Polyesters shrinkage during curing

Low profile plastics are added to reduce shrinkage during cure. They are normally thermoplastics that include polyvinyl acetates, polymethyl methacrylate, and copolymers with other acrylate, vinyl chloride-vinyl acetate copolymers, polyurethane, polystyrene, polycaprolactone, cellulose acetate butyrate, saturated polyester, and styrene butadiene copolymers. More details about the low profile additive (LPA) mechanism are published in the literature. ... 

A polyester thermoset material prepared by polymerisation of bisphenol and epichlorohydrin, with high strength and low shrinkage during curing, used as a bonding matrix to hold fibres together or used as a coat, adhesive or foam. 

Substance added to thermosetting moulding compounds, particularly polyesters, to counteract shrinkage during cure, and uneven surface finish. 

Fillers are very important in polyester coatings because these resins are unnsually prone to build up of internal stresses. The stresses in cured paint films arise for two reasons shrinkage during cure and a high coefficient of thermal expansion. 

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... 

Laminating resins have been offered by Akzo (Diacryl 101), Dow (Derakane Vinyl Esters) and Showa (Spilac). Typical of these is Diacryl 101, which is manufactured by esterification of the addition product of ethylene oxide to bis-phenol A with methacrylic acid. They exhibit lower curing shrinkage than the polyester laminating resins during cure. The structure of Diacryl 101 is... 

Thermal contraction and volume shrinkage during the cure are the disadvantage of polyester systems. 

During cure, polyester resins typically shrink a relatively high amount, 8 to 10 volume percent [17]. Once the curing film has formed multiple bonds to the substrate, however, shrinkage can freely occur only in the direction perpendicular to the substrate. Shrinkage is hindered in the other two directions (parallel to the surface of the substrate), thus creating internal stress in the curing film. Fillers and reinforcements are used to help avoid brittleness in the cured polyester film. 

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