Surface Isocyanate Research Articles

Facile preparation of isocyanate-functionalized poly(styrene-co-maleimide-co-maleic anhydride) particle and its application as a versatile support for nano-sized TiO2 photocatalyst

Polymer-supported catalysts have attracted intensive research attentions due to easy handling, facile separation and outstanding recycling performance. Herein, a simple, efficient and universal strategy was developed to fabricate isocyanate-functionalized polymer microspheres bearing highly reactive surface isocyanate groups, which could serve as a versatile support for the immobilization of photocatalyst. Firstly, self-stabilized precipitation polymerization of maleimide, maleic anhydride and styrene was performed in the presence of divinyl benzene (crosslinker) to prepare imide-functionalized poly(styrene-co-maleimide-co-maleic anhydride) (PSMM) microspheres. By simply adjusting the solvent composition and monomer feed ratio, monodisperse PSMM particles with diameter in the range of 0.52–1.01 μm were successfully obtained, which were further modified with hexamethylene diisocyanate (HDI). As a proof-of-concept, TiO2 nanoparticles were readily and covalently bound to the surface of HDI-functionalized PSMM (PSMM-HDI) particles through reaction with isocyanate groups, leading to the formation of PSMM-HDI supported TiO2 (PSMM-HDI@TiO2). Furthermore, anhydride groups on the surface of PSMM was hydrolyzed to endow PSMM-HDI@TiO2 with better dispersibility and adsorption performance. The degradation of methylene blue under UV-light was performed to evaluate the photocatalytic performance of the resultant PSMM-HDI@TiO2. Compared with pristine TiO2, the PSMM-HDI@TiO2 exhibited not only higher degradation efficiency, but also facile separation and better reusability.

Surface modification of sisal fibers to be used as a reinforcement in polypropylene composite materials

Sisal fibers have taken special focus by material investigators and commercial environment because they are economical, biodegradable and lightweight(1). Composite manufactured using natural fibers can supply properties that can be compared to other composites reinforced with synthetic fibers, as previous studies have shown (2-6). Thus, fibers that come from nature sources, such as wood, nuts fruit, jute, kenaf, hemp, sisal, etc. are being introduced in composite manufacturing (7-9). Sisal fiber has relevant economical and ecological properties (10), but it is a lignocelulosycal fiber with hydrophylic character, so it is difficult its usage with hydrophobic matrix, and it is required to use coupling agents in order to improve its interface adhesion. This work starts with sisal fibers submitted to different types of primary treatments, and for each one of these treatments, sisal fibers are submitted to secondary treatments of maleinization, mercerization, silanization, formation of nascent surface isocyanates, carboxylation and methacrylate treatment. The efficiency of these treatments has been evaluated using morphology characterization techniques by FTIR-ATR, electronic microscopy (SEM). With some of the treated fibers, thermoplastic composites have been prepared and these have been used to prepare standard probes that have been thermally and mechanically tested, as well as other additional interesting physicochemical characteristics.

Bonding the Terminal Isocyanate-Related Functional Group to the Surface Manganese Ions to Enhance Li-Rich Cathode's Cycling Stability.

Capacity fading of Li-rich cathodes in the cycling process is mainly caused by the irreversible side reactions at the interface of electrode and electrolyte by reason of the lack of a corrosion resistant surface. In this work, isocyanate-related functional groups (-N═C═O groups and polyamide-like groups) were tightly bonded on the surface of Li-rich oxides through a urea decomposition gas heat-treatment. The surface isocyanate functionalization inhibits the side reaction of PF5 hydrolysis to give LixPFyOz and HF species at the surface of Li-rich materials in the cycle process. As compared to the untreated Li-rich sample U0, the samples with the spinel-like layer and isocyanate functionalized surface exhibited an enhanced cycle stability. The capacity retention of the treated sample U3 reached as high as 92.6% after 100 cycles at the current density of 100 mA/g, larger than 66.8% for the untreated sample. Even at a higher current density of 1000 mA/g, sample U3 gives a capacity retention of 81.7% after 300 cycles. The findings of this work reveal the importance of surface isocyanate functionalization in restraining the surface side reactions and also suggest an effective method to design Li-rich cathode materials with better electrochemistry performance.

