The Extent of Tebuconazole Leaching from Unpainted and Painted Softwood

Exposure to water and high air humidity may affect the preservation of wood products as many preservatives are water-soluble and thus likely to leach. In this study, depletion of a common fungicide, tebuconazole (TAZ), from treated wood was investigated using a 14C-labeled tracer. The wood species and treatment technique were chosen to be representative of products such as windows and doors; specifically, ponderosa pine was dip treated with a solvent-based, metal-free formulation. The impact of different aqueous settings including high air humidity, and either simulated continuous or intermittent rain was evaluated over a period of two months. Along with the exposure type, the effect of end-grain sealing on TAZ loss was explored. Despite the exposure of treated wood to laboratory-simulated harsh environmental conditions, more than 60% of the originally sorbed TAZ remained in the wood under all scenarios. While high air humidity did not lead to TAZ depletion, simulated continuous rain led to a TAZ leaching mainly from the end grain. TAZ leaching was found to be higher for unpainted wood, where up to 40% of the originally sorbed TAZ was prone to depletion from an end grain. End-grain sealing with water-based primer and paint led to a substantial two-fold reduction of TAZ leaching. Unexpectedly, wood exposure to intermittent rain caused additional TAZ loss that could not be explained only by water leaching

Advancing Molecular Weight Determination of Lignin by Multi-Angle Light Scattering

Due to the complexity and recalcitrance of lignin, its chemical characterization is a key factor preventing the valorization of this abundant material. Multi-angle light scattering (MALS) is becoming a sought-after technique for absolute molecular weight (MW) determination of polymers and proteins. Lignin is a suitable candidate for MW determination via MALS, yet further investigation is required to confirm its absolute MW values and molecular size. Studies aiming to break down lignin into a variety of renewable products will benefit greatly from a simple and reliable determination method like MALS. Recent pioneering studies, discussed in this review, addressed several key challenges in lignin’s MW characterization. Nevertheless, some lignin-specific issues still need to be considered for in-depth characterization. This study explores how MALS instrumentation manages the complexities of determining lignin’s MW, e.g., with simultaneous fractionation and fluorescence interference mitigation. Additionally, we rationalize the importance of a more detailed light scattering analysis for lignin characterization, including aspects like the second virial coefficient and radius of gyration

Distinguishing Enolic and Carbonyl Components in the Mechanism of Carboxylic Acid Ketonization on Monoclinic Zirconia

This study contributes toward understanding the mechanism of catalytic formation of mixed ketones in an attempt to improve their selectivity vs symmetrical ketones. A pulsed microreactor placed inside a gas chromatograph–mass spectrometer instrument was used to identify the source of carbonyl group and quantify its distribution among products of zirconia-catalyzed cross-ketonization reaction of a mixture of carboxylic acids, with the carbonyl group of one of the acids selectively labeled by ¹³C. A concept of enolic and carbonyl components in the ketonization mechanism was introduced to distinguish the sources of alkyl and acyl groups, respectively. The least branched acid was found to be the predominant source of CO₂, the essential byproduct of ketonization. Thus the least branched acid is the preferred source of the alkyl group of the cross-ketone product, while the most branched acid provides the acyl group. Increased branching at the α carbon next to the carbonyl group decreased the reactivity of both the enolic and the carbonyl components. Following a pseudo first order kinetic analysis, the relative reaction rates for a common enolic component with a pair of different carbonyl components were measured by the method of competing reactions to obtain mechanistic insights. The distinction between two possible paths in the cross-ketonization mechanism was characterized quantitatively by assessing the difference in activation energies; the results obtained were explained by the steric effect of substituents. On the basis of detailed kinetic analysis, the rate-limiting step most likely occurs after the enolic component activation

An Approach to the Estimation of Adsorption Enthalpies of Polycyclic Aromatic Hydrocarbons on Particle Surfaces

Current atmospheric models incorporate the values of vaporization enthalpies, <i>Δ<i>H</i></i>_vap, obtained for neat standards, thus disregarding the matrix effects on volatilization. To test the adequacy of this approximation, this study measured enthalpies of vaporization for five polycyclic aromatic hydrocarbons (PAHs) in the form of neat standards (<i>Δ<i>H</i></i>_vap) as well as adsorbed on the surface of silica, graphite, and graphene particles (<i>Δ<i>H</i></i>_vap^eff), by using simultaneous thermogravimetry-differential scanning calorimetry (TGA-DSC). Measurement of the corresponding activation energy values, <i>E</i>_a^vap and <i>E</i>_a vap^eff, by TGA using a derivative method was shown to be the most reliable and practical way to assess <i>Δ<i>H</i></i>_vap and <i>Δ<i>H</i></i>_vap^eff. Enthalpies of adsorption (<i>Δ<i>H</i></i>_ads) were then calculated from the differences between <i>E</i>_a^vap and <i>E</i>_a vap^eff, thus paving a way to modeling the solid–gas phase partitioning in atmospheric particulate matter (PM). The PAH adsorption on silica particle surfaces (representing n−π* interactions) resulted in negative values of <i>Δ<i>H</i></i>_ads, indicating significant interactions. For graphite particles, positive <i>Δ<i>H</i></i>_ads values were obtained; i.e., PAHs did not interact with the particle surface as strongly as observed for PM. PAHs on the surface of graphene particles evaporated in two stages, with the bulk of the mass loss occurring at temperatures lower than those with the neat standard, just as on graphite. Yet, unlike graphite, a small PAH fraction did not evaporate until higher temperatures compared to case of the neat standards and other particle surfaces (37.4–145.7 K), signifying negative, more PM-relevant values of <i>Δ<i>H</i></i>_ads, apparently reflecting π–π* interactions and ranging between −7.6 and +32.6 kJ mol^–1, i.e., even larger than for silica, −3.3 to +8.3 kJ mol^–1. Thus, current atmospheric models may underestimate the partitioning of organic species in the particle phase unless matrix adsorption is taken into account

Triacylglyceride Thermal Cracking: Pathways to Cyclic Hydrocarbons

Thermal cracking of triacylglyceride (TG) oils results in complex mixtures, containing nearly 20% cyclic hydrocarbons, which can be further processed into middle-distillate transportation fuels and byproduct chemicals. The occurrence patterns of cyclic products obtained via the thermal cracking of several TG feedstocks, such as canola and soybean oils, as well as triolein and tristearin (conducted at 430–440 °C in the absence of catalysts under vacuum), were investigated to probe possible formation mechanisms. Detailed gas chromatographic characterization furnished full molar homology/molecular size and partial isomeric profiles for cyclopentanes, cyclopentenes, cyclohexanes, cyclohexenes, aromatics, and polycyclic aromatic hydrocarbons (PAHs). It was found that the data were inconsistent with previously proposed mechanisms involving the Diels–Alder reaction as a single pathway. An alternate mechanism was proposed and supported with experimental evidence based on the intramolecular cyclization of alkenyl and alkadienyl radicals formed as a result of TG cracking. The product homology profiles corroborate the proposed mechanism and show the depletion of medium-size alkenes coupled with the accumulation of corresponding monocyclic hydrocarbons (those with the matching number of carbon atoms). Similarly, the product mixtures were depleted of long-chain alkyl-substituted monocyclic hydrocarbons because of the formation of the corresponding PAHs as long as sufficient time is available. Entropy appears to determine the type and size of cyclic hydrocarbons formed