Abstract
In this work, the waterborne graphene oxide/polyurethane-acrylate (GO-WPUA) oligomer was prepared based on isophorone diisocyanate (IPDI), polyether polyol (NJ-220), graphene oxide (GO), dimethylol propionic acid (DMPA) and hydroxyethyl methylacrylate (HEMA). A series of the UV-curable waterborne graphene oxide/polyurethane-acrylate composites containing different content of GO were obtained with oligomer, monomers (BA and TPGDA) and photoinitiator Darocur 1173. The structure, viscosity, particle size and surface tension of emulsions were measured. Some mechanical performances, solvent resistance, the water absorption and thermal property of films were investigated. When the content of GO is 0·01%, the UV-curable film has the best mechanical property. The obtained composites have great potential application such as coatings, leather finishing, adhesives, sealants, plastic coatings and wood finishes.
Introduction
UV-curable coatings have been found in wide applications because of their advantages, such as few volatile organic compounds (VOC), lower energy consumption, reduced cycle time, increased production capacity, high chemical stability, and very rapid curing features at ambient temperatures. They could be replaced by solvent based products to become the most favoured domestic and industrial coatings.1, 2 The UV-curable coatings consist of oligomer, monomer and photoinitiator. The properties of coating film, such as hardness, abrasive resistance, flexibility and weatherability, mainly depend on the oligomer structure and its concentration in the formulation. Therefore, looking for more new structure and special property oligomer would play the key role in the development of UV-curable chemistry. 3
Recently, UV-curable waterborne polyurethane-acrylate (PUA) have gained increasing attention and exhibit rapid development due to their versatility, environmental friendliness, excellent mechanical performance, abrasion resistance, and toughness and excellent resistance to chemicals and solvents. Representatively, PUA is a segmented PU oligomer tipped with acrylic functionality, such as hydroxy-ethylacrylate (HEA) or hydroxyethyl methyl acrylate (HEMA). The hard segments consist of isocyanate and HEA or HEMA, and the soft segments generally are formed by polyester or polyether polyol. The incompatibility between the soft and hard segments brings about the separation of the two phases, which can be prevented partly by hydrogen bonds between urethane –NH and polyether (–O–) or polyester carbonyls. The degree of microphase separation has a great effect on the properties of the cured films, such as hardness, flexibility, abradability, etc. One way to improve the properties of these coatings is that adding inorganic particles into the organic polymeric matrix which leads, under proper conditions, to the formation of a hybrid material.
Graphite (GP), which is naturally abundant, is a layered material formed by a number of two dimensional graphene crystals weakly coupling together and is well known as traditional carbon based filler recognising as the best conductive filler for its excellent conductive properties and well dispersion in polymer matrix. 4 Compared with graphite, the structure of graphene oxide (GO) has no difference but the sp3 hybridisation in carbon atoms indicates that the individual layers are considerably bent. 5 In this study, graphite oxide (GPO) is used as a medium to obtain stable GO dispersion in deionised water: GPO is a product from oxidation of graphite, maintaining the original layered structure of graphite. 6 GO, a typical pseudo-two-dimensional oxygen-containing solid in bulk form, has multiple oxygen containing functional groups improving the dispersion of graphene, such as hydroxyls and epoxides in the basal plane and carboxyl groups at plane edges, 7 which can be easily prepared by chemical modification. Such surface functionalisation leads to good GO dispersion in water. 8 Using exfoliated GO sheets in water, composites based on water soluble polymers, such as poly(vinyl alcohol) 9 and poly(allylamine) hydrochloride 10 have been reported. Additionally, the interfacial interaction between GO and the matrix, which is similar to that observed for functionalized carbon nanotube based nanocomposites, may be improved due to the functional side groups bound to the surface of GO sheets. 11 The surface functionalised GO can also react with isocyanate to improve its hydrophobicity and dispersibility in N, N-dimethylformamide (DMF) because of the presence of hydroxyl groups, 12 which allows for preparation of various polymer composites containing GO. Polymer/GO composites based on organic solvent soluble polymers, such as polystyrene (PS) 13 and poly (methyl methacrylate) (PMMA) 14 have been prepared by solution blending. Jeong et al. 15 reported a dramatic increase in the glass transition temperature (Tg) of PMMA in PMMA/GO composites. Some prominent reports have explored the intriguing applications of graphene oxide–polymer nanocomposites, such as organic conductive films and heat resistant material. 16 In this work, well dispersed GO in DMF was prepared by ultrasonic dissection of graphite oxide. Then, a series of PUA/GO composites were prepared by in situ dispersion method. UV-GO-WPUA-film was obtained by ultraviolet light polymerization and characterised using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) measuring apparatus to determine their structures, surface morphologies, etc. Moreover, the mechanical and water resistance properties of the composites films were also determined.
