Abstract:
Gmelina arborea is a versatile but moderately refractory timber species whose heartwood
is impermeable to chemical treatment due to tyloses deposition which occlude its vessels.
This makes its utilisation unsustainable for a broad range of technical applications.
Bioincision is an emerging procedure capable of improving the permeability of wood to
fluid treatment, but information on its suitability in improving the permeability of Gmelina
arborea heartwood is limited. Therefore, the effect of bioincision on permeability,
anatomical and mechanical properties of Gmelina arborea heartwood was investigated.
Five 34-year-old Gmelina arborea trees were harvested at the University of Ibadan
plantation. A bolt of 300 cm was obtained from the base of each tree. Heartwood of each
bolt was extracted and converted into standard dimensions. Wood samples (n=100) were
bioincised with two white-rot fungi: Inonotus dryophilus (ID, 999) and Ganoderma
adspersum (GA, CBS109416) for 9 weeks, while unincised samples (n=50) served as
control. Ten samples (20 mm x 20 mm x 60 mm) each from bioincised and unincised
treatments were pressure-impregnated for 90 minutes with Tanalith (5.5% concentration)
for permeability tests. Thereafter, samples from bioincised and unincised (n=30) were
pressure-treated with liquid dye and depth of penetration was evaluated. Ten samples (10
mm x 10 mm x 10 mm) each were obtained from bioincised treatments to assess effect of
fungi on wood anatomy. Tanalith absorption (Kg/m3) and retention (Kg/m3) were
calculated. Axial Penetration Depth (APD, mm); Axial Penetration Area (APA, %);
Tangential Penetration Depth (TPD, mm); Radial Penetration Depth (RPD, mm); Lateral
Penetration Area (LPA, %) were measured. Modulus of Elasticity (MOE, MPa); Modulus
of Rupture (MOR, MPa); Maximum Compressive Strength (MCS//, N/mm2); Janka
Hardness (JH, N) of unincised and bioincised samples were determined using standard
methods. Data obtained were analysed using descriptive statistics and ANOVA at α0.05.
Unincised samples had least absorption (112.0±8.5) and retention (6.2±0.5), while GA
incised samples had highest (135.0±16.6 and 7.4±0.9), respectively. The APD
significantly varied from 7.0±1.7 (unincised samples) to 31.2±4.1 (GA incised samples),
implying higher degradation of vessel tyloses by GA. The APA increased from 0.07±0.03
(unincised samples) to 3.1±1.9 (ID incised samples). The TPD ranged from 0.4±0.2
(unincised samples) to 3.0±2.0 (GA incised samples), indicating increased lateral
penetration. The RPD were 0.1±0.1 and 4.8±2.2 in unincised and GA incised samples,
respectively. The LPA varied significantly from 0.001±0.001 (unincised samples) to
17.0±9.4 (GA incised samples). Both fungi induced delamellation of axial parenchyma
cells and degraded tyloses within the wood vessels. Fungal hyphae of GA and ID were
predominantly found in vessels and ray parenchyma cells. The MOE ranged from
7305.0±298.1 (GA incised) to 7771.1±256.0 (unincised samples). The MOR varied
significantly from 70.8±6.1 to 77.9±3.9 in GA incised samples and unincised samples,
respectively. The MCS// were 42.2±1.8 and 43.1±1.4 in GA incised samples and unincised
samples, respectively. The JH increased from 2241.0±115.5 (unincised samples) to
2593.1±208.7 (GA incised samples).
Bioincising Gmelina arborea heartwood with Ganoderma adspersum effectively dissolved
occlusions within the vessels. Wood bioincision improved permeability, with negligible
effects on the mechanical properties.
