Polymer Film Micro Fracture Mechanisms under High Strain Shear in Folding Boxboard Creases
High strain shear during boxboard creasing causes polymer film micro fractures when local elongation exceeds film yield capacity along the outer bend radius.
Bleached Chemical Pulp
Fiber Processing
Industrial papermaking fibers produced through alkaline digestion and multi-stage chemical bleaching form high-whiteness substrates. Process plants produce bleached chemical pulp by removing lignin from wood chips using sodium hydroxide and elemental chlorine-free bleaching agents. Delignification preserves individual cellulose fiber length while raising optical brightness above eighty-eight percent ISO.
Mechanical pulping alternatives leave residual lignin that causes yellowing upon light exposure.
Brightness Retention
Removing hydrophobic lignin molecules increases fiber flexibility and improves inter-fiber bonding capacity during sheet formation. Paper grades manufactured from bleached chemical pulp maintain stable optical properties under ambient light and thermal stress. Chlorine dioxide and ozone treatments eliminate residual chromophores without degrading the cellulose polymer chains.
Refining treatments beat the purified fibers to develop external fibrillation, which increases sheet density and internal bond strength. The high purity of these fibers reduces chemical additive consumption during wet-end sizing and surface coating applications. Paperboard layers made with bleached fibers show low residual chemical content, making them suitable for direct food packaging.
Process monitoring uses kappa number measurements before bleaching to control chemical dosage and preserve yield.
Tensile Strength
Mechanical testing of paper formed from purified fibers demonstrates elevated tensile and tearing resistance. Packaging grades utilizing bleached chemical pulp resist rupture during high-speed converting and web handling operations. Virgin kraft fibers provide longer average fiber length than recycled pulp stocks, resulting in superior burst strength.
The absence of lignin permits tight hydrogen bonding across adjacent cellulose structures within the consolidated web.