Moisture absorption and desorption in a UV cured urethane acrylate adhesive based on radiation source

A photopolymerizable urethane acrylate (UA) adhesive was cured using two different sources: a conventional UV‐lamp and a UV‐emitting light emitting diode (LED). Moisture uptake in cured specimens was characterized by immersion in deionized water at 21.8, 30, 37.5, and 45°C for a period of 6 months. Additionally, desorption experiments were performed for selected specimens under vacuum at room temperature. Material degradation in the form of mass loss was observed in all samples after attainment of a maximum water uptake level, with the phenomenon being more pronounced at higher immersion temperatures. This degradation is attributed to leaching and dissolution of uncured monomers and lower weight molecular species from the samples. A two stage moisture uptake model is proposed to account for mass loss and excellent agreement between the tested mass loss and the loss‐rate parameters determined from the model is shown. Performance of specimens was characterized with dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). It was found the LED source was not as effective in curing surfaces, due to which there is a higher level of mass and lower T_g from hygrothermal exposure as compared to the core regions of the LED cured specimens and the overall lamp cured specimens. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of sequential interpenetrating polymer networks of polyurethane acrylate and polybenzoxazine

High‐performance ultraviolet (UV) curable polyurethane acrylate (PUA) coating alloyed with thermally curable polybenzoxazine (PBA) is developed. The hybrid polymer networks of PUA and PBA‐a were prepared by sequential cure methods, i.e., UV cure of the PUA followed by thermal cure of the PBA fraction. The effects of sequential cure were investigated in terms of mechanical, thermal, and physical properties of the resulting polymer alloys. The fully cured PUA/PBA‐a alloy films showed only single glass transition temperature (T_g) suggesting high compatibility between the two polymer networks, possibly of an interpenetrating polymer network type. The storage modulus in a glassy state and T_g of PUA/PBA‐a alloys were found to substantially increase with increasing PBA‐a content. Furthermore, degradation temperature at 10% weight loss of the PUA/PBA‐a alloy films was relatively high whereas the char yield at 800°C was found to increase with a PBA‐a component. Hardness was enhanced, whereas water absorption and water vapor permeation rate of the alloy were suppressed by the incorporation of the PBA‐a into the polymer alloys. As a consequence, the properties of UV curable PUA networks can be positively tailored and enhanced by forming hybrid network with PBA‐a. POLYM. ENG. SCI., 54:1151–1161, 2014. © 2013 Society of Plastics Engineers     

Design and synthesis of bio-based UV curable PU acrylate resin from itaconic acid for coating applications

UV curable PUA resin was successfully synthesized from polyol based on sustainable resource originated from itaconic acid (IA), isophorone diisocyanate (IPDI) and 2-hydroxyethyl methacrylate (HEMA). A polyol was synthesized by condensation reaction of IA with 16-hexanediol in the presence of p-Toluenesulfonic acid (pTSA). The synthesized PUA resin was characterized for its structural elucidation by using Fourier Transform Infrared Spectrophotometer (FTIR), ¹H and ¹³C NMR spectroscopy. The synthesized UV curable PUA resin was incorporated in varying concentrations in conventional PUA coating system. The effects of varying concentration of synthesized UV curable PUA resin on rheology, crystallinity, thermal and coating properties were evaluated. The rheological behavior of the resins were evaluated at variable stress and result showed decrease in viscosity of resin as concentration of synthesized UV curable PUA resin increases in conventional PUA resin. The cured coatings have been evaluated for glass transition temperature (T_g) and thermal behavior by differential scanning calorimeter and thermogravimetric analysis respectively. The degree of crystallinity of the coatings was determined from X-ray diffraction patterns using the PFM program. It was found that increase in the mass proportion of IA based PUA in coatings, the coating becomes more rigid and crystalline. The synthesized UV curable PUA coatings showed interesting mechanical, chemical, solvent and thermal properties as compared to the conventional PUA. Further, cured coatings were also evaluated for gel content and water absorption.     