Experimental
Materials
Graphite powder, concentrated sulphuric acid, sodium nitrate, butyl acrylate (BA), triethylamine (TEA), dibutylbis(lauroyloxy) tin (DBLT) and N, N-dimethyl formamide (DMF) were obtained from Sinopharm Chemical Reagent Co., Ltd. Potassium permanganate was supplied by Jinshan County Chemical Plant, in Zhenjiang, Jiangsu, China. Hydrogen peroxide (30%) was produced by Lingfeng Chemical Reagent Co., Ltd, in Shanghai, China. Polyether polyols (NJ-220, Mn = 2000 g mol−1) was produced by Ningwu Chemical CO., Ltd, in Jurong, Jiangsu, China. Dimethylpropionic acid (DMPA) was produced by PERSTOP Co., in Helsingborg, Sweden. Isophorone diisocyanate (IPDI) was supplied by Rongrong Chemical Ltd, Shanghai, China. Hydroxyethyl methyl acrylate (HEMA) was provided by Yinlian Chemical Ltd, Wuxi, Jiangsu, China. Tripropyleneglycol diacrylate (TPGDA) and Darocur 1173 were supplied from Mingda Macromolecule Science and Technology CO., Ltd, Suzhou, Jiangsu, China.
Preparation of graphite oxide (GPO) and graphene oxide (GO)
Graphite oxide (GPO) was prepared from natural flake graphite by modified Hummers method.17, 18 A certain amount of concentrated sulfuric acid (H2SO4, 23 mL) was added into a 250 mL flask filled with graphite (GP, 1 g) powder and sodium nitrate (0·5 g) at room temperature. The mixture was then cooled to 0°C in an ice water bath. After that, solid potassium permanganate (3 g) was slowly (∼1 g/5 min) added to the mixture. The resultant mixture was stirred by a motordriven stirring bar for ∼1 h and the temperature was controlled below 20°C. Then, the ice bath was removed and the system was heated at 35°C for 2 h in a water bath, and then deionised water (46 mL) was added slowly into the system and it was stirred it for another 30 min. The temperature was controlled below 98°C. The system was heated at 90–100°C for 30 min in a water bath after finishing adding distilled water. Then, the water bath was removed and deionised water (140 mL) and 3%H2O2 (10 mL) aqueous solution were added to reduce the residual KMnO4 till no bubble was appeared. Finally, the system was centrifuged at 3000 rev min−1 for 10 min, and the obtained powder was washed by distilled water and 5% hydrochloric acid until the pH value of the upper layer suspension arrives at near 7. Waterless GPO powder was obtained by high speed centrifugation, removal of the supernate, and then drying in vacuo at 60°C for 12 h.
The obtained yellow–brown powder (GPO) was re-dispersed into deionised water (1 mg mL−1) and exfoliated by mild ultrasound for 5 h, and there forms a yellow–brown homogeneous suspension after filtering the trace black residues. The graphene oxide (GO) was obtained. The synthetic route of GPO and GO are shown in Fig. 1.
Synthetic route of GPO and GO
Preparation of UV-curable pure waterborne polyurethane-acrylate (WPUA) oligomer
A certain amounts of polyether polyols (NJ-220, 10 g), N, N-dimethyl formamide (DMF, 12 g) and dimethylpropionic acid (DMPA, 0·9895 g) were added into a four necked flask equipped with a mechanical stirrer, thermometer and reflux condenser. Then, isophorone diisocyanate (IPDI, 5·503 g) was added and the mixture was heated to 40°C. Dibutylbis(lauroyloxy) tin (DBLT) was added as catalyst and the mixture was heated to 60°C. Next, raising the temperature to 80°C and keeping the temperature for 4 h. Hydroxyethyl methyl acrylate (HEMA, 3·222 g) was added into the system and reacted at 60°C for 5 h. When the temperature was cooled down to 40°C, triethylamine (TEA) was added into the flask subsequently and reacted at 40°C for 30 min. The mixture was then dispersed into deionised water under vigorous stirring for 30 min. The pure waterborne polyurethane-acrylate (WPUA) oligomer was obtained. The synthetic route of pure waterborne polyurethane-acrylate (WPUA) oligomer is shown in Fig. 2.
