Surface functionalized zinc oxide (ZnO) nanoparticle filled organic–inorganic hybrid materials with enhanced thermo-mechanical properties

Progress in Organic Coatings 89 (2015) 82–90

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Surface functionalized zinc oxide (ZnO) nanoparticle filled organic–inorganic hybrid materials with enhanced thermo-mechanical properties Kishore K. Jena 1 , Ramanuj Narayan, K.V.S.N. Raju ∗ Polymers and Functional Materials Division, IICT, Hyderabad, India

a r t i c l e

i n f o

Article history: Received 9 June 2014 Received in revised form 4 March 2015 Accepted 21 May 2015 Keywords: AFM Sol–gel HR-TEM APTES DMTA

a b s t r a c t The aim of this work is to use surface modified ZnO nanoparticles in combination with hyperbranched reactive polymer network to prepare moisture cure eco-friendly hybrid coatings and study their structure property relationship. The surface of the ZnO nanoparticles has been modified with silane coupling agent to get organo functional modified ZnO nanoparticles and were used for coatings formulation. The structure–properties of HBPUU (hyperbranched polyurethane urea)-modified nano ZnO hybrid materials were compared with HBPUU–nano-ZnO hybrid coatings. The viscoelastic, thermal and surface morphology of these coatings were characterized by Dynamic Mechanical and Thermal Analyzer (DMTA), Thermogravimetric Analyzer (TGA), Atomic Force Microscope (AFM), High Resolution Transmission Electron Microscopy (HR-TEM) and Contact Angle Instrument. TGA and DMTA data suggest higher thermal stability and glass transition temperature (Tg ) for the coatings prepared using modified nano ZnO (5%) as compared to nano ZnO (5%) hybrids. The contact angle data suggest better hydrophobic character of the hybrid coatings prepared using modified ZnO. The AFM result suggests that the surface roughness value of modified nano ZnO hybrid coatings is less when compared to their corresponding nano ZnO based hybrid coatings. © 2015 Published by Elsevier B.V.

1. Introduction The development of organic–inorganic hybrids materials for coatings has drawn considerable interest in recent years. They are widely used to develop eco-friendly coatings with enhanced performance for different functional purposes. The challenge is to obtain better phase homogeneity of organic and inorganic materials used for hybrid preparation. The reactive & functional polymers, grafting, surface modification of nano particles and polymers, in situ preparation etc. are being used for the said purpose. Organic–inorganic hybrid composites have recently attracted intense industrial and academic interests due to their remarkable and enhanced properties compared to unfilled resins. These materials exhibit the combined characteristics of organic

∗ Corresponding author at: Polymers & Functional Materials Division, Indian Institute of Chemical Technology, Hyderabad 500007, India. Tel.: +91 4027193991; fax: +91 4027193991. E-mail address: [email protected] (K.V.S.N. Raju). 1 Present address: Chemical Engineering Department, Petroleum Institute, Abu Dhabi, United Arab Emirates. http://dx.doi.org/10.1016/j.porgcoat.2015.05.022 0300-9440/© 2015 Published by Elsevier B.V.

polymer (e.g., flexibility, ductility, dielectric property) and inorganic materials (e.g., rigidity, high thermal stability, strength, hardness, high refractive index) [1–3]. Therefore, these materials could be widely used in the applications of protective coatings [4,5], high refractive index films [6], light-emitting diodes [7], solar cell [8] and optical waveguides materials [2,5]. Silane coupling agents are widely used to increase the interfacial adhesion between fillers and polymers [9–11]. Because of the poor dispersion of nanoparticles in polymer matrix and the poor interactions between nanoparticles and polymer, silane coupling agent such as 3-aminopropyltriethoxysilane (3-APTES), GPTMS, TMSPM have been used to modify the surface of nanoparticles [10–12]. Nanoparticles have been widely used as filler in the preparation of nano-composites materials [13–18]. The main disadvantages of incorporation of the nanoparticles into polymers are agglomeration and incompatibilities of nanoparticles with the organic matrix [19]. Homogeneous dispersion of nanoparticles is absolutely important for the formation of homogeneous nanoparticles films, well-ordered nanoporous films, or transparent nanocomposites. Nanoparticles tend to aggregate in an organic matrix due to their high surface energy. Aggregation of nanoparticles would tamper with the properties of materials. Sometimes the

