Jute hydrophobization via laccase-catalyzed grafting of fluorophenol and fluoroamine

Abstract

Two fluorinated monomers, 4-[4-(trifluoromethyl)phenoxy]phenol (TFMPP) and 1H,1H-perfluorononylamine (PFNL), were efficiently grafted onto the exposed lignin of jute's surface by a laccase mediated reaction. Their grafting onto the lignin-exposed jute was demonstrated by Fourier transform infrared-attenuated total reflection spectroscopy (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The coupling of fluorophenol and fluoramine onto a complex lignin model compound (2-methoxy-4-propylphenol) (MP) was confirmed by nuclear magnetic resonance (¹H NMR). Laccase-catalyzed grafting of both fluorinated monomers led to 41.94% and 46.35% increase in contact angle for TFMPP and PFNL, respectively. An oil static contact angle of 117.16° and oil wetting time values higher than 30 min obtained for PFNL-grafted jute also demonstrated the oleophobic behavior of jute samples after laccase-mediated oxidation. The laccase-related oxidation and formation of homopolymers and copolymers was also confirmed by UV-visible spectra of treatment solutions supernatant in the UV-visible region (200–700 nm).

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Introduction

Jute is a rich lignocellulosic fiber with extensive applications from home textiles to industrial products, including clothes, paper, fiberboards, geotextiles, fiber-reinforced composites, and cellulose nanofibrils. This high product coverage is due to their abundance in nature and attractive properties including excellent moisture absorption, low density, low price, and biodegradability. In spite of these impressive characteristics, jute fabrics have a high hydrophilic and hygroscopic tendency, which seriously affects their possible final applications as components of resins composites, packaging devices, floor covering, and decorative items. Physical and chemical approaches including alkali treatment,^1–3 graft copolymerization,^4–6 UV irradiation,⁷ silicon, and fluorocarbon treatment⁸ have been applied to improve their hydrophobicity. For example, S. Mishra et al. grafted copolymerization of acrylonitrile (AN) using a combination of NaIO₄ and CuSO₄ as initiator in an aqueous medium to reduce the absorption water of modified sisal fibers.² Kutlay, Sever et al. modified jute fabrics by a micro-emulsion silicon based agent Perisoft MSA (MS) and a fluorocarbon-based agent (FA) Periguard UFC to improve jute's hydrophobicity and interfacial adhesion between the polyester matrix and the jute fiber to make high-performance composites.⁸ However, drawbacks related with environmental impact and resource depletion were observed within these approaches.

Enzymatic-assisted oxidation has been presented as a promising and environmentally friendly alternative method for surface modification, matching the eco-friendly requirements of modern society. Laccase (EC 1.10.3.2) is a multi-copper polyphenol oxidase that can catalyse phenols, aromatic amines, or vinyl monomers resulting in the formation of corresponding phenoxyl radicals, aromatic amino radicals, or C–C radicals in presence or absence of mediators.^9–12 C. Mai et al. reported that lignin, composed of guaiacyl, syringyl, and p-hydroxyphenyl units, is a suitable substrate and its phenolic sites can be oxidized to phenoxyl radicals by laccase.¹² Then, the reactive radicals initiate the grafting of foreign functional molecules to endow improved properties or create new functions to corresponding lignocellulosic fibers.^13–16 For example, Dong et al. investigated the phenolic groups of dodecyl gallate and lignin forming phenoxyl radicals by a laccase-oxidized mechanism, respectively. Then phenoxyl radicals of dodecyl gallate successfully combine with lignin by laccase-catalysed mechanism.^13,16 Carsten Mai et al. reported the grafting of acrylamide onto the lignin matrix catalyzed by fungal laccase in combination with dioxane peroxide in aqueous organic solvent mixtures.¹¹ However, to the best of our knowledge, the hydrophobic interfacial modification of jute fabrics by laccase-mediated grafting with perfluoroalkyl amine and fluorophenol in aqueous organic/non-ionic surfactant solvent has not been attempted.

