Weather-resistive barriers

Figure 29.3 Weather-resistance barrier installation in a wall structure. Adapted from Hall and Hoigard [26].

US Department of Energy. Weather resistive barriers. Technology Fact Sheet 769. Jun. 2000. 

Butt TK. Water resistance and vapor permeance of weather resistance barriers. J ASTM Int 2005 2 1. 

It is through the solid state characteristics of polymers that we - as users - primarily interact with them. For convenience, we can divide the principal properties of polymers into five categories mechanical, optical, surface contact, barrier, and electrical. Weather resistance is a sixth category that can influence each of the other five categories. In order to understand these properties we must be able to quantify them. In this chapter we shall concentrate on measurement techniques, since it is through these methods that we learn how a polymer will behave during use. 

Because the primary threat to active security barriers is that vehicles will attempt to crash through them, their most important attributes are their size, strength, and crash resistance. Other important features for an active security barrier are the mechanisms by which the barrier is raised and lowered to allow authorized vehicle entry, and other factors such as weather resistance and safety features. 

EVAs (polyolefin copolymer) have exceptional barrier properties, good clarity and gloss, stress-crack resistance, low temperature toughness/ retains flexibility, adhesion, resistance to UV radiation, etc. They have low resistance to heat and solvents as well as exceptional weathering resistance. 

Adhesives have very broad range of performance requirements. The performance spectrum ranges from pressure sensitive products where almost minimal adhesion is required, to extremely high performance adhesives with strength equivalent to that of metals. But the scope of the adhesive s performance goes well beyond adhesive strength. Flowability, force to adhere and mechanical, thermal, electrical, barrier, and optical properties as well as chemical and weather resistance and rheological behavior all must be considered in adhesive formulations. These essential parameters are discussed below from the point of view of the influence of fillers. 

Bottles and containers are the major products of blow molding. The major novelties in this technology are probably due to application of multilayered products to improve mechanical performance, barrier properties, and weathering resistance. These are products of different polymer layers and as such they are not discussed here. 

Nano-clay incorporated polymer coatings are important for modifying properties of surfaces. Nano-clay incorporated thermoset polymer nanocoatings exhibit superior properties such as super-hydrophobicity, improved wettability, excellent resistance to chemicals, corrosion resistance, improved weather resistance, better abrasion resistance, improved barrier properties and resistance to impact, scratches, etc. [116]. The parameters such as dipping time, temperature, nature of surfactant, and purity of nanomaterials decides the coating thickness. Clay-epoxy coating... 

Outside the chemically resistant layers comes the structural portion, which is designed primarily for strength. The exterior surface of the pipe, again, is rich in resin and usually is opaque. Ultraviolet (UV) screeners should be used in outdoor piping to improve its weather resistance. When chlorine has a relatively high hydrogen content, the barriers to UV and visible radiation can prevent photochemical initiation of the hydrogen-chlorine reaction. 

Finishing coats are also fine barrier layers, but applied as the last layer rather than the first one. Because they have to cure in air, UP resins remain tacky due to the influence of atmospheric oxygen, have an unpleasant odor, are not weather resistant, and swell up with a whitish color in rain. 

These types of asphalt have poor adhesion to wet surfaces, but some have a damp-bonding ability. Type II asphalt has excellent vapor-barrier properties and better weather resistance than types III or IV. Contrary to type... 

Hepatic mixed-function oxidase activities demonstrated seasonal trends, with higher specific activities in the cold weather months in both populations with few differences in enzyme activities or cytochrome levels between the two populations. Metabolism of aldrin, dieldrin and DDT was similar between the two populations. R fish have larger relative liver size and, therefore, a greater potential for xenobiotic metabolism. However, biotransformation appears to be of minor importance in chlorinated alicyclic insecticide resistance in mosquitofish barriers to penetration appear to be of greater importance and an implied target site insensitivity appears to be the most important factor in resistance. 

Nylon, amorphous PET. PETG Excellent abrasion resistance, moisture sensitive Good barrier properties, not weatherable. clarity dependent on processing, orientation greatly increases physical properties... 

The main apparent technical problems posed in relation with these types of potential noise barriers would be their noise abatement capability, structural performance, fire resistance, weatherability, chemical activity, and environmental effects. To assess the quality of new products of such materials, a series of mechanical, noise abatement, and flammability tests should be performed on a number of samples from the panels made of recycled rubber products. The primary function of these panels, i.e., their noise abatement capability is among the most important aspect of their performance. 

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