Solution spray synthesis and surface modification of SiO2 nanoparticle for development of UV curable concrete coatings

Accepted Manuscript Solution spray synthesis and surface modification of SiO2 nanoparticle for development of UV curable concrete coatings V.M. Hatkar, V.J. Patil, Y.E. Bhoge, J.S. Narkhede, U.D. Patil, R.D. Kulkarni PII:

S0042-207X(17)30994-6

DOI:

10.1016/j.vacuum.2017.10.021

Reference:

VAC 7650

To appear in:

Vacuum

Received Date: 25 July 2017 Revised Date:

20 September 2017

Accepted Date: 15 October 2017

Please cite this article as: Hatkar VM, Patil VJ, Bhoge YE, Narkhede JS, Patil UD, Kulkarni RD, Solution spray synthesis and surface modification of SiO2 nanoparticle for development of UV curable concrete coatings, Vacuum (2017), doi: 10.1016/j.vacuum.2017.10.021. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Solution spray synthesis and surface modification of SiO2 nanoparticle for development of UV curable concrete coatings V. M. Hatkara, V. J. Patila, Y. E. Bhogea, J. S. Narkhedea, U. D. Patila, R. D. Kulkarnia,b*, a

University Institute of Chemical Technology, North Maharashtra University, Jalgaon (MS) b

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India-425001.

Institute of Chemical Technology, Mumbai (MS) India.

*Corresponding author. Tel: (022) 33612222; Mob: (+91) 9404366700;

Abstract

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E-mail: [email protected]

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SiO2 nanoparticles (SNP) were synthesized using patented solution spray reactor using precursor tetraethylorthosilicate (TEOS) while ammonium hydroxide as precipitant in presence of Tween-80 surfactant at room temperature and the surface modification was carried out with functional organosilanes (e.g. γ -methacryloxypropyltrimethoxy silane (GMPTS)). The functional group, crystal structure, morphology and size of SNP were characterized using FTIR, XRD and FESEM analysis, respectively. Spherical shape particles

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of SNP of average particle size 30-80 nm were obtained. Transparent UV curable nanocomposite coatings for concrete were formulated using SNP in multifunctional acrylated epoxy phenol novolac oligomer and cured under UV light. Effect of SiO2 nanoparticles was

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evaluated for performance properties of nanocomposite coatings. Keywords: SiO2, UV curing, waterborne, epoxy acrylate, solution spray reactor, surface

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modification etc.

The film forming process initiated by ultraviolet (UV) radiation rather than thermal curing or air drying process in which reactive liquid oligomer converted into solid cross-linked networks [1-2]. Multifunctional acrylated epoxy phenol novolac (MAEPN) oligomer are most attractive aspirant in UV cure prepolymer because of superior mechanical strength and outstanding thermal, chemical and outdoor properties UV curable adhesives, coatings and electronic encapsulation. [3-5]. The concrete structures damages over time owing to deterioration of their elements which are exposed to the outer environment or corrosive chemical environment. Moreover the concrete is a porous material, this porosity of concrete permits water and chemicals vapour to penetrate into and migrate through it. This migration

ACCEPTED MANUSCRIPT through concrete causes alkaline and other aggressive soluble salts to degrade concrete surfaces. To protect these porous concrete surface organic coatings were applied over it to enhance the shelf life [6-7]. Nanotechnology helps to enhance the performance properties of concrete coatings. Smaller particle size of SNP enhances the performance properties by incorporation in UV cure coatings [8-9]. SNP have been used to improve the thermal stability

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and mechanical performances, especially in terms of hardness and anti-scratch resistance. Moreover, specific optical, chemical, and electronic properties can be imparted to the polymers [10]. The variety of methods have been employed for synthesis of micron and nanosize SiO2, such as high temperature [11], sol-gel method [12], Hydrothermal [13],

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microreactor [14] flame synthesis [15] etc. The patented solution spray reactor system having ease of operation, low temperature requirement, less energy consumption and cost-effective

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technique for preparing nanomaterials on large scale with controlled size, phase and morphology [16]. Solution spray process was previously used for synthesis of prussian blue, iron oxide [17], barium sulphate [18], calcium carbonate [19] and lead chrome [20-22] Bismuth vanadate [23] zinc vanadate [24] nanomaterials.