In this study, a highly active laccase, which is from ascomycete Myceliophthora thermophila, was chosen to be an initiator. According to several literature references,^17–22 the application of fluorinated functional compounds impart hydrophobic or oleophobic properties to modified materials. For this reason, fluorophenol {4-[4-(trifluoromethyl)phenoxy]phenol, TFMPP} and fluoroamine (1H,1H-perfluorononylamine, PFNL) are chosen herein for laccase grafting-assisted onto jute fabrics (see structures in Fig. 1). However, the extremely high hydrophobicity of perfluoroalkyl amine leads to poor solubility in aqueous organic solvents, which seriously affects the grafting polymerization reaction between lignin and fluorinated functional monomers by laccase-mediation. A non-ionic surfactant, a green surfactant, can maintain the stability and activity of enzymes, and dissolve perfluoroalkyl amine with a suitable mixing speed and concentration, compared with ionic surfactants.^23,24 Therefore, triton X-100 (a common non-ionic surfactant) was chosen to be a part of the solvent for the first time when laccase mediated perfluoroalkyl amine is grafted onto available lignin at jute's surface. And the grafting polymerization reaction between lignin and perfluoroalkyl amine can be analogous to emulsion polymerization.

Fig. 1 Chemical structures of fluorinated monomers: (a) fluorophenol, (b) fluoroamine and (c) lignin model compound.

To proceed with the work, the reacting conditions for laccase-mediated grafting of TFMPP and PFNL were optimized and confirmed by surface characterizations (FTIR-ATR, XPS, SEM) and nuclear resonance (NMR) techniques. The hydrophobic and oleophobic performance of grafted-jute fabrics were evaluated in terms of water and oil contact angle and wetting time.

Experimental

Materials and reagents

Laccase (6600 U mL⁻¹, 50 °C) from ascomycete Myceliophthora thermophila was supplied by Novozymes (Bagsvaerd, Denmark). The 100% raw jute fabric with a 7/7 (warp/weft) cm⁻¹ yarn density, was supplied by Longtai Weaving Company (Changshu, China). Triton X-100 was purchased from Merck Company. Dimethyl sulfoxide (DMSO, water < 0.02%) was purchased from Cortecnet Company. Sodium dodecyl sulfate (SDS), 4-[4-(trifluoromethyl)phenoxy]phenol (TFMPP), 1H,1H-perfluorononylamine (PFNL) and 2-methoxy-4-propylphenol (MP) (Fig. 1) were commercially available analytical grade products purchased from Sigma-Aldrich Company. The water was distilled and all chemicals used were reagent grade.

Pretreatment of jute fabrics

In order to remove the textile sizing agent and waxiness and thus expose the maximum lignin content at the surface of the jute, the fabrics were extracted with benzene/ethanol (v/v, 2 : 1) for 12 h using a Soxhlet extractor. The fabrics were then washed with distilled water for 3 h to remove water-soluble materials.²⁵

Enzymatic grafting of fluorophenol and fluoroamine onto jute fabrics

The enzymatic grafting of monomers was performed by a laccase pre-oxidation of jute fabrics by adding 528 U mL⁻¹ of laccase to 1 g of jute fabric in 40 mL acetate buffer (pH 5, 0.1 M) for 30 min. Further, different concentrations of fluorophenol (5 mM, 10 mM, 20 mM, and 50 mM) dissolved in 1 : 2 (organic : aqueous) solution of methanol : acetate buffer, pH 5, 0.1 M and fluoramine (5 mM and 10 mM) were added to 50 μL of non-ionic surfactant (triton X-100) and mixed with 10 mL acetate buffer (pH 5, 0.1 M), under vigorous stirring (1600 rpm) until total dissolution. Both monomer solutions were added to their respective vials containing the enzymatically pre-treated jute and the reaction proceeded at 50 °C for 24 h under shaking at 135 rpm. After the reaction, the supernatant solutions were collected and the jute fabrics were washed with an aqueous solution containing 1% sodium dodecyl sulfate (SDS) for 2 h to remove the monomers and oligomers adsorbed onto the fiber.

