Simultaneous Enhancements of UV-Shielding Properties and

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Simultaneous Enhancements of UV-shielding Properties and Photostability of Poly(vinyl alcohol) via Incorporation of Sepia Eumelanin Yang Wang, Ting Li, Piming Ma, Huiyu Bai, Mingqing Chen, Yi Xie, and Weifu Dong ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.5b01734 • Publication Date (Web): 13 Mar 2016 Downloaded from http://pubs.acs.org on March 15, 2016

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ACS Sustainable Chemistry & Engineering

Simultaneous Enhancements of UV-shielding Properties and Photostability of Poly(vinyl alcohol) via Incorporation of Sepia Eumelanin Yang Wang, Ting Li, Piming Ma, Huiyu Bai, Yi Xie, Mingqing Chen, Weifu Dong* * Corresponding author. E-mail: [email protected]. The Key Laboratory of Food Colloids and Biotechnology, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University, 1800 Lihu Road, Wuxi 214122, China Keywords: sepia eumelanin, poly(vinyl alcohol), UV-shielding, photostability

ABSTRACT: Sepia eumelanin (SE), a biomacromolecule, was developed to prepare the excellent UV-shielding polymer material with better photostability. UV-vis transmittance spectra showed that poly(vinyl alcohol) PVA/SE film blocked most of ultraviolet light below 300 nm even with low concentration of SE (0.5wt%), which still kept its high transparency in visible spectrum. Rhodamine B photodegradation measurement further confirmed the excellent UVshielding properties of PVA/SE film. FTIR indicated that the carbonyl absorption bands resulted from phtodegradation for PVA/SE film did not change after UV exposure for 2700 h. Tensile properties of neat PVA were deceased intensely after UV irradiation, however, these of PVA/SE film were reduced a little. Moreover, AFM indicated that the surface roughness of PVA/SE film

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was much lower than that of neat PVA one. It could be concluded that SE reduced PVA degradation rate dramatically, revealing enhanced photostability of PVA/SE film. The mechanism for outstanding UV-shielding properties and photostability of PVA/SE film was illuminated, based on the formation of charge transfer complexes (CTCs) between SE and PVA, photothermal conversion and well-known radical scavenging capabilities of SE.

INTRODUCTION The UV spectrum in the sunlight can be divided into three regions: UVC (220-280 nm), UVB (280-320 nm), UVA (320-400 nm). The UV-light with short wavelength and high energy can destroy the covalent bonds of organic substances. Therefore, prolonged exposure to UV radiation has been revealed to damage human health or polymeric materials.1 During the last few decades, much attention has been focused on developing photoprotective materials, especially inorganic UV absorbents (e.g., TiO2, ZnO, SiO2, and Al2O3) embedded in a polymeric matrix.2 These inorganic nanoparticles possess outstanding optical, catalytic, electronic and magnetic properties, which are significantly different from their bulk states. Unfortunately, the traditional inorganic UV absorbents would simultaneously induce photodegradation of polymeric matrix due to photocatalytic activity as a side-effect.3, 4 Recently, it had been reported that graphene oxide (GO) based UV-shielding materials display markedly enhanced performance without selfdegradation.5 Actually, relatively complicated syntheses process and high production cost are big challenges for GO in real application. In particular, Hernán Míguez et al presented a novel UV reflecting mechanism and fabricated the selective UV-reflecting dielectric mirror based on ZrO2 /SiO2 multilayers. The films exhibited strong UV-reflecting property and highly visible light transmittance while without photodegradation.6, 7


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Molecular composites with biopolymers as the reinforcing agent and flexible polymers as the matrices have received a tremendous amount of attention owing to their unique and fascinating properties that potentially rival those of the most advanced materials in nature.8 Melanin, well-known multifunctional biomacromolecules that are widely found in the hair, skin, eye and brain of living animals,9 and display photoprotection, metal ion chelation, antibiotic activity, thermoregulation, free radical scavenging and some involvement in nervous systems.10, 11

