Design and Development of False Ceiling Board Using Polyvinyl Acetate (PVAc) Composite Reinforced with False Banana Fibres and Filled with Sawdust

This work deals with design and development of false ceiling board from polyvinyl-acetate (PVAc) composite reinforced with false banana fibres and filled with sawdust. The aim was to develop a light weight and good strength performance false ceiling board using raw materials that are fully biodegradable including sawdust, thus solving the problem of its disposal. The false banana fibres were characterized for its tensile strength, elongation, and moisture content since these parameters affect the composite properties. Hand lay-up method combined with compression molding followed by curing was utilised in the manufacture of the false ceiling composites. The optimum proportions of the raw materials were identified using central composite design software, and the results were 40% sawdust, 40% binder (PVAc), and 20% fibres. The mechanical properties of the developed composite board were evaluated in terms of its tensile strength, flexural strength, and compressive strength. In addition, the composite physical properties were also evaluated including its density and moisture absorption. The optimum results obtained were tensile strength of 12.54N/mm, compressive strength of 7.03N/mm, and flexural strength of 5.13N/mm.


Introduction
The utilization of composites as load bearing structures has been increasing at a faster rate. One of the composite material advantage is its ability to be designed with desirable characteristics suiting the intended purpose [1]. Of late, coarse cellulosic fibers have received significant consideration as alternatives for synthetic fiber as composite reinforcements. This is because the plant fibers impart certain advantages to the composites for instance low density, high stiffness, low cost, renewability, biodegradability, eco-friendly, and high degree of flexibility throughout processing [2,3]. The properties of natural fiber greatly affect the performance of its reinforced composites. These properties include fiber fineness, fiber length, distribution, its arrangement, and fiber percentage in the composite plus the stacking orientation in the composite structure [4]. These natural fibers can be extracted from conventional sources as well as from nonconventional sources like agricul-tural by-products. The natural fibres can be a suitable substitute of synthetic fibres because they are available at a low cost and possess inherent environmentally friendly properties [5].
Natural fibres (NF) are preferable for their appropriate stiffness, mechanical properties, and high disposability [6]. Natural fibre-based composites are becoming important composite materials in automotive, packaging, building, and civil engineering fields, due to their light weight, high strength to weight ratio, and corrosion resistance among other advantages [7]. Among the natural fibres, false banana fibres (Ensete Fibers) are widely used natural fibres in the southern parts of Ethiopia. It is a lingo-cellulose fibre, obtained from the pseudostem of false banana plant (Musa sepientum) with relatively good mechanical properties. The properties of false banana fibre include low cost, low density, biodegradability, renewability, good mechanical properties, and nontoxicity [6]. According to Muller [8], false banana fibres have been used for the production of ropes and can be used as a reinforcing fiber in composite materials [9][10][11][12][13]. Banana fibers have also been used with other fibers to produce hybrid composites [14]. Manickam and coworkers studied the mechanical and water intake properties of banana-carbon hybrid fiber-reinforced polymer composites [15]. They found out that the hybrid composites had comparable properties with carbon fiber-reinforced composite but had higher water intake because of inclusion of banana fibers. The effect of alkaline treatment on banana fibers on the performance of banana fiber/epoxy composites has been studied [16,17].
The composite bulk properties can be enhanced by in cooperating fillers during its manufacture. These fillers can be ballast, sand, CaCO 3 , and sawdust. This work is aimed at using sawdust as a filler which is one of the major industrial wastes resulting from wood exploitation and processing. These sawdust are being disposed in uncontrolled conditions leading to environmental pollution. They can be used to provide heat energy, but resulting pollutants such as ash and air pollutants emanated through the combustion gases, carbon monoxide (CO), volatile organic compounds (VOCs), nitrogen oxides (NOx), sulfur oxides (SOx), and particular emissions (PE) affect human respiratory system [18]. Currently, the disposal of waste to the environment has laid additional pressure to the already fragile environment due to pollution [19].
A number of researchers are working on different ways to dispose-off the variety of agricultural and industrial wastes to minimize their effect on the environment. According to Ataguba et al. reports [20], some of the waste products as sawdust can be recycled into new products that are more environmentally friendly. Natural fiber-reinforced composite boards have been manufactured using sawdust and natural fibres, in order to replace the conventional materials like wood, metals, and asbestos [21,22]. Yakubu produced a composite ceiling board from agro-waste used in houses to reduce sound and heat while giving additional aesthetics [23].
Apart from reinforcing fibers and fillers, the matrix part also affects the performance of composite material. The matrix used can be thermoset or thermoplastic, and for this work, polyvinyl acetate (PVAc) was used. Shedge and Patel reports that polyvinyl acetate resin is a selective binder, due to its well-known adhesion property with cellulosic materials because of the presence of polar acetyl groups [24]. The acetate of the binder can form physical bond with cellulosic material, and the best results are obtained with resin forming a sheath around each individual fibre.
The main aim of this study was to develop a false ceiling board using polyvinyl acetate composite filled with sawdust and reinforced with false banana fibres. The raw materials are eco-friendly, biodegradable, and helps to increase the potential use of the waste sawdust rather than disposing it to the environment. The mechanical properties (tensile strength, flexural strength, and compressive strength) and physical properties (moisture absorption and density) of the manufactured composite material were evaluated and reported.

