Thermogravimetric and Fourier‐transform infrared analyses on the cure behavior of polycardanol containing epoxy groups cured by electron beam

In this study, the curing behavior of polycardanol containing epoxy groups (diepoxidized polycardanol) was exploited in terms of thermal stability and the cure reaction conversion by means of thermogravimetric analysis and Fourier‐transform infrared spectroscopy, respectively. The effect of photo‐initiator type and concentration and electron beam absorption dose in the presence of cationic photo‐initiators (triarylsulfonium hexafluorophosphate (P‐type) and triarylsulfonium hexafluoroantimanate (Sb‐type) on the cure behavior of diepoxidized cardanol (DEC) resin was investigated. The thermal stability of DEC with Sb‐type photo‐initiator was higher than that with P‐type one, being increased with increasing the concentration and electron beam absorption dose. The conversion of cure reaction was gradually increased with increasing the dose, showing the maximum at 800 kGy. The results revealed that Sb‐type photo‐initiator, the concentration of 2 or 3 wt %, and electron beam absorption dose of about 800 kGy may be preferable for initiating epoxy ring opening in the DEC molecules as well as for efficiently curing the DEC resin by electron beam irradiation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41599.     

Electron beam curing of polymer composites

Electron‐beam (E‐Beam) curing of an epoxy polymer matrix and its composite (reinforced with IM7 Carbon fibers) was studied using a cationic photoinitiator. Photoinitiator concentration, dose, and process temperature were varied to understand their influence on E‐beam curing. Optimal photoinitiator concentration was found to be 5 phr. The curing was due to a primary α reaction with a strong dependence on dose, and a secondary β reaction with a weak dependence on dose and a strong dependence on initiator concentration. The extent of cure increased rapidly with dose until 100 kGy and it approached a plateau value beyond 100 kGy. This plateau value corresponded to incomplete curing by 27% for resin and 22% for composite at a process‐temperature of 22°C. The causes for incomplete curing appear to be the secondary β reaction and diffusional limitation. Increase in process temperature resulted in higher extent of cure at a dose level. The material used in this study was also found to be thermally curable and the reaction onset temperature (measured in a DSC ramp experiment) reduced from about 150°C at 0 kGy to about 50°C at 30 kGy. This indicates that simultaneous thermal curing during E‐beam curing of resin and composite is possible. After thermal post‐curing, the T_g of the E‐beam cured resin increased from 130°C at 200 kGy to a value greater than 370°C and the modulus decreased by 10%. The service temperature and the modulus of the 100% thermally cured resin and the thermally post‐cured (after E‐Beam irradiation) resin were comparable.     

Electron Beam Curing of the System Cycloaliphatic Diepoxide‐Epoxidized Natural Rubber‐Glycidyl Methacrylate in Presence of Cationic Initiators

Electron beam curing of the system cycloaliphatic diepoxide‐epoxidized natural rubber‐glycidyl methacrylate containing a cationic initiator was carried out. Storage modulus, glass transition temperature and pendulum hardness were measured as function of EB dose, photoinitiator concentration, content of epoxidized natural rubber, post cure temperature and post cure time. At electron beam doses larger than 100 kGy a highly cross‐linked polymer network is generated which shows a two phase morphology. Microscale elastomeric domains are incorporated into a continuous epoxy resin phase. Dynamical mechanical analysis and pendulum hardness measurement show that an increase of the ENR ratio leads to a more elastic polymer network. Post curing results in increased glass transition temperatures. This EB cured polymer system is believed to provide both toughness and favorable viscoelastic properties to be used as component of EB curable composites.     

Ultraviolet‐curable epoxidized sunflower oil/organoclay nanocomposite coatings

Hybrid nanocomposite coating films, prepared by the incorporation of epoxidized sunflower oil into organoclay, can be cured by ultraviolet radiation with either cationic or hybrid initiation. The organoclay used in this study was prepared by a cationic exchange process in which sodium ions were replaced by alkyl ammonium ions. The effects of types of photoinitiators on energy consumption in the curing process were studied. Formulations with a hybrid photoinitiator required less energy in the curing process than those with a cationic photoinitiator. Moreover, the physical properties of dried films were examined as a function of the organoclay incorporation, and it was found that the hardness of the films increased as the amount of organoclay in the formulation increased. The X‐ray diffraction patterns of an ultraviolet‐curable organoclay‐incorporated film showed an exfoliated structure of the organoclay in the ultraviolet‐curable coating film. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Colour and gloss properties of pigment‐printed synthetic leather using an ultraviolet‐curable water‐borne polyurethane acrylate binder and two photoinitiators at different ratios

