The protective coatings of the lignocellulose-based composite boards formed using the drying and semi-drying oils

Abstract

Modern eco-friendly thermal insulation materials are produced using lignocellulose containing materials. The boards made of such composites are susceptible to excess humidity that accelerates the biodegradation process. In this work, hydrophobic protective coatings on the lignocellulose-based composite boards (LCB) formed using drying oils such as a tung tree, linseed, and semi-drying hempseed oil were studied. The LCBs were made of hemp shives, corn starch binder and flame retardants such as expanded graphite or multifunctional aqueous mixture based on phosphorus and nitrogen organic compounds. The hydrophobic coatings were formed in the vacuum desiccator by covering boards with specific oil types. After this, LCBs covered with oil were maintained at 40℃, 90℃, or 120℃. The respective protective films were formed by the autooxidation and polycondensation mechanisms. The hydrophobic protective coatings were imaged by scanning electronic microscopy (SEM) to monitor (Fig.1) the hemp shivs with the respective film made of either hemp seed, linseed or tung tree oil. Also, it was demonstrated that the compressive strength (at 10% of relative deformation) of such composite boards with the oil protective coatings compared to the untreated boards increased up to 4.5 fold and could reach up to 14 MPa, the bending strength increased by 2.78 fold up to 19 MPa, the water absorption decreased around 4-fold (from 1.34 kg/m2 to 0.37 kg/m2 ), swelling in thickness decreased from 7.51% to 4.59%, while the thermal conductivity remained unchanged and was around 0.085 W/(m·K). It was concluded that the most desired properties of such materials were obtained when the tung tree oil was used for coating.