Kinetics of photodegradation and nanoparticle surface accumulation of a nanosilica/epoxy coating exposed to UV light

Temperature effect on the kinetics of photodegradation and surface accumulation of nanoparticles in an epoxy nanocoating exposed to ultraviolet light (UV) was investigated. A model epoxy coating containing 5% untreated nanosilica was selected. Exposed film specimens were removed at specified UV dose intervals for measurements of chemical degradation of the epoxy component, and nanosilica accumulation on specimen surface release as a function of UV dose for four temperatures. The chemical degradation was measured using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and UV–visible spectroscopy. Atomic force microscopy was employed to determine the kinetics of nanosilica accumulation on the nanocoating surface during UV exposure. The temperature dependence behaviors of kinetic parameters obtained by various measurement techniques will be used to better understand the degradation mechanism and surface accumulation of nanoparticles in exterior nanocoatings.     

Detrended fluctuation analysis of UV degradation in a polyurethane coating

Changes in the intrinsic structure of paint surfaces resulting from extended UV exposure can significantly alter the appearance of paint due to a breakdown in the resin that binds the pigments and flattening agents. In this study, the coating structure of a solvent-based poly-urethane was analyzed to establish correlations between the intrinsic spatial scaling properties of the coating and UV exposure time. Atomic force microscopy and laser scanning confocal microscopy were employed to map surface structures over a range of scales from 80 nm to 80 εm. The roughness of the polyurethane surface was characterized in terms of scaling exponents using detrended fluctuation analysis to identify long-range, power law relations, and to correct for inhomogeneities in the surface structure. The time-dependence of the roughening process was also determined and correlated with changes in gloss. AMSTA-AR-CCB-TA, Watervliet, NY 12189-4050. Email: majohn@pica.army.mil and pcote@pica.army.mil     

Structure and properties of polyurethane/nanosilica composites

Nanosilica particles were directly introduced into polyester polyol resins through in situ polymerization and blending methods, then cured by isophorone diisocyanate (IPDI) trimers to obtain nanocomposite polyurethanes. FTIR and TGA analyses indicated that more polyester segments had reacted with silica particles during in situ polymerization than during the blending method, accompanied by higher T_g and more homogeneous dispersion of nanosilica particles in the polymer matrix from in situ polymerization. Maximum values in T_g, tensile properties, macrohardness, abrasion resistance, and UV absorbance were obtained when the particle size of silica was about 28 nm. The polyurethane/nanosilica composites obtained by in situ polymerization generally had better mechanical properties than those by the blending method except for some unexpected macrohardness at relatively high silica content. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1032–1039, 2005     

Surface properties and surface patterning of UV-curable coating using perfluorosilane-treated nanosilica

In this work, a one-step film formation method is demonstrated to obtain the patterned surface of an acrylate photocuring coating using nano-silica particles treated with a perfluoroalkoxysilane ((heptadecafluoro-1,1,2,2-tetra hydrodecyl) triethoxysilane) as a nanoadditive. Nanosilica particles were treated with perfluoroalkoxysilane and used in a UV-curable matrix. The typical patterns on the surface of the UV-cured films are revealed in AFM images. The surface properties of the cured films were investigated by measuring water contact angle and surface energy. The degree of conversion of the samples was obtained by FTIR analysis and pendulum hardness was measured using a Konig hardness meter. Scratch resistance of cured films was measured by standard scratch measuring pens. The characteristics obtained from AFM analysis showed that rough surface patterns in this system are controlled linearly by changes in the treated nano-particle concentration. The subtraction of surface energy of the cured film was clear and the water contact angle showed a 60% increase with the addition of a fluorinated nano-particle concentration. Surface hardness decreased and scratch resistance increased as the concentration of treated nanoparticles increased, while the final degree of conversion of the film remained unchanged.     

