1 Introduction

Plastic pollution has become a significant problem due to the increasing dependence on plastic products and the inability of recent recycling technologies to handle the amount of plastic waste produced. From 1950 to 2015, 8300 million tons of plastic were produced, of which 5800 million tons were used once before disposal. Global plastic production has changed from one area to another, as shown in Fig. 1. In total, 4600 million tons have been disposed of in landfills [1]. Despite pledges from various brands to recycle plastic waste, these pledges are insufficient for ending the plastic waste crisis [2].

Plastic waste is a significant issue in develo** countries. Many countries, including the Philippines, Vietnam, and Indonesia, face this problem; plastic recycling cannot handle the amount of plastic waste produced because their economies rely on low-cost, single-use items [3,4,5]. The Philippines is the world’s third-largest producer of plastic waste to date. In 2010, the Philippines produced 0.5 kg of plastic per person per day, resulting in 1.80 million metric tons of mismanaged plastic waste. Plastic waste in the Philippines is mainly generated by packaging (35–45%) and construction (20%). Only 9% of plastic packaging waste is being recycled to date, primarily at the industry level [6, 7].

Fig. 1
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Source: Plastics Europe Market Research Group (PEMRG) and Conversion Market & Strategy GmbH (W. D’ambri‘eres 2019). The reproduction is permitted

Global plastics production

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Political agreements worldwide have developed a framework to establish community-scale plastic recycling programs. A community-scale method for recycling plastic allows the technique to reach the greater population while increasing the country’s overall recycling rate [8]. This approach may be challenging in regions with significant government interventions; however, in the Philippines, the government works closely with local communities. Plastic waste reduction in the Philippines is made by recycling plastic at the community level.

The community-scale method benefits the local economy by creating new job opportunities and introducing useful upcycled plastic items, such as plastic pots. Plastic pots deviate from the garbage dump for an extended period while creating value for society by providing for their housing needs. An article published by the World Economic Forum has proposed that entrepreneurial investments may solve the plastic waste crisis. In this article, we show the mismanagement of plastic worldwide and demonstrate an approach for interested entrepreneurs to make revenue by collecting and recycling plastic [9].

Plastic pots are a simple example. Plastic waste is useful in various manners [10, 11]. There are many techniques for recycling different types of plastic [12,13,14]. Not all steps shown in Fig. 2 must be followed to produce useful items. Shredder flakes are used for various purposes other than feeding for extruders because they are utilizable as raw materials. The extrudate is useful for more than just molding; for example, the extrudate is applicable in three-dimensional (3D) printing [15,16,17]. Plastic recycling begins with separation from garbage, which is accomplished by thoroughly washing and drying. The plastic is then shredded into flakes and fed into an extruder. The plastic extruder melts the flakes, and the molten plastic is molded into desired shapes [18].

Fig. 2
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Steps for recycling plastic products

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The differences in mechanical properties between high-density polyethylene (HDPE) and various plastics are highlighted in Table 1. The solid mechanical properties of HDPE bottle caps makes them suitable and safe for recycling in school and laboratory environments [19]. Grade, tacticity, and molecular weight determine the melting temperature of HDPE material, ranging from 120 to 180 \(^{\circ }\)C.

Table 1 Various types of plastics and their mechanical properties [20]
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In this article, we create a relatively simple plastic recycling system that transforms HDPE plastic bottle caps into reusable plastic products. This recycling system is deployed at a community scale. In this work, we make a plastic flowerpot from consumer plastic. The project is used as a mobile educational model for demonstrating the recycling mechanism and develo** a community recycling culture. In this case study, we focus on the last two parts-shredding and extrusion-of recycling bottle caps for technical reasons:

  • Collection of caps

  • Washing and drying

  • Shredding

  • Extrusion and molding [21, 22]

The overall system flow is shown in Fig. 3.

Fig. 3
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Flow of the overall recycling system

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The general concept design for producing flowerpots from recycled bottle caps is shown in Fig. 4. This design is developed by reverse engineering and following the technology steps. Figure 4a presents the 3D model of the shredder, and Fig. 4b displays the 3D model of the extruder. In this subsection, we study each part separately.

Fig. 4
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3D model of the shredder and extruder

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In the next section, we discuss our motivation for this project. Section 3 considers the technical specifications of the shredder and extruder machine, Sect. 4 shows the experimental results, and Sect. 5 covers the expenses related to the entire system. In Sect. 6, we discuss the use of the station to spread awareness. In Sect. 7, we present the conclusion.