Natural melanins are categorized into two major types according to the difference in

precursors and colors: brown-black eumelanins and yellow-reddish pheomelanins. Both of these pigments are derived from the common precursor dopaquinone formed through the enzymatic oxidation of tyrosine. Normally, eumelanin extracted from the cuttlefish has been used as a standard for natural melanins due to their high purity and simple isolation process.12 In particular, it is still under debate whether eumelanin is highly cross-linked heteropolymer or oligomers condensed into nanoaggregates. The nanoparticle characteristics usually deposited in specialized membranebound organelles are known to be one of the most special features of eumelanin.13, 14 It has been reported that sepia eumelanin (SE) nanoparticles are spherical in shape.15 Although the exact chemical structure of melanins is still not clear, it is well known there are many functional groups in melanins, such as -NH- and -OH.16-18 As mentioned above, the eumelanin plays an important role in protection of skin from UV radiation. The mechanism has been investigated and confirmed that eumelanin is capable of dissipate UV radiation through nonradiative mean due to electronic effects at the molecular level.19, 20 In this paper, eumelanin, a biomacromolecule from sepia, was developed to be used as UV-absorber in a polymeric matrix to design novel UVshielding materials with better photostability in outdoor application.


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Properties of PVA (polyvinyl alcohol) like the transparency over the whole visible spectrum and good adhesion to hydrophilic surfaces make it a good choice for the fabrication of optical devices and polarizing films,21 such as sunglasses, goggles, window glasses, sun visor, etc. Therefore, it is necessary to modify PVA with UV absorbent to prepare anti-ultraviolet films to protect skin, eye and immune system of humans, simultaneously increase its lifetime in outdoors. Our previous studies revealed that synthetic melanin nanoparticles dramatically enhanced the mechanical properties of PVA, as a result of strong interfacial interaction arose from hydrogen bonds between nanoparticles and PVA.22 Herein, PVA/SE nanocomposites were prepared by green and simple solution-cast method from aqueous medium. It was showed that a significant improvement in UV-shielding performance and photostability of PVA films was achieved by loading a small amount of SE, and meanwhile, the films still kept good transparency. The result was promising to large-scale production of significant UV-shielding material for photosensitive substance. EXPERIMENTAL SECTION Materials. Poly(vinyl alcohol) (PVA) (GB12010-89, polymerization degree: 1700; degree of hydrolysis: 99 mol%) was obtained from Sinopec Ningxia Energy Chemical Industry Works. Extraction of Sepia Eumelanin Ink sacs were obtained by dissection of Sepia officinalis. Sepia eumelanin (SE) was extracted from the ink of Sepia by centrifuging (18,000 rpm) for 15 min. After several washing processes of centrifugation and redispersion in water, a dispersed solution of clean SE was obtained. The solid mass was dried under vacuum at 50 ℃ for 24 h to yield dry powder of SE.


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Preparation of PVA/SE Nanocomposites PVA/SE nanocomposite films were prepared by casting method. SE (prescribed amount) was added into aqueous PVA solution (100 mL), and stirred for 3 h to form homogeneous mixture. After that, the mixtures were poured into a Petri dish and dried at 60 ℃ for 24 h until an equilibrium weight was reached, and then dried in vacuum oven at 80 ℃ for 6 h to eliminate water completely. The thickness of films was 100±5 µm.

UV-shielding measurement of PVA and PVA/SE films The degradation behavior of Rhodamine B solution (1×10-5 M) under UV light was applied to evaluate the UV-shielding performance of nanocomposite films. Neat PVA or nanocomposite films was put on the top of the Rhodamine B solution to protect Rhodamine B from degradation by UV radiation. The wavelength of UV light was 365 nm, and light power reaching the surface of the film was 0.85 W/m2. At given time (t), the absorbance at 552 nm of Rhodamine B solution were monitored by UV-vis spectrophotometer. The UV-shielding performance was calculated as I =At/A0×100%, where A0 is the absorbance of the original Rhodamine B solution without UV radiation, At is the absorbance of Rhodamine B solution protected with film under UV radiation. UV ageing To study the photostability of the samples, the films were irradiated with UV light for 2700 h with an irradiation wavelength of 365 nm, and irradiance of 90 W/m2. The films were irradiated with ultraviolet rays on a glass Petri dish. Characterizations The morphology of the SE nanoparticles were observed using scanning electron microscopy (HITACHI S4800) and transmission electron microscopy (Philips TECNAI 20).