This study reports on the colour and gloss properties of pigment‐printed polyurethane‐based synthetic leather using an ultraviolet (UV)‐curable water‐borne polyurethane acrylate binder and two types of photoinitiators (Omnirad 819 DW and Omnirad 500) at different ratios. The UV curing of printed synthetic leather samples was conducted with gallium and mercury lamps, either singly or in combination, at three different power levels. Chemical changes in the cured films because of the polymerisation of the UV‐curing process were analysed by Fourier Transform‐infrared spectroscopy, which showed that the polymerisation reaction occurred after UV curing in both the clear and in the pigmented films. The Omnirad 500 photoinitiator is more effective in surface curing and the Omnirad 819 DW photoinitiator is more effective in deep curing. The Omnirad 500 photoinitiator caused the gloss values to drop significantly, especially in the formulation including both photoinitiators, Omnirad 819 DW and Omnirad 500, at a 1:2 ratio, respectively. In the formulation including a higher ratio of the Omnirad 819 DW photoinitiator, higher gloss values were obtained compared with the formulation including a higher ratio of the Omnirad 500 photoinitiator. Considering all the results, the highest gloss value of 20.96 was obtained with samples printed with the formulation of the two photoinitiators at an equal ratio (1:1) cured under a gallium/mercury lamp combination at a power level of 90 W/cm. Moreover, the highest K/S value of 10.86 was obtained with samples printed with the formulation of the two photoinitiators at an equal ratio cured under the gallium lamp at 90 W/cm.     

阳离子光引发剂研究进展

阳离子型光引发剂是一类新型的紫外光固化材料的引发剂。本文介绍了阳离子光引发剂的主要种类及各自的特点 ,讨论了其光引发机理 ,并简述了阳离子光引发剂的的发展概况和主要用途。     

Kinetic studies of a UV-curable powder coating using photo-DSC, real-time FTIR and rheology

The curing kinetics of UV-curable powder coatings based on commercial unsaturated polyesters were monitored using photo-DSC, Real-Time FTIR-ATR and a modified rheometer equipped with a UV source. The effect of physical and chemical factors on curing such as type of photoinitiator, photoinitiator concentration, temperature and atmosphere of curing were evaluated. Coatings containing amounts of photoinitiator from 0.5 to 10 wt% were cured at different temperatures in less than 10 s reaching conversions approximately of 60%. The increase of the temperature of curing reduces the final conversion and also the rate of polymerization due to the chain transfer process and depolymerization that dominates the photopolymerization at high temperatures. The reactivity of the photoinitiators was similar for all the studied photoinitiators apart from benzophenone that was found to be the slowest initiator.     

Morphologies and applied properties of free radical/cationic UV‐cured CPUA/TMPTMA/CER composite films

A UV‐cured composite film was prepared by free free‐radical photopolymerization from a blend containing oligomer cycloaliphatic polyurethane acrylate (CPUA) and reactive diluent trimethylolpropane trimethaacrylate (TMPTMA) with the same weight (coded as UT) in the presence of free free‐radical photoinitiator Irgacure 754. It was proved to be a homogeneous system featuring only one phase by means of scanning electron microscopy (SEM). Cycloaliphatic epoxy resin (CER) was introduced to enhance mechanical properties of the UV‐cured UT composite film in the presence of cationic photoinitiator Irgacure 250, and a series of UV‐cured CPUA/TMPTMA/CER composite films with different component ratios were prepared by free radical/cationic hybrid UV UV‐curing technique. Results of conversion curves, SEM, and Fourier‐ transform infrared spectroscopy illustrated that UT was cured faster than CER, leading to dynamically asymmetric photopolymerization‐induced phase ‐separation behaviors. The thermal and mechanical properties were evaluated via thermal degradation analysis, dynamic mechanical analysis, and stress–strain curves. Surface properties such as pencil hardness, pendulum hardness, shrinkage rate, contact angle, flexibility, and glossiness were also studied. All these measurements revealed that component ratios, intermolecular attractions, photopolymerization velocities, and viscosities had remarkably influenced on the morphologies and applied properties of UV‐cured composite films, and interpenetrating polymer network films had better comprehensive performances than other UV‐cured composite films with different microstructures. POLYM. COMPOS., 36:1177–1185, 2015. © 2014 Society of Plastics Engineers     

