UV-curable Hybrid Coatings Research Articles

Construction of waterborne flame-retardant itaconate-based unsaturated polyesters and application for UV-curable hybrid coatings on wood

Developing a strategy to improve the flame retardancy and water resistance of waterborne bio-based coatings on wood is an effective route to enhance safety and applicability of timbers. In this work, the waterborne itaconate-based unsaturated polyester (IAF) were synthesized from biomass-derived itaconic acid (IA) and flame retardants FRC-6 by melt polycondensation in one pot, which was investigated as an ideal waterborne resin for UV-curable coating applications. A series of UV-cured hybrid coatings on wood were prepared consisting of IAF, N-(Hydroxymethyl) acrylamide (NMA), and γ-methacryloxypropyltrimethoxysilane (MPS) in various proportions via UV-curing and sol-gel process. The incorporation of MPS enhanced the rigidity, cross-linkage, and water resistance of UV-cured hybrid coatings, but the excessive silicone gel limited the further improvement of coating performances due to the phase separation and reduced film-forming property. Moreover, the UV-cured hybrid coatings appeared exceptional charring properties and endowed wood with superior flame retardancy. It was noticed that P/N/Si synergistically promoted the formation of remarkable, dense, and stable char layer on wood as a barrier, retarding the spread of heat, oxygen, or flammable volatile and the further combustion of substrates. Besides, the free radical capture of phosphorus and the dilution effect of inert gas played an essential role in gas-phase flame retardancy.

Castor-oil-based UV-curable hybrid coatings

Castor-oil-based UV-curable hybrid coatings

Castor-oil-based UV-curable hybrid coatings with self-healing, recyclability, removability, and hydrophobicity

Restrained by the irreversibility of the permanently cross-linked networks formed by double bonds, UV-curable thermosets with self-healing and reprocessing properties especially those derived from renewable feedstocks are highly desired for practical applications. In this work, repairable, recyclable, removable, and hydrophobic UV-curable polyurethane coatings derived from renewable castor oil were constructed by the employment of dynamic hindered urea bonds (HUBs). The resulting UV-curable materials not only showed high biobased contents (45.1%–47.6%), but also exhibited good thermal, mechanical, coating, and hydrophobic performance (a Tg of 67.0–77.8 °C, a tensile strength up to 16.6 MPa, a pencil hardness of 3H–5H, a flexibility of 2 mm, a water contact angle of 90.8–105.9°, etc.). Furthermore, due to the rapid dissociation or exchange of HUBs and intramolecular hydrogen bonds, the resulting UV-curable coatings exhibited excellent repairability, weldability, recyclability, and removability at moderate temperatures. For instance, the selected sample (PU-Si2) demonstrated a scratch healing efficiency up to 97.0% at 140 °C for 60 min and a welding efficiency (tensile strength) of 91.3% at 120 °C for 60 min. In particular, the UV-cured PU-Si2 sample could be physically recycled at least 4 times with enhanced performance in tensile properties, and the resulting PU-Si2 coatings were easily removed or recycled by using low-toxicity organic solvents like ethyl acetate and dimethylformamide.

Ambient temperature and UV-cured hybrid coatings from acetoacetylated non-isocyanate polyurethanes

Preparation of ambient and UV curing non-isocyanate polyurethane (NIPU) coatings has been reported using a series of acetoacetylated non-isocyanate polyurethane (AA-NI-PUPO) oligomers. Synthesized oligomers were characterized using various techniques such as Fourier transform infrared and nuclear magnetic resonance spectroscopy. AA-NI-PUPOs showed significantly lower viscosity compared to their non-acetoacetylated counterparts. Ambient temperature-cured systems were formulated by mixing AA-NI-PUPOs and different primary amine compounds in stoichiometric proportions. Michael addition reaction of acrylates and AA-NI-PUPOs was initiated by UV curing using a photobase generator as the catalyst. NIPU coatings were studied for various thermo-mechanical properties and corrosion resistance. The selected UV-cured and ambient-cured samples showed instant and 1-h tack-free time, respectively. Results revealed that with proper selection of acetoacetylated resin and crosslinker type, coatings with properties comparable to conventional PU coatings could be formulated. Moreover, UV-curable coatings with up to 90 wt% solid could be formulated using conventional monomeric acrylates as a reactive diluent. The study demonstrates the feasibility of formulating solvent-free rapid ambient curing non-isocyanate polyurethane coatings.

