Mechanical interaction between cellulose microfibrils and matrix substances in wood cell walls induced by repeated wet-and-dry treatment

We measured the lattice spacing of the cellulose in sugi (Cryptomeria japonica D. Don) and hinoki (Chamaecyparis obtusa Endl.) cell walls under wet and dry conditions. We gave all specimens repeated wet-and-dry treatments and tried to induce substantial changes in the microstructure of the wood cell wall. Macroscopic dimensions, measured using a micrometer, showed well-known behaviors, that is, shrinkage by drying and swelling by wetting, which were unaffected after the repeated wet-and-dry treatments in both longitudinal and tangential directions. On the other hand, lattice spacing, measured using an X-ray diffractometer, showed different results. In particular, d (200) lattice spacing expanded considerably with drying in the early stages of repeated wet-and-dry treatments. The d (200) lattice spacing in the dried specimen then became gradually smaller in the later stages, whereas no such dynamic change was observed in d (004) lattice spacing throughout the repeated wet-and-dry treatments. Once the d (200) lattice spacing in the dried specimen had become smaller after giving wet-and-dry treatments, it did not recover, even after soaking in distilled water for 1 month. These results suggest that repeated drying and re-swelling caused structural changes in the wood cell wall, specifically an interfacial separation between cellulose microfibrils and matrix substances.