2 Motivation

In our facilities, we consume over 50 bottles of water per day on average. Even though we sort our waste and appropriately dispose of it, most of it ends up in a landfill [1]. Being aware of the shortcomings of the waste management system, we decided to solve the issue on our end by fabricating a recycling station to transform the bottle caps into functional products.

We designed a recycling station by considering mobility and durability. We moved the station within our facilities and to other facilities within the local community. Local schools, shop** complexes, and offices would borrow recycling stations during events and recycle their plastic waste. The presence of a recycling station would be eye-catching and allow them to spread the message about the importance of recycling.

We have held recycling drives within our community, and we will continue to hold them to spread awareness about the shortcomings of the government waste management system and the community’s role in aiding the recycling effort.

3 Study the technical specification of the recycling machine

In this study, the objective is to utilize plastic waste to make pots. The rechecking machine differs from traditional technology in two manners: a shredder is used for flaking the consumer plastic and an appropriate extruder is used for heating and melting plastic without degradation in the polymer. The extruder works by mechanical pressure. In the following subsection, we study each machine separately.

3.1 Shredding

Postconsumer plastic waste is shredded into flakes to melt quickly and evenly. A shredder is a simple and inexpensive technology suitable for adaptation in laboratory prototy** [23,24,25,26,27]. A plastic shredder is designed and built on a medium scale for deployment at a community waste collection and recycling facility. This shredder subpart (SSP) is designed with a capacity of 15 kg per hour.

We want the edges to flow so that the remaining flakes are pushed toward the center of the SSP. There is one cutting action per edge on the outer knives to prevent excess material from rotating along the exterior wall. The specifications of the worm gear motor (CMRV075-90L-2,2KW-112Upm) are a power of 2.2 KW and a speed of 70 rpm, resulting in a torque of approximately 190 Nm at the output shaft. Forum posts on the Precious Plastic website highlight builders that have used other configurations with less power, leading to mixed results. We conclude that 190 Nm is more than what is needed. Nevertheless, we try to approximately approach this value to ensure that the machine does not clog and that it stops when we attempt to shred thick plastic pieces.

The assembled SSP is shown in Fig. 5a. To successfully shred the plastic waste, the knives and fixed knives are arranged as shown in Fig. 5b and Fig. 5c.

Fig. 5
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Components of the shredder subpart

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A circular hole is drilled on the knives to create a mark to prevent misalignment and improper sequencing, as shown in Fig. 6a. This part requires a high degree of precision to fit the bearings tightly. With the holes prepared, the knives are placed onto the shaft. If the shaft of the shredder is cylindrical, the knives slip. Thus, to ensure that the SSP functions flawlessly and the knives are rigid and grip well while cutting, the shaft is shaped like a hexagon, as shown in Fig. 6b. For shredder machines, blades should be designed considering their thickness. The thickness of the blade influences the shredding force, cutting edge stresses, and blade durability.

Fig. 6
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Shapes of the knives

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Based on the sieve output size, three sizes of flakes are produced using the shredding machine: an extruder, an injector, and a sheet press. As shown in Table 2, each sieve size shreds various sizes of plastic flakes.

Table 2 Sieves with different sizes of perforations
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In general, extruders work best when the materials are small. Perforated sheet metal is used in a shredder machine as a bent sieve attached to an SSP under the knives, as shown in Fig. 7a. The caps are held inside the SSP until the shreds are small enough to pass through the sieve holes. Changing the numbers and sizes of holes affect the flake size and shredding processing time. The sieve holes are designed to have diameters of 12 mm, 8 mm, and 4 mm. The diameter of the hole depends on the diameter of the spiral screw on the extruder.

Fig. 7
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Sieve and shaft coupling designs

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The connector between the two shafts is formed from a solid steel block. Since the coupling hole does not extend through, this keyway attaches to the output shaft of the worm gear motor (CMRV075-90L-2,2KW-112Upm). We utilize mechanical coupling between the motor and the shredder to reduce the breakdown risk, reduce the resonance frequencies, and decouple the gear motor and crusher mass moments of inertia, as shown in Fig.  7b. The machine is designed in a part-by-part manner to facilitate assembly, as shown in Fig. 8a.

Fig. 8
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Fabrication and construction of the plastic shredder machine

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Inlet units are utilized to insert plastic waste material, followed by shredding units (knives) and outlet units. The couplings guarantee the transfer of large amounts of torque, which is required for our application. A pyramid hopper is built from 1-mm thick sheet metal and welded together.

