[
    {
        "id": 1,
        "chunk": "# UV-curable waterborne polyurethane-acrylate: preparation, characterization and properties  \n\nHeping Xu, Fengxian Qiu ∗,  Yingying Wang, Wenling Wu, Dongya Yang, Qing Guo  \n\nSchool of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, China",
        "category": " Abstract"
    },
    {
        "id": 2,
        "chunk": "# a r t i c l e i n f o",
        "category": " Abstract"
    },
    {
        "id": 3,
        "chunk": "# a b s t r a c t  \n\nArticle history:   \nReceived 8 April 2011   \nReceived in revised form 28 July 2011   \nAccepted 25 August 2011   \nKeywords:   \nUV-curable   \nWaterborne polyurethane-acrylate   \nSolvent resistance   \nMechanical properties  \n\nThe waterborne polyurethane-acrylate (PUA) oligomer was firstly prepared based on isophorone diisocyanate (IPDI),  polyether polyol (NJ-210), dimethylol propionic acid  (DMPA) and  hydroxyethyl methyl acrylate (HEMA) via  in  situ  and  anionic self-emulsifying method. The UV-curable polyurethane-acrylate (UV-PUA) was obtained with oligomer, monomers (BA and TPGDA) and photoinitiator Darocur 1173. FT-IR, DSC  and  TGA  were  employed to  investigate the  structures and  thermal properties of  the  UV-PUA films. The  effects  of BA/TPGDA (R)  value, the  content of Darocur 1173 and  the  UV  curing  time  on  the performances were investigated. Some mechanical performances, solvent resistance and the gel content of UV-PUA films  were  measured. When the  ratio  of BA/TPGDA was  5/5,  the  UV-PUA film had  the  best solvent (water, alkali  and  ethanol) resistances. Besides, with the  ratio  of the  BA/TPGDA increasing, the  surface drying time increased. When the  content of  Darocur  1173 was $4\\%$ ,  the  gel  content  achieved the  maximum while the  surface  drying time  achieved the  minimum. The  obtained UV-curable polyurethane-acrylates are promising as oligomers for  UV-curable coatings, plastics, inks  and  adhesives.  \n\n$\\mathfrak{C}$ 2011 Elsevier B.V. All rights reserved.",
        "category": " Abstract"
    },
    {
        "id": 4,
        "chunk": "# 1. Introduction  \n\nPolyurethanes (PU) have been found in wide applications such as coatings and adhesives due to their unique properties, and great efforts have been made in chemistry and physics. Waterborne polyurethane (WPU) has been developed largely because of its excellent mechanical properties, fire resistance, low toxicity and lack of environmental hazard, but suffers from poor water and alkali resistance because of the hydrophilic group such as carboxyl group in their molecule chains. Compared with the polyurethane resin, polyacrylate-type products show an outstanding performance in the weatherability, water resistance, and solvent resistance, therefore there is a complementary role in the performance of polyurethane (PU) and polyacrylate (PA). Waterborne polyurethane-acrylate (WPUA) can obtain various properties and enhanced performance resulted from its specific segmented structure and modification with acrylate. And it can be satisfactorily applied in coatings for wood and automobiles, biologic materials, electronic materials, textiles, leather and printing inks [1–3].  \n\nRecently, environmental legislation is increasingly strict with coatings industry. The waterborne coatings using ultraviolet (UV)- curing technology have gained increasing interests due to their advantages such as less environmental pollution, low energy consumption, high chemical stability, cost efficient, high curing speed and very rapid curing even at ambient temperatures [4–7]. These environmental friendly products are used to reduce the volatile organic compounds (VOC) released to the atmosphere by solventborne systems and are expected to exhibit same performance as that of conventional solvent-borne systems [8–11]. The UV-curable WPUA coating has the features of instant drying, solvent-free formulations, reduced energy consumption, coating on heat sensitive substrate, low space and capital requirement for curing equipment [12–18]. The UV-curable coatings consist of oligomer, monomer