Thus, the objective of present investigation to design the method for room temperature and facile synthesis of SNP using patented solution spray reactor system with the help of non-

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ionic surfactant to produced fine and control morphological nanostructured SNP. To enhance the reinforce characteristic by homogeneous dispersion of SNP, its surface modified using GMPTS. Low viscosity integrated UV curable acrylated epoxy phenol novolac oligomer

concrete substrate.

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(MAEPN) was synthesized for development of UV curable nanocomposites coatings for

Tetraethyl orthosilicate (Si(OC2H5)4), ammonium hydroxide (NH4OH) were purchased from

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Merck Specialities Pvt. Ltd., Mumbai., trimethylolpropane, acrylic acid, ethyl acetate, phenol, formaldehyde, sulfuric acid, toluene, sodium hydroxide, epichlorohydrin, zirconium oxychloride octahydrate (ZrOCl2.8H2O) were procured from S D Fine-chem Ltd, Mumbai. N,N,N-triethylamine was purchased from Himedia laboratories Pvt. Ltd, Mumbai. Irgacure 819 (bis(2,4,6-trimethylbenzoyl)-phenyl phosphine oxide), Darocure 1173 (2-hydroxy-2methyl-1-phenyl-propan-1-one), and GMPTS (Silane A-174 NT) were supplied by Ciba Speciality Chemicals Ltd., Mumbai and Momentive Performance Materials INC. India, respectively and BYK 163 procured from Aroma Agency, Mumbai. All chemicals were used as received without any further purification.

ACCEPTED MANUSCRIPT The spherical shape SNP nanoparticles were synthesized according to solution spray process as reported in previous work [17-18, 22-23]. The atomized streams of equimolar (0.1 M) solutions of TEOS precursor and ammonium hydroxide precipitant (each solution containing 10 g/L of Tween-80) were sprayed independently and simultaneously at solution spray reactor and mix to form finer size of nanoparticles. It was thereafter centrifuged and

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precipitate SNP were dried at 80°C for 90 min. The grafting of silane coupling agent γ-methacryloxypropyltrimethoxysilane on moist surface of SNP was carried out by refluxing SNP with 5 % (w/w on SNP) of GMPTS in 50 ml 1:1 (v/v) mixture of methanol: distilled water and 50 ml isopropyl alcohol. The surface

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modified/treated SiO2 nanoparticles (tSNP) were vacuum dried.

Multifunctional trimethylolpropane acrylate (TMPA) monomer were synthesized as per reported method [25] by reacting trimethylolpropane with excess acrylic acid using 5 %

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(w/w) zirconium oxychloride catalyst at 75°C for 6 hrs and characterized for acid value (AV) and hydroxyl value (HV) after the completion of reaction the catalyst was recovered by low temperature centrifuge. Synthesis of MAEPN oligomers was carried out according to reported method [26] by reacting residual acrylic acid present in multifunctional trimethylolpropane acrylate (TMPA) monomers with MAEPN oligomer in presence of

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triethyl amine as a catalyst and hydroquinone as a polymerization inhibitor. The reaction was carried out at 90-100°C until the acid value drops to < 5 mg of KOH/g resin. Formulation of UV cure nanocomposite coatings consist of SNP incorporated in MAEPN oligomer with uniform and stabilized dispersion through breaking of all agglomerates was

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achieved using interchangeable dispersion mill (bead mill). Mixture of photoinitiators, Darocure 1173 (2-hydroxy-2-methyl-1-phenyl-propan-1-one) and Irgacure 819 (bis(2,4,6-

