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.     

Critical role of particle/polymer interface in photostability of nano-filled polymeric coatings

Nanoparticle-filled polymeric coatings have attracted great interest in recent years because the incorporation of nanofillers can significantly enhance the mechanical, electrical, optical, thermal, and antimicrobial properties of coatings. Due to the small size of the fillers, the volume fraction of the nanoparticle/polymer interfacial area in nano-filled systems is drastically increased, and the interfacial region becomes important in the performance of the nano-filled system. However, techniques used for characterizing nanoparticle/polymer interfaces are limited, and thus, the mechanism by which interfacial properties affect the photostability and the long-term performance of nano-filled polymeric coatings is not well understood. In this study, the role of the nanoparticle/polymer interface on the ultraviolet (UV) stability of a nano-ZnO-filled polyurethane (PU) coating system was investigated. The effects of parameters influencing the particle/polymer interfacial properties, such as size, loading, surface modification of the nanoparticles, on photodegradation of ZnO/PU films were evaluated. The nature of the interfacial regions before and after UV exposures were characterized by atomic force microscopy (AFM)-based techniques. Results have shown that the interfacial properties strongly affect chemical, thermo-mechanical, and morphological properties of the UV-exposed ZnO/PU films. By combining tapping mode AFM and novel electric force microscopy (EFM), the particle/polymer interfacial regions have been successfully detected directly from the surface of the ZnO/PU films. Further, our results indicate that ZnO nanoparticles can function as a photocatalyst or a photostabilizer, depending on the UV exposure conditions. A hypothesis is proposed that the polymers in the vicinity of the ZnO/PU interface are preferentially degraded or protected, depending on whether ZnO nanoparticles act as a photocatalyst or a photostabilizer in the polymers. This study clearly demonstrates that the particle/polymer interface plays a critical role in the photostability of nano-filled polymeric coatings.     

UV-waterborne polyurethane-acrylate nanocomposite coatings containing alumina and silica nanoparticles for wood: mechanical, optical, and thermal properties assessment

The effect of alumina and silica nanoparticles on mechanical, optical, and thermal properties of UV-waterborne nanocomposite coatings was investigated. The addition of nanoalumina and nanosilica was shown to decrease the hardness because of nanoparticle aggregation. In comparison to the neat coating and despite the presence of aggregates, the scratch resistance of nanocomposite coatings was significantly improved. As expected, the gloss of UV-waterborne coatings was reduced following the addition of nanoparticles due to an increase of the surface roughness. Alumina and silica nanoparticles were found to enhance the glass transition temperature of PUA nanocomposite coatings by hindering the mobility of macromolecular chains at the interface around the nanoparticles. Finally, the interest and efficiency of grafting trialkoxysilanes was demonstrated with the study of nanosilica behavior. Not only was the dispersion of nanosilica enhanced following trialkoxysilanes grafting onto silica nanoparticles, but also the scratch resistance and the adhesion of UV-waterborne coatings containing nanosilica markedly increased even with 1 wt% content. Silica which is recommended in the wooden furniture and kitchen cabinet manufacturing industry as nano-reinforcement provides improved properties well suited in surface coating applications to efficiently protect surface of wood substrates.     

Nanoindentation and morphological analysis of novel green quasi-ceramic nanocoating materials

The eco-friendly (green) silicone nanocoating compositions containing titanium nanoparticles were developed and tested for the changes in nanomechanical properties using the nanoindentation technique. Titanium-based nanoparticles were incorporated by two different methods. The nanocoating compositions were studied with the Fourier Transform Infrared spectroscopy (FTIR) and Raman spectroscopy. The surface morphology of the nanocoatings was studied with Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM). The nanomechanical properties of the nanocoatings were studied using the standard nanoindentation test method and the new substrate independent nanoindentation test method. The results obtained from the two test methods confirm the validity of the model used to develop the substrate independent nanoindentation test method. In brief, this study discusses the development of silicone based nanocoating materials and nanomechanical properties of green nanocoatings containing two different types of nanoparticles, evaluated using two different test methods.     

