Effect of silane modified nano zno on UV degradation of polyurethane coatings

Progress in Organic Coatings 79 (2015) 68–74 Contents lists available at ScienceDirect Progress in Organic Coatings journal homepage: www.elsevier.com/locate/porgcoat Effect of silane modified nano ZnO on UV degradation of polyurethane coatings To Thi Xuan Hang a,∗ , Ngo Thanh Dung a , Trinh Anh Truc a , Nguyen Thuy Duong a , Bui Van Truoc a , Pham Gia Vu a , Thai Hoang a , Dinh Thi Mai Thanh a , Marie-Georges Olivier b a b Institute for Tropical Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoï, Viet Nam Université de Mons (UMONS), Faculté Polytechnique, Service de Science des Matériaux, 20 Place du Parc, Mons, Belgium a r t i c l e i n f o Article history: Received May 2014 Received in revised form 25 September 2014 Accepted 10 November 2014 Keywords: Polyurethane coatings Silane modified nano ZnO UV resistance Electrochemical impedance spectroscopy a b s t r a c t Nanosized ZnO modified by 2-aminoethyl-3-aminopropyltrimethoxysilane (APS) was prepared using the precipitation method Modified nano ZnO by silane (ZnO-APS) was characterized by XRD, SEM, TEM and UV–vis measurements The degradation of the polyurethane coating, the polyurethane coatings containing 0.1 wt% nano ZnO and the polyurethane coatings containing nano ZnO-APS at two concentrations (0.1 and 0.5 wt%) during QUV test was evaluated by gloss measurement and electrochemical impedance spectroscopy The coating surface after QUV test was observed with SEM The results show that nano ZnO-APS has spherical structure with particle size around 10–15 nm Nano ZnO improved the UV resistance of the PU coating and surface treatment by APS enhanced the effect of nano ZnO The presence of nano ZnO-APS at 0.1 wt% concentration significantly improved the UV resistance of polyurethane coating © 2014 Elsevier B.V All rights reserved Introduction The main factors of the environment which cause the weather degradation of organic coatings are ultraviolet radiation, oxygen and water To reduce damages due to UV radiation, UV absorbers are often incorporated in organic coatings Organic absorbers suffer from migration and degradation over time, so they not exhibit long-term stability in coatings Inorganic UV absorbers not migrate so they can provide long-term protection and are more and more widely used Due to their small size, the nanoparticles can be used at low concentration without disturbing the other coating properties Zinc oxide is an inorganic UV absorber having a wide band gap energy and used as UV stabilizer in organic coatings [1–4] The nano ZnO was investigated as UV absorber in a polyurethane/acrylic clear topcoat The influence of ZnO concentration and film thickness on the UV protection was investigated and the results show that the presence of nano ZnO at 2.0 g/m2 can block more than 99% UV radiation [1] The nano ZnO and silica-coated nano ZnO improved the exterior durability and physic-mechanical properties of the acrylic waterborne coatings for wood [2,3] The presence of nano ∗ Corresponding author Tel.: +84 0912178768; fax: +84 37564484 E-mail address: ttxhang@itt.vast.vn (T.T.X Hang) http://dx.doi.org/10.1016/j.porgcoat.2014.11.008 0300-9440/© 2014 Elsevier B.V All rights reserved zinc oxide particles reduces the photo-degradation of the aromatic polyurethane coating [4] The effect of nano ZnO on the properties of poly(styrene butylacrylate) latex/nano ZnO composites was also previously studied The results show that increasing nano ZnO content and its dispersibility could enhance the UV shielding properties of the nanocomposites and that 60 nm ZnO particles could shield UV rays more effectively than 100 nm ZnO particles [5] Nano ZnO at low concentrations improved corrosion, scratch and abrasion resistances of coatings such as alkyd, epoxy and polyurethane coatings [6–8] However, the nanoparticles tend to produce some agglomerates and migrate to coating bulk at high loadings [9–11] The enhancement of physico-thermal and mechanical properties is strongly connected with the interfacial interactions with