A Sustainable Approach In Additive Manufacturing With Recycled ABS

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A Sustainable Approach in Additive Manufacturing with Recycled ABS

Author: Alisha Tandukar

Degree Programme: Materials Processing Technology

Date: 16/11/2020

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DEGREE THESIS Arcada

Degree Programme: Materials Processing Technology Identification Number: ²¹¹²⁸

Author: Alisha Tandukar

Title: A Sustainable Approach in Additive Manufacturing with Recycled ABS

Supervisor (Arcada): Faizan Asad Commissioned By:

Abstract:

The objective of this thesis is to test suitability of recycled ABS in 3D printing and to find the effects of recycling on the mechanical properties of plastic filaments. It is well known fact that recycling usually effects on mechanical properties of material (Elina Iunolainen, 2017). To study the effect of recycling, various mechanical properties like tensile strength, young’s modulus and melt flow index are compared between virgin ABS samples and recycled ABS samples. Some fresh samples are first printed using virgin ABS filament. Another set of samples are prepared using recycled ABS. The recycling is done by using an extruder and shredder for at least 3 cycles. The extruded filament is then used to print recycled samples.

During extrusion of ABS samples, it was clear that there are high chances of contamination of plastic filaments with other impurities and moisture. Moreover, the extruded filament was very rough and had varying diameters. The extrusion temperature and extrusion speed were raised to obtain filament with smooth surface. The filament was dried at 80℃ for 20 mins to remove the moisture.

Tensile test showed that the Young’s modulus value for virgin ABS sample and recycled ABS sample are nearly equal i.e. 1.94 MPa and 1.88 MPa respectively. It is also seen that the stress and strain at yield value for virgin ABS sample and recycled ABS sample are nearly equal. But, virgin ABS sample undergo very long plastic deformation and absorbs large amount of energy before breaking than recycled ABS sample. Recycled ABS samples are strong and can handle same amount of stress as virgin ABS samples but cannot handle larger torsion or flexing.

The result of melt flow index test showed that virgin ABS has better flow properties than recycled ABS but the difference was fairly low even after third cycle.

Keywords: Acrylonitrile Butadiene Styrene (ABS), 3D Printing, Fused Deposition modelling, Extrusion, Tensile Testing, Melt Flow Index, Youngs Modulus

Language: English

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FIGURES

Figure 1. Increasing trend of plastic waste recycling in EU member states (European Commission,

2019) ...4

Figure 2. Recycling rate of plastic packaging waste in the EU Member States (European Commission, 2019) ...5

Figure 3. Tessellated 3D model of a tensile piece ...7

Figure 4. Fused Deposition Modelling (WhiteClouds, 2019) ...7

Figure 5. Molecular structure of ABS (Omnexus, 2020) ...8

Figure 6. Extrusion of plastic (TechMiny, 2018) ... 10

Figure 7. Tensile test specimen (plastikcity.co.uk, 2018) ... 11

Figure 8. Stress strain curve (Nipun, 2015) ... 12

Figure 9. Melt Flow Indexer (polymerdatabase.com, 2015-2020) ... 13

Figure 10. Circular Economy in Helsinki Metropolitan Area (Helsinki Region Environmental Services (HSY), 2019) ... 14

Figure 11. KFM Eco Ex Extruder at Arcada ... 16

Figure 12. Cooling water bath ... 16

Figure 13. Recycled filament on first cycle and third cycle ... 17

Figure 14. Creality CR-10S and the samples printed at Arcada UAS ... 18

Figure 15. Tensile Test of ABS ... 19

Figure 16. Melt flow index test ... 20

Figure 17. Tensile test comparison between virgin ABS and recycled ABS ... 22

Figure 18. Failed print and proper print comparison ... 24

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TABLES

Table 1. Parameters for 3D printing of ABS ...9

Table 2. Parameters used for extrusion ... 17

Table 3. Extrusion parameters and results ... 21

Table 4. Tensile test results ... 22

Table 5. Result of MFI test (average) ... 23

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1. INTRODUCTION

1.1. Background

Plastic pollution is one of the most alarming problem that the world is facing today. People are using plastic on almost daily basis. But single use of plastic and lacking the facility to recycle them has now become one of the most concerning challenge. Packaging plastics like plastic bag, wrappers, cups and bottles, straws, plastic plates and spoons, etc. end up being waste immediately after consuming them. Plastics are made up of certain chemicals that do not decompose easily.

