Normalized Index
Tensile breaking force divided by sheet grammage yields a standardized strength metric independent of basis weight variations across paper and board grades. Standardized testing according to tensile index ISO 1924 measures maximum force sustained per unit width of a test strip before structural failure. Test pieces of fifteen-millimeter width undergo constant rate of elongation loading until fracture occurs.
Normalizing tensile force by basis weight allows direct comparison of structural fiber bonding across sheets of differing thickness and grammage. Higher index values reflect superior fiber-to-fiber hydrogen bonding and individual fiber strength. The standard excludes corrugated board structures, tissue products, and non-woven fibrous materials.
Test Procedure
Pneumatic clamps hold specimen strips under controlled initial web tension prior to mechanical extension. Linear rate of strain application increases stress across the sample until fracture. Force gauges record peak load, while extensometers track stretch percentage to calculate the tensile index ISO 1924 value.
Paper Quality
Refining pulp increases hydrogen bonding capacity throughout the sheet structure. Achieving a high tensile index ISO 1924 depends on fiber orientation during wet-end formation and mechanical stock preparation. Sack paper specifications require high tensile index values to prevent bag rupture under impact loading.
Wet-end chemical additives such as cationic starch enhance bonding energy, raising strength values without increasing fiber refine levels.
