Article pubs.acs.org/IECR
Synthesis and Properties of Photosensitive Silicone-Containing Polyurethane Acrylate for Leather Finishing Agent Yong Yu,†,‡ Bo Liao,§ Guonai Li,†,‡ Shengling Jiang,∥ and Fang Sun*,†,‡ †
State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, People’s Republic of China ‡ College of Science, Beijing University of Chemical Technology, Beijing 100029, People’s Republic of China § Second Institute, Equipment Academy of Second Artillery, Beijing 100085, People’s Republic of China ∥ College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, People’s Republic of China S Supporting Information *
ABSTRACT: A photosensitive silicone-containing polyurethane acrylate prepolymer (Si-IPDI-HEA) was synthesized and characterized adequately by FTIR, 1H NMR, and GPC analyses. The effect of the monomers on the photopolymerization kinetics of Si-IPDI-HEA was investigated by real-time infrared spectroscopy (RT-IR). The results showed that the resin of SiIPDI-HEA with common acrylic monomers exhibited a high polymerization rate and double-bond conversion. The influence of the monomer and silicone on the microstructure and properties of the UV-cured film also was systematically studied. It was found that, with the increase of the functionality of the monomer, the thermostability, Tg, hardness, tensile strength, tensile modulus, and dispersion surface energy of the UV-cured film were increased, whereas the contact angle and elongation at break were decreased. The introduction of silicone into the prepolymer could enhance the thermostability of the UV-cured film, and reduce the dispersion surface energy by the change of the microstructure. More importantly, the leather finishing agent containing Si-IPDI-HEA has excellent comprehensive performance and potential application in the leather finishing agent.
1. INTRODUCTION
energy consumption, room temperature treatment, high efficiency, and spatial and temporal control. The particular molecular structure of organosilicon endows it with many unique properties, for example, low surface tension, resistance to high and low temperatures, excellent flexibility, and chemical inertness.8−11 Therefore, the introduction of organosilicon into a leather finishing agent could enhance the hydrophobicity, softness, smoothness, and resistance to high and low temperatures of the leather finishing agent, which can increase the commercial and aesthetic value of the leather. Zhou12 and Wu13 synthesized polysiloxane-modified acrylate core−shell emulsions by an emulsion polymerization, and found films with soft and smooth feeling, good water resistance, and mechanical strength. Yi14 synthesized a waterborne siliconmodified polyurethane resin, and enhanced the smooth performance, flexibility, and adhesive force of the leather finishing agent. However, UV-curable leather finishing agents containing silicone are rarely reported currently. In the present paper, a photosensitive silicone-containing polyurethane acrylate resin (Si-IPDI-HEA) for a leather finishing agent was synthesized and characterized. The photopolymerization properties, physical and mechanical properties, thermal properties, and surface morphology of UV-cured films of Si-IPDI-HEA system were evaluated. It was
Leather finishing agents have been researched extensively and developed rapidly in materials science for their unique functions. A leather finishing agent is a leather auxiliary which is used in leather surface coating to protect and beautify the leather, thereby prolonging the lifetime of the leather, and significantly improving the quality and the commercial value of the leather products.1,2 A traditional leather finishing agent contains a large amount of organic solvent in order to achieve application performance, resulting in severe environmental pollution. Therefore, much research work has been carried out on developing waterborne leather finishing agents to diminish pollution. Kang3 synthesized a water-soluble polyacrylate used for a leather finishing agent, which showed good luster, excellent wear resistance, strong water resistance, and good adhesion. Peng4 studied the properties of waterborne polyurethane leather finishing agents (FU-800 series), and the results indicated that FU-800 series leather finishing agents had outstanding adherence and water resistance, comfortable handling, natural appearance, good elasticity, and environmental protection. Although a waterborne leather finishing agent is an environmentally friendly system, thermal treatment of a waterborne leather finishing agent takes much time and energy. Hence, UV-curable leather finishing agents have attracted much attention in recent years.5−7 The photopolymerization technique is one of the fastest developed environmentally friendly polymerization technologies because of its distinct advantages such as solvent-free formulations, low © 2013 American Chemical Society
