Environmentally benign 100% bio-based oligoamide microcapsules

Accepted Manuscript Title: Environmentally benign 100% bio-based oligoamide microcapsules Authors: E.M. Soares-Latour, J. Bernard, S. Chambert, E. Fleury, N. Sintes-Zydowicz PII: DOI: Reference:

S0927-7757(17)30330-8 http://dx.doi.org/doi:10.1016/j.colsurfa.2017.04.008 COLSUA 21518

To appear in:

Colloids and Surfaces A: Physicochem. Eng. Aspects

Received date: Revised date: Accepted date:

19-1-2017 5-4-2017 5-4-2017

Please cite this article as: E.M.Soares-Latour, J.Bernard, S.Chambert, E.Fleury, N.Sintes-Zydowicz, Environmentally benign 100% bio-based oligoamide microcapsules, Colloids and Surfaces A: Physicochemical and Engineering Aspectshttp://dx.doi.org/10.1016/j.colsurfa.2017.04.008 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Environmentally benign 100% bio-based oligoamide microcapsules

E.M. Soares-Latour1, J. Bernard2, S. Chambert3, E. Fleury2 and N. Sintes-Zydowicz1*

1

Université de Lyon, IMP, CNRS 5223, Université Lyon1, Villeurbanne, F-69622, France

2

Université de Lyon, IMP, CNRS 5223, INSA de Lyon, Villeurbanne, F-69621, France

3

Université de Lyon, ICBMS, CNRS 5246, Chimie Organique et Bioorganique, INSA de

Lyon, Villeurbanne, F-69621, France

Graphical abstract

Highlights   

Biobased PA 4,4 microcapsules are prepared via interfacial polycondensation The microcapsules membrane is mainly composed of PA 4,4 oligomers Cotton and nylon textile fabrics are successfully impregnated by PA 4,4 microcapsules



The thermal degradation of PA 4,4 microcapsules occurs in the range 200 – 350°C

1

Abstract Our aim was to investigate the synthesis of alternative bio-based microcapsules, offering similar thermal and mechanical properties as formaldehyde-based ones and being directly applicable to the textile field. In this prospect, oligoamide microcapsules were generated by interfacial polycondensation from two bio-based monomers: succinyl chloride and 1,4butanediamine. Optimization of the process afforded the preparation of monodispersed microcapsules with a d(0.5) diameter of 3 µm, exhibiting excellent stability over time. The expected amide groups in the microcapsules membrane were confirmed by FTIR, whereas SEC analysis suggested that microcapsules membrane was composed of oligoamide 4,4 ̅̅̅̅𝑛 around 5. The chemical structure of model plane membranes prepared by chains with a 𝐷𝑃 interfacial polycondensation with jojoba oil as organic phase, was investigated by

13

C NMR

and MALDI-TOF. The plane membranes appeared composed of PA 4,4 oligomers, in accordance with the information provided by SEC. The microcapsules exhibited a thermal degradation occurring in the range 200 – 350°C, and a large melting endotherm peak centred on 200°C. Thanks to the accurate thermal and mechanical properties of oligoamide 4,4, those microcapsules loaded with jojoba oil were successfully applied on cotton and polyamide fabrics which were submitted to laundering and rubbing tests.

Keywords: Microcapsules, Interfacial polycondensation, Polyamide 4,4, Bio-based monomers, Cosmetotextiles

Introduction The growth of the textile industry has been significantly stimulated over the last decade by the development of smart textiles [1-4]. Intelligent fabrics span over a wide panel of applications 2

ranging from fashion, sport, protecting clothing, cosmetics or healthcare. These research fields have strongly benefited from the association of microencapsulation and fabrics technologies [5,6]. Fixation of microcapsules into textiles substrates brings new properties to the fabrics. For example, microcapsules can indeed be loaded with fragrances [7], skin softeners [8], dyes [9,10], thermochromic molecules [11], antimicrobial agents and drugs [12], phase-change materials [6] or insect repellents [13]. Microcapsules can be produced through physical or chemical techniques [14]. In regard to textile applications, these cargos must fulfil several requirements in terms of dimensions (ideal sizes ranging between 1 and 40 microns), thermal stability (up to 150°C) and mechanical robustness in order to withstand the conditions of deposition on textile and washing cycles. Such requirements are routinely met with cross linked microcapsules obtained by in situ polycondensation of formaldehyde and urea or melamine [15, 16]. However, the recent classification of formaldehyde as a substance of very high concern by REACH, the EU’s main framework for chemical regulation, has lately darkened the future of melanime-formaldehyde microcapsules. Alternatives are greatly sought after. In the quest for credible alternatives to this encapsulation technology, the conception of microcapsules, displaying appropriate thermal and mechanical properties is therefore highly desired. In this context, polyamides, biocompatible polymers, exhibiting excellent thermal and mechanical properties (melting temperature comprised between 170 and 320°C, tensile strength ranging from 55 to 100MPa, and tensile elongation up to 300%) are promising candidates to build microcapsules for textile applications. Routes to microcapsules having walls made of polyamide have been previously described [17-23]. However, in spite of their potential environmental and economic impact, microcapsules from bio-based monomers have been only scarcely described so far [24-26] and to the best of our knowledge, polyamide microcapsules from bio-based monomers has not

3

been reported yet. In this general context, we present herein a rather simple and straightforward method for the construction of mechanically and thermally stable oligoamide 4,4 microcapsules from renewable resources through interfacial polycondensation in jojoba oil/water emulsion conditions and subsequently investigate the suitability of the resulting micro-containers for the conception of smart cotton and nylon fabrics through deposition by padding.