Printability of Methacrylated Gelatin upon Inclusion of a Chloride Salt and Hydroxyapatite Nano‐Particles

3D biomaterial printing requires an ink to have suitable printability characteristics, as well as creating a final construct of controllable swelling and stiffness. To tune such properties, the impact of adding different levels of chloride salts (NaCl and CaCl₂) and hydroxyapatite nano‐particles (nHA) to a highly concentrated and photo‐crosslinkable methacrylated gelatin (GelMA) is investigated. By adding up to 100 mm CaCl₂ or 1.11 m NaCl, the GelMA viscosity decreases from that of control GelMA (no salt). Interestingly, a 25G needle and strong photo‐polymerization kinetics are able to overcome the low viscosity of the 50CaG ink during printing. Adding further CaCl₂ increases GelMA viscosity, while decreasing both the swelling and dynamic modulus of the UV‐cured construct observed in water. As all UV‐cured constructs have a dynamic modulus greater than 1 MPa, this novel system is able to match the dynamic modulus of articular cartilage—a feat not previously reported for a GelMA‐based system. Lastly, nHA inclusion improves ink printability, as well as decreases swelling and increases dynamic modulus of the final construct. Overall, this study leads to the successful development of a new advanced functional ink which will be beneficial in the 3D printing of biomaterials toward tissue engineering applications.     

Novel reactive diluents for UV/moisture dual‐curable coatings

The novel silicone‐modified polyacrylate reactive diluents for UV/moisture dual‐curable coatings were synthesized from N,N‐bis[3‐(trimethoxysilyl)propyl]amine and multifunctional acrylates such as ethoxylated trimethylolpropane triacrylate and polyethyleneglycol diacrylate through Michael addition reaction. Their structures were characterized by NMR and FTIR and their average molecular weights were determined by vapor pressure osmometry. With FTIR, it was found that the obtained diluents could be cured both by UV radiation and moisture mode. The ²⁹Si‐NMR showed that dimer was the main condensation product at the initial stage of moisture curing. The rheological behavior of the diluents investigated by rotary viscometer indicated they were very close to Newtonian fluid, and the viscosity of coatings decreased evenly with increasing concentration of reactive diluents in the coatings. In particular, they were found to be highly efficient in diluency and reactivity for UV polymerization. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1500–1504, 2005     

Effects of hygrothermal ageing on mechanical properties of flax pulps and their polypropylene matrix composites

The aim of this work was to study the kinetics of water uptake and its influence on mechanical behavior of both flax pulps and their composites with a maleic anhydride polypropylene copolymer (MAPP) modified polypropylene (PP) matrix by immersion in distilled water at 30, 50, 70, and 100°C. Both the influence of two different MAPP compatibilizers and the optimum doses of each ones were analyzed. The kinetics of water uptake was studied from weight measurements at regular interval times. The diffusion coefficient was dependent on the immersion temperature and MAPP content. Tensile modulus and strength of single flax fiber decreased by water immersion. Both flexural strength and modulus of composites decreased as a result of the combined effect of thermal ageing and moisture absorption. MAPP coupling agent increases moisture resistance and mechanical properties for MAPP‐modified systems with respect to the unmodified ones. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3438–3445, 2006     

Thermoplastic polymers as modifiers for urea–formaldehyde wood adhesives. III. In situ thermoplastic‐modified wood composites

Acrylic monomers and free‐radical initiators were dispersed in an aqueous urea–formaldehyde (UF) suspension and polymerized in situ to afford a suspension containing 5 wt % thermoplastic (5 g of thermoplastic/100 mL of suspension). The viscosity of the thermoplastic‐modified UF suspension (65 wt % solids at 25°C) ranged from 240 to 437 cP versus 121 cP for the unmodified UF control. Wood‐flour composites (sugar maple and 50 wt % adhesive) were prepared with thermoplastic‐modified UF suspensions and cured with the same cycle used for the composites prepared with the unmodified UF adhesive (control). The effect of the thermoplastic‐modified UF adhesive was evaluated on the notched Izod impact strength and equilibrium moisture uptake of the wood‐flour composites. The notched Izod impact strength of the composites prepared with modified UF adhesives increased by as much as 94% above that of the control. The increase depended on the initiator and the monomer composition. The modification affected the equilibrium moisture uptake and rate of moisture uptake in the wood‐flour composites. Preliminary results for particleboard prepared with 10 wt % modified UF adhesive (5% thermoplastic in the UF resin) and unoptimized cure conditions confirmed a significant effect of the thermoplastic modification on both the internal‐bond strength and thickness swelling of the particleboard. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Moisture Uptake by Some Uncured Adhesive Films

The uptake of moisture by epoxy-based adhesives and fibre reinforced composites after cure has been the topic of many studies. The extent of moisture uptake by uncured adhesive films and composite prepregs, and the effect which this has on the performance of such systems after cure, has received much less attention. It is, nonetheless, recognised as an important consideration and most aerospace lay up facilities include controlled humidity conditions.     