Received: Revised: Accepted: Published: 564
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Waters). Tetrahydrofuran, 1.0 mL/min, was used as the mobile phase. The GPC instrument was calibrated using multiple linear polystyrene (PS) standards. Thermal stability was determined with an STA-449C simultaneous thermal analyzer (Netzsch). Measurements were collected from 30 to 500 °C with a heating rate of 10 °C/min. Dynamical thermal mechanical analyses (DMTA) were performed on DMTA-IV (Rheometric Scientific Co.). Measurements were collected from −50 to +200 °C with a heating rate of 5 °C/min, at a frequency of 1 Hz. The tensile properties of Si-IPDI-HEA cured films were measured with a material testing instrument (Instron-1211) at 25 °C. The rate of extension was 10 mm/min. Pencil hardness apparatus AR015 (Tianjing Instrument Co.) was employed to measure the hardness of Si-IPDI-HEA cured films. The adhesion force of UV-cured films was tested by ASTM D3359. For this adhesion test, a grid of 1 mm squares was cut into the sample and adhesive tape (Scotch, USA) was applied and rapidly removed. The sample was then visually inspected to determine if any loss of adhesion between any of the small squares of coating and the surface had occurred. With this method, the adhesion force can be assessed qualitatively on the 0 to 5B scale. The viscosity of the systems consisting of Si-IPDI-HEA/ PPG-IPDI-HEA with monomers were tested by a rotary viscometer (NDJ-79, China) at room temperature (20 °C). The gloss of the leather was tested by a photometer (TASCO TMS-724). The contact angles of water on the UV-cured film surface were measured on a contact angle microscope (OCA20, Data Physics Co., Germany). The surface morphology of the UV-cured films of Si-IPDI-HEA was observed with using scanning electron microscopy (SEM, S-4700 Hitachi) with an accelerating voltage of 20.0 kV. The surface element of UVcured films of Si-IPDI-HEA was characterized by an energy dispersive spectrometer (EDS, S-4700 Hitachi). 2.4. Preparation Procedure of UV-Cured Film. The prepolymer and monomer were mixed with a certain weight ratio, and subsequently, 1173 of 0.1 wt % was added to the mixture to form a stock photosensitive liquid. The photosensitive liquid was coated onto a mold made from glass slides. Then, the photosensitive liquid layer was exposed under a highpressure mercury lamp (10 mW/cm2) for 60 s to obtain the UV-cured film (76 × 13.8 × 0.3 mm). 2.5. Photopolymerization. Si-IPDI-HEA systems with all kinds of monomers were employed as the photopolymerizable resins, with varying concentrations of monomers and the newly synthesized Si-IPDI-HEA. All samples were investigated by real-time infrared spectroscopy (RT-IR). RT-IR with a horizontal sample holder (Nicolet5700, Thermo Electron, equipped with an extended range KBr beam splitter and an MCT/A detector) was used to monitor the extent of polymerization. Photopolymerization was carried out at room temperature (20 °C). The mixture of Si-IPDI-HEA, monomers, and photoinitiators was placed in a mold made from glass slides and spacers of 15 ± 1 mm diameter and 1.2 ± 0.1 mm thickness. A horizontal transmission accessory (HTA) was designed to enable mounting of samples in a horizontal orientation for FTIR measurements. A UV spot light source (EFOS Lite) was directed to the sample with a light intensity of 10 mW/cm2 (Honle UV meter). The decrease of the =C−H absorption peak area from 6100.70 to 6222.50 cm−1 in the near-IR range accurately reflects the extent of the polymerization since the change of the absorption peak area was
found that the Si-IPDI-HEA not only maintains the properties of polysiloxane and polyurethane but also can rapidly polymerize under UV irradiation. The introduction of silicon into the prepolymer could enhance the hydrophobicity of the UV-cured film by the change of the microstructure. Moreover, in order to investigate the effect of the silicon on the performance of the resin, we also synthesized a polyurethane acrylate resin (PPG-IPDI-HEA) without silicone as a reference.
