Canadian Forest Service Publications
Minimizing the Impact of Mountain Pine Beetle Veneer on Plywood Glue Dry-Out and Delamination. 2008. Xu, H.; He, G.; Dai, C. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, Victoria, BC. Mountain Pine Beetle Working Paper 2008-12. 16 p.
Available from: Pacific Forestry Centre
Catalog ID: 28991
Delamination currently accounts for approximately 85% of customer complaints about plywood as a sub-flooring product. It has become a critical issue for many plywood mills. The dryness of mountain pine beetle (MPB) veneer coupled with an inability to sort MPB-killed material from a mill's regular species mix can result in problems in over-drying and high veneer temperature, further exasperating glue dry-out and subsequent panel delamination. With potentially as much as 50% of a mill's future log supply being derived from MPB-killed material, a manufacturing strategy that reflects the impact of the change in raw material is needed.
This project quantified the impact of key parameters during plywood manufacturing on glue dry-out and bond quality using mountain pine beetle veneers. A multi-step pressing method was applied to MPB plywood manufacturing for minimizing the impact of glue dry-out on plywood bonding properties. The following conclusions and recommendations were drawn from this study based on laboratory tests:
- Mountain pine beetle plywood produced from bluestained and non-bluestained veneers did not show significant differences in glue dry-out and bond quality. Mountain pine beetle veneers could be used for plywood manufacturing without being further sorted into bluestained and non-bluestained veneers.
- Among all key factors, the assembly time gave the most significant impact on glue dry-out and bond quality. A long assembly time (i.e., 25 min) should be avoided in the lay-up process for minimizing glue dry-out.
- Veneer characteristics, including veneer moisture and temperature, also showed significant impact on glue dry-out and bond quality. Appropriate veneer moisture contents (3-5%) and low veneer temperature (about 21ºC) distinctly reduced glue dry-out compared to dry veneer and high veneer temperature.
- Glue spread rate generally gave a positive impact on glue dry-out and bond quality, but this impact was not significant in the experimental range compared to other key parameters.
- Hot pressing factors, including press pressure, temperature and time, had less significant impact on glue dry-out compared to veneer characteristics and lay-up parameters. However, increasing press temperature, pressure and time could help minimize the impact of glue dry-out induced by inappropriate veneer conditions and long assembly time.
- The multi-step pressing method compared to the conventional one-step pressing method produced better bond quality resulting in higher percentage wood failure without significant thickness loss of MPB plywood. It is recommended that the plywood industry look into modifying their existing presses to adopt this new pressing method.