Open access peer-reviewed chapter

Thermoplastic Recycling: Properties, Modifications, and Applications

Written By

Taofik Oladimeji Azeez

Submitted: 27 August 2018 Reviewed: 20 September 2018 Published: 27 September 2019

DOI: 10.5772/intechopen.81614

From the Edited Volume

Thermosoftening Plastics

Edited by Gülşen Akın Evingür, Önder Pekcan and Dimitris S. Achilias

Chapter metrics overview

2,054 Chapter Downloads

View Full Metrics


The increasing rate of plastic waste generation coupled with undesirable disposal, especially in the urban areas, has resulted to environmental threat in the globe which has been attributed to legislation, poor biodegradability, economic growth, rural to urban migration, increase in consumption, and standard or cost of living. This chapter will focus on overview, properties of virgin and recycled thermoplastics, recycling techniques, and applications of different types of thermoplastic articles such as HDPE, LDPE, PVC, PET, and polypropylene (PP) with improved properties based on modifications using eco-friendly materials for sustainable applications in order to save human existence from the menace of environmental and economic issues.


  • thermoplastics
  • recycling
  • modifications
  • properties
  • applications

1. Introduction

Globally, poor solid waste management remains an issue of concern in an environment due to inadequate policies, legislation, and public enlightenment on waste disposal [1]. The policies of the government on the environment are merely by mouth with poor implementation. The enlightenment programs remain poor with lack of needed coverage, intensity, and continuity so as to change the attitude toward the management of the waste disposal to the environment. However, the poor activities of government agencies for a safe environment may be attributed to improper funds, inadequate facilities and human resources, low technology know how, and taxation system [2]. Integrated solid waste management, 3R (i.e., reduce, reuse, and recycle) principles have contributed to minimization of waste in the environment. Successful means of solid waste management required an integration of technical, economic, and sociocultural involvement. The generation and disposal of plastic waste in environment have been undesirable activities that posed serious threat to humans’ existence due to large quantities, low biodegradability, and its significant effect on economic growth [3]. In Japan, the waste quantities increased from 46 million tons in 2001 to 65 million tons in 2010 and are expected to have 0.7 kg/capita/day production in 2050 [4] and range from 0.44 to 0.66 kg/capita/day production in Nigeria [5]. The increase in solid waste generation in which plastics are included, in the urban area, is dependent on the increase in migration from rural to urban area, rate of consumption and standard of living, lifestyle, population density, and climatic changes [5, 6] (see Table 1).

S/N Waste material Percentage (%)
Japan (%) Nigeria (%)
1 Paper and cardboard 34 4
2 Organics 32 78
3 Plastics 17 9
4 Metals 6 4
5 Glass 5 3
6 Inorganic 4 1
7 Special waste 2 1
Total 100 100

Table 1.

Solid waste generated [4, 5].

In the USA, about 30 million tons of plastic wastes were produced in 2009 and only about 7% was recycled. Plastic wastes end up in landfills, beaches, rivers, and oceans, thereby causing environmental problems [7]. In the UK, about 5 billion of plastic wastes are generated every year [8]. In some developed countries like Japan, plastic waste is found to be the third major municipal and industrial waste [4] but second in developing countries like Nigeria [9, 10]. Based on production and utilization of plastics in Japan, about 90% of the plastics are thermoplastics (a type of plastic that undergoes a reversible chemical reaction for its curing and melting at high temperature) used for containers and packaging materials (films, sheets, bottles), daily necessities, household appliances, and automobiles as presented in Table 2 and Figure 1 [10, 11]. About 60–70% of thermoplastics are polyolefins, while PET, PS, and PVC make other compositions [12]. In Europe and developing countries, the incineration and landfill techniques used for management of plastics waste covered about 74%, despite advanced effect. Plastics are less expensive, weight saving, durable articles which can readily be molded into a variety of products and found useful in a wide range of applications [13], but its production and usage caused several environmental problems through disposal [14, 15]. Moreover, durability of thermoplastics is a consequence for disposal and accumulation in landfills.

Plastics Japan (%)
1 Polyethylene 24.1
2 Polypropylene 23.1
3 Polyvinyl chloride 15.2
4 Polystyrene 7.0
5 PET 4.0
6 ABS 3.5
7 Others 13.3

Table 2.

Recycling and generation of thermoplastics [11].

Figure 1.

Existing, recycled, and new entrants of plastic wastes [10].

Plastic recycling refers to a process of achieving useful products from waste plastics after its reprocessing or re-melting. Recycling is one of the most important actions currently available that provides a solution on environmental and ecological threats posed by reduce oil usage, carbon dioxide emissions, and the quantities of waste requiring disposal [14, 16]. Despite plastic recycling remaining to be the best means of minimizing plastic waste, its quality is influenced by polymer cross-contamination, additives, non-polymer impurities, and degradation [17]. Recycling of thermoplastics posed many benefits such as provision of raw materials for manufacturing industry, reduced environmental threat to humans since it is non-biodegradable, minimized incineration and landfill issues, less energy consumption for sustenance, and it serving as a source of income and providing job opportunity [18]. However, economic factors that influenced the viability of thermoplastic recycling include the price, cost of recycling compared with forms of required disposal, suitability for specific applications, lack of information about the availability of recycled plastics, and quantity and quality of supply recycled thermoplastics compared with virgin thermoplastics [17, 18]. Thermoplastic recycling follows the pattern of Figure 2.

Figure 2.

Thermoplastic recycling process chart.

Waste polymer recycling can be carried out by four approaches in accordance with ISO 15270, namely:

  1. Primary recycling refers to the recycling of the scrap material of controlled history. This process remaining to be the most popular as it ensures simplicity, low cost, and applicability to clean uncontaminated single-type waste. It involves melting with use of solvents and remolding of clean materials [19].

  2. Mechanical recycling: waste plastic is recycled or reprocessed by mechanical process using melt extrusion, injection, blowing, vacuum, and inflation molding method after sorting [2, 20, 21]. This method utilizes a 100% utilization and conversion of waste plastic to produce the same or other valuable products but with reduced qualities which can be enhanced by the application of additives. It may or may not be necessarily separated depending on desired products and quality. It is applicable to reprocessing plastics that require pretreatment or decontamination.

