Acaciahybrid has been planted in Malaysia’s forest plantation for wood resources. Evaluation of the wood showed that the wood has density446 kg m-3, good dimensional stability and low acid buffering capacity (0.10 mmol l-1).The amount of reactive polyphenols from 80 °Cwater extractionwas 45.5% which is consideredhigh for wood. The polyphenols tremendously decreased at extraction temperatures of 120 °Cand over. Particleboards of Acaciahybrid bonded with urea formaldehyde (UF) resin consistently showed better physical and mechanical properties than recycled wood. Thickness swelling of the boards was 15%, water absorption 30%, modulus of elasticity 26.25 MPa and modulus of rupture 3811 MPa. The boards quality continuedto be high when bonded with melamine urea formaldehyde (MUF) and phenol formaldehyde (PF) resins whencompared to spruce particleboards. Internal bond strength of the boards was rangedfrom 0.9 to 1.3 MPa. The work showed that the Acaciahybrid is potential for high quality particleboards.
Decay of Acaciahybrid boards due to Pleurotus ostreatus, Trametes versicolor, Pycnoporus sanguineusand Coniophora puteanawasinvestigated. Internal bond strength of boards bonded with UF and MUF resins strongly deteriorated (86 to 100% loss) due to decay fungi. T. versicolorand C. puteanacaused severe loss in weight (14.9%to 37.3%) of the boards.Improved decay resistance of the boards was achieved when bonded with PF resin.The board was dimensionally stable and has high degree of internal bond strength even after decay fungi exposures.Maximum weight loss was 8.3% due to P. ostreatus.Internal bond strength of the boards after decay test was between 0.5 and 1.1 MPa.Investigation onthe effect of Acaciahybrid extractives(hot water extraction at 80, 100, 120 and 160 °C) to wood gluing wascarried outusing automatic bonding evaluation system (ABES). Significant increment in shear strength (5.2 MPa) of wood veneers was obtained when the UF resin wasmixed with extractives from 80 °Cextraction with 8% solids content. The effect of extractives on the UF resin was likely to be influenced by the amount of reactive polyphenols.Subtle changes occurred in the thermal behaviour ofUF resinmixed withextractives at temperatures between 240 and 340°Cprobablycaused by the decomposition of UFpolymer.The FTIR analysis showed that the resin and extractive mixtures have similar structural peaks to those of atypical UF resin.
The extractives were characterised using MALDI-TOF mass spectrometer. Extractives from 80, 100 and120°Cextraction containedcompoundswithmolecular weightbetween332and647Daprobably of simple polyphenols. Fourmajorcompoundswereconsideredwith molecular weightsof 544, 560, 566, and582Da. Extractives from 80 and 100 °Cextractioncontainedpolymerswithrepetitiveunit of74or148Dawhichcould be oflignans. Extractivesof high temperature extraction (160°C)hadtwodifferentcompounds, hexose polymers with 162 fragment unit and acetylxylose with 174 Da fragment.Better performanceof Acaciahybrid particleboards could be related to reaction of simple polyphenols (galloyl glycosides, lignin glycosides and flavonoids) in the extractives with formaldehyde of the resins which involved methylolation and condensation processes. This is supported by the significant weight loss of UF and extractives mixtures from thermal analysis.