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trimethylbenzoyl)-phenyl phosphine oxide) were used in the formulation. Darocure 1173 is a liquid, easy to incorporate, non-yellowing, compatible with other photoinitiators and leads to surface curing of applied coatings, whereas Irgacure 819 is particularly used in pigmented system to facilitate through curing. Additionally, the outstanding absorption properties of Irgacure 819 allows curing of thick sections. BYK 163 has been used as a dispersing agent to get proper wetting and dispersion of SNP/tSNP in binder system and for enhancing levelling properties of coatings. The UV cure clear coat formulations were applied on concrete panel at 25µ film thickness. The applied panel were immediately cured under UV irradiations using UV curing system ACS-UV-C-33-06 with medium pressure mercury vapour lamps. The overall curing time is less than 30 seconds.

ACCEPTED MANUSCRIPT Synthesized SNP, oligomers and coatings were evaluated by analytical characterisations such as acid value, hydroxyl value, epoxy equivalent weight, FTIR spectroscopy (Shimadzu FTIR8400 Spectrophotometer) using KBr Pellets methods. Viscosity was recorded on Brookfield DV II+ viscometer using spindle number 01 at at 25°C and 100 rpm. Dispersion and surface morphology of nanoparticles in coatings film was determined by FESEM analysis (S-4800,

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Hitachi, Japan). The phase and morphological analysis of nanoparticles was conducted using D-8 Advance XRD of Bruker, Germany at 40kV and a current of 30 mA with CuK radiation (1.54060 -1.54439). Thermal analysis of UV cure nanocomposite coatings was performed using TGA analysis (Shimadzu TGA-50) with N2 as the purge gas, in the range of 40–700°C

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temperature range at a heating rate of 20°C min. Performance characteristics of UV cure nanocomposites coatings were evaluated by using standard test method such as pencil

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hardness (ASTM D 3363-00), mar resistance (ISO 1584), impact resistance (ASTM D 2794 93), cross - hatch adhesion test (ASTM D 3359–02), solvent resistance (ASTM D 5402-93), acid / alkali resistance (ASTM D 3260-01), gloss measurement was carried out using MicroTRI-gloss (BYK Gardner, USA) (ASTM D 523-89) and stain resistance test were carried out according to CFFA - 141 [ASTM D1308-02].

Solution spray reactor provides the intimate thin film contact between the highly atomized

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precursor and precipitant solutions would permit the synthesis of SNP in nano-range. The FESEM micrograph shown in Fig. 1 (a) indicates the formation of spherical shape SNP with average size of 30-80 nm synthesized in solution spray reactor at 10 g/L Tween-80 loadings. The FTIR spectra of pure GMPTS in Fig. 2 (a) shows stretching frequencies at 818, 940,

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1087 and 1193 cm-1 are due to Si-O-Si and Si–O–CH3 stretching while 1296-1320 cm-1 and 1410-1446 cm-1 are Si–CH2 symmetric bending and methylene C-H in plane bending

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frequencies respectively. The C=O and C=C α-β unsaturated ester stretching frequencies were observed at 1718 and 1634 cm-1 respectively while the absorption band at 3351-3934 cm-1 was attributed to Si-OH stretching. The pristine SNP (Fig. 2 b) shows only the peaks at 480, 800, and 1100 cm-1 are assigned to the Si-O asymmetric, symmetric, rocking and bending modes in SiO2. The broad absorption band at 3500 cm-1 is due to the –OH stretching vibration of H2O in sample. While the absorption bands of nonpolar/polar part and alkyl chains observed at 2854-2856 and 2924-2926 cm-1 are due to the symmetric and asymmetric vibrations of –CH2– and –CH3 groups of surfactant Tween-80. This confirms the adsorbed layer of surfactant on the surface of SiO2 nanoparticles. The FTIR spectra of tSNP (Fig. 2 c) showed the all absorption peaks of GMPTS and pristine SNP which confirm their surface

