Curing Of Polyesters Research Articles

Synthesis and characterization of unsaturated polyester/carborundum composites

Two unsaturated polyesters, one based on phthalic anhydride PEP and the other based on isophthalic acid PEI, were synthesized. The chemical structure of the two polyesters was characterized by IR and 1H and 13C NMR spectroscopy. The effect of styrene concentration on the curing of polyesters was also studied. It has been found that the percent of polyester/styrene (70/30 wt %) gave the highest percent of curing. Different concentrations of carborundum (0–70 wt %) were used to prepare polyester composites. A comparative study was done on the properties of the two prepared polyesters PEP and PEI and their composites in term of their thermal, mechanical, electrical, and physical properties. The results indicate that the polyester based on isophthalic acid (PEI) and its composites gave higher compressive strength values and lower water absorption than those based on phthalic anhydride (PEP). The presence of carborundum improved the thermal stability than the cured polyesters and electrical properties. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Studies of the aging effect on the level of isocyanate residues in polyester-based can coating systems

A methyl ethyl ketone oxime-blocked isocyanate was used as a crosslinking agent in the curing of polyester–polyurethane (PEPU) can coatings. The completeness of cure was assessed from the amount of residual (un-reacted) isophorone diisocyanate (IPDI) trimer that was presented in the coating after curing. This amount of residual trimer depended strongly on the temperature at which the curing was undertaken and time given for curing. The degree of cure was also assessed, correlating with the reduced IPDI trimer migration potential. The amount of residual IPDI trimer that was extractable from a typical PEPU coating rose markedly (15- to 20-fold) if the wet coating was aged up to 6 months before use. The presence of a TiO2 pigment increased the aging effect. An aluminum flake pigment had an even greater effect. The TiO2 pigment increased aging by different degrees according to the type of surface modification that had been applied to the pigment. The grade having the greatest alumina content, as a result of surface modification, gave the greatest aging. The undesirable effects of aging were counteracted by the addition of more catalyst to the aged coating just before the coating was used to coat panels. Deactivation of the acidic polymerization catalyst system (based on organotin compounds) is thought to be the cause of this aging. These findings have allowed improvements to be made to the specifications of the pigments and the catalysts used, with respect to the consistent industrial production of low migration coatings.

Enzymatic synthesis and curing of biodegradable crosslinkable polyesters

The lipase-catalyzed synthesis and curing of polyesters that possess an unsaturated fatty acid moiety in the side chain is described. Lipase-catalyzed polymerization of divinyl sebacate and glycerol in the presence of unsaturated fatty acids produced a crosslinkable polyester possessing the unsaturated group. Candida antarctica lipase showed high catalytic activity for their synthesis. Effects of reaction parameters, such as enzyme amount, temperature, and feed ratio of substrates, have been systematically investigated. The polymerization under reduced pressure improved the polymer yield and molecular weight. Divinyl adipate was also enzymatically polymerized with glycerol and linoleic acid to give the crosslinkable polyester. The polymer obtained using linoleic or linolenic acid, was cured using a cobalt naphthenate catalyst or thermal treatment to give a crosslinked, transparent, polymeric film with a high-gloss surface. The cured film was characterized by pencil-scratch hardness testing and FT-IR spectroscopy. The biodegradability of the obtained film was evaluated by biochemical oxygen demand (BOD) measurement in an activated sludge.

Jute reinforced polyester structures

AbstractLarge diameter pipes and structures are manufactured with jute reinforced polyester resin. A modified filament winding machine is used to take the jute cloth on the rotating mold acting as a collapsible mandrel. The effect of calendering, fillers and poly(vinyl acetate) on jute reinforcing cloth and the results on the ultimate mechanical properties of the composite are studied. The effect of load during the curing of polyester and its effect on the strength of structure is reported. These findings are used in manufacturing of large diameter structures with improved mechanical properties.

Determination of the magnitude and distribution of the initial stresses in glass-reinforced plastics

Photoelastic stress analysis is used to demonstrate the effect of coupling agents on the residual microstresses, i.e., the stresses that develop at near the glass-resin interface during the curing of polyester and epoxy glass-reinforced plastics and, as a rule, remain throughout the life of the product. Coupling agents of different chemical composition applied to the surface of the glass fibers have different effects on the components of the state of stress and thus can act as a powerful regulating factor.