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dispersion of nanoparticles even determines the composite material’s structure and properties. In most cases, it is very difficult to achieve the homogeneous dispersion of nanoparticles in a polymer matrix. Therefore, the enhancement of dispersion of nanoparticles in a matrix is a significant characteristic of nanocomposites. Surface modification of nanoparticles with coupling agents can be employed to offer better compatibility of nanoparticles with dispersing media, to prevent nanoparticles from aggregation, as well as to render the nanoparticles with chemical reactivity. This also avoid homogeneity and compatibility problems between the two phases and thus to design the materials with well-adjusted properties makes possible their potential use in industrial applications, such as coatings for various kinds of protection [20]. In this work, we have planned to develop hyperbranched polyurethane urea silica–ZnO hybrid coatings using surface modified ZnO nanoparticles. For this purpose the ZnO nanoparticles were treated with the coupling agent 3-aminopropyl triethoxy silane (APTES) by sol–gel process to graft the APTES chain onto the surface of ZnO nanoparticles. This APTES modified ZnO nanoparticles were mixed with 2nd generation NCO terminated hyperbranched polyurethane prepolymer. This was cured under ambient moisture condition to get chemically linked hyperbranched polyurethane urea silica ZnO Hybrid coatings. They were characterized by XRD, FTIR, TGA, DMTA, AFM, tensile test, and contact angle measurement.

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Table 1 Reactant used in the preparation of HBPUU–APTES–ZnO hybrid coatings. Sample code

Hyperbranched polyester (2nd generation)

OH:NCO ratio

APTES–ZnO

HBPUU–ZnO (5%) HBPUU–APTES–ZnO (5%) HBPUU–APTES–ZnO (10%) HBPUU–APTES–ZnO (20%)

Glycerol + bis-MPA Glycerol + bis-MPA Glycerol + bis-MPA Glycerol + bis-MPA

1:1.6 1:1.6 1:1.6 1:1.6

0% 5% 10% 20%

sample was named as 3-aminopropyl triethoxysilane modified ZnO (APTES–ZnO). 2.4. Preparation of hyperbranched polyurethane-urea (HBPUU)–ZnO composites HBPUU–ZnO hybrid composite film was prepared by adding 5 wt.% of ZnO nanoparticles into the solution of HBPU. The mixture was then stirred for 2 h to get homogeneous hybrid. Then the mixture was cast onto Teflon disk, dried in a vacuum oven at 60 ◦ C for 12 h to remove solvent. The films were stored at room temperature and humidity condition for one week to get complete cured film. 2.5. Preparation of HBPUU–APTES–ZnO composites

Isophorone diisocyanate (IPDI:Z and E isomer in 3:1 ratio), 2,2bis(hydroxymethyl)propionic acid (bis-MPA), dibutyltindilaurate (DBTL), APTES and ZnO nano powder (particle size 50–70 nm) were purchased from Aldrich (Milwaukee, WI). Glycerol, dimethylformamide (DMF) and methyl isobutyl ketone (MIBK) (dried over 4 A˚ molecular sieves) was purchased from Fluka chemicals (Mumbai, India).

HBPUU–APTES–ZnO hybrid composite films were prepared by adding APTES–ZnO (5%), APTES–ZnO (10%) and APTES–ZnO (20%) into the solution of NCO-terminated HBPU. The mixture was then stirred for 2 h to get homogeneous hybrid. Then the mixture was cast onto Teflon disk, dried in a vacuum oven at 60 ◦ C for 12 h to remove solvent. The films were stored at room temperature and humidity condition for one week to get complete cured film. The details of the hybrid composite preparation are reported in Table 1. Fig. 1 shows the steps involved in the modification of ZnO nanoparticles. Fig. 2 shows the steps involved in the synthesis of hybrid coatings. Fig. 3 shows the formation of hybrid macromolecules trough sol–gel process.