the binder and the dispersion degree of the nanoparticles in nanocomposite coatings [3] In order to improve the dispersion in polymer matrix, the surface of nano ZnO can be functionalized by silane compounds [12,13] Modification of nano ZnO surface by 3-aminopropyltriethoxysilane improved dispersion of nano ZnO particles in epoxy coating and its anti-corrosion and anti-bacterial properties Nano ZnO nanoparticles modified by 3-(trimethoxysilyl)propyl methacrylate can be homogeneously dispersed in the polyurethane acrylate matrix [13] In this work nano ZnO modified by 2-aminoethyl-3aminopropyltrimethoxy silane (ZnO-APS) as UV absorber for organic coatings was prepared The synthesized nano ZnO-APS T.T.X Hang et al / Progress in Organic Coatings 79 (2015) 68–74 was characterized by FTIR, XRD, SEM and TEM The degradation of the polyurethane coatings containing different concentrations in nano ZnO-APS was evaluated and compared to the polyurethane coating and the polyurethane coatings containing nano ZnO after different exposure times to QUV test by gloss measurement and electrochemical impedance spectroscopy The surface of coatings after QUV test was observed by SEM Experimental 2.1 Materials Sodium hydroxide, Zn(CH3 COO)2 , 2-aminoethyl-3-aminopropyltrimethoxy silane (APS) were purchased from Merck The used bicomponent polyurethane coating was based on Desmophen A160 with equivalent weight of 1065 and Desmodure N75 hardener with the equivalent weight of 255 The two components were supplied by Bayer 2.2 Preparation of nano ZnO Nano ZnO was prepared by using the precipitation method [14] A solution containing 10 ml of ethanol and 0.2 g of NaOH was slowly added under vigorously stirring to a solution of 30 ml of ethanol and 0.51 g of Zn(CH3 COO)2 The resulting solution was maintained at 70 ◦ C for 90 Then the solution was cooled by using an ice bath and stirred for h at ◦ C The resulting white precipitate was aged for 12 h at ◦ C, and then filtered and washed several times with distilled water and ethanol The ZnO precipitate was dried at 50 ◦ C in a vacuum oven for 24 h 2.3 Modification of nano ZnO by 2-aminoethyl-3-aminopropyltrimethoxysilane The functionalization by APS was performed by mixing under vigorous stirring ethanol solution containing 0.15 g of nano ZnO and 0.015 g APS The temperature was maintained at 60 ◦ C for h The white precipitate was washed several times with ethanol Silane modified nano ZnO (ZnO-APS) was dried at 50 ◦ C in a vacuum oven for 24 h 69 TEM observations were carried out using JEM 1010 transmission electron microscopy operating at 80 kV UV–vis spectra were obtained using a GBC Cintra 40 spectrometer 2.6 QUV test of coatings The coatings were tested in the UV-condensation chamber ATLAS UVCON UC-327-2 with fluorescent UV lamps UVB 313 according to ASTM standard G53-96 (4 h UV at 70 ◦ C + h of condensation at 50 ◦ C) 2.7 Gloss measurements The gloss of coatings was measured at 60◦ with a Micro-TRIgloss from BYK-Gardner 2.8 Electrochemical impedance measurements The electrochemical impedance measurements were performed using an Autolab PGSTAT30 over a frequency range of 100 kHz to 10 mHz with six points per decade using 30 mV peak-to-peak sinusoidal voltage The assessment of the coating performance was determined after QUV test by EIS after h of immersion in 3% Na2 SO4 electrolyte solution The exposed area was 12.56 cm2 For each system, three samples were tested to ensure reproducibility Results and discussion 3.1 Characterization of nano ZnO-APS Fourier transformation infrared spectroscopy (FT-IR) was used to confirm the presence of APS in modified ZnO Fig shows FTIR spectra of APS, nano ZnO and silane modified ZnO (ZnO-APS) The spectrum of APS shows a band at 3370 cm−1 characteristic of OH and NH2 groups The bands at 2940 cm−1 and 2840 cm−1 are (a) Transmittance 818 1083 2940 2840 455 873 1041 1384 1633 (c) 2922 1636 (b) 3451 Carbon steel sheets (150 mm × 10 mm × mm) were used as substrates Sheets were polished with abrasive papers from 80 to 600 grades and cleaned with ethanol Polyuretane coating and polyuretane