Deposition of Hydrophobic Functional Groups on Wood Surfaces Using Atmospheric‐Pressure Dielectric Barrier Discharge in Helium‐Hexamethyldisiloxane Gas Mixtures

Abstract

This work examines the functionalization of sugar maple (Acer saccharum) and black spruce (Picea mariana) wood surfaces using an atmospheric‐pressure dielectric barrier discharge in He and He/HMDSO (hexamethyldisiloxane) gas mixtures. Wood samples were placed on one of the electrodes and the plasma was sustained by applying a 3.5 kV peak‐to‐peak voltage at 12 kHz. Analysis of the discharge stability through current–voltage (I–V) characteristics revealed a filamentary behaviour, in sharp contrast with the homogeneous He discharge obtained with a glass sample. Optical emission spectroscopy performed near the wood vicinity revealed strong N2 and ${\rm N}_{{\rm 2}}^{{\rm + }} $ emissions, suggesting that wood outgassing plays an important role in the evolution of the discharge regime. Analysis of the surface wettability through water contact angle (WCA) measurements indicated that freshly sanded wood samples treated in He/HMDSO plasmas became more hydrophobic with WCAs in the 120°–140° range depending on treatment time and wood species. Attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy measurements on samples exposed to He/HMDSO plasmas revealed the deposition of hydrophobic Si(CH3)3‐O‐Si(CH3)2, Si(CH3)3 and Si(CH3)2 functional groups as well as an increase of the CH‐to‐OH band intensity ratio. For relatively thick coatings, the WCA following natural aging under uncontrolled conditions remained constant at 132° ± 3° which highlights the stability of the plasma‐deposited thin films, a very promising result for structural and decorative outdoor applications.

Dimensional Stabilization of Wood

“…It has a water contact angle value of 130° [30]. HMDSO can be mixed with different gases, such as He [33], N 2 [29] and SF 6 [34], and used as a precursor during plasma treatment, which improves the hydrophobic characteristics of wood surfaces. The results suggest varying degrees of successful water repellency, depending on the gas mixture, plasma exposure time, wood species, and distance between plasma source and wood substrate.…”

Creation of superhydrophobic wood surfaces by plasma etching and thin-film deposition

“…Hexamethyldisiloxane (HMDSO) has also been shown to be a viable film precursor to create hydrophobicity on various wood surfaces [2,9,17,[20][21][22]. Fluorine-containing monomers such as CF 4 [23], and SF 6 [9] have been reported to modify the hydrophobicity of spruce, chestnut poplar, and pine wood surfaces.…”

“…These concerns have inspired the search for alternative methods that modify only the outer surface layer of the wood. Vapor phase approaches such as those that use glow discharges or plasmas for the functionalization of wood surfaces are of much interest [17].…”

Nanocomposite coatings and plasma treatments for wood-based products

“…Massines et al (2012) presented various processes to obtain thin film deposition using atmospheric pressure plasma-enhanced chemical vapour deposition (AD-PECVD), as well as different reactor configurations and discharge modes. Furthermore, the durability of such films on a living material such as wood should be investigated, as only one group presented results on the ageing of wood treated with He/HMDSO (Levasseur et al, 2012). Furthermore, the durability of such films on a living material such as wood should be investigated, as only one group presented results on the ageing of wood treated with He/HMDSO (Levasseur et al, 2012).…”