Using low-field NMR and MRI to characterize water status and distribution in modified wood during water absorption

In this study, synergism between two wood modification methods was investigated with the aim of providing insights into improving wood hydrophobicity. Loblolly pine (Pinus taeda) was modified using two variants of the same treatment procedure: in the first case, paraffin wax emulsion (PWE) impregnation was followed by thermal modification (TM); in the second case, the order was reversed, and TM was followed by PWE impregnation. The treated samples were then immersed in distilled water for 1, 6, 24, 48 or 96 h. Low-field nuclear magnetic resonance (LF-NMR) and nuclear magnetic resonance imaging (MRI) were employed to evaluate the concentration of different water components, as well as the water distribution. The results indicated that the combined treatment showed much better performance than either treatment individually, particularly when PWE impregnation was followed by TM. Moreover, through the use of MRI, we characterized the role of both methods in the synergistic relationship, which showed that the PWE impregnation increased the wood hydrophobicity through decreasing free water absorption, while the TM performed the same function through bound water absorption. In addition, paraffin wax penetrated the newly formed cracks caused by TM, which also contributed to the synergistic mechanism between PWE impregnation and TM.