The influence of binder content on the water transport properties of waterborne acrylic paints

Diffusion coefficients and sorption isotherms of water in waterborne acrylic paint films and in the pure binder of the paints have been measured by gravimetric sorption. Solubility of water was found to enhance with the increased binder content in the paint films while the diffusivity of water decreased significantly. Sorption isotherms in the paint and pure copolymer films were correlated with the Flory Huggins theory and ENSIC model, respectively. Fickian diffusion was observed in both types of films and the kinetic data were best correlated with a numerical model which takes into account the concentration dependency of the diffusion coefficient and the dimensional change of the film due to sorption. It was concluded that the utilization of a simplified analytical solution may lead to significant errors in the estimation of diffusivities.     

Corrosion performance of waterborne coatings for structural steel

Among recently developed waterborne coatings, epoxy and acrylic based coatings have a special place. To study this kind of anticorrosive coatings, use is normally made of natural exposure and laboratory tests. The literature has recently reported that the salt spray test is not suitable for selecting/studying anticorrosive waterborne coatings. In this paper, the authors present the main results obtained in an experimental study involving laboratory tests and natural exposure in two atmospheric test sites of different corrosivity categories. The natural exposure and accelerated tests are complemented by other measurements in the laboratory, involving water uptake, adhesion and electrochemical measurements, to understand the anticorrosive performance of the paint systems under study. As accelerated tests, salt spray and prohesion were used. Indirect measurements of adhesion were made using cross-cut and pull-off tests. Electrochemical impedance spectroscopy (EIS) and noise (EN) were used for electrochemical characterization. The study concludes that the best anticorrosive behaviour was shown by epoxy-polyamide paint systems, including zinc-rich primers. The correlation between the results of salt spray and natural exposure in marine test sites was significantly better than that obtained using the prohesion test. The electrochemical results showed that it is very important to pay special attention when interpreting this kind of results.     

Effect of water drying conditions on the surface property and morphology of waterborne UV-curable coatings for engineered flooring

UV-curable coatings are widely used on wooden materials such as flooring and furniture, because they have excellent properties, including high hardness, gloss, mar and chemical resistance, and are also environmental friendly, containing no solvents. Recently, waterborne UV-curable coatings have been studied as a viable alternative, since solvents are added to spray applications to lower viscosity. We investigated the effects of water drying conditions on the surface properties and morphology of waterborne UV-curable coatings at the flash-off step. Temperature conditions studied were 22 °C, 50 °C, and 80 °C, with various drying times. We evaluated surface properties such as pendulum hardness, pencil hardness, and adhesion strength. Also observed was surface morphology, comparing surface properties using optical microscopy after drying and UV-curing. Insufficient drying caused cracking, peeling and blistering at the surface of a cured coating. Sufficient drying was very important for the best application and ideal surface morphology of waterborne UV-curable coatings.     

Rheology parameters controlling spray atomization and roll misting behavior of waterborne coatings

Formation of small coating droplets is a phenomenon common to spray and roll application of coatings. Generation of small droplets, referred to as atomization, is the mechanism of controlling the quality and thickness of the applied coating layer in spray technology. In roll coating application, small coating droplets are formed at the nip–exit region under certain conditions. Because of the high-shear rates at roll nips and spray nozzles, it is common to relate high-shear viscosity with atomization and roll misting behavior of coatings. This paper will review the relative importance of shear and extensional flows, and the response of coatings to such flows, in affecting misting and atomization behavior. Experimental efforts to quantify the effect of shear and extensional rheological parameters have clearly established a lack of correlation of high-shear viscosities with both spray atomization and roll misting behavior of coatings. However, extensional viscosity is shown to have a strong correlation. Finally, how rheology modifiers can be selected to circumvent misting problems in roll coating applications and atomization problems in spray applications is discussed.     

Ultraviolet,water, and thermal aging studies of a waterborne polyurethane elastomer-based high reflectivity coating

A waterborne aliphatic polyurethane-based coating was studied for accelerated ultra-violet (UV), water (WT), and thermal (TH) aging for a period of 1000 h. To monitor the coating durability, samples were tested every 200 h. ATR-FTIR spectroscopy was used to monitor the chemical changes occurring during the aging process. UV–vis with integrating sphere was used to track the change in diffused reflectance, while the optical microscope and the scanning white light interferometry (SWLI) were used for surface characterization. FTIR studies of coatings subjected to UV exposure indicated a decrease in functional groups such as CONH, CH, CO, and COC. The appearance of functional groups such as NH is attributed to chain scission of the polyurethane binder in the coating. Investigation of the degradation mechanism in water and thermal aging showed physical effects through water penetration and the mismatch in the coefficient of thermal expansion as the primary causes of degradation. In all aging scenarios, the reduction of reflectivity was largely due to physical defects caused by the different aging mechanisms.     

