On paraffin sizing of medium density fiberboards (MDF). Part 1: Influence of the chemical composition of paraffin and type of emulsifier on the hydrophobic properties of MDF

The main objective of the conducted research work was to explore the influence of chain length and amount of n-paraffins as well as the chemical composition of technical paraffins (chain length and amount of n- and iso-alkanes) on the thickness swelling, water absorption and internal bond strength of MDF. Pronounced differences in the sizing efficiency of n-paraffins with different chain length (C-20, C-28, C-36) were found. On using 0.1% paraffin (based on dried fibers) sizing efficiency increases between C20 and C28. Higher paraffin content (> 0.25%) has an insignificant influence on the swelling behaviour of MDF. In the range between 0.1% and 1.0% (solid based on dry fibers) paraffin has no negative impact on the physical-mechanical properties of the boards. The influence of paraffin chain length on the equilibrium moisture content (EMC) seems to be negligible. Further investigations were carried out using technical paraffins with different chemical composition (chain length and amount of n- and iso-alkanes) as a sizing agent for MDF. The results show that technical paraffins with a high content of long-chain-n-alkanes are more effective sizing agents than technical paraffins with low-chain-n-alkanes. Moreover, the type of used emulsifier (anionic, cationic) was also investigated. Anionic and cationic emulsifiers were equivalent in their sizing effect.