Decomposition of plastic is a very slow process and could take very long time. But in that period of time, it does a lot of damages to the environment and living creatures. Plastic waste present in the ocean break down into tiny fragments chemically or mechanically in presence of sunlight.

These microplastics are easily swollen by marine animals and cause great damage to marine life.

Microplastics might also enter human body via food they take or via water they drink. This might in future cause great risk to human survival.

Plastic waste is almost everywhere. If recycled properly this plastic waste can be used as a raw material for other production lines. One of the method that seems to make use of such recycled plastics is “3D printing”. 3D printing uses plastics in form of thin filaments. Such filaments can be made from recycled plastics by melting and extruding them. Recycling usually affects mechanical properties of plastics. This might be due to the change in chemical and molecular properties of plastics with every heat cycle or due to the development of micro tears or presence of other impurities. This thesis studies the viability of recycled ABS in 3D printing by studying the effects of recycling on the mechanical properties of ABS filaments.

1.2. Objectives

This thesis focuses on testing the suitability of recycled thermoplastics as raw material for 3D Printing. The comparison will be made between the virgin ABS filament and filament prepared by using recycled ABS. The main objectives of this thesis are:

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2 1. To study the material properties of recycled ABS.

2. To test the suitability of recycled ABS for 3D printing.

3. To study the mechanical properties like Young’s modulus, tensile strength and melt flow index of recycled ABS and compare with those of virgin ABS.

4. To study the scope of 3D printing for sustainability and circular economy.

1.3. Compliance with Degree Programme Theme

This degree thesis on 3D printing and plastic recycling is very closely related to the degree programme. 3D printing is basically used as a tool to make prototypes in quicker and cheaper way.

But now, researchers are integrating this technology in almost every field of science like manufacturing and product development, food technology, medicine, bio-printing, etc.

Plastic is the most versatile material and almost most of the products that we see around us are made up of plastics. “Plastics are basically organic compounds that are made up of large number of small repeated units known as monomers by the process called polymerization.” (A. D.

JENKINS (UK), 1996). Because material science engineering is the detailed study of almost everything around us like polymers, biomaterials, metals, ceramics, composites, etc. this thesis is very closely related to the degree programme in material processing. One can use their material science skills to improve properties of plastic parts making them stronger, lighter, easier to process and recycle.

1.4. Relevance to the Existing Knowledge

ABS seems to be one of the most 3D printed material. It is applicable in wide range of products where high dimensional stability, lightweight and toughness are major concern. Since, ABS products are more tough, stable and durable than PLA, they can be seen used in various household appliances, electronics enclosures, pipes and fittings, etc.

Since the recycled plastics can come from various secondary sources, there is high chance of presence of foreign impurities. Moreover, recycling promotes decrease in molecular weight which results in loss of impact properties of plastics. “The reduction in molecular weight with every

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3 recycling cycle increases the mobility of the chains, allowing the formation of thinner lamellae and a higher degree of crystallization.” (Luiz Gustavo Barbosa, 2017).

However, if recycled properly the recycled plastic can have nearly similar mechanical properties as virgin plastic. A similar thesis was published by Sara Hajifathaliha (Hajifathaliha, 2020) wherein the author studies the mechanical behavior of virgin and recycled form of PLA, PETG, PET. The results suggested minimal difference in mechanical properties between virgin and recycled PET and PTEG. But for PLA there was significant decrease in mechanical strength seen.

Similarly, in a thesis published by Elina Iunolainen (Iunolainen, 2017), regarding testing of recycled PP, significant decrease in tensile strength and increase melt flow index value or decrease in molecular weight and material viscosity

By studying above reports, this thesis tries to study the effects of recycling on mechanical properties of ABS and test the suitability of recycled ABS for 3D printing.