Synthetic route of pure waterborne polyurethane-acrylate (WPUA) oligomer
Preparation of UV-curable waterborne graphene oxide/polyurethane- acrylate (UV-GO-WPUA) oligomer
A certain quality of GO dissolved in DMF was exfoliated by mild ultrasound for 5 h in the ultrasonic cleaning machine. A certain amounts of NJ-220, GO solution and DMPA were added into a four necked flask equipped with a mechanical stirrer, thermometer and reflux condenser. Then, IPDI was added when the mixture was heated to 40°C and DBLT was added as catalyst when the mixture was heated to 60°C. Next, raising the temperature to 80°C and keeping the temperature for 4 h. HEMA was added into the system and reacted at 60°C for 5 h. When the temperature was cooled down to 40°C, TEA were added into the flask subsequently and reacted at 40°C for 30 min. The mixture was then dispersed into deionised water under vigorous stirring for 30 min. With various proportion of GO, a series of UV-curable waterborne graphene oxide/polyurethane-acrylate (GO-WPUA) oligomers were obtained. The synthetic route of UV-curable waterborne graphene oxide/polyurethane-acrylate (GO-WPUA) oligomer is shown in Fig. 3 and the formula is shown in Table 1.
Synthetic route of UV-curable waterborne graphene oxide/polyurethane-acrylate (GO-WPUA) oligomer
Proportion of oligomer
Preparation of UV-WPUA and UV-GO-WPUA films
UV-WPUA and UV-GO-WPUA were prepared by casting the newly synthesised oligomer, butyl acrylate (BA) and tripropyleneglycol diacrylate (TPGDA) onto a poly (tetrafluoroethylene) drying at 65°C for 3 h. Because water was used as diluents in this system, it needed the flash-off step, where water was evaporated before UV curing. During the water in the aqueous dispersion to be removed, physical entanglement occurred could be acquired because of the large molecular weight of the prepolymer.19, 20 Then, with the UV light that was produced by a lamp (main wave length: 365 nm, the power of the lamp: 1000 W, the UV energy per second: 1000 J s−1 and the distance between the thin film sample and the centre of UV lamp was 20 cm) irradiating, the Darocur 1173 was activated and the radicals could be produced. The formed radicals broke the acrylate double bond of the monomers and oligomers which resulted in crosslinking; then the UV-WPUA film could be obtained. The waterborne UV-PUA film was cured through two-step process; and the photodissociation mechanism of Darocur 1173 was shown in Fig. 4.
Photodissociation mechanism of Darocur 1173
Measurements and characterisation
Water absorption (or swelling degree) of UV-WPUA and UV-GO-WPUA films
The measurements of water absorption or swelling degree of the UV-WPUA and UV-GO-WPUA films were the same procedures. The procedures for these measurements were briefly described as follows. The UV-WPUA and UV-GO-WPUA films were cut into the size of 30×30 mm and put into water (or 5%NaOH or ethanol) at 25°C after being weighted. 24 h later, the film was taken out, rub dry by wiping off the surface water with apiece of filter paper, and then weighted again. The water absorption (or swelling degree) ω was calculated by as the following equation (1)
Hardness, tensile strength and elongation at break of UV-WPUA and UV-GO-WPUA films
The hardness was measured with a sclerometer (KYLXA, Jiangdu Kaiyuan Test Machine Co., Ltd, Jiangdu, China); measurements were done three times for each sample, and the average value was calculated.
Tensile strength testing and elongation at break testing for all of the specimens were carried out on a tensile tester (KY-8000A, Jiangdu Kaiyuan Test Machine Co., Ltd., Jiangdu, China) at room temperature and at a speed of 50 mm min−1. All measurements had an average of three runs. The dumbbell type specimen was 30 mm long at two ends, 0·2 mm thick and 4 mm wide at the neck.
Apparent viscosity of WPUA and GO-WPUA emulsions
The apparent viscosity of the WPUA and GO-WPUA emulsions was measured by a numerical viscometer (NDJ-9S, Shanghai Precision and Scientific Instrument Co. Ltd, Shanghai, China); when the shear rate was 2000 s−1, the high shear rate guaranteed highly reliable measurements at a temperature of 25°C.
