Modified Densification Process for Increasing Strength Properties of Pine and Gmelina Wood from Community Forests

Abstract

Densification is a process for improving the strength properties of wood from the felling of young trees, which is a common harvest practice in community forests. A series of experiments was conducted to refine the process with particular regard to the determination of suitable pretreatment and treatment conditions. Samples of pine and gmelina measuring $23cm(L){\times}20cm(W){\times}2cm(T)$ underwent pretreatment through immersion in a 1:1 $CH_3COOH-H_2O_2$ solution at concentrations of 15%, 20%, and 30%. Samples pretreated with the 20% solution showed the greatest improvement in strength; further experiments were conducted to determine the optimum treatment conditions in terms of temperature and duration following immersion. Test samples with the same dimensions as those in the pretreatment experiment were soaked in a 1:1 20% $CH_3COOH-H_2O_2$ solution and warmed in a water bath. The test samples were then individually hot pressed to the target thickness, which was 30% less than the original thickness and held at $150^{\circ}C$ or $170^{\circ}C$ for 15 or 30 minutes. The treated samples were cut for an analysis of their density, recovery of set, and bending strength. Pine and gmelina exhibited the best characteristics after treatment at $150^{\circ}C$ for 30 and 15 minutes, respectively. The results suggest that the modified densification process had increased the bending strength of the wood, but the temperature and duration of treatment must be carefully considered for different wood species.

Fig. 1. Sample preparation (A, control; B, for densification).

Fig. 2. Sample sizes for density (a), recovery of set (b), and bending strength (c).

Fig. 3. Density changes of gmelina and pine wood.

Fig. 4. MOE changes of gmelina and pine wood.

Figu. 5. MOR changes of gmelina and pine wood.

Table 1. Recovery of set of pine wood and gmelina wood after the densification process

Table 2. Density, Recovery of Set, MOE and MOR of pine wood and gmelina wood as result of desification proccess carried out at various temperatures and lengths of time.