2.2. Hyperbranched polyurethane synthesis

2.6. Characterization techniques

The hyperbranched polyurethane used in this study was prepared from glycerol based 2nd generation HBP and IPDI as described in our previous work [21]. Briefly about the synthesis, hyperbranched polyester and IPDI were charged into a four-neck round bottomed flask equipped with nitrogen inlet, mechanical stirrer and a thermometer. The DMF and MIBK were chosen as solvent for the synthesis of hyperbranched polyurethane. The reaction was continued under continuous nitrogen flow at 70 ◦ C.

XRD pattern for the hybrid samples were analyzed using a Siemens/D-5000 X-ray diffractometer using Cu K␣ radiation of

2. Materials and methods 2.1. Materials

2.3. Modification of ZnO nanoparticles The introduction of reactive NH2 groups onto the surface of the ZnO nanoparticles was achieved by the reaction of APTES silane coupling agent and hydroxyl groups of the ZnO surface. 10 g ZnO powder and 50 g toluene were added into a round bottomed flask and stirred at room temperature using a magnetic stirrer. After 5 min, the suspension was treated in an ultrasonic bath for 10 min. 1 g (0.0055 mole) of APTES was added into the suspension and it was stirred at room temperature. After a yellow-transparent dispersion was obtained, the reaction mixtures were then refluxed for a further 24 h. The solvents in the dispersion were evaporated to dryness by using a rotation evaporator. After that, APTES modified ZnO powder was washed to remove unreacted APTES molecules with ethanol (three times). The powder was dried at 50 ◦ C for 1 h. After the powder was grinded, it was dried at 100 ◦ C for 2 h. The

Fig. 1. Shows the steps involved in the modification of ZnO nanoparticles.

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Fig. 2. Synthetic procedure of HBPUU–APTES–ZnO hybrid coatings.

˚ FTIR spectra of the HBPUU–APTES–ZnO hybrid wavelength 1.54 A. thin films coated on dry KBr disk were recorded on Thermo Nicolet Nexus 670 spectrometer with resolution setting 4 cm−1 and range of 400–4000 cm−1 . Each sample was scanned 68 times. Curve fitting simulations were performed using Origin software program. TEM micrographs of the hybrid films were taken with JEM-ARM200F, Jeol, Japan instrument working at 200 kV. Prior to the observation, the hybrid materials were diluted in ethanol and a few drops of the suspension were deposited at the surface of a copper observation grid. AFM images of the hybrid films were recorded by a (Dualscope 95-200, Denmark), in contact mode. The scan dimension and the roughness analysis were performed on 5 × 5 ␮m2 . Q 500 (PerkinElmer Inc., USA) was used to study the thermal decomposition profile of different hybrid coatings at a constant heating rate of 10 ◦ C/min in an inert nitrogen atmosphere from 25 to 600 ◦ C. DMTA IV instrument (Rheometric Scientific, United States) in tensile mode at a frequency of 1 Hz and heating rate of 3 ◦ C min−1 was used to study the viscoelastic behavior of the hybrid coatings. Contact angle was measured by using G10 (KRUSS) system. The static mechanical properties of the samples of the cast films were measured with the help of Shimadzu Autograph 10kNG Universal Testing Machine (Kyoto, Japan) using a load cell of 10 kN at a crosshead speed of 10 mm/min. The gauge length of the specimens was fixed at 50 mm.

3. Results and discussion 3.1. X-ray diffraction (XRD) analysis XRD curves of HBPUU–ZnO (5%), HBPUU–APTES–ZnO (5%) and HBPUU–APTES–ZnO (10%) hybrid films are shown in Fig. 4. XRD curves exhibit a broad peak at 18–30◦ (2 angle), which

suggests that diffraction occurs mostly by the amorphous polymer region. In the comparison between the HBPUU–ZnO (5%) and HBPUU–APTES–ZnO (5%) hybrid shows the broad peak intensity is decreased more in case of HBPUU–APTES–ZnO (5%) hybrid than HBPUU–ZnO (5%). This might be observed due to the interaction of inorganic materials with polymer [22]. This confirms that the ZnO nanoparticles are dispersed homogeneously in the HBPUU–APTES–ZnO (5%) hybrid than HBPUU–ZnO (5%) and evidenced by AFM.