Improved adhesion of TiO2‐based multilayer coating on HDPE and characterization of photocatalysis

Multilayered photocatalytic TiO₂‐based coating was prepared by spin coating on a high‐density polyethylene (HDPE) substrate. The multilayered coating consisted of a polyurethane (PU) barrier layer and two layers of TiO₂ nanoparticles bound with PU. The adhesion between the HDPE substrate and protective PU coating was enhanced by oxygen plasma treatment of the substrate. The improved adhesion contributed to the photocatalytic degradation of palmitic acid. Long‐term activity of the photocatalytic coating in degradation of palmitic acid under UV illumination was followed by FTIR‐ATR. The catalytic activity of the coating was maintained in three identical cycles where palmitic acid was added and UV‐irradiated for 6 h. According to FTIR measurements, the palmitic acid was almost completely decomposed after 6 h, but gas chromatography (GC) analysis showed total decomposition to require 12 h UV illumination (∼ 97% of palmitic acid decomposed in 12 h). Study of the degradation of palmitic acid by GC as a function of time indicated that the degradation kinetics was pseudofirst order, and the rate constant obtained was 0.31 h⁻¹. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Novel floating photocatalysts based on polyurethane composite foams modified with silver/titanium dioxide/graphene ternary nanoparticles for the visible‐light‐mediated remediation of diesel‐polluted surface water

Photocatalyst loading on a floating substitute is accepted as a promising method for the remediation of diesel‐polluted surface water. Therefore, novel photocatalysts based on polyurethane foams modified with silver/titanium dioxide/graphene ternary nanoparticles (PU–Ag/P25/G) were synthesized and investigated. Scanning electron microscopy, energy‐dispersive X‐ray spectrometry, X‐ray diffraction, Fourier transform infrared spectroscopy, and UV–visible spectroscopy showed the coexistence of Ag, Degussa P25 (P25), and graphene and the nanoscale dispersion of nanoparticles in the matrix and on the surface of the polyurethane (PU) foam. The diesel adsorption capacity of the photocatalyst reached 96 g/g. The maximum diesel degradation was found to be 76% in a period of 16 h. Compared with polyurethane‐foam‐supported P25/graphene (PU–P25/G) and polyurethane‐foam‐supported P25 (PU–P25), all of the adsorption isotherm and degradation kinetics followed the order PU–Ag/P25/G > PU–P25/G > PU–P25 > PU; this was due to the loading of different nanoparticles. Moreover, the degradation efficiency was reduced only 5% after five consecutive reactions; this showed good stability and reusability of the photocatalyst for surface water restoration. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43400.     

Photocatalytic degradation and heat reflectance recovery of waterborne acrylic polymer/ZnO nanocomposite coating

This work aims to clarify the photocatalytic degradation mechanism and heat reflectance recovery performance of waterborne acrylic polymer/ZnO nanocomposite coating. To fabricate the nanocomposite coating, ZnO nanoparticles (nano-ZnO) were dispersed into acrylic polymer matrix at the various concentrations from 1 to 6% (by total weight of resin solids). The photocatalytic degradation of nanocomposite coating under ultraviolet (UV) light irradiation has been investigated by monitoring its weight loss and chemical/microstructural/morphological changes. As the topcoat layer, its heat reflectance recovery has been evaluated under UV/condensation exposure by using an artificial dirty mixture of 85 wt% nanoclay, 10 wt% silica particles (1–5 μm), 1 wt% carbon black, and 2 wt% engine oil. After 108-cycle UV/condensation exposure, infrared spectra and weight loss analysis indicated that the maximal degradation for nanocomposite coating is observed at 1 wt% nano-ZnO. On the other hand, after 96 hr of UV light exposure, the nanocomposite coating with1 wt% nano-ZnO could restore effectively the reflective index of solar-heat reflectance coating (from 58.45 to 80.78%). Finally, the photodegradation mechanism of this waterborne acrylic polymer coating has been proposed as the UV-induced formation of CC CO conjugated double bonds. As a result, its self-cleaning phenomenon can be achieved as the recovery of heat reflectance.     

