Structure/property relationships in flexible alkoxysilane automotive coatings

Flexible automotive coatings are susceptible to scratch and mar damage, especially during finishing and assembly operations. One-component (1K) flexible clearcoats exhibit very good scratch and mar resistance, but unfortunately suffer from poor durability and environmental etch resistance. Two-component clearcoats offer improvements in both etch and durability, but at the expense of scratch and mar. In this paper, the concept and properties of 1K flexibilized silane clearcoats for use on automotive plastics will be introduced and their structure/property relationships examined as they apply to scratch and mar. The role of coating crosslink density, toughness, glass transition temperature (T_g), and surface profile on the scratch damage of coated plastic substrates will be described. In addition, a new scratch methodology, termed Scratcho, is utilized to determine relative scratch performance and is compared to conventional scratch resistance testing. Results to date indicate that hardness, as affected by the glass transition temperature, and crosslink density, as it contributes to higher essential work values, both affect resultant scratch propensity of the flexible coatings. The relative ranking of different coating systems employing alternate crosslinkers (e.g., isocyanate and melamine) is also presented and compared to the newly developed silane crosslinked coatings. Presented at the 28th International Waterborne, High-Soids, and Powder Coatings Symposium, Feb. 21–23, 2001, in New Orleans. LA. 377 Fairall St., Ajax, Ont., L1S 1R7, Canada. 401 Southfield Rd., P.O. Box 6231, Dearborn, MI 48121-6231.     

On composite likelihood estimation of a multivariate INAR(1) model

In several circumstances the collected data are counts observed in different time points, while the counts at each time point are correlated. Current models are able to account for serial correlation but usually fail to account for cross‐correlation. Motivated by the lack of appropriate tools for handling such type of data, we define a multivariate integer‐valued autoregressive process of order 1 (MINAR(1)) and examine its basic statistical properties. Apart from the general specification of the MINAR(1) process, we also study two specific parametric cases that arise under the assumptions of a multivariate Poisson and a multivariate negative binomial distribution for the innovations of the process. To overcome the computational difficulties of the maximum likelihood approach we suggest the method of composite likelihood. The performance of the two methods of estimation, that is, maximum likelihood and composite likelihood, is compared through a small simulation experiment. Extensions of the time‐invariant model to a regression model are also discussed. The proposed model is applied to a trivariate data series related to daily traffic accidents in three areas in the Netherlands.     

Influence of various parameters on the electrochemical treatment of landfill leachates

The influence of some basic parameters of an electrolytic system on the effectiveness of the treatment of landfill leachates is investigated. The controlling parameters of the system examined were: (i) the leachate input rate, (ii) pH and temperature, (iii) the amount of electrolyte (NaCl) added, (iv) the voltage applied and (v) the concentration of Fe²⁺ (added as FeSO₄ · 7H₂O). The performance of the system was assessed in terms of the COD, BOD₅ and NH₄ ⁺ reduction in the leachate samples as well as in terms of the energy consumption of the system (i.e., kWh consumed per kg of COD removed). These two parameters are referred to as the optimization parameters of the system. By implementing a 2⁶ factorial experiment, linear models, which interrelate each optimization parameter with the controlling parameters of the system, were generated. Using these models, effective treatment of landfill leachates by electrochemical oxidation can be designed.     

Comparison of the efficacy and safety of 2% dorzolamide and 0.5% betaxolol in the treatment of elevated intraocular pressure. Dorzolamide Comparison Study Group

A multicenter, parallel-design, randomized, double-masked study was conducted to compare the efficacy and safety of 2% dorzolamide with those of 0.5% betaxolol in the treatment of elevated intraocular pressure (i.o.p). A total of 311 adults with ocular hypertension or open-angle glaucoma were randomly allocated to receive either 2% dorzolamide administered topically TID or 0.5% betaxolol administered topically BID plus placebo administered topically QD for 12 weeks. After the washout of previous ocular hypotensive drugs, patients with IOP > or = 23 mm Hg in at least one eye at 10 AM or 4 PM on study day 1 were randomly allocated to receive one of the study treatments. Throughout the study, IOP was measured 2 and 8 hours after instillation of study medication for the morning peak effect (hour 2) and afternoon trough effect (hour 8). After 12 weeks of therapy, the mean change in IOP was not significantly different between the dorzolamide and betaxolol treatment groups at hour 8 (-3.6 mm Hg in both groups) or hour 2 (-5.4 vs -5.3 mm Hg, respectively). The differences between treatments (and 95% CIs associated with these differences) in mean IOP changes from baseline were 0.02 mm Hg (-0.870 to 0.901) for hour 8 and -0.14 mm Hg (-0.959 to 0.685) for hour 2. The ocular adverse experience (AE) most frequently reported by patients was ocular burning and/or stinging, and the most frequently reported nonocular AEs were taste perversion, upper respiratory infection, and headache. Only the incidence of taste perversion was significantly different between treatment groups (14.6% for the dorzolamide group and 0.0% for the betaxolol group). Two percent of patients in each treatment group discontinued the study due to AEs. This study confirmed the similar IOP-lowering effect of 2% dorzolamide and 0.5% betaxolol. Both treatments were generally well tolerated, and their safety profiles were similar.     