Materials and Methods Chemicals 1,4-butanediamine (DAB) and succinyl chloride (CS) were purchased from Aldrich. Jojoba oil (Olvea, France) was kindly purchased by Euracli (Chasse sur Rhône, France) and the copolymer poly(maleic anhydride-st-methyl vinylether - MAMVE) with a ̅̅̅̅̅ 𝑀𝑤 equal to 220 000 g/mol, was purchased from International Specialty Product (USA). All reagents and products are commercially available and were used as received. The chemical structure of jojoba oil was examined by

13

C NMR in CDCl3 and ESI-MS

(SUPPORTING INFO). Jojoba oil chemical formula is the following:

CH3 (CH2)7

CH

CH

(CH2)n

C

O

(CH2)m

CH

CH

(CH2)7

CH3

O

Quantitative

13

C NMR spectrum indicated an average number of methylene groups equal to

29.3, whereas LSIMS pointed out the presence of various species corresponding to (n+m) values comprised between 17 and 27.

Microcapsule synthesis 4

The copolymer poly(maleic anhydride-st-methyl vinyl ether - MAMVE), used as surfactant was first dissolved in deionized water at 80°C and hydrolysed with aqueous ammonia in order to reach neutral pH. At this pH value, MAMVE presents a proportion of anhydride groups equal to 49 mol% (determined by

13

C NMR) in accordance with its two acidity constants

(pKa1 = 1.8 and pKa2 = 6.6). The obtained aqueous solution (75 mL) was then put into a double jacket reactor allowing the set of the system temperature at 10°C at which hydrolysis of acyl chloride groups is limited. The emulsion was prepared by mixing the aqueous phase and an organic solution composed of jojoba oil (15 mL) and succinyl chloride (0.015 mol, 2.35g) with a IKA S25N-18G ultraturrax during 5 minutes. After this emulsion step, the ultraturrax was turned off and the 1M aqueous solution (75 mL) of 1,4-butanediamine (0.075 mol, 6.67g) was slowly added at a controlled speed (550 mL/h) thanks to a syringe pump, under blade stirring. At the end of the diamine addition, the stirring was maintained for 15 minutes in order to ensure the formation of the PA 4,4 membrane. Half of the dispersion was left to age at room temperature in order to characterize the influence of time on the dispersion. The other half was reserved for the different analyses.

Application of microcapsules to fabrics Microcapsules impregnation of textile fabrics as well as the rubbing and laundering tests were realized in IFTH, Ecully (France). Two kinds of microcapsules suspensions were applied to the textile substrates, according to the addition or not of a binder. Different commercial formaldehyde-free binders were used: Sanitized T-99-19 (supplied by Clariant), Protorez FFO 01 (Tanatex Chemicals), and Perapret PU New and Fixapret NF (BASF). These binders were selected according to their technical properties (SUPPORTING INFO). Each binder was dissolved in water (5 wt%, except Sanitized 1 wt%), and the aqueous solution of binder was then added to the microcapsules suspension to reach a final concentration of binder in the 5

coating suspension equal to 0.25wt% (except Sanitized 0.05 wt%). The microcapsules suspensions were then applied to nylon and cotton fabrics using a MATHIS type foulard machine. The same microcapsules suspension batch was used for all the impregnations. The area weight of nylon and cotton fabrics was equal to 140g/m2. Fabrics had been chemically bleached before microcapsules application. The foulard machine with two rollers was used at 2 m/min of working speed and 1 bar of pressure of rollers. A fabric of 3.5 cm width and 12 cm length was passed through the bath containing the microcapsules suspension and subsequently through squeeze rollers. The padded fabrics were dried in a ZIMMER oven at 120°C for 3 minutes. For the laundering durability test, the microcapsule-coated fabrics were treated for 1 hour at 40°C, with an ECE standardized washing and a spin-drying speed of 800 rpm. Samples were dried on a horizontal surface. All samples were examined by SEM after one cycle. For the rubbing procedure, samples were subjected to rubbing using a standard Crockmeter device. They were rubbed for 10 cycles of 10 seconds by a finger covered with a cotton fabric sample at a pressure of 10 N. All samples were examined by SEM after rubbing.

Model Synthesis PA 4,4 membrane model 10 mL of a jojoba oil solution containing succinyl chloride (8 mmol) was slowly and carefully added to 50 mL of an aqueous solution of 1,4-butanediamine (40 mmol) at room temperature in a flat bottom reactor. After 12 hours of reaction, the membrane was recovered and dried at 50°C to constant weight.