  3. Chemical or feedstock recycling: waste plastics serve as raw materials and convert into monomer or other products such as fuel oils and cooking gas through decomposition and depolymerization of feedstock with the use of thermal energy or catalyst [22, 23]. This method seems to be economical but reduced the yield of new products [24] and less than the yield of the mechanical recycling of thermoplastics due to no loss of materials and accumulation caused by pipeline blockage as a result of shutdown of the machine, thereby lowering melting points during solidification stages. Pipeline blockages or clogs may be difficult to remove. This method involves decomposition of waste polymers to lower-molecular-weight species for reuse with applications of solvents like benzene, chlorobenzene, trichloroethylene, toluene, and xylene called dissolution/reprecipitation (DR) or solubilization before pyrolysis (applied high temperature and pressure in the absence of oxygen) [25]. This provides an insight to the solution of clogged pipeline issues but at increased processing cost and time with high-energy consumption compared to mechanical recycling.

  4. Energy recovery: This is an effective means to reduce the quantity of organic materials by incineration, with difficult environment pollution control from the waste plastics [24, 26]. It involves cement kiln and waste power generation.

This chapter focuses on modifications of thermoplastic materials (HDPE, LDPE, PVC, PET, and PP) and mechanical recycling for enhanced properties, performance, and quality of the products for sustainable applications.


2. Recycling of modified virgin and waste thermoplastics

The choice of recycling of waste thermoplastics depends on processing equipment such as injection, single-screw extruder and film blowing machine, and processing conditions (temperature, time, content of materials, and rheological behavior) and product uses [27, 28, 29, 30, 31, 32]. The application of additives or modifiers like compatibilizer (nonreactive and reactive), fillers or fibers (inorganic and organic) have been attributed to ease processing and improvement in compatibility [28, 31]. More so, the recycling of waste thermoplastics is cheaper than virgin types, but its inferior properties [20, 21], contaminations, and poor suitability [33] remain an issue of concern for effective applications. Blending technology remains a proffer solution due to low cost to produce, lower technical risk, and eco-friendly materials when compared to developing new polymers [28]. Sorting or separation before recycling through manual [34] application of principle of density and solubilization with the use of solvents (hexane, benzene, xylene, and toluene) provides solution to contamination [2] but not cost effect and risk. Techniques for modifications of thermoplastics may be due to the use of different waste or virgin thermoplastics and natural materials, thereby producing composites with enhanced properties and durability [35]. This can be influenced by processing, crystallization, and phase morphology as reported by Lin et al. [32]. The use of different waste or virgin thermoplastics seems to be uneconomical due to cost of blended and non-compatibility of the thermoplastics which may require a new compatibilizer. The use of natural materials for modification of virgin and waste thermoplastics remains a potential technique for thermoplastic recyclates. Therefore, the major reasons for modification of plastic resins in the industries include to meet specific processing and performance specification of a plastic product that is not satisfied by a single component, to upgrade the properties of postconsumer plastic wastes, for scientific research, for interest and development, and for financial optimization [31, 32]. However, degradation of thermoplastic materials by chemical processes is a function of reaction between the components and the environment. The reduction in photodegradation of thermoplastics by ultraviolet absorber as an antioxidant shows a retardation effect of oxidation [36]. Therefore, the aging process of thermoplastics can be influenced by the synergistic action of factors like electromagnetic radiation and thermal energy on the oxidation, favoring the initiation of degradation by excision of chain and radicals of thermoplastics [36].

2.1 Modifications and properties of recycling of virgin and waste HDPE

The incorporation of the carbon nanotube, zeolite, LDPE, PP, natural fillers, and fibers with treatment into the waste polymer for reuse has resulted to an improvement of the composite strength and enhancement of compatibility of blended components of composites as presented in Table 3. The improvement has been reported to be a function of compatibilizer types, size and particle shape, branching, and dimensions of polymeric chains as reported by [37]. In the case of natural fibers or fillers, it seems fibers or fillers containing compatibilizer which may or may not have been identified. Moreover, the melting flow rate of recycling of postconsumer or waste HDPE remains inconsistent with stabilization, and the consistency can be achieved with a mixture of phosphite and phenolic. This might be uneconomical. The enhancement in mechanical properties and performance of the HDPE matrix and composite product by additives (sodium hydroxide (NaOH), sodium lauryl sulfate (SLS), and acetic anhydride) have also been attributed to increased interfacial adhesion coupled with its improved water absorption [21], biodegradability, biocompatibility, antimicrobial activity, and non-toxicity with the use of chitosan compounds [38]. The density of recycled virgin and waste HDPE is within the range of 0.02–0.96 g/cm3 [36, 39]. Increase in density can be ascribed to chemocrystallization, annealing effects and changes in lamellar orientation, fiber loading, moisture absorption, and aging of HDPE products [35]. Annealing effect involves changes in spherulite size of HDPE material after heat effect, and aged surface shows loss of gloss observed as a result of environmental effect through oxidative stress and disappearance of crystalline molecule of the HDPE materials produced by a surface contraction. The surface contractions initiate micro-cracks and lead to embrittlement of ductile HDPE polymers [35].

Materials Modification Tensile strength (MPa) Tensile modulus (MPa) Flexural strength (MPa) Flexural modulus (MPa) Hardness Impact strength (J/m2) References
Virgin HDPE 21 189 6.8 [33]
Virgin HDPE Using LDPE 22.5 860 135 [28]
Virgin HDPE 3% Carbon nanotube and 2 cycles 36 1700 5 [40]
Waste HDPE Natural zeolite, clinoptilolite (K2,Na2,Ca)Al6Si3O72. 23H2O of 1–2% with particle size <40 μm 21.8 218 25 [37]
Waste HDPE 24.619 836.25 27.114 1390.7 21 859.3 [20]
Combretum dolichopetalum fiber 32.427 939.6 18.2 1568.1 28 496.0462
Acetic anhydride-treated Combretum dolichopetalum fiber 38.5153 1220 8.5111 19944.24 33 787.3806
NaOH-treated Combretum dolichopetalum fiber 34.9041 984.99 32.067 2277.15 39 469.5912
Waste HDPE 27.628 792.59 34.519 1390.7 24 962.8 [21]
Cissus populnea fiber 30.4827 839.022 36.1904 1425.89 30 155.795
Cissus populnea fiber treated with NaOH 29.6903 793.05 39.3962 1568.44 35 398.62
Cissus populnea fiber treated with SLS 31.8013 823.245 39.568 1455.68 38 394.683

Table 3.

Mechanical properties of modified virgin and waste HDPE materials.