Model-based analysis of photoinitiated coating degradation under artificial exposure conditions

Coating degradation mechanisms of thermoset coatings exposed to ultraviolet radiation and humidity at constant temperature are investigated. The essential processes, photoinitiated oxidation reactions, intrafilm oxygen permeability, water absorption and diffusion, reduction of crosslink density, and development of a thin surface oxidation zone are quantified and a mathematical model for degrading coatings developed. Front-tracking techniques are used to determine the rate of movement of the oxidation and ablation fronts, the positions of which define the extension of the surface oxidation zone. Three previous and independent experimental investigations with two-component, densely crosslinked, epoxy?Camine model coatings were selected for verification of the mathematical model. Simulations can match and explain transient mass loss and coating thickness reduction data and are in agreement with infrared measurements of carbonyl groups formed in the surface zone. The thickness of the stable surface oxidation zone, which is established after an initial ablation lag time, is estimated by the model to 0.5?C2???m in good agreement with previous measurements. Simulated concentration profiles of active groups, oxygen, and radicals in the stable surface oxidation zone are presented and analyzed. The mathematical model can be used for obtaining a quantitative insight into the degradation of thermoset coatings and has potential, after further development, to complete commercial coatings and dynamic exposure conditions, to become a supplementing tool for predicting in-service coating behavior based on accelerated laboratory measurements.     

Surface degradation process affected by heterogeneity in nano-titanium dioxide filled acrylic urethane coatings under accelerated UV exposure

The objective of this study was to investigate the effect of nanoparticle dispersion on surface morphological changes and degradation process in polymeric coatings during exposure to ultraviolet (UV) radiation. Three types of nano-titanium dioxide (nano-TiO₂) were selected and dispersed into acrylic urethane (AU) coating to generate degrees of nanoparticle dispersion states. Two accelerated exposure conditions: wet (30 °C and 75% relative humidity (RH)) and dry (30 °C and 0% RH), were selected. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) was used to monitor surface chemical degradation. Laser scanning confocal microscopy (LSCM) was used to characterize nanoparticle dispersion and surface/subsurface morphological changes in the AU coatings during UV exposure. For a given nanoparticle, similar surface morphological changes of the coatings indicated the similar degradation processes under the wet and dry conditions, but the degradation was faster under the wet condition. Surface morphological changes were closely related to the nanoparticle dispersion in three coatings, and the heterogeneity in nanoparticle dispersion significantly affects the degradation process and dominates the degradation patterns.     

Highly branched polyurethane acrylates and their waterborne UV curing coating

A series of UV curable highly branched waterborne polyurethane acrylates (BWPUAs) were synthesized using an “oligomeric A₂ + B₃” approach. The thiol-endcapped difunctional oligomeric A₂ was synthesized first by the addition reaction of isophorone diisocyanate, α,α-dimethylol propionic acid and 2-hydroxyethyl acrylate, then further underwent thiol-Michael reaction with 1,6-hexamethylene bis(thioglycolic acetate). Trimethylolpropane triacrylate was used as a B₃ monomer. The molecular structures were characterized with FT-IR and ¹H NMR spectroscopy. 1,6-Hexanediol diacrylate (HDDA) was incorporated into the polymeric chain for preparing the HDDA-modified BWPUAs (BWPUA-Hs). For the comparison, the linear waterborne polyurethane acrylate (LWPUA) was synthesized. The UV curing kinetics study results by using the photo-DSC approach showed that the BWPUAs possessed higher photopolymerization rate and final unsaturation conversion in the UV cured films compared with the LWPUA, which increased with the increase of unsaturation concentration in BWPUA. Moreover, the photopolymerization performance, and water and solvent resistance properties were greatly enhanced by the incorporation of HDDA segment into the BWPUA chain. The dynamic mechanical thermal analysis results showed that the elastic modulus in the rubbery plateau, and the glass transition temperature of UV cured film increased with increasing unsaturation concentration in BWPUA, whereas decreased with the introduction of HDDA flexible segment. The thermogravimetric analysis confirmed the high thermal stability of UV cured BWPUA films. All UV cured BWPUA and BWPUA-H films showed better flexibility and middle refractive indices due to the thioether linkage in the polymer network.     