3.2. FTIR analysis FTIR absorption spectra of HBPUU–ZnO (5%), HBPUU–APTES–ZnO (5%), HBPUU–APTES–ZnO (10%) and HBPUU–APTES–ZnO (20%) are illustrated in Fig. 5. All the composite films exhibit the characteristic absorption peaks of polyurethane and urea are shown at 1728 cm−1 (C O stretching), and 3300–3500 cm−1 (N H stretching) [23,24]. The reactions between NCO group of HBPU and primary amino groups of modified-ZnO that is confirmed by the disappearance of characteristic NCO band at 2240 cm−1 shown in Fig. 4. The sol–gel reaction of the hybrid composites can be monitored with FTIR as shown in Fig. 4. The absorption band around 1100 cm−1 , which is observed in all hybrid composites except HBPUU–ZnO (5%). HBPUU–APTES–ZnO (5%), HBPUU–APTES–ZnO (10%) and HBPUU–APTES–ZnO (20%) hybrid coatings show a novel peak appeared at around 995 cm−1 (designated to the formation of covalent bond Si O Zn). The band at 995 cm−1 corresponds to Si O Zn [25], which indicates that the covalent bond was made between ZnO and APTES on the nanoparticles surface. The study of hydrogen bonding interaction between the polymer matrix and ZnO nanoparticles, we have deconvoluted the C O zone

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Fig. 3. Hybrid macromolecules develop through sol–gel process.

of the HBPUU–ZnO (5%) and HBPUU–APTES–ZnO (5%) hybrid coating (Fig. 6). The deconvolution result suggests that the peak contribution for the hydrogen bonded carbonyls from urea as well as urethane zone was highest for the sample HBPUU–APTES–ZnO (5%) and lowest for HBPU–ZnO (5%). This might be observed due to the APTES which distributes the nanoparticles homogeneous in the polymer matrix at higher concentration. 3.3. TEM analysis

Fig. 4. X-ray diffraction patterns of the HBPUU and HBPUU–ZnO hybrid samples.

HR-TEM has proven to be a powerful tool for studying the dispersion and dimension of nanosized materials embedded within a polymer matrix. Fig. 7 shows HR-TEM images of hybrid materials. It is observed that nanosized ZnO chemically interact with the polymer matrix and disperse uniformly throughout the hybrid network due to the attractive forces between nanoparticles and polymer matrix which results in an increase in the Tg value (DMTA results). From the TEM images the size of SiO2 –ZnO in the hybrid materials

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Table 2 TGA data of different hybrid films along with the pure polymer. TON (◦ C)

Sample code

T1MAX (◦ C)

T2MAX (◦ C)

TEND (◦ C)

Wt.% remaining at N2 env. ◦

HBPUU–ZnO (5%) HBPUU–APTES–ZnO (5%) HBPUU–APTES–ZnO (10%) HBPUU–APTES–ZnO (20%)

264.8 268.9 272.5 281.3

292.1 297.2 305.1 329.5

318.1 326.1 330.7 350.2

351.1 359.4 372.8 401.3

O2 env. ◦

◦

350 C

450 C

500 C

350 ◦ C

450 ◦ C

500 ◦ C

26.1 29.4 30.6 32.7

16.3 19.5 21.4 23.1

13.8 15.3 16.2 18.1

– 28.9 30.2 31.8

– 19.1 21.1 22.6

– 14.7 15.4 18.0

influence on the thermal and mechanical properties of the resulting hybrid materials. 3.4. AFM analysis The AFM images of the HBPUU–ZnO (5%), HBPUU–APTES–ZnO (5%), and HBPUU–APTES–ZnO (10%) are illustrated in Fig. 6, and the surface roughness values are summarized in Table 4. Both Fig. 8 and Table 4 suggest that the surface roughness values decrease in case of HBPUU–APTES–ZnO (5%) than HBPUU–ZnO (5%) hybrid coating and suggest that in HBPUU–APTES–ZnO (5%) hybrid ZnO nanoparticles are dispersed homogeneously in the polymer matrix and making good compatibility between organic and inorganic phase. 3.5. TGA analysis

