Solvent Selectivity
Chemical separation technique used to distinguish between different types of regenerated cellulose fibers in a blend. The sodium zincate method is specifically effective at dissolving viscose while leaving modal or cotton fibers largely unaffected. It utilizes a solution of sodium hydroxide and zinc oxide at controlled temperatures to achieve this selectivity.
Testing Mechanism
High alkalinity combined with the zincate ion disrupts the hydrogen bonding in the less crystalline viscose polymer. Modal fibers, which possess a more oriented and crystalline structure, resist this dissolution under the specific laboratory conditions. The sample is agitated in the reagent for a fixed period before the residue is collected and neutralized.
Manual agitation or mechanical stirring ensures that every fiber surface is exposed to the chemical solution.
Performance Requirement
Accuracy depends on the strict maintenance of the temperature at 0 degrees Celsius or room temperature as specified by the standard. Deviation from these parameters can lead to the partial dissolution of the modal fiber, which skews the final blend percentage. Technicians must thoroughly wash the residue with dilute acetic acid to remove all traces of the reagent.
Utilization Scope
This approach allows for the verification of labels in the high end intimate apparel market where modal is preferred for its softness. It enables buyers to detect the unauthorized substitution of cheaper viscose in a premium product.