and photoinitiator, so the coating film properties, 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 PUA would play the key role in the development of UV curable chemistry [19]. In the process of photo-polymerization, the content of the photoinitiator would determine the degree of the polymer curing [20]. Besides, the photoinitiated radical polymerization of acrylate resins, the presence of radical scavengers, the reactivity and viscosity of the acrylate formulation, the wavelength and intensity of the UV radiation all could affect the performance of the UV curing film. Studer et al. [21] comprehensively investigated the effect of all these UV curing parameters on acrylate conversion.  \n\nIn this work, the UV-PUA oligomer was prepared with isophorone diisocyanate (IPDI), polyether polyol (NJ-210), dimethylol propionic acid (DMPA), hydroxyethyl methyl acrylate (HEMA) via in situ and anionic self-emulsifying method; and the UV-PUA system was composed of the oligomer, photoinitiator Darocur 1173 and monomers (BA-TPGDA). The effects of the ratio of the BA/TPGDA, Darocur 1173 and the curing time on the performance of the UV-PUA films were investigated. The UV-PUA films were characterized and analyzed by Fourier transform infrared spectroscopy (FT-IR), Differential scanning calorimetry (DSC), solvent resistance, gel content and mechanical properties.",
        "category": " Introduction"
    },
    {
        "id": 5,
        "chunk": "# 2. Experimental",
        "category": " Materials and methods"
    },
    {
        "id": 6,
        "chunk": "# 2.1. Materials  \n\nPolyether polyols (NJ-210, $M n{=}1120\\mathrm{g/mol}_{\\cdot}^{\\cdot}$ ) 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. Butyl acrylate (BA), triethylamine (TEA), acetone, dibutylbis (lauroyloxy) tin (DBLT), and N-methyl -2-pyrrolidone (NMP) were obtained from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China. Tripropyleneglycol diacrylate (TPGDA) and Darocur 1173 were supplied from Mingda Macromolecule Science and Technology CO., Ltd., Suzhou, Jiangsu, China.",
        "category": " Materials and methods"
    },
    {
        "id": 7,
        "chunk": "# 2.2. Preparation of UV-PUA oligomer  \n\nA certain amounts of NJ-210 (10.802 g) and IPDI $(8.325{\\mathrm{g}})$ were added into a four-necked flask equipped with a mechanical stirrer, thermometer and reflux condenser. Then, DBLT was added as catalyst and the mixture was heated to $60^{\\circ}\\mathsf C$ and keeping the temperature for $2\\mathrm{h}$ to prepare the –NCO terminated prepolymer. Next, the above prepolymer was reacted with a certain amount of DMPA $(1.221\\mathrm{g})$ dissolved in small amount of NMP at $80{-}85^{\\circ}C$ for another $^{2\\mathrm{h}}$ , and the –NCO terminated prepolymer containing carboxyl group was obtained. Then the reactant was cooled down to $60^{\\circ}\\mathsf C$ HEMA $(4.875\\mathrm{g})$ was added into the system and reacted at $60^{\\circ}C$ for $^{5\\mathrm{h}}$ . When the temperature was cooled down to $40^{\\circ}\\mathsf C$ TEA were added into the flask subsequently and reacted at $40^{\\circ}C$ for $30\\mathrm{min}$ . The mixture was then dispersed into deionized water under vigorous stirring for $30\\mathrm{min}$ . The synthetic route of UV-PUA oligomer was shown in Fig. 1.",
        "category": " Materials and methods"
    },
    {
        "id": 8,
        "chunk": "# 2.3. Preparation of UV-PUA film  \n\nUV-PUA films were prepared by casting the newly synthesized oligomer, BA and TPGDA onto a poly (tetrafluoroethylene) drying at $65^{\\circ}\\mathsf{C}$ for $3\\ensuremath{\\mathrm{h}}$ . Because water was used as diluents in this system, it needed the flash-off step, where water was evaporated before UVcuring. 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 [22–24].  Then, with the UV light that was produced by a lamp (main wave length: $365\\mathrm{nm}$ the power of the lamp: 1000 W, the UV energy per second: $1000\\mathrm{J}/s$ and the distance between the thin film samples and the center of UV lamp was $20\\mathrm{cm}$ ) 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-PUA film could be obtained. The waterborne UV-PUA film was cured through two-step process as shown in Fig. 2 and the photodissociation mechanism of Darocur 1173 was shown in Fig. 3.",