Anti-Yellowing UV-Curable hybrid coatings prepared by the Sol–Gel method on polystyrene

This study is aimed to develop UV-curable hybrid sol–gel coating in order to improve the surface properties of polystyrene (PS) against chemical degradation problem. First, hybrid sol-gels were synthesized using TEOS, VTMS, C2H5OH, distilled water, 1 M HCl, 1 M NH4OH, TiO2 and inorganic (Al2O3, SnO2, ZrO2) and organic (Tetrahydrofuran (THF)-C4H8O) chemicals. Second, the synthesized hybrid sol-gels were coated on the surface of PS plates using an applicator and pre-treated at −80 °C for 24 h and the coated plates were cured under UV light at 40 °C for 1 h. The original PS plates and coated PS plates were subjected to a yellowing test for 26 h. Third, colour (CM-2600d. Konica Minolta Optics Inc. Japan) and gloss (Multi Gloss 268 Plus. Konica Minolta Optics Inc. Japan) measurements, hardness (TroniC–Hildebrand Shore D), FT-IR (Perkin Elmer Spectrum 100 model FTIR spectrometer), SEM (SEM-ZEISS Supra 40 V P), TGA (TGA, Setaram Labsysevo model), AFM (AEP-Nanomap-500LS) and contact angle (KSV0 CAM 200) analyses of the original and UV-cured hybrid sol gel-coated PS plates were performed before and after the yellowing test. As a result, it was observed that the surface properties of the PS plates coated with the hybrid sol-gel prepared using C4H8O organic compound of 0.5 g improved significantly.

Flame resistance, physical and mechanical properties of UV-cured hybrid coatings containing low-hydroxyl-content sols via an anhydrous sol-gel process

Abstract As one of a series of our studies, starting with silica sol (TM2) and Si-P binary sol (SP5), two series of low-hydroxyl-content sols (LHCSs) were synthesized using an anhydrous sol-gel method. The stable storage time of LHCS-containing hybrid coatings was improved relative to that of hybrid coatings containing TM2 and SP5. The flame resistance and thermal stability of UV-cured hybrid coatings consisting of LHCS, epoxy acrylate of bisphenol A (SM6104) and tripropylene glycol diacrylate (TPGDA) were investigated by means of thermogravimetric analysis (TGA), limit oxygen index (LOI), cone calorimetry and a flammability test. The results indicated that the flame resistance of LHCS-containing hybrid coatings was further improved over that of hybrid coatings containing TM2 and SP5. The improvements mainly included a longer ignition time and lower combustion heat. Hybrid coatings applied on the surface of wooden floors could offer long-lasting and significant protection against fire, showing outstanding practical value. In addition, the physical and mechanical properties of LHCS-containing hybrid coatings were negatively affected by the decrease of hydroxyl group contents and the Ti-containing component. A UV-curable phosphorus-containing resin (RAYLOK 1722) was introduced into the hybrid coatings containing LHCS. However, hybrid coatings containing RAYLOK 1722 showed only a small improvement in flame resistance, and their physical and mechanical properties were damaged by RAYLOK 1722.

Grafting of hyperbranched polymer onto the nanosilica surface and their effect on the properties of UV-curable coatings

The nanosilica is first treated with 3-mercaptopropyl trimethoxysilane (MPTMS) to introduce mercapto groups as growth points, and then hyperbranched polymer is grafted on the nanosilica surface via repeated step of thiol-ene click reaction between the acrylate double bond of trimethylolpropane triacrylate (TMPTA) and mercapto groups of trimethylolpropane tris 3-mercaptopropionate (Trithiol). FTIR results confirm that the grafting procedure is feasible, and TGA results indicate the grafting ratio is as high as 45.0 %. The curing kinetic, monitored by photo-DSC, shows that both terminal acrylate double bonds and mercapto groups can accelerate the curing speed of the UV-curing organic–inorganic hybrid coatings. The mechanical and physical properties of UV-curable hybrid coatings containing modified nanosilica at different generations are also investigated.