Thermal and mechanical properties of polyurethane rigid foam/modified nanosilica composite

Surface modification of fumed nanosilica was performed by using n‐(2‐aminoethyl)‐3‐aminopropyltrimethoxysilane as a coupling agent. Then, modified nanosilica was utilized in the preparation of polyurethane rigid foam. The characterization and the study of properties were done by some techniques, such as Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, dynamic mechanical analysis, and thermomechanical analysis. Also, tensile test was examined to evaluate the static mechanical properties. With the increasing of modified nanosilica, thermal and static mechanical properties were enhanced, but dynamic mechanical behavior was different from static mechanical behavior because of the different properties of interfacial domain and bulk matrix. The presence of functional groups on the nanosilica surface affected stoichiometry and reduced hard phase formation in bulk polymer. The decrease in glass transition temperature (T_g) confirmed this statement. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Evaluating UV/H2O2 exposure as a DEHP degradation treatment for plasticized PVC

Millions of tons of plasticized poly(vinyl chloride) (PVC) materials are disposed every year. A biologically sustainable and green method for removal of toxic plasticizers from polymer systems after disposal is highly desired since plasticizers can leach out into the environment over decades. Here we compare the surface and bulk structural changes of DEHP‐plasticized PVC after two treatments intended to degrade bis‐2‐ethylhexyl phthalate (DEHP) in PVC plastic: short wave (254 nm) UV with and without the addition of 35 wt % H₂O_2. Sum frequency generation vibrational spectroscopy (SFG) reveals the addition of aqueous H₂O₂ decreases CH₃ signals on the surface of the films up to 8 h, due to increased molecular disorder and the removal of alkyl chains. Secondary ion mass spectrometry demonstrates that the degradation of DEHP after 8 h of reaction is similar with and without the use of H₂O₂. However, FTIR results reveal that the introduction of H₂O₂ reduces bulk DEHP degradation and leads to competing radical chain scission reactions with PVC. Therefore, simple short wave UV exposure may be an effective means to degrade DEHP within and on PVC plastic and the addition of H₂O₂ is only beneficial if additional degradation of PVC is needed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40649.     

Relationship between the thermal degradation chemistry and flammability of commercial flexible polyurethane foams

In this article, we report the use of a variety of analytical methods, in particular, solid‐state ¹H‐NMR and ¹³C‐NMR to characterize the relationship between the condensed‐phase chemistry and burning behavior as determined by a series of combustion tests for two commercially derived flexible polyurethane foams, one combustion‐modified. The combustion tests showed that the foams met several regulatory requirements in terms of their fire performance, whether or not they were combustion‐modified. Both foams passed the MV SS 302 and CAL 117 small‐flame tests. The nonmodified foam failed the Crib 5 test, but this test had a much larger ignition source. The particular problem with the nonmodified foam was melt drip into the flame zone. This led to a steady maintenance of the fuel feed and a rapid escalation of the fire. In contrast, the combustion‐modified foam showed little melt drip and self‐extinguished. Thermal analysis data for the two foams showed that melamine acted in part as an endothermic heat sink. This alone did not account for the much reduced melt flow and drip of the combustion‐modified foam, but the solid‐state ¹H‐NMR data clearly showed that the molecular mobility of the combustion char from combustion‐modified foam was lower than the unmodified foam char, which indicated that the flame‐retardant formulation in the combustion‐modified foam acted by a condensed‐phase mechanism. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3024–3033, 2006     

Effect of silane modified nano ZnO on UV degradation of polyurethane coatings

Nanosized ZnO modified by 2-aminoethyl-3-aminopropyltrimethoxysilane (APS) was prepared using the precipitation method. Modified nano ZnO by silane (ZnO-APS) was characterized by XRD, SEM, TEM and UV–vis measurements. The degradation of the polyurethane coating, the polyurethane coatings containing 0.1 wt% nano ZnO and the polyurethane coatings containing nano ZnO-APS at two concentrations (0.1 and 0.5 wt%) during QUV test was evaluated by gloss measurement and electrochemical impedance spectroscopy. The coating surface after QUV test was observed with SEM. The results show that nano ZnO-APS has spherical structure with particle size around 10–15 nm. Nano ZnO improved the UV resistance of the PU coating and surface treatment by APS enhanced the effect of nano ZnO. The presence of nano ZnO-APS at 0.1 wt% concentration significantly improved the UV resistance of polyurethane coating.     

Preparation and characterization of the waterborne polyurethane modified with nanosilica

The nano-SiO₂ is used to modify the waterborne polyurethane, and the morphology and performance of the waterborne polyurethane (are studied in) prepared by the in-suit polymerization method and the blending method. The properties and structure have been characterized by fourier transform infrared spectra (IR), differential scanning calorimetry (DSC), Thermal gravimetric (TG), transmittance electron microscopy (TEM) and Dynamical Mechanical Analysis(DMA). The experiment results show that, compared with the blending method, the in-suit polymerization has more advantages in that the nano-SiO₂ is evenly dispersed in the waterborne polyurethane, obviously in microphase separation and better in resistance to high temperature and water.     

