Investigation on wax-impregnated wood: part 2: study of void spaces filled with air by He pycnometry, Hg intrusion porosimetry, and 3D X-ray imaging

Although available on the market, hot melting wax treated wood is not studied in detail as such lacking knowledge on the quantification of wax and remaining air voids. Therefore, in this paper Scots pine (Pinus sylvestris L.) and beech (Fagus sylvatica L.) samples were impregnated with a hot melting amid wax. The apparent densities were measured with helium pycnometry and mercury intrusion porosimetry. The pore size distribution was determined by using mercury intrusion porosimetry and samples were visualized with 3D X-ray tomography. The remaining air void spaces were calculated with all three methods. The apparent densities ranged from 1.18 g cm-³ till 1.19 g cm-³ for treated pine and 1.21 g cm-³ till 1.23 g cm-³ for treated beech. As a result of the wax impregnation, the pore volume decreases from 65-68% to 12-13% for pine and from 53-58% to 7-9% for beech. The pore size distribution shifts to smaller pores. The ratio of the micropores measured by mercury intrusion porosimetry is overestimated. On the one hand blocked large pores are compressed by the movement of wax deposits under high pressure during the mercury intrusion porosimetry (“movement-effect”). On the other hand large pores remain unaccessible or are only accessible via smaller openings (“bottle-neck-effect”). Non-invasive 3D X-ray imaging detects such macropores but the size of the detected pores is limited by the obtained resolution. Therefore both mercury intrusion porosimetry and X-ray tomography are complementary techniques