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.
EVOH Laminate
Polymer Structure
Extrusion and lamination technologies combine synthetic polymers with paperboard substrates to produce composite materials capable of blocking atmospheric gases. An evoh laminate incorporates a thin layer of ethylene vinyl alcohol copolymer bonded between functional polyolefin films and cellulose board. This multi-layer construction protects dry food, pharmaceutical and liquid contents from ambient oxygen, volatile organic aromas and external moisture ingress.
The material functions primarily as an impermeable barrier substrate for extended shelf-life packaging, terminating its role at the mechanical boundary where the package seal joins or where mechanical shredding separates the layers during disposal.
Barrier Performance
Ethylene vinyl alcohol exhibits gas permeation resistance orders of magnitude higher than standard polyethylene or polypropylene coatings. An evoh laminate maintains low oxygen transmission rates when dry, typically below zero point five cubic centimetres per square meter over twenty-four hours at one atmosphere of pressure. Hydrophilic hydroxyl groups along the vinyl alcohol chain provide this dense molecular network, though high relative humidity can plasticize the polymer and reduce gas barrier performance.
Converters counteract moisture sensitivity by encapsulating the barrier resin between outer layers of hydrophobic low-density polyethylene using functional maleic anhydride tie layers. This multi-ply extrusion coating allows paperboard cartons to replace glass jars and metal cans for moisture-sensitive food items.
Recycling Interface
Repulping multi-layer composite structures presents distinct operational challenges in conventional paper mill hydrapulpers. The non-polar polyolefin coatings and polar barrier resins in an evoh laminate resist water penetration and fiber liberation under standard mechanical agitation. Screen baskets separate unpulped plastic fragments from recovered cellulose fibres, but fine polymer flecks can pass into accepted stock and cause surface defects on recycled paper machines.
Standard flotation and chemical washing systems remove the synthetic layers, though total fiber yield declines in proportion to the plastic coating thickness. Modern sorting protocols classify these barrier paperboards under specialized recycling streams to recover clean fiber while diverting polymer fractions to thermal recovery or specialized polymer separation facilities.