UV-visible spectroscopy analysis

The supernatant solutions resulting from oxidation treatments were evaluated by UV-visible spectroscopy. For this, the samples were diluted 100 times with acetate buffer and the UV-vis spectra (200–700 nm) were evaluated using a UV-visible spectroscope (J&M Analytische Mess und Regeltechnik GmbH, Germany).

FTIR-ATR spectroscopy

FTIR-ATR spectra of the different treated jute fabrics were recorded using a Nicolet iS10 infrared spectrophotometer (Thermo Nicolet, USA). All the spectra were tested in the range of 4000–650 cm⁻¹ at a resolution of 4 cm⁻¹ and 32 scans per sample.

SEM-EDS analysis

The grafted fabrics were scanned in different places of the sample using an electron microscope, model LEICA S360 with a backscattered and secondary electrons detector, at 5000 magnification, equipped with an EX-250 energy dispersive spectrometer (Horiba, Japan) to distinguish different element contents via different colors shown on the jute surfaces. The samples were coated with a thick layer of gold before scanning and all the images were carefully taken using the same sample position of weft and warp.

XPS analysis

X-ray photoelectron spectroscopy was performed to confirm the surface chemical compositions of differently treated jute fabrics using a PHI-5000C ESCA system, equipped with an Mg-Kα X-ray source (Laboratory of Surface Chemistry, Fudan University, China).

Grafting of fluorophenol and fluoroamine to lignin model compound

To further demonstrate feasibility of the grafting reaction, the lignin model compound (2-methoxy-4-propylphenol, MP) replaced jute-lignin to graft with two monomers. Both monomers, fluorophenol (TFMPP) and fluoroamine (PFNL), were dissolved as mentioned before at 2.3. For the coupling reaction, two approaches were followed:

(1) The lignin model compound (2-methoxy-4-propylphenol, MP) (10 mM) was mixed with each monomer (5 mM) at a ratio of 2 : 1 in 50 mL acetate buffer (pH 5, 0.1 M);²² then, 2 mL of laccase was added to the solution to start the coupling reaction;

(2) The model compound (10 mM) was pre-oxidized by adding 2 mL laccase and the reaction proceeded for 30 min; afterwards, each monomer (5 mM) was added to the solution and the reaction was carried out at 50 °C for 4 h under shaking at 135 rpm.

UV-visible evaluation of enzymatic oxidation products

The ability of laccase to oxidize both monomers, TFMPP and PFNL, grafting with MP was monitored by UV-visible spectroscopy. At each 10 minutes of reaction an aliquot of solution was taken and diluted 100 times for UV-vis (200–900 nm) measurement.

¹H NMR analysis of coupling products

The enzymatic-coupling products of the lignin model compound (2-methoxy-4-propylphenol, MP) and both TFMPP and PFNL was confirmed by ¹H NMR. First, the reaction solution was mixed with equal volume of ice cold methanol for protein precipitation.²² The mixture was centrifuged at 0 °C for 15 min at 10 000g and the supernatant solution was freeze-dried. Dimethyl sulfoxide (DMSO) was used as suitable solvent to dissolve the powders after freeze drying. ¹H NMR spectra were acquired on a Bruker DRX-500, AVANCE 400, and Varian Inova 750 spectrometers at 25 °C (¹H: 499.82 MHz). Chemical shifts (DMSO) are reported near 2.5 ppm. Mnova Software 9.0 (Mestrelab Research) was used to analyze all the spectra.

Hydrophobicity and oleophobicity of grafted-jute fabrics

The hydrophobic and oleophobic properties of modified jute fabrics were tested by water/oil contact angle and wetting time determination. A dosing volume of water/oil droplet of 3 μL was placed in the samples using a Hamilton 500 μL syringe at a suitable distance to the testing platform. The contact angle was measured by the different shapes of water/oil droplets on the jute fabric's surface and the pictures were captured when the droplet (3 μL) fell onto the jute surface at room temperature by using a SCA-20 live camera. The wetting time was recorded until specular reflectance of a droplet completely disappeared.^15,26 Each sample was tested in at least five spots and the results were presented as the average between them.

