Chemical Splitting
Water molecules break the covalent bonds within polymer chains through a reaction that permanently reduces molecular weight. This hydrolytic degradation proceeds when moisture infiltrates the internal structure of cellulose, starch, or synthetic binders used in paper coatings. Acidic catalysts accelerate the cleavage of these chains by providing hydrogen ions that increase the rate of bond breakage.
Physical strength drops as the average length of the polymer segments decreases under the influence of persistent humidity.
Mechanism Mechanics
Moisture transport happens through pores in the sheet structure and the gaps between individual fibres. Absorption occurs when ambient vapour moves into the amorphous regions of the material where the lack of crystalline alignment allows water entry. Bond rupture follows the chemical reaction between water and the functional groups of the polymer.
Chain scission results in shorter fragments that no longer contribute to the mechanical integrity of the substrate. Reduced fibre bonding manifests as lower tensile strength and decreased folding endurance in finished packaging.
Material Consequences
Paperboard producers evaluate the susceptibility of substrates to this process by measuring changes in elongation and burst resistance after exposure to accelerated ageing conditions. Converting lines that use water-based adhesives must control the application volume to prevent excessive swelling that promotes deep structural compromise. High relative humidity during transit or storage triggers the process in hygroscopic materials.
Moisture-resistant barriers or synthetic coatings act as the primary defense against internal chemical damage. Proper selection of sizing agents and alkaline additives manages the internal pH to hinder the speed of this bond dissociation.