2. LITERATURE REVIEW

Literature review of this thesis gives some important explanation about 3D printing technology and extrusion technology and how these technologies can be used for plastic recycling. It will also explain about the vital role of 3D printing as an excellent tool for plastic waste management and circular economy.

2.1. Plastic Recycling

Plastics are wide range of synthetic or semi synthetic organic solid materials suitable for manufacturing of industrial products. They show characteristic properties like resistance to chemical, durable, inexpensive and easy to use. Plastics are used in almost all fields of development like agriculture, transport, medical, electrical and electronics, building and construction, packaging, sports, etc. Despite having lots of advantages, they possess some disadvantages too. Some plastics are hard to recycle, non-renewable, toxic and possess threat to animals. These plastics take very long time to decompose and during this process, it can cause huge damage to the environment. Marine animals, birds, even humans who swallow microplastics are subjected to health risks.

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4 Plastic recycling is the method of reprocessing various forms of plastics into varied other forms, unlike their original form. Before recycling, plastic wastes need to go through various stages like sorting, washing, shredding, identification and classification and extrusion (Compactor Management Company, 2017-18). Depending upon the requirement, manufacturers give various shapes and properties to their products. Selection of a specific process depends upon many factors such as quantity and production rate, shape and detail of the product, nature of material, etc. Large volume of plastic that if recycled properly can be used as a raw material for other production lines.

Recently, more and more people are getting conscious about environmental impacts of plastic pollution. People and the government are waking up and are raising their hands towards waste management and recycling activities. “In the EU, the recycling of plastic waste was estimated to increase by 18 percentage points i.e. from 24% in 2005 to 42% in 2017.” (European Commission, 2019)

Figure 1. Increasing trend of plastic waste recycling in EU member states (European Commission, 2019)

“In 2017, the highest recycling rate of plastic packaging waste was recorded in Lithuania (74%), followed by Bulgaria (65%), Cyprus (62%, 2016 data), Slovenia (60%), Czechia (59%), Slovakia (52%), Netherlands (50%), and Estonia, France and Finland (each 27%).” (European Commission, 2019)

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Figure 2. Recycling rate of plastic packaging waste in the EU Member States (European Commission, 2019)

According to regional waste management agencies, “Finns recycled plastic at double or even triple the rate of the previous year 2018. Recycling in Vantaa rose more than 180 percent and that in Helsinki and Espoo was estimated to be more than 90 percent.” (yle News, 2019)

3D printing can be the best example of using the recycled plastics as a raw material. The filament made from recycled plastics can have similar mechanical strengths to that of virgin plastic. Also, the chemical and mechanical properties of the recycled filament can be changed with the addition of suitable additives.

2.2. 3D Printing

2.2.1. General Overview and History

“3D Printing”, is a beautiful example of technological advancement and has recently developed itself as a very versatile technique in modern manufacturing. In 3D printing, digital file is processed and turned into three-dimensional solid object using an additive process or layer by layer deposition process. Recently 3D printers are being more versatile and cheaper. Because of this, 3D printers are easily available to homes and businesses. The things that were even hard to imagine some decades before are now turning into reality because of 3D printing. 3D Printing enables us to print three-dimensional objects of any geometry.

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6 Additive manufacturing was first immersed in 1987 when Charles Hull invented Stereolithography. In the beginning of its journey, 3D printing was struggling to occupy its position in business and manufacturing industries. Because the printing process was too slow, expensive and the idea was too complicate to understand, industries were embarrassed and could not afford this technology (Hod Lipson, 2010). But now, lots of issues are resolved.

Currently, 3D printing has become more efficient, cheaper and reliable. It can be used to print various materials including plastics, metals, glass, tissues, clothes, foods, etc.