Waterborne polyurethane: the effect of the addition or in situ formation of silica on mechanical properties and adhesion

A series of composites consisting of commercial waterborne polyurethane (PU) and silica were prepared by in situ synthesis (sol-gel method) and compared to those prepared by the addition of commercial silica (blending method). Adhesion resistance, mechanical resistance, small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) measurements were performed in order to evaluate the effect of silica addition. The adhesion resistance reached a maximum at 3 wt.% of added silica. Comparing the sol-gel composites with the analog composites obtained by the addition of commercial nanosilica, it was observed that although the composites containing commercial silica displayed higher mechanical resistance, better adhesion was obtained with the in situ method. The DSC results showed increasing crystallinity with increasing silica addition.     

Preparation and properties of polymerizable silica hybrid nanoparticles with tertiary amine structure

To increase the photopolymerization rate and improve the properties of UV coatings, polymerizable silica hybrid nanoparticles with tertiary amine structure were prepared. Organic compound with isocyanate group was first grafted onto the surface of nanosilica by reaction of nanosilica with isophorone diisocyanate, then the nanosilica bearing isocyanate group reacted with N,N-di(3-propionic acid, 1,4,7-trimethyl-3,6-dioxaoctane-8-yl acrylate, ester) ethanolamine synthesized from tripropylene glycol diacrylate and ethanolamine. The preparation was characterized by ¹H nuclear magnetic resonance (NMR) and Fourier transform infrared spectrometry (FT-IR). Thermogravimetric analysis (TGA) showed that the organic compounds grafted onto the silica decomposed from 256 °C to 650 °C and the grafting percentage based on nanosilica was 105%. The morphology analysis of nanosilica and modified silica by field-emission scanning electron microscopy (FE-SEM) indicated that the silica kept nanosized scale after modification, while the nanosilica dispersion was improved and formation of agglomerates unlikely. Determination of viscosities of coatings with modified nanosilica, it was found that viscosities of the coatings decreased in comparison with the viscosities of coatings with unmodified nanosilica. Compared with pure organic coating, the photopolymerization rate of coatings were faster when modified nanosilica was used from 1 wt% to 5 wt%, but slower when the loadings of modified nanosilica was 7 wt% because co-initiating effects of tertiary amine compound grafted on nanosilica counterbalanced the effects of UV scattering by silica on photopolymerization rate. The hardness and abrasive resistance of cured films also increased and improvement degree was different when the various amounts of modified nanosilica were used.     

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.     

聚氨酯丙烯酸酯/SiO_2纳米杂化涂层的制备及其性能研究

采用不同相对分子质量的聚乙二醇(PEG-200、400、600)分别与六亚甲基二异氰酸酯(HDI)反应合成预聚体,再以此预聚体对纳米SiO2进行表面接枝改性,制备了聚氨酯改性纳米SiO2;将改性纳米SiO2分散到聚氨酯丙烯酸酯(PUA)中光固化制备了PUA/SiO2纳米杂化涂层。讨论了PEG相对分子质量对PUA/SiO2纳米杂化涂层的耐热性能和力学性能的影响,并以FT-IR、差示扫描量热法(DSC)等进行表征。结果表明,改性后的纳米SiO2粒子优化了PUA树脂的性能,且以PEG-400与HDI合成的预聚体来改性纳米SiO2用于制备的PUA/SiO2纳米杂化涂层具有较好的耐热性和抗冲击性。     

The effect of nanosilica on mechanical,thermal and morphological properties of epoxy coating

In this study, nanosilica of very high specific surface area is used as reinforcing filler for preparing an epoxy-based nanocomposite coating. For appropriate dispersion of nanoparticles in the polymer matrix, ultrasound waves were applied after mechanical mixing. The resulting perfect dispersion of nanosilica particles in epoxy coating revealed by transmission electron microscopy ensured the transparency of the nanocomposite. Nanoindentation was used to determine some mechanical properties such as hardness and elastic modulus. The obtained results show 26 and 21% increases in hardness and elastic modulus, respectively for resin filled with 5% nanosilica compared to neat epoxy. DMA results show that the glass transition temperature of samples is increased with increasing silica nanoparticles. The result of TGA shows significant improvement of the thermal decomposition temperature of epoxy coating containing 5% nanosilica compared to neat epoxy. Scanning electron microscopy (SEM) micrographs of fractured surfaces show increased roughness with nanosilica addition.     