coatings containing 0.1 wt% nano ZnO and nano ZnO-APS at two concentrations (0.1 wt% and 0.5 wt%) were prepared and applied on carbon steel The nano ZnO and ZnO-APS were dispersed by magnetic stirring and then sonication with ultrasonic waves at 35 kHz frequency for 20 The liquid paint was applied by spin coating at 600 rpm for and dried at ambient temperature for days The dry film thickness was 30 ± ␮m (measured by Minitest 600 Erichen digital meter) 3370 2.4 Polyurethane coating preparation 3433 Fourier transform infrared spectra were obtained using the KBr method on a Nexus 670 Nicolet spectrometer operated at cm−1 resolution in the 400–4000 cm−1 region X-ray diffraction measurements were performed with a Siemens diffractometer D5000 with Cu K␣ X-ray diffraction FE-SEM observations were carried out using a Hitachi 4800 spectrometer 440 2.5 Analytical characterizations 4000 3500 3000 2500 2000 Wavenumber / 1500 1000 500 cm-1 Fig FTIR spectra of (a) 2-aminoethyl-3-aminopropyltrimethoxysilane (APS); (b) nano ZnO and (c) nano ZnO-APS 70 T.T.X Hang et al / Progress in Organic Coatings 79 (2015) 68–74 vibration of OH group The band at 1041 cm−1 is attributed to Si O Si The disappearance of the peak at 818 cm−1 , characteristic of Si O CH3 , and the presence of new peak at 873 cm−1 which could be assigned to the Si O Zn bond, indicate the complete reaction between the ZnO nanoparticles and the hydrolyzed APS [15] The bands at 2922 cm−1 and 1384 cm−1 due to CH2 groups of APS These results indicate that APS has been successfully grafted onto the surface of ZnO nanoparticles 3.1.1 XRD analysis The XRD patterns of the nano ZnO and nano ZnO-APS are presented in Fig For nano ZnO the XRD pattern shows typical peaks at 2 = 31.7◦ , 33.9◦ , 36.2◦ , 47.3◦ , 56.4◦ , 62.7◦ and 67.8◦ corresponding to (1 0), (0 2), (1 1), (1 2), (1 0), (1 3) and (1 2) respectively, which can be indexed to hexagonal wurtzite ZnO in the standard data (JCPDS, 36-1451) The pattern of nano ZnO-APS presents the same peaks as nano ZnO The pattern of nano ZnO is shaper than that of nano ZnO-APS This result can be explained by the nano ZnO functionalization surface by APS Fig XRD patterns of (a) nano ZnO and (b) nano ZnO-APS attributed to the vibration of CH3 and CH2 groups The band at 1083 cm−1 is relative to Si O vibration and characteristic band at 818 cm−1 originates from the symmetric stretch of Si O CH3 [15] FT-IR spectrum of ZnO nanoparticles shows the peaks at 3451 cm−1 and 1636 cm−1 due to the stretching vibrations of the OH group on the surface of ZnO nanoparticles and a high intensity broad band around 455 cm−1 due to the Zn O vibration [16] FT-IR spectrum of ZnO-APS displays the bands characteristic of OH and NH2 groups and Zn O at 3433 cm−1 and 440 cm−1 The band at about 1633 cm−1 can be assigned to the deformation 3.1.2 SEM images SEM images of nano ZnO and nano ZnO-APS are shown in Fig It can be seen that they present a spherical shape with size in 10–15 nm range As observed in Fig 3a, the nano ZnO are agglomerated in clusters having size around 20–40 nm Although the morphology of nano ZnO-APS is similar to nano ZnO with a spherical shape, the corresponding nanoparticles are well separated without formation of agglomerates 3.1.3 TEM images Fig shows the TEM image of nano ZnO and nano ZnO-APS These results confirm the ZnO spherical shape with a size in the 10–15 nm range The morphology of nano ZnO-APS is similar to nano ZnO Fig SEM images of (a) nano ZnO and (b) nano ZnO-APS Fig TEM images of (a) nano ZnO and (b) nano ZnO-APS T.T.X Hang et al / Progress in Organic Coatings 79 (2015) 68–74 71 110 1.0 Gloss retention / % Absorbance 105 0.5 (a) 100 95 90 (b) 85 0.0 200 300 400 500 600 700 800 Wavelength / nm Fig UV–vis spectra of (a) nano ZnO and (b) nano ZnO-APS 3.1.4 UV–vis analysis The UV absorption properties of nano ZnO-APS were evaluated and compared to those of nano ZnO UV–vis absorption spectra of 0.01 wt% nano ZnO-APS and nano ZnO ethanolic solutions are presented in Fig For nano ZnO the absorption in the range of 360–230 nm was observed This result is in agreement