2.2 Modifications and properties of recycling of virgin and waste LDPE

The high quantity of waste LDPE and its average mechanical properties coupled with influence of aging of the product have not motivated utilization in many packaging applications such as bags, film, and pallet covers, but modifications may improve the mechanical properties. Also, the qualities of LDPE composites have been linked with poor interfacial adhesion between both phases of individual constituents which explain weak mechanical properties. This interfacial adhesion has a direct relation to compatibility. The processing conditions of machine also influenced the compatibility of the polymers. Some modifications of LDPE are presented in Table 4. The use of virgin and waste or recycled PP to modify LDPE using twin and single-screw extruder has been reported by Sylvie and Jean-jacques [12]. In the report, PP increases some mechanical properties such as tensile strength and modulus with reduced impact strength of the LDPE for single extruding machine, although the twin extruding machine gave better mechanical properties due to improvement in homogeneity of the polymer. The use of compatibilizer such as EPDM, graft copolymer (PE-g-poly (2-methyl-1,3-butadiene), and ethylene-propylene copolymer enhanced the interaction between the polymers and resilience, thereby improving the mechanical properties of the LDPE/PP composites. The use of compatibilizer in virgin and recycled polyolefins influenced the quality of the composites based on technology and recycled waste of LDPE by the addition of EPDM compatibilizer [41]. The presence of ethylene-propylene diene monomer (EPDM) revealed the variation in properties such as wide-angle x-ray diffraction (WAXD), differential scanning calorimetry (DSC), and mechanical properties of virgin and recycled LDPE/PP [36]. The destruction of thermal and mechanical properties of virgin LDPE and PP as well as blended LDPE/PP was found to be greater than those from recycled polyolefins because of the absence of antiaging in the virgin products. The impact EPDM modifier have been reported on stability of LDPE/PP products based on natural and influenced ageing conditions with improved mechanical (tensile and impact strength) properties of the LDPE/PP with increase in modifier content. The impact EPDM modifier significantly improved the compatibility of recycled LDPE and PP and reduces the recrystallization of PP in the blends during aging and decreases the formation of the imperfect β polymorph crystal which depends on the presence of additives resulting in chain mobility retardation, presence of shear stress changing the chain structures, and fast cooling conditions at foil production as reported by Borovanska et al. [36]. Moreover, the significant improvement in rheological property such as viscosity, crystallinity index, and tensile properties of the recycled LDPE can be achieved by linear low-density polyethylene (LLDPE) blend with a ratio of 4:1 and applicably good for film products at 60% blended LLDPE [15]. The modification of recycled LDPE by PP using injection molding machine was also reported that the tensile properties increases with reduction in impact strength as increase in PP content as well as reduced processing temperature [42].

Thermoplastics Modification Tensile strength (MPa) Tensile modulus (MPa) Hardness Impact strength (J/m2) References
Virgin LDPE Starch grafted with maleic anhydride 16.34 520.16 [45]
Virgin LDPE Virgin PP 25.1 5.5–6.5 [36]
Waste LDPE Natural zeolite, clinoptilolite (K2,Na2,Ca)Al6Si3O72. 23H2O of 1–2% with particle size <40 μm 19.5–22.9 195.73–232.14 18–26 [37]
Waste LDPE Waste 10% PP 8.7–12.1 241–336.1 23–37.2 [41]
Waste LDPE Waste 10% PP + EPDM 7.6–8.5 211.1–236.1 46.4–53 [36]
Waste LDPE 30.33 240.7 2.3 583 [47]
Waste LDPE Husk filler 31.58 565.7 13.15 600 [48]
Okpa filler 35.14 861.2 17.53 583 [47]
Virgin LDPE 10% PP using single-screw extruder 9.4 205 15.2 [12]
Waste LDPE 10% PP 10.0 248 12.3 [12]
Virgin LDPE 10% PP using twin screw extruder 9.6 226 8.5
Waste LDPE 10% PP using twin screw extruder 10.3 256 12.6
Waste LDPE 10% PP + 5% graft copolymer using twin screw extruder 11.8 280 12.5
Waste LDPE 10% PP + 5% EPDM using twin screw extruder 10.1 245 16.5

Table 4.

Mechanical properties of unmodified and modified virgin and waste LDPE.

The effect of wood flour of Pinus radiata as fillers at a constant loading of 45 wt.% of recycled post-consumed plastic waste reported to be influenced by virgin PP [43]. In the report, the addition of virgin PP improved tensile and flexural moduli and flexural strength of wood plastic/LDPE composites (WPC). The highest mechanical properties of recycled LDPE composites have been reported for wood polymer composites with virgin PP (5%) and lower mechanical properties with higher virgin PP content of 55 and 71.5% compared to PE. The moisture absorption of WPC with virgin PP blend reported to be higher than without PP with adverse effect on the mechanical properties when immersed in water. More so, the use of virgin PP delay degradation and lower the thermal stability of WPC. This is also stay in agreement with report of Zhao et al. [44]. The decrease in tensile strength with increasing starch content in starch/LDPE composites attributed to incompatibility of the hydrophobic LDPE and hydrophilic starch and the increase in stiffness attributed to better dispersion of starch in LDPE matrix [45]. This incompatibility demands the use of compatibilizers such as styrene/ethylene-co-butylene/styrene grafted with maleic anhydride (SEBS-g-MA) and anhydride grafted polypropylene (PP-g-MA), Mixture Irganox 1098/Irganox 1078-Irgafos 168/Chimassorb 944 [44, 46].

The novel application of natural materials (filler or fibers) is to enhance undesirable properties and poor biodegradation of LDPE matrix. The use of rice husk, bambara, and mahogany fillers with improved tensile strength and modulus, flexural strength and modulus, and hardness with reduction in impact strength has been reported [47, 48, 49]. The increase in mechanical, thermal, and biodegradation behaviors of the composites was attributed to improved interfacial adhesion and compatibility. The reduction in impact strength is a result of fiber dispersion, uneven distribution, and micropore formation in the composites. It can be deduced that natural fillers or fibers contain a compatibilizer which has not been identified. There is also limited report on the modifications of fillers and fibers for enhancement of mechanical, physical (water absorption, density, etc.), thermal, and electrical properties (conductivity, dielectric properties, etc.) of LDPE matrix. Chemical recycling (pyrolysis) had been a major technology for waste or postconsumer LDPE to save the environment, but not cost-effective; emissions of some constituents and required additives or modifiers (catalysts) for considerable yields of the products in many applications [24, 30]. Incorporation of natural zeolite, clinoptilolite ((K2,Na2,Ca)Al6Si3072), improved the strength of the filled composites, rheological behavior, thermal, compatibility of the individual polymeric components, morphology, and texture of the moldings from recycled polyolefins which strongly depends on the type of zeolite, size and shape, branching, dimensions, and types of polymeric chains [37].

