Surface-sealed wood

FIGURE 1.236 Modular constructed injection mold made from surface-sealed wood... 

Sealer n. (1) A liquid coat which seals wood, plaster, etc., and prevents the surface from absorbing paint or varnish may be transparent may at as a primer for a following coat or as a finish for the surface. (2) A coat, applied in hquid form, which is laid over a tar-like substance to prevent its bleeding through an applied paint film. Wicks ZN, Jones FN, Pappas SP (1999) Organic coatings science and technology, 2nd edn. Wiley-Inter science. New York. 

In modern usage and for many applications, primers usually are thin films (75 //m or less), and may be used on both metal and wood surfaces. On wood, their function is to seal the grain or to provide a smooth base for topcoats. On concrete, they should be compatible with the alkaline surface and help improve both adhesion and the life of subsequent coats. 

In order to prevent such damages, surfaces are sealed and/or biocides are deposited in the wood. Surface sealing is typically done by painting with substances containing biocides, UV blockers, and materials that prevent moisture penetration. 

In Roman times tar and pitch from Pinaceae resinous wood were used to treat the inner surface of amphorae to store fluids such as wine [ 145,149] and to seal ship planks [89,144], Heating treatments applied to natural resins and resinous wood profoundly modify the chemical composition of the original material. Diterpenoid compounds undergo aromati-zation, demethylation and decarboxylation reactions, with the formation of new compounds of a lower molecular weight that show a high degree of aromatisation [87,88]. In tar and pitch produced from Pinaceae resin and woods, retene is considered as a stable end product of these reaction pathways and nor-abietatrienes, simonellite and tetrahydroretene represent the intermediates of these reactions [87,89,150]. 

When painting wood, the most important step is to thoroughly sand the wood to a smooth finish. All burrs and rough spots must be removed, and the surface should be silky smooth to the touch. After cleaning the wood, one should give it two coats of primer. This neutral colored paint soaks into the grain and seals it. Once dried, the wood is ready for two more coats of the final color. 

Chromium(VI) oxide nitrate is a dark red liquid which boils at 63 to 65° at 0.7 mm. Hg pressure. It is soluble in carbon tetrachloride. In water, it reacts immediately to form chromic and nitric acids. It is a more powerful oxidizing agent than vanadium (V) oxide nitrate, and care must be taken to avoid contact with hydrocarbons. It is corrosive to most metallic surfaces, except aluminum, and reacts in the same manner as vanadium (V) oxide nitrate does toward paper, wood, and rubber. It cannot be stored for so long a time as vanadium (V) oxide nitrate but is relatively stable in a sealed ampul in the absence of light and moisture. It can be purified by distillation in vacuum over lead(IV) oxide. 

In the standing, living tree the bordered-pit membranes between softwood fibers act as valves to prevent the spread of air or bubbles into sap-filled cells in the event of tree injury and potential rupture to vertical water columns. Unfortunately, they perform a similar function in the processing of wood into commercial products. For example, during wood drying, substantial capillary and surface tension forces are developed upon water retreat from the fiber lumens through the pits, and the membranes move effectively (particularly in earlywood) to seal the apertures in the direction of water... 

Extractive exudation is a common feature of larches, pines, and spruces, and is particularly marked in heartwood samples. It can be controlled to some extent by sealing with an aluminium primer. During high temperature drying of resinous samples of radiata pine heartwood some migration of extractives occurs so that resin accumulates either on or near the surface in a way that is deleterious to wood finishing. 

Oil and petroleum products evaporate in a slightly different manner from water and the process is much less dependent on wind speed and surface area. Oil evaporation can be considerably slowed down, however, by the formation of a crust or skin on top of the oil. This happens primarily on land where the oil layer does not mix with water. The skin or crust is formed when the smaller compounds in the oil are removed, leaving the larger compounds, such as waxes and resins, at the surface. These then seal off the remainder of the oil and prevent evaporation. Stranded oil from old spills has been re-examined over many years and it has been found that when this crust has formed, there is no significant evaporation in the oil underneath. When this crust has not formed, the same oil could be weathered to the hardness of wood. 

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