BBE 1001 Lecture Notes - Lecture 8: Volume Fraction, Supreme Headquarters Allied Powers Europe, Sorption
16 Dec 2017
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Moisture impacts on size, shape, & use (wood) Moisture could reside in cell wall or lumen. Moisture has a strong affinity to the cell walls, whose polymeric components provide water sorption sites. Cell wall: s2 (mainly) of secondary layer. Center remains the same size, outside of cell gets larger (cell wall absorbs it) S2 layer is thicker and vertical microfibrils. Length of microfibrils are much greater than diameter. Ray cells: outside to center, holes that attach to cell wall, keeps tree from peeling. Keep from swelling from inside to outside of tree. Microfibrils get turned so they are no longer completely vertical. Does not shrink or swell in radial direction as much as in the tangential direction. % swelling = (increase in dimension or volume/dry dimension or volume)*100. % shrinkage = (decrease in dimension or volume/green dimension or volume)*100. In most board the widest face is the tangential side. Longitudinal shrinkage: the smallest change ~0. 1% or less.
