Structural bonding of ash (Fraxinus excelsior L.): resistance to delamination and performance in shearing tests

• Published in: European journal of wood and wood products 2014-05, Vol.72 (3), p.297-309
• Main Authors: Knorz, Markus, Schmidt, Michael, Torno, Stefan, van de Kuilen, Jan-Willem
• Format: Article
• Language: English
• Subjects: Adhesion tests; Adhesive joints; Adhesives; Assembly; Bearing capacity; Biomedical and Life Sciences; Bond strength; Bonded joints; Bonding strength; Ceramics; Composites; Delamination; Finger jointing; Formaldehyde; Fraxinus excelsior; Glass; Hardwoods; Isocyanates; Life Sciences; Load bearing elements; Machines; Manufacturing; Melamine; Natural Materials; Originals Originalarbeiten; Phenols; Polymers; Polyurethane; Polyurethane resins; Processes; Resorcinol; Shear tests; Shearing; Urea; Wood Science & Technology
• ISSN: 0018-3768; 1436-736X
• DOI: 10.1007/s00107-014-0778-8

The utilization of ash ( Fraxinus excelsior L.) allows for a significant enhancement of the load-bearing capacity in structural laminated products. However, such applications fundamentally require high-strength and durable bonds between lamellas and in finger joints. Therefore, the aim of the present survey was to evaluate ash bondings in terms of resistance to delamination (EN 302-2) and shear performance (EN 392). Investigations were performed with five adhesives: phenol-resorcinol-formaldehyde (PRF), melamine-urea-formaldehyde (MUF-1, MUF-2), polyurethane (PUR), emulsion polymer isocyanate (EPI) and varying closed assembly times as key bonding parameter. For all tested adhesives and closed assembly times, the shear test showed high wood failure percentages and bond strength values that compare to solid ash. In contrast, for resistance to delamination, significant differences were found between the adhesives as well as between closed assembly times, with improving resistance to delamination for increasing closed assembly times. The best performance was determined for the PRF-adhesive and long closed assembly times. However, standard requirements for resistance to delamination could not be met by any of the adhesives. The resistance to delamination showed no correlation with the shear performance for any of the adhesives. Microscopic examination of the bonded joints revealed that both the penetration behavior of the adhesives and glueline thicknesses clearly correlated with the closed assembly time.