2.2.2. 3D Printing Process

Depending on the technique used, 3D printers can be classified into two major groups. The first group “selective deposition printers” –deposits layers of raw materials by squeezing melted paste or raw material through nozzle. Examples include fused deposition modelling (FDM), polyjet printing and laminated object manufacturing (LOM). These are simple to use and are found in homes, schools and offices. The second group “selective binding printers” –binds powdered or light-sensitive photopolymers using heat or light. As they use lasers or heat guns, they are too fragile and dangerous for common uses. Examples include stereolithography (SL) and selective laser sintering (SLS) (Hod Lipson, 2010).

2.2.3. Fused Deposition Modelling

Since this thesis aims to study the properties of 3D printed filaments, the particular process suited for this thesis project is FDM method. FDM all starts with a 3D design file. The design is completed and STL file is created using software like AutoCAD, SolidWorks, MakerBot, etc. STL stands for “Standard Tessellation Language”. The information about a 3D model is encoded using a process called tessellation. Tessellation is the process of tiling a surface with one or more geometric shapes such that there are no overlaps or gaps. Tessellations encodes the information about the geometry of model (Chakravorty, 2017). Below is the image of tessellated 3D model of a tensile piece that is covered by many small triangles.

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Figure 3. Tessellated 3D model of a tensile piece

After the 3D model is sliced, it is ready to be feed into the 3D printer. When a file is uploaded, 3D printer prints the object layer by layer.

Figure 4. Fused Deposition Modelling (WhiteClouds, 2019)

During printing, the melted plastic is extruded through the heated nozzle of the printer onto the build platform. The extrusion head of the printer moves in x-y directions while the build platform is free to move in z direction. Once a layer is finished, the platform moves down in the z direction by single unit and a new layer is deposited over the previous one. This process is repeated until the part is completed. The MakerBot automatically generates the support structures if the model overhangs or needs support. After the printing is completed, the support structures have to be removed by our hands (Maria Cristina Tanzi, 2019). In FDM, materials mostly used are thermoplastics like PLA, ABS or Polyurethane.

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8 2.2.4. ABS as 3D Printing Material

Since FDM is the most common method of 3D printing, various range of plastics like ABS, PLA, PP, nylon, and few composites are suited for this method. This thesis mainly studies the material and mechanical properties of ABS.

Figure 5. Molecular structure of ABS (Omnexus, 2020)

ABS (Acrylonitrile Butadiene Styrene) is one of the most commonly used 3D printing plastic. It contains base of elastomers linked with polybutadiene making it more flexible, chemical resistant, heat-stable, shock resistant and high dimensional stability. It is tough and lightweight material which can melt and cool without changing its chemical properties. The operating temperature of ABS is 230℃ − 260℃. It has excellent mechanical properties and great resistance to heat, pressure and wear and tear compared to PLA. However, there are some drawbacks associated with 3D printing of ABS. Proper temperature maintenance is necessary and the print needs to cool down slowly otherwise it might result in cracks, curling or wrapping. So, the printing platform must be

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9 heated and enclosed. Moreover, ABS filaments are not biodegradable but biocompatible and recyclable. But recycling ABS requires huge amount of energy. (Omnexus, 2020)

The table below shows the parameters for 3D printing of ABS:

Table 1. Parameters for 3D printing of ABS

3D Printer MakerBot Replicator

Bed Temperature (Heated bed required) 95 − 110℃

Encloser Recommended (ABS is more sensitive to

temperature changes) Kapton Tape on Built Surface Required (ABS is slurry)

Extruder Temperature: 220 − 250℃

Cooling Fan Not required (ABS need to cool slowly)

2.3. Extrusion

2.3.1. Mechanism

It is a continuous and high-volume manufacturing process that is used to manufacture parts of fixed cross-section profile. It is a well-known technology that has been developed over the last century and has found beneficial applications in many diverse industrial fields such as polymer, ceramics, metal, food and pharmaceutical products processing. An extruder is used in extrusion, which pushes or maintains the flow of melted plastic towards the die by screw mechanism. Raw plastic pellets can be mixed with colorants or additives to manufacture colored parts.