Particle size and polydispersity of WPUA and GO-WPUA emulsions
Particle size is the important parameter in deciding the end use industrial applications of aqueous polyurethane dispersions. The WPUA and GO-WPUA emulsions were added to 100 mL test tubes and diluted with deionised water. The particle diameter and polydispersity were measured by a laser particle size analyser (BIC-9010, Brookhaven Instrument Co., Holtsville, NY, USA).
Surface tensions of WPUA and GO-WPUA emulsions
The surface tensions of WPUA and GO-WPUA emulsions were measured by a surface tension meter (DCAT 11, German dataphysics).
Contact angle of UV-WPUA and UV-GO-WPUA films
The equilibrium contact angle is defined as the angle between the solid surface and a tangent, drawn on the drop surface, passing through the atmosphere–liquid–solid triple-point. The contact angle of UV-WPUA and UV-GO-WPUA coating films were measured by a commercial CAM200 optical system (KSV Instruments, Finland). The test liquids used in this experiment were distilled water.
Structure characterisation of GO-WPUA oligomer and UV-GO-WPUA films
FT-IR spectrum of the UV-PUA film was obtained between 4000 and 400 cm−1 with an FTIR spectrometer (AVATAR 360, Madison and Nicolet). A minimum of 32 scans was signal averaged with a resolution of 2 cm−1 in the 4000–400 cm−1 ranges.
Thermal properties
Thermogravimetric analysis (TGA) of the UV-GO-PUA film was performed on a Netzsch instrument (STA 449 C, Netzsch, Seligenstadt, Germany). The programmed heating range was from room temperature to 600°C at a heating rate of 10°C min−1 under a nitrogen atmosphere. The measurement was taken with 6–10 mg samples.
SEM
To investigate the morphology of the film, the fracture surface was investigated with a 20 kV accelerating voltage with a field emission scanning electron microscope (S-4800, Hitachi Corp., Tokyo, Japan).
TEM
The morphology of the GO was observed by TEM (TECNAI-12, Philips Co., Eindhoven, The Netherlands) with an acceleration voltage of 120 kV. The GO were dispersed in deionised water in an ultrasonic bath for 10–30 min and then prepared by the deposition of the emulsion onto a copper net after it was stained by phosphorwolframic acid.
XRD
The XRD pattern was recorded by the reflection scan with nickel filtered Cu Kα radiation (D8, Bruker-AXS, Karlsruhe, Germany). The X-ray generator was run at 50 kV and 70 mA. All of the XRD measurements were performed between 5 and 80°.
Results and discussion
Physical properties of WPUA and GO-WPUA emulsions
The physical properties of aqueous dispersions such as apparent viscosity, particle size, surface tension and contact angle were shown in Table 2. The viscosity of a UV-curable system is considered one of the most important parameters, affecting the processability and the photopolymerisation rate of the cured film. Therefore, a suitable viscosity of the UV-curable system is very important to the properties of the final cured film. From Table 2, compared with the pure WPUA dispersion, almost all of the GO-WPUA dispersions remain stable, which indicates GO has no obvious impacts on apparent viscosity of UV-curable system. Surface tension σ of WPUA and GO-WPUA dispersion is a significant physical performances parameter. It is depend on the number and size of polarity base in the chain of big molecule. The smaller the surface tension is, the better the performance of infiltration is. As is demonstrated in Table 2, with increasing GO content, the value of surface tensions of all the dispersions increases first and then decreases, which is because that the higher the surface energy is, the greater the surface tension is, due to the increase of the polar groups on the surface of the system. When the content is more than 0·01%, the contact is hindered between GO and DMF decreasing the value of surface tensions. From Table 2, the smaller the particle size of emulsion, the more transparent in appearance, which shows particle size directly affected the emulsion appearance. The content of GO has great influence on the particle size of emulsions due to the addition of inorganic particles, changing the microstructure of emulsions. Moreover, with the same level in the viscosity and surface tension, when the content of GO is 0·010%, the particle size reaches the minimum.
