The Physico-Mechanical, Mineralogical, and Thermal Characterization of Geopolymeric Laterite Bricks Containing Polyethylene Terephthalate Bottle Powder

Abstract

Compressed earth blocks (CEBs) obtained by laterite material geopolymerization have great potential as building materials; however, plastic waste recycling remains an important challenge for the 21st century. Samples of lateritic materials (LAT) from the locality of Kompina and its surroundings (Littoral-Cameroon) were collected, given the region’s association with polyethylene terephthalate powder (P). They were used to make geopolymeric laterite bricks using a phosphoric acid solution (A) concentrated at 10 mol/L, at a fixed value of 20% phosphoric acid, and values of 0, 5, 10, 15, and 20% polyethylene terephthalate (PET) powder. To assess the suitability of these formulations for construction, the CEBs were tested and their physico-mechanical and thermal characteristics determined, including water absorption rate, compressive strength (CS), thermal conductivity, and effusivity. It was revealed that water absorption decreased for the LAT1 and LAT6 formulas, at 6.73% and 5.01%, respectively, with the lowest value being recorded when 10% of the PET powder was used. The water absorption increased beyond this percentage; the CS values did too, with a peak at 10% PET powder, reaching 6.92 MPa and 6.96 MPa for LAT1 and LAT6, respectively, and values decreasing beyond this point. The thermal conductivity and effusivity decreased, with the lowest values at 20% of the PET powder being 0.289 W·m⁻¹·K⁻¹ and 1078.46 J·K⁻¹·m⁻²·s^−1/2, and 0.289 W·m⁻¹·K⁻¹ and 1078.2 J·K⁻¹·m⁻²·s^−1/2 for LAT1 and LAT6, respectively. Based on the results obtained, we conclude that the formulation LAT-P10A20 is the most recommendable.

1. Introduction

Laterites can be defined in many ways, depending on the field in question, such as pedology, engineering, or mining. For engineers, they are materials with porous structures and varying hardness and thickness, often consisting of nodules scoriaceous in appearance; chemists associate them with Fe₂O₃(FeO)-Al₂O₃-SiO₂-H₂O matrices based on kaolinites in which a high proportion of Al³⁺ is replaced by Fe²⁺ or Fe³⁺ [1,2]. Oyelami C. A. et al. [3] proposed a definition based on field observations; they later described lateritic soils as strongly weathered tropical or subtropical residual soils, well graded, and generally covered with sesquioxide-rich concretions.

Cameroon has been facing an urban crisis for many years, marked by strong demographic growth that creates high demand for housing and infrastructure, according to Djobo [4]. The lack of decent housing is felt everywhere in the country. Urban planning experts had estimated this need at around one million housing units in 2010; in 2023, the estimation is more than five million, and this will grow year after year, according to the projections drawn up by the Central Bureau of Censuses and Population Studies (BUCREP) using the third general population and housing census. However, whether it is the construction of 10,000 housing units in the cities of Douala and Yaoundé, 100 housing units in the regional capitals, or housing across the whole of Cameroon and even in Africa, the same observation remains: the vast majority of building materials are imported. However, the exploitation of local mineral resources and the development of local techniques will not only reduce these imports but also facilitate access to decent housing.

Geopolymerization technology has received considerable attention over the past few decades. It involves a chemical reaction between alumino-silicate material and an activator solution at ambient or slightly elevated temperatures. Tchakouté et al. [5] highlight that products obtained by geopolymerization can harden relatively quickly. This technology provides effective solutions for recycling solid waste into construction materials [6,7], as well as for securing and optimizing mining operation performance by mitigating safety hazards caused by the surface storage of tailings; additionally, Wei S. et al. [8] describe how cemented tailing backfill can replace remaining pillars for roof support in underground mining operations. Moreover, this is one of many technologies being tested in aerospace engineering to facilitate manned moon landings, as well as the construction of lunar bases to support scientific and technical research using lunar regolith materials, as emphasized by Bo L. et al. [9]. However, brick stabilized by a hydraulic binder, in this case ordinary portland cement (OPC), remains the most widely used in Cameroon for the construction of modern buildings, even though the manufacture of OPC releases a substantial quantity of CO₂; this has a considerable environmental impact, since it contributes to atmospheric global warming [10,11,12]. Indeed, the manufacturing of one tonne of OPC generates about 0.55 tonnes of CO₂ of chemical origin and 0.39 tonnes of fuel [13,14] during calcination. Moreover, Sore et al. [15] point out that the material transport and other processes involved make the manufacture of portland cement energy-consuming.