        "category": " Materials and methods"
    },
    {
        "id": 9,
        "chunk": "# 2.4. The hardness of UV-PUA films  \n\nThe hardness was measured with a sclerometer (KYLXA, Jiangdu Kaiyuan Test Machine Co., Ltd., Jiangdu, China);  \n\nmeasurements were done three times for each sample, and the average value was calculated.",
        "category": " Materials and methods"
    },
    {
        "id": 10,
        "chunk": "# 2.5. The tensile strength and elongation at break of UV-PUA composite films  \n\nTensile 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 at a speed of $50\\mathrm{{mm}/\\mathrm{{min}}}$ . All measurements had an average of three runs. The dumbbell-type specimen was $30\\mathrm{mm}$ long at two ends, $0.2\\mathrm{mm}$ thick and $4\\mathrm{mm}$ wide at the neck.",
        "category": " Materials and methods"
    },
    {
        "id": 11,
        "chunk": "# 2.6. The water absorption (or swelling degree) of UV-PUA films  \n\nThe measurements of water absorption or swelling degree of the UV-PUA films were the same procedures. The procedures for these measurements were briefly described as follows. The PU or PUA films were cut into the size of $30\\mathrm{mm}\\times30\\mathrm{mm}$ and put into water, $5\\%\\mathsf{N a O H}$ and ethanol at $25^{\\circ}\\mathsf{C}$ after being weighted. $24\\mathrm{h}$ later, the film was taken out, rub dry by wiping off the surface water with a piece of filter paper, and then weighted again. The water absorption (or swelling degree), $\\omega$ , was calculated by as follows Eq. (1):  \n\n$$\n\\omega=\\frac{W_{2}-W_{1}}{W_{1}}\\times100\\%\n$$  \n\nwhere $W_{1}$ is the mass of the film before being put into the water, etc. $W_{2}$ is the mass of the film after being put into the water, etc.",
        "category": " Materials and methods"
    },
    {
        "id": 12,
        "chunk": "# 2.7. The gel content of UV-PUA films  \n\nThe UV-PUA films were cut into the size of $2\\mathsf{c m}\\times2\\mathsf{c m}$ , then the sample was put into a solvent (acetone) for $48\\mathrm{h}$ , and dried for $^{72\\mathrm{h}}$ at $30^{\\circ}\\mathsf C$ to give a constant weight. The gel content was calculated according to the following formula (2):  \n\n$$\nG=\\frac{W}{W_{0}}\\times100\\%\n$$  \n\nwhere $W_{0}$ is the mass of the film before being put into the toluene.   \n$W$ is the mass of the film after being put into the toluene.",
        "category": " Materials and methods"
    },
    {
        "id": 13,
        "chunk": "# 2.8. The surface drying time of UV-PUA films  \n\nPut the UV-curable emulsion (the water had been evaporated) under the UV lamp irradiating for a certain amount of time, then gently pressed the UV-curable film with finger. If there is no trace on the film, the time of the UV lamp irradiating was the surface drying time of UV-PUA films.",
        "category": " Materials and methods"
    },
    {
        "id": 14,
        "chunk": "# 2.9. Structure characterization of the UV-PUA oligomer and the UV-PUA films  \n\nFT-IR spectrum of the UV-PUA film was obtained between 4000 and $400\\mathrm{cm}^{-1}$ with an FTIR spectrometer (AVATAR 360, Madison, Nicolet). A minimum of 32 scans was signal-averaged with a resolution of $2{\\mathrm{cm}}^{-1}$ in the $4000{-}400{\\mathrm{cm}}^{-1}$ ranges.",
        "category": " Materials and methods"
    },
    {
        "id": 15,
        "chunk": "# 2.10. Thermal properties  \n\nDifferential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) of the UV-PUA film were performed on a Netzsch instrument (STA 449 C, Netzsch, Seligenstadt, Germany). The programmed heating range was from room temperature to $500^{\\circ}{\\mathsf C}$ at a heating rate of $10^{\\circ}C/\\operatorname*{min}$ under a nitrogen atmosphere. The measurement was taken with $_{6-10\\mathrm{mg}}$ samples. DSC and TG curves were recorded.  \n\n![](images/68d7d16bc5f5ca88da8190750e5a6e5e47275299a3c12d4b503c21c7664439bf.jpg)  \nFig. 1. The synthetic route of the UV-PUA oligomer.",