Low‐energy electron beam‐induced cationic polymerization with onium salts

Demand for higher polymer performance with very short cure times has resulted in the development of low energy electron beam processes. This article presents the results of such a process for curing two epoxy systems, namely 3,4‐epoxycyclohexylmethyl‐3′,4′‐epoxycyclohexane carboxylate and di‐glycidyl ether of bisphenol A (DGEBA), using the cationic photoinitiator salts, triarylsulfonium hexafluoroantimonate, and diaryliodonium hexafluoroantimonate, respectively. Glass transition temperature measurements were done using a modulated DSC method while the degree of conversion was measured using FTIR spectroscopy. Results indicate that for both epoxy systems a relatively low dosage of not more than 5 Mrad was sufficient to achieve up to 60% conversion, with up to 80% conversion achievable using 30 Mrad. The diaryliodonium salt appeared to be more effective than the sulphonium salt in the above study. The effect of varying photoinitiator concentration and the resulting glass transition temperature has been studied. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3099–3108, 2001     

Thermal,mechanical, and corrosion resistance properties of vinyl ester/clay nanocomposites for the matrix of carbon fiber‐reinforced composites exposed to electron beam

Vinyl ester/clay nanocomposites with 1, 3, and 5% nanoclay contents were prepared. X‐ray diffractography patterns and Scanning Electron micrographs showed that nanocomposites with the exfoliated structure were formed. Thermogravimetric analysis, water absorption test, and Tafel polarization method, respectively, revealed the improvements in thermal resistance, water barrier properties, and corrosion resistance properties of the samples with an increase in the amount of the incorporated nanoclay. Tensile tests showed that nanoclay also enhanced the mechanical properties of the polymer, so that the tensile strength of the samples with 5% nanoclay was more than 3 times higher than tensile strength of pure vinyl ester samples. Overall, the best properties were observed for the samples containing 5% nanoclay. Pure vinyl ester and nanocomposite with 5% nanoclay content were exposed to the electron beam radiation and their mechanical properties improved up to 500 kGy irradiation dose. Finally, pure vinyl ester and vinyl ester/nanoclay (5%) matrixes were reinforced with carbon fiber and the effect of electron beam irradiation on their mechanical properties was examined. The tensile strength and the modulus of the samples initially increased after exposure to the radiation doses up to 500 kGy and then a decrease was observed as the irradiation dose rose to 1000 kGy. Moreover, nanoclay moderated the effect of the irradiation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42393.     

Efficient Benzodioxole‐based unimolecular photoinitiators: From synthesis to photopolymerization under UV‐A and visible LED light irradiation

The narrow emission spectra of light emitting diodides (LED) as irradiation source has brought great challenge for the development of efficient photoinitiators sensitive to LED light. This paper described a series of novel unimolecular type II photoinitiators, containing thioxanthones as chromophores and benzodioxoles as coinitiators. The structures of the photoinitiators were characterized by ¹H NMR, ¹³C NMR and high‐resolution mass spectrometer. Study on the photophysical properties of the photoinitiators indicated that electron donors/acceptors as spacers between thioxanthone and benzodioxole affected both the UV–Vis absorption and the fluorescence emission. The long wavelength absorptions from 385 nm to 402 nm as well as low fluorescence quantum yields make the investigated benzodioxole derivatives quite attractive as efficient photoinitiators under UV‐A and visible LED light irradiation. With a proper molecular design, the unimolecular photoinitiator exhibited higher initiation efficiency than the thioxanthone derivatives from the literature. Possible initiation mechanism was also proposed based on the photolysis study. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43239.     