Chemical materials have been used as catalysts in the pyrolysis of plastics to obtain liquid products with higher yield and selectivity. Hence, numerous experiments were performed to find out the best catalyst to produce the most desirable products, taking the economic factor into consideration. Pyrolysis of plastic waste to fuel involves many limitations that prohibit the industrial plastic recycling process including the difficulty in modifying it from batch process to continuous process. In industrial process, plastic waste is fed into the reactor directly through hopper for melting in pyrolysis reactor with high melting point (300°C and above, depending on the types of plastic). Therefore, any temperature lower than its meting point may result to solidification of the plastics in the process pipelines, hence causing blockage of the pipelines.

2.3 Modifications and properties of recycling of virgin and waste PVC

The increase in commercial vehicles and road usage with construction resulted to increase in demand of bitumen for pavement and road construction. Yet, the durability of the bitumen depends on appropriate binder for enhancement of performance of bitumen. The use of little quantity of virgin thermoplastics provides a reasonable performance with bitumen but is uneconomical compared with only bitumen. The utilization of waste PVC for effective performance as bitumen binder in pavement and road construction products seems to be interesting because of its low cost and because it is one of the abundant thermoplastics that causes environmental threat [50]. The applications of PVC have been reported to hinder and be not suitable for many applications because of incompatibility as a result of many factors [51]. PVC possesses high melting points which hindered the mixing, and it is impractical to make any further attempts to incorporate it in some applications like bitumen road construction. Recycled LDPE/PVC blends have been modified using EPDM as effective toughening, compatibilizer, and dispersant agent in applications. Recyclability of PVC waste can be achieved mechanically without modifications or use of new plasticizer since the separation of other mixed plastics is possible through triboelectrostatic technology [50, 52]. The technology of triboelectrostatics depends on the ability of polymer to the electron loses or gains because electrons gains and charges negatively may be as a result of higher affinity of polymers, whereas loss of electrons and positively charge may be attributed to polymer with the lower affinity. Because of high electronegativity of chloride ions, it can mix with many polymers such as PET, PP, PS, and PE with enhanced properties as reported by Hamad et al. [50]. The use of wood fillers or fibers as natural modifiers have been reported to improve mechanical properties of recycled PCV rather the recyclability [53], and slightly reduction in mechanical (tensile, flexural, hardness and impact) and structural properties (i.e., decrease in molecular weight due to molecular chain scission caused by shear stress involved in reprocessing) [54]. The reduction in properties exists because of incompatibility or poor intermolecular interaction which can be modified by surface techniques.

2.4 Modifications and properties of recycling of virgin and waste PET

Polyethylene terephthalate (PET) is a transparent semicrystalline, long-chain thermoplastic polyester which can be produced by a polymerization of terephthalic acid with ethylene glycol and remains the most used thermoplastics in many applications [55, 56]. It is characterized as easy to handle, durable, strong, thermally with low glass transition temperature, and chemically stable with low gas permeability [57]. It exhibits brittle behavior, good mechanical properties, and dimensional stability as well as good gas and chemical resistance which resulted to its wide applications [58]. Waste PET may be in bottles, foils, and cords from tire [57, 58]. Globally, the rate of generation of waste PET is about 20 million tonnes that amounted to about 15% which is alarming due to population growth, urbanization, standard of living, and cost of production, but the recycling rate of waste PET found to be 29.3% lower [56]. The issue with the reuse of waste PET may be associated with size, content, mixing process, type of mixer, temperature, time profile during mixing process, and contaminations or additives like stabilizers and pigments [58, 59]. In bitumen asphalt modification for the road construction, the mixing process may be wet or dry process. The wet process involves blending of thermoplastics and bitumen in a mixer and then mixing of thermoplastic modified bitumen to aggregates, while the latter involves incorporation of thermoplastics to very hot aggregates prior to mixing with bitumen [56]. Waste PET recycling employs dry process, and it can be modified to achieve better feasibility in terms of adhesion between the aggregates and binder, stability, and even mixing and minimizes the pore formation and moisture absorption. Appropriate recycling process conditions of waste PET make significant environmental and economy impacts through conservation of natural resources, environmental pollution, energy, and enhancement of engineering and physical properties of construction materials [58]. An increase in recycled PET content caused a decrease in melt flow index or rheological properties of the aggregate [29]. Recycled PET exhibits pseudo-plastic behavior, and it has been used to improve the rheological properties of asphalt as well as increased the viscosity and stiffness and enhanced the softening of stone mastic asphalt (SMA) [58].

Incorporation of recycled PET with appropriate content and size increased the compressive, tensile, and flexural strength/s and ductility of concrete, creates lightweight aggregate of development of building materials, or decreases the bulk density of the composites, thereby helping polymer concrete in saving energy and minimizing the problem of solid waste posed by PET as well as other thermoplastics provided the impurities were removed prior to reprocessing [58].

Synthetic thermoplastics such as HDPE and acrylonitrile butadiene styrene (ABS) blend nano silicon (IV) oxide (SiO2), and polylactic acid (PLA) can modify PET waste to improve its performance using the extrusion process based on a different mixing ratio. The use of virgin HDPE has been reported to improve rheological and mechanical properties when compared to waste PET using a less than 5% virgin HDPE [60]. The mechanical properties of composites of recycled PET improved with increase in incorporated nano silicate (SiO2) content blended with ABS [61]. Modification of PET waste by the addition of small amounts of virgin PLA using melt mixing technology also shows reduction in viscosity of the composites with higher thermal sensitivity and mechanical properties compared to recycled PET [50, 62]. It should be noted that the performance of recycling of waste PET was hindered due to the presence of impurities, decomposition, and degradation of polymer chains as reported by Imamura et al. [57]. The modifications by compatibilizer like ethylene glycidyl methacrylate (EGMA) modified PE copolymer significantly improved the miscibility of recycled PET with PP, PE, and PS molecules, respectively, unlike linear low density polyethylene copolymer (LDPE) [57]. The use of natural materials to modify the properties of recycled PET such as fibers or fillers is not available in literature. The efficacy and performance of recycled PET applications required optimum conditions of modified process, PET size and content, and additive or modifier content.