2. EXPERIMENTAL SECTION 2.1. Materials. Hydroxyl-terminated polysiloxane (Q43667, Mn = 2400, hydroxyl group content 1.41 mg of KOH/ g) was obtained from Dow Corning Corp. Polypropylene glycol (PPG-2000) was provided by Hangzhou Maohang Chemical Co., Ltd. Hydroquinone (HQ) was provided by Beijing Yili Fine Chemical Co. Isophorone diisocyanate (IPDI) was obtained from Qingdao Xinyutian Chemical Co. 2Aminoethanol was provided by Tianjin Chisheng Trade Co. Dipropylene glycol diacrylate (DPGDA), 2-hydroxyethyl acrylate (HEA), isobornyl acrylate (IBOA), 1,6-hexanediol diacrylate (HDDA), and trimethylolpropane triacrylate (TMPTA) were purchased from Eternal Specialty Chemical (Zhuhai) Co., Ltd. Photoinitiator 2-hydroxyl-2-methyl-1phenylpropane-1-one (Darocur 1173) was obtained from Ciba Geigy Co. Dibutyltin dilaurate (DBTDL) was supplied by Shanghai Chemical Reagents Co. Polyurethane acrylate resin (PPG-IPDI-HEA) was synthesized in our laboratory. A commercial solvent-based leather finishing agent (720, a PU type resin) was obtained from Shanghai Heying Chemical Co. 2.2. Synthesis of Si-IPDI-HEA Oligomer. Si-IPDI-HEA was synthesized through the following procedure. First, Q43667 (20.00 g, 8.33 mmol) was added to a four-necked flask equipped with a mechanical stirrer, a thermometer, and a cooler; then IPDI (3.70 g, 16.67 mmol) was dropwise added into the flask over 5 min. The reaction mixture was stirred at 45 °C in the presence of DBTDL (0.03 g) as a catalyst until the value of isocyanate had reached the theoretical one of monoisocyanate by titration.15 Subsequently, HEA (1.94 g, 16.67 mmol) and HQ (0.03 g 0.27 mmol) were added into the flask, and the reaction mixture was stirred for about 3 h until the absorption peak of the −NCO group in the infrared spectra disappeared. The product was purified by column chromatography. IR (KBr, cm−1): 3330, 1535 (N−H), 2960, 2869 (−CH3, −CH2), 1723 (CO), 1640 (CC), 1302, 1260 (Si−CH3), 1192 (C−N), 1098, 1020 (Si−O−Si), 802 (Si−CH3). 1 H NMR (δ, CDCl3, ppm): 0.072 (SiCH3), 0.49−0.53 (SiCH2), 0.83−1.26 (CH3CH2, CH3 of IPDI), 1.58−1.70 (CH2 of IPDI), 2.90−2.97 (CONHCH2), 3.59−3.64 (SiCH2O, CONHCH), 4.20−4.34 (OCH2CH2O, COCH2O), 6.11−6.18 (COCHCH2), 5.85−5.87, 6.42−6.46 (COCHCH2). 29 Si NMR (δ, CDCl3, ppm): −21.98 (−Si(CH3)2−O−). GPC (multiple PS standards): Mn = 2183, Mw = 4903, polydispersity index (PDI) = 2.24. 2.3. Characterization of Si-IPDI-HEA. The Fourier transform infrared (FTIR) spectra were identified according to a Nicolet 50XC spectrometer (Nicolet) and scanned between 400 and 4000 cm−1. The 1H NMR spectra were characterized by an AV600 MHz (Bruker) spectrometer, using CDCl3 as a solvent and tetramethylsilane as an internal standard. The molecular weight of the prepolymer was determined by a Waters 515-2410 gel permeation chromatograph (GPC, 565
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directly proportional to the number of the (meth)acrylate double bond that had polymerized. After baseline correction, conversion of the functional groups could be calculated by measuring the peak area at each time of the reaction and determined as the following: DC/% = (A 0 − A t ) ·100/A 0
(1)
where DC is the degree of (meth)acrylate double bond conversion at t time, A0 is the initial peak area before irradiation, and At is the peak area of the double bonds at t time. The rate of photopolymerization is calculated by the differential of conversion of double bond versus irradiation time.16 2.6. Calculation of Gel Yield. Gel yield is expressed as gel yield = W / W0·100%
(2)
where W0 is the weight of liquid film before curing; W is the weight of cured film which was obtained by extracting with ethanol for 30 min and drying to constant weight after irradiating the liquid film under a UV lamp for 60 s.
