Virgin Softwood Pulp Ratio Verification in Technical Packaging Papers
Verifying virgin softwood content in packaging paper relies on fiber morphology analysis, ISO chemical pulp identification, and trace chemical markers
Tear Strength
Force Resistance
A measurement of the internal resistance of paper to a tearing force determines the durability of packaging material during transport and handling. This property, known as tear strength, represents the work required to propagate a tear through a specified length of a sheet. It is highly dependent on fiber length and fiber bonding.
Packaging papers like multiwall sacks and carrier bags require high resistance to tearing to prevent failure.
Measurement Dynamic
Testing this property usually employs the Elmendorf method, which measures the energy lost by a falling pendulum as it tears through a pre slit sample of paper. The instrument records the force in millinewtons, and the tear strength is typically reported for both the machine direction and the cross direction. Cross direction tear is almost always higher because most fibers lie parallel to the machine direction, forcing the tear to break across the fiber axes.
To build a sheet with high tear strength, paper mills often limit the amount of refining, since too much refining can shorten fibers and weaken the overall network. Blending long softwood fibers into the furnish is a standard method for raising this force resistance.
Convert Performance
Converting lines and automatic filling systems demand consistent toughness to avoid costly line stoppages. When rolls of paper run through high speed converting equipment, high tear strength prevents small edge nicks from propagating into major sheet breaks. This is especially true for sack paper used to package cement and chemicals.
Monitoring this parameter ensures that the packaging remains intact from the filling station to the end consumer.