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Progress in Organic Coatings 71 (2011) 117–120

Contents lists available at ScienceDirect

Progress in Organic Coatings

journa l homepage: www.e lsev ier .com/ locate /porgcoat

hort communication

haracterization and conductive property of polyurushiol/silver conductiveoatings prepared under UV irradiation

ongzhi Liua,b, Jianrong Xiaa,b, Jinhuo Lina,b,∗

College of Chemistry and Materials Science, Fujian Normal University, Fuzhou 350007, ChinaFujian Key Laboratory of Polymer Materials, Fuzhou 350007, China

r t i c l e i n f o

rticle history:eceived 12 July 2010

a b s t r a c t

Polyurushiol/silver (PU/Ag) composite conductive coatings were prepared from urushiol and AgNO3

under UV irradiation by using in situ radical reduction approach. The effects of the silver nitrate load-

eceived in revised form 4 November 2010ccepted 23 November 2010

eywords:rushiolV irradiation

ing and the irradiation time on the surface resistivity of polyurushiol/silver (PU/Ag) composite filmswere investigated. The result from XRD analysis showed that the formation of Ag particles, and the sur-face resistivity of polyurushiol/silver (PU/Ag) composite films reached the value of 0.26 � cm, when thecontent of Ag particles in composite films was 23.8 wt%, and the irradiation time 90 s. Additionally, Agparticles were well dispersed in the composite films. And the films had good thermo-stability.

gonductive coatings

. Introduction

Lacquer, a natural polymer, has been used for thousands of yearsn China [1,2]. It contains urushiol (60–65%), gummy substance5–7%), glycoprotein (2%), and water (20–30%) [3–9]. Urushiol, the

ain component of the lacquer, plays a main role as the matrix andkeleton of lacquer films, which is catalyzed by Rhus laccase in therying process [10,11]. Recently, Hu and co-authors [12] reportedhat urushiol could be cured within 2 min under UV irradiationithout any photoinitiator in the presence of air.

Herein, we report a simple method for the preparation of polyu-ushiol/silver (PU/Ag) composite conductive coatings. However,t is difficult to disperse metal particles homogeneously into aolymer matrix by ex situ methods [13–15]. In order to form aonductive network within the polymer matrix, Ag particles wererepared via an in situ route, so as to disperse Ag particles well

n PU matrix. The surface resistivity of PU/Ag composites was mea-ured. Its dependencies on AgNO3 concentration and the irradiationime were also investigated. The morphology and properties of con-uctive films were characterized by scanning electron microscopy

SEM), powder X-ray diffraction, and TGA.

∗ Corresponding author at: College of Chemistry and Materials Science, Fujianormal University, Fuzhou 350007, China. Tel.: +86 591 8353 8756;

ax: +86 591 8353 8756.E-mail address: jhlin@fjnu.edu.cn (J. Lin).

300-9440/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.porgcoat.2010.11.019

© 2010 Elsevier B.V. All rights reserved.

2. Experimental

2.1. Materials

Lacquer was purchased from Institute of lacquer, Xi’an, China;96 wt% urushiol was obtained after extraction with ethanol; Silvernitrate (AgNO3) and absolute ethanol used in the experiment areanalytical grade reagents.

2.2. Preparation of polyurushiol/silver (PU/Ag) Composites

In a typical experiment, 0.15 g of silver nitrate and 1.00 g ofabsolute ethanol were added in a flask. After being subjected toultrasonic irradiation for 30 min, 0.50 g of 96 wt% urushiol wasadded to the above mixture. And then the solution was stirred for 1h with a magnetic stirrer. All of the above experiments were oper-ated in the camera obscura. Finally, the liquid mixture was droppedon a clean glass slide under ambient atmosphere to form the sam-ple films, the thickness of which was about 40 �m. The samplefilms were then continually exposed to a high pressure mercurylamp for certain time (the irradiation time was shown in Table 2),and PU/Ag-A composites were obtained. By changing the amountof silver nitrate and repeating the preparation procedure, PU/Ag-Xcomposites were obtained. The formulations of the preparation of

the composites are summarized in Table 1. The main wavelengthand power capacity of the lamp were 365 nm and 2 kW. Addition-ally, the light intensity at the film surface was 103 mW/cm2 (UV-Alight radiometer, Photoelectric Instrument Factory of Beijing Nor-mal University), and the surface of the films stood 10 cm far away

118 Y. Liu et al. / Progress in Organic C

Table 1The formulations of the as-prepared composites.