A facile and versatile route to functional poly(propylene) surfaces via UV-curable coatings

A convenient UV-curable coatings assisted surface functionalization strategy is presented to convert commodity Poly(propylene) (PP) films into diverse functional materials. To ensure a covalent integration between PP surface and functional UV-curable coatings, 3-(trimethoxysilyl) propyl acrylate (TMSPA) was functionalized on the surface of oxidized PP film. Two distinct UV-curable coatings differing primarily in the chemical nature of monomers were separately tethered on the surface of TMSPA functionalized PP films. The monomers applied in this study include 1H,1H,2H,2H-heptadecafluorodecyl acrylate (HFDA) and 2-isocyanatoethyl methacrylate (ICEMA). The use of HFDA as monomer resulted in PP film with fluorinated surface chemical nature, which would be attractive for applications desiring low surface energy, low dielectric constant, low flammability, low refractive index, and superior chemical resistance. Employing ICEMA monomer as part of UV-curable mixture resulted in PP film offering a high density of surface isocyanate groups (–NCO) that could be conveniently conjugated to a variety of amines to give a range of functional surfaces. For proof of concept, the –NCO groups on the surface of PP film were conjugated with amine terminated polyethylene glycol to give PP film that exhibited antifouling nature. In a separate experiment, the surface –NCO groups were conjugated to 2-aminoethanesufonic acid (AESA) to fabricate an anionic PP surface capable of effectively interacting with cationic species. The conjugation of surface –NCO groups with l-lysine imparted pH responsive wettability switching behaviour to the surface of PP film. Finally, poly(ethylene imine) (PEI) was conjugated to surface –NCO groups and the resulting surface PEI moieties were used as reducing and stabilizing agent to synthesize catalytically active gold nanoparticles (AuNPs) confined to the surface of PP film. All the surface functionalization's were fully corroborated by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), water contact angle (WCA) goniometry, and scanning electron microscopy (SEM). Considering the potential for incorporation into the existing industrial processes and resourcefulness of the surface functionalization via UV-curable coatings, we envision that the herein reported strategy holds an excellent potential to transform commodity PP films into a wide range of specialty materials for diverse applications at large scale.

Residual Isocyanates in Medical Devices and Products: A Qualitative and Quantitative Assessment.

We conducted a pilot qualitative and quantitative assessment of residual isocyanates and their potential initial exposures in neonates, as little is known about their contact effect. After a neonatal intensive care unit (NICU) stockroom inventory, polyurethane (PU) and PU foam (PUF) devices and products were qualitatively evaluated for residual isocyanates using Surface SWYPE™. Those containing isocyanates were quantitatively tested for methylene diphenyl diisocyanate (MDI) species, using UPLC-UV-MS/MS method. Ten of 37 products and devices tested, indicated both free and bound residual surface isocyanates; PU/PUF pieces contained aromatic isocyanates; one product contained aliphatic isocyanates. Overall, quantified mean MDI concentrations were low (4,4′-MDI = 0.52 to 140.1 pg/mg) and (2,4′-MDI = 0.01 to 4.48 pg/mg). The 4,4′-MDI species had the highest measured concentration (280 pg/mg). Commonly used medical devices/products contain low, but measurable concentrations of residual isocyanates. Quantifying other isocyanate species and neonatal skin exposure to isocyanates from these devices and products requires further investigation.