For extrusion of ABS, the pellets should be pre-dried for 3 hours at 70-80℃. The extrusion temperature should be maintained between 210-240℃ and the length to diameter ratio of the screw should be 20-30.

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Figure 6. Extrusion of plastic (TechMiny, 2018)

An extruder can be divided into four distinct zones namely feed zone, compression zone, metering zone and die zone.

Feed zone: It consists of hopper from which the polymers pellets are feed into the extruder.

Depending upon the requirement, various anti-oxidants, colorants, or UV-inhibitors can be added to the hopper. It also serves to preheat the plastic pellets.

Compression zone: It consists of a constantly rotating screw fitted inside a heated barrel. The rotating screw pusses the plastic pellets towards the heated barrel. The gap between the screw and barrel goes on decreasing. This causes the plastic melt to move forward and repels any trapped air back to the feed zone.

Metering zone: It is also a high-pressure zone. The diameter of the screw goes on increasing along the tip. It pushes the plastic melt to the die at constant rate with uniform temperature and pressure.

Die zone: It is the last zone of the extruder which pushes the melt to the die. It consists of a perforated steel plate called breaker plate that prevents foreign particles or un-melted granules from entering the die.

2.3.2. Applications of Extrusion

 Extruders can be used for mixing or compounding of plastics or metals

 They can be used for the production of continuous profiles such as tubes, pipes, sheets, etc.

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11 2.3.3. Advantages

 It has ability to create long shaped products with complex cross-sections.

 Low cost of manufacturing and short cycle time makes it suitable for mass production.

 All kinds of thermoplastics, glasses and metals can be used.

 The surface finish is excellent with very excellent mixing.

2.3.4. Disadvantages

 Surface cracking occurs when the surface of the extruder splits due to speed, temperature or friction.

 Risk of mixing of oxides and impurities

2.4. Tensile Testing

Tensile testing is one of the most fundamental tests for engineering. It provides valuable information about a material and its associated mechanical properties. These properties can be used for design and analysis of engineering structures and for developing new materials that better suits a specified use. In particular, Tensile Test is used for determining properties such as young’s modulus, ultimate tensile strength, yield strength, ductility, Poisson’s ratio and fracture stress.

Tensile test is performed by stretching a sample of define cross-sections apart until failure. Two grips are used to hold the sample firmly. Then the upper grip starts moving upward, causing tension in the test specimen. At the end of the test, a Force/Extension curve is obtained, which can be used to explain the materials reactions to forces. A typical tensile test sample is “dumbbell” or “dog bone” shaped as shown in figure below.

Figure 7. Tensile test specimen (plastikcity.co.uk, 2018)

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12 The tensile of plastic sample shows four-stage evolution of modulus during tensile tests. The first stage is initial proportional limit where the strain produced is directly proportional to the stress applied. The largest value of elastic limit for which a material behaves elastically is known as yield point where physical changes in shape start to occur. If a specimen is loaded beyond this point, the deformation is said to be plastic and the material will take on a permanent deformation even when the load is removed. The stress continues to rise until it hits the ultimate tensile strength point which is the ultimate strength of the material and finally, there is breaking point where the specimen breaks.

Figure 8. Stress strain curve (Nipun, 2015)

2.5. Melt Flow Index

“Melt Flow Rate (MFR) is the measure of mass of polymer that flows through a capillary at a specified temperature and pressure during a measured time period.” (Polymer Solutions News Team, 2019). It is the most popular but least accurate method of determining material’s viscosity.

In this analysis method, mass of polymer that flows for a fixed amount of time is measured and the result can be used to explain various flow properties of melted plastic. MFR is one of the most important and common test method used in quality and production control tests in plastics or resin industries. For MFR test, ASTM D1238 and ISO 1133 are generally used as the standards.

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13 During MFR test, plastic sample in the form of pellet or powder is inserted into a heated barrel.

Inside the barrel, the plastic melts into a viscous fluid and flows through a capillary over a fixed time period using a dead weight piston. The weight of the sample that exits the instrument during that time period is the melt flow rate of that sample. MFR is generally expressed in terms of grams per 10 minutes.