3. RESULTS AND DISCUSSION 3.1. Photopolymerization Kinetics. RT-IR was employed to investigate the photopolymerization of the oligomer Si-IPDIHEA. The most important parameters characterizing the photopolymerization of a resin are the final degree of double bond conversion (DC) and the rate of polymerization (Rp) after a given irradiation time. The effect of reactive monomers on the photopolymerization kinetics of Si-IPDI-HEA is shown in Figure 1. It is found that the Rp’s of the systems with different monomers were not obviously different. However, DCs of the systems decreased with the increase of the degree of functionality of the monomers. The reason is that a three-dimensional gel structure forms more easily in the system containing monomer with a high degree of functionality, leading to the fact that the uncured double bonds trapped in the polymeric networks cannot polymerize further. The effect of the ratio of Si-IPDI-HEA to monomer HDDA on photopolymerization kinetics is shown in Figure 2. When the ratio increased from 10/90 to 90/10, the DC increased regularly, but the change of Rp was irregular. This can be explained by the viscosity of the resin and the concentration of double bonds.17 As more Si-IPDI-HEA was added, the viscosity of the resin became higher, which could influence the polymerization rate from two aspects. On the one hand, high viscosity often accelerates the polymerization because it can hinder the termination of active free radicals. On the other hand, high viscosity also limits the movement of molecules, resulting in the decrease of the polymerization rate. Meanwhile, the concentration of double bonds of the resin became lower with the increase of Si-IPDI-HEA content, leading to a small rate of polymerization. As a result, different ratios of the prepolymer to the monomer led to different photopolymerization behaviors. 3.2. Yellowing Resistance. The yellowing resistance of the UV-cured films of Si-IPDI-HEA with different monomers was investigated by the change of transmittance before and after having been placed at 120 °C in air for 4 h. As is shown in Figure 3, the transmittance of the UV-cured films of Si-IPDIHEA systems has reduced by 2−7% after having been placed at 120 °C for 4 h, and in the range 400−800 nm, the transmittance of the UV-cured films of Si-IPDI-HEA systems
Figure 1. (a) Effect of monomers on double bond conversion of SiIPDI-HEA. (b) Effect of monomers on rate of polymerization of SiIPDI-HEA. System composition: Si-IPDI-HEA/monomer = 50/50 (wt %); photoinitiator 1173, 0.1 wt %.
Figure 2. Effect of monomer concentration on photopolymerization kinetics of Si-IPDI-HEA. System composition: Si-IPDI-HEA/HDDA = 10/90, 30/70, 50/50, 70/30, 90/10 (wt %); photoinitiator 1173, 0.1 wt %.
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Figure 3. Yellowing resistance of the systems of Si-IPDI-HEA with different monomers (a) before being placed at 120 °C for 4 h and (b) after being placed at 120 °C for 4 h. Cured film composition: Si-IPDIHEA/monomer = 50/50 (wt %); photoinitiator 1173, 0.1 wt %.
Figure 4. (a) TG curves of UV-cured films of the Si-IPDI-HEA systems. (b) DTG curves of UV-cured films of Si-IPDI-HEA systems. Cured film composition: Si-IPDI-HEA/monomer = 50/50 (wt %); photoinitiator 1173, 0.1 wt %.
Table 1. Thermal Decomposition Parameter of Examined UV-Cured Films of Si-IPDI-HEA Systemsa
can also maintain above 80%. It is proved that the system of SiIPDI-HEA has good yellowing resistance. 3.3. Thermogravimetric Analysis. Figure 4 shows the thermal gravitmetric analysis (TG) and differential thermal gravimetric (DTG) curves of UV-cured films of the Si-IPDIHEA systems. The temperature of 10% weight loss and the peak temperature at the maximum weight loss rate of examined UV-cured films of Si-IPDI-HEA systems are listed in Table 1. From Figure 4 and Table 1, it can be easily found that the thermal stability of the cured films is higher with a higher degree of functionality of the monomer. This is because the degree of cross-linking of the system increased with the increase of degree of functionality of the monomers. The DTG curves show that the system with IBOA appears to have a two-step thermal degradation, and the degradation rate of the first step is very fast. This degradation process may involve the cleavage of the six-membered ring of IBOA to form a stable linear chain. The degradation temperature of the second step is very high, which could be attributed to the break of the molecular main chain. In addition, the temperature of 10% weight loss and the peak temperature at the maximum weight loss rate of the SiIPDI-HEA system are higher than those of the PPG-IPDI-HEA
system composition (wt %) Si-IPDI-HEA/HEA/1173 = 50/50/0.1 Si-IPDI-HEA/IBOA/1173 = 50/50/0.1 Si-IPDI-HEA/HDDA/1173 = 50/50/0.1 Si-IPDI-HEA/DPGDA/1173 = 50/50/0.1 Si-IPDI-HEA/TMPTA/1173 = 50/50/0.1 PPG-IPDI-HEA/DPGDA/1173 = 50/50/0.1
T10% (°C)
Tmax1 (°C)
Tmax2 (°C)
315 308 330 348 370 331
319 316 − 389 − 378
419 422 419 420 450 410
a T10% is the temperature of 10% weight loss. Tmax is the peak temperature at maximum weight loss rate.
