Moisture and weathering

Adhesives (qv) used to make plywood are classified as either the exterior adhesive or the lesser quaHty interior adhesive. The terms relate to the abUity of the adhesive to survive exposure to moisture and weather. PhenoHc resins (qv) are commonly used as adhesives to make plywood. The difference between interior and exterior phenoHc resin adhesive is the filler level. Exterior rated plywood uses higher resin content adhesives. Interior rated plywood uses either highly extended (below 24% resin soHds) or protein-based adhesives. The adhesive is appHed to the veneer by roU coating, spraying, curtain coating, or foam extmsion. 

Foundry core oil. CNSL resins are known to impart good scratch hardness to sand core after they are baked [133,134,137,167]. It also provided resistance to moisture and weathering and good green strength, and surface finish to molded articles. 

Urea and melamine are tetra- and hexa-functional molecules. However, the formation of a network polymer is prevented by adding alcohols such as w-butanol and by condensing with formaldehyde at low temperatures under basic conditions. While phenol resins have better moisture and weather resistance than urea resins, the latter are preferred for light-colored... 

Of great practical interest are sealants and compounds from low-molecular silicone elastomers, which in the presence of such solidifying agents as alkoxyaminosilanes (ADE-3, AHM-9), acetoxyorganosilanes, etc. solidify at room temperature in contact with humidify in air. They have good moisture and weather resistance, endure high and low tempera-... 

Glass reinforced composites are noted for their resistance to moisture and weathering, but they tend to lost their strength in the presence of high humidity and elevated temperatures... 

Although linear polyester resins do not readily undergo heat curing, they form extremely flexible paint films with excellent adhesion to metal substrates. Poiyisocyanate resins are more resistant to hydrolysis than amino resins. Polyester-polyurethane paints therefore exhibit improved resistance to moisture and weathering but are more expensive. 

ZnO has a hardness of 4.5 it is used mainly as a filler for elastomers, PP, and polyesters. The composite made of PP filled with ZnO shows a great resistance to moisture and weathering. ZnO can also react with free carbonyl groups in polyester resins, leading to composites with remarkable physical properties. 

Xanthate dmms should be kept as cool and dry as possible. Protection from moisture is the most important factor. A combination of moisture and hot weather causes sodium ethyl xanthate to ignite spontaneously (14). 

Many factors influence the corrosion of metals in the atmosphere, including the natural phenomena that make up the vagaries of climate and weather. Of these, the feature of greatest importance is moisture in its various forms, since, other factors apart, the amount of corrosion that takes place is largely a question of whether and how long a period the surface of the metal is wetted ( time of wetness ). 

The main value of salt-spray tests is in the evaluation of the effectiveness of phosphate coatings in restricting the spread of rust from scratches or other points of damage in a paint film. This feature is of particular interest to the motorcar industry, as vehicles are often exposed to marine atmospheres and to moisture and salt when the latter is used to disperse ice and frost from road surfaces. Great care is needed in the interpretation of a salt-spray test, as it has been found to favour thin iron phosphate coatings more than is justified by experience with natural weathering. In the motorcar industry the present custom is to use zinc phosphate coatings on the car bodies and all other parts exposed to the outside atmosphere. 

The architect continues to look for products that can he multifunctional. As an example in roofing, the product could perform a part or all of the functions. The roof has to provide structural integrity, temperature and sound insulation, vapor and moisture control, weather resistance, elastic qualities for change in weather, fire protection, aesthetic appeal, and so on. 

Modeling The numerical model UNSAT-H was used to predict the annual and cumulative percolation through the cover. The model was calibrated with 12 months of soil moisture content and weather data. Following calibration, UNSAT-H predicted a cumulative percolation of 50 cm for the ET cover and 95 cm for a conventional cover over a 10-year period. The model predicted an annual percolation of approximately 0 cm for both covers during the first year. During years 3-10 of the simulation, the model predicted less annual percolation for the ET cover than for the conventional cover. 

Effects of solarization were found related to a combination of many parameters, though most authors agreed that soil temperature and moisture, climate and weather, and type and properties of mulching film are key factors for solarization results (Katan et al. 1987 Stapleton and DeVay 1995). 

Weathering is clearly a more complicated case than heat ageing alone, because there are temperature effects added to the light and probably other agents such as moisture and ozone as well (see Sections 4.4 and 6.8). Not surprisingly there is no very widely accepted relationship equivalent to Arrhenius. The result is that many workers have developed empirical relations which are usually only shown to be applicable to a narrow range of materials and conditions. 

Cellulosics are inherently moisture- and UV-sensitive, requiring efficient stabilization. Cellulose acetate is particularly sensitive to water and weathering. 

Herbs harvested for drying need to be collected with as little moisture on them as possible. A dry, warm, but not too sunny day provides ideai conditions. The ideal time is after overnight moisture has dissipated but before strong sunlight has caused the voiatiie oiis to evaporate. In most cases this is around midmorning, depending on the climate and weather conditions. 

The pressure in Denver is about three-fourths of that at sea level. While changes in elevation have pronounced effects on atmospheric pressure, temperature and moisture also affect atmospheric pressure. Changes in the moisture and temperature of air masses produce high and low pressure systems that move across the continent dictating our weather. Pressure increases underwater because the water pressure adds to the atmospheric pressure. Ten meters (33 feet) of water is equivalent to 1 atmosphere of pressure. 

---