Fig. 5. FTIR spectra of HBPUU–ZnO and HBPUU–APTES–ZnO hybrid composite films.

is found to be in the range between 5 and 20 nm (Fig. 7a–c). These results further strengthen the fact that the hybrid films showed good interfacial interaction between the inorganic and organic matrix and the ZnO nanoparticles are well dispersed in hybrid materials without aggregation. The nanometer level dispersion of inorganic materials within the polymer matrix also establishes an

TGA thermograms of weight loss as a function of temperature for HBPUU–ZnO (5%), HBPUU–APTES–ZnO (5%), HBPUU–APTES–ZnO (10%) and HBPUU–APTES–ZnO (20%) hybrid materials were studied, as measured under an N2 atmosphere. The concluding TGA results are illustrated and summarized in Fig. 9(a) and Table 2. The onset temperature (TON ) corresponding to the maximum rate of weight loss (TMAX ) and the endset decomposition temperature (TEND ) of hybrid samples are reported in Table 2. Evidently, the thermal decomposition onset temperature of HBPUU–APTES–ZnO (5%) is shifted toward the higher temperature range than that of HBPUU–ZnO (5%). This might be observed due to the better interaction of the modified nano-particles with polymer matrix [26,27]. As the modified-ZnO content was increased to 10% APTES, the onset degradation of hybrid sol–gel materials is upward to 272.5 ◦ C, which confirms the further enhancement of thermal stability of

Fig. 6. FTIR peak deconvolution of carbonyl zone of HBPUU–ZnO (5%) and HBPUU–APTES–ZnO (5%) hybrid coatings.

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Fig. 7. HRTEM images of HBPUU–ZnO (5%) (a), HBPUU–APTES–ZnO (5%) (b), HBPUU–APTES–ZnO (10%) (c), hybrid films and EDAX spectrum profile of HBPUU–ZnO (5%) (d), HBPUU–APTES–ZnO (5%) (e), HBPUU–APTES–ZnO (10%) (f) hybrid films.

HBPUU by the incorporation of larger loaded inorganic particles. Fig. 9(b) and Table 2 show the TGA curve and data of the hybrid samples recorded in O2 environment. The results show that the residual weight percentage was lower than the hybrid analyzed in N2 environment. This behavior could be observed due to the fast oxidation process of the hybrid materials in oxygen environment.

3.6. DMTA study The thermo-mechanical properties of hybrid composite materials were also investigated through the performing of DMTA tests. The DMTA measured results based on the storage modulus and Tg of HBPUU–ZnO (5%), HBPUU–APTES–ZnO (5%), HBPUU–APTES–ZnO (10%) and HBPUU–APTES–ZnO (20%) of hybrid materials are given in Fig. 10 and summarized in Table 3. The storage modulus of hybrid material is remarkably increased from 3.22 × 108 Pa of HBPUU–ZnO (5%) to 1.11 × 109 Pa of HBPUU–APTES–ZnO (5%) at around 40 ◦ C. Moreover, it is also found that a further increase in modifiedZnO concentration resulted in an enhanced mechanical strength

(storage modulus) of hybrid materials. The Tg also is shifted to higher temperature in HBPUU–APTES–ZnO (5%) than HBPUU–ZnO (5%). This might be observed due to an increase in particle–matrix interaction, better dispersion and less tendency toward aggregation. The tan ı of HBPUU–APTES–ZnO (5%), HBPUU–APTES–ZnO (10%) and HBPUU–APTES–ZnO (20%) hybrid materials is higher than the HBPUU–ZnO (5%). The Tg and Tan ı max values of hybrid materials are listed in Table 3 and shown in Fig. 8. The Tg and storage modulus of the hybrid materials are significantly increased with increasing modified ZnO nano-particles content. This might be probably associated with the higher inorganic materials loading in polymer matrix leading to a higher interfacial interaction between the organic and inorganic phases [28–30]. As the motions of the polymer chain were hindered by inorganic particles, the Tg and E were increased significantly.