2.5 Modifications and properties of recycling of virgin and waste polypropylene

Due to favorable qualities of PP like density, versatility, photodegradation, and cheapness in cost of production, it is replacing many materials used for artifacts such as packaging products and automobile bumpers. The increasing rate of use of polypropylene coupled with inherent incompatibility of polyester and polyolefins seeks for improvement in the performance of PP in many applications [63]. The improvement in PP performance has been achieved through modification techniques by incorporation of grafted maleic anhydride (PP-g-MAH), clay-based nano-fillers, inorganic nanoscale particles, and poly(trimethylene terephthalate) (PTT) blends using organically modified montmorillonite (Cloisite nanoclays) as compatibilizers for the purpose of improving compatibility, mechanical, crystallization, and melting behavior of PP composites [64, 65, 66]. PTT is an aromatic polyester with combined properties of PET and poly(butylene terephthalate) (PBT). The factors that influence the properties of the PP composites are mix or blend ratio, crystallization temperature, compatibility process time, and size [63]. There is loss of mechanical properties for composites of LDPE and HDPE modified with PP which is due to incompatibility of recycled PP/LDPE and PP/HDPE composites [39]. The modification of recycled PP with HDPE reveals a partial compatibility which caused an improvement in tensile strength and elongation with the use of EPDM compatibilizer [67]. The modification of recycled LDPE/PP with 1% montmorillonite nanoclay exhibits appreciable improvement in strength, physical properties, and stability of bitumen [68].


3. Microstructural behavior of recycled thermoplastic matrix and its modifications

The microstructural behavior in this content is limited to Fourier-transform infrared spectroscopy and scanning electron microscopy as discussed in subSection 3.1.

3.1 Fourier-transform infrared spectroscopy

FTIR analysis of recycled thermoplastics exhibits no extra peaks for the blends, neither any shifts nor changes in the absorption bands of the carbonyl, hydroxyl, and carboxylic groups of HDPE, LDPE, PET, PVC, and PP resins which indicates the absence of any specific interaction, entanglement, or chemical reaction between the polymers and modifiers as reported by Mamoor et al. (Figure 3) [29]. In the case of modification of recycled thermoplastics using untreated natural fiber, there exists a shift or change in the absorption peaks of the carbonyl, hydroxyl, and carboxylic groups of the fiber-reinforced recycled thermoplastics, thereby influencing the physical and mechanical properties of the matrix and interfacial between the fiber and HDPE as reported by researchers [21, 69]. This resulted in improved quality of the thermoplastic products. The shift, change, appearance, and disappearance of absorption peaks correspond to reaction of the functional groups. This functional group dictates chemical reaction between the polymers and modifier, resulted to change in absorption peak correlate change in strength and modulus of the thermoplastics.

Figure 3.

FTIR of recycled thermoplastics (a) HDPE [29], (b) LDPE [30], (c) PCV [29], (d) PET [29], and (e) PP [29].

3.2 Scanning electron microscopy

The scanning electron microscopy depicts the morphology of virgin and recycled thermoplastics at fracture surfaces when stressed and characterized the ductile, toughness, stiffness, and brittle nature of HDPE, LDPE, PCV, PET, and PP without modification [32], but improvement in compatibility using EPDM compatibilizer has been reported [2, 70]. The improvement in rheological morphology does not indicate an improvement in compatibility as well as mechanical properties [71]. Modification of recycled HDPE with treated natural fiber using NaOH, SLS, acetic anhydride, CaCO3 filler, and zeolites as well as synthetic fibers is characterized with improvement in polymer dispersion, even distribution of fibers, interfacial adhesion, fiber tearing, micro-crack formation, modifier content and size, nature of the modifier, and reduction in void formation [20, 43, 72, 73, 74, 75]. This indicated the enhanced compatibility which corroborates the improvement in physical, mechanical, and thermal properties of the modified recycled thermoplastics and dictates its applications.


4. Application of recycled thermoplastics

4.1 Applications of recycled HDPE

The application of the HDPE composites is a function of the favorable properties coupled with cost implication of the production, and it may be affected by additional modified agents such as fiber or filler, NaOH, acetic anhydride, zeolite, and sodium lauryl sulfate. The use of recycled HDPE composites has been reported for many applications such as packaging (food storage containers and bottles for milk jugs) [13, 28, 38], banners, swimming pool installation, corrosion protection for steel pipelines, folding chairs and tables, electrical and plumbing boxes, plastic surgery (skeletal and facial reconstruction) [27], modified asphalt for pavement and road construction [29, 59, 75], housewares, industrial wrapping and gas pipes [30], and storage sheds, enhancing the economic, health, and social values as well as minimizing environmental issues that might be posed by HDPE disposal [38]. Applications of recycled HDPE in the encapsulation of radioactive, hazardous, and mixed wastes have been reported by Lageraaen and Kalb [76].

4.2 Applications of recycled LDPE

Incorporation of recycled LDPE at concentrations ranging from 2 to 5% by mass of bitumen possesses consistent desirable properties for bitumen asphalt applications [51, 69]. Utilization of LDPE for production of liquid milk packaging [16], bread packaging and sandwich bags, housewares, toys, buckets, wire and cable jacketing, and carpet [13, 38, 68] and use of recycled thermoplastics for encapsulation of hazardous, radioactive, and mixed waste disposal save the environment from economic, environmental, and health issues [76].

4.3 Applications of recycled PVC

Polyvinyl chloride waste has been used in plumbing pipes and fittings, but its utilization as a binder in bitumen applications has been found unsuccessful due to high melting points which hindered the mixing as a result of poor compatibility [51]. PVC sheets have been reported to be employed for making food trays, cling film and blister packages [13], household appliances, packaging, construction, medicine such as human rehabilitation, electronics, automotive and aerospace components [29], and building floor applications [52].

4.4 Applications of recycled PET

Recycled PET could be used for making waterproof [13] water and soft drink bottles, thermally stabilized films (e.g., capacitors, graphics, film base and recording tapes, etc.), electrical components, and textile products [58] if properly modified. The use of recycled waste PET as a modifier in bitumen road and pavement construction is hindered by mixing ratio and processing conditions due to high melting point [51]. It is widely used in making automobile part, electronics, food packaging, house ware, lighting product, power tools, sports tools, x-ray sheets, and photographic applications [55, 59].

