Permeability of wood impregnated with polyethylene wax emulsion in vacuum

Abstract

Polyethylene wax (PEW) has emerged as a commonly used material for maintaining the quality of wood. The emulsification of solid PEW before being injected into wood can effectively overcome the shortcomings of the high-temperature melting and injection process of solid PEW. The permeability of Eucalyptus (Eucalyptus saligna) and Mongolian Scotch pine (Pinus sylvestris var. Mongolica) to PEW emulsion in vacuum environment was investigated using impregnation tests, and steaming pretreatment and microwave irradiation pretreatment were applied. The small particle size and low viscosity of the PEW emulsion, whose median particle size was 0.256 μm and viscosity was 52.2 mPa s (at 60 r/s), facilitated its penetration into the wood capillary system. The weight percent gain (WPG) of Eucalyptus and Mongolian Scotch pine post impregnation in vacuum was positively correlated with both the vacuum-holding time and the impregnation temperature, but after 60 min of impregnation the WPG of both wood species decreased significantly. Both pretreatment methods could substantially improve the wood permeability and effectively promote the penetration of the PEW emulsion into the wood. The maximum WPG was achieved when Eucalyptus and Mongolian Scotch pine were respectively steamed for 80 min and 120 min. There was an increase of 0.24 times for the former and an increase of 0.53 times for the latter compared to unpretreated wood. Both species exhibited the highest WPG after water immersion for 60 min (with average moisture content close to their fibre saturation point) and microwave irradiation for 30 s, which was respectively 0.28 and 0.75 times higher than that of unpretreated wood. There was a significant variation in WPG between the two species with the same pretreatment method. The relatively lower density and better-developed capillary system of Mongolian Scotch pine allowed more efficient penetration of PEW emulsion. It is recommended that, considering the time cost and practical enhancement, microwave irradiation should be given priority to when pretreating wood.