Interfacial Friction
Surface lubricity variations in chemical wood pulp occur when short-chain polysaccharides migrate to the exterior of the fibre during the cooking or bleaching stages. The phenomenon of hemicellulose slip refers to the reduction in friction between fibres or against processing equipment caused by these sticky or slippery compounds. It affects the handling of the pulp web and the final bonding strength of the paper sheet.
This interaction is most pronounced in alkaline environments where the solubility of the hemicellulose is high.
Machine Performance
Pumping systems and refiners experience different load levels depending on the chemical composition of the pulp slurry. If hemicellulose slip is excessive, the mechanical energy transferred to the fibres during refining drops because they slide past the bars rather than being sheared. This leads to a sheet with lower burst strength and poor internal bonding.
Operators must adjust the chemical balance or the refining intensity to compensate for the loss of friction. Slippery fibres also cause issues with web tracking on the fourdrinier wire.
Finishing Quality
Coating adhesion on the surface of the finished board depends on a clean and receptive fibre matrix. Presence of hemicellulose slip on the top layer of the board can interfere with the binding of mineral pigments or synthetic latex. This results in picking during the printing process where the ink lifts the coating away from the base sheet.
Controlling the wash cycles in the pulp mill is the primary method for managing these surface residuals. Proper retention aid chemistry also helps keep these small molecules trapped within the sheet rather than letting them migrate. This prevention is necessary to maintain the integrity of the surface during high-speed offset printing.
Testing the surface tension of the base sheet provides a quick indicator of potential adhesion problems.