Physical properties of emulsions
Physical properties of WPUA and UV-GO-WPUA films
The mechanical properties for WPUA and UV-GO-WPUA films are listed in Table 3. From Table 3, compared with UV-WPUA film, UV-GO-WPUA films have huge advantages, which was because GO has a larger interfacial area of contact and the larger diameter than thickness. 21 With the increasing GO content, the hardness of the UV-GO-WPUA films increase gradually. This is mainly because on the one hand, GO itself has excellent mechanical properties. On the other hand, the GO is familiar with the hard segment of UV-GO-WPUA. In the system, there are hydrogen bonding and some compatibility between the GO and WPUA. With the increasing hard monomer content (GO), the density of the hard segment in the molecular chains increases, the cross-linked degree improves because of the hydrogen bonding formation. At larger hard segment content, the phase of the hard segment exhibits higher impact strength, higher hardness. However, hardness becomes inferior beyond optimum concentration of GO, which is because the intermolecular forces between GO and WPUA is much higher than the hydrogen bonding, and increases the molecular inter-atomic forces. Compared with the pure UV-WPUA films, the value of the water absorption of UV-GO-WPUA coating films is higher. Because of the hydrophily of GO, the UV-GO-WPUA films showed certain water absorbing quality. The value of the contact angle of the pure UV-WPUA coating films is higher than UV-GO-WPUA coating films. With the addition of GO, there are a large number of hydrophilic groups such as –OH and –COOH, which make the greatly contact between films and distilled water. From Table 3, when the content of GO is 0·01%, the tensile strength of the film reaches the maximum and the other physical properties are well under this condition.
Mechanical properties and solvent resistance of films
FT-IR spectra
The FTIR spectra of the GO, GPO, UV-GO-WPUA dispersions films are shown in Figs. 5 and 6.
FT-IR spectra of GO, GPO, WPUA and GO-WPUA dispersions
FT-IR spectra of GO, GPO, WPUA and UV-GO-WPUA films
As shown in Fig. 5:
the spectral analysis is used mainly to check the completion of the polymerisation reaction, in terms of the disappearance of the –NCO band at 2270 cm−1, and the appearance of the N–H band at 3310–3500 cm−1. The disappearance of the peak at 2270 cm−1, which corresponded to –NCO group in FT-IR spectra of WPUA and GO-WPUA dispersions, proves the polymerisation. The result shows that the –NCO had reacted with –OH coming from NJ220 and GO into –NHCOO and the –NCO groups, indicating that there has a covalent bond between GO dispersing in the resin matrix and resin, which is more conducive to GO evenly dispersed in the resin matrix. Connection, it is more advantageous to functionalisation graphene evenly dispersed in the resin matrix. A strong absorption peak at about 1680 cm−1 is ascribed to the stretching vibration of carbamate carbonyl of –C = O groups. The absorption peak typically at 1460 cm−1 ( = CH2), indicating that the C = C bond of HEMA had been grafted into the polyurethane chains. The stretching vibrations of carbon–hydrogen bonds in –CH2 and –CH3 groups are observed at 2800–3000 cm−1 range. The absorption band at 1108 cm−1 is corresponded to the stretching vibration peak of C–O–C group. The above results show that polyurethane is synthesised successfully
there is a slight absorption peak at ∼3428 cm−1, which shows the –OH group of GO had not been completely reacted.
As can be seen from Fig. 6, there is absorption peak at 1730 cm−1, which is because the effect of the carbonyl of GO. The disappearances of the C = C bond at about 1631 cm−1 (C = C) and 1412 cm−1 ( = CH2) in the system, indicate the (C = C) had been completely reacted after UV-curing.
Thermal properties of UV- WPUA and UV-GO-WPUA films
The TG curves of the UV-WPUA and UV-GO-WPUA-3 films were shown in Fig. 7. As can be seen from Fig. 7, the decomposition temperatures (Td) of UV-WPUA film at 5, 10 and 50% mass losses are 212, 292 and 377°C respectively. The decomposition temperatures of UV-GO-WPUA-3 composite film at 5, 10 and 50% mass losses ware 236, 306 and 382°C respectively. The results indicate that the UV-GO-WPUA-3 composite film has better thermal properties than UV-WPUA film. On the one hand, because a small amount of GO is restored into grapheme and GO itself has good heat resistance, whose initial decomposition temperature is 2800°C under vacuum. On the other hand, the reaction between oxygen containing functional groups such as hydroxyl of GO and –NCO from IPDI made the formation composite materials which were helpful to improve the thermal stability. Owing to the special piece of layer structure of GO, when GO evenly disperses in the resin, the movement of resin molecular chain segments and thermal decomposition will be hindered. Therefore, the decomposition temperatures of films are improved.
