Polyesters bond strength

These tests are useful as a screening test to evaluate new bonding agents and methods of surface preparation. It must be remembered that polyesters have a bond strength three times that of polyethers. 

Epoxies, isocyanate cured polyester, and cyanoacrylates are used to bond acetal copolymer. Generally, the surface is treated with sulfuric-chromic acid. Epoxies have shown 150- to 500-psi shear strength on sanded surfaces and 500- to 1000-psi on chemically treated surfaces. Two-component epoxies give slightly lower bond strengths. However, they bond acetal to itself and to many other materials. 

Polyethylene and Polypropylene Acceptable bonds have been obtained between treated polyolefin surfaces with polar adhesives, such as epoxies, or solvent cements containing synthetic rubber or phenolic resin. The solvent adhesives are applied to both surfaces and the solvents allowed to evaporate before the parts are joined. Recommended epoxies are the anhydride-cured and amine-cured types. Also suitable is a two-component, polyamide-modified epoxy compound. Other adhesives that provide adequate bond strength to treated polyolefins include styrene-unsatmated polyester and solvent-type nitrile-phenolic (15). 

In an attempt to increase the cohesive strength of the polyesters at high temperatures, the polyesters were cross-linked. This was accomplished by incorporating a UV-sensitive diester into the polymer backbones and then effecting cross-linking with UV radiation. Unexpectedly, cross-linking caused a dramatic deterioration in the bond strength of the adhesives. 

The mode of bond failure in the unexposed films was mainly cohesive. However, when a cross-linked polymer matrix was formed with UV exposure, the mode of bond failure was interfacial at all testing temperatures. We believe that by cross-linking the polymer with UV radiation, the modulus of the polyester was increased. This in turn caused the cohesive strength to be much greater than the interfacial bond strength. As a result, the mode of bond failure became interfacial, or adhesive (10) (Figure 8). 

The maximal decrease in compressive strength (up to 40%) is observed in the polyester composites, which is caused by destruction of the bonds between polyester molecules and between binder and filler. 

These adhesives have been found to adhere strongly to metals, glass, wood, ceramics, masonry, asphalt, leather, and plastics like polystyrene, phenolics, polycarbonates, ABS, cellulose acetate, polyesters, rubbers, and some polyolefins. In general, the most favorable results are noted in the bonding of steel and aluminum, perhaps because the bond strengths are more easily observed before substrate failure. 

Flexible circuit boards consist primarily of polyimide-based carriers. The problem of bonding the copper foil on the polyimide carrier has not yet been solved satisfactorily. Due especially to their low bonding strength at elevated temperatures, the production of such materials is very limited. Nevertheless, adhesives for copper-polyimide systems were developed, where one-component epoxy resins (e.g., epoxy-polyester mixtures) and reactive hot melts (e.g., phenolic resin-nitrile rubbers) reached importance. 

Features High functionality polyester polyol produces foams with extreme solv. resist., good bond strength, adhesion, and tack without creep Properties Gardner 0+ liq. m.w. 2600 dens. 10.0 Ib/gal vise. 24,000 cps acid no. 0.5 hyd. no. 90 Lexorez 3130-35 [Inolex]... 

Impurities in the water have a great effect on the water resistance of the joints. The maximal strength decrease of glass-reinforced plastics is caused by distilled water. The strength of steel joints cemented with adhesive based on the Epoxy-1000 resin decreased by 44% when subjected for 60 days to rainwater, by 21% with river water, and by 18% with sea water. Adhesives based on PN polyester resin form comparatively water-resistant joints with glass-reinforced plastics [211], while steel joints cemented by these adhesives are not water-resistant. When subjected to warm (60°C) water for 400 h and to boiling water for 120 h, the strength of steel joints bonded by polyester adhesives decreased 3—4 times. 

The thermal properties of polyesters are of the greatest importance for their end applications. The important features of a polymer, such as bond strength, inter-and intra-molecular forces, resonance stability, crystallinity, structural imperfections and molecular weight, are responsible for their thermal behaviour. Long oil polyester resin and styrenated polyester resin are made flame retardant by the incorporation of bis-pyridine, bis-tribromophenoxo copper complex and polydibromophenylene oxide. 

Epoxies are preferable to other resin systems in that they can be formulated to bond to moist hardened concrete and yet be able to cure within the wet environment of the fresh concrete. Polyesters do not generally bond reliably under wet conditions. The system must also be selected with due regard to the temperature of application. Resins claimed to have good bonding performance at 20 C may give rather poor bond strengths at the lower cure temperatures prevalent on UK construction sites during much of the year. 

It is reported that sandwich panels are being produced in the USA by pultrusion. In this process a plywood core is completely encased in a 3 mm thick glass polyester skin, resin penetrating the plywood during production to give increased bond strength and moisture resistance. 

High strength bonds to polyester, nylon, polyurethane and metals. 

Epoxy, polyester, polyurethane, and thermosetting acrylic have been used to bond modified PPO to itself and other materials. Bond strengths are approximately 600 to 1500 psi on sanded surfaces and 1000 to 2200 psi on chromic acid etched surfaces. 

Thermoplastic polyester resin can be solvent cemented using hexafluoroisopropanol or hexafluoroacetone sesquihydrate. The solvent should be applied to both surfaces and the parts assembled as quickly as possible. Moderate pressure should be applied as soon as the parts are assembled. Pressure should be maintained for at least one to 2 min maximum bond strength will not develop until at least 18 hr at room temperature. Bond strengths of thermoplastic polyester bonded to itself wiU be in the 800 to 1500 psi range. 

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