The volume of the pyramid hopper is shown in Eq. 1:

$$\begin{aligned} V= \frac{H}{3} \times \left[ \frac{X^2 \times Y-x^2 \times y}{X-x}\right] , \end{aligned}$$
(1)

where H is the height between bases (160 mm); X is the length of upper bases (228 mm); Y is the width of upper bases (215 mm); x is the length of lower bases (155 mm); and y is the width of lower bases (126 mm).

By using Eq. 2 and the measurements given above, we obtain the volume as follows:

$$\begin{aligned} V= \frac{160}{3} \times \left[ \frac{(228)^2 \times 215-(155)^2 \times 126}{228-155}\right] =6.288 L \end{aligned}$$
(2)

Torque transmitted by the shaft is given in Eq. 3 as follows:

$$\begin{aligned} T= \frac{(P \times 60 \times 1000)}{(2 \times \pi \times N)} \end{aligned}$$
(3)

where P is the power transmitted by the electric motor (2.2 KW) and N is the evolution of the shaft in rpm (30 rpm).

The shaft diameter is estimated using Eq. 4:

$$\begin{aligned} d^3= \frac{16}{\pi S_s} \sqrt{(k_b+m_b)^2(k_t \times m_t)^2} \end{aligned}$$
(4)

where \(S_s\) is the ultimate tensile strength for steel; \(m_b\) is the maximum bending moment; d is the diameter of the shaft; \(m_t\) is the torsion moment; \(k_b\) = 1.5; and \(k_b\) = 1.0, as mentioned in the American Society of Mechanical Engineers (ASME) guidelines.

This calculation facilitates the assembly, as shown in Fig. 8b. The basic power electronic setup utilized to evaluate the shredder machine is a contactor and protective circuit breaker combined with on and off buttons. For the final device, the shredder machine must be able to run in both directions in case of jamming. Furthermore, adding an emergency stop button at the top is necessary. An electrical wiring diagram for the plastic shredder machine is shown in Fig. 9.

Fig. 9
figure 9

Electrical diagram of the plastic shredder machine

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The components that comprise the shredder are shown in Table 3. The shredder shreds 920 gs of HDPE in five minutes during the testing phase.

Table 3 Shredder components list
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After the fabrication of the shredder, we test it using clean bottle caps. Two phase electric motors are used for crushing HDPE bottle caps. Various input masses are measured with a stopwatch to calculate the machine throughput capacity. Table 4 shows the mass of the input and the time taken to crush the input mass during the test. Three tests are conducted consecutively. Different quantities of HDPE bottle caps are collected and weighed, and the average is recorded (3 kg). The machine shredder has a high efficiency rate of approximately 92%.

Table 4 Time and mass of shredding
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Furthermore, the shedding rate of the machine is obtained as 0.0275 kg/s. In the following subsection, we examine the extrusion machine after we study and manufacture the shredder.

3.2 Extrusion machine

The process of molding involves melting dried plastic flakes into densified plastic shapes. To melt the flakes, we use an extruder [28,29,30]. Plastic flakes are extruded, and the melts are loaded and pushed through a nozzle. We enhance the dispenser mechanism to control the extrusion based on the characteristics of plastic melt materials, such as filling and compressive strength. Therefore, we use a one-step dispenser system: the spiral screw feeder pushes and dispenses the plastic material. Material flows to the extruder without air bubbles when the motor speed is low at approximately 20 rpm. A small nozzle hole, a proper heating temperature and an appropriate speed of plastic pushing, help to minimize the bubbles.

Fig. 10
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Single spiral screw manufactured in a laboratory

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Steel is our preferred barrel material due to its strength and high melting point. Nickel chrome wire and uniform spacing achieves optimal heating and accurately predicts the barrel’s internal environment. The nozzle size significantly impacts the material output; a larger nozzle allows more material to flow at a lower pressure.

