Effect of PF impregnation and surface densification on the mechanical properties of small-scale wood laminated poles
The wood poles in the United States are from high-valued trees that are becoming more expensive and less available. Wood laminated composite poles (LCP) are a kind of alternative to solid poles. Considerable interest has developed in last century in the resin impregnation and wood surface densification to improve its physical and mechanical properties. In this study, southern pine lumbers were impregnated with a low molecular weight, water-soluble PF (phenol formaldehyde) resin and compressed while heated to make the surface densified. Furthermore, small-scale LCP were fabricated with treated trapezoid southern pine strips cut from treated lumbers and untreated trapezoid southern pine strips cut from control lumbers respectively. In comparison with the control wood, bending MOE and MOR of treated wood were improved from 11.573 to 16.517 GPa and from 90.68 to 125.63 MPa respectively, and an analysis of variance indicated that both the MOE and MOR differences were significant at 5% probability level. While compared with the control poles bending MOE and MOR of LCP fabricated with treated strips were improved respectively from 9.077 GPa to 10.381 GPa, and 67.67 to 73.28 MPa, and an analysis of variance indicated that these differences were not significant at 5% probability level. Compared with the control poles, the glue line shear strength of LCP fabricated with treated strips decreased from 7.50 to 7.23 MPa for the air-dried samples, from 3.58 to 3.22 MPa for the two hour boiling treatment samples, and these differences were not significant at 5% probability level.