Paperboard Moisture Sorption Dynamics and Water Vapor Permeability Fundamentals
Paperboard moisture sorption and vapor permeability govern pack structural integrity and shelf life through fiber swelling, stiffness loss, and mass flux.
Extrusion Polyethylene
Barrier Application
Molten polymer resin applied continuously onto moving paperboard substrates forms an impermeable moisture and grease protection layer. Applying extrusion polyethylene at high temperature bonds the plastic film directly to raw cellulose fibers without separate adhesives. Converting mills run chill rolls to solidify the resin coating before winding rolls under tension.
Grammage of the applied plastic controls both barrier durability and final package weight.
Thermal Bonding
High-temperature application causes thermal oxidation at the polymer surface to enhance web adhesion. Incorporating extrusion polyethylene into liquid packaging board prevents liquid penetration through structural carton walls during storage. Resin density determines film flexibility and pinhole resistance across thin coatings.
Defective resin melting produces gauge variation or localized pinhole leaks in converted packaging. Polyolefin melt index selection balances flow properties in the extruder die against puncture resistance on packaging lines. Extruder temperature profiles control oxidation levels necessary for fiber adhesion.
Sealing Limit
Repulping coated board requires mechanical fragmentation to detach plastic films from underlying wood fibers. Polymer films fail to disperse in water and require screen separation during hydrapulping operations. Recycled pulp quality drops when non-fibrous resin particles pass through slotted screens into finished paper sheets.
Film thickness limits govern whether a paperboard structure complies with repulpability guidelines.
Polymer Barrier Coatings and Pulpability Test Standards
Polymer barrier paperboard compliance requires passing 0.15mm laboratory slot screening with under 15 percent reject mass to prevent EPR fee penalties.