ACCEPTED MANUSCRIPT modification with GMPTS. The XRD peaks shown in Fig. 3 indicate a typical broad halo, clearly assigned to amorphous SiO2. No well-defined peaks are observed in all the samples indicate that a high percentage of these particles are amorphous nature of SNP. Final AV and HV of TMPA monomer found to be 151 and 94 mg of KOH/g of sample respectively, while viscosity of TMPA monomer was 124 centipoise (cP) at 25°C and 100

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rpm. FTIR spectrum of TMPA monomer shown in Fig. 2 (d) shows the sharp absorption band at 1726 cm-1 which represent to C=O stretching frequency of aliphatic ester. Also the absorption band at 1078 cm-1 represents the C-O stretch of C-O-C ether linkage of ester group (-O-CO-C-) revealing the formation of ester. The asymmetric stretching frequencies of the –CH2 and -CH3 group are observed at 2885 and 2983 cm-1. The absorption band at 1621

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cm-1 was attributed to the presence of asymmetric C=C stretching frequency. Band at 1413 cm-1 belongs to =C-H in plane bending frequency of acrylic double bond. Final AV and

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viscosity of MAEPN oligomers was 3.64 mg of KOH/g of sample and 1028 centipoise (cP) at 25°C. Fig. 2 (e) shows sharp band at 1726 cm-1 represent to C=O stretching frequency of aliphatic ester and confirms the ester formation. IR absorption band at 1615 cm-1 is attributed to the presence of asymmetric C=C stretching frequency. Band at 1390 cm-1 belongs to =C-H in plane bending frequency of acrylic double bond. Band at 3529 cm-1 appears due to the O-H

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stretching frequency of secondary hydroxyl group which confirms the opening of the epoxide ring by acrylic acid leading to the formation of a secondary alcohol. C-O stretching vibration of C-O-H appears near at 1052 cm-1. The above physicochemical characteristics confirm the successful synthesis of multifunctional monomer and oligomer and ready to use for

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preparation of UV curable nanocomposite coatings. The dispersion study of SNP and tSNP in UV cure nanocomposite was performed using

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FESEM analysis. Fig. 1 (b) shows FESEM micrographs of pristine nanocomposite coating film with no white spot of nanofiller. The Fig. 1 (c) with 2 % loading of untreated SNP indicates agglomerated SNP by white spots. Fig. 1 (d) shows the homogeneous dispersion of tSNP in polymer matrix is attributed to the surface modification of SNP by silane coupling agent. Surface modification has led to the improvements in compatibility between organic polymer and inorganic SNP through formation of hydrogen bonding and cross linking with polymer matrix. The TGA curves of the UV curable nanocomposite coatings are shown in Fig. 4. The main decomposition of the films takes place in the first step of degradation is slow at 180-300°C, the second step of rapid degradation from 300 to 500°C. The next step of decomposition is at a temperature higher than 500°C corresponding to the advanced fragmentation of the macromolecules formed in the second stage, secondary reactions of

ACCEPTED MANUSCRIPT dehydrogenation, thermal cracking, disproportionation and gasification. The 5 to 15 % weight loss observe in sample pristine coating sample than those of the other SNP/tSNP filled samples, but the char yield at 500°C of sample with SNP/tSNP loaded is the highest. Thermal properties improved by incorporation of tSNP than SNP filled nanocomposite coating sample. This improvement is attributed to the formation of networks between polymer and

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inorganic nanoparticles through surface modifying agent and restriction of the nanoparticles on the long-range chain mobility of the acrylic oligomer, which led to the restrained movement of free radicals generated by thermal decomposition of acrylic matrix within the nanocomposite or the trapping of the generated free radicals by nanoparticles.

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The performance properties of MAEPN oligomers filled with SNP/tSNP based UV cure clear coating formulations were performed by standard test methods and presented in Table 1.