4.5 Applications of recycled PP

Recycled polypropylene can be used for packaging articles, automobile bumper, foams, bottle tops, carpets, and household components [13] and in making straws and sweet wrappings, PP powder, and PP mulch at concentrations ranging from 2 to 5% by mass of bitumen consistently desirable for bitumen asphalt applications [51]. The recycled PP is also applicable in 3D printing filament [77]. An application of recycled PP is dependent on good compatibility with modified materials with synergistic effects.


5. Conclusion

Globally, disposal of postconsumer or waste thermoplastics into the environment is alarming and posed a serious economic, environmental, health, and social burden. Employing appropriate technology, especially mechanical recycling with modifications of thermoplastics, can save the world from threat that might be posed by thermoplastic wastes. Appropriate additives such as natural fibers and fillers with eco-friendly, less expensive, available, and degradable potentials should encourage saving the world from this serious menace. The use of recycling technique with appropriate modification will not only exhibit conservation of the waste thermoplastics but altered the physical, rheological, mechanical, electrical, and thermal properties of the recycled thermoplastics for effective applications. An effective and sustainable application of recycled thermoplastics depends on optimization of process conditions, parameter, modifying agents and techniques, equipment, and time. Hence, the quality and performance of the recycled aggregates or composites are enhanced.


Conflict of interest

There is no conflict of interest.