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UV-vis spectra were observed by a TU-1901 ultraviolet-visible (UV-vis) spectrophotometer from 200 nm to 800 nm. The attenuated total reflection (ATR) was measured to recorded infrared spectra using a Nicolet 6700 FTIR spectrometer equipped with a diamond crystal and a liquid-nitrogen-cooled MCT-detector. The same side of films exposed to UV light was detected for each FTIR measurement. The surface topography images of degraded films were observed by atomic force microscope (AFM) (Bruker MuLtimode 8) with Nanoscope 7.20 image processing software. Root Mean Square (RMS) roughness (Rq), defined as the standard deviation of the Z values within the given area, were determined from the following equation: =

∑( )

(1)

Where Zt is the Z value for a given point, Za is the average of the Z values with the given area, and n is the number of points within the given area. The Rq values were obtained from AFM image processing software. Tensile properties were measured by using a universal tensile tester (Instron 5967, USA). Five specimens of each sample were tested and the averaged results were presented. Results and discussion Morphological Characterization Typical scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed that the SE nanoparticles were roughly spherical in shape, with diameters of approximately 100-200 nm (Figure 1 a,b). Figure 1c revealed a well-known, monotonic, and broad-band UV-vis absorption spectrum of 200-800 nm for SE nanoparticles


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in water. This featureless broad spectrum atypical of organic chromophores, which normally related to its photoprotective functionality.16


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c 1.5 Absorbance

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1.0

0.5

0.0 200

300

400

500

600

700

800

Wavelength (nm)

Figure 1. (a) SEM and (b) TEM images of SE nanoparticles. (c) UV-vis absorption spectra of SE (The inset showed a photograph of SE dispersed in water).

UV-shielding performance of PVA/SE Films Figure

2

showed

UV-visible

transmittance

spectra

of

PVA

and

PVA/SE

nanocomposites in the wavelength range from 200 to 800 nm. The neat PVA was nearly transparent for 220-800 nm wavelength of light. In contrast, the PVA/SE films could block the UV light below 300 nm even with low content of SE (0.5 wt%). In detail, the resulting nanocomposites (0.5 wt% SE) could block almost 100% of UVC, more than 98.5% of UVB and 30% of UVA, and the transparency were still very high in the visible region, being close to that of neat PVA film. The light transmittance (τv) were evaluated using the international ISO 9050:2003 (as showed in Table 1).With increasing SE concentration, the UV-shielding performance of the PVA/SE films increased. When increasing SE content to 2 wt%, the UV light was almost completely shielded under 340 nm, whereas the transparency deceased.


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0.5 wt%

PVA

100

Transmittance (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1 wt%

2 wt%

5 wt%

PVA 1 wt% SE

0.5 wt% SE

80

2 wt% SE

60

5 wt% SE

40

20

0 200

300

400

500

600

700

800

Wavelength (nm)

Figure 2. UV-vis light transmittance spectra (bottom) and optical images (top) of PVA and PVA/SE nanocomposites. In order to further examine the UV-shielding performance of PVA/SE films, a Rhodamine B solution protected with neat PVA or PVA/SE films was exposed to UV light, and the decay curves of the absorption intensity of the Rhodamine B solution at 552 nm was shown in Figure 3. Rhodamine B solution protected with neat PVA displayed a significant degradation, which reached 68% after UV irradiation for 60 min. Incorporation of a small amount SE, the degradation rate of Rhodamine B was obviously decreased. When SE concentration was 0.5wt%, 6% of Rhodamine B degraded. With increasing SE concentration to 5wt%, the degraded content of Rhodamine B dropped only 0.6%. In addition, compared to the original Rhodamine B, the solution protected with neat PVA showed an obvious discoloration due to the large photodegradation of Rhodamine B, whereas that protected with PVA/SE nanocomposite film displayed slight change after UV irradiation and was similar to


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original color of Rhodamine B. The results revealed PVA/SE films had excellent UVshielding performance. The reasons for the good UV-shielding were that SE nanoparticles could rapidly convert the photon energy of UV light into heat to prevent from the harmful photodegradation.19 The UV-shielding performance of obtained PVA/SE films was comparable to that of film by using other inorganic UV-absorbers,23 which illustrated SE could be used as a better UV-absorber for preparation of transparent UV-shielding film.