Further, plastic is currently integrated into essential products for humans and our environment. Its multiplicity of uses makes it a tool whose much-diversified properties are studied. Its shaping facility, resistance to shock, temperature variation, humidity, etc., make it useful in many fields, such as packaging, building, roadworks, automotives, and electricity, among others. However, the Cameroonian Ministry of Environment and Nature Protection recorded around 600,000 tonnes of plastic waste in 2018. Worse still, according to the report of Fondation Ellen Mac Arthur [16], plastic packaging is set to reach 318 million tonnes globally by 2050, and if nothing is done to intervene, there will be more plastic than fish in the oceans.

Hence, this work aims to propose a solution both for the recycling of PET plastic waste and the stabilization of lateritic materials by geopolymerization using phosphoric acid as an activator to produce CEBs. A 10M concentration is retained throughout based on the existing work of Aurelie RKT et al. [17]. Most studies on geopolymerized lateritic materials associated with solid waste are carried out using calcined laterite. In this work, raw earth materials were used to reduce both costs and pollution; the results will contribute to the lack of decent housing being remedied and encourage people to use local raw materials.

2. Materials and Methods

2.1. Sampling, Preparation of Materials, and Characterization

The soil horizon is a basic sampling unit, but in pedology and geotechnics, one major problem of its use lies in sample representativeness. The precautions that need to be taken when collecting samples in the field depend on the analysis being performed [18]. Herein, lateritic material (LAT) samples were collected in a study area of the locality of Kompina (Littoral Region, Cameroon) and its surroundings, between the parallels 4°21′ to 4°25′ North and the meridians 09°34′ to 09°38′ East (Figure 1). This study will focus on two lateritic soil samples taken from the B-horizon of two different pits and source rocks of distinct ages; namely, LAT1 was taken from sandstone of the Bongue series from the Tertiary–Pleocene, and LAT6 was taken from Cretaceous–Senonian sandstone [19]. These raw material samples were identified using geotechnical tests in the regional delegation of the Littoral Region for the National Laboratory for Civil Engineering of Cameroon (LABOGENIE) (

Table 1. Parameters of the studied samples.

Sample	Liquidity Limit (%)	Plasticity Index	γd max (g·cm−3)	OWC (%)	VBS (g/100 g)	% of Gravel	% of Sand	% of Silt	% of Clay	GTR Classification
Lat 1	55.7	25.8	1.626	23	0.94	47	12.4	32	9	A2
Lat 6	52.8	24.6	1.652	23.8	1.33	45	11.2	34	10	A2

). It emerges from these results that the samples are of class A2 according to the GTR classification, and they were both gravelly–silty laterite. The cleaned and crushed PET bottles were collected from “Namé Recycling”, based in Douala, and the powder used in this work was obtained by an artisanal micronization process (Figure 2), which involved melting, grinding, and then sieving the PET bottles.

The mineralogical compositions of raw materials and different formulas were determined using a Picker powder X-ray diffractometer with a graphite crystal, equipped with an automated sample changer; CuKα radiation with a scan speed of 3–65° 2θ angles at 2°/min was also used [20,21]. The patterns were recorded on magnetic tape as a series of 3100 consecutive data points, where each data point is the integrated intensity over a 0.02° 2θ interval. Figure 3 presents the mineralogical composition and proportion of raw materials.

The lateritic soil (after drying in an oven at 105 °C for 24 h) and PET powder were sieved, respectively, using 5 mm and 160 μm sieves. For the geopolymerization process, 10M H₃PO₄ was used [4].

2.2. Stabilization of Lateritic Materials Associated with PET Powder

The bricks were obtained by the geopolymerization of a lateritic material (LAT)–polyethylene terephthalate powder (P) mixture associated with a solution of phosphoric acid (A). The phosphoric acid/laterite (A/LAT) mass ratio used in this work was 0.2, and its ratio corresponds to the following PET powder/phosphoric acid (P/A) mass ratios: 0.25, 0.5, 0.75, and 1. To obtain a consistency that both allowed for optimal brick compaction and was similar to that of the optimum proctor of the raw materials studied, a quantity of water is added according to the dosage of the A+P+LAT mixture. The phosphoric acid-based geopolymer is composed of an amorphous matrix and crystalline compounds. The amorphous substances are composed of structural units such as Si–O–P, Al–O–P [22], –Si–O–Si–O–, Si–O–Al–O–P [23], and Si–O–P–O–Al [24]. The proportions of the mixtures are presented in

Table 2. The mixing proportions of the geopolymer brick formulations.

