Department of Forest and Wood Science

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Browsing Department of Forest and Wood Science by Author "Alawode, Abiodun Oluseun"

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    Properties and potential use of Irvingia gabonensis and Irvingia wombolu kernel extract as an eco-friendly wood adhesive
    (Stellenbosch : Stellenbosch University, 2019-04) Alawode, Abiodun Oluseun; Tyhoda, Luvuyo; Meincken, Martina; Stellenbosch University. Faculty of Agrisciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: The wood composite industry relies mostly on formaldehyde-based adhesives derived from non-renewable petrochemical sources. However, due to formaldehyde emission from the composite products bonded with these adhesives and its carcinogenicity, there is a growing need for green alternatives from renewable sources. There is again interest in the domestication of the Irvingia tree species due to the potential use of various parts of the tree as raw materials for a wide range of applications such as biodiesel production, cosmetics, perfumes, soap and weight-loss supplements. The aim of this study was to extensively investigate the properties and potential use of Irvingia gabonensis (IG) and Irvingia wombolu (IW) kernel extracts as natural wood adhesives with desirable bonding properties. Bondtite®, a commercial formaldehyde-based adhesive was used as control in this study. Irvingia gum was extracted from the kernels of IG and IW through three extraction methods. The methods were based on the solvent/solute media and were compared in terms of yield and extract properties. The extracts were characterised using Fourier Transform Infrared (FTIR) spectroscopy to examine functional groups that are present in the extract. Thermogravimetric Analysis (TGA) was used to investigate the thermal stability and decomposition parameters of the extracts. Differential Scanning Calorimetry (DSC) analysis was used to determine melting parameters of the extracts. The strength properties of the extracts were tested using a standard method based on the use of glass fibre paper strips. The FTIR spectra of the Irvingia extracts indicate that absorption peak areas of the hydroxyl group decreased with the increase in carbohydrate content. The TGA results showed that the initial decomposition temperature of all extracts, ranges from 138.3–149.11 oC and 129.5–145.3 oC for IG and IW respectively. The curing temperature could therefore be set around 150 oC. It was discovered through DSC analysis that Irvingia adhesives have a lower melting temperature compared with other wood adhesives. The strength properties results showed that tensile strength per gram of the kernel extracts ranged from 5.0 to 13.6 KN/mg and 7.4 to 14.7 KN/mg for IG and IW, respectively. The moduli of elasticity ranged from 17.9 to 44.1 GPa and 31.3 to 46.7 GPa for IG and IW, respectively. To enhance the strength properties of the extracts, further investigation was carried out on the effect of four different modifiers on Irvingia kernel extracts earmarked for use as natural wood adhesives. Hexamethometylmelamine (Hexamine) was used as a crosslinker to develop an effective crosslinking reaction between methoxyl groups in hexamine and hydroxyl groups in the extracts, modifiers and wood. FTIR, DSC and TGA were conducted for advanced characterisation of the modified adhesives properties. The adhesive properties of the modified extracts were tested on wood veneers according to the American Society for Testing and Materials standard (ASTM D – 906-98). The successful modification of the Irvingia-based wood adhesives was proven with the emergence of new peaks in the FTIR results. The derivative thermogravimetric results showed that (DTG)MAX temperature for all modified samples was between 460 oC and 480 oC, except for the glyoxal-modified samples (IWLY and IGLY). The DSC results showed that the curing temperatures of all Irvingia adhesives are in a close range, irrespective of species and modification methods between 112 and 114 oC. The shear strength of the modified adhesives ranged from 1.72 to 4.05 MPa and 1.74 to 3.89 MPa for IG and IW respectively. The highest values of adhesive shear strength of the modified samples were about 16% higher than panels bonded with IGN (unmodified) adhesives. In a nutshell, modification of the Irvingia-based adhesives resulted in better properties, which contributed to the strength of the adhesives as observed in this study. The main advantage of these modified adhesives is that they do not contain formaldehyde or phenol, both of which are considered potent environmental contaminants. Finally, the possibility of using the natural-based adhesive derived from Irvingia kernel extracts on wood panel products was examined. The modulus of elasticity (MOE) of the panels ranged from 458 to 1281 MPa and 660 to 1 580 MPa for IG and IW while the modulus of rupture (MOR) of the panels ranged from 3.31 to 7.38 MPa and 5.11 to 6.88 MPa for IG and IW respectively. The mean values of MOR and MOE for the panels produced with Irvingia-based adhesives were 5.8 and 1251 MPa respectively. The values are within the minimum required MOR and MOE (5.5 and 1034 MPa respectively) for panel grade 1-L-1 as specified in the American National Standard (ANSI) A208.1. These panels are recommended to be used as core material for solid doors.