Chemical depth profiling of automotive coating systems using slab microtome sectioning with IR/UV-VIS spectroscopy and optical microscopy

Chemical surface/near-surface analysis and depth profiling of high performance automotive coating systems can be done efficiently by commonly available infrared (IR), ultraviolet-visible (UV-VIS) and optical microscopy (OM) measurement technologies. The different stages of mass loss for acrylic/melamine-crosslinked clearcoats modeled after those used in high performance automotive coating systems were explored as a function of exposure time/conditions. Two approaches were used. Transmission mode IR experiments were conducted to monitor mass loss in isolated clearcoats. OM was used to monitor mass loss in clearcoats that are part of actual multilayered coating systems. UV-screener (UVA) permanence and interphase mixing (i.e., between clearcoat and basecoat layers) as well as general chemistry depth profiling studies of model acrylic/melamine-crosslinked and acrylic/melamine+silane-crosslinked clearcoats were done as a function of system preparation and exposure time/conditions. UVA depth profiles were obtained using slab microtomy sectioning co-planar to the surface, followed by solvent extraction and UV-VIS solution analysis to monitor UVA content as a function of section mass and thickness. General chemistry depth profiles were obtained using slab microtomy sectioning (as mentioned previously), followed by ATR (IR) analysis to monitor changes in the photooxidation index values and the spectral envelop in the 2600–3800 cm⁻¹ range. The approaches described herein do not require expertise/equipment that is available to only a few, thus increasing the potential utility of such tools. Marshall R&D Laboratory, Philadelphia, PA, 19146.     

Visualization of astaxanthin localization in HT29 human colon adenocarcinoma cells by combined confocal resonance Raman and fluorescence microspectroscopy

Astaxanthin, a carotenoid found in plants and seafood, exhibits antiproliferative, antioxidant and anticarcinogenic properties. We show that astaxanthin delivered with tetrahydrofuran is effectively taken up by cultured colon adenocarcinoma cells and is localized mostly in the cytoplasm as detected by confocal resonance Raman and broad-band fluorescence microspectroscopy image analysis. Cells incubated with beta-carotene at the same concentration as astaxanthin (10 microM) showed about a 50-fold lower cellular amount of beta-carotene, as detected by HPLC. No detectable Raman signal of beta-carotene was found in cells, but a weak broad-band fluorescence signal of beta-carotene was observed. beta-Carotene, like astaxanthin, was localized mostly in the cytoplasm. The heterogeneity of astaxanthin and beta-carotene cellular distribution in cells of intestinal origin suggests that the possible defense against reactive molecules by carotenoids in these cells may also be heterogeneous.     

Coproduction of EPA and Fucoxanthin with P. tricornutum – A Promising Approach for Up- and Downstream Processing

Eicosapentaenoic acid (EPA) and fucoxanthin, a carotenoid, provide a broad variety of health benefits in human nutrition. In this study, an up- and downstream process for the coproduction of EPA and fucoxanthin using the diatom Phaeodactylum tricornutum in flat-panel airlift photobioreactors is proposed. The approach represents a promising alternative to conventional sources for both compounds, viz. marine fish and macroalgae. The productivity as well as the biomass-specific product content were optimized during cultivation. Subsequently, both compounds were extracted, separated and purified using pressurized liquids.     

A systematic assessment of the technical feasibility and economic viability of small hydroelectric system installations

This study presents a general computer program developed for performing a preliminary evaluation of small hydroelectric (SHE) system installations providing the user with sufficient technical and financial information in order to justify further investment in such installations. It also assesses pertinent non-financial attributes, such as local/national environmental and socio-economic impacts. The program also takes into account the specific technoeconomical constraints applicable in Greece. As a case study, a SHE installation in the geographical area of Central Macedonia of Greece, is thoroughly analyzed.     

Use of reactable light stabilizers to prevent migration and to improve durability of coatings on plastic substrates

One of the challenges of coating plastic substrates for exterior automotive applications involves the tendency for light stabilizers, which inhibit UV degradation of the coating, to migrate out of the topcoat and into the underlying plastic substrate. The consequent depletion of the stabilizer from the topcoat could account for significantly poorer durability for coatings applied on plastic than on a nonpermeable substrate such as steel. These studies investigate the migration of both nonreactable and reactable UV absorbers (UVAs) and hindered amine light stabilizers (HALS) in fully formulated 2K urethane coatings applied on thermoplastic olefin (TPO) and steel substrates. Extensive migration of the nonreactable stabilizers occurs during accelerated exposure of the cured coating, and this migration correlates with poorer performance on TPO. Functionalization of the stabilizer with a group which covalently reacts into the coating will prevent much of this migration, and the improved degree of retention of the reactable light stabilizers in the topcoat correlates with improved performance on TPO substrates. In addition, stabilizer variables, such as the type and extent of functionalization as well as their chemical structure, have an effect on both the migration and performance of the stabilizers.     

Thermal Analysis of Amorphous Phases in Hydroxyapatite Coatings

The amorphous phase in hydroxyapatite coatings has been examined by using X-ray diffractometry, Fourier transform infrared spectroscopy, optical microscopy, and thermal analysis methods. The amorphous phase mostly consists of a dehydroxylated calcium phosphate. When heated, crystallization of hydroxyl-rich areas produces hydroxyapatite, followed by diffusion of hydroxyl ions, thus increasing the amount of crystalline phase. Hydroxyl-deficient amorphous areas crystallize to oxyapatite at 700°C. Thus, crystallization occurs over a range of temperatures and is dependent on the hydroxyl content of the amorphous phase and the partial water-vapor pressure. The activation energies of crystallization to hydroxyapatite, diffusion of hydroxyl ions, and crystallization to oxyapatite are 274, 230, and 440 kJ/mol, respectively. Shrinkage from these processes leads to a crack network and decreases the mechanical strength of the coating.