system under the same conditions, resulting from the stability of the Si−O bond. 3.4. Dynamic Mechanical Thermal Analysis (DMTA). Dynamic mechanical thermal analysis (DMTA) is utilized to investigate the dynamic mechanical behavior of the UV-cured films. As shown in Figure 5, the UV-cured film of each system had only one damping peak, which suggests that the prepolymer Si-IPDI-HEA has good compatibility with acrylic monomers; meanwhile, the intensity of damping peaks of UV567
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Figure 6. Temperature spectra of cured films of Si-IPDI-HEA and PPG-IPDI-HEA systems. Cured film composition: Si-IPDI-HEA (PPG-IPDI-HEA)/IBOA = 50/50 (wt %); photoinitiator 1173, 0.1 wt %.
3.5. Hardness of the Cured Films. As is shown in Table 2, with the increase of the functionality of monomers, the Table 2. Pencil Hardness of Cured Films of Si-IPDI-HEA Systemsa
Figure 5. (a) Temperature spectrum of Tan δ of cured films of SiIPDI-HEA systems. (b) Temperature spectrum of E′ of cured film of Si- IPDI-HEA system. Cured film composition: Si-IPDI-HEA/ monomer = 50/50 (wt %); photoinitiator 1173, 0.1 wt %.
a
team
system composition (wt %)
gel yield (%)
hardness
1 2 3 4 5 6 7 8 9
Si-IPDI-HEA/HEA = 50/50 Si-IPDI-HEA/IBOA = 50/50 Si-IPDI-HEA/HDDA = 50/50 Si-IPDI-HEA/DPGDA = 50/50 Si-IPDI-HEA/TMPTA = 50/50 PPG-IPDI-HEA/HEA = 50/50 PPG-IPDI-HEA/HDDA = 50/50 PPG-IPDI-HEA/DPGDA = 50/50 PPG-IPDI-HEA/TMPTA = 50/50
94.96 95.28 96.08 96.12 98.05 − − − −
5B 3B H 2H 5H 6B 2H 3H 6H
1173 was the photoinitiator, and its concentration was 0.1 wt %.
hardness of UV-cured films of Si-IPDI-HEA was enhanced, which can be ascribed to the increase of the gel yield with the increase of the functionality of monomers, leading to a compact film surface. We compared the hardness values of the UV-cured films of Si-IPDI-HEA systems with those of PPG-IPDI-HEA systems. It can be observed that the hardness values of the films of SiIPDI-HEA systems were lower than those of PPG-IPDI-HEA systems due to the soft polysiloxane chain of Si-IPDI-HEA. 3.6. Tensile Property and Adhesive Force of the Cured Film. The tensile properties of the cured films of SiIPDI-HEA systems with different monomers are shown in Table 3. As shown in Table 3, the tensile strength of the cured films increased with the increase of the functionality of monomers, and the elongation at break exhibited a contrary trend. The tensile strength of the cured film containing HEA was the minimum among all investigated systems, because HEA is a monofunctional monomer, resulting in a low cross-linking degree. However, the system containing the monofunctional monomer IBOA exhibited good strength and elongation at break that may be ascribed to its ring structure. In addition, the tensile strength of the films of the PPG-IPDI-HEA system was higher than those of Si-IPDI-HEA systems, but the elongation at break was lower than those of Si-IPDI-HEA systems, which
cured films with monofunctional monomers is higher than that of multifunctional monomers, while the Tg of the cured films presented a contrary trend except for the cured film with IBOA. This is because the degree of cross-linking of the system increased with the increase of the functionality of monomer, leading to the restriction of intermolecular movements, and reduction of internal friction. However, the cured film with IBOA showed a higher Tg, resulting from the rigid structure of IBOA. In addition, the storage modulus (E′) of systems containing multifunctional monomers is higher than that of monofunctional monomers, indicating that the increase of the functionality of monomer can enhance the degree of crosslinking of the system, thereby improving rigidity of cured films. As shown in Figure 6, the Tg and the width of the damping peak of the UV-cured film of the system of Si-IPDI-HEA were greater than those of PPG-IPDI-HEA, because the introduction of the silicon chain improved the thermostability of the UVcured film and reduced the compatibility between the prepolymer and the monomer. The storage modulus of the PPG-IPDI-HEA system was higher than that of Si-IPDI-HEA, demonstrating that the PPG-IPDI-HEA system has higher rigidity compared with the Si-IPDI-HEA system. 568
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Table 3. Tensile Properties of Cured Film of Si-IPDI-HEA Systemsa system composition (wt %)
tensile strength (MPa)
