Radiation unsaturated polyesters

The free radicals then initiate curing by attacking residual double bonds in acrylic oligomers and monomers, or in styrene and unsaturated polyester resins. Since most pigments absorb u.v. radiation and can prevent it reaching sufficient photoinitiator molecules, this technique is best suited to transparent coatings or thin pigmented layers (e.g. inks). 

Coating materials may be based on short or medium-oil alkyds (e.g. primers for door and window frames) nitrocellulose or thermoplastic acrylics (e.g. lacquers for paper or furniture finishes) amino resin-alkyd coatings, with or without nitrocellulose inclusions, but with a strong acid catalyst to promote low temperature cure (furniture finishes) two-pack polyurethanes (furniture, flat boards) unsaturated polyester resins in styrene with free-radical cure initiated by peroxides (furniture) or unsaturated acrylic oligomers and monomers cured by u.v. radiation or electron beams (coatings for record sleeves paperback covers, knock-down furniture or flush interior doors). 

Unsaturated polyester finishes of this type do not need to be stoved to effect crosslinking, but will cure at room temperature once a suitable peroxide initiator cobalt salt activator are added. The system then has a finite pot life and needs to be applied soon after mixing. Such a system is an example of a two-pack system. That is the finish is supplied in two packages to be mixed shortly before use, with obvious limitations. However, polymerisation can also be induced by ultra violet radiation or electron beam exposure when polymerisation occurs almost instantaneously. These techniques are used widely in packaging, particularly cans, for which many other unsaturated polymers, such as unsaturated acrylic resins have been devised. 

Ultralow-monol polyols, 223 Ultrapek, 327, 328 Ultraviolet (UV) radiation, 209 Ultraviolet spectroscopy, 490 Unimolecular micelle, 58 United States, phenolic production in, 375 Unsaturated maleate/O-phthalate/ 1,2-propanediol polyester prepolymer, 101-102 Unsaturated polyester resins (UPRs), 19, 29-30, 58-59... 

Solid urethane and polyester acrylates may be used as main components of radiation curable powders. Together with suitable unsaturated polyesters, powders are formed, which give low-film-flow temperatures and allow separating of film formation from curing. This technology has been used successfully in powder coating of wood and plastics. ... 

The free-radical cure mechanism of the vinyl ester resins is well understood. In most respects, it is similar to that of the unsaturated polyester resins. To initiate the curing process, it is necessary to generate free radicals within Ike resm mass. Organic peroxides are tlie most common source of free radicals. These peroxides will decompose under the influence of elevated temperatures or chemical promoters, e.g., organometallics or tertiary amines, to form free radicals. Generation of free radicals also can be effected by ultraviolet or high-energy radiation applied directly to the resin system. The free radicals thus formed react to open the double bond... 

Pucic I, Ranogajec F (2003) Phase separation during radiation crosslinking of unsaturated polyester resin. Radiat Phys Chem 67(3—4) 415—419... 

A simultaneous IPN of epoxy with unsaturated polyester, cross-linked using microwave radiation, has been reported (1). The radiation was intended to yield a more isotropic structure because of uniform heating also, it could reduce grafting reactions between the two networks and produce a more classical IPN structure. Unfortunately, the mechanical properties and morphology of the network were not reported. 

As an alternative to PEG treatment of waterlogged wood, attempts have been made to use a radiation curing method involving a range of monomers and resins. The aim of such treatments is to reduce treatment times and achieve a more stable artefact. Styrene, vinyl acetate, acrylonitrile, acrylates and methacrylates are the most studied monomers in the treatment of waterlogged archaeological wood. The most widely used of these monomers is the water-soluble vinylpyrrolidone and methacrylamide and the non-water soluble chemicals such as n-butyl methacrylate monomer or unsaturated polyester resin. 

Crosslinking - Reaction or formation of covalent bonds between chain-like polymer molecules or between polymer molecules and low-molecular compounds such as carbon black fillers. As a result of crosslinking, polymers such as thermosetting resins may become hard and infusible. Crosslinking is induced by heat, UV or electron-beam radiation, oxidation, etc. Crosslinking can be achieved either between polymer molecules alone as in unsaturated polyesters or with the help of multifunctional crosslinking agents such... 

Few institutions have been involved in this conservation method. In most cases, the work is limited to laboratory research studying monomer impregnation with more or less satisfactory results. Up to now, radiation treatment of waterlogged wooden artifacts on a large scale was performed by impregnation with unsaturated polyester resins only. The different processes studied since the late 1960s are summarized as follows. 

Jurkin, T. and Pudc, 1.2006. Post-irradiation crosslinking of partially cured unsaturated polyester resin. Radiat. Phys. Chem. 75 1060-1068. 

Pucid, I. and Jurkin, T. 2008. Radiation and postirradiation crosslinking and structure of two unsaturated polyester resins. Polym. Eng. Sci. 48 176 -1777. 

Pucid, I. and Ranogajec, F. 1995. DC-electrical conductivity as a method for monitoring radiation curing of unsaturated polyester resins. 1. Measurement conditions and comparison with extraction analysis data. Radiat. Phys. Chem. 46 365-370. 

When polymerization is used as the hardening principle, reactive components combine to form the binder, e.g., unsaturated polyesters with styrene or acrylate monomers. Here, one component often behaves as a reactive solvent for the other, and low-emission coating systems are the result. Cross-linking can be carried out at room temperature (cold curing) or by radiation curing. 

Polyester Paints. Binder based on unsaturated polyester resins (copolymerized with styrene), low emission of organic solvents, catalytic curing by organic peroxides or UV radiation, highly resistant to abrasion, alcohols, and other chemicals (cleaning agents). 

In motor vehicles, long glass fiber-reinforced parts with a matrix consisting of unsaturated polyester resin (SMC/sheet molding compounds) are used for example in front-ends, radiator grills, or bumper (frames). After utilization, they are discarded as waste by workshops or as part of the plastic and composite material share in used vehicles. 

UNSATURATED POLYESTER AND ACRYLICS 213 Radiation curing polyesters and acrylics... 

Nanocomposites of thermoset polymers like unsaturated polyester and epoxy can be fabricated by this method. In this process, the monomers/ prepolymers are allowed to intercalate the layer spacing of the clay platelets. Polymerization will then be initiated either by the application of heat or radiation or by introducing suitable organic initiator. The intercalated monomer swells the clay and during polymerization increases the interlayer spacing and results in the formation of intercalated or exfoliated nanocomposites. 

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