Characterization of waterborne polyurethane for ecofriendly functional floor plate

Three types of nonmetallic mineral particles (CaCO₃, TiO₂ and loess) were incorporated into waterborne polyurethane acrylate (PUA) to improve the surface properties of ecofriendly floor tiles. Several properties of PUA containing nonmetallic mineral materials were measured by Fourier transform infrared spectroscopy (FT-IR), a dynamic mechanical thermal analyzer (DMTA), swelling tests, and contact angle measurement. Upon decreasing the molecular weight between crosslinks (variation of molecular weight of the polyol), the modulus and glass transition temperature (T_g) of the PUA film increased because of the increase in crosslinking density. Resistance properties such as swelling and contact angle against water were enhanced with the addition of nonmetallic mineral particles because of the increase in the hydrophobic nature of the polymer matrix.     

水性聚丙烯酸酯的合成及性能研究

本研究首先以2,4-甲苯二异氰酸酯（TDI）、聚丙二醇（PPG）、2,2-二羟甲基丁酸（DMBA）、三乙胺（TEA）、乙二胺（EDA）、2-丁炔-1,4-二醇（BDO）等为主要原料,采用自乳化法合成了性能较为优异的水性聚氨酯分散体（WPU）。本实验通过改变NCO/OH值、EDA含量、BDO含量、和筛选不同数均分子量的聚醚二醇合成了一系列水性聚氨酯乳液,随后考察了不同共聚组分对WPU胶膜耐水性的影响,并借助SEM,力学实验研究了不同共聚组分对乳胶粒形态和PU胶膜的力学性能的影响。     

水性聚氨酯胶膜的耐水性能研究

采用预聚体法,以聚酯多元醇、甲苯二异氰酸酯、二羟甲基丙酸(DMPA)制备了聚酯型水性聚氨酯乳液,考察了亲水扩链剂DMPA用量、NCO/OH值、中和剂的种类、中和度、扩链剂乙二胺用量对乳液涂膜耐水性的影响,制备了耐水性较好的水性聚氨酯乳液。     

低温等离子体壳聚糖水性聚氨酯整理棉织物

探讨低温等离子体预处理和壳聚糖水性聚氨酯共混整理对棉织物白度、折皱回复性和透湿性的影响。分析了共混乳液成膜后的红外光谱图,将水性聚氨酯与壳聚糖以不同比例共混后整理到经等离子体预处理与未经等离子体预处理的棉织物上,测试了各织物的白度、折皱回复角和透湿率。结果发现:共混膜同时具有聚氨酯与壳聚糖的特征基团并产生新的特征峰;随着整理液中壳聚糖含量的增加,织物白度下降,折皱回复角下降,透湿率增加;采用等离子体处理后织物白度增加,折皱回复角下降,透湿率增加。认为壳聚糖水性聚氨酯共混比例和等离子体预处理均对整理出的棉织物性能有影响。     

Virus attenuation by microbial mechanisms during the idle time of a household slow sand filter

The biosand filter (BSF) is a household slow sand filter that is operated intermittently such that an idle time of typically 18-22 h occurs in between daily charges of water. Virus attenuation during the idle time was investigated over repeated daily filtration cycles to capture the effect of media aging that encompasses processes occurring throughout the filter depth rather than restricted to the schmutzdecke at the media surface. A threshold aging period of about one to two weeks was required before virus attenuation began. The observed rates of MS2 and PRD-1 reduction were first-order and reached maxima of 0.061- and 0.053-log per hr, respectively, over seven-to-ten weeks. Suppression of microbial activity by sodium azide eliminated virus reduction during the idle time thus indicating that the operative media aging process was microbially mediated. The mechanism of virus reduction was not modification of media surfaces by physical/chemical or microbial processes. Instead, it appears that the activity of the microbial community within the filter is responsible. The most likely biological pathways are production of microbial exoproducts such as proteolytic enzymes or grazing of bacteria and higher microorganisms on virus particles. Implications of these findings for BSF design and operation and their relevance to other biological filtration technologies are discussed.