elongation at break (%)
0.48
82.66
0.73
8.07
250.21
84.43
8.17
12.25
210.95
9.04
16.86
238.78
10.56
6.31
255.99
18.94
137.22
183.08
Si-IPDI-HEA/HEA = 50/50 Si-IPDI-HEA/IBOA = 50/50 Si-IPDI-HEA/HDDA = 50/50 Si-IPDI-HEA/DPGDA = 50/50 Si-IPDI-HEA/TMPTA = 50/50 PPG-IPDI-HEA/IBOA = 50/50 a
tensile modulus (MPa)
1173 was the photoinitiator, and its concentration was 0.1 wt %.
may be due to the soft polysiloxane chain in Si-IPDI-HEA systems. The adhesion force of the Si-IPDI-HEA systems on inorganic glass, PVC leather, and PU leather, respectively, was tested. The results showed that Si-IPDI-HEA systems had a better adhesion force on three different substrates (see Supporting Information, Table S1), which reached 4B, even 5B. 3.7. Contact Angle and Dispersion Surface Energy of the Cured Film. To investigate the hydrophilicity/hydrophobicity of the surface of the cured fiilms, we measured the water contact angle on the film surface and calculated the dispersion surface energy (γSd). Here, γlv is the surface tension at the liquid−vapor interface, γsl is at the solid−liquid interface, and γsv is at the solid−vapor interface: γ sl = γ sv − γ lv cos θ
Figure 7. (a) Contact angles of cured films. (b) Dispersion surface energies (γSd) of cured films. Cured film composition: prepolymer/ monomer = 50/50 (wt %); photoinitiator 1173, 0.1 wt %.
(3)
According to Fowkes’ theory,18 the interface tension could also be calculated by the following formulation: γ sl = γ s + γ lv − 2(γl dγSd)1/2
surface morphology of the UV-cured films became dense with the increase of the functionality of monomers. Compared with the PPG-IPDI-HEA system (Figure 9), there were a great number of irregular protuberances in the surface of the UVcured films of the Si-IPDI-HEA system, and EDS results showed that the content of Si in the irregular protuberances was higher than that of other areas. Therefore, it is speculated that the reason for the form of the irregular protuberances was the enrichment of silicone, which may lead to an increase in the hydrophobicity of the films. In addition, the number of the irregular protuberances gradually reduced with the increase of the functionality of the monomers. This could be attributed to that fact that higher cross-linking density and viscosity of the system with multifunctional monomers hinder the enrichment of silicone. 3.9. Performance of Leather Finishing Agent Containing Si-IPDI-HEA. Although Si-IPDI-HEA possesses advantages for a leather finishing agent, it needs cooperation with acrylic monomers or other resins to obtain a leather finishing agent with excellent properties. We have designed the formulation containing Si-IPDI-HEA for a leather finishing agent and tested its performance, meanwhile, compared with the formulation containing PPG-IPDI-HEA, and leather finishing agent 720, which is widely used in the commercial market. From Table 4, it is found that the leather finishing agent containing Si-IPDI-HEA has an excellent comprehensive
(4)
Equations 3 and 4 give γSd = [γ lv(1 + cos θ )]2 /4γl d lv
(5)
γld
H2O (γ = 72.7 mN/m, = 23.9 mN/m) was used as the testing liquid. The water contact angles (θ) on plane solid surface films were measured. From θ, the γSd values can be calculated with eq 5. Figure 7 shows that the contact angle of UV-cured films decreased with the increase of the functionality of monomers, while the corresponding dispersion surface energy increased. This may be because the increase of the functionality of monomers can increase not only the surface tension of the monomers, but also the cross-linking density and viscosity of the system that can hinder the migration of the hydrophobic silicon chain to the surface of the cured film. Compared with the PPG-IPDI-HEA system, the contact angles of the UV-cured films of the Si-IPDI-HEA system were much higher and the dispersion surface energy showed a contrary consequence. It is demonstrated that the introduction of silicone chain into the prepolymer can enhance the hydrophobicity of the cured film. 3.8. Surface Morphology Analysis by SEM and EDS. The surface morphology of UV-cured films of Si-IPDI-HEA with different monomers was observed. Figure 8 shows that the 569
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Figure 8. SEM images of UV-cured film of Si-IPDI-HEA system. Cured film composition: Si-IPDI-HEA/monomer = 50/50 (wt %); photoinitiator 1173, 0.1 wt %.