TGA curves of UV-WPUA and UV-GO-WPUA-3 films
SEM and TEM
The SEM images of GP, GO, UV-WPUA film and UV-GO-WPUA-3 film sections are shown in Fig. 8a–d respectively. From Fig. 8a, graphite has flake structure, which is composed of flat layers. As can be seen from Fig. 8b, the flat layer structure of graphite has been destroyed to form GO after strong oxidation and exfoliation. The formation of fold lamella structure of GO is due to the presence of oxygen containing functional groups on the surface of the system during the oxidation. These functional groups destroyed the perfect sp2 hybrid orbitals of carbon atoms in the GP, instead of a large number of sp3 hybrid orbitals. That is also mainly because sp3 hybrid orbitals cannot be in the same plane, GO has formed the fold structure and the formation of the surface of the GO is more obvious after ultrasonic dissection. Comparing Fig. 8c and d, the surface of UV-WPUA is smooth level off and has almost no crack. Graphene oxide makes slice layer surface of UV-WPUA have some creases, changing the morphology of UV-WPUA. From Fig. 8d, the creases of GO and the slice layer surface of UV-WPUA intertwine together, which indicate GO has a stronger interaction with polyurethane.
Images (SEM) of a GP, b GO, c UV-WPUA film and d UV-GO-WPUA-3 film
The TEM image of GO dispersing in the deionised water is showed in Fig. 9. From Fig. 9, graphene oxide can disperse well in the deionised water and stacked in the form of slice layer, which indicates that GO can disperse in waterborne polyurethane primly and evenly.
Image (TEM) of graphene oxide
XRD
X-ray diffraction analysis of the flake graphite, graphite oxide GPO, UV-WPUA film and UV-GO-WPUA-3 film are shown in Fig. 10. For the natural flake graphite, a strong sharp and highly symmetrical diffraction peak is observed near 2θ = 26°, which indicates that flake graphite is highly crystalline. This peak is attributed to the flake graphite layer packing orderly. A new broad diffraction halo is observed near 2θ = 11° instead of the highly symmetrical diffraction peak at 2θ = 26° after strong oxidation in high temperature, which indicates crystallisation degree of graphite declined dramatically. By Bragg equation (2d sin θ = λ, d represents layer spacing, θ represents the complementary angle of incidence angle in X-ray and λ represents the wavelength of incident wave), the layer spacing can be calculated according to the transformation of the diffraction peak. The value of the layer spacing of graphite is 0·0194 μm which is lower than graphite oxide (0·0460 μm). In addition, compared with graphite, GPO layer spacing increases because the graphene sheet layer surface produced large amounts of oxygen functional groups after oxidation and lamellar spacing enlarged. For the pure UV-WPUA film, a broad diffraction halo is observed near 2θ = 20° and this diffraction halo is associated with the amorphous phase of the PUA. Comparing UV-GO-WPUA-3 film with the pure UV-WPUA film, the diffraction peak shifts to the right, this shows that the addition of graphene oxide can improve the crystallinity of the UV-WPUA film.
XRD patterns of graphite, GPO, UV-WPUA film and UV-WPUA-3 film
Conclusions
The stable graphene oxide (GO) dispersion in deionised water was prepared by ultrasonic dissection of graphite oxide which was obtained by the Hummers method. A series of GO-WPUA materials with different GO content were successfully prepared. The physical properties of GO-WPUA dispersions, mechanical properties, chemical resistances and thermal properties of obtained UV-GO-WPUA films were investigated. The structure and surface morphology of the prepared GO-WPUA dispersions and UV-GO-WPUA films were characterised with FT-IR, SEM and TEM measuring apparatus. The viscosity of emulsion changes little with the range of GO content from 0·005 to 0·030 wt-%. The GO content has great effect on the particle size of emulsions; and when the content of GO is 0·010%, the particle size reaches the minimum. Compared with UV-WPUA film, UV-GO-WPUA films have better mechanical properties. When the content of GO is 0·01%, the composite film has the biggest tensile strength. The prepared UV-GO-WPUA composite film has better thermal properties than UV-WPUA film. The obtained results indicate that the UV-GO-WPUA composites have great potential applications in different regions such as coatings, leather finishing, adhesives, sealants, plastic coatings and wood finishes.
Footnotes
Acknowledgements
This project was supported by the Society Development Fund of Zhenjiang (SH2013020 and SH2012014), Project of Science and Technology of Suzhou (SG201338) and Sponsored by Qing Lan Project (2012–2015).