Hydrophobic Efficiency
Alkyl ketene dimer functions as a synthetic surface additive to increase liquid holdout in wood fibre networks. The molecule reacts with hydroxyl groups on cellulose to form stable covalent bonds that reduce the surface energy of individual fibres. Paper mills utilize akd sizing to achieve resistance against aqueous penetration during printing and high speed conversion processes.
Chemical Mechanism
Reaction conditions require alkaline pH levels to facilitate the formation of the beta-lactone ring bond between the chemical agent and the fibre substrate. This transformation occurs primarily within the dryer section of a paper machine where heat drives the polymerization of the dimer. Manufacturers manage the curing window closely because the internal resistance to liquid develops fully only after the sheet leaves the final press roll and reaches ambient moisture equilibrium.
Production parameters influence the conversion rate of the sizing agent, since excess moisture during the sheet formation phase interferes with the bond stability of the hydrophobic layer.
Performance Boundary
Aqueous barrier properties depend on the density of the fibre mat and the distribution of the additive through the vertical cross section of the substrate. High concentrations of the substance eventually reach a point of diminishing returns where internal bond strength drops due to interference with natural hydrogen bonding between fibres. Printers monitor the Cobb test value as the standard measure to confirm that the substrate maintains the required liquid resistance for specific coating or ink applications.
Successful application prevents strike-through on porous sheets without altering the tactile surface characteristics of the base stock.
