Properties and potential use of Irvingia gabonensis and Irvingia wombolu kernel extract as an eco-friendly wood adhesive

Alawode, Abiodun Oluseun (2019-04)

Thesis (PhDFor)--Stellenbosch University, 2019.

Thesis

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.

AFRIKAANSE OPSOMMING: Die saamgestelde-hout-produkte industrie maak hoofsaaklik gebruik van formaldehied-gebaseerde lyme wat verkry word van nie-hernubare petrochemiese bronne. As gevolg van die formaldehied vrylatings van die saamgestelde produkte wat verbind word met die lyme asook die carcinogeniteit, is daar ʼn toenemende behoefte aan groen alternatiewe van hernubare bronne. Daar is tans ʼn toenemende belangstelling in die kweek van Irvingia boom spesies as gevolg van die potensiaal in die gebruik van die rou materiaal in verskeie aanwendings. Die gebruikse sluit in bio-diesel produksie, kosmeties, perfuum, seep, gewig verlies aanvullers en dies meer. Die doel van die studie was om die eienskappe en potesiële gebruik van Irvingia gabonensis (IG) en Irvingia wombolu (IW) pit ekstraksie as natuurlike hout lym, met aanvaarbare las eienskappe, volledig te ondersoek. Bondtite®, ‘n kommersiële formaldehied-gebaseerde lym was gebruik as kontrole in die studie. Irvingia gom was onttrek van die pitte van IG en IW deur drie onttrekkings metodes. Die metodes was gebaseer op die oplossing/opgeloste middel en vergelyk in terme van opbrengs en aftreksel eienskappe. Die ekstraksie was geklassifiseerd volgens die Fourier Transvorm Infrarooi (FTIR) spektroskopie om die funksionele groepe wat teenwoordig is te eksamineer. Termogravimetriese Analise (TGA) was gebruik om termiese stabiliteit en ontbindingsparameters te ondersoek. Differensiële Skandering Kalorimetrie (DSK) analise was gebruik om die smeltpunt van die ekstrasies te bepaal. Die sterkte eienskappe van die ekstraksies is bepaal deur die standaard metode van glasvesel-papier repe. Die FTIR spektra van die Irvingia ekstrasies toon die absorbsie piek areas van die hidroksielgroep verminder in koolhidraat inhoud. Die TGA resultate toon dat die aanvanklike ontbindings temperatuur van al die ekstraksies, wissel tussen 138.3–149.11 oC en 129.5–145.3 oC vir IG en IW onderskeidelik, dus, kan ‘n settings temperatuur van 150 oC gebruik word. Dit was ondervind, deur die DSK analise, dat Irvingia ekstrasies ʼn laer smeltpunt het as ander hout lyme. Die sterkte eienskappe resultate toon dat trekkrag per gram van die pit ekstraksies wissel tussen 5.0 tot 13.6 KN/mg en 7.4 tot 14.7 KN/mg vir IG en IW, onderskeidelik. Die modulus van elastisiteit wissel van 17.9 tot 44.1 GPa en 31.3 tot 46.7 GPa vir IG en IW, onderskeidelik. Verdere ondersoek is ingestel om die sterkte eienskappe van die Irvingia ekstraksies te verbeter deur middel van vier natuurlike aanvullers vir hout lym te gebruik. Hexamethometylmelamien (Hexamien) was gebruik as kruisverbinding om ‘n effektiewe kruisbinding reaksie te vorm tussen die metoksielgroepe in hexamien en die hidroksielgroepe in die ekstraksies, asook tussen die aanvullers en die hout. FTIR, DSK en TGA was gebruik vir die gevorderde karakterisering van die gemodifiseerde lym eienskappe. Die lym eienskappe van die gemodifiseerde ekstraksies was getoets op hout spaanders volgens die Amerikaanse Gemeenskap vir Toets en Materiaal standaarde (ASTM D – 906-98). Die verbeterde gewysigde Irvingia hout gebaseerde lym was bewys deur die verskyning van nuwe FTIR piek resultate. Die afgeleide termogravimetriese resultate toon dat die (DTG)MAKS temperatuur vir al die gemodifiseerde monsters tussen 460 en 480 oC wissel, behalwe vir die glyoksal gemodifiseerde monsters (IWLY en IGLY). Die DSK resultate toon dat die set temperatuur (112 – 114 oC) van al die Irvingia ekstrasies naby mekaar is, ten spyte van spesie en modifiserings metode. Die skuifkrag van die gemodifiseerde lyme wissel van 1.72 tot 4.05MPa en 1.74 tot 3.89MPa vir IG en IW onderskeidelik. Die laagste skuifkrag waarde vir die Irvingia lyme was hoër as die die 1MPa vir bord produkte van kruis laag verbinding lae, volgens die EN 16352 (2015) standaard. In kort, die modifisering van die Irvingia gebaseerde lyme, het beter resultate tot gevolg gehad wat bydra tot die sterkte van die lym in die studie. Die hoof voordele van die lyme is dat hulle nie formaldehied of fenol, beide is skadelik vir die omgewing, bevat nie. Laastens, die moontlikheid van die gebruik van natuurlike lyme vanaf Irvingia pit ekstraksies op hout bord produkte, was ondersoek. Die modulus van elastisitet (MOE) van die panele wissel van 458 tot 1281MPa en 660 tot 1580MPa vir IG en IW, terwyl die breekkrag (MOR) van die panele wissel van 3.31 tot 7.38MPa en 5.11 tot 6.88MPa vir IG en IW onderskeidelik. Die gemiddelde waardes vir MOR en MOE vir die Irvingia gebaseerde lym vervaardigde panele, was 5.8 en 1251MPa onderskeidelik. Die waardes is binne die minimum vereistes vir MOR en MOE (5.5 en 1034MPa onderskeidelik) vir paneel graad 1-L-1 soos gespesifiseerd in die ANSI A208.1. Die panele word aanbeveel vir die gebruik as kern-materiaal in soliede deure.

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