Agricultural residues and the wood of umbrella tree (Musanga cecropioides) as raw materials for the development of reduced emission particleboards
von Travolta Achalle Achale
Datum der mündl. Prüfung:2020-01-31
Betreuer:Dr. Markus PD. Euring
Gutachter:Dr. Markus PD. Euring
Gutachter:Prof. Dr. Ralph Mitlöhner
Name:Dissertation- Travolta Achalle.pdf
Format:PDFDescription:The Dissertation Titled " Agricultural residues and the wood of umbrella tree (Musanga cecropioides) as raw materials for the development of reduced emission particleboards" investigated the technical possibility of producing particleboards of reduced formaldehyde emission using the wood of Umbrella tree, Cacao tree prunings and Bean crop residues as raw materials.
EnglischAgainst the background of the soaring wood prices, the existing wood and waste wood scarcity in the wood-based panel industry, the demand for a more efficient use of the raw material wood, and the fact that wood materials with high formaldehyde emission are no longer accepted by consumers, eco-friendly alternatives for wood and formaldehyde-containing binders should be extensively researched. The focus of this thesis was to investigate the possibility of producing particleboards with low formaldehyde emission using alternative materials. This goal and additionally the reduction of the panels’ density shall be achieved by using the wood of fast-growing tree species, the umbrella tree (Musanga cecropoides), and the prunings of the cocoa tree (Theobroma cacao). In addition to its fast growth, the umbrella tree stands out because it places few demands on the location and is available in large quantities. Cocoa tree prunings (25 t/ha yearly) accumulate regularly and are usually left in the fields to rot, and in some cases burned. In this work, a meaningful material use is ensured. In addition to the umbrella tree wood and the prunings of cacao tree (wood materials), it also investigated whether the residues of the annual crop bean (Phaseolus vulgaris) are suitable for particleboards production. This study was conducted in two phases, the raw material characterization phase (first phase) and the particleboards manufacturing phase. The first phase involved a comprehensive investigation of the physical and chemical properties of the raw materials. In addition to the study raw materials, wood chips of Norway spruce (Picea abies) were used for comparison. The bean crop residues were divided into two categories based on the harvesting and processing season; the rainy season bean crop residues (referred to in this study as bean shells) consisted of 100 percent bean shells and the dry season bean crop residues, consisted of a mixture of bean shells and bean stems. Based on the results of the physical and chemical analysis of the study raw materials, the following conclusions can be made: • The evaluation of the bulk densities revealed that the bulk densities of the bean crop residues of both seasons (for both the surface and core layer chips) were well below the bulk densities of the wood materials. Amongst the wood materials, the chips of umbrella tree wood showed comparatively lower bulk densities for both the surface and core layers chips (127 kg/m3 and 92 kg/m3 respectively) compared to the chips of cacao tree prunings. • Analysis of the pH and buffering capacities revealed a higher pH value (6.4) for the bean crop residues of the dry season compared to 5.6 for the bean shells. Amongst the wood material, the cacao tree prunings and umbrella tree wood had similar pH values of 6.8 and 6.2 respectively, compared to spruce wood (5.4). • The umbrella tree wood and cacao tree prunings, despite their high pH values, exhibited the least buffering capacity values of 0.54 mmol NaOH/100 g and 0.57 mmol NaOH/100 g respectively. The buffering capacity values of the bean shells (14.27 mmol NaOH/100 g) and the bean crop residues of the dry season (6.24 mmol NaOH/100 g) were substantially higher than the rest of the study raw materials. • Examination of the extractives content of the research raw materials revealed that the umbrella tree wood contained the least amount of water-soluble extractives (0.28% for cold water and 1.1% for hot water) but contained the highest amount of ethanol-cyclohexane extractives (3.6%) compared to the rest of the wood materials. The water-soluble extractives content of the bean crop residues of both seasons ranged from 14.58% to 14.7% for cold water and 14.25% to17.5% for hot water. • The analysis of pentosan content showed values of 13% and 16.7% for umbrella tree wood and cacao tree prunings respec-tively, which were seen to be higher than the values of the bean crop residues as well as the value of spruce wood. The pentosan content of the bean shells (8.2%) was not any different from that of spruce wood (8.5%); rather, it was seen to be relatively lower than the value of the dry season bean crop residues (10.2%). • The klason lignin contents of cacao tree prunings (39.2%) and umbrella wood (37%) were substantially higher compared to the klason lignin contents of the bean crop residues of both seasons, and the spruce wood (29.4%). • Finally, the ash contents of the bean crop residues (8.5 -8.9%) were much higher in comparison to the ash content of the wood materials. Amongst the wood materials, cacao tree prunings and umbrella tree wood contained higher amounts of ash (2.1% and 1.85% respectively) compared to spruce wood (0.36%). The particleboards’ manufacturing phase of this study was divided into four parts. The first part investigated the possibility of producing UF-resin (K340) bonded particleboards of reduced formaldehyde emissions based on the raw material; umbrella tree wood, and cacao tree prunings. For comparison purposes, particleboards of spruce wood were also produced. In addition to this, the first part also investigated the effects of coarser core layer chips on the properties of the particleboards of umbrella tree wood and cacao tree prunings. The results of the mechanical-technological properties suggest that it is technically feasible to produce particleboards of reduced formaldehyde emissions of the density 650 kg/m3 and 550 kg/m3 of the standard DIN EN 312:2010 (type 2) from the raw materials, umbrella tree wood, and cacao tree prunings when bonded with UF-resin K340. However, the coarseness of the core layer chips must be appropriate for the boards to achieve high enough bending and stiffness strengths. The