Glassy state of wood polymers in native and thermally modified wood: effects on long-term material performance in service

Abstract

This research analyses the effect of a glassy state of wood polymers, as found in some dense naturally durable wood species and in thermally modified wood (TMW), on their equilibrium moisture content, mechanical and fungal resistance (durability) performance. In the EN350-class I durability range, moisture and fungal durability are argued to become controlled by the physical state of wood polymers rather than their chemical composition. Glassy polymers may assist the dimensional stability and fungal resistance of wood, as characterised by standardised accelerated laboratory tests. However, for long-term mechanical performance and fungal resistance in service, strong cross-links must prevent the natural (aging) relaxation of the glassy state. Physical aging is expected to occur in TMW, as opposed to naturally durable wood species. The current test methodology for dimensional and fungal stability does not take physical aging effects in wood polymers into account.