Effects of small molecular weight silicon‐containing acrylate on kinetics,morphologies, and properties of free‐radical/cationic hybrid UV‐cured coatings

A series of UV‐curable, silicon‐containing mixtures were prepared by adding different micro amounts of small molecular weight silicon‐containing acrylate KH570 to an interpenetrating polymer network system composed of cycloaliphatic polyurethane acrylate, trimethylolpropane triacrylate, cycloaliphatic epoxy resin, free‐radical photoinitiator Irgacure 754 and cationic photoinitiator Irgacure 250 with a weight ratio of 15 : 15 : 65 : 1 : 4. Hybrid coatings with different addition amounts of KH570 (0.2, 0.6, 1.0 wt %) were cured from the mixtures by UV‐initiated free‐radical/cationic dual curing technique. Final reactant conversions and photopolymerization rates of the hybrid UV‐cured coatings were improved with the increase of KH570 content, as evaluated by conversion profiles. The morphologies and microstructures were characterized by scanning electron micro‐scopic, atomic force micrographic, and fourier transform infrared spectrophotometer measurements. Thermal, mechanical, and surface properties of the hybrid UV‐cured coatings were investigated. The increase in KH570 content caused a decrease in mechanical properties besides the breaking elongation. Thermo‐gravimetric analysis revealed that the incorporation of silicon into cross‐linked network structure resulted in high thermal stability. The surface properties of hybrid UV‐cured coatings, such as hardness, contact angle, flexibility, and glossiness were also examined. It is found that transparent hybrid coating with the addition of 1.0 wt % KH570 exhibited a relatively higher contact angle as a direct result of a relatively higher hydrophobic surface. These researches showed that micro amounts of small molecular weight silicon‐containing acrylate could greatly influence the morphologies of liquid nitrogen quenching cross sections and properties of hybrid UV‐cured coatings and could be used to modify UV‐cured coatings for some superior properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40655.     

UV-LED光固化体系光引发剂的新进展

本文综述了可用于UV-LED光固化体系光引发剂的研究进展，包括传统光引发剂及其衍生物（硫杂蒽酮类、二苯甲酮类和酰基膦氧化物）、新型基团的光引发剂（咔唑基、萘酰亚胺基、吩嗪基、苯丙二茂基、咪唑基和三嗪基）以及高分子光引发剂。传统光引发剂的改性和大分子光引发剂的合成，可以提高引发剂的稳定性。新型光引发剂的吸收波长与UV-LED光固化的发射波长匹配性较好，但该类光引发剂常需要加入助剂。此外，描述了氧阻聚对光固化体系的影响，指出了目前UV-LED光引发剂存在的不足，并展望了其发展应用前景。。     

3D打印用长波紫外光固化树脂的制备

通过优化引发剂的种类和用量,得到一系列阳离子和自由基混杂体系光固化树脂,并用旋转流变仪和SLA型3D打印机进行长波紫外光固化和3D打印成型。结果表明:与芳基鎓盐类阳离子光引发剂PAG202相比,芳茂铁盐类阳离子光引发剂261具有长波紫外光固化的适应性,而光敏增感剂PAS-50对光引发剂261敏化显著,在长波紫外光下光引发剂261/PAS-50体系能快速引发树脂固化。最佳配方时,固化树脂的弯曲模量高于国内外同类树脂的,且具有较低的固化收缩率。     

Ultraviolet‐curing behavior and mechanical properties of a polyester acrylate resin

Ultraviolet (UV) curing technology has been widely used in many applications because it has several distinct advantages compared to solvent‐based processes or thermal‐curing technology. The effects of photoinitiator types and their contents as well as reactive diluent types and their contents on the UV‐curing behavior and mechanical properties of a UV‐curable polyester acrylate resin were investigated in this study. Three photoinitiators, Irgacure 184, Darocur 1173, and benzophenone, were used in this study. Hexanediol diacrylate, tripropylene glycol diacrylate, and trimethylol propane triacrylate were used as reactive diluents to modify the properties of the acrylate resin. The change of chemical structure during UV curing was monitored by FTIR. A universal testing machine was used to measure the tensile properties of various UV‐cured acrylate films of different compositions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3921–3928, 2004     

紫外光固化含硫密封剂的制备及性能

以聚硫代醚橡胶为基础胶,利用Thiol-ene点击反应制备了紫外光固化含硫密封剂。考察了光引发剂种类和用量以及烯烃种类、多元硫醇种类等对硫化后密封剂力学性能、热分解温度、玻璃化转变温度的影响。结果表明,相比于光引发剂184,光引发剂1173的固化效果更好,固化后的密封剂热稳定性更佳,且随着光引发剂用量的增加,密封剂的力学性能和热稳定性均下降,光引发剂1173的用量宜为0.03份（质量,下同）。采用三丙二醇二丙烯酸酯（TPGDA）作为固化剂固化的聚硫代醚密封剂力学性能较好,而且随着TPGDA用量的增加,密封剂的力学性能和热稳定性均上升,TPGDA的用量宜为1.00份。多官能度硫醇的加入可提高密封剂的交联度及玻璃化转变温度。     