Plastic-delivery screw extruders are mechanically coupled to the gearbox motor (CMRV075-90L-2,2KW-112Upm). The spiral screw feeder ensures that the plastic slides smoothly during heating. The nozzle and orifice determine the size of the extruded line of melted plastic. The spiral screw is coupled to the motor and operates inside the extruder, as shown in Fig. 10.. A powerful motor forces plastic to adhere to the conveyor spiral screw. The orifice size determines the dimensions of the extruded melt line. We prepare three different nozzle sizes for this study (1 mm, 1.6 mm, and 3 mm). The specifications of the designed screw are as follows: pitch of the screw (Pc) of 21 mm; diameter (D) of 26 mm; total length of the spiral screw (L) of 600 mm; and angle of the blades of approximately 19\(^{\circ }\), as shown in Fig. 10a. We design a screw with a different pitch-to-diameter ratio (Pc/D), as shown in Fig. 10b. Adjusting the spiral screw rotation speed adjusts the amount of liquid ejected.

The material is loaded into the machine through the feed throat (an opening near the barrel rear). The rotating spiral screw rotates at 15–30 rpm, forcing the plastic flakes into the heated barrel. The temperature control system built to heat the barrel is shown in Fig. 11a. A wiring diagram for the extrusion machine is shown in Fig. 11b.

Fig. 11
figure 11

Extrusion electrical diagram

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The geometry of the feed zone of the screw is given by the following data:

Barrel diameter \((D_b)\) = 25 mm

Screw lead (s) = 22 mm

Number of flights \((\nu )\) = 1

Flight width \((W_{FLT})\) = 13 mm

Channel width (W) = 20 mm

Depth of the feed zone (H) = 8 mm

Conveying efficiency \((n_F)\) = 0.35

Screw speed (N) = 15 to 30 rpm

Bulk density of the polymer \((\rho _o)\) = 800 Kg/\(\hbox {m}^3\)

The solids conveying rate in the feed zone of the extruder are calculated according to the following equation [31]:

$$\begin{aligned} G & = 60 \cdot \rho _o \cdot N \cdot n_F \cdot \pi ^2 \cdot H \cdot D_b \cdot (D_b - H) \\ & \quad \cdot\left( \frac{W}{W + W_{FLT}}\right) \cdot \sin {\phi } \cdot \cos {\phi } \end{aligned}$$
(5)

with the helix angle \(\phi \):

$$\begin{aligned} \phi = \tan ^{-1}\left[ \frac{S}{\pi \cdot D_b}\right] \end{aligned}$$
(6)

By using the above given geometry data with Eqs. 5 and 6, we obtain the following equation:

$$\phi = \tan ^{-1}\left[ \frac{0.022}{3.14 \cdot 0.025}\right] = 15.656$$
(7)
$$ \begin{aligned} G & = 60 \cdot 800 \cdot 20 \cdot 0.35 \cdot \pi ^{2} \cdot 0.008 \cdot 0.025 \cdot (0.025 - 0.008) \\ & \quad \cdot \left( {\frac{{0.02}}{{0.02 + 0.13}}} \right) \cdot \sin 15.656 \cdot \cos 16.656 = 1.776\;{\text{Kg}}/{\text{h}} \\ \end{aligned} $$

Molten plastic temperatures are rarely equal to barrel temperatures due to viscous heating and other factors. Generally, the barrel is heated according to a preset profile in which three or more independent controlled heater zones gradually increase the temperature from the rear to the front. As plastic flakes are pushed through the barrel, they melt gradually, reducing the probabilities of overheating and polymer degradation. We fabricate the extruder in our mechanical workshop. The extruder is assembled for testing, as shown in Fig. 12a. As a result of the initial tests, the extruder is mounted on a frame, and satisfactory results are obtained, as shown in Fig. 12b.

Fig. 12
figure 12

Fabrication of the extrusion machine

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The extruder comprises a worm gear motor, screw, coil heater, extrusion barrel, hopper, frequency inverter, and temperature controller. The details of the components are listed in Table 5.

Table 5 Extruder components list
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In the following section, we test the whole system starting with the shredder and finishing with the extruder.

4 Experimental results

To conduct our experiments, we collected plastic bottles from our premises and the local community. Everybody was instructed to separate the plastic bottles from the rest of the waste to minimize the possibility of contamination. The caps were prewashed using a washing machine. The washing machine was set to a forty-degree quick wash program, and a small amount of laundry detergent was added. The caps were left in the machine to dry.

Once the caps were clean and dry, they were shredded to obtain flakes. Plastic flakes were forced into the heated barrel by a rotating screw (usually a screw rotating at 15–20 rpm). As a result of the intense pressure and friction within the barrel, additional heat was generated. If sufficient pressure and temperature were maintained across the barrels, the material was extruded satisfactorily. The different specifications of the hardware and mechanical parts of the recycling plastic machine are shown in Table 6.