        "category": " Materials and methods"
    },
    {
        "id": 16,
        "chunk": "# 3. Results and discussions",
        "category": " Results and discussion"
    },
    {
        "id": 17,
        "chunk": "# 3.1. The effect of ratio of BA/TPGDA (R) on the properties of UV-PUA films  \n\nFixed the content of the Darocur 1173 $(3\\%)$ , NCO:OH ratio (2.0) and the weight of the PUA oligomer $(10.8{\\mathrm{g}})$ , a series of UV-PUA films were prepared through changing the R value. The proportion of the UV-curable was listed in Table 1.",
        "category": " Materials and methods"
    },
    {
        "id": 18,
        "chunk": "# 3.1.1. The mechanical properties of UV-PUA films  \n\nThe mechanical properties for UV-PUA films were listed in Table 1. From Table 1: (1) With the increasing of TPGDA content, the hardness of the UV-PUA films increased gradually. This was because the polarity of the hard monomer TPGDA was familiar with the hard segment of PU. There have been hydrogen bonding and some compatibility between the PU and TPGDA phases in the systems. With the increasing of hard monomer content, the density of the hard segment in the molecular chains increased, the cross-linked degree improved because of the hydrogen bonding formation. At larger hard segment content, the phase of the hard segment exhibited higher impact strength, higher hardness. However, hardness became inferior beyond optimum concentration of acrylate. (2) With the ratio of BA/TPGDA decreasing, the tensile strength of the UV-PUA films firstly increased then decreased, while the elongation at break of the UV-PUA films firstly decreased then increased. When the BA/TPGDA was 5/5, the tensile strength reached the maximum.  \n\nTable 1 The effects of BA/TPGDA (R) on the properties of UV-PUA films.   \n\n\n<html><body><table><tr><td>Sample item</td><td>UV-PUA-1</td><td>UV-PUA-2</td><td>UV-PUA-3</td><td>UV-PUA-4</td><td>UV-PUA-5</td></tr><tr><td>BA/TPGDA (R)a</td><td>9/1</td><td>7/3</td><td>5/5</td><td>3/7</td><td>1/9</td></tr><tr><td>Hardness (Shore A)</td><td>86</td><td>89</td><td>91</td><td>92</td><td>94</td></tr><tr><td>Tensile strength (MPa)</td><td>1.57</td><td>2.32</td><td>2.98</td><td>2.46</td><td>2.28</td></tr><tr><td>Elongation at break (%)</td><td>98.54</td><td>89.23</td><td>86.76</td><td>90.07</td><td>92.02</td></tr><tr><td>Water absorption (%)</td><td>12.13</td><td>8.98</td><td>5.32</td><td>10.31</td><td>14.50</td></tr><tr><td>Swelling degree (%) (5% NaOH)</td><td>22.64</td><td>18.06</td><td>7.54</td><td>7.48</td><td>16.69</td></tr><tr><td>Swelling degree (%)(Ethanol)</td><td>46.57</td><td>32.18</td><td>15.42</td><td>23.61</td><td>28.06</td></tr></table></body></html>\n\na BA/TPGA was the percentage based on the whole monomers.  \n\n![](images/12d3c300acd0323d5178ceca35c8d62f061990b71f81de7e53dc5f2f4c53d036.jpg)  \nFig. 2. The cured process of the waterborne UV-PUA film.  \n\n3.1.2. The water absorption (or swelling degree) of UV-PUA films The water absorption or swelling degree of the PUA films was measured and the results were shown in Table 1. As shown in Table 1: (1) when waterborne UV-PUA emulsions are used as resins for coating and adhesives, the water resistance is an important property. The UV-PUA-3 film had the lowest water absorption showing that the UV-PUA-3 film had the best water resistance. Besides, the UV-PUA-3 film also had excellent alkalinity and ethanol resistance compared with other UV-PUA films. (2) When the ratio of BA/TPGDA was the same, the solvent resistance of UV-PUA film was that the water resistance was the best while the ethanol resistance was the worst.",
        "category": " Results and discussion"
    },
    {
        "id": 19,
