Formaldehyde emissions from non-structural wood composites are regulated and the regulation target is urea-formaldehyde (UF) resin. UF resins are hydrolytically unstable and constantly emit formaldehyde as a function of temperature and relative humidity. When heated, wood also generates formaldehyde, but this was of little concern until 2010 when formaldehyde regulations became much more demanding. This regulation motivated the industry to account for all formaldehyde sources, synthetic as from resin, and biogenic as from wood. This effort represents first steps towards quantifying biogenic and synthetic contributions to formaldehyde emissions in non-structural wood composites. It is possible to distinguish the 13C/12C isotope ratio of UF resins from the isotope ratio of plant biomass. Conditions during and after composite hot-pressing promote reactions that generate formaldehyde from wood and UF resin, and the kinetic isotope effect continuously lowers the product isotope ratios as a function of yield. If such isotope fractionation did not occur, it would be a simple matter to quantify contributions of wood and UF resin to formaldehyde emissions using static isotope ratios. Isotope fractionation, therefore, complicates the requirements for distinguishing biogenic and synthetic formaldehyde in wood composite emissions. Those requirements are 1) establish the reference carbon isotope ratios in wood and in UF resin (just the formaldehyde portion of UF), and 2) estimate the kinetic isotope effects in formaldehyde generation by wood and cured UF resin. The latter requirement fixes a range for the respective isotope ratios; the numerical ranges enable a simple model of the average isotope ratio for a mixture of biogenic and synthetic formaldehyde in wood composite emissions. Finally, the measured isotope ratio of captured emissions would be compared to the model. This work did not achieve all aspects of the requirements mentioned, but a solid foundation was established for future completion of the ultimate goals. In reference to requirement 1, the carbon isotope ratio of experimental Pinus taeda wood was accurately measured (including some isolated fractions) using isotope ratio mass spectroscopy (IRMS). IRMS of UF resin first requires removal of urea carbons- UF resin was subjected to acid hydrolysis and capture of the resin formaldehyde into aqueous ammonium hydroxide. This provided a nearly quantitative conversion (negligible isotope fractionation) of resin formaldehyde into hexamine for IRMS. Using this hexamine method, the formaldehyde carbon isotope ratios of two industrial UF resins were accurately measured, demonstrating basic feasibility for the project goal. Estimating the kinetic isotope effect (Requirement 2) required creation of a thermochemical reactor, where wood or cured UF resin was heated under N2 flow such that the emitted formaldehyde was easily captured. In this case, conversion of captured formaldehyde into hexamine was abandoned in favor of silica gel cartridges loaded with sodium bisulfite. Isolation and IRMS of the formaldehyde-bisulfite adduct were effective and considered easily transferable to industrial settings. This system was employed to measure fractionation in cured resin as a function of relative humidity, and in Pinus taeda wood as a function of relative humidity, temperature, and time. More information about isotope fractionation is required; but most notable was the fractionation behavior in wood where evidence was found for multiple formaldehyde generating reactions. Overall, this work established feasibility for the goals and laid the foundation for future efforts. / Master of Science / Home-interior products like cabinetry are often produced with wood composites adhesively bonded with urea-formaldehyde (UF) resin. UF resins are low cost and highly effective, but their chemical nature results in formaldehyde emission from the composite. High emissions are avoided, and the federal government has regulated and steadily reduced allowable emissions since 1985. The industry continuously improved UF technologies to meet regulations, as in 2010 when the most demanding regulations were implemented. At that time, many people were unaware that wood also generates formaldehyde; this occurs at very low levels but heating during composite manufacture causes a temporary burst of natural formaldehyde. Some wood types produce unusually high formaldehyde levels, making regulation compliance more difficult. This situation, and the desire to raise public awareness, created a major industrial goal: determine how much formaldehyde emission originates from the resin and how much originates from the wood. These formaldehyde sources can be distinguished by measuring the carbon isotope ratio, 13C/12C. This ratio changes and varies due to the kinetic isotope effect. Slight differences in 13C and 12C reactivity reveal the source as either petrochemical (synthetic formaldehyde) or plant-based (biogenic formaldehyde). This work demonstrates that achieving the industry goal is entirely feasible, and it provides the analytical foundation. The technical strategy is: 1) establish reference isotope ratios in wood and in UF resin, and 2) from the corresponding wood composite, capture formaldehyde emissions, measure the isotope ratio, and simply calculate the percentage contributions from the reference sources. However, a complication exists. When the reference sources generate formaldehyde, the respective isotope ratios change systematically in a process called isotope fractionation (another term for the kinetic isotope effect). Consequently, this effort developed methods to measure fractionation when cured UF resin and wood separately generate formaldehyde, with greater emphasis on wood. Isotope fractionation in wood revealed multiple fractionation mechanisms. This complexity presents intriguing possibilities for new perspectives on formaldehyde emission from wood and cured UF resin. In summary, this work demonstrated how source contributions to formaldehyde emissions can be determined; it established effective methods required to refine and perfect the approach, and it revealed that isotope fractionation could serve as an entirely novel tool in the materials science of wood composites.

published_or_final_version / Pathology / Master / Master of Medical Sciences

No description available.

Thesis (Ph. D.)--Columbia University, 1932. / Vita. Bibliography: p. 31.