3.7. Contact angle measurement Table 4 shows the contact angle of HBPUU–APTES–ZnO (5%) is more compared to HBPUU–ZnO (5%) that means the obtained data

Table 3 DMTA data of HBPUU–APTES–ZnO hybrid films. Sample code

HBPUU–ZnO (5%)

HBPUU–APTES–ZnO (5%)

HBPUU–APTES–ZnO (10%)

HBPUU–APTES–ZnO (20%)

Tg (◦ C) Tan ␦max E at 40 ◦ C [Pa] E at (Tg + 5 ◦ C) in [Pa] ␧ (mole/cm3 ), at 40 ◦ C ␧ (mole/cm3 ), at (Tg + 5 ◦ C)

112.7 1.15 3.22 × 108 6.34 × 107 4.12 × 10−2 6.5 × 10−3

131.4 0.69 1.11 × 109 2.18 × 108 1.42 × 10−1 2.13 × 10−2

135.2 0.58 1.17 × 109 2.26 × 108 1.49 × 10−1 2.19 × 10−2

149.1 0.54 1.21 × 109 2.53 × 108 1.54 × 10−1 2.37 × 10−2

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Fig. 8. The AFM topography images (2D) of (a) HBPUU–ZnO (5%) (b) HBPUU–APTES–ZnO (5%) (c) HBPUU–APTES–ZnO (10%) and HBPUU–APTES–ZnO (10%) (3D) hybrid films.

suggest that the contact angle depends on the silane coupling agent (APTES). Due to the silane coupling agent the nanoparticles are more interacted with polymer matrix and make the hybrid more hydrophobic. The water contact angle is increased with the increasing modified-ZnO content in the hybrid materials, reflecting to an increase of hydrophobicity of coating materials. Thus, the incorporation of inorganic materials into the polymer matrix does indeed change the surface characteristics of the hybrid materials significantly. The above result might be obtained due to the decrease in surface polarity [31,32]. This increased hydrophobic property leads the hybrid materials to be potentially used in the application of corrosion protection coatings.

3.8. Tensile properties The tensile properties of the hybrid films were determined by Universal Testing Machine (UTM) and are summarized in Table 4. Table 4 exhibits the effects of modified-ZnO on the tensile properties of the hybrid films. The tensile strength is increased in HBPUU–APTES–ZnO (5%) compared to HBPUU–ZnO (5%), which is a result of the enhancement in the crosslink density between the organic and inorganic phases [32]. Considerable improvement in the tensile strength of the hybrid films is observed with an increasing modified-ZnO content. In general, the elongations at break decreased for the hybrid films with rigid inorganic materials filled.

Table 4 Contact angle, tensile strength, and roughness data of different hybrid films. Sample code

Max. stress (N/mm2 )

Elongation (%)

Contact angle after 40 days curing

Roughness value (AFM)

HBPUU–ZnO (5%) HBPUU–APTES–ZnO (5%) HBPUU–APTES–ZnO (10%) HBPUU–APTES–ZnO (20%)

13.122 15.672 16.789 23.982

43.784 40.541 38.982 36.744

69 76 81 85

12.8 nm 5.3 nm 6.3 nm 8.3 nm

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coating. Higher modified-ZnO content increased modulus, Tg , and tensile strength of the hybrid films. The modified-ZnO seemed to have more obvious influence on the surface roughness, thermal, Tg , contact angle and tensile strength of the hybrid. This may be due to formation of highly crosslinked inorganic network in the hybrid. Based on these properties this hybrid material can be considered as a resistant coating for different metals and metal alloys. Acknowledgment Kishore K. Jena would like to acknowledge Council of Scientific and Industrial Research (CSIR, New Delhi, India) for the research fellowship. References

Fig. 9. TGA thermograms of different HBPUU–APTES–ZnO hybrid films.

Fig. 10. The DMTA plot of tan ı vs. temperature curves of the different hybrid coatings.

