In the EN ISO 3521 standard developed by the International Standards Organization (ISO), a test method for determining the total volume shrinkage of unsaturated polyester and epoxy resins is presented.
For the purposes of this international standard, overall volume reduction refers to the sum of shrinkage during curing and shrinkage after a casting has cured when cooled to ambient temperature. In principle, the total volume shrinkage is calculated from the specific gravity of the final sample before and after curing.
During the tests, the specific gravity of the resin composition is first determined:
Total volume shrinkage is then calculated as a percentage of the change in specific gravity before and after curing as follows: Overall volume reduction = Uncured specific gravity = Uncured specific gravity - Cured specific gravity x 100.
The specific gravity at the time of mixing is determined at known intervals for the mixed components and the results are estimated as zero time.
For components reacting at high temperature, the specific gravity of the mixture is determined by calculating from the individual specific gravity of the components.
After curing and conditioning, the specific gravity of the final sample at 23 degrees Celsius is determined by weighing it in silicone oil.
The shrinkage of unsaturated polyester and epoxy resins also depends on the processing applied. Pure unsaturated polyester resin with approximately 50% styrene content shrinks more than epoxy resin. The volumetric shrinkage of unsaturated polyester resin ranges from 5% to 13%, depending on the polymerization temperature. Unsaturated polyester resins typically shrink by 7-12% during the crosslinking reaction. The high volumetric settling shrinkage of these resins is problematic for applications requiring high surface quality and tight thickness tolerances. Existing solutions to reduce the volumetric settling shrinkage of these resins often increase their viscosity or reduce the mechanical properties of the final products.
Among the numerous tests, measurements, analyses, and evaluations our organization provides for businesses in various sectors, we also offer testing services for determining the total volume shrinkage of unsaturated polyester and epoxy resins within the scope of the EN ISO 3521 standard, thanks to our trained and expert staff and advanced technological equipment.
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