Effect of nanosilica content on properties of polyurethane/silica hybrid emulsion and its films

Polyurethane/silica hybrid emulsion (PUSi) was synthesized by the reaction of isophorone isocyanate, polyether polyol, hydrophilic nanosilica (A200), dimethylol propionic acid, trimethylol propane, and 3‐aminopropyltriethoxysilane (KH550). The films of the waterborne polyurethane (WPU) were prepared. The structure of the polyurethane was characterized by Fourier transform infrared spectrometer (FTIR), thermogravimetry (TG), and differential scanning calorimetry (DSC). The particle size distribution and morphology of emulsion were examined. Influence of nanosilica content on the mechanical properties and solvent absorption of the cast films were also measured quantificationally. FTIR indicates that  NH₂ of KH550 reacted with  NCO of polyurethane. TG analysis indicates that nanosilica can improve thermal stability of polyurethane. There is no clear effect of nanosilica on the glass transition of soft segments. It was found that greater mechanical properties of WPU were obtained when chemical networks were formed by sol‐gel process. As the nanosilica content increases, water absorption and ethanol absorption decreased. The particle size increases with increase of A200 content. PUSi hybrid emulsions are endowed with pseudoplasticity. The apparent viscosity of emulsions increased and then decreased with addition of A200. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

水性聚氨酯的改性及水性聚氨酯涂料

介绍了几种水性聚氨酯的改性技术,并对水性聚氨酯涂料的配制及其应用作了相关概述。     

UV-shielding by a polyurethane/f-Oil fly ash-CeO2 protective coating

A waste material called oil fly ash (OFA) was acid-functionalized, yielding f-OFA-COOH, which was then reacted with cerium oxide (CeO₂) to make CeO₂-functionalized OFA, or f-OFA-CeO₂. Pristine OFA and f-OFA-CeO₂ were used to make waterborne polyurethane (WBPU) dispersions, referred to as WBPU/OFA and WBPU/f-OFA-CeO₂, respectively, with defined OFA and f-OFA-CeO₂ content. All the dispersions were applied to mild steel as organic coatings to evaluate their protective properties, such as their hydrophobicity, adhesive strength and UV-shielding resistance. These protective properties varied based on the OFA and f-OFA-CeO₂ content. The highest water contact angle, minimum water swelling and maximum adhesive strength were found using WBPU/f-OFA-CeO₂-20 coating (using 2.00 wt% f-OFA-CeO₂), which also showed the maximum ultraviolet (UV) absorption via UV–vis spectroscopy analysis. This UV shielding result also matched field test results, as that coating was found to exhibit the lowest UV degradation near a marine atmosphere, as shown by X-ray photoelectron spectroscopy (XPS) analysis. The least affected hydrophobicity was also recorded for the sample with the WBPU/f-OFA-CeO₂-20 coating.     

Surface modification of nanosilica with acrylsilane-containing tertiary amine structure and their effect on the properties of UV-curable coating

In order to improve the dispersion of nanosilica and the mechanical properties of UV-curable coating, nanosilica was modified with acrylsilane-containing tertiary amine structure, which was synthesized by the Michael addition reaction between 3-aminopropyl triethoxysilane and tripropylene glycol diacrylate. The prepared acrylsilane was characterized by ¹H NMR, ¹³C NMR, and FTIR. The modified nanosilica was characterized by FTIR, TGA, and SEM. The TGA analysis showed that the grafting percentage of acrylsilane based on nanosilica was 72.4 wt%. The SEM results showed that the agglomeration of nanosilica was reduced and the dispersion was improved due to the acrylsilane modification. The viscosities of UV-curable coatings with modified nanosilica were determined and it was found that the viscosities of the coatings decreased in comparison with the viscosities of coatings with unmodified nanosilica. The photo-DSC results indicated that both nanosilica and modified nanosilica also decreased the UV-curing speed and final percentage conversion, while the conversion of the coatings containing modified nanosilica was faster than that with unmodified nanosilica owing to the tertiary amine structure and acrylate structure on the surface of the modified nanosilica.     

