Improvement of Water Resistance of Hemp Woody Substrates through Deposition of Functionalized Silica Hydrophobic Coating, while Retaining Excellent Moisture Buffering Properties

This paper reports on the development of a novel treatment for hemp shiv that improves resistance to liquid water and protects hemp shiv from biodegradation without impacting the natural ability of the shiv to buffer moisture vapor. The hydrophobic surface was produced by depositing silica nanoparticles, which were prepared by the functionalization of silica nanoparticles with hexamethyldisilazane (HMDS). The surface chemical composition was determined showing replacement of surface silanols on the silica nanoparticles with trimethyl groups. The specific surface area of silica nanoparticles decreased after the trimethylsilyl treatment. The surface modifications reduced the level of hysteresis between absorption and desorption isotherms and also the total amount of moisture absorbed by the silica nanoparticles. The surface of the hemp shiv was initially hydrophilic but became hydrophobic once the material was treated, demonstrating contact angle with water of 120°. The results show the coating layer of functionalized silica on the hemp shiv reduced water absorption from 400% (untreated shiv) to 250%. However, the moisture buffer value results showed that the coating films do not limit the access of moisture to adjacent pores in the hemp shiv, and the functionalized silica coating layer retains the moisture buffering ability of hemp shiv.