with literature [15,17] By comparison with nano ZnO, nano ZnO-APS absorbed in the same range of wavelengths but the corresponding absorbance is lower These results indicate that after silane modification, nano ZnO-APS can also be used as UV absorber in organic coatings to block UV radiation 3.2 QUV test of coatings The coatings were exposed in QUV test chamber up to 216 h and the degradation of coatings was evaluated by gloss measurement and electrochemical impedance measurements after different exposure times, the surface of coatings after QUV test was analyzed by SEM 3.2.1 Gloss measurement Coating gloss was measured after different exposure times to QUV test and the coating gloss retention is presented in Fig Gloss retention is defined as the percentage change in the specimen gloss during QUV test relative to its initial gloss value The gloss of coatings increased slightly during first 96 h of QUV test Then the gloss retention of coatings decreased when the exposure time increased The increase of coatings gloss at the beginning of exposure can be explained by interchain crosslinking between free radical of adjacent chains of resins formed by UV radiation [18] The loss of gloss of coatings is representative of the degradation of coatings due to effects of ultraviolet radiation The UV radiation causes polymer chain breakdown and as a result a decrease of coating gloss After 216 h of QUV test, gloss retentions of PU coatings containing nano ZnO-APS or nano ZnO were higher than one of the U coating The highest gloss retention was obtained with coatings containing 0.1 wt% of nano ZnO-APS (99.5%) after 216 h of exposure in comparison with the gloss retention of PU coatings which was only 82.2% After 216 h of exposure the gloss retentions of PU coatings containing 0.1 wt% of nano ZnO was lower than one of the PU coating containing 0.1 wt% of nano ZnO-APS, but higher than one of the PU coating containing 0.5 wt% of nano ZnO-APS These results show that nano ZnO improved the UV resistance of PU coatings and surface treatment by APS enhanced the effect of nano ZnO The effect of nano ZnO-APS depends on its concentration 80 50 100 150 200 250 QUV test time / h Fig Gloss retention versus exposure time to QUV test of ( ) Pure PU coating; (△) PU coating containing 0.1 wt% nano ZnO; (᭹) PU coating containing 0.1 wt% nano ZnO-APS; (♦) PU coating containing 0.5 wt% nano ZnO-APS in PU coating The highest efficiency was obtained with the ZnO-APS concentration of 0.1 wt% 3.2.2 Surface observation by SEM The coatings surface before and after 216 h exposure to QUV test were observed by SEM Fig presents the SEM micrographs of pure PU coating and PU coatings containing nano ZnO and nano ZnOAPS at different concentrations before exposure to QUV test It can be seen that the pure PU coating surface is smooth and homogenous The PU coating containing 0.1 wt% of nano ZnO shows the agglomeration of nano ZnO The PU coating containing 0.1 wt% nano ZnO-APS has uniform surface morphology with well dispersed nano ZnO-APS, while the surface of PU coating containing 0.5 wt% nano ZnO-APS shows the agglomeration of nano ZnO-APS These results indicate that the functionalization surface by APS improved the dispersion of nano ZnO in PU coating, but the dispersion degree decreased with the increase of ZnO-APS concentration Fig shows the surface micrographs of PU coating and PU coatings containing nano ZnO and nano ZnO-APS after 216 h exposure to QUV test The pure PU coating presents large cracks of 100 nm width at the surface This indicates drastic changes of coating during exposure to QUV test For PU coating containing 0.1 wt% nano ZnO it is observed a small crack on the surface, but failure degree was lower in comparison to pure PU coating For PU coating containing 0.1 wt% nano ZnO-APS, no crack is observed With higher nano ZnO-APS concentrations (0.5 wt%) it can be seen a small crack on the surface, but the failure degree was lower in comparison to pure PU coating and PU coating containing 0.1 wt% nano ZnO This result indicates the improvement in UV resistance of the PU