UV light, protection

Up to 52 wt % is permitted to be shipped in uv light-protected polyethylene dmms. Double headed aluminum dmms are permitted for 70% shipments but have not been used for some years. 

To act as UV stabilizers, UV absorbers must be present at a finite concentration in order to fully absorb harmful UV light. At practically used concentrations, this means that a finite absorbing thickness is required. In the case of thin films [poly(ethylene) for agricultural use] or fibers (polypropylene fibers) this thickness criterion is not met and UV absorbers offer inadequate UV light protection. 

Fig. 7. Typical coextruded sheet structures used for barrier food packaging. Functional properties (a) retortability, high oxygen and moisture barrier (three extruders) (b) heat sealability, oxygen and moisture barrier, low taste and odor transfer, thermoformabdity (four extruders) (c) oxygen and moisture barrier, uv light protection, heat sealability, ther-moformability (five extruders).

CAUTION avoid skin and eye exposure to UV light. Protect your eyes with goggles. 

In terms of resin chemistry, the clearcoats are based on a hydroxy-functional polyester and aciylic-resin blend. The polyester is responsible for providing the high flexibility at low temperature. The hardener is based on hexamethy-lene diisocyanate (HDI) trimer. Ultraviolet absorbers (UVA), and hindered amine light stabilizers (HALS) are additives added to absorb UV light, protect the basecoat pigments and to quench free radicals that could deteriorate and decompose the backbone resins. 

Stabilizers. Antioxidants provide protection against UV light and thermal oxidative degradation. Hindered phenols are the most common nonstaining antioxidants. For SBR latices, two additional type of stabilizers must be used. 

The optimum wavelength for UV sterilization is around 260 nm. A suitable source for UV light in this region is a mercury lamp giving peak emission levels at 254 nm. These sources are generally wall- or ceiling-mounted for air disinfection, or fixed to vessels for water treatment. Operators present in an irradiated room should wear appropriate protective clothing and eye shields. 

Polypropylene (PP) is a crystalline polymer suitable for low-stress applications up to 225°F (105°C). For piping applications this polymer is not recommended above 212°F (100°C). Polypropylene is shielded, pigmented, or stabilized to protect it from uv light. Polypropylene is often a combination of polyethylene and polypropylene which enhances the ductility of the polymer. 

The adhesive was developed for application to seal food containers with alumina foils and to seal glass plates. In this case, the vinyl polymerization step can be carried out by UV light radiation through the already mounted glass plates with a photoactive radical initiator to cure the viscous adhesive material. Another application of this material is the development of diffusion barrier containing protective coatings on medieval stained glasses (31). 

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