Synthesis of model PA 4,4 fragments

6

Small fragments of polyamide 4,4 were synthesized for characterization concerns (Scheme 1). While using standard organic chemistry protocols, the synthesis of those fragments are scarcely described in the literature, probably due to the high chemical functionalization which produces compounds poorly soluble in regular solvent systems requiring simple extraction or rinsing as purification protocols. Briefly, n-butylamine (1) was reacted with succinyl chloride (2) to give the diamide 3, bearing two unfunctionalized ends. In order to produce fragments resulting from hydrolysis of the acyl chloride functions during the course of the polymerization reaction, compounds having two carboxylic acid functions were also produced. Starting from 1,4-diaminobutane (4), the opening of succinic anhydride (5) gave us a direct access to the corresponding carboxylic diacid 6 in reasonable yield. The access to the next generation of compounds required the synthesis of a protected intermediate of 1,4-diaminobutane (4 ) with a rather acid and basic stable mono protection of only one amino group. To do so, the mono Boc-protected amine 7 was first obtained using Boc anhydride. The second amino function was then Cbz protected before removing the Boc group using TFA, giving access to the desired Cbz protected amine 8 [27]. Succinyl chloride (2) was reacted with more than two equivalents of the mono protected amine 8 and the obtained intermediate was directly hydrogenated and then reacted with succinic anhydride (5) in water to give the diacid 9 in a 10% overall yield. The first of these three steps is mainly responsible for the observed modest yield.

Synthesis of Compound 3 To a solution of succinyl chloride (2.2 mL; 20 mmol) in dichloromethane (20 mL) and triethylamine (6.13 mL; 44 mmol) was added a solution of n-butylamine (4.0 mL; 40 mmol) in dichloromethane (50 mL). The reaction is stirred for 2 hours at RT before being filtered. The filtrate is then extracted twice with a HCl solution (0.01 M) and twice with a NaOH

7

solution (0.01 M). The organic phase is then dried with sodium sulfate and solvents are evaporated to give compound 3 (1.51 g; 6.6 mmol; 33%) as a slightly orange powder. 1H NMR (300 MHz, CDCl3)  0.90 (t, 6H, 2xCH3), 1.22 (sextet, 4H, 2xCH2-CH2-CH3), 1.47 (quintet, 4H, 2xCH2-CH2-CH2), 2.50 (s, 4H, 2xCH2-CO), 3.23 (q, 4H, 2xCH2-CH2), 5.98 (broad s, 2H, 2x NH). 13C NMR (75 MHz, DMSO-d6) 14.0, 19.9, 31.3, 31.6, 38.5, 171.5. ESI MS 229 [M+H]+, 251[M+Na]+, 267 [M+K]+.

Synthesis of Compound 6 To a solution of 1,4-diaminobutane (0.5 mL; 5 mmol) in DMF (25 mL), succinic anhydride (1.1 g; 11 mmol) is added. The mixture is stirred at 70°C for 15 hours. THF (70 mL) is added and the obtained precipitate is filtrated and washed with THF to give compound 6 (0.923 g; 3.2 mmol; 64%) as a white solid. 1H NMR (300 MHz, DMSO-d6)  1.36 (4H, 2x CH2-CH2NH), 1.22 (sextet, 4H, 2xCH2-CH2-CH3), 1.47 (quintet, 4H, 2xCH2-CH2-CH2), 2.50 (s, 4H, 2xCH2-CO), 3.23 (q, 4H, 2xCH2-CH2), 5.98 (broad s, 2H, 2x NH).

13

C NMR (75 MHz,

DMSO-d6) 14.0, 19.9, 31.3, 31.6, 38.5, 171.5. ESI MS 229 [M+H] +, 251[M+Na]+, 267 [M+K]+.

General Experimental Details Starting compounds and reagents were obtained from Aldrich. NMR spectra were recorded on Bruker AC or DRX spectrometers at 75.47 MHz (100.61 MHz, or 125.77 MHz) for 13C NMR and 300.13 MHz (or 400.13 MHz, or 500.13 MHz) for 1H NMR. Chemical shifts () are given in parts per million (ppm) and were measured relative to the signal of tetramethylsilane (= 0). Mass spectra were recorded by the Mass Spectrometry Center of the University of Lyon, using electrospray (ESI) technique.

8

Determination of the apparent partition coefficient of 1,4-butanediamine The apparent partition coefficient of DAB was determined in similar conditions as the ones used for the preparation of microcapsules but without succinyl chloride and surfactant. At the end of the emulsification step, 75 milliliters of aqueous 1,4-butanediamine solution (1M) were slowly added under blade stirring to the jojoba oil-water emulsion at a controlled speed thanks to a syringe pump. At the end of the addition, the stirring was maintained for 15 minutes and the emulsion was then centrifugated at 7500 rpm for 1 min to separate the aqueous and the organic phases. The concentration of the 1,4-butanediamine in the aqueous phase [𝑁𝐻2 ]𝑎𝑞 was then determined by pH titration with a titrated 1M HCl solution. The partition coefficient of the 1,4-butanediamine was then calculated from its initial ([DAB]0) and final concentration ([DAB]aq) in the aqueous solution, according to equation 1:

K=

[DAB]aq

Eq.1

[DAB]org

With

[𝐷𝐴𝐵]𝑎𝑞 = 0.5 × [𝑁𝐻2 ]𝑎𝑞

And

[𝐷𝐴𝐵]𝑜𝑟𝑔 =

([𝐷𝐴𝐵]0 − [𝐷𝐴𝐵] 𝑎𝑞 )×𝑉𝑎𝑞 𝑉𝑜𝑟𝑔

Eq.2 Eq.3

The titration was performed in duplicate from two different batches in order to verify the reproducibility of the partition of the 1,4-butanediamine.

Determination of the required HLB value of jojoba oil by creaming The oil-in-water emulsions were prepared by mixing jojoba oil and water containing various ratios of Tween 20 and Span 80, under blade stirring for 5 minutes. The degree of creaming was evaluated by measuring the volume of the creamed jojoba oil 3 minutes after stopping stirring.