Effects of silane precursors on curing behavior of UV-curable hybrid coatings

This study demonstrates the effect of some commonly used silane precursors on curing behavior and photopolymerization kinetics of UV-curable hybrid coatings. Tetraethoxyorthosilane (TEOS), vinyltrimethoxysilane (VTMS), and 3-methacryloxypropyltrimethoxysilane (MPS) were polymerized under acidic conditions by the sol–gel method. The resulting structure of the tested siloxane oligomers was characterized using 29Si-NMR and 1H-NMR spectroscopy. Photo-DSC was used to evaluate photocuring enthalpy. A fully integrated model was applied to investigate propagation rate coefficients and to identify the most effective termination mechanism (monomolecular, bimolecular, or mixed). Results showed that oligomers containing MPS effectively promoted total heat of the polymerization process and consequently affected the maximum rate of polymerization and final double bond conversion. Enthalpy rating for samples containing MPS was higher than that of those containing VTMS, showing that MPS was more compatible with the acrylate systems. In addition, evaluations for photopolymerization kinetic constants proved that non-functional oligomers containing TEOS caused radical trapping and increased activity of the monomolecular termination mechanism.

Fluorine-containing photocurable hybrid coatings via anhydrous sol-gel method

In this study, fluorine-doped photocurable hybrid coatings were prepared by combining UV-curing technology with an anhydrous sol–gel method. First, methacryloxymethyl triethoxysilane (MEMO) was hydrolyzed via an anhydrous sol–gel process. Then MEMO was mixed with acrylic oligomers and predetermined amounts of fluoroacrylate resin. UV curable hybrid coatings were applied on corona-treated plexiglass substrates. The addition of fluorine showed a significant impact on the properties of the coatings. As the fluorine content was increased in the formulations, flame retardancy and the contact angle values of the coatings increased. It was found that the optical transmittance of the coatings was higher than 95%. The surface morphology of the hybrid films was characterized by scanning electron microscopy (SEM). The chemical composition of the surface of the coatings was identified by energy dispersion spectrum (SEM–EDS) technique. SEM studies indicated that inorganic particles were dispersed homogenously throughout the organic matrix. J. VINYL ADDIT. TECHNOL., 2014. © 2014 Society of Plastics Engineers

Characterization and Properties of UV-Curable Hyperbranched Polyurethane Acrylate-Polyurethane Diacrylate/SiO2 Hybrid Coatings

A series of new UV-curable hybrid coatings were prepared with hyperbranched polyurethane acrylate-polyurethane diacrylate (HBPUA-PUDA) and organic SiO2 as formation, and 2-hydroxyl-2-methyl-l-phenyl-1-propanone (Darocur 1173) was used as photo-initiator. The effect of organic SiO2 content on the thermal stability and conversion of C=C bonds of the UV-cured HBPUA-PUDA/SiO2 films were evaluated using thermal gravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). The morphology of SiO2 were observed by using transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), and the elemental composition of SiO2 was tested by energy dispersive spectrometer (EDS). The results revealed that when organic SiO2 content was less than 30 wt%, the average particle size of SiO2 was about 95 nm and the particles were well-dispersed in the organic phase. The mechanical properties, abrasion resistance and transmittance of the films were also investigated. The results showed that with the increase of organic SiO2 content, the adhesive force and pendulum hardness were increased obviously, while the transmittance and flexibility were decreased. When the content of the organic SiO2 was 30 wt%, the film of HBPUA-PUDA/SiO2 showed the optimal comprehensive performance as follows: pendulum hardness was 0.74, transmittance was 93.1%, adhesion was 0 grade, flexibility was 2 mm, impact strength was 43 Kg x cm and mass loss of 300 cycles was 12.9 mg.

Preparation and stability of silica sol/TPGDA dispersions and its application in the UV-curable hybrid coatings for fire protection

A series of silica sols modified by γ-methacryloxypropyltrimethoxysilane (MPS) were synthesized by the acid-catalyzed sol–gel method, and then the solvent in these sols were extracted under several vacuum distillation conditions. The stability of the sol after the distillation can be improved by means of increasing the dosage of MPS and incorporating reactive diluent TPGDA into the sol as new dispersion medium. Optimized samples have maintained stable for over 180 days. The sol dispersions and UV-curable organic compounds were mixed to form the hybrid coatings for fire protection. Effects of the distillation treatment and the cosolvent anhydrous ethanol added into the reaction solution on thermal and combustion performances and physical properties of the hybrid coatings were studied by thermogravimetric analysis, microscale combustion calorimeter, limit oxygen index test and UL-94 horizontal test, etc. The results showed that the distillation treatment for the sol was necessary to improve thermal performance and physical properties of the hybrid coatings. In addition, in the flammability experiment, hybrid coatings showed a quick and efficient protection of the substrate.