Materials and Experiments
2.1. Materials. In this study, sawdust having a particle size of 1.8 mm, evaluated using a sieve analyzer, was used as fillers, and false banana fibres were used as reinforcing fibers. The fibres were locally sourced in Ethiopia, and its characterized properties compared with other conventional natural fibres are presented in Table 1.
The physical properties of false banana fibre, such as tensile strength, elongation at break, and moisture content, are moderate compared to other natural fibres as shown in Table 1. After characterization, the composite was developed according to constituent ratios suggested by central composite design software. The steps used, in order to develop the product, included preparation of the raw material (sawdust, resin, and fibres) followed by mixing the resin with the sawdust plus the fibres until a homogeneous mixture was achieved. Layer-by-layer stacking was done before it was cold pressed pneumatically at a pressure of 80 kg/m 2 followed by drying and curing at room temperature.

Experimental Tests
2.2.1. Tensile Strength. The tensile strength of the manufactured sample, size of (5 × 15 × 1) cm, was tested using universal tensile testing machine as per the ASTM D1037 test standard [26]. The composite tensile strength was calculated using Equation (1) [27]: where δt is the tensile strength (N/mm 2 ), W t is the failure tensile load (N), b is the width of the specimen (mm), and t is the thickness of the specimen (mm).

Compressive Strength.
Compressive strength test was carried out using universal tensile testing machine as per the ASTM D1037 test standard [26], and the specimen size was a cube of (2:5 × 2:5 × 2:5) cm. The compressive strength was calculated using Equation (2).
where T c is the compressive strength (N/mm 2 ), W c (N) is the failure load, and b and t are the width and the thickness of the sample (mm), respectively.
where σ is the flexural strength (N/m 2 ), P is the maximum test load (N), S is the dimension between load points (mm), b is the sample width (mm), and t is the sample thickness (mm).

Water Absorption.
Water absorption test was carried out by immersing the composite sample in water for 2 hours and 24 hours at room temperature as per ASTM D570 test standard [30]. The water absorption of the composite material was determined using Equation (4).
where W t is the weight of the composite after immersion in water and W o is the weight of the dried sample.
2.2.5. Density. Density of the manufactured composite was obtained both theoretically (weight ratio method) and areal density (by using Archimedes principle) which was also used to evaluate the void fraction % of the composite material.  Table 2. The optimal values according to the response surface method were 40% sawdust, 40% resin, and 20% fibres, as per the experimental results. The optimal mechanical properties obtained were tensile strength of 12.54 N/mm 2 , compressive strength of 7.03 N/mm 2 , and flexural strength of 5.13 N/mm 2 .