Chain‐extended polyurethane–acrylate ionomer for UV‐curable waterborne coatings

Conventional and chain‐extended UV‐curable waterborne polyurethane–acrylate (PUA) ionomers were prepared from diisocyanate, polyethylene glycol (PEG), dimethylolpropionic acid, and hydroxyethyl methacrylate, and identified with FTIR spectra and 500‐MHz ¹H‐NMR spectra. The number‐average molecular weight (M_n) and polydispersity of chain‐extended PUA were determined by gel permeation chromatography. For the synthesis of chain‐extended PUA, water was employed as the chain extender. The two kinds of PUA prepolymer could be easily dispersed in water in the form of self‐emulsified latex after the carboxyl group attaching to the backbone of PUA was neutralized with tertiary amine. The effects of M_n of PEG, carboxyl content, and type of diisocyanate on the interfacial tension and rheological behavior of PUA dispersions were investigated. The chain‐extended PUA prepolymer could photopolymerize to a greater extent than the conventional PUA, as indicated by differential photocalorimetry. The photopolymerization kinetics of chain‐extended PUA, based on different substrates, were also investigated. The differential scanning calorimetry analysis for the photo‐cured films from PUA dispersions suggested that lower M_n of PEG tended to favor phase mixing between soft and hard segment phases, and higher M_n of PEG would provoke phase separation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1818–1831, 2002; DOI 10.1002/app.10384     

A study of the effects of postcure treatments on polyester–melamine coating matrices

The effect of postcure high energy (γ), ultraviolet (UV) and thermal treatment on the properties of polyester–melamine clearcoats of a range of compositions has been investigated. Two initial cure conditions were used, of which one was “optimally” cured and the other under‐cured. It was found that postcure treatments, particularly γ and UV, led to coatings of similar mechanical and thermal properties irrespective of initial cure, although the change in properties on postcure treatment was greater for the under‐cured samples. The results were interpreted in terms of the effect of the treatments on the structure of the crosslinked matrices. The study suggests the possibility of the development of a dual‐cure process for polyester–melamines, whereby cure optimization and property improvement can be achieved. This could also be used to “correct” for small variations in thermal cure levels brought about by adventitious on‐line fluctuations in cure oven conditions. POLYM. ENG. SCI. 46:532–539, 2006. © 2006 Society of Plastics Engineers     

UV固化聚氨酯丙烯酸酯的非催化合成及性能

在不使用任何催化剂的条件下,合成了UV固化的聚氨酯丙烯酸酯树脂。采用傅里叶变换红外光谱、核磁共振氢谱、碳谱对合成树脂进行了表征,并采用综合热分析仪对固化膜的耐热性进行分析。试验结果表明:随着活性单体官能度的增大,固化膜的耐热性提高;随着双官能团单体三缩丙二醇二丙烯酸酯(TPGDA)用量的增加,固化膜的耐热性略有提高,但变化不明显;其他性能测试表明:固化膜具有优异的综合性能。     

羧基含量对UV固化PUA/EA核壳复合乳液性能的影响

以自制的亲水性聚氨酯丙烯酸酯(PUA)预聚体为高分子乳化剂,与自制的环氧丙烯酸酯(EA)树脂充分混合后,采用相反转乳化法制备了可UV固化的具有不规则核壳结构的PUA/EA复合乳液。利用傅里叶变换红外光谱对水性PUA合成过程以及复合乳液UV固化前后进行了表征,表明合成得到了目标产物且UV固化良好。透射电镜(TEM)测试表明,复合乳液呈不规则的核壳结构,且EA含量不同时核壳结构也不同。重点讨论了羧基含量对乳液相反转过程、PUA预聚体的乳化能力、复合乳液以及固化后涂膜性能的影响,结果表明,相反转过程中体系黏度与电导率有类似的变化趋势,最大值均随羧基含量的增加而增加,且出现得越来越晚;PUA预聚体的乳化能力随羧基含量的增加而增加,但超过2.3%后变化不再明显;此外,随羧基含量的增加,乳液的平均粒径变小、外观越来越透明、黏度变大、贮存稳定性变好,而相似文献   