100

original solution

80

At/A0 (%)

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pr ote cte ne dw at PV ith A

60

Neat PVA 0.5 wt% SE 1 wt% SE 2 wt% SE 5 wt% SE

40

20

protected with PVA/SE film

0

10

20

30

40

50

60

Time (min)

Figure 3. Photodegradation curves of Rhodamine B solutions protected by neat PVA and PVA/SE nanocomposite films (The inserted photographs: the original Rhodam B solution, the solution protected with neat PVA and nanocomposite film, respectively)

Evaluation of optical band gap The study of the optical absorption spectra is one of the most productive methods in developing and understanding the structure of UV-shielding materials. Figure 4a showed the


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absorption spectra of PVA and PVA/SE films. As could be noticed, the pure PVA revealed low absorbance, while PVA/SE films exhibited high absorbance and prominent peaks were observed (in the range of 300-250 nm). Furthermore, the quantity termed optical energy gap (Eg) is also an important parameter for designing and modeling optically functional materials. For optical transitions caused by photons of energy (hν) greater than the energy gap of the material, the densities of both the conduction and valence extended electronic states is assumed to depend on the square root of energy leading to an absorption coefficient. Using the observed UV-Vi spectra, the optical energy band gap was calculated by Tauc’s expression. ℎ = (ℎ − )

(2)

The absorption coefficient (α) of fabricated films was determined from the absorbance (A) values after correction for reflection using the equation. =

.

= (

.

)

(3)

Where, A is the absorbance and d is the film thickness, h is Planck’s constant, ν is the frequency of the incident photons, β is a constant, Eg is optical energy band gap, and the exponent (n) is an empirical index, which depends on the nature of electronic transition responsible for the absorption (1/2, 3/2, 2 and 3 for direct allowed, direct forbidden, indirect allowed and indirect forbidden transition, respectively).24 The dependence of (αhν)1/n and photon energy (hν) was plotted for material using different values of n, and the best fit was obtained for n=2. It is showed that the transition process is indirect in K-space and interaction with photons are feasible. The plots of (αhν)1/2 versus hν at room temperature were shown in Figure 4b. The extrapolation of linear portions of these plots with the energy


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axis i.e., (αhν)1/2=0, gave the values of optical band gap Eg for films. The Eg for pure PVA was around 5.01 eV, indicating that the material was an insulator. Incorporation of SE (5 wt%) resulted in a gradual decrease in band gap energies from 5.01 eV to 3.43 eV. The observed variation in Eg with increasing SE content may be understood in terms of the formation of the stable charge transfer complexes (CTCs) between SE and PVA, which could inhibit the formation of other CTCs between the polymer and generated active oxygen species (leading to the initiation reaction of photodegradation of polymer).25-28 Therefore, it suggested that PVA/SE should show the improved photostability. On the other hand, the intramolecular interactions between PVA and melanin at the molecular level was confirmed by the FTIR analyses in our previous report.22

a

4 PVA 0.5 wt% SE 1 wt% SE 2 wt% SE 5 wt% SE

3

Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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2

1

0 200

300

400

500

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700

800

Wavelength (nm)


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b

80 PVA 0.5 wt% SE 1 wt% SE 2 wt% SE 5 wt% SE

-1

(cm eV)

1/2

60

1/2

40

(αhν)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


20

0 2

3

4

5

6

Photon energy (eV)

Figure 4. (a) UV-vis absorption spectra of PVA and PVA/SE nanocomposites. (b) Tauc’s plots for the determination of directed band gaps.