  1. 1. Achilias DS, Andriotis L, Koutsidis IA, Louka DA, Nianias NP, Siafaka P, et al. Recent advances in the chemical recycling of polymers (PP, PS, LDPE, HDPE, PVC, PC, nylon, PMMA), material recycling. In: Achilias DD, editor. Material Recycling-Trends and Perspectives. Rijeka, Croatia: IntechOpen; 2012. pp. 3-64
  2. 2. Achilias DS, Roupakias C, Megalokonomos P, Lappas AA, Antonakou EV. Chemical recycling of plastic wastes made from polyethylene (LDPE and HDPE) and polypropylene (PP). Journal of Hazardous Materials. 2007;149(3):536-542. DOI: 10.1016/j.jhazmat.2007.06.076
  3. 3. Christine T. Recycling electronic wastes in Nigeria: Putting environmental and human rights at risk. Northwestern Journal of International Human Rights. 2012;10(3):154-172
  4. 4. El-newehy M. Plastic Waste Management. King Saud University; 2016. pp. 1-35
  5. 5. Igbinomwanhia DI. Status of waste management. In: Integrated Waste Management. Rijeka, Croatia: IntechOpen; 2011. pp. 11-34
  6. 6. Angaye TCN, Abowei JFN. Review on the environmental impacts of municipal solid waste in Nigeria: Challenges and prospects. Greener Journal of Environmental Management and Public Safety. 2017;6(2):018-033. DOI: 10.15580/GJEMPS.2017.2.062117079
  7. 7. Weber R, Gaius C, Tysklind M, Johnston P, Forter M, Hollerti H, et al. Dioxn- and POP- contaminated sites-contemporary and future relevance and challenges: Overview and background, aims and scope of the series. Environmental Science and Pollution Research International. 2008;15(5):363-393
  8. 8. European Commission (EC). White Paper on Climate Change, SEC2009. pp. 386-388
  9. 9. Nzeadibe TC, Iwuoha HC. Informal waste recycling in Lagos, Nigeria. Communications in Waste and Resource Management. 2008;9(1):24-31
  10. 10. Aderogba KA. Polymer wastes and management in cities and towns of Africa and sustainable environment: Nigeria and European experiences. Social Sciences. 2014;3(4-1):79-88. DOI: 10.11648/
  11. 11. Plastic Waste Management Institute. An Introduction to Plastic Recycling. Tokyo, Japan: Plastic Waste Management Institute; 2016
  12. 12. Sylvie B, Jean-jacques R. Study and characterization of virgin and recycled LDPE/PP blends. European Polymer Journal. 2002;38:2255-2264
  13. 13. Zare Y. Recycled Polymers: Properties and Applications. Vol. 2. Rijeka, Croatia: IntechOpen; 2016. pp. 27-50
  14. 14. Edmonds N. Plastics 101 Introduction; Plast New Zeal Ind Assoc2016. pp. 1-40
  15. 15. Fråne A, Stenmarck Å, Rüdenhausen M, Zu C, Gíslason S, Raadal HL, et al. Nordic Improvements in Collection and Recycling of Plastic Waste [Internet]. Norden, Denmark; 2015. Available from:
  16. 16. Choudhury A, Mukherjee M, Adhikari B. Mixtures of recycled milk pouches with a virgin LDPE-LLDPE blend. Progress in Rubber, Plastics and Recycling Technology. 2005;21(3):219-230
  17. 17. Pivnenko K, Jakobsen LG, Eriksen MK, Damgaard A, Astrup TF. Challenges in plastics recycling. In: di Pula SM, editor. Proceedings Sardinia 2015: Fifteenth International Waste Management and Landfill Symposium. Cagliari, Italy: CISA Publisher; 2015. pp. 1-7
  18. 18. Hopewell J, Dvorak R, Kosior E. Plastics recycling: Challenges and opportunities. Philosophical Transactions of the Royal Society B. 2009;364:2115-2126
  19. 19. Grigore ME. Methods of recycling, properties and applications of recycled thermoplastic polymers. Recycling. 2017;2(24):1-11. DOI: 10.3390/recycling2040024
  20. 20. Azeez TO, Onukwuli OD, Walter PE, Menkiti MC. Influence of chemical surface modifications on mechanical properties of combretum dolichopetalum fibre—high density polyethylene (HDPE) composites. Pakistan Journal of Scientific and Industrial Research Series A: Physical Sciences. 2018;61(1):28-34
  21. 21. Azeez TO, Onukwuli DO. Effect of chemically modified cissus populnea fibers on mechanical, microstructural and physical properties of cissus populnea/high density polyethylene composites. Engineer Journal. 2017;21(2):25-42. DOI: 10.4186/ej.2017.21.2.25
  22. 22. Garcia JM, Robertson ML. The future of plastics recycling. Science. 2017;358(6365):870-872. DOI: 10.1126/science.aaq0324
  23. 23. Ademiluyi T, Akpan C. Preliminary evaluation of fuel oil produced from pyrolysis of low density polyethylene water-sachet wastes. Journal of Applied Sciences and Environmental Management. 2007;11(3):15-19
  24. 24. Park JJ, Park K, Park J, Kim DC. Characteristics of LDPE pyrolysis. Korean Journal of Chemical Engineering. 2002;19(4):658-662
  25. 25. Wong SL, Ngadi N, TAT A. Solubilisation of low density polyethylene (LDPE) for pyrolysis. In: 4th International Graduate Conference on Engineering Science and Humanity. Johor Bahru, Malaysia: Universiti Teknologi Malaysi; 2013. pp. 1-7
  26. 26. Garcıa JM. Catalyst: Design challenges for the future of plastics recycling. Chem. 2016;1:813-815
  27. 27. Miller P, Sbarski I, Iovenitti P, Masood S, Kosior E. Rheological properties of blends of recycled HDPE and virgin polyolefins. Polymer Recycling. 2001;6(4):181-186
  28. 28. Kukaleva N, Simon GP, Kosior E. Modification of recycled high-density polyethylene by low-density and linear-low-density polyethylenes. Polymer Engineering and Science. 2003;43(1):9-12
  29. 29. Mamoor GM, Shahid W, Mushtaq A, Amjad U, Mehmood U. Recycling of mixed plastics waste containing polyethylene, polyvinylchloride and polyethylene terephthalate. Chemical Engineering Research Bulletin. 2013;16:25-32
  30. 30. Achilias DS, Antonakou Ε, Roupakias C, Megalokonomos P, Lappas A. Recycling techniques of polyolefins from plastic wastes. Global NEST Journal. 2008;10(1):114-122
  31. 31. Jesmy J, Jyotishkumar P, Sajeev MG, Sabu T. Recycling of polymer blends. In: Grigoryeva O, Fainleib A, editors. Recent Developments in Polymer Recycling. Transworld Research Network: Kerala, India; 2011. pp. 187-214
  32. 32. Lin J, Pan Y, Liu C, Huang C, Hsieh C, Chen C-K, et al. Preparation and compatibility evaluation of polypropylene/high density polyethylene polyblends. Materials. 2015;8:8850-8859
  33. 33. Parmar H. Rheology of peroxide modified recycled high density polyethylene [thesis]. Melbourne, Australia: RMIT University; 2007
  34. 34. Stefan T. Recycling of mixed plastic waste—Is separation worthwhile? [thesis]. Stockholm, Sweden: Royal Institute of Technology; 2000
  35. 35. Luzuriaga S. Utilization of compatibilization and restabilization methods in the recycling of commingled municipal plastic waste [thesis]. Brunensis: Masaryk University in Brno; 2009
  36. 36. Borovanska I, Krastev R, Benavente R, Pradas MM, Lluch AV, Samichkov V, et al. Ageing effect on morphology, thermal and mechanical properties of impact modified LDPE/PP blends from virgin and recycled materials. Journal of Elastomers and Plastics. 2014;46(5):427-447
  37. 37. Borovanska I, Cerrada ML, Zipper P, Djoumaliisky S. Recycled polyolefin blends: Effect of modified natural zeolite on their properties and morphology. Polymer-Plastics Technology and Engineering. 2016;55(5):486-497
  38. 38. Lima PS, Brito RSF, Santos BFF, Tavares AA, Agrawal P, Andrade DLACS. Rheological properties of HDPE/chitosan composites modified with PE-g-MA. Journal of Materials Research. 2016;32(4):2017
  39. 39. Bonelli CMC, Martins AF, Mano EB, Beatty CL. Effect of recycled polypropylene on polypropylene/high-density polyethylene blends. Journal of Applied Polymer Science. 2001;80:1305-1311
  40. 40. Svensson S. Reprocessing and characterisation of high density polyethylene reinforced with carbon nanotubes [thesis]. Borås: University of Borås; 2017
  41. 41. Borovanska I, Dobreva T, Benavente R, Djoumaliisky S, Kotzev G. Quality assessment of recycled and modified LDPE/PP blends. Journal of Elastomers and Plastics. 2012;44:1-19
