Dimensional Stability, Uv Resistance, and Static Mechanical Properties of Scots Pine Chemically Modified with Alkylene Epoxides

Unprotected wood exposed outdoors suffers from photodegradation due to absorption of UV light by lignin and dimensional changes because of moisture absorption or desorption by free hydroxyl groups in wood constituents. Chemical modification of cell wall polymers is one of the effective methods of inducing dimensional stability and UV resistance in wood. In this work, etherification of Scots pine (Pinus sylvestris L.) was carried out with alkylene epoxides. Extracted blocks of Scots pine were modified with propylene oxide (PO) and butylene oxide (BO) between 30 and 75 C for different durations and under varying alkaline conditions. Different weight percent gains (WPG) were obtained. WPG increased with temperature, reaction time, and NaOH concentration. The dimensional stability, mechanical properties, and UV resistance of chemically modified wood were evaluated. Etherified wood exhibited an improvement in dimensional stability, but the efficacy dropped with successive water-soaking, oven-drying cycles, indicating a loss of modifying chemical. After four soak-dry cycles, both modifications retained positive anti-swelling efficiency (ASE) values; however, at WPG values >30%, the PO modified material exhibited a reduction in ASE, indicating cell wall degradation. Both PO and BO modified wood exhibited a loss in static mechanical properties measured as modulus of elasticity and modulus of rupture, with the reduction being dependent upon the level of modification. Modification of wood with PO provided partial photo stability to wood polymers, whereas BO was more promising in improving dimensional stability.