Modification of hardwood samples in the flowing afterglow of N2–O2 dielectric barrier discharges open to ambient air

Abstract

The effect of O 2 addition in the gas feed of an open-to-air N 2 -O 2 dielectric barrier discharge (DBD) on the surface modification of sugar maple hardwood samples is reported. After treatment by N 2 -O 2 plasma, an increase of the contact angle with water and a decrease of the contact angle with diiodomethane was observed. X-ray photoelectron spectroscopy and Fourier-transform infra-red analyses further reveal a decrease of the O/C as well as increase of the C=O peak and surface aromaticity. When O 2 is added to the nominally pure N 2 DBD, the discharge transits from a homogeneous regime to a filamentary regime with increased dissipated power and neutral gas temperature. As a result, surface modification by N 2 -O 2 plasmas becomes similar to those occurring under a low-temperature heat treatment of wood surfaces. In such conditions, a mechanism involving the thermally-activated deacetylation and depolymerisation of hemicelluloses and cross-linking between lignin and furfural and hydroxylmethylfurfural, leading to the increase of wood hydrophobicity is proposed.

Interaction of N and O atoms with hardwood and softwood surfaces in the flowing afterglow of N2‐O2 microwave plasmas

“…Oxygen atoms created by reaction (7) will then be consumed in reaction (5) to form an excited NO(B) state which will decay to NO(X) by emission of the NO β system. It is worth highlighting that reaction (7) and reaction (5) are in competition for the consumption of N atoms.…”

“…It is worth highlighting that reaction (7) and reaction (5) are in competition for the consumption of N atoms. Since reaction (7) is much quicker than reaction (5), [9] the intensity of the NO β emission will first increase with the incorporation of NO and will then decrease at a given concentration when not enough N atoms remain to react with O atoms by reaction (5). As a consequence, when the population of NO becomes strictly equal to the population of N atoms, all N atoms become consumed by reaction (7) such that the creation of NO(B) and thus the emission from NO β vanish.…”

“…). In previous studies, we investigated the role of each of the plasma‐produced species on the modification dynamics of wood surfaces in the flowing afterglow of N 2 , O 2 , and N 2 ‐O 2 dielectric barrier discharges at atmospheric pressure (open‐to‐air configuration) . It was found that O atoms and ozone produced in the flowing afterglow play a very important role in the improvement of the wettability with water and most likely lead to an etching of the wood surface (mostly cellulose and hemicelluloses).…”

“…In previous studies, we investigated the role of each of the plasmaproduced species on the modification dynamics of wood surfaces in the flowing afterglow of N 2 , O 2 , and N 2 -O 2 dielectric barrier discharges at atmospheric pressure (open-to-air configuration). [4,5] It was found that O atoms and ozone produced in the flowing afterglow play a very important role in the improvement of the wettability with water and most likely lead to an etching of the wood surface (mostly cellulose and hemicelluloses). In order to further understand the specific role of these plasma-produced species on the wood surface modification dynamics, in particular regarding the etching kinetics by O atoms, we have performed additional investigations in the flowing afterglow of a N 2 -O 2 reduced-pressure plasma sustained by surface wave in the microwave regime.…”

Enhancing the water repellency of wood surfaces by atmospheric pressure cold plasma deposition of fluorocarbon film

“…Additionally, the plasma-wood interactions are complex because the plasma source produces active species that can provide a large number of chemical and physical changes in the main constituents presented in the wood surface, including cellulose, lignin, hemicelluloses and extractives. 36 Depending on the plasma conditions applied and the initial conditions of the substrate, the surface energy of the wood increases or decreases.…”