Investigations of the flax fiber/thermoplastic polyurethane eco‐composites: Influence of isocyanate modification of flax fiber surface

In this study, alkali and isocyanate surface modifications were applied to flax fiber (FF) to improve its adhesion to bio‐based thermoplastic polyurethane (TPU) matrix. In addition to these treatments, isocyanate treated FF was subjected to curing process. TPU/FF composites were prepared at a constant 30 wt% loading of the total by using melt‐blending method. Their mechanical properties, modulus of elasticity, melt‐flow, water uptake and morphological properties were investigated. All of the surface modifications resulted in better mechanical properties with respect to untreated FF. Cured isocyanate treated FF loaded composite exhibited the best results in the case of tensile strength, Young's modulus and storage modulus. Isocyanate treatments caused reduction in melt flow rate due to enhancement in interfacial interactions between phases. It was observed from the SEM micrographs that surface treated fibers dispersed more homogeneously in the TPU matrix. Results confirmed that surface modifications improved the adhesion of FF to TPU matrix. POLYM. COMPOS., 38:2874–2880, 2017. © 2015 Society of Plastics Engineers

Elucidating N2O Formation during the Cyclic NOx Storage and Reduction Process Using CO as a Reductant.

The N2O formation pathway and effect of H2O on N2O formation during the NOx storage and reduction (NSR) process using CO as a reductant were investigated over a Pt-BaO/Al2O3 catalyst. The NSR activity measurements and transient in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments were performed to evaluate N2O evolution and elucidate the N2O formation mechanism. N2O is formed in the lean, rich, and delay2 phases. In the lean phase, N2O formation is related to the reactions between surface isocyanate and gaseous NO/O2 and NO is more responsible for N2O formation than O2. Moreover, N2O production decreases with H2O because of the hydrolysis of isocyanate species. In the rich phase, the amount of N2O formation also decreases in the presence of H2O at a higher temperature because of the high reduction ability of H2 generated from the water-gas shift (WGS) reaction. During the delay2 phase, N2O is mainly formed by nitrite species reacting with Pt(0)-CO. Furthermore, the presence of H2O decreases the stability of nitrites and results in more N2O production at a low temperature.

Kinetic modeling of NO selective reduction with C3H6 over Cu-SSZ13 monolithic catalyst

• Kinetic model for lean NO reduction with C 3 H 6 on Cu/CHA monolith is developed. • Model includes the key intermediates detected by DRIFTS. • Model predicts steady state C 3 H 6 and NO conversions vs. temperature quantitatively. • Model predicts transient behavior for C 3 H 6 + O 2 and C 3 H 6 + NO + O 2 reaction systems. • Model provides useful insights into non-ammonia pathways for lean NO x reduction. A mechanistic-based kinetic model is developed for selective catalytic reduction of NO with C 3 H 6 on Cu chabazite (Cu-SSZ13) monolithic catalyst based on bench scale flow reactor studies and in-situ DRIFTS measurements. The SCR mechanism involves reaction between oxygenates (partially oxidized hydrocarbon species) and NO to form isocyanates species ( NCO), detected by DRIFTS, which are further reduced to N 2 . We have shown in an earlier study that reaction intermediates, most likely surface isocyanates, poison the active sites on the catalytic surface resulting in the inhibition of other reactions (Raj et al., 2013 [7]). The kinetic model was developed in steps, starting with steady-state CO oxidation, followed by C 3 H 6 oxidation, and then the C 3 H 6 + NO + O 2 reaction system. This approach ensured consistency in the parameter estimation and resulted in a more robust model. The models for CO + O 2 , C 3 H 6 + O 2 and C 3 H 6 + NO + O 2 were also validated using a new set of steady state experiments. The monolith model predicts the observed negative order with respect to C 3 H 6 and positive order with respect to O 2 for the C 3 H 6 oxidation reaction. For the C 3 H 6 + NO + O 2 reaction system, the predicted NO and C 3 H 6 conversions agree well with both steady state and transient experimental data. The model captures the significant shift of C 3 H 6 light-off to higher temperature in the presence of NO due to formation of the inhibiting NCO surface species as well as slow transients associated with surface intermediates and their effect on the extent of reactions.