Formulations	LAT-P0A0	LAT-P0A20	LAT-P5A20	LAT-P10A20	LAT-P15A20	LAT-P20A20
Lateritic soil (LAT) (g)	150	150	150	150	150	150
H3PO4 (A) (g)	0	30	30	30	30	30
PET (P) (g)	0	0	7.5	15	22.5	30
H2O (g)	34	20	18	15	10	10
Ratio P/A	0	0	0.25	0.5	0.75	1

.

Brick formulation consisted of four steps (Figure 4): 1—the laterite and PET powder were manually mixed; 2—phosphoric acid was added, and this was manually mixed for about 5 min; 3—a certain amount of water was also added, followed by manual mixing for about 5 min; and 4—static compaction at a pressure of 8 MPa was carried out in a cubic mold (4 × 4 × 4 cm³) for physico-mechanical tests and in a prismatic mold (4 × 4 × 1 cm³) for thermal tests, using a LABOTEST France hydraulic press with a capacity of 60 KN. After demolding, the bricks were kept at room temperature (25 °C) in a polyene film for 7 days. After these first 7 days of curing, the samples were then placed in the open air and maintained at 25 °C in the laboratory.

2.3. Characterization of the CEBs

Physico-mechanical and thermal analyses were carried out on 7- and 28-day-old bricks, and compressive strength (XP P 13-901) [25] tests were performed on both those dry and wet. The physical properties of 4 × 4 × 4 cm³ bricks were determined, including their bulk density and water absorption. After the samples were dried at room temperature and their dry weight was stabilized, the bricks were immersed in water at a temperature of 25 ± 3 °C for 24 h, and it was in these samples that wet strength was determined. After removing the samples from the water, they were wiped with a clean cloth and subsequently weighed; their wet mass was compared to their dry mass to determine the amount of water absorbed according to ASTM C642 [26]. The bulk density of the bricks was determined using the graduated cylinder method according to NF EN ISO 17892-2 [27], which involved weighing the paraffined samples and then immersing them in a cylinder containing an initial volume of water; following this, the final water volume was reported, and the bulk density was determined by the ratio of the mass of the paraffin-free sample to the volume of water displaced. The thermal characteristics were determined based on ASTM D5470 [28] using the hot plane method, which consists of placing a thin heating mat between two samples of the same composition. The evolution of the temperature in the center of the plane is measured using a thermocouple. The thermal properties tested in this constant pressure study of 4 × 4 × 1 cm³ specimens were thermal conductivity λ (W·m⁻¹·K⁻¹) and thermal effusivity E (J·K⁻¹·m⁻²·s^−1/2). A HUATO S220-T8 Thermal Properties Analyzer was used to establish these parameters. Once the HUATO S220-T8 is on, the hot surface is inserted between two test specimens, and the assembly is stabilized using a stabilization device. After 180 s, the results are displayed automatically on the screen. The test device is illustrated in Figure 5.

3. Results and Discussions

3.1. Physical Properties of CEBs

Figure 6 presents the samples used to determine the bulk density, water absorption, compressive strength (a), and thermal conductivity and effusivity (b). After determining the water absorption at 25 °C (Figure 7) of stabilized (Figure 7a) and unstabilized (Figure 7b) CEBs, it emerged that water absorption varies from 5.01% to 7.14%, respectively, for the formulas LAT-P10A20 and LAT-P0A20 (LAT6), and between 6.73% and 8.24% for LAT-P10A20 and LAT-P0A20 (LAT1), respectively (Figure 8). After 24 h in water, the unstabilized samples were completely dislocated. Regardless of the raw material source (LAT1 or LAT6), the stabilized CEBs were very sensitive to the amount of PET powder used in the mix.