9

In a polydisperse system consisting of ni droplets of radius ri, the mass creaming rate (𝑢̅), has been defined as: 8π

𝑢̅ = ∑𝑖 27ηV 𝑔𝑛𝑖 𝑟𝑖5 (𝑑1 − 𝑑2 )

Eq.4

Where 𝑉 is the total volume of the disperse phase; 𝜂 is the viscosity of the emulsion; 𝑔 is the acceleration due to the gravity and (𝑑1 − 𝑑2 ) is the density difference between the dispersed and the continuous phase [28]. The degree of separation of an emulsion is a function of droplet size and size distribution, all other factors being kept constant. Since larger droplets cream rapidly, an emulsifier blend giving the smallest droplet size would produce the most stable emulsion.

Characterization The average diameter and the size distribution of microcapsules were determined by static laser light scattering using a Mastersizer 2000 (Malvern instruments, UK). Turbidity analysis was performed on Turbiscan MA2000 (Formulaction, France). The samples were scanned by the optical reading head, acquiring transmission and backscattering data every 20 microns over the height of the samples. The backscattering measurement is directly dependent of the size and the volume fraction of the emulsion droplets, since the measured backscattered flux (BS) can be linked to l* as follows: 1

𝐵𝑆 ≈ [𝑙 ∗]

1⁄ 2

With [𝑙 ∗ ] =

Eq.5 2𝑑 3Φ(1−g)𝑄𝑠

Eq.6

Where 𝑙 ∗ is the penetration length of light in the analyzed scattering medium, 𝑑, the mean diameter of the droplets and Φ, their volume fraction; g and 𝑄𝑠 , optical parameters given by Mie theory. Scans were repeated over time, each one providing a curve and all curves were overlaid on one graph to show stability over time. 10

For the determination of the required HLB value of jojoba oil, the backscattering intensity was measured along the height of each emulsion every minute during 18 minutes. Scanning electron microscopy (SEM) and cryo-SEM experiments were performed on a Hitachi S800 at 5 kV and FEI Quanta 250FEG with a Gatan alto 1000E cryogenic platform respectively at the CT laboratory of the University of Lyon. Microcapsule suspension was diluted 10 times with water before each SEM observation. The samples of the microcapsules-impregnated padded fabrics were fixed on a standard sample holder and sputter coated with gold. 13

C NMR spectra were recorded on a Bruker ADVANCE III 400 MHz spectrometer at 300 K

with 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as solvent, and D2O as internal probe. A small amount of chloroform (0.05 mL) was added to assure the complete dissolution of the polymer membrane of the microcapsules. The pulse angle was 70° and the delay time was 10 s for the spectra recorded in quantitative conditions. MALDI TOF measurements were performed in reflectron mode on a Voyager DE-PRO from Perkin Elmer equipped with a N2 laser ( = 337 nm) with dithranol as matrix and HFIP as solvent and an acceleration voltage of 20 000V. FTIR spectra were recorded on a Thermo-Fisher Nicolet iS10. The microcapsules were dispersed in KBr pellets. Size Exclusion Chromatography was kindly performed by Trevira GmbH on a HPLC 1100 Agilent by using a PSS PFG column with HFIP as eluent and an infra-red detector. Thermal gravimetric analysis was performed using a TGA Q500 TA Instruments thermal gravimetric analyser. Samples weigthing 2 – 10 mg were heated at 10°C/min from 25°C to 600°C in a stream of helium. Microcapsules were analysed after freeze-drying, washing in cyclohexane to eliminate jojoba oil and drying at ambient air.

11

DSC measurements were performed on purified microcapsules using a DSC Q200 from TA Instruments. The measurements were carried out under helium atmosphere with a heating rate of 10°C/min. First run: Heating 30°C to 150°C at 10°C/min; Isotherm at 150°C during 1 minute; Cooling to -50°C at 20°C/min Second run: Heating -50°C to 250°C at 10°C/min; Isotherm at 250°C during 1 minute; Cooling to -50°C at 20°C/min Third run: Heating -50°C to 250°C at 10°C/min; Isotherm at 250°C during 1 minute The transitions were deduced from the second heating curve.

Results and Discussion The aim of this work was to develop a green alternative to melamine-formaldehyde-based microcapsules (for textile applications) by exploiting interfacial polymerization of monomers issued from biomass under oil-in-water emulsion conditions (Scheme 2). To do so, polyamide 4,4 (PA 4,4), a surprisingly poorly explored polymer [29,30], was envisioned as the main constituent of these bio-based microcapsules. The selection of this macromolecular system was driven by 1) the straightforward access to 1,4-butanediamine and succinyl chloride monomers from succinic acid, reported as one of the top value added chemicals from biomass [31,32] and 2) the high thermal stability of PA 4,4 (temperature of degradation above 300°C) [29,30]. Jojoba oil, a widely used biocompatible mixture of high-molecular weight monounsaturated esters extracted from Jojoba seeds (Simmondsia chinensis) was chosen as dispersed medium for generating the oil-in-water emulsions. Thanks to its recognized ability to induce cutaneous regeneration, jojoba oil is used in many cosmetic [33-36] formulations, such as lotions, moisturizers, massage oils and soothing creams in association with various essential oil such as Eucalyptus globulus, tea tree or lavender oils [37-38], as well in

