Zero-span tensile strength of papermaking fibres

摘要

The zero-span tensile strength (ZSTS) of pulp handsheets is regarded as an index of fibre strength. When a pulp is beaten or refined, its ZSTS generally increases. It has been considered for a long time that the increase in interfibre bonding resulting from beating or refining is responsible for the increase in ZSTS. Fibres, particularly their ends, are considered more effectively gripped when better bonded. The evidence presented in this report demonstrates conclusively that bonding and fibre length have little effect on ZSTS. In fact, it is the straightening of the fibre kinks and crimps resulting from beating or refining that is responsible for the increase in ZSTS. Commercial papermaking fibres are seldom free from kinks and crimps. Fibre segments spanning the zero-span gap transmit load simultaneously only when all are straight and kink-free. These findings imply that unless papermaking fibres are straight, or have been straightened, the zero-span test will not reflect their strength. The argument for rewetting dry sheets for the purpose of eliminating the effects of bonding on ZSTS is unsupported.