possibility to produce non-formaldehyde containing particleboards based on the raw materials, umbrella tree wood, and cacao tree prunings, was the focus of the second part of the particleboards’ manufacture. To achieve this, an isocyanate-based adhesive (PMDI) and a natural binder based on animal protein, blood albumin, were used. The wood chips of the core layer and the surface layers were separately blended with the different adhesives. Particleboards of the densities 650 kg/m3 and 550 kg/m3 were produced in a pilot plant scale. Evaluation of the mechanical-technological properties revealed that despite the higher internal bond (IB) strengths of the boards of cacao tree prunings compared to the boards of umbrella tree wood, their bending strengths (BS) and stiffness characteristics (MOE) on the other hand were considerably lower compared to the boards of umbrella tree wood. It was also revealed that combining the chips of umbrella tree wood and cacao tree prunings in the ratio of 50:50 percent (w/w) on both the surface and the core layer will results in particleboards with superior bending strengths and MOE compared to the boards made exclusively from cacao tree prunings. In addition, the formaldehyde release of the boards of both binder systems was observed to be negligible compared to the limit of E1. The recorded formaldehyde values of the board could be attributed to the so-called natural formaldehyde of the raw materials because the binder systems contained no free formaldehyde. The overall findings indicated that the production of non-formaldehyde containing particleboards of the density 650 kg/m3 for general purpose applications including furniture (DIN EN 312:2010) is technically possible with umbrella wood as raw material when bonded with PMDI. Also, a mixture of umbrella tree wood and cacao tree prunings in the ratio of 50:50 percent (w/w) will results in particleboards with high enough mechanical strengths to meet the requirements of DIN EN 312:2010 when PMDI is used as the glue. The IB values of all the boards bonded with blood albumin exceeded the minimum value specified by the DIN EN 312:2010 standard. However, their MOR (except for the boards made from a mixture of both materials, of the density 650 kg/m3) and MOE failed to achieve the required values. The third part of the project focused on investigating the feasibility of bean shells (bean crop residues of the rainy season) to serve as a substitute raw material for wood in both the core and surface layers of particleboards. Three-layered particleboards (density 650 kg/m3) of umbr- ella tree wood, cacao tree prunings, and industrial wood chips were produced in three production series’. In the first and the second series, the proportions were 100 percent bean shells on the surface layers and 100 percent of the various wood materials in the core layer. That is a 40% substitution of the wood chips of each board with bean shells. The panels of the first series were bonded with PMDI and the second series by UF-resin (340). In the third production series, however, 20 percent (w/w) of the surface layers and 20 percent (w/w) of the core layer of each board were substituted with bean shells. The boards of the third series were also bonded with PMDI (resin load of 4% on the SL and the CL). The substitution level of the wood chips with bean shells was also 40%. The results of the evaluation of the physical and mechanical properties were compared to the required minimum values for commercial particleboards (DIN EN 312:2010 standard for type 2 PB). The particleboards of first production series (100% bean shells on the surface layer and 100% wood materials on the core layer) were able to exceed the minimum required values of internal bond strength, bending strength and modulus of elasticity. In addition, the formaldehyde release (evaluated by the flask and perforator methods) of the boards of the first series was also negligible. The panels bonded with UF-resin (series 2), as well as the particleboards manufactured with bean shells substituted in both the core layerand the surface layers (third series) did not have high enough mechanical strength to satisfy the requirement for type 2 particleboards of the DIN EN 312:2010 standard. Overall, based on the mechanical performance of the boards of the first production series, bean shells can be considered as an alternative surface layer material for particleboards of satisfactory performance for use in interior fittings and furniture applications. The fourth part of the experimental work was to investigate the possibility of producing UF-resin bonded particleboards of the standard DIN EN 312:2010 by substituting 10%, 15% and 20% of the chips of the umbrella tree wood with chips of bean crop residues of the dry season in the core layer of the boards. In addition to these boards, another variant of particleboards made exclusively from the bean crop residues was manufactured. The results revealed that increasing the amount of bean crop residues (from 10%, 15%, and 20%) in the composite matrix significantly reduces the internal bond strength of the particleboards but bending strength, MOE, and the water-related properties are not significantly affected. It is technically possible to produce particleboards with high enough IB and BS to satisfy the requirement of type 2 particleboards of the DIN EN 312:2010 standard by replacing up to 20% of the chips of umbrella tree wood with chips of the bean crop residues in the core layer of the board when bonded with UF-resin (350). However, the MOE values of the boards were slightly lower than the minimum required value (1800 N/mm2). The properties of the particleboards manufactured exclusively from the bean crop residues did not meet the requirements of this standard. The formaldehyde release of all the boards (perforator values) exceeded the E1 limit value of 8.0 mg/100 g of dry board. The overall findings of this project indicate that umbrella tree wood, cacao tree prunings and the bean crop residues of both seasons are valuable and potential alternative biomass that could be used wholly or as a substitute for wood in particleboards production. In the future, there could be a possibility to use these previously unused materials for chipboard and to establish them locally in products, for example in Cameroon.
Keywords: particleboards of umbrella tree wood, particleboards of cacao tree wood, particleboards of annual crop residues