12

cosmetotexiles [39]. The ultimate purpose of our work was the encapsulation of essential oil for cosmetotextile applications. Nevertheless, in a first step, we aimed to check the suitability of PA 4,4 microcapsules in terms of thermal properties and mechanical resistance to textile applications. Then we decided to work without any added essential oil. As the size and size distribution of the microcapsules formed by interfacial polymerization are mainly governed by the characteristics of the initial oil-in-water emulsion [22], our initial efforts were devoted to determine experimental conditions which reproducibly affords the formation of stable micrometric emulsion droplets. In this view, the optimum HLB of the emulsifier system for a given composition of oil and water phases provided a useful starting point in the selection of emulsifiers leading to a stable emulsion. According to the Griffin’s method, the required Hydrophilic Lipophilic Balance (HLB) for the oil phase was determined based on two different methods, i.e. the degree of creaming and the turbidimetric method. Two emulsifiers (Tween 20, HLB = 16.7 and Span 80, HLB=4.3) were mixed in different ratios to cover a HLB range from 9 to 16 in the prepared set of 8 o/w emulsions (En where n is the HLB value) at a total blend concentration equal to 1% w/v. (Table 1). The emulsions with a HLB value above 12 were found instable and creamed as soon as agitation was stopped, whereas E9, E10, E11 and E12 exhibited a creamed volume of jojoba oil of around 25 % v/v. The backscattering results pointed out two kinds of instability phenomena for all the emulsions: coalescence or flocculation phenomena, characterized by a decrease of the backscattered intensity, occurred in the lower part of each sample whereas creaming was detected at the top through an increase of the backscattered intensity over time. The backscattering intensity obtained in the lower part of each sample at two values of time (t=0 and t=10 min after the preparation of the emulsion) was plotted versus the sample height (Figure1). The emulsion stability was defined according to the intensity variation in time. E10

13

and E11 showed very similar profiles and exhibited the weakest intensity variation in time. Through these results, one can conclude that the required HLB value of the jojoba oil was comprised between 10 and 11, in accordance with previously reported works [35,36]. To limit emulsion instability and ensure good colloidal stability to the microcapsules, statistical biodegradable copolymer (maleic anhydride-st-methyl vinyl ether - MAMVE), widely used for pharmaceutical applications [40], was selected owing to its high thermal stability and its efficient stabilization against coalescence [41]. Its HLB value equal to 10 and its glass temperature of 155°C made it a good candidate to stabilize the jojoba oil-water emulsion. To carry out encapsulation experiments, the content of MAMVE was fixed at 8.5 % w/v, concentration at which no variation of the backscattering flux was observed over 20 minutes. In order to build microcapsules with suitable dimensions for industrial applications, conditions of emulsification were investigated. Emulsions were prepared at stirring speed (varying between 4000 and 19 000 rpm) for 5 minutes, and analysed by static laser light scattering. Size and the size distribution appeared to significantly decrease when the stirring rate was increased (Figure 2), and d(0.5) diameter of 3 m was finally reached at 19 000 rpm. A minimal emulsification duration is generally required to reach a plateau of droplet size and a narrow size distribution. Nevertheless, in order to limit the amount of hydrolysed acyl chloride groups, the emulsification duration must be minimized [22]. The kinetics of acyl chloride groups was determined by recording pH variation during the emulsification step. About 15 mol% of the acyl chloride groups were hydrolysed after one minute (Figure 3). The hydrolysis kinetics then slowed down and the proportion of hydrolysed acyl chloride groups reached about 22 mol% after 5 minutes. An emulsification duration of 5 minutes finally appeared as a good compromise for the preparation of the microcapsules. Before the preparation of microcapsules, the ability of DAB to dissolve into the jojoba droplets, quantified through the value of the partition coefficient towards the dispersed phase,

14

referred as K, was determined in the emulsification conditions [17]. A value of 1.2 was found, corresponding to a diamine partition coefficient of about 8 mol%. Partition coefficient value is well known to be an important parameter in the formation of polycondensate membranes that imparts the membrane formation kinetics [42]. Nevertheless partition coefficient values are relative to experimental conditions and have been used to estimate the relative tendency of diamines to transfer to the organic phase under polymerization conditions [43]. For instance, DAB partition coefficient appeared close to the value obtained with D-230 Jeffamine to Linpar 18 Paraffin [22], and revealed DAB as a suitable diamine for the formation polyamide microcapsules by interfacial polycondensation.

Characterization of the PA 4,4 microcapsules Microcapsules were prepared at 10°C in duplicate as described in the experimental part with a MAMVE concentration of 8.5% w/v, an emulsification duration of 5 minutes and a stirring rate of 19 000 rpm. The microcapsules were analyzed by static laser light scattering and observed by optical microscopy. The size distribution graphs reproducibly exhibited a major population with d(0.5) diameter equal to 3 m, and a minor one centered on 20 m (Figure 4), indicating the presence of larger microcapsules in negligible amounts (volume%). SEM observation confirmed the static light scattering results (Figure 5a) with microcapsule sizes below 2 m. The microcapsules were also observed by cryo-SEM after cryo-fracture (Figure 5b). Engulfed in the surfactant film, microcapsules appeared spherical and did not exhibit any porosity at the external surface. The latter point agreed the homogeneous and close structure of the external face of oily core polyamide microcapsules prepared by interfacial polycondensation [22, 42], supporting the point that the PA 4,4 membrane grows in the organic phase. Some marks left by the microcapsules pull-off during the cryo-fracture

