Chemical Parameter
Quantitative chemical measurements state the weight proportion of complex aromatic polymers remaining in processed bast fibres after retting or degumming. Spinning facilities test residual lignin content to determine fibre softness and bleaching requirements for fine linen yarn production. Laboratory reports state this value as a percentage of dry fibre mass on incoming raw material inspections.
Process Impact
Retting and alkaline boiling break down the pectic and lignified binder matrix holding individual bast ultimates together in raw stems. High residual lignin content keeps fibre bundles stiff, reducing drafting flexibility during wet spinning and causing yarn unevenness. Chemical treatment steps in Chinese mills adjust alkali concentrations and bath durations based on incoming raw fibre tests.
Gravimetric analysis measures insoluble residue following acid hydrolysis to quantify remaining lignin levels precisely. Spectrophotometric methods offer rapid optical quantification for routine mill floor monitoring. Excessive lignin removal damages cellulose structures, lowering overall fibre tenacity.
Process engineers balance chemical treatment parameters to achieve target softness without sacrificing yarn tensile strength.
Specification Limit
Acceptance standards set maximum permissible lignin limits based on target yarn count and fabric hand requirements. High residual lignin content limits raw fibre suitability to coarse industrial yarns or heavy duck weaves. Buyer contracts specify upper percentage limits, rejecting raw lots that exceed agreed chemical thresholds regardless of fibre length.