Results and discussion

Laccase-assisted grafting of fluorophenol and fluoramine onto jute surface

UV-visible spectroscopy. The UV-visible spectra of treated solutions after TFMPP and PFNL covalent grafting onto jute fabrics are shown in Fig. 2a and b, respectively. In order to ensure adequate progress of the reaction in the heterogeneous system, the reaction time was 24 h. Fig. 2a shows increase of the normalized optical density with the TFMPP concentration. New colored polymer species are present in the reaction solution which can be detected in the visible region of the spectra. The mechanisms associated with TFMPP grafting include both copolymerization between TFMPP homopolymers and the exposed lignin of jute and formation of TFMPP homopolymers which can also react with lignin, giving rise to colored copolymers.

Fig. 2 UV-vis spectra of reaction solutions taken from (a) TFMPP (laccase + jute for 30 min, TFMPP addition for 24 h) and (b) PFNL (laccase + jute for 30 min, PFNL addition for 24 h) covalent grafting reaction pots using different monomer concentration.

The PFNL grafting mechanism involves only reaction of the amino group of a monomer with subsequent grafting onto lignin jute. From Fig. 2b, similar spectra are observed for both monomer and conjugate, confirming the absence of intermediate polymer species in the reaction solution.

FTIR-ATR spectroscopy. FTIR-ATR spectra of jute-grafted samples with TFMPP are shown in Fig. 3a. In this spectrum, the weakening of the water peak (3330 cm⁻¹) is observed when TFMPP is grafted onto the jute surface, owing the reduced amount of hydroxyl groups. Peaks in the range of 2920–2842 cm⁻¹ are attributed to –CH₂ and –CH stretching of benzene rings of TFMPP. The new peaks at 1547 cm⁻¹ and 835 cm⁻¹ are attributed to the C–F stretching vibration on the TFMPP-grafted samples. FTIR–ATR spectra of samples grafted with PFNL are also shown (Fig. 3b). The new peaks exist at around 2900 and at 1540 cm⁻¹ possibly owing to the C–H and C–F stretching vibrations of PFNL. These results confirm that TFMPP and PFNL were efficiently grafted onto jute's surface.

Fig. 3 FTIR-ATR spectra of grafted samples with (a) TFMP and (b) PFNL with respective controls (jute + laccase; jute + TFMPP; jute + PFNL; untreated jute).

SEM and EDS analysis. Scanning electron microscopy images of grafted and non-grafted samples are shown in Fig. 4. All the control samples, namely the samples incubated only with laccase, only TFMPP and only with PFNL, present a smooth surface with few impurities (Fig. 4a–d). On the other hand, grafted jute samples evidence a film-like coverage with a rougher and irregular surface (Fig. 4e and f) resulting from the covalent grafting of TFMPP and PFNL.

Fig. 4 SEM micrographs of jute fabrics: (a) untreated jute, (b) jute + laccase, (c) jute + TFMPP, (d) jute + PFNL, (e) jute + Lac + TFMPP, (f) jute + Lac + PFNL.

Energy-dispersive X-ray spectroscopy (EDS) is applied herein as a SEM complementary technique for analysis of untreated and grafted jute samples (Fig. 5). The surface elemental distribution maps reveal that only C and O are detectable on untreated jute fabric surfaces (Fig. 5a). Unlike untreated jute, TFMPP-grafted jute surfaces show, besides C and O, the presence of F element resulting from the grafting of TFMPP (Fig. 5b). The efficient grafting is also confirmed for PFNL-grafted jute which reveals the presence of C, O, F, and N homogeneously distributed along the surface of the jute (Fig. 5c), leading to enhanced hydrophobic behavior.

