Performance of hydroxyapatite mineralised beech and pine wood: Wettability and biological resistance

This study investigates the effects of hydroxyapatite (HAp) mineralisation on the water-related properties and biological resistance of beech and pine wood. As HAp synthesis also produces the highly water-soluble by-product NH 4 NO 3 , particular emphasis was placed on comparing unleached and leached samples to distinguish the effects of HAp and NH 4 NO 3 . During outdoor exposure, HAp effectively inhibited mould and blue stain fungi. In laboratory mould tests, this effect was observed only in leached samples, suggesting that the HAp mineral layer contributes to protection by physically blocking the wood pores. Fungal decay tests showed a significant improvement in unleached HAp-synthesised samples, with the highest median Δ m value for B-HAp samples at 6.4% and for P-HAp samples at 5.6%; both corresponded to durability class 2. In contrast, leached samples showed lower resistance, with beech and pine classified in durability classes 4 (Δ m for B-HAp-L 20.4%) and 3 (Δ m for P-HAp-L 11.8%), respectively. However, the soil contact test showed limited protection for all HAp synthesised samples. Overall, using the Meyer–Veltrup model, mineralisation with HAp was found to improve D Rd rel. factors for pine in both leached and unleached samples, with values of 4.7 and 4.4, respectively. HAp synthesised beech samples showed comparable improvements (D Rd rel. = 4.1), although these were considerably smaller in the leached samples (D Rd rel. = 1.8). Higher D Rd rel. factors resulted from improved decay resistance, as HAp treatment did not improve water-related properties.