Sample AgNO3 (g) Urushiol (g) Absolute ethanol (g) Ag (%)a

PU/Ag-A 0.15 0.50 1.00 14.70PU/Ag-B 0.20 0.50 1.00 18.20PU/Ag-C 0.25 0.50 1.00 21.20PU/Ag-D 0.30 0.50 1.00 23.80

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PU/Ag-E 0.35 0.50 1.00 26.20PU/Ag-F 0.40 0.50 1.00 28.20

a Theoretical value, obtained from the calculation based on the amount of silveritrate and urushiol.

rom the lamp envelope. All the irradiation experiments had beenarried out in the presence of air at 65–75 ◦C.

.3. Characterization

The surface resistivity was determined (according to nationaltandard of People Republic of China GJB/2604-96) using four probelectrical meter (Suzhou Telecom Instrument Factory). Every mea-urement was repeated three times and the average value wasalculated. The morphology of composites was observed usingScanning Electron Microscopy (JSM-6380LV scanning electronicroscope, Japan). The XRD patterns were obtained by using a

hilips X’Pert SUPER powder X-ray diffractometer with Cu K�adiation (� = 1.5418 A). The thermo-gravimetric analysis (TGA)as carried out using METTLER TGA/SDTA851 thermo-gravimetric

pparatus (Switzerland, Metter Toledo Inc.) under nitrogen atmo-phere with a heating rate of 10 ◦C/min. The scanned temperatureange was from ambient temperature to 600 ◦C.

. Results and discussion

.1. Surface resistivity of composite films

The surface resistivity of PU/Ag conductive film was investigatedt room temperature, and the results were given in Table 2. Whenhe irradiation time was 120 s, it was evident that the surface resis-ivity decreased as the yielding Ag loading increased. Although theielding Ag loading was 14.7 wt% (PU/Ag-A) or 18.2 wt% (PU/Ag-B),he surface resistivity was very high and almost the same. It coulde explained that the conductive network had not been formed inU matrix. However, when the yielding Ag loading was 21.2 wt%PU/Ag-C), the surface resistivity sharply decreased by eight ordersf magnitude. This could be due to the fact that a good conduc-ive network had been formed in PU matrix. Especially, the surfaceesistivity dropped slowly with the further addition of silver nitrate.n the other hand, Table 2 shows the relation between the surface

esistivity and the irradiation time. The result indicated that as irra-iation time increased, the surface resistivity decreased. When the

rradiation time increased to 180 s, the yielding Ag loading reached4.7 wt% (PU/Ag-A) or 18.2 wt% (PU/Ag-B), and the surface resis-ivity was still very high. It was conceivable that the generated Agarticles were not in contact with each other so as to develop a goodonductive network. Furthermore, it needed 90 s at least to obtain

able 2he effect of yielding Ag loading and irradiation time on the surface resistivity.

Irradiation time (s) Surface resistivity (� cm)

PU/Ag-A PU/Ag-B PU/Ag

30 – – 1.44 ×60 – – 1.35 ×90 – – 22.4

120 1.25 × 108 1.20 × 108 1.35150 1.23 × 108 1.19 × 108 –180 1.23 × 108 1.20 × 108 –

oatings 71 (2011) 117–120

lower surface resistivity with the yielding Ag loading of 21.2 wt%(PU/Ag-C), 23.8 wt% (PU/Ag-D) and 26.2 wt% (PU/Ag-E). Neverthe-less, it could be seen that the irradiation time was only 60 s for alower surface resistivity with the yielding Ag loading of 28.2 wt%(PU/Ag-F). Therefore, as the silver nitrate loading increased, theirradiation time decreased correspondingly to obtain a low sur-face resistivity. Thus, it can be concluded that the concentration ofAgNO3 and the irradiation time played an important role in the for-mation of PU/Ag composites. Moreover, the surface resistivity wasvery low and basically unchanged after the silver nitrate loadingand irradiation time were PU/Ag-D and 90 s. As a result, the bestsilver nitrate loading and irradiation time were PU/Ag-D and 90 s.

