063). According to ASTM D2960-05 (Standard TestMethod of Controlled Laundering Test Using Naturally SoiledFabrics and Household Appliances), the load weight was fixedto 3 kg. Fabrics were washed at 30 °C with a washing programset for mixed fabrics. Washing was performed for 15 min,rinsing for 10 min, and spinning for 10 min. That program wasselected in order to be as close as possible to the StandardNormal Home Laundry Test Conditions fixed by the AmericanAssociation of Textile Chemists and colorists (AATCC). Fivewashing cycles were performed. Pieces of fabrics, before andafter each washing cycle, were observed by SEM, following thesame procedure described for the observation of capsules. Thenumber of capsules/cm2 fabrics was determined by analyzingthe images with freeware Image-J 1.46r. Finally, sputtering ofthe samples with carbon instead of gold, allowed performing anelemental microanalysis in order to elucidate if some of theparticles observed in the samples were really polysulfone/vanillin capsules.2.8. Aroma Durability. A survey was designed in order to

assess how the population perceived vanillin aroma in fabricscoated with PSf/vanillin microcapsules. A jury of threevolunteers was selected in order to have reproducibilityamong the results and to include different smelling sensitivities,since smelling is a sense which differs strongly amongpopulation. This jury was asked to rate the aroma intensityfor each piece of fabric, before washing and also after eachwashing cycle.Five washings were performed and for each one, five different

fabric samples were assessed. The variables studied aresummarized in Table 1. These were the sample number,

which ranged from the first to the 25th piece of fabrics; theobserver, which ranged from the first person to the third; thewashing cycle, which ranged from no washing to five washings;the aroma intensity, which ranged from not detecting anyaroma (0), to slightly detecting it (1) to smelling it with high

intensity (2); and the aroma detection, which ranges from notdetecting any aroma (0) to detect aroma (1).The survey stated two main hypotheses, which were

validated for their statistical significance for a confidenceinterval of 95% against their null hypotheses. This confidencelevel indicates a 95% of probability of being right with theconclusions extracted. In order to make the statistical datatreatment and make the hypothesis contrast, the statisticalsoftware JMP Pro 9.0.3 from SAS Institute Inc. was used.The first null hypothesis stated that all the observers perceive

the same aroma intensity. The alternate hypothesis was that theobservers do not perceive the same aroma intensity. Thus, thefactor assessed was the observer and the response assessed wasthe aroma intensity. To validate this hypothesis, the p valueobtained from the Pearson chi-square test was comparedagainst the established confidence interval and the data wasrepresented throughout a mosaic plot, as both factor andresponse variables were categorical.The second hypothesis stated that the washing cycles

influence the aroma intensity. Thus, in this case, the factorassessed was the washing cycle and the response variable wasthe aroma intensity.Finally the correlation between the aroma detection in a

fabric and the number of washings was modeled, in order to beable to predict the probability of smelling vanillin in fabrics afterbeing subjected to different number of washings. Logisticregression was used, since the independent variable wascontinuous and the dependent variable was categorical. Thelogistic plot was obtained fitting the poll’s data in a typicallogistic equation as shown in eq 1.64

=+ +P y( )

11 eax b (1)

3. RESULTS AND DISCUSSION3.1. Microcapsules Production and Characterization.

Microcapsules were successfully prepared by phase inversionimmersion precipitation method. Figure 2 shows an image of acapsule, together with surface and cross section details.Mean size of the capsules was calculated from ImageJ analysis

of several micrographs. A total of 300 capsules were measuredand results showed diameters between 2.5 and 50 μm.Cross-section structure of the capsules presented big voids

along the whole wall thickness and a big central void (Figure2b). The surface of the capsules was porous, which allowed therelease of vanillin to the surrounding medium (Figure 2c).Previous studies demonstrated the encapsulation capacity anddetermined the release rate in polysulfone/vanillin capsulesprepared by the same procedure that has been used in thepresent work.37,45

Figure 3 summarizes already published results about vanillinand DMF release capacity of the capsules, before and after theDMF removal treatment. It can be observed that 1 g ofcapsules, introduced into 80 mL of distilled water after theirproduction, released a maximum of 600 ppm of vanillin and500 ppm of DMF approximately. However, after undertaking aDMF removal treatment, DMF release was not detected,whereas vanillin release increased. This meant that thetreatment succeeded in removing the DMF, and in addition,it increased vanillin content in the product. On the basis ofvanillin maximum release, it was estimated that the vanillincontent in the capsules before treatment was 48 mg of vanillinper gram of capsules. After vanillin treatment, the estimated

Table 1. Variables Assessed

name type values

sample number categorical 1−25observer categorical 1−3washing cycle continuous 0−5aroma intensity categorical 0−2aroma detection categorical 0−1



amount of vanillin per gram of capsules was 80 mg. However, itwas possible that this extra vanillin could have beenincorporated over the capsule surface. If it was the case, theperfume would not be protected, and therefore, it could bereleased immediately. To elucidate if vanillin crystals werelocated over the capsule surface after the vanillin treatment,XRD analysis was performed. Results showed that the extravanillin was not in the surface; thus, it had been absorbed intothe capsule porosity.37

DSC results for pure vanillin, polysulfone polymer, andpolysulfone/vanillin capsules (after DMF removal treatment)are shown in Figure 4.

