PRODUCTION AND CHARACTERIZATION OF SAND-PLASTIC COMPOSITE FLOOR TILES

The amount of plastic waste generated in developing nations like Nigeria is increasing day by day, which is non-biodegradable and causes environmental pollution. Among the plastics used, low-density polyethylene is abundant. These plastics can be removed from the environment and recycled into useful products. In this study, low-density polyethylene plastic waste was utilized in the manufacture of ﬂoor tiles to curb its generation. The tiles were produced by mixing ﬁne sand with molten plastic waste in different proportions. The physical and mechanical properties of the ﬂoor tiles such as water absorption, density, tensile and compressive tests, modulus of elasticity as well as impact strength and friction tests were investigated. The water absorption ranged from 0 . 02 − 0 . 38 %(m/m), while the density varied between 998 . 5 and 1289 kg/m 3 . The tensile strength and modulus of elasticity fell within the range of 0 . 050 to 0 . 232 MPa and 0 . 924 to 2 . 806 MPa, respectively. This result proved the applicability of recycled plastic waste in the formulation of ﬂoor tiles.


Introduction
Plastic waste is now a global problem and one that must be addressed in order to solve worldwide problems concerning resources and energy. Plastics are a generic group of synthetic or natural materials consisting of highmolecular-weight chains composed predominantly if not entirely of carbon. They are classified into two categories, namely thermoplastics and thermosetting plastics, moreover, are found in different forms, e.g. as bags, furniture, cups, basins, drinking and food containers, etc. [1].
The increasing consumption of plastic products in various fields generates a significant amount of waste products, equating to more than 12% of municipal solid waste. Since plastics are non-biodegradable, that is, cannot easily reenter the natural carbon cycle, the life cycle of plastic materials ends at solid waste disposal facilities and in water bodies. However, the full extent of plastic pollution goes far beyond macroplastic litter. Microplastics can contain additives, which have the potential to leach into the surrounding environment, resulting in toxicity to organisms, including carcinogenesis and disruption of the endocrine system in humans [2].
There are several methods for disposing of municipal and industrial plastic waste such as landfill, incineration, Recieved: 23 January 2022; Revised: 7 February 2022; Accepted: 9 February 2022 * Correspondence: alsanja@gmail.com true material recycling and chemical recovery. Treating plastic waste suitably is crucial to waste management and important in terms of energetic, environmental, economic and political viewpoints. Some plastics can safely be recycled, while others cannot so litter the environment [3].
A large and increasing amount of household plastic waste is being produced. The composition of waste varies from country to country, since it is affected by socioeconomic characteristics, consumption patterns and waste management programmes. Nevertheless, generally speaking, the proportion of plastics concerning the composition of waste is high. The largest component of plastic waste is polyethylene, followed by polypropylene, polyethylene terephthalate and polystyrene [4].
Polyethylene is the most common plastic and can be classified into several different categories based mainly on its density and branching. Important grades pf polyethylene are high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE). Plastic is recycled worldwide since it reduces environmental impacts associated with the improper disposal of plastic waste. Therefore, this study focused on the production of floor tiles by mixing sand and plastic waste in different proportions. The characterization of the tiles will provide some insight into the suitability of applying sand-plastic composites in building constructions.

Sample collection and preparation
The plastic waste was collected from the University of Uyo Water Company landfill site in Uyo, South-South Nigeria. The LDPE plastic waste was washed with water to remove dust and other impurities. The washed sample was sun dried for 48 h and shredded into smaller pieces (Fig. 1a). A clay-free sample of fine sand (Fig. 1b) was obtained from Ifiayoung stream in Uyo, sun dried for 24 h, then oven dried at 105 • C for 4 h before being sieved through a 125 µm mesh.