FTIR Most polymeric materials are susceptible to degradation when they are exposed to harsh environments, such as ultraviolet light. It is important to stabilize polymer under sunlight to prolong its lifetime in outdoor application. In order to investigate the influence of SE on the photodegradation of PVA, the PVA/SE films were exposed to UV irradiation intensively. Figure 5 showed the ATR-FTIR spectra of films before and after UV irradiation with different time. The wide absorption band at about 3287 cm-1 was attributed to O-H stretching vibration of hydroxyl group. The carbonyl peak (C=O) at 1725 cm-1 was corresponded to aldehyde group, which was a typical oxidation band arisen from photodegradation.29, 30 After


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UV exposure, the hydroxyl (O-H) peak of PVA became weak with increasing the irradiation time and shifted to higher wavenumbers, on the contrary, the carbonyl peak (C=O) increased rapidly. The blue shift of -OH group was attributed to decrease of hydrogen bonding due to the oxidation reaction of hydroxyl groups. However, there was no change at the carbonyl absorption bands for PVA/SE film even with irradiation time of 2700 h, except a little lower at 3287 cm-1. Therefore, it was noticeable that SE decreased the degradation rate remarkably. The reasons for excellent anti-degradation of PVA/SE could be explained like this. Firstly, SE dissipated UV radiation via converting the absorbed photon energy into heat to keep harmful UV light out.20, 31 Secondly, as discussed above, the formation of CTCs between SE and PVA prevent the other CTCs between oxygen and PVA (resulting in initiation reaction of photodegradation). Finally, as reported in the literature, at the beginning of the photodegradation, the oxygen radicals were generated during the dehydration and oxidation of the main chain to generate C=C. Then, those radicals were considered to be a 3D ether bridge made by an attack on the PVA main chain.32 As free radical scavenger, SE also reacted with radical species, as well as reduced oxygen and generated active oxygen species.11, 13, 33 The related mechanism was shown in Figure 6.


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Absorbance

a

0h 24 h 48 h 120 h 480 h 960 h 1800 h 2700 h

2700 h 1800 h 960 h 480 h 120 h 48 h 24 h 0 h 1800

3600 3400 3200 3000

1700 1600 1500

OH C=C

C=O

2700 h

0h

4000

3500

3000

2500

2000

1500

1000

-1

Wavenumber (cm )

b OH

Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


4000

3500

0h 2700 h

3000

2500

2000

1500

1000

-1

Wavenumber (cm )

Figure 5. ATR-FTIR spectra of irradiated (a) PVA and, (b) PVA/SE-2wt% nanocomposite film.


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Figure 6. Schematic illustration of the reaction mechanism of PVA when irradiated by UV, and the UV-shielding properties and photostability of the PVA/SE.

Tensile properties The photostability effect of SE on PVA was further explored by measuring the tensile properties of the samples before and after the UV irradiation (Table 1 and Figure 7). After UV exposure of 2700 h, the tensile strength (σ) and elongation at break (εmax) of neat PVA were dramatically reduced from 77.2 MPa and 28% to 29.5 MPa and 5%, respectively. However, tensile properties of PVA/SE nanocomposite film decreased a little. For example, σ and εmax of PVA/SE (2 wt%) film diminished from 116 MPa and 74% to 107 MPa and 68% after UV irradiation, respectively. The drop of tensile properties of films was attributed to a decrease of PVA molecular weight, which was owning to chain scission during UV ageing. It


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was further confirmed that introduce of SE reduced PVA degradation rate largely. As shown as in photographs (Figure 7), neat PVA film became brittle and yellow after UV exposure, in contrast, PVA/SE films still retained original color and flexibility. The results also agreed well with the FTIR data. According to above results, it was believed that PVA/SE nanocomposites displayed not only UV-shielding but also photostability properties. In other words, SE was very efficient to block UV light and avoided simultaneous photodegradation, which was very different some traditional inorganic UV absorbents. Table 1. The light transmittance (τv), tensile Strength (σ) and elongation at break (εmax) of PVA and PVA/SE nanocomposites Before UV exposure Sample

After UV exposure

τv (%) σ (MPa)

εmax (%)

σ (MPa)

εmax (%)

PVA

97.7

77.2±1.1

28±4.2

29.5±1.6

5±0.2

0.5 wt%

89.7

91.3±2.5

63±3.1

76.4±3.3

47±1.7

1 wt%

71.8

102±2.9

66±2.6

91.5±3.6

56±2.3

2 wt%

48.0

116±2.6

74±4.3

107±1.7

68±1.5

5 wt%

20.0

138±3.2

44±2.3

131±2.2

41±1.8


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200

a 180

PVA/SE-2wt%

PVA

160

Stress (MPa)

140 Before UV exposure After UV exposure

120 100 80 60 40 20 0 PVA

b

0.5 wt%

1 wt%

2 wt%

5 wt%

120 Before UV exposure After UV exposure

100 Elongation at break (%)

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80

60

40

20

0 PVA

0.5 wt%

1 wt%

2 wt%

5 wt%

Figure 7. (a) Tensile properties, and (b) elongation at break of PVA and PVA/SE nanocomposites before and after UV exposure for 2700 h (The inset showed photographs of samples).