As it can be observed, in the case of vanillin, an endothermicpeak was encountered around 85 °C. Integration of the peakarea gave a value of −138.27 J/g. Phase change data found inthe literature showed that this peak corresponded to themelting of the compound, which was reported to be at 81.5 °Cbeing the melting heat −136.91 J/g.65 At the same temperature,a peak was appreciated in PSf/vanillin capsules, which waslogical as they contained vanillin. However, the polymer did notsuffer any changes in the range of temperatures assessed; thiswas because its glass transition temperature is at 185 °C.66

Thus the wall of the capsules can resist temperaturesconsiderably higher than those used in conventional washings.On the other hand, vanillin melting is not expected to have any

Figure 2. SEM images of (a) microcapsules sample general view, (b) cross-section of a capsule, and (c) surface magnification of a capsule.

Figure 3. From left to right: Vanillin release before (○) and after (●) vanillin treatment; DMF release before (○) and after (●) vanillin treatment.

Figure 4. Calorimetric curves for vanillin, polysulfone, and microcapsules.




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negative effect on capsules properties, despite the fact that itcan increase the release rate.3.2. Antibacterial Activity. As vanillin has previously

shown significant inhibitory activities against S. aureus,53 in thisinvestigation we have tested the antimicrobial effect of PSf/Vanillin microcapsules. Figure 5 shows the inhibitory activity ofvanillin in different states against S. aureus. Images wereobtained one day after the beginning of the incubation process.

As may be seen in the left image of Figure 5, significantinhibitory effects were observed in the most concentratedvanillin/ethanol solutions. Similar results had been previouslyreported.53 From the left image of Figure 5 we concluded that,in order to observe clear holes around the well, a minimum of1.8 mg of the active ingredient were required. According to thisresult and in order to be sure that there was enough vanillin toinhibit the growth, it was decided to use 0.1 g of polysulfone/vanillin capsules in the test, which corresponds approximatelyto 8 mg of vanillin.As it shows the right image of Figure 5, when vanillin was

added in a solid state or in an encapsulated form, significantinhibitory activities against S. aureus were observed.With the aim to determine for how long could last the

inhibitory activity of vanillin against S. aureus, it was decided tostudy the inhibitory effect over time, measuring daily the clearzones until completing a week. Table 2 shows the results.

The aim of Table 2 is not to compare, neither to quantify,the inhibitory effects of the different preparations. Its purpose isto show that, in all the cases, antibacterial activity was detectedand, in addition, it was sustained on time. However, the mostinteresting data are the inhibition diameter of polysulfone/vanillin capsules. It shows that polysulfone/vanillin capsulescould inhibit the growth of the bacteria, even being theantibacterial agent entrapped into a polymeric matrix. On theother hand, inhibition diameter barely changed on time, thus,

capsules effectively inhibited S. aureus growth for at least 1week. Therefore, PSf/vanillin microcapsules presented promis-ing results for the inhibition of S. aureus growth.

3.3. Addition to the Fabrics and Durability. Figure 6shows images of the fabric with capsules added, before the

laundry and after the first, second, third, fourth or fifth washingcycles respectively. As it can be observed, the density ofcapsules suffered an important decrease after the secondwashing cycle.Although several rounded particles were observed in figures f,

g and h, they were not PSf/vanillin microcapsules. This wassuspected by their little size and aggregate formation. Besidestheir different appearance, the hypothesis was confirmed by

Figure 5. Inhibitory activity of vanillin against S. aureus..

Table 2. Inhibitory Effect of Vanillin in Different States overS. aureus

inhibition diameter (cm)

days 10 wt % 5 wt % solid vanillin PSf/vanillin mcs

1 2.10 ± 0.30 1.70 ± 0.30 1.40 ± 0.20 0.95 ± 0.202 2.00 ± 0.20 1.75 ± 0.40 1.30 ± 0.20 0.95 ± 0.103 2.10 ± 0.10 1.75 ± 0.20 1.30 ± 0.10 0.95 ± 0.104 2.10 ± 0.30 1.80 ± 0.50 1.30 ± 0.40 0.93 ± 0.105 2.20 ± 0.50 1.75 ± 0.10 1.30 ± 0.40 0.95 ± 0.106 2.10 ± 0.10 1.75 ± 0.20 1.30 ± 0.10 1.00 ± 0.507 2.20 ± 0.10 1.75 ± 0.20 1.30 ± 0.20 0.95 ± 0.10