Formulation and Production of Floor Tiles
35 g of plastic waste was continuously introduced into a fabricated melting pot made of stainless steel and heated to a temperature of 160 • C , whilst being stirred continuously to ensure homogeneous melting. 105 g of fine sand was then added to the melted plastic waste before being well mixed. The mixture was transferred into a stainlesssteel mould with the dimensions of 10.0 × 10.0 × 1.5 cm coated with a lubricating oil to facilitate demoulding. The mixture in the mould was compressed by applying

Water absorption
Water absorption tests were carried out in accordance with the ASTM-C373 standard test method. Each sample was oven dried at 110 • C to constant weight (W o ) before being immersed in distilled water at room temperature (25 • C) for 24 h. The samples were removed from the distilled water, cleaned with a cotton fabric and weighed (W t ). The amount of water absorbed (W a ) by each sample was calculated using

Density
The density of each sample was calculated using

Young's Modulus of Elasticity
Young's Modulus of Elasticity (Y ) is a measure of stress per unit strain and was calculated using

Friction Test
A friction test was conducted using the Cussons friction test device graduated from 0 − 90°and was performed based on the ASTM D1037-94 standard test method. The sample was placed on an inclined plane of the piece of equipment and the angle at which the specimen slid freely down the surface was recorded. The coefficient of friction was calculated by: where θ denotes the angle of repose.

Compressive Strength
A compressive strength test was carried out using a universal testing machine and performed based on the ASTM D790 standard test method. The specimens with dimensions of 20 by 20 mm were prepared and tested on a support span of 130 mm in length as per the standard test method. The load at which each sample was compressed as a result of the force applied on it by the machine was recorded. The compressive strength was calculated using Compressive Strength = Maximum Load Cross-sectional Area (7)

Physical Properties of Floor Tiles
The physical properties of floor tiles are presented in Table 1. Water absorption is the ability of a bisque tile to absorb water or moisture. The calculated water absorption of the floor tiles was between 0.02 and 0.38%(m/m). The lowest water absorption (0.02%(m/m)) was obtained in Batch C with a composition of 50%(m/m) LDPE and 50%(m/m) fine sand. The amount of water absorbed closely resembled that of ceramic tiles of 0.03%(m/m). Generally, tiles with a high level of water absorption have a low resistance to chloride and sulphate as well as to water penetration [5]. The density of the tiles ranged from 998.5 kg/m 3 to 1289.6 kg/m 3 as is shown in Table 1. The lowest density, calculated in Batch E, was due to the large quantity of LDPE in the formulation. The density decreased as the proportion of LDPE increased. A rise in the density resulted in an increase in the compressive strength and a decrease in water absorption by the tile [6].

Mechanical properties of the formulated tiles
The mechanical properties of the batches are shown in Table 2. The tensile strength of the floor tiles was between 0.050 and 0.232 MPa. The tensile strength of a material is a measure of the force required to pull a material to the point where it breaks. Batches A and E exhibited the lowest and highest tensile strengths, respectively, possibly due to the amount of LDPE used as a binding agent in their formulations. The Young's modulus of elasticity with regard to the batches of tiles ranged from 0.924 to 2.810 MPa as depicted in Table 2. The Young's modulus of elasticity is a measure of the stiffness of an elastic material and it is an important parameter in evaluating the deformation of materials subjected to a working load. The lowest Young's modulus of elasticity that was calculated in Batch A may result in a lower stiffness compared to that of Batch E that yielded the highest.
The compressive strength of the tiles presented in Table 2 was between 91.7 and 133.0 MPa. Batches D and B exhibited the highest and lowest compressive strengths, that is, 133.0 MPa and 91.7 MPa, respectively. This implies that the impact strength of Batch D to compressive loading will be greater than that of Batch B. Impact strength is the resistance of a material to fracture by being hit, expressed in terms of the amount of energy absorbed before the fracture. The impact strength of the batches ranged from 819.05 to 1720 KJ/m 2 . Since Batches D and B exhibited the highest and lowest impact strengths, respectively, Batch B will easily be fractured. Table 2 shows that the coefficient of friction of the floor tiles is between 0.51 and 0.60. However, given that these values are similar, all the floor tiles responded similarly to sliding freely over the same surface. The coefficient of friction depends on the surface finish of the floor tiles and the values obtained are in good agreement with the acceptable value of 0.5 outlined by the ASTM standard test method [7].

Conclusion
Floor tiles were successfully developed from plastic waste and fine sand. Although the physical and mechanical properties of Batch D yielded the best results, this recycled plastic waste can be used to produce some industrial products like floor tiles which are resistant to highly corrosive environments like offshore platforms.