3.2. SEM of PU/Ag composites

The morphologies of PU/Ag composite conductive coatings areshown in SEM images presented in Fig. 1. Comparing with theUV cured PU film (Fig. 1a), PU/Ag composite films exhibit dis-tinctly different morphology. The SEM micrograph (Fig. 1b) ofPU/Ag-D revealed the generated Ag particles were uniformly dis-persed throughout the polyurushiol matrix, yielding conductivecomposite coatings. In summary, the low surface resistivity ofPU/Ag composite conductive coatings prepared by UV irradiationis due to forming a good conductive network in the polyurushiolmatrix.

3.3. XRD of PU/Ag composites

X-ray powder diffraction pattern of the PU/Ag composites wasshown in Fig. 2. Three distinct diffraction peaks at 38.1◦, 44.3◦

and 64.4◦, corresponding to the (1 1 1), (2 0 0) and (2 2 0) crys-talline planes of cubic Ag (JCPDS cards 4-0783), respectively, wereobserved in the pattern of the PU/Ag-D sample. Therefore, we canconclude that the silver particles exist on the surface of the PU/Agcomposites.

3.4. Thermal properties of PU/Ag composites

To study the thermal stability of PU/Ag composites, TGA wasused to trace the degradation process. The TGA curves of PU andPU/Ag-D sample are shown in Fig. 3. It was clear that onset ofdecomposition temperature for PU/Ag composites was 365.2 ◦C.When the temperature was 502.5 ◦C, the residual mass of PU/Agcomposites was 67.8%. However, the residual mass of PU was only20%. By comparison with PU, PU/Ag composites had excellent ther-mal stability.

3.5. Preparation mechanism of PU/Ag composites

PUCu+ could be prepared by UV irradiation. According to theirproposed mechanism [16], PU/Ag composite conductive coatingscould be also prepared by UV irradiation. The reaction can beillustrated in Scheme 1. The urushiol semiquinone radicals andhydrogen radicals were generated when urushiols were irradiated

-C PU/Ag-D PU/Ag-E PU/Ag-F

108 1.32 × 108 1.34 × 108 1.20 × 108

108 1.25 × 108 1.26 × 108 0.320.26 0.30 0.260.25 0.22 0.18– – –– – –

Y. Liu et al. / Progress in Organic Coatings 71 (2011) 117–120 119

Fig. 1. SEM images of the cured films. (a) PU irradiated for 120 s. (b) PU/Ag-D irra-diated for 120 s.

7060504030200

200

400

600

800

1000

Inte

nsi

ty (

a.u.)

2θ (degrees)

(111)

(200)

(220)

Fig. 2. XRD pattern of the PU/Ag-D.

600500400300200100

20

40

60

80

100

Weight/%

Temperature/ºC

a

b

Fig. 3. TGA curves of the cured films. (a) PU irradiated for 120 s. (b) PU/Ag-D irradi-ated for 120 s.

OH

OH

R

UV irradiation

R

O .

O .

R

O .

O .

UV crosslinking

Ag+

+ H. Ag + H

+

O

O

R

Polyurushiolchain Silverparticles

Scheme 1. Schematic preparation of PU/Ag composites.

by UV. And then silver ions reacted with hydrogen radicals. Finally,the polymerization of urushiol occurred.

4. Conclusions

PU/Ag composite conductive coatings were successfully pre-pared by in situ method under UV irradiation. It was found that theestablishment of conductive networks is possible due to certain

silver nitrate loading and irradiation time. The best silver nitrateloading and irradiation time were PU/Ag-D and 90 s. Furthermore,the PU/Ag composite conductive coatings prepared by UV irra-diation have excellent electrical conductivity and good thermalstability.

1 anic C

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dF

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57 (2006) 215–222.

20 Y. Liu et al. / Progress in Org

cknowledgments

This work was supported by the National Nature Science Foun-ation of China (50973020) and the Education Department Doctoroundation of China (20070394001).

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