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  • Author: Y.-C. Zhang x
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Abstract

Knowledge of pH and buffering capacity of raw fiber materials is important for understanding the effects of raw material on the curing rate of urea formaldehyde (UF) resin, used for panel manufacturing, especially with some less-desirable wood materials such as bark, top, and commercial thinnings.

The effects of pH and buffering capacity as well as catalyst content on the gel time of UF resin were investigated. The results obtained from this study indicate that bark has a lower pH value as well as higher acid and alkaline buffering capacities than wood of the same species due to their extractives. The pH values of the raw fiber materials studied decrease with increased absolute and relative acid buffering capacity due to the increased absolute acidity mass in the solution.

At lower levels of added catalyst, the effect of raw material pH on UF resin gel time is significant, while it is insignificant at higher catalyst contents. This may be due to the acidity of wood, which is the main acid catalyst source of the mixture at lower levels of added catalyst, while at higher levels, catalyst is the main source. With higher catalyst contents, all studied raw materials mixed with UF resin result in a longer gel time than does UF resin alone.

Mono- and 1,1-dinitrocyclobutanes (highly diluted in Ar) were pyrolyzed at temperatures 860–1300 K in reflected shocks. Activation energies for their initial fragmentations were derived from measurements of relative rates of species loss, compared to cyclobutyl chloride and isopropyl bromide: k uni(NCB) = 9.66 × 1012 exp (-25264/T), s-1, k uni(DNCB) = 6.26 × 1012 exp (-21087/T), s-1 The production and decay of NO2 was monitored in real time via its absorption at 405 nm. The identity and amounts of the species produced during 1.3 ms residence time were determined by FTIR and GC analysis of samples extracted from the tube terminus, after being quenched by an expansion wave. Plausible mechanisms that account for the observed product distributions are proposed. In a computational Appendix, the results of density functional theory (DFT) calculations are presented for enthalpies and entropies of several mono-substituted cyclobutanes and for 1,1-dinitrocyclobutane, as well as for selected fragmentation products.

Abstract

This study demonstrates that relative sea level trends calculated from long-term tide gauge records can be used to estimate relative vertical crustal velocities in a region with high accuracy. A comparison of the weighted averages of the relative sea level trends estimated at six tide gauge stations in two clusters along the Eastern coast of United States, in Florida and in Maryland, reveals a statistically significant regional vertical crustal motion of Maryland with respect to Florida with a subsidence rate of −1.15±0.15 mm/yr identified predominantly due to the ongoing glacial isostatic adjustment process. The estimate is a consilience value to validate vertical crustal velocities calculated from GPS time series as well as towards constraining predictive GIA models in these regions.