15

step, as well as crystalized jojoba oil core were noticed. The membrane thickness was roughly estimated to be around 0.35 m. The stability of the microcapsule suspension over time was also investigated. The size, the size distribution and the morphology of the microcapsules were regularly examined over time during several months. No significant variation was observed. Nevertheless the volume intensity of the minor size distribution centered at 20 m was slightly increased after 15 months. These results were confirmed by SEM. Some microcapsules appeared quite elongated (Figure 15c). We assumed that the polyamide membrane was swollen by the aqueous surrounding medium with time, according to the low hydrophobicity of PA 4,4 [44]. The swelling may induce the membrane plasticization favoring coalescence phenomena between microcapsules.

Chemical structure of the PA 4,4 microcapsule membrane After reaction, the microcapsules were freeze-dried, washed in cyclohexane and water and dried at 80°C under vacuum, to be analysed by FTIR spectroscopy as dispersed in KBr pellets. The FTIR spectrum highlighted the expected specific vibration bands of amide groups at 1645 cm-1 (C=O stretching), 1542 cm-1 (C-N stretching and N-H bending) and around 700 cm-1 (O=C-N bending) which prove the presence of amide groups in the microcapsule membrane. Moreover, specific vibration bands of residual jojoba oil appeared at 3327, 2921, 2052, 857, 719 cm-1 (alkenes) and 1739 and 1172 cm-1 (ester groups). The solubility behaviour of purified capsules was also checked with and without a washing step in water. The microcapsules were dried at 80°C under vacuum before solubility experiments. After few tests it appeared that 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) with 0.05 mL of chloroform was the sole efficient solvent for the water-unwashed PA 4,4 microcapsules whereas no solvent was able to efficiently solubilize PA 4,4 microcapsules

16

previously water-washed. The elimination of MAMVE by water washing followed by a drying step, should modify the shell structure of the microcapsules, reinforcing hydrogen bonds between PA 4,4 chains and leading to their insolubility. Further analyses of water-unwashed microcapsules were attempt by

13

C NMR, however

without any valuable result. Indeed, the large quantities of jojoba oil, as well as residual monomers hampered the analysis of the peaks corresponding to PA 4,4 chains in the

13

C

NMR spectra. Moreover, MALDI-TOF spectrum of the water-unwashed microcapsules surprisingly displayed no peak corresponding to the polymer but only the peaks of the matrix. Then, surprisingly, the chemical structure of the microcapsules membrane could be investigated by neither NMR nor MALDI-TOF mass spectrometry. Anyway, in order to get some information about the chemical structure of the PA 4,4 membrane, a model surfactant-free PA 4,4 membrane was prepared in duplicate by interfacial polycondensation between succinyl chloride and 1,4-butanediamine, with jojoba oil as organic phase without stirring [17]. Contrarily to the PA 4,4 microcapsules, the PA 4,4 plane membrane was soluble in HFIP independently of the washing steps. The thorough examination of the

13

C NMR spectrum of the unwashed PA 4,4 membrane pointed out the

presence of jojoba oil and numerous NH2, NH3+ and COOH ending groups as well as diaminobutane and succinic acid, suggesting the presence of oligomers. The washing of the plane membrane in water and cyclohexane lead to the elimination of jojoba oil and residual ̅̅̅̅̅ monomers, and the average number polymerisation degree (𝐷𝑃 𝑛 ) of the PA 4,4 membrane was calculated from the

13

C resonances of ending and repeat units, and found equal to 10

(SUPPORTING INFO). The washed and unwashed PA 4,4 plane membrane were also analysed by MALDI-TOF. Both spectra exhibited mainly linear species with -NH2 and COOH ends with a maximal degree of polymerisation equal to 24 and some cyclic structures (SUPPORTING INFO). Nevertheless, it is worth noting that the MALDI-TOF spectrum of

17

the water-unwashed membrane exhibited a quite low spectral resolution as well as intense low molar mass species peaks. The analysis of the duplicate membrane exhibited the same results, pointing out the reproducibility of the membrane formation. Even if previous results reported that the chemical structure of plane and microcapsule membranes may be slightly different [17], the study of the PA 4,4 plane membranes by 13C NMR and MALDI-TOF may suggest that the microcapsules membranes were composed of oligomers. This feature appeared to be common to membranes obtained by interfacial step polymerisation in dispersed media [45,46]. Finally, the microcapsules after freeze-drying, washing in cyclohexane and drying at 80°C under vacuum, were analyzed by size exclusion chromatography in HFIP. Three isomolecular oligoamide models, DP3CH3, DP3COOH and DP5COOH (Scheme 1), were used as standards for assessing the molecular weight of the oligoamide 4,4 microcapsules. The retention time of the three oligoamide models ranged from 1035 to 1054 seconds, in accordance with their molar masses (Figure 6). The chromatogram obtained for the microcapsules exhibited a relatively large major peak centered at 1033 s, very close to that of DP5COOH, suggesting that the microcapsules were mainly composed of oligomers chains with DP equal to 5. This result appeared in accordance with the chemical structure of the plane membrane determined by 13C NMR and MALDI-TOF spectra.

