Strain free resin

Soils stabilized with urea-formaldehyde have strengths comparable to the phenoplasts and like those materials are less sensitive to testing strain rate than other chemical grouts. (For optimum mechanical properties and to keep free formaldehyde levels low, one molecule of urea should be provided with three molecules of formaldehyde.) Little data are available, but it is probable that aminoplasts break down comparatively quickly under cyclic wet iry and freeze thaw conditions. The creep endurance limit is probably a relatively high percentage of the UC. Except as noted above, the resins have good stability and are considered permanent. 

Mechanical Damping. The elastic energy behavior of resins at low temperatures was determined from the stress-strain relation. Small inelastic contributions, not detectable with that method can be determined by damping measurements using a free torsion pendulum. The mechanical loss, tan 8m, is plotted vs. temperature in Fig. 10. Low-temperature values were similar for the resins considered. No major structural dependence is indicated. (It is not within the scope of this paper to consider the relaxation maxima of resins.)... 

Vinyl ester resins are similar to unsaturated polyester resins in that they are cured by a free radical initiated polymerisation. However, they differ from the polyesters in that the unsaturation is at the ends of the molecule rather than along the polymer chain. Unlike polyesters, vinyl esters show a greater resistance to hydrolysis as well as lower peak exotherm temperatures and less shrinkage upon cure. Cured vinyl ester resins exhibit excellent resistance to acids, bases and solvents. They also show improved strain to failure, toughness and glass transition temperatures over polyesters. They can be used in filament winding, pultrusion, resin injection, vacuum moulding and conventional hand lay-up. 

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