4. Conclusions In this work a series of HBPUU–APTES–ZnO hybrid coatings were prepared, and their surface property and thermo-mechanical properties were evaluated. For this, initially the ZnO nanoparticles surface was modified by APTES silane coupling agent to obtain the NH2 modified-ZnO surface. In the next step, modified-ZnO was incorporated into the HBPU matrix to get the HBPUU–APTES–ZnO hybrid coating. More homogeneous hybrid coating was obtained at modified-ZnO hybrid than pure-ZnO and the storage modulus and tensile properties were increased in the modified-ZnO hybrid

[1] J. Zou, Y. Zhao, W. Shi, X. Shen, K. Nie, Preparation and characters of hyperbranched polyester-based organic–inorganic hybrid material compared with linear polyester, Polym. Adv. Technol. 16 (1) (2005) 55–60. [2] S. Frings, H.A. Meinema, C.F. van Nostrum, R. van der Linde, Organic–inorganic hybrid coatings for coil coating application based on polyesters and tetraethoxysilane, Prog. Org. Coat. 33 (2) (1998) 126–130. [3] J. Zou, W. Shi, X. Hong, Characterization and properties of a novel organic–inorganic hybrid based on hyperbranched aliphatic polyester prepared via sol–gel process, Compos. Part A 36 (5) (2005) 631–637. [4] A. Rekondo, M.J. Fernandez-Berridi, L. Irusta, Synthesis of silanized polyether urethane hybrid systems. Study of the curing process through hydrogen bonding interactions, Eur. Polym. J. 42 (9) (2006) 2069–2080. [5] R. Nass, E. Arpac, W. Glaubitt, H.J. Schmidt, Modelling of ORMOCER coatings by processing, J. Non-Cryst. Solids 121 (121) (1990) 370–374. [6] G. Philipp, H.J. Schmidt, New materials for contact lenses prepared from Siand Ti-alkoxides by the sol–gel process, J. Non-Cryst. Solids 63 (1) (1984) 283–292. [7] H.J. Schmidt, Multifunctional inorganic–organic composite sol–gel coatings for glass surfaces, J. Non-Cryst. Solids 178 (3) (1994) 302–312. [8] P.C. Chiang, W.T. Whang, M.H. Tsai, S.C. Wu, Physical and mechanical properties of polyimideytitania hybrid films, Thin Solid Films 447 (2004) 359–364. [9] A. Taniguchi, M. Cakmak, The suppression of strain induced crystallization in PET through sub micron TiO2 particle incorporation, Polymer 45 (19) (2004) 6647–6654. [10] Z.H. Lua, G.J. Liu, S. Duncan, Poly(2-hydroxyethyl acrylate-co-methyl acrylate)/SiO2 /TiO2 hybrid membranes, J. Membr. Sci. 221 (1) (2003) 113–122. [11] P. Innocenzi, A. Sassi, A. Brusatin, M. Guglielmi, D. Favretto, R. Bertani, A. Venzo, F. Babonneau, A novel synthesis of sol–gel hybrid materials by a nonhydrolytic/hydrolytic reaction of (3-glycidoxypropyl)trimethoxysilane with TiCl4 , Chem. Mater. 13 (10) (2001) 3635. [12] Y.L. Liu, C.S. Wu, Y.S. Chiu, W.H. Ho, Preparation, thermal properties, and flame retardance of epoxy-silica hybrid resins, J. Polym. Sci. Part A: Polym. Chem. 41 (15) (2003) 2354–2367. [13] S.R. Isaacs, H. Choo, W.B. Ko, Y.S. Shon, Chemical, thermal, and ultrasonic stability of hybrid nanoparticles and nanoparticle multilayer films, Chem. Mater. 18 (1) (2006) 107–114. [14] D. Mrabet, M.H. Zahedi-Niaki, T.O. Do, Synthesis of nanoporous network materials with high surface areas from the cooperative assemblage of alkyl-chain-capped metal/metal oxide nanoparticles, J. Phys. Chem. C 112 (18) (2008) 7124–7129. [15] S. Lee, H.J.S. Shin, M.D. Yoon, K. Yi, Refractive index engineering of transparent ZrO2 -polydimethylsiloxane nanocomposites, J. Mater. Chem. 18 (2008) 1751–1755. [16] M.K. Corbierre, N.S. Cameron, M. Sutton, K. Laaziri, R.B. Lennox, Gold nanoparticle/polymer nanocomposites: dispersion of nanoparticles as a function of capping agent molecular weight and grafting density, Langmuir 21 (13) (2005) 6063–6072. [17] H. Chen, S.X. Zhou, G.X. Gu, L.M. Wu, Modification and dispersion of nanosilica, J. Dispers. Sci. Technol. 25 (6) (2004) 837–848. [18] G.D. Chen, S.X. Zhou, G.X. Gu, H.H. Yang, L.M. Wu, Effects of surface properties of colloidal silica particles on redispersibility and properties of acrylic-based polyurethane/silica composites, J. Colloid Interface Sci. 281 (2) (2005) 339–350. [19] F. Bauer, V. Sauerland, H. Ernst, H.J. Gläsel, S. Naumov, R. Mehnert, Preparation of scratch- and abrasion-resistant polymeric nanocomposites by monomer grafting onto nanoparticles, Macromol. Chem. Phys. 204 (3) (2003) 375–383. [20] Z. Zeng, J. Yu, Z.X. Guo, Preparation of functionalized core–shell alumina/polystyrene composite nanoparticles, Macromol. Chem. Phys. 206 (15) (2005) 1558–1563. [21] K.K. Jena, D.K. Chattopadhyay, K.V.S.N. Raju, Synthesis and characterization of hyperbranched polyurethane-urea coatings, Eur. Polym. J. 43 (5) (2007) 1825–1837.