Figure 9. SEM images of UV-cured film of PPG-IPDI-HEA system. Cured film composition: PPG-IPDI-HEA/monomer = 50/50 (wt %); photoinitiator 1173, 0.1 wt %.
Table 4. Performance of Leather Finishing Agent on PU Leather item
testing method
formulation with Si-IPDI-HEA
adhesion force folding resistance hydrolysis resistance antisticky
ASTM D3359 coating appearance after folding for 6 × 104 times at −20 °C coating appearance after boiling for 15 days at 80 °C
5B no change no change
5B crack no change
5B no change coating falloff
folded coating after pressing with 4 kg force at 80 °C for 2 h
nonsticky
sticky to death
coating appearance after scrubbing 2000 times with alcohol
10.0 good
19.4 good
sticky to death 9.4 good
gloss (60°) alcohol resistance
formulation with PPG-IPDI-HEA
720
monomer and silicone both have a great influence on properties of the UV-cured films. The increase of the functionality of monomers can increase the thermostability, Tg, hardness, tensile strength, tensile modulus, and dispersion surface energy, and decrease the contact angle and elongation at break. Especially the surface microstructure of UV-cured films of SiIPDI-HEA was characterized by SEM and EDS. It is proved that the introduction of silicon into the prepolymer could improve the thermostability and reduce the dispersion surface energy of UV-cured film by the change of microstructure. More
performance, and satisfies application requirements of leather finishing agents. 3.10. Conclusion. A novel photosensitive silicone-containing polyurethane acrylate prepolymer (Si-IPDI-HEA) used for a leather finishing agent has been synthesized and characterized by FTIR, 1H NMR, and GPC analyses. The effect of the monomers on the photopolymerization kinetics of Si-IPDIHEA was investigated by RT-IR. The results showed that, with the increase of the functionality and concentration of the monomer, the double bond conversion was decreased. The 570
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importantly, the leather finishing agent containing Si-IPDIHEA possesses excellent comprehensive performance; thus, SiIPDI-HEA has a potential application in leather finishing agents.
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(16) Li, S. J.; He, Y.; Nie, J. Photopolymerization of hybrid monomer 3-(1-propenyl)oxypropyl acrylate. J. Photochem. Photobiol., A: Chem. 2007, 191, 25−31. (17) Li, G. N.; Jiang, S. L.; Sun, F. Synthesis and property of watersoluble hyperbranched photosensitive polysiloxane urethane acrylate. Ind. Eng. Chem. Res. 2013, 52, 2220−2227. (18) Fowkes, F. M. Attractive forces at interfaces. Ind. Eng. Chem. Res. 1964, 56, 40−52.
ASSOCIATED CONTENT
* Supporting Information S
Synthesis procedure, reaction equation, IR and NMR spectra, and adhesion force of the Si-IPDI-HEA and PPG-IPDI-HEA systems. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*Tel.: +86-10-64449336. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS Financial support from the National Natural Science Foundation of China (Grant 51273014) is gratefully acknowledged.
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REFERENCES
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dx.doi.org/10.1021/ie403534f | Ind. Eng. Chem. Res. 2014, 53, 564−571
