Physico-Mechanical Properties of Wood and Non-Wood Plaster of Paris Bonded Composite Ceiling Boards

© 2020 The Authors. This article is licensed under a Creative Commons Attribution 4.0 License Abstract. Woody (Alzibia zygia) and Non-woody (rattan and yarn strands) fibres were used comparatively to improve the physicomechanical properties of Plaster of Paris bonded composite which is used as ceiling boards. The addition of fibre reinforcement in a discrete form improves the engineering properties of the Plaster of Paris. The woody and nonwoody residues were varied in 10, 20, 30, 40, and 50% of the whole mix while the Plaster of Paris used were in the ratio 100 (control), 90, 80, 70, 60, and 50 %. The mean density of the composite produced is 3250 kg/m3. The mean thickness swelling after 2 and 24 hours is 0.84 % and 0.88 % respectively with the mean water absorption at 13.8% after 2 hours and 16.2 % after 24 hours. The MOR and MOE of the composites produced ranged from 1.21-1.22 N/mm, 2431-51488N/mm for sawdust, 1.17-1.22 N/mm, 10027-49940 N/mm for yarn strands and 1.201.22 N/mm, 23566-86210 N/mm for the rattan strands. The results showed physicomechanical properties of POP-bonded fibre reinforced composites were increased for both wood and non-wood fibres and rattan strands compared best.


INTRODUCTION
Reinforced Plaster of Paris Composite ceiling boards is a new decorative and finishing material that is gaining increasing importance and usage. Plaster of Paris or gypsum is a very soft sulfate mineral of chemical formulae CaSO42H2O which presents itself often as monoclinic, massive, flat, or elongated and generally prismatic crystals with its colour ranging from colorless to white [1]. In recent years, asbestos materials for making ceiling boards have been banned in many advanced countries due to its carcinogenic nature, with agencies in construction industries having identified its real and potentially adverse effect on humans [2]. Locally sourced building materials that would facilitate sustainable development remain underdeveloped to a socially and economically acceptable level, owing to the low level of development of the economy [3].
Authors [4] reported that composite is designed to take advantage of the desirable characteristics of constituent materials by choosing an appropriate combination of matrix and reinforcement material, thus producing a new material that meets the exact requirements of a particular application. Yarn is a long continuous length of interlocked fibres suitable for use in the production of textiles, sewing, crocheting, knitting weaving, embroidery, and rope making, while rattan is a stick made from the stem of the rattan palms. Rattan canes are numbered among the important commercial non-timber forest products employed in the furniture industry in the tropics, however, over 30% of rattan harvested at any time particular for furniture manufacture are wastes [5]. Alzibia zygia is a deciduous tree nine to thirty meters tall with a spreading crown and a graceful architectural form and its bole tall and clear, around 240 cm in diameter. It has a dark grey and smooth surface [6]. These materials experimented as reinforcement to improve the properties of Plaster of Paris to produce durable, affordable, and environmentally friendly (noncarcinogenic substances) material suitable structurally as ceiling boards.

METHODOLOGY
Materials Collection. Sawdust of Alzibia zygia collected from the Bodija plank market in Ibadan was graded and sieved to remove impurities, then oven-dried to around 101 °C to reduce the moisture content of the fibre. Rattan, yarn fibres and Plaster of Paris were purchased from a retail outlet also in Ibadan.
Procedure. The materials were then weighed and batched in accordance to the research methods (Tables 1, 2, and 3). The mixing was done manually with potable water and added into a prepared wooden mold. The mixture was allowed to sit for some minutes before curing take place. The produced composite materials were then subjected to the test to investigate their physical and mechanical properties ( Table 1-3).


The following tests were carried out on the specimens.
Density. After curing, the samples were weighed on a digital weighing scale and their corresponding weight in kilograms was recorded. The density of the materials was calculated with the following equation (1): where  is the density in (kg/m 3 ); w is the weight of the composite produced;  is the volume of the produced composite.
Specific gravity. The specific gravity was calculated using this equation (2): where SG is the specific gravity of samples; c  is the density of composites produced (kg/m 3 ); w  is the density of water in (1000 kg/m 3 ).
Water Absorption and Thickness swelling. The specimen from each specimen was submerged horizontally under 50 mm of distilled water maintained at a room temperature of about 27 °C. The amount of water absorbed after 2 hours and 24 hours were recorded.
w1 and w2 is the initial and final weight before and after soaking respectively.
t1 and t2 is the initial and final thickness before and after soaking.
Modulus of Rupture (MOR). This was conducted to approximate the bending strength of the produced composite materials. The samples were tested using the universal test machine (UTM) of the Department of Agricultural and Environmental Engineering, University of Ibadan.
where P is the maximum force/ load in (N); L -span of the board (mm); B -width of the test specimen (mm); H -thickness of the test specimen (mm).
Modulus of Elasticity (MOE): where P is the maximum force / load in (N); L -span of the board (mm); B -width of the test specimen (mm); H -thickness of the test specimen (mm); D -deflection at mid-point.

RESULTS AND DISCUSSION
Density and specific gravity.   Table 4 shows the densities and specific gravity of the material produced. The densities varies from 3200 kg/m 3 to 3900 kg/m 3 (wood fibre), 2700 kg/m 3 to 4500 kg/m 3 (rattan fibre), 2000 kg/m 3 to 4500 kg/m 3 (yarn fibre) and 4700 kg/m 3 (POP only). Samples produced with POP alone have higher densities due to the presence of reinforced fibres (which tends to be lighter) in other samples. Increase in the fibre content of the composite produced decreases the density and specific gravity of the material which is in accordance to the report on wood composite by [5].
Thickness Swelling and Water Absorption. Table 5 and 6 shows the water absorption and thickness swelling percentage of the composite materials respectively. Cumulatively, the higher the fibre content in the composite, the higher the water absorption, which may be due to the hydrophilic nature of the wood and the other fibres. The behaviour of the produced composites was similarly reported by [8], that the presence of hydroxyl groups inside the cellulose and hemicelluloses attract the water molecules and form hydrogen bonding. Moreover, due to the porous structure of wood fibres, the composites with higher wood content absorb more water which penetrates into the pores according to the principle of capillary flow. The yarn fibre absorbed the lowest amount of water content.  Table 6 shows the results of the thickness swelling test. Generally, the change in thickness of the produced composites is very minimal after 2 and 24 hours. The yarn fibre has the best performance under the thickness swelling test. As reported by [2] increase in the fibre ratio of the composites increases the thickness swelling after water immersion.

CONCLUSION
Fibre-POP composites was produced from wood (Alzibia zygia), rattan (Laccosperma secundiflorum), and yarn. The composites were tested for strength and physical properties. The results derived implied that: 1. The mechanical properties of Rattan reinforced composite in terms of Modulus of Rupture and Modulus of Elasticity has the highest value meaning that bending strength of rattan reinforced composite is high.
2. The use of fibre to reinforce Plaster of Paris considerably increased the strength properties of the material.