Use of fluoropolymer permanent release coatings for molded polyurethane foam production

The problem of adhesion of polyurethane foams to fluoropolymer permanent release mold coatings was studied. Two coatings, based on polytetrafluoroethylene (PTFE) and perfluoroalkoxy polymer (PFA) aqueous dispersions, respectively, were applied on aluminum plates, and the foam release performance evaluated. The PTFE coating displayed gradual loss of antiadhesion properties with consecutive exposure to the reactive mixture, which was associated with isocyanate surface penetration. Penetrant mass uptake experiments, performed on free films, indicated that PTFE retains about 10 times more isocyanate than PFA, probably because of its porous surface morphology. A synergistic effect was found by applying a very small quantity of a waterborne release agent on the PTFE coating, before every foam molding cycle. The release agent formed a protective barrier that minimized contact of the coating with the reactive mixture, allowing for stable and robust foam release performance. The problem of polyurea build-up, associated with the use of aqueous release agents, was not observed because of the small amounts of compound used.

In situ FT-IR spectroscopic investigation of gold supported on tungstated zirconia as catalyst for CO-SCR of NOx

The possibility for application of gold supported on tungstated zirconia as catalyst in the selective catalytic reduction of NOx with CO (CO-SCR) has been investigated by means of in situ FT-IR spectroscopy. Tungstated zirconia containing 18wt% of WO3 was prepared by co-precipitation. Gold was deposited on zirconia and tungstated zirconia by cationic adsorption using [Au(en)2]Cl3 as a precursor (en=ethylenediamine). The FT-IR spectra obtained during the interaction of CO with NOx species adsorbed on the Au/ZrO2–WOx and Au/ZrO2 samples revealed the formation of surface isocyanates attached to the gold particles. The generation of Au–NCO species occurred at low temperature (25–50°C). The W-containing sample was characterized by higher activity in the ad-NOx+CO reaction than the W-free one. It is shown that the nitrate species or adsorbed NO2 are essential for the generation of surface isocyanates and the oxidation of NO by oxygen is an important step. The obtained results suggest that Au catalysts supported on tungstated zirconia might be of interest for the selective reduction of NOx with CO at low temperatures.

Elucidating NH3 formation during NOx reduction by CO on Pt–BaO/Al2O3 in excess water

The reduction of NO was investigated with CO, H2, CO+H2O and CO+H2 as the reducing species on a Pt–BaO/Al2O3 monolith catalyst over an intermediate temperature range (200–300°C). NH3 is a major product of the NO+CO+H2O system under conditions of CO inhibition. The data are interpreted by the known NH3 formation route in which the NO is reduced by H2 formed by the water gas shift (WGS) reaction. In the absence of water, the strong adsorption of CO leads to sharp transitions between a high rate mass transport controlled regime and a lower rate kinetically controlled regime between 200 and 300°C. Differential kinetics and integral experiments are reported at 270°C. The intrinsic order with respect to CO in the latter regime is −1. When water is added with the CO feed, the regime transitions are more gradual and mitigated by the enhancement afforded by the hydrogen formed by the WGS reaction. Kinetic evidence for the effect of hydrogen is the much lower inhibition by CO during the WGS reaction (−0.23 order). When H2 is added to the NO+CO mixture (without H2O) in the CO inhibited feed regime NH3 and CO2 are the major products even for low H2/NO feed ratio (∼1). Collectively, the steady-state findings are consistent with the major NH3 formation pathway involving reaction of surface H (from WGS) and OH (from water) with adsorbed NO and N. The NH3 formation route involving the hydrolysis of a surface isocyanate species formed from the reaction of NO and CO, is only of secondary importance.

