Chemical Dissolution Test Procedures for Wool Polyester Blends
Chemical dissolution separates wool from polyester using alkaline sodium hypochlorite, requiring d-factor and moisture regain corrections for accurate declarations.
Alkaline Sodium Hypochlorite
Reagent Profile
Aqueous chemical formulations buffered to high pH function as selective wet-dissolution media in quantitative fibre blend analysis. In standard test protocols such as ISO 1833-4, alkaline sodium hypochlorite dissolves natural protein fibres while leaving cellulosic and synthetic components intact. The working solution contains approximately 35 grams per litre of active chlorine, stabilized with sodium hydroxide at roughly five grams per litre to prevent premature decomposition.
The reagent ceases to be selective when applied to regenerated protein fibres that possess modified cross-linking, or when operating temperatures exceed ambient thresholds.
Digestion Chemistry
Hydroxyl ions facilitate the swelling of animal fibres while hypochlorite anions attack disulphide bonds within cystine linkages. This dual action cleaves the polypeptide chains into soluble peptide fragments. Wool, silk and specialty hair fibres break down rapidly under this targeted oxidative cleavage.
Synthetic fibres like polyester, polyamide and acrylic exhibit negligible mass loss when exposure times remain strictly within laboratory limits. Cellulosic structures resist dissolution, though minor surface degradation occurs if exposure extends beyond forty minutes.
Procedural Exposure
Quantitative analysis requires specimens to be immersed in freshly prepared solution at a liquor ratio of one hundred to one by weight. Continuous mechanical agitation maintains uniform concentration gradients around each yarn structure during the standard thirty-minute cycle at twenty degrees Celsius. Laboratory technicians subsequently isolate the undissolved residue on a tared sintered glass crucible under gentle vacuum suction.
Rinsing follows a strict sequence of cold distilled water, dilute acetic acid to neutralise residual alkalinity, and a final thorough wash with warm deionized water. Failure to neutralise the residue leaves persistent salts that skew dry weight determinations.
Gravimetric Correction
Insoluble residues retain slight damage or collect insoluble non-fibrous residues that require mathematical adjustment through empirical d-factors. For clean polyester, this correction factor is typically 1.00, confirming zero nominal loss during digestion. Unbleached cotton requires a d-factor of 1.01 to offset minor polysaccharide degradation caused by oxidative side reactions.
Acetate and triacetate components present greater instability, suffering partial hydrolysis that renders this specific reagent unsuitable for their quantitative separation. Laboratory verification rests entirely on the oven-dry mass balance obtained after completing standardized desiccation.