Figure 6. SEM images from (a) microcapsules, (b) fabrics, (c) fabricswith microcapsules before washing, (d) fabrics with microcapsulesafter 1st washing, (e) after 2nd washing, (f) after 3rd washing, (g) after4th washing, and (h) after 5th washing.





elemental analysis. Figure 7 shows a detailed image of theselittle particles encountered after washing, together with a PSf/vanillin capsule. The framed areas were microanalysed.In Figure 7a, a polysulfone capsule with diameter 33.42 μm is

observed. Elemental composition of its surface area was: 75.07wt % carbon, 17.42 wt % oxygen, and 7.50 wt % sulfur. Thepresence of sulfur was attributed to polysulfone. On the otherhand, Figure 5b shows an aggregate of particles with diameter2.76 ± 0.50 μm. The elemental analysis detected 42.81 wt %carbon, 35.97 wt % oxygen, 1.50 wt % sodium, 5.18 wt %aluminum, 6.83 wt % silica, and 7.70 wt % calcium. Sulfur wasnot detected, thus those aggregates could not be polysulfonecapsules and otherwise they should be residual detergent.Detergent composition indicated a 15−30 wt % in zeolites(aluminicosilicate minerals of alkali and alkaline metals), whichjustified the finding of these elements in the fabrics afterlaundry. Table 3 summarizes the number of capsulesencountered per cm2 in each sample, together with theirmean diameter.

The number of capsules decreased every washing cycle. Inaddition, another important fact was observed: smaller capsulesresisted more washing cycles. Thus, maybe durability of thecapsules in fabrics could be improved by adjusting micro-capsules diameter to 10 μm. This could be achieved by usingmore precise nozzles, but it was not in the scope of the presentwork. Correspondence between % of microcapsules encoun-tered and the weight loss measured after every washing cycle isshown in Figure 8.As it can be observed, the main loss of weight happened

during the second washing cycle; after that no significantchanges were detected. Microcapsules density data, besides thelarge standard deviation, showed the same trend in its meanvalues. Maximum weight loss was 66.16 ± 4.75%, and it wasacquired after the second washing cycle, after that the weightloss curve reached a plateau. In the case of capsules, most ofthem were lost during the first and second washing cycles, but

no plateau was reached, capsules are still being lost in the third,fourth and fifth washing cycles. It was logical that the loss ofcapsules does not affect significantly the weight of the samples,because of their low density: 144 kg/m3.45 In addition, newmaterials (zeolites) attached to the fabrics. However, we thinkthat the main weight changes are due to the binder, seitex100,which was used to attach the capsules. Thus, most of the binderis lost during the first and second washing cycle, but probably athin layer of binder, the bottom one, which is in direct contactwith textile, may remain for longer time maintaining somecapsules stuck to fabrics.

3.4. Odor Durability. Each one of the three observersassessed the aroma intensity perceived for each fabric sampleafter each washing cycle. The results obtained from the plot areavailable as Supporting Information. It must be noticed that,before the first washing cycle, all of the observers agreed that allof the samples released a strong vanillin aroma, thus scoring avalue of 2 in terms of aroma intensity. These observations weretaken into account when building the poll database used toperform both hypothesis contrast and when building the modelto predict the probability of aroma release after a certainnumber of washing cycles.The first hypothesis testing was performed for all three

observers. Thus, a p value of 0.0393 was obtained from thePearson chi-square test. As this value was smaller than theestablished significance level of 0.05, the null hypothesis wasrejected, and it was concluded that there existed differences inthe aroma perception among the three observers. However,when comparing the second observer with the third observer, ap value of 0.7910 from Pearson chi-square test was obtained.This indicated that both observers had the same olfactionsensibility. This assessment gave robustness to the modelingdone, since survey data was recorded from people with differentolfactory sensibilities. Thus the model proposed below is morerepresentative of the whole population. This conclusion can beeasily observed from Figure 9.The second hypothesis was validated against a confidence

interval of 95%, showing that there was a statistically significantcorrelation between the perfume release of a fabric and thenumber of washing cycles. In fact, this correlation was valid fora 99.99% confidence interval as it had a p value obtained fromchi-square test smaller than 0.0001. Validation of thishypothesis allowed correlating the number of washing cycleswith the duration of the aromatic finishing. If no statisticalcorrelation had been found, it would have meant that the aromadisappeared because of some other factor, which had not beenconsidered in this experimental design. After the hypothesis

Figure 7. Microanalyzed areas for (a) polysulfone/vanillin capsule and (b) particle aggregate.