        "chunk": "# 3.1.3. The gel content and the surface drying time of UV-PUA films  \n\nThe gel content and the surface drying time of UV-PUA films were shown in Fig. 4. With the ratio of BA/TPGDA increasing: (1) The gel content of UV-PUA films firstly increased then decreased When the BA/TPGDA was 5/5, the gel content was $89.68\\%$ , and reached the maximum. (2) The surface drying time of UV-PUA films decreased. Because the BA had a good dilute effect on the UV-PUA emulsion and reduced the viscosity of the system. On the one hand, the molecular motion ability of the UV-PUA emulsion enhanced and the $\\mathsf{C}{=}\\mathsf{C}$ quantity increased, on the other hand, oxygen could more easily spread to the system which consumed more and more free redical, so that the odds of the light polymerization would reduce, the UV-curing time would increase and the system even could not be fully cured [25].  \n\n![](images/2e619a23a57ca1d5aeaf973c4d8a60feca5009cc846a96a106972a17fd90e48d.jpg)  \nFig. 3. The photodissociation mechanism of Darocur 1173.  \n\n![](images/0bc802040e14ce395c97653c7a734c7bbcd77e23ce9c3b1b735a2ca9f01be4f6.jpg)  \nFig. 4. The gel content and the surface drying time of the UV-PUA films at the different ratio of BA/TPGDA.  \n\n3.1.4. Structure characterization of the UV-PUA film The structure of the UV-PUA film was characterized by FTIR as shown in Fig. 5. The spectral analysis was mainly used to check the completion of polymerization reaction, in terms of disappearance of the NCO band at $2270\\mathrm{cm}^{-1}$ illustrating the NCO had basically been reaction. Besides, the spectrum of UV-PUA film exhibited a strong absorption band at 3383 and $3378\\mathrm{cm}^{-1}$ , which should be ascribed to the hydrogen bonding between $\\mathsf{N{\\mathrm{-}}H}$ and carbonyl groups. It could be seen that there was a progressive change in the absorption pattern of $\\scriptstyle{\\mathsf{C}}=0$ stretching region at $1730\\mathrm{cm}^{-1}$ , which might be attributed to the presence of acrylate group. The absorption peak of $\\mathsf{C}{=}\\mathsf{C}$ usually at $1631\\mathrm{cm}^{-1}$ $\\scriptstyle\\left[=C\\right]$ and $1412\\mathrm{cm}^{-1}$ $\\scriptstyle(={\\mathsf{C H}}_{2})$ ), but after UV radiation, the spectrum of UV-PUA film the $\\mathsf{C}{=}\\mathsf{C}$ bond disappeared, which illustrated that the $\\mathsf{C}{=}\\mathsf{C}$ bond of the polyurethane chains has been polymerized.  \n\n![](images/4edeadccd03d0f8fca5294e24f3717dd935752f10f015a413d2f3050a24a9b5f.jpg)  \nFig. 5. The FT-IR spectrum of the UV-PUA film.  \n\n![](images/2661cbe1a8633bbecc13095dc28803eb928bce60d2a0d3e444921f95b32d0e8d.jpg)  \nFig. 6. The DSC curves of the UV-PUA films.",
        "category": " Results and discussion"
    },
    {
        "id": 20,
        "chunk": "# 3.1.5. Thermal properties  \n\nThe DSC and TGA curves of the UV-PUA films were shown in Figs. 6 and 7. From Fig. 6, it can be seen that the hard segment glass transition temperature $(T_{g})$ appeared at $55.0\\substack{-58.0^{\\circ}C}$ in the DSC curves. Furthermore, an endothermic peak at $64.0\\substack{-68.0^{\\circ}C}$ in curves could be observed resulting from crystallization melting of the soft segment. From Fig. 7, the decomposition temperatures $(T_{d})$ of UV-PUA-4 film at $5\\%$ , $10\\%$ and $50\\%$ mass losses were $118^{\\circ}{\\mathsf{C}}$ , $152^{\\circ}\\mathsf C$ and $370^{\\circ}\\mathsf C$ respectively. The decomposition temperatures $(T_{d})$ of UV-PUA-3 film at $5\\%$ , $10\\%$ and $50\\%$ mass losses were $118^{\\circ}{\\mathsf{C}}$ , $150^{\\circ}\\mathsf C$ and $370^{\\circ}\\mathsf C$ respectively. The decomposition temperatures $\\left(T_{d}\\right)$ of UV-PUA-2 film at $5\\%$ , $10\\%$ and $50\\%$ mass losses were $118^{\\circ}{\\mathsf{C}}$ , $148^{\\circ}\\mathsf C$ and $362^{\\circ}\\mathsf{C}$ , respectively. The results indicated that the UV-PUA film had the good thermal properties.  \n\n![](images/3dea25e9102507ba10791e16afff121b406537f86f114b4315ffb3fe2f8113cf.jpg)  \nFig. 7. The TGA curves of the UV-PUA films.  \n\n![](images/2b9ba01b6cb26a2eb312c935c2386b37b15892d1be4d4f5aec70ca96bb2a03fd.jpg)  \nFig. 8. The gel content and the surface drying time of the UV-PUA films at the different content of the Darocur 1173.",
        "category": " Results and discussion"
    },
    {
        "id": 21,