coatings with the incorporation of nano ZnO or nano ZnO-APS in coatings This can be attributed to the UV blocking property of nanoZnO [4,5] The surface treatment of nano ZnO by APS enhanced its efficiency The efficiency nano ZnO-APS depends on its concentration and the best UV resistant coating was obtained with concentration of 0.1 wt% for which the ZnO-APS dispersion is verified The increase of nano ZnO-APS concentration did not lead to higher effect on UV resistance of PU coating 3.2.3 Electrochemical impedance measurements In order to assess the change of barrier property of coatings during QUV test, electrochemical impedance diagrams of coatings were measured before and after QUV test Figs and 10 present the 72 T.T.X Hang et al / Progress in Organic Coatings 79 (2015) 68–74 Fig SEM images before QUV test of (a) Pure PU coating; (b) PU coating containing 0.1 wt% nano ZnO; (c) PU coating containing 0.1 wt% nano ZnO-APS; (d) PU coating containing 0.5 wt% nano ZnO-APS impedance diagrams of coatings before and after 216 h of exposure to QUV test, respectively The impedance modulus at low frequencies were high and superior to 108  cm2 The barrier properties increased with the incorporation of nano ZnO or nano ZnO-APS compared to the clear polyurethane coating For this system, the initial behavior is close to a pure capacitive behavior with a phase angle close to −90◦ in whole frequency range For pure PU coating, a resistive behavior is observed at low frequencies before QUV test The improvement of barrier properties of coatings by the presence of nano ZnO and nano ZnO-APS can be explained by the enhancement of coating density due to the adsorption of the epoxy resin on the nano ZnO and nano ZnO-APS thereby reducing the transport paths for the corrosive electrolyte to pass through the coating system [7–9] After 216 h of QUV test, the impedance modulus of all coatings decreased The impedance modulus at low frequencies of coatings containing nano ZnO or nano ZnO-APS were much higher than one Fig SEM images after 216 h of QUV test of (a) Pure PU coatings; (b) PU coating containing 0.1 wt% nano ZnO; (c) PU coating containing 0.1 wt% nano ZnO-APS; (d) PU coating containing 0.5 wt% nano ZnO-APS T.T.X Hang et al / Progress in Organic Coatings 79 (2015) 68–74 11 10 10 90 10 10 10 73 10 75 8 10 10 45 10 10 30 10 15 10 10 -3 10 -2 10 -1 10 10 10 10 10 10 lZl100mHz / Ω cm2 60 - Phase / deg ⏐Z⏐ / Ω cm2 10 10 10 10 10 10 10 Frequency / Hz 90 75 60 10 10 ⏐Z⏐ / Ω cm2 10 45 30 15 10 10 10 -3 -2 10 -1 10 10 10 10 10 10 - Phase / deg of the PU coating The impedance modulus at low frequencies of coatings containing 0.1 wt% nano ZnO-APS was higher than one of the PU coatings containing 0.1 wt% nano ZnO For coatings containing ZnO-APS, the PU coating containing 0.1 wt% nano ZnO-APS kept a quite high impedance modulus at low frequencies The increase of concentration of ZnO-APS in PU coatings decreased the impedance modulus of coatings It was proposed by Kittel et al [19] and the group of Bierwagen [20–22] that the impedance modulus at low frequencies measured versus exposure time could serve as an estimation of the corrosion protection of a painted metal Fig 11 plots |Z|100 mHz versus QUV test time It is observed that the |Z|100 mHz values of all coatings decreased rapidly during first 72 h of QUV test This result indicates a rapid loss of the protective properties of the film The fall of |Z|100 mHz during the first 72 h of QUV test was attributed to the degradation of coatings due to the UV radiation After this 10 100 150 200 250 QUV test time / h Fig Electrochemical impedance diagrams (bode presentation) obtained before QUV test of ( ) Pure PU coating; (△) PU coating containing 0.1 wt% nano ZnO; (᭹) PU coating containing 0.1 wt% nano ZnO-APS; (♦) PU coating containing 0.5 wt% nano ZnO-APS 10 50 10 Frequency / Hz Fig 10 Electrochemical impedance diagrams obtained after 216 h of QUV test of ( ) Pure PU coating; (△) PU coating containing 0.1 wt% nano ZnO; (᭹) PU coating containing 0.1 wt% nano ZnO-APS; (♦) PU coating containing 0.5 wt% nano ZnO-APS Fig 11 |Z|100 mHz