In situ FTIR investigation of the role of surface isocyanates in the reduction of NOX by CO and C3H6 over model Pt/BaO/Al2O3 and Rh/BaO/Al2O3 NOX storage and reduction (NSR) catalysts

Monometallic Pt- and Rh-containing model NOX storage and reduction (NSR) catalysts were investigated by in situ FTIR spectroscopy in order to determine the type of species present on the surface under simulated lean exhaust conditions and to identify potential reaction intermediates during reduction by CO and propylene. The effect of precious metal selection, temperature, and water presence on the NOX storage and reduction chemistry was considered. The formation of surface isocyanate (NCO) species was observed during all cycling experiments, even in the presence of H2O, which prompted additional investigation on the role of these species in the NOX reduction mechanism. Stability and reactivity experiments with BaO/Al2O3, Pt/BaO/Al2O3 and Rh/BaO/Al2O3 confirmed that the reactions of NCO with NO and O2 – producing N2 – are metal catalyzed pathways, while the reaction of NCO with H2O – producing NH3 – is not. The contribution of NCO-related pathways to the overall N2 production mechanism could be significant, since quantification of the FTIR results suggests that up to 30% of the total N2 produced could be directly related to the reaction of surface isocyanates with O2.

Reduction by CO of NO x species stored onto Pt–K/Al 2O 3 and Pt–Ba/Al 2O 3 lean NO x traps

In this paper the results obtained in our previous studies on the reduction of nitrates by CO over Pt–K/Al 2O 3 and Pt–Ba/Al 2O 3 catalysts are compared and discussed in order to define the chemistry that leads to nitrogen evolution during the regeneration of the different lean NO x traps. The reaction mechanisms and pathways leading to N 2 formation under dry conditions are investigated by complementary transient dynamic experiments and FT-IR analyses. In both cases, the reduction of stored NO x by CO occurs according to a Pt catalyzed surface pathway that does not involve the release of NO x in the gas phase as a first step, is effective already at low temperature and leads to nitrogen. The proposed reaction scheme implies the formation of surface isocyanate species followed by their reaction with residual stored NO x to give nitrogen. This is the exclusive route for nitrogen formation.

The NOx Reduction by CO on a Pt−K/Al2O3 Lean NOx Trap Catalyst

The reduction by CO under dry conditions of NOx species stored at 350 °C onto a Pt−K/Al2O3 lean NOx trap catalyst is investigated by means of transient response methods (CO-TPSR and CO-ISC experiments) and complementary FT-IR spectroscopy. The results show that the pathway for the reduction of stored NOx by CO under dry and near isothermal conditions (and in the absence of CO2) is the same as that proposed by some of us in a previous work for a Pt−Ba/Al2O3 catalyst. In particular, (i) the reduction of stored NOx by CO occurs according to a Pt-catalyzed surface pathway that does not involve, as a first step, the release of NOx in the gas phase, is effective already at low temperature, and leads to nitrogen; (ii) the reaction scheme implies the formation of surface isocyanate species, followed by the reaction of these species with residual NOx to give nitrogen; and (iii) the reaction of NCO species with nitrates to give nitrogen is slightly slower than the reduction of nitrates to give NCO species; but on the Pt−K/Al2O3 catalyst, this last step is faster than on the Pt−Ba/Al2O3 system. As a consequence, the amount of isocyanate species present on the surface at the end of the reduction is lower for Pt−K/Al2O3 than for the Pt−Ba/Al2O3 catalyst.

Investigating the mechanism of the H 2-assisted selective catalytic reduction (SCR) of NOx with octane using fast cycling transient in situ DRIFTS-MS analysis

A mechanistic study of the H 2-assisted Selective Catalytic Reduction (SCR) of NOx with octane as reductant over a Ag/Al 2O 3 catalyst was carried out using a modified DRIFTS cell coupled to a mass spectrometer. Using fast transient cycling switching of H 2, with a time resolution of a few seconds, it was possible to differentiate potential reaction intermediates from other moieties that are clearly spectator species. Using such a periodic operation mode, effects were uncovered that are normally hidden in conventional transient studies which typically consist of a single transient. In experiments based on a single transient addition of H 2 to, or removal of H 2 from, the SCR feed, it was found that the changes in the concentrations of gaseous species (products and reactants) were not matched by changes at comparable timescales of the concentration of surface species observed by IR. This observation indicates that the majority of surface species observed by DRIFTS under steady-state reaction conditions are spectators. In contrast, under fast cycling experimental conditions, it was found that a surface isocyanate species had a temporal response that matched that of 15N 2. This suggests that some of the isocyanate species observed by infrared spectroscopy could be important intermediates in the hydrogen-assisted SCR reaction although it is emphasised that this may be dependent on the way in which the infrared spectra are obtained. It is concluded that the use of fast transient cycling switching techniques may provide useful mechanistic information under certain circumstances.