Table 6 Mechanical specifications of the plastic recycling machine
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Two experiments were conducted to determine the efficacy of the system components. The first experiment examined shredding and filtering parameters. A single coil heater and multicoil heaters were used in the second experiment to evaluate the extrusion. The final step was to produce flowerpots.

4.1 Shredder sieve test

We tested the shredder prototype without a sieve to determine the flake sizes it would produce. In this process, the flakes varied in length, and the process was rapid. To reach flakes of a specific size, we fabricated three sieves with different sizes of perforation holes (5 mm, 8 mm, and 10 mm), as shown in Fig. 13.

Fig. 13
figure 13

Perforated sieves with various hole sizes

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A 10 mm sieve hole was used in the facility because the specifications did not specify the size of the perforations. The diameters of the holes were 10 mm, while the spacing and row spacing were 6 mm. The resulting shreds were more delicate than those obtained after sieving. Nevertheless, the sieves proved too soft for practical use. Most of the flakes swayed around by the knives, and they did not fall through. The particle masses were overly large while feeding more plastic into the shredder that it caused the significant sideways movement of the shredder. Two factors caused this phenomenon: first, the perforation was too delicate. Between the knife blades and sieve was space that prevented shreds from passing through. Another sieve perforation was available with a relatively large perforation relative to the fine sieve. The hole size was 10 mm, the spacing was 20 mm, and the hole location was the same as the finer perforation. The processing time and material buildup were acceptable for practical applications. Shredding HDPE plastic produced satisfactory results, as illustrated in Fig. 14.

Fig. 14
figure 14

Plastic flakes of varying sizes

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The parameters of the shredder appropriate for producing flakes are represented in Table 7. Our flowerpots were made using extrusion with a tiny sieve to produce flakes between 4 mm and 5 mm in diameter. In tests with the fine sieve, most bottle caps were pushed into the center by the edge flows.

Table 7 Parameters of the shredder
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The results demonstrated that the machine had a hopper capacity of 6.288 ls, centrifugal tension of 9.74 N, maximum tension of 233.4 N, shredding force of 578.5 N, shaft diameter of 29.5 mm, bending stress of 86 MPa, shearing stress of 37 MPa, and torque of 29.21 Nm.

4.2 Extruder test

It is necessary to test the operation of the extruder and the rotation rate of the spiral screw before molding any shape with different blending materials. The goal is to fabricate a plastic recycling pot. Initially, the gear motor speed control (CMRV075-90L-2,2KW-112Upm) is utilized to adjust the recycled plastic flow diffusion value. The parameters of the single-coil heater extruder are listed in Table 8.

Table 8 Extruder test with a single heater
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This test uses a laboratory-made extrusion head while maintaining a nozzle diameter of 3 mm (core hole). Because of the global supply chain problem, we utilize an oven coil heater around the barrel, as shown in Fig. 15a. We mold several plastic shapes that are almost perfect. The rotating spiral screw is not ideal due to the improper material distribution. The filament is stripped against the drive screw, and the extruder is clogged. We add one more heater coil in the middle of the barrel; thus, the output is a grinding plastic filament. The following tests use two heaters and a 6-mm nozzle diameter, and the molding speed is reduced, as shown in Fig. 15b. To minimize melts pushed through the barrel, we change the spiral screw speed.

Fig. 15
figure 15

Extruder with different heater setups

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The results are presented in Fig. 16 and show a complex relationship between the nozzle diameters and plastic flow. Figure 16a illustrates the variations in volumetric and mass flow for different nozzle diameters while the molding time remains constant for all sample shapes. Flow data show that the flow is relatively stable for small nozzle diameters (2, 3, 5, and 6 mm). However, the flow decreases with time when the nozzle diameter is larger than 6 mm, as shown in Fig. 16b.

Fig. 16
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Melted plastic drip** through the extruder nozzle

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In this test, we use the four heaters around the barrel of the extruder and a nozzle diameter of 3 mm, as shown in Fig. 17a. The heaters have a diameter of 34 mm and are 55 mm long. The heaters operate at 200 W using AC 220 V-240 V. This modification allows us to successfully reach the melting point of plastic, as shown in Fig. 17b. The thermal camera capture of different points in the extruder is seen in Fig. 17c.

Fig. 17
figure 17

Reaching the melting point of plastic with four heaters

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The parameters of an extruder with a four-heater band are shown in Table  9. Experimental tests show that the recycling material is suitable for extraction, distribution, layering, and molding.