3.2.
Tensile Strength. Figure 1 shows the effect of single factors on composite tensile strength. It can be seen that when the proportions of the constituents increased, the strength of the composite increased. As the proportion of the sawdust increased, the tensile strength increased but only slightly. This could be because sawdust was used as a filler to contribute the bulk properties but not directly affecting the strength properties [31]. The low increase in tensile modulus could be ascribed to two probable explanations, one being a poor dispersion of the sawdust particles throughout the matrix, and the other is the moisture pick-up in the sawdust [32]. The other reason could be its size of 1.8 mm was too short to carry any significant load. As for the increase in resin ratio, there was a great increase in tensile strength probably due the fact that when the resin proportion increased, efficient wetting of the constituent parts was realised. This in turn increased the gluing power of the resin which translated into increased tensile strength. Under loading situation, the resin plays the main part of transmitting the forces across the composites. For composite to perform well under shear forces, the resin phase must not only show acceptable mechanical properties but must also bond well with the reinforcing fibre. The tensile 3 International Journal of Polymer Science load for a composite is reliant on reaction of a composite to tensile loads and also reliant on the strength properties of the reinforcing fibres, since they are strong in relation to the resin system on its own. The increase in fibre proportion also resulted in increase in tensile strength. The reason was that more fibres were available to carry the load [33]. The moderately lower values for the composites manufactured are attributable to the nonuniform stress transmission because of the random orientation of the fibres in the matrix. Figure 2 shows the combined effect of factors on the tensile strength of the composite. It can be seen that the combined effect on tensile strength of resin and sawdust was higher than the combined effect of sawdust and fibres. The effects of factors (sawdust, resin, and fibre) were positive over tensile strength of the composite material; when the factors increased up to optimum level, the tensile strength also increased linearly. But the factor values above optimum per-centage caused the tensile strength of the composite material to reduce. The tensile strength reduced above optimum values due to the poor interface bonding between the matrix, fillers, and fibres, and also, there was incomplete wetting of the fibre by the resin at a higher fibre proportion [33].
ANOVA analysis was performed to check the influence of the input variables on the tensile strength of the manufactured composite. ANOVA Table 3 shows the factors (sawdust, resin, and fibre) had significant influence on the tensile strength with P values of less than 0.05. The proposed model was also significant with a P value of <0.0001.

International Journal of Polymer Science
where A is the sawdust proportion, B is the resin proportion, and C is the fibre proportion. Figure 3 shows the effect of single factors on the composite compression strength. It can be seen that as the ratio of the composite constituents increased, the compression strength of the composite increased. As the ratio of the sawdust increased, the compression strength increases but only slightly. This could be due to the fact that sawdust was used as a filler to increase the bulk properties but not directly affecting the strength properties. As for the increase in resin, there was a higher increase in compression strength perhaps due the fact that as the resin ratio increased, complete wetting of the constituent parts was amplified. This in turn increased the bonding power of the resin translating to increased compression strength. The increase in fibre proportion also resulted in increase in compression strength.