Validation of the reciprocity law for coating photodegradation

Accelerating the photodegradation of commercial polymeric materials has great practical importance in the weathering community. However, questions exist as to whether high radiant flux exposure results can be extrapolated to in-service exposure levels. Based on the reciprocity law, the photoresponse of a material is dependent only on the total energy to which the specimen is exposed, and is independent of the exposure time and the intensity of the radiation taken separately. An experiment to validate the applicability of the reciprocity law for polymeric coatings has been carried out using the NIST integrating sphere-based ultraviolet (UV) weathering device. A nonpigmented, non-UV stabilized acrylicmelamine coating was exposed to six different UV radiation intensities ranging from 36 W/m² to 322 W/m², and in the spectral region between 290 nm and 400 nm. Chemical changes in the coating due to UV exposure were measured with transmission Fourier transform infrared (FTIR) spectroscopy and UV-visible spectroscopy. Using two dose-damage models, the reciprocity law photoresponse for this polymeric system was verified for different photodegradation mechanisms, including chain scission, oxidation, and mass loss. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004, in Chicago, IL.     

SiO2/聚氨酯纳米复合物的在位合成及其在环氧树脂中分散行为的研究

以水性阳离子聚氨酯纳米粒子为纳米微囊,利用原位水解法使正硅酸乙酯(TEOS)在囊内水解、聚合生成二氧化硅(SiO2)纳米粒子,从而合成出SiO2/聚氨酯纳米复合物的稳定水基乳液,实现纳米复合物中SiO2纳米粒子的均匀分散和良好的界面结合。并以此作为已表面改性的纳米粒子实现SiO2纳米粒子在环氧树脂的均匀分散。通过能谱扫描、透射电镜和乳液粒子粒径与分布等测试方式对含有环氧树脂的水性SiO2/聚氨酯纳米复合物进行测试。结果表明,SiO2/聚氨酯纳米复合物可以在环氧树脂中均匀分散且不团聚,同时也可促进环氧树脂在水中的分散。     

Synthesis and properties of nanosilica‐reinforced polyurethane for grouting

A polyurethane/nanosilica (PU/SiO₂) hybrid for grouting was prepared in a two‐step polymerization using poly(propylene glycol) diols as the soft segment, toluene 2,4‐diisocyanate (TDI) as the diisocyanate, 3,3′‐dichloro‐4,4′‐diaminodiphenylmethane (MOCA) as the chain extender, and acetone as the solvent. The size and dispersion of nanosilica, the molecular structure, mechanical properties, rheological behavior, thermal performance, and the UV absorbance characteristic of the PU/SiO₂ hybrid were investigated by transmission electron microscopy (TEM), FTIR, mechanical tests, viscometry, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and UV spectroscopy. Nanosilica dispersed homogeneously in the PU matrix. The maximum values of mechanical properties such as tensile strength, elongation break, and adhesive strength showed an addition of nanosilica of about 2 wt %. Resistance to both high and low temperatures was better than with PU. And the UV absorbance of the PU/SiO₂ hybrid increased in the range of 290–330 nm with increasing nanosilica content. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4333–4337, 2006     

Investigation of corrosion protection properties of an epoxy nanocomposite loaded with polysiloxane surface modified nanosilica particles on the steel substrate