The rate of water absorption thus decreases with the incorporation of the PET powder for the same quantity of activating solution, with the lowest value occurring at 10% PET. These values provide enough information on the ability of PET powder to waterproof stabilized CEBs. The presence of fine particles of this powder, associated with the action of the H₃PO₄ solution, significantly reduces the pores in the geopolymer matrix. The laterite CEB absorption rate values, associated with PET powder and stabilized with H₃PO₄ solution, do not exceed 14%, and therefore meet the requirements for construction material standards [29].

The bulk density values of CEBs stabilized at room temperature (25 °C) are shown in Figure 9. These values vary from 1.69 g·cm⁻³ (LAT-P20A20) to 2.13 g·cm⁻³ (LAT-P0A20) for LAT1 and from 1.72 g·cm⁻³ (LAT-P20A20) to 2.22 g·cm⁻³ (LAT-P0A20) for LAT6. The general observation is made that the bulk density increases with the addition of the activating solution. Moreover, it decreases with an increase in PET powder in the mixture; this is because the phosphoric acid, by its active principle, will decrease the space between the grains. However, the PET powder, with a lower density than that of the lateritic material, decreases the density of the mixture.

3.2. Wet and Dry Compressive Strengths

Figure 10a,b show the dry compressive strengths (CSs) of raw and stabilized CEB samples of LAT1 and LAT6, respectively, at room temperature (25 °C) with a standard deviation of 1.1. It appears that the compressive strength increases with the addition of the activating solution; at 28 days of age, CS varies from 2.02 to 1.94 MPa for the raw material LAT1 and LAT6 CEBs, respectively, to 4.42 and 4.5 MPa for the LAT1-P0A20 and LAT6-P0A20 CEBs, respectively. More interestingly, it increases with the addition of PET powder from 4.42 MPa and 4.5 MPa for LAT1-P0A20 and LAT6-P0A20 CEBs, respectively, to 6.92 and 6.96 MPa for LAT1-P10A20 and LAT6-P10A20 CEBs, respectively, and decreases beyond 10% powder. Indeed, these stabilized CEB CS values are influenced by the strong cohesion generated by the activating solution in the lateritic material and the waterproofing of the mixture generated by the fine PET particles. This cohesion thus makes it possible to obtain very compact bricks with interesting mechanical properties. The CS values of the stabilized CEBs without PET powder (4.42 MPa and 4.5 MPa for CEBs LAT1-P0A20 and LAT6-P0A20) demonstrate that the lateritic material stabilizes in an acidic environment. This phenomenon is also observed in [30,31,32], in the formation of Poly(phospho-ferro-siloxo) networks resulting from the reaction between phosphoric acid, amorphous phases of aluminosilicates, and iron oxides.

The wet CS (Figure 11) of 28-day-old CEBs evolves in a concordant manner with that of dry CS. It increases with the increase in phosphoric acid content and PET powder, up to the limit of the LAT-P10A20 formula, and decreases beyond 10% PET. However, different wet sample formulations show a drop in strength of approximately 54.7% and 52.1% compared to the dry strength, respectively, for LAT 1 and LAT 6. This drop in strength was also observed by the authors of [33,34], who studied the effect of water on the physico-mechanical characteristics of phosphate and alkali-geopolymer materials, respectively. In these works the geopolymerization precursors used were meta-kaolin and calcined laterite, and the maximum drop in strength under wet conditions was 60% compared to the dry strength for all samples.

Considering the results obtained in this work, it appears that CEBs made from the LAT-P10A20 formula are superior in water absorption and compressive strength. Indeed, these results show that in a phosphated acid environment, the addition of PET powder up to 10% in a LAT-A20 mixture considerably reduces voids in the stabilized material, demonstrated by a decrease in water absorption. This new organization in the internal structure of the material has as a corollary: the increase in the compressive strength. As asserted by Djobo et al. [35], the evolution of compressive strength essentially depends on the improvement of the geopolymer network.

3.3. Microstructural Properties

Figure 12 presents the X-ray powder diffraction patterns observed for raw materials and geopolymer materials associated with PET powder and synthesized in an acidic environment. The stabilized material patterns show the presence of the previously identified crystallized minerals of lateritic soil [36]; no newly formed crystalline phases were detected in the different formulas, only goethite (Fe[O(OH)]), quartz (SiO₂), and kaolinite (Al₂Si₂O₅(OH)₄). Hence, the binder is of an amorphous character typical of geopolymers [37].