versus QUV test time of ( ) Pure PU coating; (△) PU coating containing 0.1 wt% nano ZnO; (᭹) PU coating containing 0.1 wt% nano ZnO-APS; (♦) PU coating containing 0.5 wt% nano ZnO-APS exposure time to QUV test, the |Z|100 mHz value of pure PU coating, PU coatings containing 0.1 wt% nano ZnO and PU coating containing 0.5 wt% nano ZnO-APS continued to decrease For the PU coating containing 0.1 wt% nano ZnO-APS the |Z|100 mHz value remained relatively stable at high values After 216 h of QUV test the |Z|100 mHz value of PU coatings containing nano ZnO and ZnO-APS were much higher than one of the pure PU coating The |Z|100 mHz value of PU coating containing 0.1 wt% nano ZnO-APS was higher than one of the PU coating containing 0.1 wt% nano ZnO Among PU coatings containing nano ZnO-APS, the coating with 0.1 wt% nano ZnOAPS has the higher |Z|100 mHz value These results show that the presence of nano ZnO-APS improved the UV resistance of PU coating and the best coatings performance was obtained with 0.1 wt% nano ZnO-APS The results obtained by impedance measurements are in agreement with the gloss measurements and SEM observations The decrease of |Z|100 mHz values in the case of pure PU coating, PU coating containing 0.1 wt% nano ZnO and PU coating containing 0.5 wt% nano ZnO-APS can be explained by the presence of cracks in the coatings after exposure to QUV test For coating containing 0.1 wt% nano ZnO-APS, no crack appeared, so that the coating has the highest gloss retention and |Z|100 mHz value after 216 h exposure to QUV test Conclusion Nano ZnO modified by 2-aminoethyl-3-aminopropyltrimethoxysilane (ZnO-APS) was successfully synthesized ZnOAPS has spherical structure and its particle size is about 10–15 nm The degradation of PU coatings containing 0.1 wt% nano ZnO and nano ZnO-APS at two concentrations (0.1 wt% and 0.5 wt%) due to exposure in QUV test was studied The presence of nano ZnO and ZnO-APS improved the UV resistance of PU coatings The surface modification of nano ZnO by APS enhanced its efficiency and the efficiency of nano ZnO-APS depends on its concentration Nano ZnO-APS at low concentration of 0.1 wt% enhanced significantly UV resistance of PU coating The increase of ZnO-APS concentration did not improve very much the UV resistance of PU coating It will be necessary to improve the dispersion of nano ZnO-APS and optimize its concentration in the coating T.T.X Hang et al / Progress in Organic Coatings 79 (2015) 68–74 74 Acknowledgments The authors gratefully acknowledge the support of Ministry of Science and Technology of Vietnam through project 132/2013/HÐNÐT and Wallonie-Bruxelles International (WBI) of Belgium through project 28 References [9] [10] [11] [12] [13] [14] [15] [16] [1] M.S Lowry, D.R Hubble, A.L Wressell, M.S Vratsanos, F.R Pepe, C.R Hegedus, J Coat Technol Res (2008) 233–239 [2] M.V Cristea, B Riedl, P Blanchet, Prog Org Coat 69 (2010) 432–441 [3] M.V Cristea, B Riedl, P Blanchet, Prog Org Coat 72 (2011) 755–762 [4] M Rashvand, Z Ranjbar, S Rastegar, Prog Org Coat 71 (2011) 362–368 [5] M.N Xiong, G.X Gu, B You, L.M Wu, J Appl Polym Sci 90 (2003) 1923–1931 [6] S.K Dhoke, A.S Khanna, T.J.M Sinha, Prog Org Coat 64 (2009) 371–382 [7] S.K Dhoke, A.S Khanna, Corros Sci 51 (2009) 6–20 [8] B Ramezanzadeh, M.M Attar, M Farzam, Prog Org Coat 72 (2011) 410–422 View publication stats [17] [18] [19] [20] [21] [22] A Anand, R.D Kulkarni, V.V Gite, 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(2006) 4505–4515  ... retentions of PU coatings containing 0.1 wt% of nano ZnO was lower than one of the PU coating containing 0.1 wt% of nano ZnO- APS, but higher than one of the PU coating containing 0.5 wt% of nano ZnO- APS... Fig UV? ??vis spectra of (a) nano ZnO and (b) nano ZnO- APS 3.1.4 UV? ??vis analysis The UV absorption properties of nano ZnO- APS were evaluated and compared to those of nano ZnO UV? ??vis absorption spectra... adjacent chains of resins formed by UV radiation [18] The loss of gloss of coatings is representative of the degradation of coatings due to effects of ultraviolet radiation The UV radiation causes