        "chunk": "# 3.2. The effect of the content of Darocur 1173 on the properties of UV-PUA films  \n\nFixed the ratio of the BA/TPGDA $\\left(R=5/5\\right)$ and the weight of the PUA oligomer $(10.8\\mathrm{g})$ , a series of UV-PUA films were prepared through changing the content of the Darocur 1173. The proportion of the UV-curable emulsion was listed in Table 2. The properties of UV-PUA films were systematically investigated.  \n\n3.2.1. The gel content and the surface drying time of UV-PUA films The gel content and the surface drying time of UV-PUA films were shown in Fig. 8. With the content of the Darocur 1173 increasing:  \n\n(1) The gel content of UV-PUA films firstly increased then decreasing. When the content of the Darocur 1173 was $4\\%$ the gel content was $92.54\\%$ and reached the maximum. It may be due to the absolutely curable velocity, which was decided by the forming velocity of the free radical on the surface of the coating. And according to the Larmbert–Beer’s law, the light intensity was degressive in the form of exponential function when the content of the photoinitiator increased. When the content of the photoinitiator was excessive, the photoinitiator closed to the surface of the coating would absorb the most part of the Ultra Voilet, the light flux reached to the interior would decrease sharply, the number of the free radical produced by the photoinitiator and the velocity of the UV curable reduced. Besides, the cured film on the surface coating might hinder the molecular movement at the bottom coating, so that the gel content reduced and the curing degree decreased [20]. (2) The surface drying time of UV-PUA films firstly decreased then increasing. If the content of the Darocur 1173 was low, the energy may not effectively be used, and the number of the generated free radicals was lower than the reaction required, thus the curing speed would be slower. With the content of the Darocur 1173 increasing, the number of the generated free radicalsc increased, the curing speed would be quicker. But if the content of the Darocur 1173 was higher than the reaction required, there would be excess free radicals generated which could easily coupling each other, then terminated the chain growth and the curing speed would be slow at last. So when the content of the Darocur 1173 was $4\\%$ , the surface drying time reached the minimum and the curing effect was the best.",
        "category": " Results and discussion"
    },
    {
        "id": 22,
        "chunk": "# 3.2.2. The mechanical properties of UV-PUA films  \n\nThe mechanical properties for UV-PUA films were listed in Table 2. With the content of the Darocur 1173 increasing: (1) The hardness of the UV-PUA films had little changed. This was maybe due to the UV-PUA films had the same quality of the PUA Oligomer and monomers which were the same as the hard segment and soft segment. (2) The tensile strength of the UV-PUA films firstly increased then decreased while the elongation at break of the UVPUA films firstly decreased then increased. When the content of the Darocur 1173 was $4\\%$ , the tensile strength was $3.03\\mathrm{MPa}$ and reached the maximum.  \n\nTable 2 The effects of Darocur 1173 content on the properties of UV-PUA films $(R=5/5)$ .   \n\n\n<html><body><table><tr><td>Sample item</td><td>UV-PUA-6</td><td>UV-PUA-7</td><td>UV-PUA-3</td><td>UV-PUA-8</td><td>UV-PUA-9</td></tr><tr><td>Content of Darocur 1173 (%)a</td><td>1.0</td><td>2.0</td><td>3.0</td><td>4.0</td><td>5.0</td></tr><tr><td>Hardness (Shore A)</td><td>88</td><td>89</td><td>91</td><td>90</td><td>89</td></tr><tr><td>Tensile strength (MPa)</td><td>2.06</td><td>2.52</td><td>2.98</td><td>3.03</td><td>2.65</td></tr><tr><td>Elongation at break (%)</td><td>104.30</td><td>98.23</td><td>94.76</td><td>92.07</td><td>96.02</td></tr></table></body></html>\n\na The percentage based on the whole UV system.  \n\nTable 3 The effects of the curing time on the properties of UV-PUA films $\\left(R=5/5\\right)$ .   \n\n\n<html><body><table><tr><td>Sample item</td><td>UV-PUA-10</td><td>UV-PUA-11</td><td>UV-PUA-12</td><td>UV-PUA-13</td><td>UV-PUA-14</td><td>UV-PUA-15</td></tr><tr><td>Curing time (s)</td><td>10</td><td>20</td><td>30</td><td>40</td><td>50</td><td>60</td></tr><tr><td>Hardness (Shore A)</td><td>85</td><td>87</td><td>91</td><td>92</td><td>91</td><td>92</td></tr><tr><td>Tensile strength (MPa)</td><td>1.86</td><td>2.82</td><td>3.14</td><td>3.13</td><td>3.15</td><td>3.14</td></tr><tr><td>Elongation at break (%)</td><td>117.21</td><td>96.57</td><td>93.42</td><td>93.39</td><td>93.41</td><td>93.40</td></tr></table></body></html>",