Nano-Silica Reinforced UV-Curable Hybrid Hard Coatings on Polymethylmethacrylate (PMMA) Substrate

Hybrid sols were synthesized through a combination of hydrolysis and condensation reactions of tetraetoxysilane and γ-Methacryloxypropyltrimethoxysilane together with the addition of a colloidal silica suspension. A transparent, hard UV-curable hybrid coatings based on hybrid sols were prepared in order to improve the scratch and abrasion resistance of PMMA substrate. The effects of the content of colloidal silica suspension on pencil hardness, transmittance, and haze were investigated. The pencil hardness of all coating films in this study can be tuned from 4H to 9H, whereas that of uncoated PMMA substrate is 1H. The higher hardness of the coatings can be attributed to the dense structure induced by the increase of network density with the addition of colloidal silica suspension. Furthermore, it is found that the transmittance of coatings slightly fluctuates between 91.8% and 93.6% with increasing colloidal silica content. These results indicate the good compatibility of the organic and inorganic components.

Synthesis, characterization and flame retardant of UV-curable hybrid coatings containing SiO2–P2O5–B2O3 via sol–gel method

A ternary sol containing silicon, phosphorus and boron modified by γ-methacryloxypropyltrimethoxysilane was synthesized by sol–gel method. The ternary sol was incorporated into the organic matrix and UV-curable organic/inorganic hybrid coating materials were obtained. Hardness, transmittance, haze, cross-cut adhesion and abrasion resistance results showed that the mechanical properties of the hybrid coatings improved effectively with no comprising on optical properties by increasing sol content. Scanning electron microscopy and Energy Dispersive X-ray spectrometer studies indicated that inorganic particles were homogenously dispersed in the organic matrix. The flame retardancy of the UV-curable coatings was investigated by thermogravimetric analysis and microscale combustion calorimeter. The results showed that the incorporation of sol into the organic network led to an improvement in the thermal stability and flame retardancy of the hybrid coating materials. It is a desirable achievement to improve simultaneously both flame retardancy and mechanical properties of the coatings.

Thermal and neutron shielding properties of 10B containing UV cured hybrid coatings

10B containing organic–inorganic hybrid coating material based on a UV-curable formulation was prepared via anhydrous sol–gel technique. UV curable coatings were applied on Plexiglas (PMMA) substrates. The molecular structure of the coating material was analyzed by ATR-FTIR spectroscopy technique. The characterization of the UV-curable coating was evaluated by various techniques such as gel content, abrasion resistance, chemical resistance, pencil hardness, pendulum hardness, MEK rubbing test, contact angle, cross-cut test, gloss, transmittance test, neutron absorption, Limiting Oxygen Index and stress–strain tests. Hybrid coatings showed a significant enhancement in radiation shielding properties. The thermal behavior of coatings was also evaluated. It is observed that the thermal stability of coatings mainly depends on their boron and silicate contents. Results of all analysis conducted on hybrid films, and coatings were discussed.

Synthesis of fluorinated/methacrylated epoxy based oligomers and investigation of its performance in the UV curable hybrid coatings

Organic–inorganic hybrid coatings based on fluorinated/methacrylated soybean oil and bisphenol A/F epoxy methacrylate were obtained by combining photopolymerization and sol–gel process. Hard and transparent hybrid coatings were prepared on polycarbonate panels and their physical and mechanical properties such as gel content, hardness, adhesion, gloss, contact angle as well as tensile strength were measured. Results from the mechanical measurements showed that the properties of hybrid coatings improved with the increase in fluorine and sol–gel precursor contents. Thermo gravimetric analysis results demonstrated that fluorine and silica incorporations significantly enhanced the thermal oxidative stability of the hybrid coating materials. The surface morphology was also characterized by scanning electron microscopy (SEM). SEM studies indicated that inorganic particles were dispersed homogenously throughout the organic matrix.