Densified wood impregnated with phenol resin for reduced set-recovery

Figures & data

Figure 1. Poplar specimens prepared for flexure tests. (A) un-densified 15 mm thickness, (B) densified to 7 mm, (C) densified to 5 mm, and (D) densified to 2 mm.

Table 1. Pressing parameters for densification.

Parameter	Value
Upper platen temp. (°C)	170
Lower platen temp. (°C)	170
Closing rate (mm s^−1)	10
Closing pressure (MPa)	10
Heated holding time (s)	120
Heat treatment upper platen temp. (°C)	200
Heat treatment lower platen temp. (°C)	200
Upper platen cooling temp. (°C)	60
Lower platen cooling temp. (°C)	60

Figure 2. Micrograph of impregnated, densified spruce with a 2 mm target thickness. (A) Penetrated phenol resin present in lumens and (B) collapsed tracheids.

Table 2. THM and resin treatment data for beech, poplar, and spruce specimens.

Species	Initial thickness (mm)	Initial density (g cm^−3)	Compressed thickness (mm)	Compressed density (g cm^−3)	Densification ratio	Weight per cent gain
Beech	6	0.72 (± 0.04)	3.96 (±0.45)	1.18 (± 0.07)	1.64 (± 0.16)	13.28(±5.83)
	10	0.71 (± 0.01)	6.47 (±0.35)	1.15 (± 0.13)	1.62 (± 0.19)	6.54(±3.45)
	15	0.72 (± 0.01)	9.11 (±0.64)	1.18 (± 0.08)	1.63 (± 0.11)	12.67(±4.55)
Poplar	6	0.34 (± 0.03)	1.95 (±0.04)	1.14 (± 0.07)	3.34 (± 0.33)	16.56(±18.10)
	10	0.33 (± 0.05)	4.79 (±0.03)	0.76 (± 0.07)	2.34 (± 0.16)	22.03(±15.56)
	15	0.31 (± 0.04)	7.77 (±0.03)	0.66 (± 0.04)	2.14 (± 0.17)	19.46(±12.19)
Spruce	6	0.42 (± 0.02)	2.05 (±0.06)	1.18 (± 0.04)	2.84 (± 0.08)	2.01(±1.56)
	10	0.42 (± 0.03)	4.77 (±0.04)	0.83 (± 0.05)	1.99 (± 0.02)	0.25(±1.22)
	15	0.42 (± 0.07)	7.79 (±0.05)	0.71 (± 0.04)	1.72 (± 0.18)	0.55(±0.80)

Note: Values are means ±1 standard deviation.

Figure 3. Mean density profiles of beech (first row), poplar (second row), and spruce (third row) specimens.

Table 3. Mechanical test data of impregnated, THM treated specimens (mean values ± 1 standard deviation), and reference values.

Species	Initial thickness (mm)	MOE (GPa)	MOR (MPa)	MOH (MPa)	Equ. Janka (N)
Beech	6	18.1 (± 2.3)	249.3 (± 31.2)	407.9 (± 113.9)	48,733.6
	10	26.2 (± 3.4)	288.1 (± 30.8)	251.8 (± 88.30)	30,083.6
	15	16.6 (± 2.4)	221.3 (± 21.0)	475.7 (± 114.2)	56,833.9
	Ref	14.31	110.1	-	6460
Poplar	6	22.4 (± 2.2)	265.8 (± 21.5)	564.0 (± 125.3)	67,383.5
	10	13.6 (± 3.0)	142.8 (± 14.4)	111.2 (± 30.80)	13,285.5
	15	10.6 (± 2.4)	117.1 (± 19.6)	114.2 (± 28.10)	13,644.0
	Ref	7.21	63.7	-	2020
Spruce	6	24.5 (± 4.6)	267.3 (± 36.9)	548.9 (± 63.80)	65,579.4
	10	17.2 (± 3.4)	184.1 (± 33.9)	158.8 (± 25.40)	18,972.5
	15	14.8 (± 2.1)	153.2 (± 16.9)	142.1 (± 27.70)	16,977.3
	Ref	9.7	63	-	1680

Figure 4. Set-recovery of THM-treated specimens grouped by initial thickness.

Table 4. Set-recovery after four wetting-drying cycles (mean values ±1 standard deviation).

Species	Initial thickness (mm)	Room temp set-recovery (%)	Boil set-recovery (%)
Beech	6	4.90 (±5.80)	4.30 (±7.30)
	10	10.9 (±6.50)	8.80 (±5.20)
	15	1.90 (±7.20)	6.80 (±8.00)
Poplar	6	19.3 (±18.4)	29.3 (±32.1)
	10	8.20 (±10.0)	16.1 (±11.6)
	15	5.70 (±9.50)	8.00 (±13.8)
Spruce	6	55.5 (±18.5)	47.1 (±15.1)
	10	38.4 (±20.5)	34.5 (±15.5)
	15	36.7 (±18.9)	35.7 (±15.4)