Psychrometric Boundary Layer Analysis in Wrapped Paperboard Pallets during Transit
Polyethylene film wraps trap moisture desorbed by paperboard during thermal swings, elevating internal relative humidity and triggering mechanosorptive failure.
Stretch Wrap Permeability
Vapour Transmission
Water transmission performance represents the rate at which gas molecules diffuse through the layers of protective polymer film that secure a pallet load. In shipping and logistics, stretch wrap permeability determines the level of protection provided to moisture-sensitive paperboard boxes during outdoor exposure or transit. This property is evaluated under specific pressure gradients and temperature conditions, terminating its protection once the film is removed.
Permeation Route
Transport of vapour occurs through the amorphous gaps between polymer crystals, where the molecules can wend their way through the stretched film. When the film is drawn tightly during wrapping, the polymer chains align to alter the diffusion path. This physical adjustment reduces the rate of moisture movement, provided that the wrapping has no holes or tears from sharp edges.
Proper tensioning during the wrapping cycle determines the achievement of the maximum barrier effect from the polymer film.
Moisture Barrier
Cartons wrapped in films that have high transmission rates are susceptible to softening and structural collapse in humid climates. If the plastic wrap is too thin, it allows atmospheric moisture to penetrate and damage the corrugated sheets. Using multi-layer wrapping with low transmission properties preserves the dryness and the strength of the paperboard.