Effect of Bark on the Physical and Mechanical Properties of Phosphate Bonded Wood Composites of Black Wattle (Acacia mearnsii De Wild)

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1 Effect of Bark on the Physical and Mechanical Properties of Phosphate Bonded Wood Composites of Black Wattle (Acacia mearnsii De Wild) Stephen Amiandamhen, Martina Meincken, Luvuyo Tyhoda, Stellenbosch University, Stellenbosch, South Africa

2 Background Annually, South African wood processing mills produce 4-6 million tons of wood waste in the form of: Forest residues Saw dust Shavings Bark, etc.

3 Background This waste poses disposal problems and is often Landfilled Land spread Burnt to power steam boilers

4 Introduction A large amount of ligno-cellulosic materials can be used to develop inorganic bonded composites for building application. These materials can be in the form of: Wood (Softwood and hardwood) Fibre crops (Kenaf, hemp, sisal, etc.) Agricultural residues (Bagasse, triticale, etc.) Pulp and paper

5 Ligno-Cellulosic Fibres Advantages Availability Cheap source of natural fibres Environmentally friendly Can be modified to suit design purpose Disadvantages Degradation in alkaline environment Low modulus of elasticity High water absorption Dimensional instability Variable physicomechanical properties

6 Inorganic Bonded Composites Durability Toughness High strength Dimensional stability Fire, water, fungi resistance, etc.

7 Ceramicrete Ceramicrete is a chemically bonded phosphate ceramic It is formed by an exothermic reaction between an acid phosphate and a divalent oxide at low temperatures MgO + KH 2 PO 4 + 5H 2 O MgKPO 4 6H 2 O Not affected by chemical composition of wood

8 Black Wattle (Acacia mearnsii) Alien invasive tree species Ecosystem engineer Variability in form, composition and properties Used for tannins, fuel wood and cheap building materials

9 Objectives To investigate the effect of bark and fly ash content on the properties of the wood composites To determine the optimum conditions that would give the best effect in the measured properties

10 Materials Wood (Acacia mearnsii), EC Biomass, PE, South Africa) Magnesium oxide (Macco Organiques, Zahradnl, Czech Republic) Monopotassium phosphate (Shijiazhuang Lvhe Fertilizer Technologies Co. Ltd, China) Fly ash (Ulula Ash, South Africa)

11 Methods Material preparation Chipping Milling Screening Conditioning Board formation Mixing Pouring Moulding Curing

12 Testing The properties of the boards were evaluated according to ASTM standards. Modulus of rupture (MOR) Modulus of elasticity (MOE) Water absorption (WA) Thickness/Volume swelling (TS/VS) Density

13 Statistical design The experiment was done on a central composite design (CCD) using STATISTICA Software v5. Bark content 10-50% of the total wood content Fly ash content 10 50% of the total inorganic content. The binder ratio of KH 2 PO 4 to MgO was kept constant at 3:1 (100 g wt.) The wood content was also kept constant at 50 g.

14 Design of the composites Board types Bark content (g) Ash content (g) Wood and bark (g) Water (ml) A B C D E F G H I J K (Control)

15 Results

16 Den (g/cc) Density K E A B G I J H C D F Samples (Increasing bark content)

17 MOR (MPa) MOR K E A B G I J H C D F Samples (Increasing bark content)

18 MOE (MPa) MOE K E A B G I J H C D F Samples (Increasing bark content)

19 WA (%) WA K E A B G I J H C D F Samples (Increasing bark content)

20 TS/VS (%) TS/VS TS VS K E A B G I J H C D F Samples (Increasing bark content)

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22 Present study Interfacial bonding Morphology Thermal properties

23 Conclusion It is clear that ground bark can be added to phosphate bonded wood composite to enhance its properties. A mixture of bark and fly ash at 50% loading respectively increases all properties including density, MOR, MOE while decreasing WA, TS and VS.

24 Acknowledgements National Research Foundation (NRF); Grant number EC Biomass, PE, South Africa Ulula fly ash, South Africa

25 Thank you