Phosphoric acid reacts with alumino-silicate material; in this study, the reaction consists of the substitution of Si⁴⁺ by Al³⁺, thus creating a sialate network, formed by a succession of SiO₄ and AlO₃ tetrahedra (Davidovits, 1994) [38], alternately linked together by oxygen atoms. This structure is similar to that of some zeolites, as described by Van Jaarsveld et al. [39]. The substitution of Si⁴⁺ by Al³⁺ creates a charge deficit, which is filled by the K⁺ cation of kaolinite. This reaction leads to a slight decrease in kaolinite phase minerals and a relative increase in quartz; this is verified in this study by a relative increase in quartz from 36% (LAT6) and 32% (LAT1) to 53% (LAT6-P10A20) and 50% (LAT1-P20A20), and a decrease in kaolinite from 55% (LAT1) and 60% (LAT6) to 42% (LAT1-P20A20) and 40% (LAT6-P5A20) (Figure 13).

3.4. Thermal Properties

From the above and for the two laterite raw materials tested, it emerges that the CEBs obtained by combining LAT+20%A present good results in compression and water absorption. It was therefore a matter of using this formula to verify the impact of the addition of 0–20% PET powder on the thermal properties of the CEBs. Figure 14a,b and Figure 15a,b are graphic representations of the thermal characteristics (conductivity and effusivity) of the different formulas (LAT, LAT-P0A20, LAT-P5A20, LAT-P10A20, LAT-P15A20, and LAT-P20A20) on LAT1 and LAT6, with a standard deviation of 0.002. These results show that the highest thermal conductivity values are given by the formula LAT-P0A20, 0.913 W·m⁻¹·K⁻¹ and 0.911 W·m⁻¹·K⁻¹, respectively, for LAT1 and LAT6, while the lowest are observed in LAT-P20A20, with 0.289 W·m⁻¹·K⁻¹ for both LAT1 and LAT6. Further, the highest thermal effusivity values are those of LAT-P0A20, at 1962.37 J·K⁻¹·m⁻²·s^−1/2 and 1961.9 J·K⁻¹·m⁻²·s^−1/2, respectively, for LAT1 and LAT6, while the lowest belong to LAT-P20A20, with 1078.46 J·K⁻¹·m⁻²·s^−1/2 and 1078.2 J·K⁻¹·m⁻²·s^−1/2, respectively, for LAT1 and LAT6. It appears that thermal conductivity and effusivity increase with the introduction of phosphoric acid, from 0.289 W·m⁻¹·K⁻¹ to 0.913 W·m⁻¹·K⁻¹ and 0.911 W·m⁻¹·K⁻¹, and from 1106.68 J·K⁻¹·m⁻²·s^−1/2 and 1107.8 J·K⁻¹·m⁻²·s^−1/2 to 1962.37 J·K⁻¹·m⁻²·s^−1/2 and 1961.9 J·K⁻¹·m⁻²·s^−1/2 from LAT to LAT-P0A20, respectively, and for LAT1 and LAT6. But conversely, these thermal characteristics decrease with increasing PET powder from 0.913 W·m⁻¹·K⁻¹ to 0.289 W·m⁻¹·K⁻¹ and from 0.911 W·m⁻¹·K⁻¹ to 0.289 W·m⁻¹·K⁻¹, from 1962.37 J·K⁻¹·m⁻²·s^−1/2 to 1078.46 J·K⁻¹·m⁻²·s^−1/2, and from 1961.9 J·K⁻¹·m⁻²·s^−1/2 to 1078.2 J·K⁻¹·m⁻²·s^−1/2 for LAT-P0A20 to LAT-P20A20, respectively, for LAT1 and LAT6.

Heat transfer takes place mainly at the contact points between the grains forming the material. The introduction of PET powder increases the distance between the grains, reducing the thermal parameters. These results are consistent with the work of Khedari et al. [40], who found that the thermal conductivity of bricks made from compressed lateritic clay stabilized with coconut fibers decreases with increasing fiber content; they also correlate with that of Millogo et al. [41], who found that thermal conductivity decreases with increasing content and length of hibiscus cannabinus fibers. Also, Binici et al. [42] investigated the effect of the addition of plastic fibers, straw, or polystyrene fabric in mud brick stabilized with cement, basaltic pumice, or gypsum on the thermal properties and the indoor air temperature of a small house. The results showed that the fiber-reinforced mud brick house was 56.3% cooler than the concrete brick house in summer. This reduction in thermal parameters is very interesting because it will allow for a reduction in air conditioning energy consumption in homes built with CEBs based on these formulas. In addition to reducing the thermal parameters of the CEBs, the thermal conductivity values obtained with the introduction of PET powder are lower than those obtained on concrete tile and cement mortar, which are approximately 1.5 W·m⁻¹·K⁻¹ [43,44,45].