Thermal properties of PA 4,4 microcapsules The thermal behavior of the microcapsules is a key point for their use in cosmetotextiles. Nylons with high linear hydrogen densities generally tend to degrade rather than melting [47,48]. Jones et al. reported that PA 4,4 degrades before melting above 300°C [29], whereas Dreyfuss observed a melting temperature above 260°C with an upper limit of 300°C [30].

18

Dried microcapsules were analyzed by TGA after freeze-drying and washing in cyclohexane (Figure 7a). The thermogravimetric diagram showed a mass loss of 20% at 200°C due to the departure of free and bounded water. The weight loss of the microcapsules in the range 200 – 350°C was assigned to the degradation of PA 4,4. A weight loss in the similar temperature range was observed for both the model plane membrane after washing in cyclohexane and water, and DP5COOH. These results may suggest similar chemical structures for these samples, in accordance with what was previously described. The final lost mass between 350 and 500°C shall be due to residual jojoba oil and MAMVE. Except the melting peak of jojoba oil around 7°C, DSC thermogram of the microcapsules (Figure 7b) exhibited only a large endothermic peak centered at 200°C during the second run, whereas no signal was observed on the third heating curve (not shown). The DSC diagrams of DP5COOH and the plane model membrane exhibited respectively an endothermic peak at 236°C and 294°C (SUPPORTING INFO). Through these results, one can assume that the large endothermic peak centered at 200°C corresponds to the fusion-degradation of microcapsules. DSC results appeared consistent with thermogravimetric ones. It is worth noting that the microcapsules exhibited relatively high melting temperatures although relatively low molar masses.

Microcapsules impregnation of textiles The microcapsules impregnated nylon and cotton textile fabrics with or without binder were observed by SEM two days after the impregnation. SEM pictures of binder-free impregnated textile fabrics exhibited the presence of microcapsules on both nylon and cotton fabrics (Figure 8a and b), pointing out that PA 4,4 microcapsules were resistant to the impregnation and the thermal fixation processes. Fixation of microcapsules was enhanced on nylon fabrics in comparison with the cotton ones, probably due to the favored interactions with the amide

19

groups of nylon fibers. The presence of binders, independently of the type, improved the fixation of the microcapsules by the formation of a film engulfing the microcapsules (Figure 8c and 8d). The resistance of the microcapsules impregnated fabrics to rubbing and laundering tests varied according to the type of fabrics. The rubbing tests induced the pull-off of some microcapsules, especially in the case of cotton fabrics, independently of the binder type. After laundering, the fibers of both nylon and cotton fabrics appeared less compact due to the disappearance of the binder coating and the microcapsules were mainly washed out. The selected binders appeared no efficient enough against the washing test. Surprisingly, impregnated cotton fabrics appeared slightly more resistant to washing test, exhibiting a few residual fixed microcapsules, whereas no microcapsule was observed on nylon ones. The irregularity and the roughness of the cotton fibers probably improved the resistance to washing, contrarily to nylon ones that are smoother and regular.

Conclusion Jojoba oil-loaded oligoamide 4,4 microcapsules were successfully synthesized from succinyl chloride

and

1,4-butanediamine,

two

bio-based

monomers,

through

interfacial

polycondensation in emulsion. The optimization of the emulsification process and the interfacial polycondensation step afforded the preparation of monodispersed microcapsules with d(0.5) of 3 µm, exhibiting good stability over time. The formation of polyamide was confirmed by the specific vibration bands of amide groups observed on FTIR spectrum. Because of the complex solubility behaviour of the microcapsule membrane as well as the presence of residual monomers,

13

C NMR and MALDI-TOF experiments did not allow the

investigation of the chemical structure of the microcapsule membrane. Nevertheless, the analysis of PA 4,4 model plane membranes by

13

C NMR and MALDI-TOF highlighted the

reproducibility of the membrane formation and pointed out that they were composed of

20

oligomers. SEC analysis of water-unwashed microcapsules in HFIP, according to oligoamide 4,4 models used as standards, suggested that microcapsules membrane was mainly composed of oligoamide 4,4 with a ̅̅̅̅ 𝐷𝑃𝑛 around 5, in accordance with the chemical structure of the model plane membranes. The thermal properties determined by TGA pointed out the particular thermal behaviour of the oligoamide 4,4 microcapsules with a degradation occurring in the range 200 – 350°C, whereas DSC curve exhibited a large endotherm peak centred on 200°C. The thermal behaviour of the microcapsules was consistent with the ones of the model plane membranes and DP5COOH model. Thanks to efficient mechanical resistance, microcapsules were successfully applied both on nylon and cotton fabrics. The adherence ability of the microcapsules on nylon and cotton fabrics was evaluated from SEM pictures. The particular favourable interactions of microcapsules with nylon fabrics allowed their fixation without the necessity of binder. Nevertheless, the binders improved the anchoring of the microcapsules on both nylon and cotton fabrics. The microcapsules appeared more numerous and engulfed in the binder coating, independently of the binder type. Both nylon and cotton fabrics underwent a decrease of microcapsules content after rubbing tests, independently of the binder type. After laundering, the binder and the microcapsules were mainly washed out. Therefore mild washing conditions would be helpful for better maintenance of PA 4,4 microcapsules. Finally, even mainly composed of low DP oligoamides, the microcapsules exhibited sufficient molecular cohesion thanks to the high hydrogen bonding density, making them good candidates for the elaboration of cosmetotextiles.

