Abstract
The effects of impregnation with nanosilver suspension as well as heat treatment on pull-off adhesion strength and specific air permeability in beech specimens were studied here. The size range of silver nanoparticles was 30–80 nm. The cross-section of specimens was cold-sprayed with unpigmented sealer-clear, polyester, and lacquer paints. Heat treatment, as the most commonly used wood modification, was applied at three different temperatures of 145, 165, and 185 °C. Results showed that the highest and lowest pull-off strengths were found in the un-impregnated and unheated specimens painted with polyester (8.98 MPa) and the unpainted unheated nanosilver-impregnated specimens (3.10 MPa), respectively. Impregnation with nanosilver resulted in the rupture of perforation plates and pit openings, and eventually, permeability increased significantly. As for the pull-off adhesion strength, the increased permeability resulted in the adhesive being penetrated in to the pores in the wood substrate, and eventually, a significant decrease in the pull-off strengths occurred. No significant correlation was found between pull-off strength versus specific air permeability, although both properties depend on the porous structure. This was due to the fact that permeability depends on the continuous pore system, while pull-off strength is dependent on the surface pore system of the substrate.
Highlights
As solid woods are natural porous media, many of their properties depend on the size of the pores, the way they are interconnected or isolated from the neighboring pores, and even the quality of the surface of the pores [1,2,3,4]
The only treatment showing a decreasing trend in permeability caused by heat treatment was NStime and height
Results of the permeability tests showed that the lowest specific gas permeability was observed in specimens before NS-impregnation or heat treatment (NS-heat-treated at 165 ◦ C (HT-165) treatment, 6.898 × 10−13 m3 m−1 ), and the highest was found in NS-heat-treated at 185 ◦ C (HT-185) after NS-impregnation (15.576 × 10−13 m3 m−1 )
Summary
As solid woods are natural porous media, many of their properties depend on the size of the pores, the way they are interconnected or isolated from the neighboring pores, and even the quality of the surface of the pores [1,2,3,4]. Thermal modification is generally considered the most commercially-used wood modification method [11]. It has been recognized as a method to improve the dimensional stabilization of wood and increase its decay resistance [11,12,13]. Thermal modification at high temperatures has decreasing effects on some mechanical properties of wood. Thermal modification is mostly carried out between the temperatures of Coatings 2019, 9, 723; doi:10.3390/coatings9110723 www.mdpi.com/journal/coatings
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