In situ FTIR characterization of NH 3 adsorption and reaction with O 2 and CO on Pd-based FCC emission control additives

The adsorption of NH 3 and its reaction with O 2 and CO over Ce n+ /Na +/γ-Al 2O 3 and Pd/Ce n+ /Na +/γ-Al 2O 3 was examined by FTIR spectroscopy in a wide range of temperatures. Ammonia undergoes decomposition on the surfaces of these materials at elevated temperatures with a fraction of the NH 3 species being oxidized by lattice oxygen to NO x , which is trapped on the surface in the form of nitrites. The presence of O 2 in the feed accelerates the formation of surface nitrite and nitrate species. The reaction of these species with ammonia at 400 °C is fast, producing N 2. The presence of CO in the gaseous feed leads to the formation of surface isocyanates, presumably through the reaction with partially dehydrogenated surface NH x species. The PdO component mildly promotes the formation of these isocyanate species. Both the NCO and NO 3 −/NO 2 − species identified on the surfaces of these materials at elevated temperatures are active intermediates, participating in further reactions which ultimately lead to the reduction of NO x and CO emissions. The contribution of these intermediates to a possible N 2 formation reaction network should be accounted for when FCC regenerators are operating under partial or incomplete burn combustion modes.

In situ FT-IR investigation of the reduction of NO with CO over Au/CeO2-Al2O3 catalyst in the presence and absence of H2

The NO+CO+H2 reaction over CeO2, Au/CeO2 (3wt% Au), Au/CeO2-Al2O3 (2.9wt% Au, 20wt% Al2O3) and CeO2-Al2O3 mixed support prepared by co-precipitation has been studied by FT-IR spectroscopy at elevated temperatures. Formation of NCO species has been detected on all of the samples. The presence of metallic gold is not necessary for the generation of the isocyanates on ceria and the mixed ceria-alumina support. The NCO species are produced by a process involving the dissociation of NO on the oxygen vacancies of the support, followed by the reaction between N atoms lying on the surface and CO molecules. Gold plays an important role in the modification of ceria leading to Ce3+ and oxygen vacancies formation, and causes significant lowering of the reduction temperature of CeO2 and CeO2-Al2O3 enhancing the reducibility of ceria surface layers. The role of H2 is to keep the surface reduced during the course of the reaction. The onset temperature, at which the interaction between the surface isocyanates and NO begins, is low (100°C). This explains the high activity of the Au/CeO2-Al2O3 catalyst with 100% selectivity in the reduction of NO by CO at low temperature (200°C) and in the presence of H2.

In situ FTIR characterization of the adsorption of CO and its reaction with NO on Pd-based FCC low NO x combustion promoters

The adsorption of CO and its reaction with NO in the 400–600 °C temperature range on Ce n+ /Na +/γ-Al 2O 3 and Pd n+ /Ce n+ /Na +/γ-Al 2O 3 type materials used commercially as FCC additives were monitored by FTIR spectroscopy. Exposure of both types of samples to CO leads to the formation of carboxylates and carbonates. The concentration of these species was higher in samples containing Pd, indicating that palladium catalyzes their formation. The Pd n+ cations initially present in these samples undergo partial reduction to form metallic Pd in the presence of CO even at room temperature. More complete reduction of Pd, along with some aggregation, was observed after exposure to CO at elevated temperatures. Exposure of both types of samples to NO/CO mixtures in the 400–600 °C temperature range leads to the formation of surface isocyanate species. Both Na + and Ce n+ promote the formation of such NCO species. However, surface isocyanate species were formed with substantially higher rates in the presence of palladium. The formation of the isocyanate species strongly correlates with changes observed in the ν OH region, indicating that hydroxyls actively participate in the surface chemistry involved and are capable of protonating the NCO species. The isocyanates are also reactive towards O 2 and NO yielding CO 2 and N 2. These results suggest that isocyanates are possibly involved as intermediates in the CO–NO reaction over the materials examined.