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Pencil hardness of nanocomposite coating film were increases from 3H to 4H with the incorporation of 2 % SNP, which further increases to 6H by incorporation of tSNP, this results confirms the incorporation of SNP/tSNP in MAEPN oligomer matrix enhance the surface hardness of coating film. Moreover nanocomposite with SNP and tSNP, approximately gain 60 % and 84 % improvement in scratch hardness respectively, as compare to pristine coating films and DUR-O-surface hardness of nanocomposite coating

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films with SNP and tSNP gain 68 and 89 % improvements, respectively. Impact resistance (in. lbs) of nanocomposite coating film with SNP and tSNP approximately gain 60 % and 120 % improvements, respectively, as compare to pristine coating film. The gloss at 60° of virgin coating observed 98°, while 2 % loading of SNP and tSNP in nanocomposites coatings show

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dramatically reduction in gloss value at 60° was 54.4° and 61.1°, respectively, according to reduction in gloss value confirms that the SNP/tSNP used as matting agent in UV curable

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nanocomposite coatings. Chemical resistance of the UV cure nanocomposite coatings is superior due to MAEPN oligomer inherently good chemical resistance. The results of MEK rub test of all batches were more than 400 double rubs represents good crosslink density. Immersions of UV cure nanocomposite coatings in alkali and acid solution up to 48 hrs of all batches shows no significant detonating effect. The enhancement in chemical resistance properties of UV cure coating is due to secondary interaction between prepolymer and SNP and crosslinked polymer network. Stain resistance test of UV cure nanocomposite coatings has been performed by applying the common household stain such as tea, vinegar, pickle, turmeric solution and vegetable oil over the concrete panels for 24 hours and removed by

ACCEPTED MANUSCRIPT smooth cotton, while, stain of permanent marker was wiped with acetone. All test panels showed good stain resistance as no permanent staining was observed. UV curable transparent nanocomposite coatings reinforced by non-agglomerated SNP shows a pronounced enhancement of scratch hardness, thermal, chemical and stain resistance without retaining the detriments cause from any other inorganic additives. The surface

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modification of SNP with functional organosilanes was enhancing the compatibility of inorganic SNP with organic UV cure oligomer which reflects in performances properties of nanocomposite coating. Acknowledgements

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Financial assistance by MHRD, New Delhi under TEQIP-II programme was acknowledged. The authors are grateful to University Institute of Chemical Technology, North Maharashtra

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University, Jalgaon (MS) India for providing FESEM, XRD, TGA and FTIR facilities. References

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20. Patil, V. J., Patil, U. D., Kulkarni, R. D., In: Int. Conf. on Advances in Chemical Engineering and Technology, Elsevier publication (2014) 68-71. 21. Patil, U. D., Patil, V. J., Kulkarni, R. D., Adv. Mater. Res. 1110 (2015) 263-266. 22. Deshpande, P. S., Patil, V. J., Mahulikar, P. P., Patil, U. D., Kulkarni, R. D., Chem. Engg. Process. Process Intensif. 95 (2015) 390-402.

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Fig. 1 FESEM images of a) synthesis SNP; b) pristine coating film; c) SNP nanocomposite coating film; D) tSNP nanocomposite coatings film Fig. 2 FTIR spectra (a) pure GMPTS; (b) pristine SNP; (c) treated SNP; (d) TMPA monomer; (e) MAEPN oligomers Fig. 3 XRD spectra of SiO2 nanoparticles Fig. 4 TGA curve of UV curable coatings film Table 1 Preparation parameters and characterizations of UV cure nanocomposite coatings

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Table 1 Preparation parameters and characterizations of UV cure nanocomposite coatings