Dual‐curable unsaturated polyester inorganic/organic hybrid films

An unsaturated polyester, based on maleic anhydride, 1,6‐hexanediol, and trimethylol propane, was formulated with tetraethylorthosilicate (TEOS) oligomers and a coupling agent to prepare inorganic/organic hybrid films. TEOS oligomers were prepared through the hydrolysis and condensation of TEOS with water, and 3‐(triethoxysilyl)propylisocyanate was used as the coupling agent between the organic and inorganic phases. The hybrid materials were cured by moisture via sol–gel chemistry and by the UV curing of unsaturated polyesters. To compare the properties of the moisture‐cured inorganic/organic hybrid films, a conventional 2K polyurethane system was also prepared. The tensile, adhesion, abrasion, and fracture toughness properties were investigated as functions of the coupling agent and relative amount of UV cure versus thermal cure. Although no difference could be observed in the tensile properties, the abrasion resistance, fracture toughness, and adhesion were enhanced by the incorporation of TEOS oligomers into polyurethane films. Also, the abrasion resistance, fracture toughness, and tensile properties were increased with both moisture and UV exposure. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 115–126, 2006     

Synthesis and study of new radial organic/inorganic hybrid epoxides

A new approach to the synthesis of reactive organic/inorganic hybrid molecules was developed. Alternating hydrocarbon and siloxane segments were introduced into the arms of radial oligomers using hydrosilation chemistry. Cycloaliphatic and glycidyl epoxy‐terminal systems with bisphenol A‐based aromatic hydrocarbon cores and siloxane units derived from 1,1,3,3‐tetramethyldisiloxane were synthesized and fully characterized (molecules 7 and 6 , respectively). The cationic UV and thermal curing behavior of these two new radial hybrid epoxies was investigated using photo‐ and thermal‐ differential scanning calorimetry. Hybrid cycloaliphatic epoxy 7 exhibited good UV curing kinetics and photopolymerized to high conversion. The glycidyl analog 6 exhibited poor UV curing kinetics, but was readily cured using 2‐ethyl‐4‐methylimidazole as a nucleophilic curing agent. Both hybrid epoxysiloxanes exhibited extensive thermal cationic cure. The physical properties of cured films of the two new radial epoxysiloxanes were studied and compared with various commercially available hydrocarbon and siloxane benchmark materials. The cured systems exhibited lower moisture uptake and better thermal stability than most hydrocarbon epoxies examined. Several visually compatible blends of the new hybrid molecules with common hydrocarbon resins were identified, and in general organic compatibility was found to be intermediate among selected siloxane‐containing benchmarks. Molecules 6 and 7 represent progress towards the goal of synthesizing highly functional organic/inorganic hybrid molecules which combine the best attributes of both hydrocarbon epoxides and siloxane materials. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis of polyurethane acrylates by hydrogenated castor oil and dimer‐based polyester diol and study on pressure‐sensitive adhesive

Synthesis of polyurethane acrylate (PUA) and preparation of the UV‐cured pressure‐sensitive adhesives (PSA) are reported. Molecular weight (M_w) (by gel permeation chromatography) and viscosity (η*) of PUA were measured. Characterization of PUA and PSA before and after UV‐curing was made by FTIR. Increase of the hydroxyls from hydrogenated castor oil/hydroxyls from dimer‐based polyester diol (OH_HCO/OH_Diol) ratio decreased the M_w and η* value of PUA. Dynamic viscoelastic properties (by dynamic rheological spectrometer) and performance of the UV‐cured PSA were also studied. Increase of the OH_HCO/OH_Diol ratio increased the storage modulus (G′), the loss modulus (G″), and complex viscosity (Eta*) of the UV‐cured PSA, which, in turn, enhanced holding power and shear adhesion failure temperature (SAFT) and yet decreased peeling strength. Substitution of OB for DBTDL depressed the M_w and η* value of PUA, while the G″ and Eta* values of the UV‐cured PSA were elevated, which, in turn, increased the holding power and SAFT and yet depressed the peeling strength. Elevation of the tackifying resin content depressed the G′, G″, and Eta* values of the cured PSA and yet increased glass transition temperatures (T_g) of PSA, measured by differential scanning calorimetry. Peeling strength of PSA elevated as increasing the tackifying resin, while the holding power and SAFT fell. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1814–1821, 2005     

Synthesis and characterization of carboxymethyl chitosan containing functional ultraviolet absorber substituent

A series of carboxymethyl chitosan (CMC) with 2.4‐dihydoxybenzophenone (UV‐0) substituent were synthesized by the Mannich reaction of CMC hydrochloride and UV‐0 in the solvent of methanol and water. The different molar degree of substitution (MS) was achieved by changing the UV‐0 content. The effects of MS on ultraviolet absorbability, crystallinity, moisture‐absorption and ‐retention property, and photostability were investigated respectively. The obtained products were characterized by means of Fourier transform infrared spectra (FTIR), proton nuclear magnetic resonance spectroscopy (¹H NMR), X‐ray diffraction, and UV spectrophotometer. It was found that the grafted products were water‐soluble, and the increased MS values could enhance the moisture‐retention property and photostability, while decreased the crystallinity and moisture‐absorption property. The ultraviolet absorption peaks became stronger by introducing UV‐0 into the CMC backbones. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Dielectric studies of water absorption and desorption in epoxy resins: influence of cure process on behaviour