This study has obtained results that align with many others in the field of soil material stabilization, specifically concerning the increase in thermal conductivity [46] caused by the incorporation of the activator into the mixture, allowing for the intensification of CEB density. The increase in the compression strength and decrease in water absorption [47,48] with the incorporation of PET powder into the mixture is the result of the combination of the induced high cohesion due to the presence of H₃PO₄ and the waterproof capacity of the PET powder. It differs from some works with regard to compressive strength [49,50] because of differences in stabilization methods and the size of fibers and plastic wastes introduced into the mixture. This information is shown in

Table 3. Comparison of the obtained results with the literature.

Mixture	Activator	Results	Source
1 Laterite, PET powder (ɸ < 160 µm)	10M H3PO4 (20%)	Increase in compression strength, decrease in water absorption, increase in thermal conductivity and effusivity, only stabilized CEBs used, and decrease with the introduction of PET powder	Current work
2 Calcined iron laterite	8M NaOH	Increase in thermal conductivity	Kaze et al. [46]
3 Clay soil, polyethylene film (50 µm thick)	-	Increase in compression strength, decrease in water absorption	Elenga et al. [47]
4 Clay soil, sugarcane bagasse fiber (ɸ < 0.2 mm)	Cement (12%)	Increase in compression strength, decrease in water absorption	Kumar et al. [48]
5 Laterite, sugarcane bagasse fiber	10M NaOH	Decrease in compression strength, increase in water absorption, and decrease in density	Rachel N.Y. et al. [49]
6 Metakaolin, microparticles from plastic bottles (ɸ < 0.2 mm)	7M NaOH	Decrease in compression strength, decrease in thermal conductivity, and decrease in the thermal effusivity	Blaise N.B. et al. [50]

below.

4. Conclusions

The majority of CEB stabilizations are performed with OPC, whose production is energy-intensive and polluting. When it comes to geopolymerization stabilization, the alumino-silicate materials are preheated to facilitate the geopolymerization process. In this work, we opted for the use of raw lateritic materials. The main objective of this work was to stabilize raw lateritic material associated with PET bottle powder in the form of geopolymerized compressed earth blocks (CEBs) using a phosphoric acid solution concentrated at 10M.

From the physico-mechanical and thermal characteristics of the raw and stabilized materials studied, it appears that the mechanical characteristics increase with the increase in PET powder at a constant phosphoric acid dosage up to the limit of the LAT-P10A20 formula and decrease beyond 10% PET powder, while the thermal conductivity and effusivity decrease. This is very important for construction in tropical countries and especially in sub-Saharan countries with high average annual temperatures. The mineralogical composition remains the same between laterite raw materials and stabilized materials, with a decrease in kaolinite concentration occurring from the former to the latter. The increase in PET powder in LAT-P-A10 CEBs reduces water absorption for both LAT1 and LAT6; reduces the bulk density for LAT-P20A20; increases the dry and wet compressive strength of 28-day-old LAT-P10A20 CEBs; and reduces the thermal conductivity and effusivity of LAT-P20A20 CEBs. Moreover, the LAT-P10A20 formula presents the best combined physico-mechanical and thermal characteristics. In addition, the production of a lateritic 1-kilogram LAT-P10A20 CEB recycles three 1.5 l PET bottles, thus contributing to the protection of our environment.

The LAT-P10A20 CEBs present the optimal combined characteristics of this study; however, to determine the optimal percentage of PET powder to introduce, intermediate percentages between 5 and 10% will have to be tested in future studies. Also, percentages beyond 20% phosphoric acid could be analyzed in further work. In addition, the compressive strength and water absorption present the same formula suitable for construction in humid environments, according to the Cameroonian norm (NC 112-114) [51], although studies on their durability are necessary before approving their use. Moreover, the reduction in PET bottles into powder by the artisanal micronization process used in this work is valuable but limited, given the polluting nature of PET bottle heating.