90

K.K. Jena et al. / Progress in Organic Coatings 89 (2015) 82–90

[22] T. Agag, T. Koga, T. Takeichi, Studies on thermal and mechanical properties of polyimide-clay nanocomposites, Polymer 42 (8) (2001) 3399–3408. [23] M.M. Coleman, K.H. Lee, D.J. Skrovanek, P.C. Painter, Hydrogen bonding in polymers. 4: Infrared temperature studies of a simple polyurethane, Macromolecules 19 (8) (1986) 2149. [24] C. Wilhelm, J.L. Gardette, Infrared analysis of the photochemical behaviour of segmented polyurethanes: aliphatic poly(ether-urethane)s, Polymer 39 (24) (1998) 5973–5980. [25] R.Y. Hong, J.H. Li, L.L. Chen, D.Q. Liu, H.Z. Li, Y. Zheng, J. Ding, Synthesis, surface modification and photocatalytic property of ZnO nanoparticles, Powder Technol. 189 (3) (2009) 426–432. [26] J.C. Woo, H.K. Se, J.K. Young, C.K. Sung, Synthesis of chain-extended organifier and properties of polyurethane/clay nanocomposites, Polymer 45 (17) (2004) 6045–6057. [27] H.R. Fischer, L.H. Gielgens, T.P.M. Koster, Nanocomposites from polymers and layered minerals, Acta Polym. 50 (4) (1999) 122–126.

[28] J. Zheng, R. Ozisik, R.W. Siegel, Disruption of self-assembly and altered mechanical behavior in polyurethane/zinc oxide nanocomposites, Polymer 46 (24) (2005) 10873–10882. [29] K.K. Jena, K.V.S.N. Raju, Synthesis and characterization of hyperbranched polyurethane hybrids using tetraethoxysilane (TEOS) as cross-linker, Ind. Eng. Chem. Res. 47 (23) (2008) 9214–9224. [30] A.K. Mishra, K.K. Jena, K.V.S.N. Raju, Synthesis and characterization of hyperbranched polyester–urethane–urea/K10-clay hybrid coatings, Prog. Org. Coat. 64 (1) (2009) 47–56. [31] P. Florian, K.K. Jena, S. Allauddin, R. Narayan, K.V.S.N. Raju, Preparation and characterization of waterborne hyperbranched polyurethane-urea and their hybrid coatings, Ind. Eng. Chem. Res. 49 (10) (2010) 4517–4527. [32] K.K. Jena, K.V.S.N. Raju, Synthesis and characterization of hyperbranched polyurethane–urea/silica based hybrid coatings, Ind. Eng. Chem. Res. 46 (20) (2007) 6408–6416.