Table 3. Density and Mean Diameter of CapsulesEncountered after Each Washing Cycle

washing cycles microcapsules/cm2 diameter range (μm)

0 110000 ± 18000 2.5−401 79000 ± 18000 2.5−282 14000 ± 1100 2.5−243 12000 ± 4900 2.5−284 2900 ± 460 2.5−175 1900 ± 460 2.5−13




validation, a model was built in order to quantify thisrelationship.The data obtained from the survey (Table 2) was used to

obtain logistic regression, which enabled us to obtain theprobability function. The model was built using the number ofwashing cycles as the independent variable and the intensity ofaroma as the dependent variable. However, the a and b functionparameters obtained from eq 1 showed that these parameterswere not statistically significant, since their p value was 0.9882when there was a slight level of smelling (1) and the p valuewas 0.9858 when there was an intense level of smelling (2).This suggested that more poll data from both levels wasrequired in order to build a significant model. Therefore, theslight intensity of the smelling (1) and the high intensity ofsmelling (2) values were combined to create new categoricalvariable called aroma detection. This variable recorded with a 0value if no smelling was detected and with a 1 if smelling wasdetected. Therefore, a new model was build using the numberof washing cycles as the factor, and the aroma detection as theresponse variable. This model showed a statistical significanceof 99.99% with a p value of 0.0001. Moreover, a and b valuesfrom eq 1 showed a p value of 0.0001 for both equationparameters. This meant that both parameters were statisticallysignificant for a confidence level of 99.99%. The model was alsotested in order to see if there was any lack of fit, showing for aconfidence interval of 95% a p-value obtained from F-test of

0.0727, which suggested that the model had no lack of fit forthe data gathered. Equation 2 describes the probability of afabric to keep its aroma after performing a certain amount ofwashing cycles.

=+ − −probability of smelling

11 e(1.631 washings 4.792) (2)

The model was validated against the experimental data and,as it can be observed in Figure 10, it fit well with the sample

data. A black line plots the model fit equation that representsthe whole population, while a gray line plots the data obtainedfrom the survey sample.This model was useful since it allowed the determination of

the probability to maintain fabrics perfumed for any washingtime. Finally, according to the validated model, we couldpredict that the probability of maintaining the aroma after twowashing cycles was 82%, whereas after the third and the fourthwashing cycles the probability was only 48% and 15%respectively.

4. CONCLUSIONSThe aim of the work was to propose and asses a method forproviding a 100% cotton fabric of antimicrobial and aromaticproperties through a microcapsules coating.

Figure 8. Correspondence between microcapsules/cm2 encountered and the weight loss measured after every washing cycle.

Figure 9. Mosaic plot showing the relationship between each observerand the smelling intensity perceived.

Figure 10. Validation of the model against survey data.






Microcapsules were successfully prepared and DSC con-firmed vanillin presence in them, besides determining that thewall did not suffer any changes due to heating in a rangebetween 20 and 100 °C. In addition, antimicrobial activity ofthe capsules against S. aureus was confirmed by the results ofthe modified agar-well test, which showed that capsulesinhibited the growth of the bacteria during, at least, 1 week.Afterward, microcapsules were added to the cotton fabric,

and their resistance to several washing cycles was investigated,together with the aroma durability. Results showed that over50% of the capsules were lost after two washings, but smallercapsules (around 10 μm) remained longer, still appearing afterthe fifth washing. Aroma durability was determined by aperception survey and the statistical analysis of the dataconcluded there was a correspondence between durability ofthe aroma and the washing cycle. To predict the probability ofmaintaining the aroma after different washing cycles a modelwas obtained, which was validated and allowed the determi-nation of the probability to maintain fabrics perfumed for anywashing time.This works sets the basis for further development of fabrics

with antimicrobial activity and pleasant aromatic finishing basedon polysulfone/vanillin capsules. Further work in this area willbe focused on narrowing the size distribution of the capsules,improving their adhesion in order to increase capsulesresistance through washings and determining the antimicrobialproperties of the finished fabrics before and after severalwashings.

■ ASSOCIATED CONTENT

*S Supporting InformationTable showing the results of the aroma durability survey isprovided. This material is available free of charge via theInternet at http://pubs.acs.org.

■ AUTHOR INFORMATION

Corresponding Author*Phone: +34977559611. Fax: +34977559621. E-mail: [email protected].

NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTS

All authors would like to acknowledge “Universitat Rovira iVirgili” for research facilities. We are also grateful to“Departament d’Economia i Coneixement” de la “Generalitatde Catalunya” in its department of Support to Universities andResearch (SUR del DEC), together with Fons Social Europeu(FSE) for funding Cinta Panisello and to Ministerio de AsuntosExteriores y de Cooperacion (MAEC) y de la Agencia Espanolade Cooperacion Internacional (AECI), for their funding toBrisa Pena.

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Polysulfone/Vanillin Microcapsules for Antibacterial and Aromatic Finishing of Fabrics