Understanding the effect of extractives on the mechanical properties of the waterborne coating on wood surface by nanoin
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Understanding the effect of extractives on the mechanical properties of the waterborne coating on wood surface by nanoindentation 3D mapping Yan Wu1,2,*
, Haiqiao Zhang1,2, Lechen Yang1,2, Siqun Wang3, and Yujie Meng4
1
College of Furnishings and Industrial Design, Nanjing Forestry University, Nanjing 210037, Jiangsu, China Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, Nanjing Forestry University, Nanjing 210037, China 3 Center for Renewable Carbon, University of Tennessee, Knoxville, TN 37996, USA 4 Nanomechanics, Inc., Oak Ridge, TN 37830, USA 2
Received: 6 August 2020
ABSTRACT
Accepted: 16 September 2020
The extractives in wood have been proved to have some effect on the permeability and adhesive quality of the waterborne coating. Due to the hydrophobic property of extractives, water in aqueous coatings does not easily enter the wood cell wall, which affects the performance of the waterborne coating. Herein, a nanoindentation 3D mapping experiment was performed on the bonding areas between the waterborne coating, extractive-free wood and control wood, respectively. The variability of the reduced elastic modulus (Er) and the hardness (H) was evaluated for an area of 100 lm by 100 lm. Overall, the Er and H of the waterborne coating were different from the values of wood. It demonstrated that the extraction procedure had a negative impact on the Er and H of the waterborne coating. The average values of Er and H of the coating area were both higher when coated on the control wood sample surface (Er: 2.836 GPa, H: 0.105 GPa) than on the extractive-free one (Er: 2.390 GPa, H: 0.079 GPa). However, the average values of Er and H in the wood increased by 50.43% and 33.67% after extraction, respectively. This study will help to understand the adhesion mechanism of the interface between the waterborne coating and the wood.
Published online: 24 September 2020
Springer Science+Business
Media, LLC, part of Springer Nature 2020
Handling Editor: Stephen Eichhorn.
Address correspondence to E-mail: [email protected]
https://doi.org/10.1007/s10853-020-05347-2
1402 Introduction In terms of chemical composition, wood is composed of a large amount of organic polymers and a small amount of oligomers. Polymers include cellulose [1], hemicellulose and lignin [2–4], which are mainly found in the cell walls of wood. Oligomers mainly refer to ash and various extractives such as lipids, phenolic compounds, terpenoids, fatty acids, resin acids, steryl esters, sterols, and waxes. Extractives are materials soluble in neutral solvents, which are not generally considered part of the wood polymer structures, so these materials should be removed before any chemical analysis of wood [5]. Although extractives only account for a small proportion of wood, its presence could affect the wood’s heating value [6], thermal stability [7], the color of heartwood [8], anisotropic shrinkage [9], contact angle and free energy [10], and, thus, have an impact on the pulp and paper manufacture [11], gluing and fin
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