Fig. 5 Energy dispersive spectrometers of differently treated jute fabrics: (a) untreated jute: only C, O were shown on the surface; (b) TFMPP-grafted jute: C, O, F were shown on the surface; (c) PFNL-grafted jute: C, O, F, N were shown on the surface.

XPS analysis. The elemental contents of untreated jute, TFMPP-grafted jute, and PFNL-grafted jute are further confirmed by XPS analysis (Fig. 6 and Table 1). The binding energy of the quantified C1s signal can be divided into different energy peaks.^27–30 The C–C (284.51 eV), C–O/C–O–C (286.08 eV), and C=O (288.16 eV) peaks of XPS appear in three samples, belong to the jute fabrics. The CF₂ peak appears at around 292.15 eV on TFMPP-grafted jute and PFNL-grafted samples, indicating the grafting of both monomers onto the exposed lignin of jute fabrics. The CF₃ (292.76 eV) peak appears only in the PFNL-grafted sample, due to the –CF₃ groups of PFNL monomer. In addition, the fluorine contents increased to 25.14 on PFNL-grafted samples and to 6.18 on TFMPP-grafted jute, justifying different hydrophobic behaviors between both samples.

Fig. 6 XPS high resolution C1s spectra of jute samples: (a) untreated jute; (b) TFMPP-grafted jute; (c) PFNL-grafted jute.

Table 1 Elemental content of jute fabrics recorded by XPS

	C%	O%	F%	N%
Untreated jute	69.67	28.52	—	—
TFMPP-grafted jute	65.82	23.80	6.18	—
PFNL-grafted jute	47.76	21.81	25.14	5.28

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Laccase-mediated coupling of fluorophenol and fluoramine onto lignin model

UV-visible spectroscopy. Enzymatic oxidization and coupling of TFMPP onto the lignin model compound (MP) was followed by UV-vis spectroscopy (Fig. 7a and b). The spectra corresponding to TFMPP coupling with MP show a smooth behavior at the first time points (230–260 nm). Then these spectra become broader and present a shift when time of oxidation increased. A new sharp peak occurring near 300 nm supports the evidence of formation of new copolymers between TFMPP and MP. The optical density of spectra do not increase with the time of reaction, possibly due to the presence of precipitates formed during oxidation that could lead to a reduced concentration of measurable solution. Fig. 7a shows that the pre-oxidization of the model compound by laccase will increase the probability of coupling, shortening the time needed for a new peak appearance.

Fig. 7 UV-vis spectra of enzymatic oxidization solution of TFMPP ((a) laccase + MP for 30 min, TFMPP addition; (b) laccase + MP + TFMP) and PFNL ((c) laccase + MP for 30 min, PFNL addition; (d) laccase + MP + PFNL) covalent grafting to lignin model compound (MP) taken at different time points.

Similarly, the UV-vis spectra corresponding to laccase-assisted covalent grafting of PFNL onto lignin model compound (MP) is followed and shown in Fig. 7c and d. A new peak is visible at around 300 nm, possibly owing to the increased colored solution that can roughly indicate the formation of new polymer species between PFNL and MP resulting from laccase oxidation.

¹H NMR analysis of coupling products. ¹H NMR spectra of TFMPP and PFNL coupling with MP (DMSO-d₆) are shown in Fig. 8. From the NMR spectrum of model compound (MP), different regions corresponding to different atoms can be depicted. These include the aliphatic region, containing the aliphatic chain and the OCH₃, the aromatic region, and the acidic region containing OH groups attached to aromatics.³¹

Fig. 8 ¹H NMR spectra of (a) MP-TFMPP and (b) MP-PFNL copolymers (DMSO-d₆).

Spectra of Fig. 8a evidence the characteristic OH broad peak (9.50 ppm) of TFMPP, and of the lignin model compound (8.60 ppm). After coupling, these hydroxyl protons disappear and the TFMPP characteristic peak remains at 7.66 ppm. All the other representative peaks of both reagents are present in the conjugate spectrum, confirming the polymerization reaction.