A degradation study of polyamide 11/vermiculite nanocomposites under accelerated UV test

Accelerated photooxidation under ultraviolet (UV) test of polyamide 11 (PA11) films filled with unmodified vermiculite clay at 5 wt% was investigated up to 600 h. Film samples of ~60‐μm thick were prepared by melt compounding using a cast extruder and exposed to UV light irradiation at λ > 295 nm. Fourier transform infrared (FTIR) spectra indicated similar structural changes occurring in both PA11 and PA11/unmodified vermiculite nanoclay (UVMC) nanocomposite along the photooxidation process, resulting in imides and carboxylic acids as the main carbonyl products. It was however observed that the formation rate of carbonyls in the PA11/UVMC nanocomposite was slower than neat PA11. This behavior is consistent with the yellowing index evolution determined by ultraviolet–visible (UV–vis) spectroscopy. Further, the photooxidation stability of the samples was also evaluated by the onset oxidation temperature determined by differential scanning calorimetry. The results indicated a better stability of the nanocomposite film than neat PA11, corroborating well the data obtained by FTIR and UV–vis techniques. POLYM. ENG. SCI., 59:2449–2457, 2019. © 2019 Society of Plastics Engineers     

Failure process of acrylic polyurethane coating under alternate wetting and drying condition

The failure process of an acrylic polyurethane coating in simulated sea water under a wet‐dry cyclic condition and immersion condition was studied with the methods of electrochemical impedance spectroscopy (EIS), Fourier transform infrared spectroscopy (FT‐IR), and scanning electron microscope (SEM). The results show that the failure rate of acrylic polyurethane coating under the condition of wet‐dry alternation is obviously greater than that under complete immersion. Under wet‐dry condition, both the porosity and the water absorptivity of the coating are also greater than those under complete immersion condition. Owing to the physical effect of wet‐dry alternation, the fillers in the coating surface layer may fall off and result in micro‐pores, which could multiply the defects in the coating and accelerate the coating degradation. FT‐IR analysis shows that the isocyanate group in the coating not only participates in the curing of coating, but also hydrolyzes with water molecule. The C‐O bonds fracture partly due to hydrolysis of the main molecule chains, which is one reason of the coating failure. The failure process for acrylic polyurethane coating under a wet‐dry cyclic condition is discussed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41989.     

Degradation of polyurethane coating materials from liquefied wheat straw for controlled release fertilizers

Polyurethane (PU) was synthesized by liquefied wheat straw and isocyanates for controlled release fertilizers (CRFs). CRFs coated by PU were buried in soil for 12 months. The degradation degree and mechanism of PU coating materials were observed by thermogravimetric analysis (TGA), Atomic Force Microscope (AFM), differential scanning calorimetry (DSC), X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Fourier transform infra‐red spectroscopy (FTIR). Significant microscopic morphology of PU exhibited many small chips or stereovision holes caused by biodegradation or hydrolytic degradation due to the presence of natural polymer wheat straw. AFM results depicted the plane and height topography changes of PU before and after 12 months burial time, showing the swelling morphology of buried PU. TGA and FTIR results confirmed the disintegration of PU polymer due to the presence of isocyanates monomers in the PU12. XPS revealed an accumulation of biofilm on the surface of buried PU, providing the evidence of biodegradation mechanism. Pot experiment indicated the resin residual coating has a positive effect on soil quality. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44021.     

Surface modification of a UV curable acrylate coating: In situ introduction of hydrophobic properties

Two polyfunctional silanes polymethyl-hydrosiloxane (I) and octakis(dimethylsiloxy)-T8-silsequioxane (II) are proposed as new co-initiators for radical acrylate photopolymerization reactions. In the presence of a type II photoinitiator such as benzophenone, isopropylthioxanthone or camphorquinone, these compounds are found reactive. The influence of oxygen is also examined. Incorporating only 1% (w/w) of I into an epoxy acrylate matrix allows the formation, under air, of a coating exhibiting a hydrophobic surface. In free radical promoted cationic polymerization, the addition of I to a BP/Φ₂I⁺ system significantly enhances, under air, both the polymerization rate and the final conversion. The autoxidation reaction of I in the presence of BP under air generates a hydrophobic polymer surface. The reaction mechanisms are discussed on the basis of laser flash photolysis experiments.