Chemical Dissolution
Deinking chemistry relies on alkaline hydrolysis to break ester bonds in printing inks and dismantle the adhesive polymers holding printed waste to paper fibres. High pH conditions saponify vegetable oils and acrylate resins present in offset and flexographic inks, converting insoluble binders into water-soluble soaps that wash away during flotation stages. This reaction targets the ester linkages of common lithographic drying oils without degrading the underlying cellulose structure of recovered paper stock, provided temperature and alkalinity remain within safe operational parameters.
Thermal Kinetics
Process temperature accelerates saponification rates within repulping vats by lowering activation energy barriers for ester bond cleavage. Caustic soda concentration governs hydroxyl ion availability, directly dictating how fast ink particles detach from recycled cellulose matrices. Industrial pulpers operate at elevated temperatures to maintain reaction velocity while chemical dosing controllers monitor liquor pH to prevent swelling damage to paper fibres.
Fiber Degradation
Excess sodium hydroxide concentration induces alkaline peeling reactions that systematically shorten cellulose chains and reduce the tear strength of recycled paper. Strong alkali solutions penetrate amorphous regions of the paper matrix, causing hemicellulose dissolution and lowering the overall mechanical yield of the recovered stock. Mill operators balance chemical strength against mechanical integrity to ensure recycled pulps retain sufficient tensile strength for subsequent papermaking operations.
