Densified wood impregnated with phenol resin for reduced set-recovery

Abstract

Thermal-hydro-mechanical (THM) densification treatments were performed on Populus spp. (poplar), Picea abies (spruce), and Fagus sylvatica (beech). Prior to THM treatment, a low-molecular weight resin was impregnated into the wood structure. Densification results, mechanical characteristics (modulus of elasticity, rupture, and hardness), and set-recovery were assessed. All wood species were exposed to the same THM treatment and the specific anatomy, density, and physical behaviors yielded results specific to wood species making comparisons between species difficult. However, the mechanical performance of all samples was largely dictated by the specimens' surface density as seen in the density profiles. Spruce specimens had high levels of set-recovery after the THM treatment, which is believed to be caused by pit aspiration from kiln drying, limiting impregnation of the resin. The THM treatment used in this study was successfully applied to poplar, spruce, and beech. The resin impregnation combined with THM treatment led to densified wood with improved mechanical properties. The improvements were the greatest in poplar, including the largest reduction in setrecovery, which was the objective of this study. When comparing mechanical properties to commercially available structural wood-composites the results from this study indicate that resin impregnated THM treated wood could be used in this application.

Creep Properties of Densified Wood in Bending

“…The densification leads to an improvement by about 64% on the MOR. When combining resinimpregnation with densification, RI-D showed further increases on the MOR due to the impregnation induced higher density and permanent swelling of the cell wall [36,37]. The thermal modification, however, slightly reduced the densification-induced MOR improvement, presumably because the non-crystalline cellulose, hemicellulose and extractives were thermally degraded [7,10].…”

Densified wood dowel reinforcement of timber perpendicular to the grain: a pilot study

“…In this study, densification is carried out using a process known as thermo-mechanical densification by heating the timber and subjecting it to a compressive force. Additionally, timber can be densified by impregnating the voids between the cell walls with different materials such as molten metals/sulphur and polymers (Bodig & Jayne, 1993;Kollmann et al, 1975;Schwarzkopf, 2020) however, this is not considered in this study. The degree to which the timber has been densified is often termed the compression ratio.…”

Geometric recovery by humidification of densified wood of eight Mexican species

“…Después de su humidificación, las probetas densificadas mostraron una recuperación radial geométrica promedio de 59,3 % (Tabla 2). Este resultado es efecto del incremento del contenido de humedad desde el estado inicial de la madera densificada de 7 %, hasta su estado saturado en promedio de 60,1 % y es comparable a los reportados por Schwarzkopf (2020) Para la madera sin densificar, el contenido de humedad promedio de todas las especies se incrementó desde 8,9 % hasta 57,8 %. Así, el efecto de la humedad retenida en la madera se manifiesta en el aumento del espesor de las probetas y se evalúa con la higroexpansión radial cuyo promedio fue de 2,8 % (Tabla 2).…”

“…Agrar. 2021; 23(2):73-80 de reducir la recuperación geométrica de la madera densificada se aplican tratamientos de impregnación con resinas sintéticas, ceras y monómeros de vinil (Khalil et al, 2014;Pelit y Emiroglu, 2020;Schwarzkopf, 2020). En el mismo sentido, existe evidencia empírica de que el densificado de la madera modifica sus características higroscópicas (Khalil et al, 2014;Hajihassani, Mohebby, Najafi y Navi, 2018).…”