In this study, it has been aimed to investigate the corrosion protection properties of an epoxy/polyamide coating loaded with different concentrations (ranged from 3 to 6% (w/w)) of the polysiloxane surface modified silica nanoparticles (nano-SiO₂). The nanocomposites were applied on the steel substrates. Field emission scanning electron microscope (FE-SEM) and UV–vis techniques were utilized in order to investigate the nanoparticles dispersion in the coating matrix. The effects of addition of nanoparticles on the corrosion resistance of the coating were studied by an electrochemical impedance spectroscopy (EIS) and salt spray test. The coating surface degradation was studied by optical microscope and Fourier transform infrared radiation (FT-IR) spectroscopy. Results obtained from UV–vis and FE-SEM analyses revealed proper and uniform distribution of surface modified nanoparticles in the epoxy coating matrix. It was shown that the coating corrosion protection properties were significantly enhanced in the presence of 5 wt% silica nanoparticles. Less degradation occurred on the surface of the coatings loaded with 5 wt% nanoparticles.     

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.     

Characterization of polyurethane adhesives containing nanosilicas of different particle size

Three nanosilicas with different particle sizes were added to a polyurethane adhesive (PU). The filled adhesives were characterized by thermal gravimetric analysis (TGA), dynamic mechanical analysis (DMA), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and contact angle measurements. Adhesive strength was evaluated from single lap shear test of solvent wiped stainless steel/polyurethane adhesive joints.Addition of nanosilica filler altered the degree of phase separation between the hard and soft segments in the polyurethane, in different extent depending on the nanosilica particle size. Furthermore, upon curing higher degree of crosslinking was obtained in the nanosilica filled polyurethane. The nanosilicas agglomerated into the polyurethane matrix. On the other hand, the addition of nanosilica increased the surface energy of the polyurethane to a greater extent by increasing the nanosilica particle size and moderate increase in the single lap shear strength of stainless steel/polyurethane adhesive joints was obtained.     

纳米SiO_2/聚丙烯酸酯组装杂化乳液的合成及表征

通过乳液聚合法成功合成了纳米SiO2/聚丙烯酸酯杂化乳液。首先将纳米SiO2经过表面官能团化处理,使其表面含有活性官能团,然后经过乳液聚合使丙烯酸酯单体在纳米SiO2表面引发聚合,合成了具有核壳结构的纳米杂化乳液。采用透射电子显微镜(TEM)对乳液的微观结构进行了表征,并对胶膜进行了机械力学性能测试和表面润湿性能测试。结果表明纳米SiO2的表面官能团化处理改善了纳米粒子在乳液中的稳定性,当纳米SiO2质量分数为0 2%时,杂化乳液胶膜的拉伸强度和断裂伸长率同时达到最大值。其表面润湿性与SiO2质量分数有关,SiO2质量分数为0 5%时其杂化乳胶膜的接触角最大,耐水性最好。     

Facile synthesis of biosourced graphitic nanoparticle anchored silica nanoparticle hybrid for the development of functional polyurethane composite

The present work demonstrates a facile approach for the generation of functional polyurethane coatings using a biosourced graphitic nanoparticle anchored silica nanoparticle hybrid. Hence, 3-aminopropyl triethoxysilane was reacted with silica nanoparticles to obtain amino groups on the surface and was further reacted with a carboxyl terminated graphitic nanoparticle obtained from the incineration of camphor. The formation of hybrid structure was established through the electron microscopy images and other spectroscopic techniques. The infrared spectroscopic measurements reveal the successful formation of carbon–silica nanohybrid through amide linkages. The synthesized hybrids were dispersed in different weight percentages into a polyether polyol and then reacted with diisocyanate to form polyurethane nanocomposite. The presence of unreacted amino groups in the carbon–silica nanohybrid is helpful in urea linkage formation, which leads to uniform dispersion in the polymer matrix. The prepared polyurethane composite possess exceptional physico-chemical properties owing to the presence of nanoparticulates. Interestingly, the resulting composite showed shape recovery behavior. The shape recovery behavior of the obtained coating under temperature of 60 °C was found to correlate with the increase in the nanomaterial content. It is also found that storage modulus of the composite at room temperature increases from 183 MPa to 432 MPa in the case of neat and 1.5% carbon-silica nanohybrid incorporated polyurethane respectively.