It is possible to visualize the peak corresponding to the NH₂ group as a broad singlet in the PFNL spectrum (Fig. 8b). The CH₂ protons showed up as a triplet (3.747, 3.716, and 3.685 ppm), due to coupling with the NH₂ group in DMSO-d₆. In the conjugate spectrum, it is possible to verify the disappearance of the OH group of MP; meanwhile, all the other peaks remain. In the conjugate MP-PFNL, the CH₂ is detected as a duplet instead of a triplet characteristic of the starting monomer. The NH₂ of the model compound is not detectable in the conjugate and the broad peak at 3.75 ppm after D₂O disappeared, confirming formation of a hydroxylamine group in the conjugate. Therefore, ¹H NMR results confirm the covalent coupling between two monomers, fluorophenol and fluoroamine, and the lignin model compound assisted by laccase.

Hydrophobic and oleophobic performances of grafted jute fabrics

Hydrophobicity. The hydrophobic performance of grafted jute fabrics was evaluated by means of water contact angle and wetting time measurements.^32–34 The water contact angle and wetting time of differently treated jute fabrics are shown in Table 2. A contact angle higher than 120° is observed for the jute fabrics grafted with TFMPP and PFNL. The highest water contact angle measured was 130.53° and 134.35° for TFMPP and PFNL (5 mM) grafted samples, respectively, corresponding to the longest water wetting time observed (30 min). Concentrations of monomers up to 5 mM are expected to provide a good polymerization yield and good surface coverage of hydrophobic groups like fluorine, leading to high hydrophobicity. Higher monomer concentrations drastically decrease the grafting yield. In this case, the monomer is less soluble and the micelles formed during product solubilization may be responsible for the low degree of polymerization, which could result in a low surface coverage of the fabrics.

Table 2 Water contact angle and water wetting time of jute fabrics

Treatment	Water contact angle (°) at 0 s	Water wetting time
Untreated jute	91.96	2.6 ± 0.42 s
Jute + laccase	100.58	19.36 ± 3.26 s
Jute + TFMPP	84.90	23.12 ± 2.91 s
Jute + PFNL	107.61	4.79 ± 2.11 min
Jute + Lac + TFMPP (5 mM)	130.53	>30 min
Jute + Lac + TFMPP (10 mM)	125.48	17.49 ± 3.11 min
Jute + Lac + PFNL (5 mM)	134.35	>30 min
Jute + Lac + PFNL (10 mM)	120.68	4.29 ± 3.96 min

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Oleophobicity. The oil contact angle and oil wetting time of different grafted jute fabrics also were evaluated (Table 3). Jute samples grafted with different concentrations of TFMPP present similar values of oil contact angles and oil wetting time when compared with untreated jute fabrics. The unsuccessful oleophobic improvement probably can be attributed to the low grafting percentage and low fluorine content in TFMPP. In contrast, a high oil contact angle of 117.16° is obtained for PFNL (5 mM)-grafted jute, resulting from the high fluorine content of perfluorinated amines at jute's surface. These samples also present an oil wetting time beyond 30 min corresponding to an excellent oleophobic behavior.

Table 3 The oil contact angle and oil wetting time of jute fabrics

Treatment	Oil contact angle (°) at 0 s	Oil wetting time
Untreated jute	0	0
Jute + laccase	0	0
Jute + TFMPP	0	2.21 ± 0.42 s
Jute + PFNL	95.4	2.54 ± 0.31 s
Jute + Lac + TFMPP (5 mM)	0	2.43 ± 0.31 s
Jute + Lac + TFMPP (10 mM)	0	3.10 ± 0.27 s
Jute + Lac + PFNL (5 mM)	117.16	>30 min
Jute + Lac + PFNL (10 mM)	108.03	>30 min

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The optimal grafting of fluorophenol (TFMPP) and fluoroamine (PFNL) onto jute fabrics lead to the increases of 41.94% and 46.35% in hydrophobicity when compared to unmodified jute fabrics, respectively. This further demonstrates that laccase efficiently mediated the covalent grafting of fluorophenol and fluoroamine monomers onto jute leading to hydrophobic surfaces.