Skin Exposure to Aliphatic Polyisocyanates in the Auto Body Repair and Refinishing Industry: A Qualitative Assessment

Although respiratory exposures have been the primary concern with isocyanates, skin exposure also can occur and may contribute to sensitization and asthma. Methodologies to assess isocyanate skin exposure in the workplace are limited and skin exposure data scarce. The goals of this study were (i) to evaluate and validate the isocyanate colorimetric indicators against a quantitative assay, (ii) to evaluate the extent of isocyanate surface contamination and skin exposure among auto body shop workers and (iii) to evaluate isocyanate skin exposure determinants. The colorimetric indicators were compared with a high-performance liquid chromatography (HPLC) quantitative assay based on the National Institute for Occupational Safety and Health Method 5525 using paired laboratory sampling. The colorimetric indicators were then used to assess surface contamination and skin exposure to aliphatic isocyanates in 35 auto body shops and 124 workers as part of an epidemiologic study. The positive sample rate was calculated for various surfaces, body parts and tasks. The color intensity of the colorimetric indicators was rated on a scale 0 (yellow color) to 5 (deep red). Side-by-side comparisons of the qualitative method with the quantitative HPLC assay were also performed in the field using paired samples. Laboratory and field evaluation validated use of the colorimetric indicators. The rate of positive surface samples for isocyanates was 46% (n = 145/313). Thirty-four percent (73/216) of samples were positive for unprotected skin and 20% (n = 22/111) for skin under latex gloves. The highest positive rate observed on skin samples was obtained after paint mixing and spraying tasks. The colorimetric indicators were highly specific for isocyanates, but false negatives occurred when compared with the more sensitive HPLC quantitative assay. The presence of surface contamination and the performance of paint-related tasks were the major determinants of isocyanate skin exposure. This study documents extensive surface contamination and skin exposure, including under gloves, to aliphatic polyisocyanates during painting and paint mixing tasks in auto body shop workers. Contaminated surfaces and aerosol deposition during spray painting may both contribute to skin exposure. The colorimetric indicator is a quick, practical and low-cost, but not highly sensitive, industrial hygiene tool to detect isocyanate surface contamination and skin exposures following the use of isocyanate-containing products.

In situ characterization of interaction of ammonia with carbon surface in oxygen atmosphere

The adsorption and oxidation of ammonia over carbons differing in the chemical structure of surface functional groups have been investigated by FTIR spectroscopy. The reactions of NH 3 with carbons have been studied both in the presence and in the absence of oxygen. As a result of NH 3 chemisorption, in addition to ammonium salts, there are formed surface amide and imide structures. At the higher temperature surface isocyanate species are formed. Thermal stabilities of surface structures, formed as a result of NH 3 chemisorption have been determined by means of FTIR spectroscopy. The activity and selectivity of carbons for the selective catalytic oxidation (SCO) of NH 3 to N 2 with excess O 2 has been shown by microreactor studies at 295–623 K. Carbon catalysts are very active for NH 3 oxidation. Nitrogen is generally the predominant product of ammonia oxidation. The selectivity to N 2, N 2O and NO is determined by the surface oxygen coverage and reaction temperature. The data obtained indicate that the N 2 is formed via selective catalytic reduction (SCR) between NH x surface species and NO formed from NH 4 + oxidation. This implies that ammonia is activated in the form of NH 4 + species for both SCR and SCO processes.