Compression Strength.
The reason could be that more compressive load was carried by more fibres, hence higher strength. The same conclusion has also been discussed [34].
The combined percentage increase of sawdust, resin, and fibre significantly affected the compressive strength as shown in Figure 4. However, it increased only up to optimum level, but above optimum values, the composite compressive strength decreased. This may be because the distribution of filler on the composite material decreased while the amount of void fraction inside the composite material increased at low matrix proportion.
ANOVA analysis was performed to check the influence of the input variables on the composite compressive strength. ANOVA Table 4 shows the factors (sawdust, resin, and fibre) had significant influence on the compressive strength of the composite with P values of less than 0.05. The proposed model was also significant with a P value of <0.0001.
Equation (6) shows a developed model equation that can be used to predict the composite compressive strength from the constituents ratios.
where A is the sawdust proportion, B is the resin proportion, and C is the fibre proportion.  being present on a given composite cross-section to carry the load at a higher fibre weight % [33]. However, further increase in fibre weight content above this value resulted in the lowering of the flexural strength. Similarly, an increase in resin proportion increased the flexural strength until an optimum value because with the increased interfacial interaction between the fibres and the matrices, the natural fibrereinforced composites become stronger [2]. Above this value, the flexural strength started to reduce probably due to strength becomes resin dependent rather than fibre    International Journal of Polymer Science dependent. The increase in sawdust proportion did not have a significant effect on the flexural strength. Figure 6 presents the combine effect of factors on flexural strength of the manufactured composite samples. It shows that the input factors had a positive effect on flexural strength. As seen, resin proportion had the highest effect on the flexural strength of the composite. This is probably due to the fact that at a higher resin proportion, high gluing effect was achieved and more load will be transferred to the reinforcing fibres. But after optimum level, the flexural strength decreased. Flexural strength designates stiffness as well as the degree of deformation of a material when it is subjected to the flexural stress and offers ductility measure of a material. The ductile materials show lower flexural modulus as it experiences a significant deformation before failure happens. While the brittle materials possess a high value of flexural modulus as it fracture without undergoing a large deformation [35].
ANOVA analysis was performed to check the influence of the input variables on the composite flexural strength. ANOVA Table 5 shows the factors (sawdust, resin, and fibre) had significant influence on the composite flexural strength with P values of less than 0.05. The proposed model was also significant with a P value of <0.0001. Equation (7) shows a developed model equation that can be used to predict the composite flexural strength from the component proportions.
where A is the sawdust proportion, B is the resin proportion, and C is the fibre proportion.
3.5. Water Absorption. Evaluation of water absorption properties of natural fibre-reinforced polymer composites is very crucial since the hydrophilic groups on the surface are susceptible to moisture and water. The water absorption rest on diverse parameters such as fibre and sawdust wettability with the polymer matrix, interfacial adhesion, fabrication method, sawdust shape, size, and content voids content, temperature, and chemical structure of the sawdust. The water loving phenomena unfavourably affect the mechanical properties of natural fibre reinforced polymer composites and accelerate the microbial deterioration. The consequence of moisture absorption by the natural fibre-reinforced composite time and again turn out to be a disturbing indication in most applications. Essentially, this absorption totally destroys the bonding force between the fibre and matrix in a massive way. Consequently, it lowers the strength of the composite in due time depending on the immersion time or nature. It also result in poor stress transfer and ultimately to specimen fracture in the long run [36,37]. The composite begins to swell when exposed to moisture giving rise to local strain in polymer matrix that causes microcracks, subsequently, decreasing the mechanical properties of composites [38,39]. The results of water absorption test of composite sample manufactured with optimum percentage of the constituents (sawdust 40%, resin 40%, and fibre 20%) are shown in Figure 7 after 2-hour and 24-hour immersion in water. As seen, as immersion time increased, the amount of water absorbed in the composite also increased which follows Fick's diffusion law [39]. This could be because the raw materials used for the composite manufacture were inherently hydrophilic due to the presence of hydroxyl groups on their surfaces. This shows that the composite developed should not be used for applications that are exposed to water. Figure 7 also shows the tensile strength of the composite reduced as the water absorbed increased. This is probably because the absorption completely terminates the bonding force between the fibre and matrix to a greater extent [39].
3.6. Density. The density of the composite material and its void fraction in percent are shown in Table 6.
From Table 6, the theoretical and actual density of the manufactured composite can be seen for different proportions of sawdust, resin, and fibres. The difference between the two densities shows the void fraction of the composite material which is a subject to the method of manufacture. At a lower proportion of resin, the void fraction was high probably due to the air voids between the fibres and sawdust which were reduced at a higher proportion since the resin filled these air voids. Figure 8 shows the damage morphology exhibited by the composite during flexural, tension, and compression loading, respectively. This shows how the forces will be distributed and propagated during composite use. The damage morphology include matrix crack and fiber pull out when the composite was subjected to tensional forces while it experienced delamination and matrix crack when it was subjected to flexural and compressional forces.

Conclusion
According to the obtained results, the developed composite from false banana fibres, filled with sawdust and polyvinylacetate, can be used to produce eco-friendly false ceiling board composite. The optimum proportion of the raw material was determined using design of expert (central composite design) software, and the best proportion was 40% sawdust, 40% resin, and 20% fibre based on the optimum composite properties. The mechanical properties of the manufactured composite at optimum level of constituent were tensile strength of 12.54 N/mm 2 , flexural strength of 5.13 N/mm 2 , and compressive strength of 7.03 N/mm 2 . In addition, the composite water absorption properties were 9.88% and 25.13% after 2 hours and 24 hours, respectively, while the density of the composite material was between 0.87 and 0.93 g/cm 3 . Therefore, the mechanical and physical properties of the developed false ceiling board composite showed good performance in terms of the evaluated properties. This study also indicates sawdust waste can be used to manufacture useful composite materials, such as false ceiling boards.

Data Availability
Sufficient data have been included in the manuscript. Additional data can be kindly requested from the authors.

Conflicts of Interest
There is no conflict of interest to declare.