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When free hydroxyl groups are transformed to acetoxy groups, the ability of the wood to absorb water is greatly reduced, rendering the wood more dimensionally stable and, because it is no longer digestible, extremely durable. In general, softwoods naturally have an acetyl content from 0.5 to 1.5% and more durable hardwoods from 2 to 4.5%.
Other polymers, such as polyethylene and polystyrene, do not normally absorb much moisture, but are able to carry significant moisture on their surface when exposed to liquid water. [ 33 ] Type-6 nylon (a polyamide ) can absorb up to 9.5% of its weight in moisture.
A slab of pykrete Pykrete is made of 14% sawdust and 86% water by mass.. Pykrete (/ ˈ p aɪ k r iː t /, PIE-creet) [1] is a frozen ice composite, [2] originally made of approximately 14% sawdust or some other form of wood pulp (such as paper) and 86% ice by weight (6 to 1 by weight).
The bulk of water contained in the cell lumina is only held by capillary forces. It is not bound chemically and is called free water. Free water is not in the same thermodynamic state as liquid water: energy is required to overcome the capillary forces. Furthermore, free water may contain chemicals, altering the drying characteristics of wood.
Sapwood (or alburnum [15]) is the younger, outermost wood; in the growing tree it is living wood, [16] and its principal functions are to conduct water from the roots to the leaves and to store up and give back according to the season the reserves prepared in the leaves. By the time they become competent to conduct water, all xylem tracheids ...
Some surprising results in studies on aerial roots of orchids show that the velamen (the white spongy envelope of the aerial roots), are actually totally waterproof, preventing water loss but not allowing any water in. Once reaching and touching a surface, the velamen is not produced in the contact area, allowing the root to absorb water like ...
Trees can explode when struck by lightning. [3] [15] [16] [17] The strong electric current is carried mostly by the water-conducting sapwood below the bark, heating it up and boiling the water. The pressure of the steam can make the trunk burst. [3] [17] This happens especially with trees whose trunks are already dying or rotting.
As more ice formed, more of the incoming solar radiation was reflected back into space, causing temperatures on Earth to drop. Whether the Earth was a complete solid snowball (completely frozen over), or a slush ball with a thin equatorial band of water still remains debated, but the ice–albedo feedback mechanism remains important for both cases.