Tensile Strain Measurement in Recycled Paperboard Grades
Recycled paperboard strain measurement requires direct optical extensometry under ISO 1924-3 to isolate true sheet elongation from clamp slippage.
Machine Direction Stretch
Elongation Capacity
Physical paper web deformation capability defines the percentage elongation at rupture measured along the manufacturing alignment axis. Machine direction stretch measures the strain a paper sheet undergoes before failing under longitudinal tension on printing and converting machinery. Fiber alignment during wet web formation creates anisotropic properties, resulting in lower stretch values in the machine direction compared to the cross direction.
Wet end draws and dryer section open draws pull the wet fiber network, orienting fibers and consuming natural stretch prior to final sheet consolidation. The parameter dictates runnability performance for packaging papers, multiwall sacks and high-speed web presses.
Converting Behavior
Multiwall sack papers demand optimized stretch properties to absorb dynamic energy during automated bag filling and drop handling. Increasing machine direction stretch allows finished sacks to deform elastically under impact without tearing open at sewn or pasted seams. Papermakers utilize micro-creping processes, such as Clupak compaction units, to introduce micro-compressions into the wet sheet before final drying.
This mechanical treatment increases machine direction elongation from two percent up to ten percent, greatly enhancing tensile energy absorption. Higher stretch values improve web runnability through flexographic printing presses by accommodating speed fluctuations and tension spikes without web breaks.
Testing Constraint
Extensibility limits depend on fiber species, refining degree and wet-end compaction intensity. Measurement standard procedures specify constant rate of elongation conditions using standardized fifteen-millimeter test strips.