Little is known about the way in which the chemical structure of an epoxy resin influences its ability to absorb and desorb moisture. This issue is addressed in a study of dicyandiamide‐ and amine‐cured epoxy resins. The dicyandiamide‐cured material will have a significantly lower preponderance of pendant hydroxyl groups than the amine‐cured material and may exhibit different behaviour when exposed to moisture. The uptake and loss of moisture was monitored gravimetrically, using broad band dielectric, dynamic mechanical thermal analysis and thickness measurements performed as a function of time at various temperatures. A comparison of the uptake and loss profiles for the first and subsequent cycles indicated significant differences in behaviour attributed to the way in which water can plasticise the matrix. Stresses frozen into the matrix during the cure process are allowed to relax as a consequence of the water hydrating the matrix and create voids and also allow matrix densification. These processes occur during the first hydration cycle and are not reversible. Subsequent hydration and dehydration appear to be reversible after the first hydration cycle. Water in the polymer is distributed between free water which is to be found in microvoids and bound water which is attached to the polymer chain. The amine‐cured epoxy resin which contains pendant hydroxyl groups has a greater capacity for water absorption than the ether‐containing backbone of the dicyandiamide‐cured material. Copyright © 2008 Society of Chemical Industry     

Effects of material parameters on the diffusion and sorption properties of wood‐flour/polypropylene composites

Composites of wood in a thermoplastic matrix (wood–plastic composites) are considered a low maintenance solution to using wood in outdoor applications. Knowledge of moisture uptake and transport properties would be useful in estimating moisture‐related effects such as fungal attack and loss of mechanical strength. Our objectives were to determine how material parameters and their interactions affect the moisture uptake and transport properties of injection‐molded composites of wood‐flour and polypropylene and to compare two different methods of measuring moisture uptake and transport. A two‐level, full‐factorial design was used to investigate the effects and interactions of wood‐flour content, wood‐flour particle size, coupling agent, and surface removal on moisture uptake and transport of the composites. Sorption and diffusion experiments were performed at 20°C and 65 or 85% relative humidity as well as in water, and diffusion coefficients were determined. The wood‐flour content had the largest influence of all parameters on moisture uptake and transport properties. Many significant interactions between the variables were also found. The interaction between wood‐flour content and surface treatment was often the largest. The diffusion coefficients derived from the diffusion experiments were different from those derived from the sorption experiments, suggesting that different mechanisms occur. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 752–763, 2007     

Preparation and properties of UV‐curable waterborne polyurethane–acrylate emulsion

Polyurethane–acrylate oligomer terminated with multiple unsaturated bonds was prepared using isophorone diisocyanate, (IPDI), methylene diphenyl diisocyanate, and polyols as monomers, using 2,2‐dimethylol propionic acid as hydrophilic chain extender, together with pentaerythritol triacrylate (PETA) as end‐capper. The UV‐curable waterborne polyurethane–acrylate (UV‐WPUA) composite emulsion was obtained by mixing the PUA oligomer with certain content of reactive diluents and then dispersing the mixture in water. The molecular structure of the polyurethane prepolymer, PUA oligomer, and UV‐cured polymer was investigated by Fourier transform infrared spectroscopy. The influence of the composition and content of the diluents and end‐capper on UV‐WPUA properties, including the emulsion stability, thermal property, water resistance, adhesion, hardness, glossiness of polymer film were studied. The results show that the WPUA emulsion has excellent stability, and the UV‐cured film features good hardness and remarkable water resistance when PETA is used as end‐capper and the end‐capping ratio of the polyurethane prepolymer is 70% and dipentaerythritol hexaacylate/dipropylene glycol diacrylate (mass ratio 1:1) is used as diluent. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45208.     

Kinetics of Moisture Cure of Silicone Sealants

The depth of moisture cure (z) has been measured for lap joints in aluminium with a conventional sealant based on polydimethylsiloxane and one based on polytrifluoro-propylmethylsiloxane. The cured sealant acts as a barrier to the permeation of water; any water which passes through this barrier causes further cure which thickens the barrier. The depth of cure is given by z = (2PV_pt)^1/2, where P is the permeability coefficient of water in cured sealant, V is the volume of sealant which reacts with 1 mole of water, p is the vapour pressure of water and t is time.