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AFM Figure 8 showed AFM height images for the surfaces of PVA and PVA/SE films before and after UV irradiation for 2700h. According the RMS roughness values obtained from AFM images, the surfaces of the PVA and PVA/SE nanocomposite films were relatively high homogenous and smoothness before the UV exposure. After UV radiation, some bright dots were observed on the surface of the neat PVA, which meant an increase in surface roughness. Normally, the increase in surface roughness was caused by the migration of low molecular weight products into gas phase.34 In this study, the surface roughness for films could be referred to the extent of degradation after UV exposure. The surface roughness of neat PVA increased after UV irradiation considerably from 0.5 nm to 10.5 nm. In the case of the PVA/SE-1wt% nanocomposite film, after the UV exposure, the surface roughness increased from 0.6 nm to 2.3 nm, whereas with 2 wt% of SE, a less increase from 1.1 nm to 1.3 nm was observed. The bright dots were observed due to photodegration of PVA. At the same time, the bright dots on the surface of PVA/SE films were much fewer than these of neat PVA. Compared with neat PVA, the lower surface roughness and fewer bright dots of PVA/SE films indicated lower degradation rate.


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Figure 8. AFM images of the PVA with different SE content. 0 (a, a’), 0.5 wt% (b, b’) and 2 wt%(c, c’), before (a, b, c) and after UV exposure for 2700 h (a’, b’, c’).


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Conclusions In this paper, SE was investigated for its potential enhancement of UV-shielding properties and photostability of polymer. It was found that PVA/SE film (0.5 wt%) blocked ultraviolet light below 300 nm up to 98.7% with high transparency in visible light, supporting the possible application of PVA/SE films in UV shields. Rhodamine B photodegradation measurement also displayed that the UV-shielding properties of PVA increased with addition of SE. Incorporation of SE into PVA resulted in a gradual decrease in band gap energies from 5.01 eV to 3.43 eV, which suggested the formation of CTCs between SE and PVA. FTIR indicated that the carbonyl absorption bands arisen from photodegradation for neat PVA films were increased largely after UV exposure, while no change was observed for PVA/SE film even with irradiation time of 2700 h. σ and εmax of neat PVA were dramatically reduced from 77.2 MPa and 28% to 29.5 MPa and 5%, respectively. In contrast, tensile properties of PVA/SE film were decreased a little. AFM micromorphology suggested that the surface roughness of neat PVA increased from 0.5 nm to 10.5 nm after UV irradiation. When addition of SE, surface roughness of PVA/SE-1wt% was decreased to 2.3 nm. Consequently, SE reduced PVA degradation rate dramatically, which was owning to formation of CTCs, the photothermal conversion and radical scavenging capabilities of SE. It provided us a simple method to prepare outstanding anti-ultraviolet material by using SE. AUTHOR INFORMATION Corresponding Author *Weifu Dong, E-mail: [email protected]. Tel.: +86-510-8532-6290; Fax: +86-5108591-7763


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Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by National Natural Science Foundation of China (51373070), Program for New Century Excellent Talents in University (NCET-12-0884) and the Research Project of Chinese Ministry of Education (No.113034A). REFERENCES 1.

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For Table of Contents Use Only

Simultaneous Enhancements of UV-shielding Properties and Photostability of Poly(vinyl alcohol) via Incorporation of Sepia Eumelanin Yang Wang, Ting Li, Piming Ma, Huiyu Bai, Yi Xie, Mingqing Chen, Weifu Dong* * Corresponding author. E-mail: [email protected].

We provided a green route to fabricate excellent UV-shielding material with better photostability based on biodegradable PVA and sustainable Sepia eumelanin. GRAPHICAL ABSTRACT FIGURE


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Simultaneous Enhancements of UV-Shielding Properties and

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