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Characterization of monomer and oligomer TMPA Novolac epoxy acrylate oligomer Parameters Acid value (mg KOH/g sample) 151.21 3.64 Hydroxyl value (mg KOH/g sample) 94.0 -124 1028 Viscosity [centipoise (cP) at 25˚C] Coating formulation Batch No. Formulation ingredients (weight percent) 1 2 3 Oligomer (TMPA+ Novolac epoxy acrylate) 94.5 92.5 92.5 Photoinitiator (Darocure 1173) 3 3 3 Photoinitiator (Irgacure 819) 2 2 2 Wetting and dispersing agent (BYK 163) 0.5 0.5 0.5 Nanofiller (Unmodified SiO2) 0 2 0 Nanofiller (Modified nanoSiO2) 0 0 2 Coating performance characteristics Parameters Film Hardness Scratch hardness (g) 1000 1200 1600 DUR-O-surface hardness (g) 1400 1800 2200 Pencil hardness (scratch) 2H 3H 5H Flexibility Impact resistance (in-lbs) 45.5 51.1 73.8 Erichsen cupping test Pass 4B 4B 4B Cross-Cut adhesion Stain resistance (a*) 4 3 4 Tea 3 3 4 Vinegar 4 4 4 Pickle 3 2 3 Marker (b*) 4 4 4 Turmeric solution (10 % in water) 4 4 4 Vegetable oil Chemical resistance MEK (No of double rubs) 400+ pass Acid resistance (10% H2SO4 soln), hr 48 hr pass Alkali Resistance (3% NaOH soln), hr 48 hr pass Appearance quality Gloss at 60° 98.1 54.6 61.2 [a* ratings for stain resistance are based on the following scale: 4 = Excellent cleanability, no stain mark over the coating surface. 3 = Good cleanability, slight stain. 2 = Poor cleanability, stain is almost intact. 1 = Non cleanable, no stain removed. (b* indicate that cleaning of marker was done using methanol)]

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Fig. 1 FESEM images of a) synthesis SNP; b) pristine coating film; c) SNP nanocomposite coating film; D) sm-SNP nanocomposite coating film

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(a) 3692.84

654.85 536.23 471.61

1634.73 2840.28

1446.66

940.33

1296.21

2944.44 1718.63

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1087.89

1546.00

%T

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1627.01

(b)

1389.76

1465.95

2853.78 2922.25

1725.38

619.17 564.20

1051.24 946.12

476.43

801.45

(c) 1210.37

1518.03

3507.67

1518.03

1630.87

1518.03 1518.03

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1518.03

3423.76

(d)1518.03 835.21

1621.22

661.61

2885.60

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0 4000

3500

1413.87

2070.65 1304.89

570.95

2896.21 2956.97

3000

(e)

1732.03

2345.52

3529.85

1078.24

2983.98

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3555.89

1615.44 1494.88 1390.72

2000

1750

827.49

1274.031204.59

1726.35

2500

987.59 1052.20

1500

1250

1000

750

500

1/cm

Fig. 2 FTIR spectra (a) pure GMPTS; (b) pristine SNP; (c) treated SNP; (d) TMPA monomer; (e) MAEPN oligomer

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Fig. 3 XRD spectra of SiO2 nanoparticles

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Fig. 4 TGA curve of UV curable coatings film

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FTIR of coating composition before and after UV curing Sample Code: Before UV curing

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35 %T

2361.91

30

5 4000

3500

3000

2500

2000

1750

1250

564.20

976.98

1056.06

1272.10

1215.19

1486.20

1500

1000

750

500 1/cm

1000

750

500 1/cm

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Sample Code: After UV curing

1397.47

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1725.38

1616.40

2951.19 2898.14

3493.20

10

3289.70 3231.84

15

818.81

20

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1940.45

25

60 %T 52.5

1765.89

22.5

1273.06

2764.09

2543.23

30

2357.09

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37.5

2060.04

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45

15 4000

3500

3000

2500

2000

1750

1500

1250

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Highlights SiO2 nanoparticles was synthesised using solution spray reactor at room temperature Surface modification of SiO2 nanoparticles using γ -methacryloxypropyltrimethoxy silane Ecofriendly synthesis of UV cure multifunctional novolac epoxy acrylate oligomer

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Transparent clear coatings was formulated using SiO2 nanoparticles for concrete coatings Effects of surface modification of SiO2 nanoparticles on performance properties of concrete

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coatings were evaluated.