Table 9 Parameters of an extruder with four heater bands
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4.3 Pot mold testing

We maintain a rotating spiral screw between 15 and 30 rpm to move the melt gradually inside the barrel extruder. We keep four heaters in a barrel. A change in the parameters of the extruded sludge has reduced sludge in the previous test. By utilizing our HAAS machine, we make a proper mold of a pot, as shown in Fig. 18.

Fig. 18
figure 18

Core and cavity of the pot mold

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The mold makes a pot with a height of 86 mm, a base diameter of 93 mm, a top diameter of 116 mm, and a wall thickness of 3 mm. The dimensions of the pot are represented in Fig. 19.

Fig. 19
figure 19

Dimensions of the pot

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The output of the extruder depends on the nozzle size; in our experiment, it is approximately 1.7 kg/h. By using the mold, we obtain the flowerpot shown in Fig. 20a. Making a pot requires various attempts to ensure the homogeneity and temperature of the molten plastic. Our attempts show that the most suitable molding temperature is 240 \(^{\circ }\)C, while the causes of pot mold deformation go beyond temperature control. The injection pressure required of the melted plastic to fill the pot mold should be more than the amount necessary inside the gravity of the injection molding machine. The attempts give us a rough idea of how much material is needed to make a single pot. From the third attempt onward, we obtain a nearly perfect flowerpot, as shown in Fig. 20b.

Fig. 20
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The molding process

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A single recycled plastic pot weighs 141 gs and requires 128 bottle caps to produce. A bottle of water costs 0.14 USD in our local market. Making the recycled pot requires 128 bottles.

The recycled plastic flowerpots are compared to plastic pots recently available on the market. Regular plastic pots are lighter and more flexible than recycled pots. However, recycled plastic pots are stronger. We have tried to compare the strengths of plastic pots available in the market to our recycled plastic pot using a hydraulic press, as shown in Fig. 21a, b.

Fig. 21
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Comparing the strengths of plastic pots using a hydraulic press

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The regular plastic pot is crushed immediately, and the load reads 0.0 kN on the hydraulic press. The regular pot is poor at dealing with compressive force, but it is quite flexible. For a recycled plastic pot, the load is 6.7 kN before drop** to 0.0 kN. This drop occurs because small chunks from the top of the pot break off, and the hydraulic press stops automatically. The recycled pot is better at addressing compressive force than a regular plastic pot. However, to obtain a better idea of the strength of the recycled plastic pot, we must improve the top of the pot and repeat the tests. Additionally, we must perform other tasks, such as testing plastic pots against changing weather and testing their long-term durability.

After obtaining the pot, we assemble a recycling station that starts with cleaning and ends with molding. The complete station is shown in Fig. 22.

Fig. 22
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Fully operational recycling station

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The recycling process is summarized in Fig. 23. From left to right, HDPE caps are first collected in our facilities. The caps are washed, dried, and shredded to obtain plastic flakes, which are melted in an extruder and molded to form plastic pots. These pots are used for various plants and are recently being used to grow aloe, as shown in Fig. 24.

Fig. 23
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Flow of the overall recycling system

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Fig. 24
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Aloe plants in the break area of our facility

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5 Expenses

The shredder and extruder substations and mold cost all approximately 2700 USD locally. This amount includes the costs of components, frames, and labor. If a small community or school wants to make a similar station, it costs 3000 USD at most. If when using the station for recycling plastic and spreading awareness of the importance of recycling, the station might be considered a valuable investment. However, to recover the money spent on the station, the pots must be sold.

A competitive price for recycled plastic pots relative to the ones available on the market is 2.75 USD. To break even with the cost of the recycling station, we must sell 328 pots, requiring 41,984 bottle caps. With the help of our local community, we collect slightly over 3000 bottle caps in the past month. If we continue collecting at this rate, we cover the cost of the station in one year and three months. If we make different products or sell the products for higher prices, we recover the station cost faster. Schools collect bottle caps relatively fast and break even quickly.

6 Spreading awareness

While everyone knows that we must recycle waste and use products responsibly, there must be some initiative by the population. This lack of effort occurs because people do not see the harmful effects of improper waste management. People do not see the positive aspects of recycling. To start a conversation and spread awareness, especially among children, we must attract their attention by physically showing them the benefits of recycling. A recycling station that shreds plastic waste into flakes, melts the flakes, and molds them into a product helps to attract attention.