Thesis (M.S.)--University of Wisconsin--Madison, 1981. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 107-109).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1981. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 150-160).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1973. / Typescript. Vita. Description based on print version record. Includes bibliographical references (leaves 110-124).

The reactions of iodomethane, diiodomethane, and formaldehyde over stoichiometric, O-terminated, and Cl-terminated α-Cr₂O₃ surfaces, were studied by thermal desorption spectroscopy. Adsorbed formaldehyde forms dioxymethylene species on the nearly-stoichiometric surface that react primarily above 600 K. Dioxymethylene decomposes via a Cannizzaro-type process with dehydrogenation to formate, and hydrogenation to methoxide. Methoxide hydrogenation produces methane and methanol near 670 K. Formate decomposition occurs at 720 K, producing acetylene, carbon monoxide, carbon dioxide and formic acid. The site requirements for these reactions are a cation/anion site pair. When the surface cations are capped with Cl, the reactivity associated with dioxymethylene intermediates above 600 K is not observed. At higher coverages, polymerization to paraformaldehyde is observed on both surfaces, and decomposition to formaldehyde is observed at 400 K in thermal desorption. Iodomethane and diiodomethane are used as sources of methyl and methylene surface species, respectively. Methyl fragments on the stoichiometric surface dehydrogenate to surface methylene and hydrogen as a rate limiting step to produce ethylene and methane at 505 K. On the oxygen-terminated surface, the methyl fragments undergo dehydrogenation and coupling to ethylene at 425 K, undergo oxygen insertion to formaldehyde at 425 K, and produce carbon dioxide, formic acid, and water above 700 K from the dehydrogenation of formate. Methylene fragments on the stoichiometric surface undergo diffusion limited coupling to ethylene at 390 to 490 K and produce methane at 520 K from dehydrogenation. On the oxygen-terminated surface, methylene undergoes oxygen insertion to produce formaldehyde at 450 K, produce carbon monoxide, formaldehyde, and water at 695 K from dioxymethylene dehydrogenation, and produce carbon dioxide, formic acid, and water above 700 K from the dehydrogenation of formate. / Ph. D.

Prior studies have found that human exposure to hazardous air pollutants (HAPs) occurs in homes; however, the depth of these assessments was limited by the extent of the analyzed data. The present Ph.D. dissertation focused on air contaminants of concern in residential buildings, the possible sources of these pollutants, and population subgroups with greater contaminant risk. This research also evaluated the effects of building characteristics and household activity patterns on indoor pollution and risk levels. To this end, an in-depth analysis was performed of data from the Relationships of Indoor, Outdoor and Personal Air (RIOPA) study, one of the most comprehensive exposure assessments to date. Using personal concentrations from the RIOPA study, a cancer risk assessment was performed to identify both important pollutants and populations at higher risk. The analyzed compounds were acetaldehyde, benzene, chloroform, carbon tetrachloride, p-dichlorobenzene (p-DCB), ethylbenzene, formaldehyde, methylene chloride, methyl tert-butyl ether (MTBE), styrene, trichloroethylene and tetrachloroethylene. Results indicate that Hispanics and non-Hispanic whites had median cumulative cancer risks (CCR) of 520×10-6 and 440×10-6, respectively, for which the main contributors were formaldehyde, p-DCB, acetaldehyde, chloroform and benzene. Statistically significant differences in CCR between and within Hispanic and whites were primarily due to exposures to p-DCB. Exposure to formaldehyde was further investigated because this compound was the largest contributor to CCR for 69% of Hispanics and 88% of whites, and because most participants had similar cancer risks from these exposures (median = 260×10-6, coefficient of variance = 28%). Results suggest that the U.S. population may be experiencing chronic exposures because of long-term formaldehyde emissions from pressed-wood materials bound with urea-formaldehyde resins. Source removal may be the most effective way to decrease these chronic exposures. Benzene was also examined further because it is a known human carcinogen. Results show that indoor benzene concentrations increased as the proximity of parked vehicles decreased. Residing in a home with an attached garage could lead to exposures to benzene ten times higher than while commuting in a car in heavy traffic, and with mean excess cancers of 17×10-6. Detached garages could reduce health risks from exposure to benzene and other gasoline-related pollutants. / text

A measurement of the stable carbon isotopic composition of atmospheric formaldehyde was undertaken as a means of testing current photochemical theories. Sulfito surfaces were shown to meet the stringent analytical requirements of the project; an extensive characterization of these surfaces was performed for the first time. Models were developed to describe the chemical evolution of the surfaces during sampling. It was established that potassium salts have more favorable properties for an atmospheric collection system than do sodium salts. Considerable selectivity in collection was also demonstrated. A highly selective multistep procedure for the isolation and chemical oxidation of collected formaldehyde was developed expressly for this project. A previously unreported combination of reagents, HgCl₂ and AgClO₄, was used in the final reaction step of the procedure. Through the use of synthetic samples, the method was shown to be isotopically reproducible and highly chemically selective. The first data for the carbon-13 content of atmospheric formaldehyde have been obtained, with an observed mean value of δ¹³C = -17‰. This value is enriched in carbon-13 over the known atmospheric sources of formaldehyde; isotopic fractionation in the atmosphere is therefore indicated. It is believed that fractionation due to photolysis can account for the observed effect.