Acknowledgements: This work was financially supported by the Region Rhône-Alpes. We thank F. Boisson (UMR CNRS 5223, IMP) and F. Delolme (FR3302, IBCP/CCMP Lyon) for their technical

21

assistance in the NMR and MALDI TOF experiments, P. Alcouffe and T. Tamet (UMR CNRS 5223, IMP) for SEM experiments at the Technological Centre of Microstructures of University Lyon1, and I. Ferreira (IFTH, Ecully, France) for her technical assistance for the microcapsules impregnation of textiles.

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Captions for figures

Figure 1: Backscattering intensity of jojoba oil-water emulsions (E9 – E12) prepared with blends of Span 80 and Tween 20, measured at the end of the emulsification step (t 0) and 10 minutes after (t10) E9 t0 ∙∙∙ ; E9 t10 E12 t0

; E10 t0

; E10 t10

; E11t0

; E11 t10

; E12 t10

Figure 2: Size distributions of jojoba oil-water emulsions prepared at various stirring rates in presence of 8.5% w/v of MAMVE as surfactant 7000 rpm

; 11 000 rpm

; 15 000 rpm

; 17 000 rpm

; 19 000 rpm

Figure 3: Hydrolysis kinetics of acyl chloride groups of succinic chloride during the emulsification step at 19 000 rpm in duplicate. The temperature of the circulation fluid was fixed at 10°C.

Figure 4: Reproducibility of the size and size distribution of the PA 4,4 microcapsules prepared by interfacial polymerization with jojoba oil as internal core.

Figure 5a: Scanning Electron Micrograph of jojoba oil PA 4,4 microcapsules

Figure 5b: Cryo Scanning Electron Micrograph of jojoba oil PA 4,4 microcapsules

28

Figure 5c: Scanning Electron Micrograph of jojoba oil PA 4,4 microcapsules after storing 15 months in their suspension medium at room temperature

Figure 6: Retention time determined by Size Exclusion Chromatography of PA 4,4 microcapsules (), after freeze-drying, washing in cyclohexane and drying at 80°C under vacuum, and DP3CH3 (), DP3COOH () and DP5COOH () oligoamide models with HFIP as eluent solvent.

Figure 7a: TGA curves of lyophilized PA 4,4 microcapsules after washing in cyclohexane and vacuum drying at 80°C ( ), dried model plane PA 4,4 membrane after washing in cyclohexane and water and vacuum drying at 80°C (), DP5COOH oligomer (---), MAMVE surfactant (— – –), jojoba oil (— ∙). Heating rate: 10°C/min

Figure 7b: DSC thermogram of PA 4,4 microcapsules, after freeze-drying, washing in cyclohexane and water and drying at 80°C under vacuum microcapsules First run: Heating 30°C to 150°C at 10°C/min; Isotherm at 150°C during 1 minute; Cooling to -50°C at 10°C/min Second run: Heating 30°C to 250°C at 10°C/min; Isotherm at 250°C during 1 minute

Figure 8a: SEM pictures of nylon fabrics after PA 4,4 microcapsules deposit

Figure 8b: SEM pictures of cotton fabrics after PA 4,4 microcapsules deposit

Figure 8c: SEM picture of nylon fabrics after PA 4,4 microcapsules deposit with Fixapret binder

29

Figure 8d: SEM picture of nylon fabrics after PA 4,4 microcapsules deposit with Protorez binder

30

Figure 1

0,5

Backscattering

0,4

0,3

0,2

0,1 20

25

30

35

40

45

50

Height sample (mm)

Figure 2

18

16

14

Volume (%)

12

10

8

6

4

2

0 0,1

1

10

100

Size (m)

31

Figure 3

% hydrolysed acyl chloride groups

30 25 20 15 10 5 0 0

1

2

3

4

5

6

7

8

9

10

Time (min)

Figure 4

12

10

Volume (%)

8

6

4

2

0 0,1

1

10

100

Size(µm)

32

Figure 5a

Figure 5b

33

Figure 5c

34

Figure 6

900

950

1000

1050

1100

1150

t(s)

35

Figure 7a

36

Figure 7b

Figure 8a

37

Figure 8b

Figure 8c

38

Figure 8d

39

Scheme 1: synthesis of model PA 4,4 fragments

40

Scheme 2: formation of bio-sourced polyamide 4,4 microcapsules by interfacial polycondensation in oil-in-water emulsion

41

Table 1: Emulsions set prepared with various ratios of Tween 20 and Span 80, according to the HLB value of the surfactant mixture

Emulsion E9 E10 E11 E12 E13 E14 E15 E16

HLB value 9 10 11 12 13 14 15 16

Tween 20 (wt%) 37.9 46.0 54.0 62.1 70.2 78.2 86.3 94.4

Span 80 (wt%) 62.1 54.0 46.0 37.9 29.8 21.8 13.7 5.6

42

Table 2: Retention time of oligoamide models and PA 4,4 microcapsules determined by size exclusion chromatography in HFIP

DP3CH3 Chemical structure Theoretical molar mass Retention time RImax(s)

DP3COOH

DP5COOH

PA4,4 microcapsules O

*

HN NH O

228,2 g/mol

288,1 g/mol

458,2 g/mol

-

1041

1054

1035

1033

43