Zur Feuchtebeständigkeit und Hydrolyseresistenz von mitteldichten Faserplatten (MDF). Tl.2: Einfluss des Aufschlussverfahrens und des Bindemittels auf die Hydrolysebeständigkeit von MDF
On the moisture and hydrolysis resistance of medium density fibreboards (MDF). Pt.2: Influence of the pulping method and the binder used on the hydrolysis resistance of MDF
Medium density fibreboards (MDF) were prepared from thermomechanical (TMP) and chemo-thermomechanical (CTMP) pulps of pine using an alkaline curing phenolformaldehyde resin (PF-resin), a tanninformaldehyde resin (TF-resin) and an adhesive based on polymeric diphenyl-methan-diisocyanates (PMDI) as binders. The hydrolysis resistance of the differently bonded MDF was assessed by measuring the change in the transverse tensile strength, thickness swelling and water absorption of the boards due to soaking in water at 40 °C and 60 °C for 24 h and 3 weeks. The results reveal that MDF prepared from CTMP were in general of higher hydrolysis resistance compared to those prepared from TMP. Highly distinctive differences in the hydrolysis resistance between TMP- and CTMP-boards were found in PMDI-bonded boards. Moreover, the results indicate that post-curing of PF-resin seems to take place in the course of water treatment at 40 °C and 60 °C. Summing up, the results reveal that both the pulping method (TMP, CTMP) and the type of binder (PF-resin, TF-resin, PMDI) are highly relevant to the hydrolysis resistance of the MDF. Moreover, the interaction between binders and pulping method depends highly on the type of binder used.