Laccase-assisted covalent grafting of fluorophenol and fluoroamine onto jute surfaces: proposed mechanism

Based on the laccase oxidation mechanism already published, we postulate herein that the phenolic hydroxyl groups of TFMPP are catalyzed via laccase-catalyzed oxidation, forming free radicals (Fig. 9a). The phenolic free radicals transfer electrons to the phenolic groups of lignin, forming copolymers between TFMPP and lignin at the jute fabric's surface as well as TFMPP homopolymers.

Fig. 9 The proposed mechanism of (a) TFMPP and (b) PFNL covalent grafting onto jute fabric's surface catalysed by laccase.

The mechanism proposed for PFNL is quite different (Fig. 9b). In this case, the amino groups of PFNL would not undergo homopolymerization, forming only copolymers between PFNL and the available lignin at jute fabrics. Despite the different routes, the grafting of both fluorinated monomers onto jute fabric's surfaces successfully endowed the remarkably hydrophobic and oleophobic performances.

Conclusions

We have successfully demonstrated the covalent grafting of two fluorinated monomers, fluorophenol, and fluoramine, onto jute's surface assisted by laccase. In vitro studies using a lignin model compound (2-methoxy-4-propylphenol) demonstrated the possibility of covalent coupling with both compounds. After reaction, the exposition of the fluorine, essential to confer the hydrophobic behavior, was confirmed. This enzymatically-assisted grafting process was carried out under mild conditions and is presented herein as an eco-friendly process, providing an attractive alternative for the chemical approaches of jute hydrophobization. This new enzymatic grafting approach (in aqueous organic/non-ionic surfactant system) provides a beneficial reference for enzymatic modification/synthesis of different materials with highly hydrophobic monomers.

Acknowledgements

The work was financially funded by National Natural Science Foundation of China (51173071), (51603087), Program for Changjiang Scholars and Innovative Research Team in University (IRT_15R26), the Portuguese Foundation for Science and Technology (UID/BIO/04469/2013 unit) and COMPETE 2020 (POCI-01-0145-FEDER-006684).