  42. 42. Strapasson R, Amico SC, Pereira MFR, Sydenstricker THD. Tensile and impact behavior of polypropylene/low density polyethylene blends. Polymer Testing. 2005;24:468-473
  43. 43. Arango C, Rodríguez-llamazares S, Castaño J, Zuñiga A. Effect of virgin heterophasic pp copolymer content on moisture absorption, thermal and mechanical properties of recycled polyethylene wood flour composites. Journal of the Chilean Chemical Society. 2014;59(1):2373-2377
  44. 44. Zhao X, Luo X, Lin X, Qi X. Rheological and thermal properties of blends of recycled LDPE and virgin LDPE. Advances in Materials Research. 2013;737:2501-2504
  45. 45. Wojtowicz A, Janssen LPBM, Moscicki L. Blends of natural and synthetic polymers. In: Janssen LPBM, Moscicki L, editors. Thermoplastic Starch: A Green Material for Various Industries. Weinheim, Germany: University of Groningen; 2009. pp. 35-53
  46. 46. Jose J, Jyotishkumar P, George SM, Thomas S. 6. Recycling of polymer blends. In: Grigoryeva O, Fainleib A, editors. Recent Developments in Polymer Recycling. Transworld Research Network: Kerala, India; 2011. pp. 187-214
  47. 47. Azeez TO, Olaitan SA, Atuanya CU, Chukwudi DO, Akagu CC, et al. Effect of filler weight fraction on the mechanical properties of bambara groundnut (Okpa) husk polyethylene composite. International Journal of Current Research. 2013;5(7):1714-1717
  48. 48. Atuanya CU, Olaitan SA, Akagu CC, Onukwuli OD. Effect of rice husk filler on mechanical properties of polyethylene matrix composite. International Journal of Current Research and Review. 2013;05(15):111-118
  49. 49. Olaitan SA, Azeez TO, Atuanya CU, Onukwuli OD, Officha MC, Menkiti MC. Effect of mahogany filler on mechanical properties of reinforced polyethylene matrix. Academic Research International. 2013;4(4):284-292
  50. 50. Hamad K, Kaseem M, Deri F. Recycling of waste from polymer materials: An overview of the recent works. Polymer Degradation and Stability. 2013;98(12):2801-2812. DOI: 10.1016/j.polymdegradstab.2013.09.025
  51. 51. Casey D, McNally C, Gibney A, Gilchrist MD. Development of a recycled polymer modified binder for use in stone mastic asphalt. Resources, Conservation and Recycling. 2008;52(10):1167-1174
  52. 52. Yarahmadi N, Jakubowicz I, Martinsson L. PVC floorings as post-consumer products for mechanical recycling and energy recovery. Polymer Degradation and Stability. 2003;79:439-448
  53. 53. Augier L, Sperone G, Garcia C, Borredon M. Influence of the wood fibre filler on the internal recycling of poly(vinyl chloride)-based composites. Polymer Degradation and Stability. 2007;92:1169-1176
  54. 54. Petch-Wattana N, Covavisaruch S, Sanetuntikul J. Recycling of wood plastic composites prepared from poly(vinyl chloride) and wood flour. Construction and Building Materials. 2012;28:557-560
  55. 55. Ahmad AF, Razali AR, Razelan ISM. Utilization of polyethylene terephthalate (PET) in asphalt pavement: A review. In: IOP Conference Series: Materials Science and Engineering; IOP Publishing. 2017. pp. 1-7
  56. 56. Choudhary R, Kumar A, Murkute K. Properties of waste polyethylene terephthalate (PET) modified asphalt mixes: Dependence on PET size, PET content, and mixing process. Periodica Polytechnica Civil Engineering. 2018;2:1-9
  57. 57. Imamura N, Sakamoto H, Higuchi Y, Yamamoto H, Kawasaki S, Yamada K, et al. Effectiveness of compatibilizer on mechanical properties of recycled PET blends with PE, PP and PS. Materials Sciences and Applications. 2014;5:548-555
  58. 58. Sulyman M, Haponiuk J, Formela K. Utilization of recycled polyethylene terephthalate (PET) in engineering materials: A review. International Journal of Environmental Science and Development. 2016;7(2):100-108
  59. 59. Kalantar ZN, Karim MR, Mahrez A. A review of using waste and virgin polymer in pavement. Construction and Building Materials. 2012;33:55-62. DOI: 10.1016/j.conbuildmat.2012.01.009
  60. 60. Navarro R, Ferrandiz S, Lopez J, Segui VJ. The influence of polyethylene in the mechanical recycling of polyethylene terephthalate. Journal of Materials Processing Technology. 2008;195:110-116
  61. 61. Shi G, He L, Chen C, Liu J, Liu Q , Chen H. A novel nanocomposite based on recycled poly(ethylene terephthalate)/ABS blends and nano-SiO2. Advances in Materials Research. 2011;150-151:857-860
  62. 62. Mantia FP, Botta L, Morreale M, Scaffaro R. Effect of small amounts of poly(lactic acid) on the recycling of poly(ethylene terephthalate) bottles. Polymer Degradation and Stability. 2012;97:21-24
  63. 63. Jafari SH, Kalati-vahid A, Khonakdar HA, Asadinezhad A, Wagenknecht U, Jehnichen D. Crystallization and melting behavior of nanoclay-containing polypropylene/poly (trimethylene terephthalate) blends. Express Polymer Letters. 2012;6(2):148-158
  64. 64. Dorscht BM, Tzoganakis C. Reactive extrusion of polypropylene with supercritical carbon dioxide: Free radical grafting of maleic anhydride. Journal of Applied Polymer Science. 2003;87:1116-1122. DOI: 10.1002/app.11561
  65. 65. Si M, Araki T, Ade H, Kilcoyne ALD, Fisher R, Sokolov JC, et al. Compatibilizing bulk polymer blends by using organoclays. Macromolecules. 2006;39:4793-4801. DOI: 10.1021/ma060125+
  66. 66. Vo LT, Giannelis EP. Compatibilizing poly(vinyli-dene fluoride)/nylon-6 blends with nanoclay. Macromolecules. 2007;40:8271-8276. DOI: 10.1021/ma071508q
  67. 67. Penava NV, Rek V, Houra IF. Effect of EPDM as a compatibilizer on mechanical properties and morphology of PP/LDPE blends. Journal of Elastomers and Plastics. 2012;45(4):391-403
  68. 68. Sadeque M, Patil KA. Marshall properties of waste polymer and nanoclay modified bitumen. The FACTA Universitatis, Series: Architecture and Civil Engineering. 2014;12(1):1-9
  69. 69. Ahmedzade P, Fainleib A, Gunay T, Grigoryeva O, Kultayev B, Starostenko O, et al. Use of maleic anhydride grafted recycled polyethylene treated by irradiation in bitumen modification. In: 6th Eurasphalt & Eurobitume Congress 2016; Prague, Czech Republic. 2016. pp. 1-9
  70. 70. Clemons C. Elastomer modified polypropylene—polyethylene blends as matrices for wood flour—plastic composites. Composites: Part A. 2010;41(11):1559-1569. DOI: 10.1016/j.compositesa.2010.07.002
  71. 71. Micic P, Bhattacharya SN, Field G. Melt strength and elastic behaviour of LLDPE/LDPE blends. International Polymer Processing. 1996;11(1):14-20
  72. 72. Fávaro SL, Ganzerli TA, de Carvalho Neto AGV, da Silva ORRF, Radovanovic E. Chemical, morphological and mechanical analysis of sisal fiber-reinforced recycled high-density polyethylene composites. Express Polymer Letters. 2010;4(8):465-473
  73. 73. Muhamed HE, Yehia MSE, Ashraf AM, Muhamed HZ. Composites from rice straw and high density polyethylene: Thermal and mechanical properties. International Journal of Engineering Science. 2015;4(4):57-64
  74. 74. Cheraghi H, Ghasemi FA, Payganeh G. Morphology and mechanical properties of PP/LLDPE blends and ternary PP/LLDPE/nano-CaCO3 composites. Strength of Materials. 2013;45(6):730-738
  75. 75. Colbert BW. The performance and modification of recycled electronic waste plastics for the improvement of asphalt pavement materials [thesis]. Michigan: Michigan Technological University; 2012
  76. 76. Lageraaen PR, Kalb PD, Adams JW, Fuhrmann M, Milian L, Weber C, et al. Use of Recycled Polymers for Encapsulation of Radioactive, Hazardous and Mixed Wastes. United States: U.S. Department of Energy; 1997
  77. 77. Iunolainen E. Suitability of recycled PP for 3D printing filament [MSc thesis, plastics technology]. 2017

Written By

Taofik Oladimeji Azeez

Submitted: 27 August 2018 Reviewed: 20 September 2018 Published: 27 September 2019