The primary objective of this project was to demonstrate the feasibility of mill production of borate-treated glulam using a commercial phenol-resorcinol-formaldehyde resin and a resin modifier. The secondary objective was to demonstrate the feasibility of finger-jointing borate-treated lumber using the radio frequency heating process to produce face laminating-stock for borate-treated glulam production.
A borate-treated glulam mill trial was conducted in the glulam manufacturing facility of Western Archrib in Edmonton, Alberta on February 18-19, 2004. Good quality lodgepole pine lumber suitable for normal glulam production were selected in Western Archrib, which were borate-treated and dried at Treeline Wood Products in Edmonton, Alberta. The treated boards were then stress-graded, cut, finger-jointed, planed and face laminated in Western Archrib. The resulted finger-jointed lumber and glulam beams were sent to the Forintek western laboratory for complete testing and statistical analysis.
This project has met all its key objectives. Based on the mill trial results, the following conclusions and recommendations can be made:
a. It is feasible to produce borate-treated laminating stock using a commercial radio-frequency finger-joint process. The resulting bond quality is not affected by the borate treatment of lumber. More cases of lower strength wood failure than expected were observed in the tension tests of the finger-jointed borate-treated lumber. More study would be needed to explain this.
b. Of the 8 borate-treated glulam beams manufactured in this mill trial, only 1 beam passed the CAN/CSA-0177-M89 requirements. The data in this study indicated that the treated blue stained (and red heart stain) wood retained more water from the treating process, resulting in higher than acceptable moisture content. The laminating stock had wet pockets in stained areas after drying. When these areas were further dried after planning, the wood shrank, causing poor bonding. Therefore, moisture control of the laminating stock after treatment with aqueous borate solution is very important to the success of borate-treated glulam production. Lodgepole pine exhibiting blue stain or red heart stain is more receptive to aqueous borate treating and the post-treatment drying process should be extended beyond that for non-stained pine.
c. The mill trial data suggest that the PRF adhesive performance at 2.5% resin modifier level was strong enough to meet the requirements of CAN/CSA-0177-M89 standard. The PRF adhesive performance at 1.5% resin modifier level was potentially also good enough; however the higher resin modifier level appeared to make the adhesive more forgiving towards moisture variations.
d. If laminating stock is dried properly after borate treatment, it appears to be entirely feasible to manufacture borate-treated glulam at an average boric acid equivalence level of 2.5% (ranged from 0-8%) using an existing commercial glulam production process. The presence of many good bonds and some poor bonds indicates that the wood had not been sufficiently dried prior to use. It is likely that a retest using properly dried and conditioned wood might yield better performance and satisfy the CSA-0177-M89 laminated beam standard.