        "category": " Results and discussion"
    },
    {
        "id": 23,
        "chunk": "# 3.3. The effect of the curing time on the properties of UV-PUA films  \n\nFixed the ratio of the BA/TPGDA $\\left(R=5/5\\right)$ , the content of the Darocur 1173 $(4\\%)$ and the weight of the PUA oligomer $(10.8\\mathrm{g})$ a series of UV-PUA films were prepared through changing the curing time. The proportion of the UV-curable emulsion was listed in Table 3. The properties of UV-PUA films were systematically investigated.",
        "category": " Materials and methods"
    },
    {
        "id": 24,
        "chunk": "# 3.3.1. The effect of the curing time on the gel content of UV-PUA films  \n\nThe effect of the curing time on the gel content of UV-PUA films were shown in Fig. 9. At the UV-curable prophase, the gel content gradually increased with the UV curing time increasing. This was due to the dual bond was not opened entirely when the curing time was too short. When the curing time reached 30 s, the gel content increased slightly but changed not obvious if the curing time continued to be increased. Because when the curing time was $30s$ dual bond was opened entirely and the curing reaction basically completed. The curing degree basically remain unchanged even if prolong the curing time.  \n\n![](images/a9cc59dcf664a384b50d047a1ea75c95b354d20da345cb14c3d1fa40581d7105.jpg)  \nFig. 9. Effect of curing time on gel content of the UV-PUA films.",
        "category": " Results and discussion"
    },
    {
        "id": 25,
        "chunk": "# 3.3.2. The effect of the curing time on the mechanical properties of UV-PUA films  \n\nThe mechanical properties for UV-PUA films were listed in Table 3. With the curing time increasing, the hardness and the tensile strength of the UV-PUA films firstly increased and subsequently had little changed while the elongation at break firstly decreased then changed little. Because, when the curing time was too short, the dual bond was not opened entirely. But when the curing time reached $30s$ , the dual bond of the UV-PUA system was opened entirely and the curing reaction basically completed. The curing degree basically remain unchanged even if prolong the curing time. So when the curing time surpassed 30 s, the hardness, the tensile strength and the elongation at break of the UV-PUA films had little changed.",
        "category": " Results and discussion"
    },
    {
        "id": 26,
        "chunk": "# 4. Conclusion  \n\nThe waterborne UV-PUA emulsion was prepared using UV-PUA oligomer, the Darocur 1173 and the monomers composed of BA and TPGDA. The proportion of BA and TPGDA, the content of the Darocur 1173 and the curing time were important effects on the properties of the cured films. The experimental results indicated that the optimum irradiation time was $30{-}40s$ after the coatings being painted on a poly (tetrafluoroethylene) plate at room temperature, the ratio of the BA/TPGDA was 5/5, and initiator dosage was $4\\%(\\mathrm{wt}\\%)$ of the latex. Almost all the UV-PUA films have good hardness, solvent resistance and mechanical properties. It is hopeful that the UV-PUA dispersions can be applied to commercial use in different regions.",
        "category": " Conclusions"
    },
    {
        "id": 27,
        "chunk": "# Acknowledgement  \n\nThis project was supported by the Agricultural Independent Innovation of Jiangsu Province (CX(11)2032), Jiangsu Planned Projects for Postdoctoral Research Funds (1002033C) and Jiangsu Province Key Laboratory of Fine Petro-chemical Technology (213164).",
        "category": " References"
    },
    {
        "id": 28,
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