Our institution has a good reputation and following in the state. We constantly have educational events to teach the general public about different topics in the science, technology, engineering, and mathematics (STEM) field. Furthermore, we receive visitors regularly. When someone visits, we provide a tour of the facility, operate the recycling station for them, and let them take small flowerpots. Figure 25 highlights our latest tour. This process allows us to show them the benefits of recycling in person. We talk to them about the status of waste management in the country and give them tips on how they can help fight against pollution. Since we began displaying the recycling station, many students have collected bottle caps and given them to us during events to recycle into different products for use.

Fig. 25
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Teaching students about recycling plastic and operating the recycling station

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Small institutes and companies may reach out to the local community to spread awareness. Allowing shop** malls or grocery stores to borrow the recycling station promotes recycling and directs attention toward the institution. The institution may then hold recycling drives and campaigns to educate the public about waste management and recycling. The recycling station is eye-catching and a great conversation starter. The recycling station helps any institution spread the message about waste management and recycling.

7 Conclusion

We have developed and built a plastic recycling station in our facility to recycle plastic waste and transform it into a useful end product. This station consists of four substations: the cleaning, shredder, extruder, and molding substations.

The cleaning substation involves washing and drying the plastic waste using a washing machine or a sink. It is essential to clean the plastic waste to remove any foul odors, to remove impurities and to ensure that we obtain homogeneous molten plastic in the extrusion stage.

The shredder substation consists of an inlet to take in plastic waste, an outlet for the shredded plastic flakes, and a worm gear motor that drives the shredding unit. The motor is attached to the shaft of the shredding unit with coupling. The shredding unit shaft is hexagonal to prevent slip** and misalignment. The rotating knives crush and tear apart the plastic to form flakes. Based on the size of the sieve holes, the pellet size ranges from 5 to 10 mm. The motor is set to 35 rpm to prevent the blades from jamming due to low rpm and to prevent the plastic waste from being thrown out due to high rpm.

The extruder substation consists of an inlet to take in the flakes, a nozzle to extrude the molten plastic, and a worm gear motor to drive the auger of the extrusion unit. Plastic flakes are pushed along the barrel by the auger and melted using two heaters. The motor is set to 15–30 rpm to allow for the proper flow and heating of the material. A 3-mm nozzle diameter is selected to ensure consistent ejection of the material.

The molding substation is a pot-shaped manual press mold. A pot is molded by collecting the extrudate and transferring it to the mold. Depending on the desired end product, the molding substation is changed or removed. We produce 2-plastic pots an hour using the station. Plastic waste from the facility is recycled on a regular basis to make pots. The pots are strong and suitable for various plants. Due to their strengths and sizes, pots are proven to be useful products made from discarded plastic caps.

This plastic recycling station is useful for more than just our facilities. Global governments may collect and manage plastic waste; however, they must do so at a relatively high rate. Our recent plastic pollution crisis is a result of this low rate. Therefore, our plastic recycling station will benefit our local community and communities worldwide in combating this issue. External parties can make a similar recycling station for 3000 USD. If the party wants to recuperate the cost of the station, they can sell the end products. A vital advantage of the recycling station is that it is eye-catching and a conversation starter. Showing someone the whole recycling process will help them understand the need for recycling, and it will help them spread the message.

In the following points, we describe the limitations and future directions of this study:

  • The recent washing process is beneficial because the plastic bottles collected are separate from other waste. The washing process must be improved by adding a wash cycle after shredding the caps. We must add a filtration system to remove sand, dust, and similar particles. Washing bags prevents the flakes from blocking pumps and makes it easier to dry them.

  • For the shredder, the size of the shredded plastic should be minimized according to the plaquing clearance and screen mesh. Moreover, the amount of shredded plastic per hour should be maximized according to the motor power and shredder design.

  • For the extruder, the amount of extruded melted plastic for the mold is filled manually (cooled fast and complex sha**). We are looking for automated mold filling to maximize production per hour according to the plastic extruder feed rate and heater power for the required heat curve.

  • Adding sensors to the shredder and extruder may help make the entire system smart and efficient. Furthermore, the sensors make the shredder and extruder safe to operate in local communities.

  • A detailed and long-term comparison of the recycled pots with resin-based planters and regular plastic pots needs to be conducted. We have performed preliminary tests using a hydraulic press. Further testing is needed to determine the exact strength of the recycled material.