Inhibition curing polyester resin

The exposed topmost layer is covered with polyethylene, cellophane, or polyester hhn to make a smooth surface. Some polyester resins are slightly inhibited by air, and hhn overlays help to complete the cure. When the resin has hardened, the part is removed and sometimes given a postbake. 

The vacuum bag is the impermeable film that is generally applied to the outside of the layup to facilitate conformability to the mold form and air removal during cure. Polyvinyl chloride (PVC) bags are useful up to 66°C and are less expensive than polyvinyl alcohol (PVA). Certain PVC polymers, however, inhibit polyester resins and prevent a tack-free cure. When high curing temperatures or steam-autoclave curing is required, the bag should be made of neoprene rubber or some similar elastomer. Film materials suitable for bag manufacture also include cellophane, polypropylene, nylon, and fluorocarbons. Silicone and butyl rubbers are also used to make vacuum bags. To make the best parts, the bag should be tailored to the part so that wrinkles will be at a minimum. 

Air Inhibition. Polyester resins are widely used in open-mold lamination or casting and quite often develop a tacky surface feel after curing. The free-radical polymerization process is sensitive to oxygen, which interferes with the surface... 

A special blend of polymers that produces an air-cure film which bonds polyester resins and coatings to epoxy resins and coatings. Can be spray, brush or roller applied. Also excellent for use as an air-cure coating for corrosion-resistant air-inhibited systems. 

Unsaturated polyesters are fast-curing, two-part systems that harden by the addition of catalysts, usually peroxides. Styrene monomer is generally used as a reactive diluent for polyester resins. Cure can occur at room or elevated temperature depending on the type of catalyst Accelerators such as cobalt naphthalene are sometimes incorporated into the resin to speed cure. Unsaturated polyester adhesives exhibit greater shrinkage during cure and poorer chemical resistance than epoxy adhesives. Certain types of polyesters are inhibited from curing by the presence of air, but they cure fully when enclosed between two... 

A1(OH)3 inhibits the curing reaction of allylester resin. CaCOs and glass fiber exert a similar effect on the cure of unsaturated polyesters. Both the reaction rate constant and the activation energy are higher in the presence of a filler than in the neat resin. Many papers have been published dealing with the rate of reaction in the presence of these fillers. There is no consensus. Some report acceleration, some no effect, others rate reduction. The reasons are also inconclusive. It is difficult to say if cure inhibitions reported in recent papers are a special case or if the results reported depend on factors which are still to be determined. 

Methods of producing FRP laminates with polyesters have been described in Chapter 2. The major process today is the hand layup technique in which the resin is brushed or rolled into the glass mat (or cloth) by hand (see Figure 2.44). Since unsaturated polyesters are susceptible to polymerization inhibition by air, surfaces of the hand layup laminates may remain under-cured, soft, and, in some cases, tacky if freely exposed to air during the curing. A common way of avoiding this difiiculty is to blend a small amount of paraffin wax (or other incompatible material) in with the resin. This blooms out on the surface and forms a protective layer over the resin during cure. 

Anaerobic locking compounds are unsaturated polyester monomers such as dimethacrylates whose cure (polymerization) is inhibited by atmospheric oxygen. When oxygen is excluded from the bond line, as in the case of threaded fasteners, the resin reacts and the resulting bulk solid locks the parts together. 

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