Influence of silica and electron beam radiation on the properties of a high vinyl styrene-butadiene-styrene block copolymer

Radiation crosslinking of polymers has gained importance over conventional crosslinking because the system is fast, pollution free and relatively simple. In high energy electron beam curing, which is one of the radiation curing methods, the material to be cured is bombarded with electrons of specified energy to produce free radials. These radicals unite to give rise to chemical crosslinks. In the process, some unwanted chain scission may also occur. The mechanical properties of such electron beam crosslinked systems can further be improved by the incorporation of nanosilica. In this work, a high vinyl (~50%) S-B-S block copolymer incorporated with varying doses of specific hydrophilic nanosilica was irradiated with electron beam at 25 and 50 kGy. Mechanical properties were studied and compared with that of the unirradiated system. The influence of a silane coupling agent was also investigated. Morphological studies were done to understand the dispersion of nanosilica in the polymer matrix. Relatively moderate amounts of nanosilica along with an optimum dose of the coupling agent were found to be effective in improving the properties. Rheological properties were also studied in details to understand the possibility of recycling the polymer.     

Curing of composite components by ultraviolet radiation: A review

Curing of polymer matrices by ultraviolet (UV) irradiation can be applied to a variety of processes in the production of composite components, as long as the component can be directly irradiated. Wet lay‐up techniques, vacuum infusion type processes with UV‐transparent membranes, filament winding, and prepreg processes have been adapted to UV curing. Unlike in thermal curing, the curing time is in the order of magnitude of minutes rather than hours, which means a significant reduction in cycle time. The radiation can be generated by a variety of sources suitable for various specific applications and different curing strategies. The most frequently used radiation sources are mercury arc lamps. Because of the absorption of radiation passing through matter, the thickness of laminates for efficient application of UV curing is limited. The curing mechanism is either radical polymerization for acrylate‐based resins or cationic polymerization for epoxies and vinyl ethers. The properties of the UV‐cured polymer matrix are determined by the cross‐linking density. This depends on the type and concentration of the photoinitiator and of the (optional) diluents, the intensity and the duration of the irradiation, and the temperature at which the curing process takes place. POLYM. COMPOS., 27:119–128, 2006. © 2006 Society of Plastics Engineers.     

Cationic electron‐beam curing of a high‐functionality epoxy: effect of post‐curing on glass transition and conversion

This paper reports on the cationic electron‐beam curing of a high‐functionality SU8 epoxy resin, which is extensively used as a UV‐curing negative photoresist for micro‐electronics machine systems (MEMS) applications. Results show that elevated post‐curing treatment significantly increased both the conversion and the glass transition. The degree of conversion and the glass transition temperature were measured by using Fourier‐transform infrared (FTIR) spectroscopy and modulated differential scanning calorimetry (MDSC^®), respectively. The glass transition temperature (T_g), which has been observed to be dependent on the degree of conversion, reaches a maximum of 162 °C at 50 Mrad and post‐curing at 90 °C. The degradation pattern of the cured resin does not show much variation for exposure at 5 Mrad, but does show significant variation for 50 Mrad exposure at various post‐curing temperatures. A degree of conversion of more than 0.8 was achieved at a dosage of 30 Mrad with post curing at 80 °C, for the epoxy resin with an average functionality of 8 a feature simply not achievable when using UV‐curing. Copyright © 2004 Society of Chemical Industry     

含乙烯基有机硅树脂的电子束固化行为研究

以八甲基环四硅氧烷、四甲基四乙烯基环四硅氧烷为单体,六甲基二硅氧烷为封端剂,碱胶为催化剂,合成了含乙烯基有机硅树脂;并研究了电子束辐射剂量对其固化行为的影响和固化涂层的热性能。红外谱图及凝胶率测试结果表明,有机硅树脂中的碳碳双键吸收峰强度随辐射剂量的增加而减弱,辐射诱导交联网络结构的形成导致固化涂层的凝胶率随剂量的增加而显著增加;辐射剂量为30 kGy时,凝胶率为46.2%;辐射剂量增加至60 kGy时为70.1%和100 kGy时为85.9%。差示扫描量热分析和热质分析结果表明,固化涂层具有优良的耐低温性和热稳定性。