Notes and references

1. A. K. Bledzki, H. P. Fink and K. Specht, J. Appl. Polym. Sci., 2004, 93, 2150–2156.
2. S. Mishra, M. Misra, S. S. Tripathy, S. K. Nayak and A. K. Mohanty, Macromol. Mater. Eng., 2001, 286, 107–113.
3. J. Gassan and A. K. Bledzki, J. Appl. Polym. Sci., 1999, 71, 623–629.
4. A. C. Karmaker and J. A. Youngquist, J. Appl. Polym. Sci., 1996, 62, 1147–1151.
5. F. Corrales, F. Vilaseca, M. Llop, J. Girones, J. A. Mendez and P. Mutje, J. Hazard. Mater., 2007, 144, 730–735.
6. J. Du, X. Luo, Z. Fu, C. Xu, X. Ren, W. Gao and Y. Li, J. Appl. Polym. Sci., 2015, 132 DOI:10.1002/APP.42456.
7. B. Kordoghli, R. Khiari, H. Dhaouadi, M. N. Belgacem, M. F. Mhenni and F. Sakli, Colloids Surf., A, 2014, 441, 606–613.
8. K. Sever, M. Sarikanat, Y. Seki, G. Erkan, Ü. H. Erdoğan and S. Erden, Ind. Crops Prod., 2012, 35, 22–30.
9. S. Kim, C. Silva, A. Zille, C. Lopez, D. V. Evtuguin and A. Cavaco-Paulo, Polym. Int., 2009, 58, 863–868.
10. S. Kim, C. Silva, D. V. Evtuguin, J. A. F. Gamelas and A. Cavaco-Paulo, Appl. Microbiol. Biotechnol., 2011, 89, 981–987.
11. C. Mai, O. Milstein and A. Huttermann, J. Biotechnol., 2000, 79, 173–183.
12. C. Mai, O. Milstein and A. Huttermann, Appl. Microbiol. Biotechnol., 1999, 51, 527–531.
13. A. Dong, Y. Yu, J. Yuan, Q. Wang and X. Fan, Appl. Surf. Sci., 2014, 301, 418–427.
14. X. Ni, A. Dong, X. Fan, Q. Wang, Y. Yu and A. Cavaco-Paulo, Polym. Compos., 2015 DOI:10.1002/pc.23699.
15. A. Dong, X. Fan, Q. Wang, Y. Yu and A. Cavaco-Paulo, Int. J. Biol. Macromol., 2015, 79, 353–362.
16. T. Kudanga, E. N. Prasetyo, J. Sipilä, P. Nousiainen, P. Widsten, A. Kandelbauer, G. S. Nyanhongo and G. Guebitz, Eng. Life Sci., 2008, 8, 297–302.
17. B. E. Smart, J. Fluorine Chem., 2001, 109, 3–11.
18. F. Yang, L. Zhu, D. Han, W. Li, Y. Chen, X. Wang and L. Ning, RSC Adv., 2015, 5, 95230–95239.
19. A. Kharitonov, J. Zha and M. Dubois, J. Fluorine Chem., 2015, 178, 279–285.
20. Y. Guo, D. Tang and F. Yang, Mater. Sci.-Pol., 2015, 33, 451–459.
21. C. Pereira, C. Alves, A. Monteiro, C. Magen, A. M. Pereira, A. Ibarra, M. R. Ibarra, P. B. Tavares, J. P. Araujo, G. Blanco, J. M. Pintado, A. P. Carvalho, J. Pires, M. F. R. Pereira and C. Freire, ACS Appl. Mater. Interfaces, 2011, 3, 2289–2299.
22. T. Kudanga, E. N. Prasetyo, P. Widsten, A. Kandelbauer, S. Jury, C. Heathcote, J. Sipila, H. Weber, G. S. Nyanhongo and G. M. Guebitz, Bioresour. Technol., 2010, 101, 2793–2799.
23. M. Azimi, N. Nafissi-Varcheh, M. Mogharabi, M. A. Faramarzi and R. Aboofazeli, J. Mol. Catal. B: Enzym., 2016, 126, 69–75.
24. G. Ji, H. Zhang, F. Huang and X. Huang, J. Environ. Sci., 2009, 21, 1486–1490.
25. M. S. Jahana and M. Sungphil, Bangladesh J. Sci. Ind. Res., 2009, 271–280.
26. R. Liu, A. Dong, X. Fan, Y. Yu, J. Yuan, P. Wang, Q. Wang and A. Cavaco-Paulo, Appl. Biochem. Biotechnol., 2016, 178, 1612–1629.
27. M. R. Guascito, D. Cesari, D. Chirizzi, A. Genga and D. Contini, Atmos. Environ., 2015, 116, 146–154.
28. Y. Zhang, X. Fan, Q. Wang and A. Cavaco-Paulo, RSC Adv., 2016, 6, 49272–49280.
29. C. P. Kealey, T. M. Klapotke, D. W. McComb, M. I. Robertson and J. M. Winfield, J. Mater. Chem., 2001, 11, 879–886.
30. J. M. Deitzel, W. Kosik, S. H. McKnight, N. C. Beck Tan, J. M. DeSimone and S. Crette, Polymer, 2002, 43, 1025–1029.
31. X. Liu, Y. Xu, J. Yu, S. Li, J. Wang, C. Wang and F. Chu, Int. J. Biol. Macromol., 2014, 67, 483–489.
32. S. Tragoonwichian, P. Kothary, A. Siriviriyanun, E. A. O'Rear and N. Yanumet, Colloids Surf., A, 2011, 384, 381–387.
33. E. I. Muresan, G. Balan and V. Popescu, Ind. Eng. Chem. Res., 2013, 52, 6270–6276.
34. R. G. Karunakaran, C.-H. Lu, Z. Zhang and S. Yang, Langmuir, 2011, 27, 4594–4602.

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