Figure 9. Melt Flow Indexer (polymerdatabase.com, 2015-2020)

Melt flow rate is generally the measure of molecular weight and viscosity of plastic sample. Higher MFR value means, the sample has short chains and has lower molecular weight. Such short chain molecules have low viscosity and higher flow rate. Similarly, lower MFR value means, the sample has high branching and has high molecular weight. Such branched molecules have high viscosity and lower flow rate.

Melt flow index value plays a vital role in quality control of the samples or sample grading. It tells about the viscosity level of the sample. The quality control department can use this value to identify good or bad samples. It can also be used for batch to batch comparison of samples.

2.6. 3D Printing in Sustainable and Circular Economy

“Circular Economy is an attractive and systematic approach in which the resources are reused and recycled to create closed systems thus decreasing the impact of material usage in the environment.

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14 It aims to enhance the lifecycle of a product by maintaining, reusing and circulating it.” (Helsinki Region Environmental Services (HSY), 2019). Circular economy helps to save economy of the country and increase the quality of life by bringing more sustainable and innovative products.

“In the case of plastics, a circular economy means recapturing and reusing existing plastics however possible, as well as limiting the creation of new, virgin materials made from nonrenewable fossil fuels.”- (Axel Barrett, 2020). Plastics trade plays a key role in global economy. More or less the economy of the country is largely based on production or utilization of plastic. But there are lots of challenges associated with the production, use and disposal and recycling of plastics. 3D printing is one of the promising technology that reuses plastics materials and feeds it back to the economy in a new form. It prevents the leaking of plastic into the environment by successfully recovering plastic waste. 3D printing can also print biopolymers and composites that lead to the formation of new sustainable products, saves energy and leave less carbon footprint. Moreover, it allows designers to consider various factors like materials choice, over designing, production costs, etc.

Figure 10. Circular Economy in Helsinki Metropolitan Area (Helsinki Region Environmental Services (HSY), 2019)

In Finland, a suitable example of circular economy is being conducted by Ekokem Group. Before this idea, the wastes were only used to recover energy by burning. But now Ekokem Group has developed a circular economy village. Here, they collect household waste from the village and the

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15 commercial waste from the industries. The collected waste is sent to eco refinery for separation of waste and extraction of metals. Some amount of waste is collected here as energy waste and remaining amount of waste is sent to plastic refinery or bio refinery. At the plastic refinery, the plastic is refined to plastic raw materials to be reutilized. At the biorefinery, bio waste is refined into bio gas, fertilizers and ammonia gas. Circular economy village built by Ekokem is taking waste management and material utilization to a whole new level.

2.7. 3D Printing as a Source of Clean and Green Manufacturing

3D printing is also supposed to be an innovation for green and clean manufacturing. While printing only required amount of material is used and there is no wastage associated with post-processing of a product. Designers can fabricate products whose shape is optimized for their application or environment. The printed prototypes can be used to test the feasible of the product. There is no need for additional energy for post-processing or cooling of the printed parts. As the printer operates on electrical power, there is no emission of gases to the environment.

3. SAMPLE PREPARATION METHODS

Two kinds of samples are used to compare the mechanical properties; one made out of virgin ABS filament and another made out of recycled ABS. One set of samples will be first printed using virgin ABS filament. Another set of samples will be prepared using recycled ABS. The recycling will be done by using extruder and shredder. To prepare a recycled filament, the virgin filament was first shredded and then extruded for 3 cycles. Then finally the filaments are used for sample (Dogbone) preparation.

3.1. Filament Extrusion

For filament production, KFM Eco Ex extruder was used. It has six temperature zones. The temperature of each zone was maintained such that the viscosity of the melted plastic was high and the melt was steadily flowing. The melt was passed through a filament die to get a continuous filament. The melt was cooled using a water bath and cold air gun. The cooled filament was pulled steadily by hands.

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Figure 11. KFM Eco Ex Extruder at Arcada

Figure 12. Cooling water bath

During extrusion, it is very vital to check the temperature of each zones and extrusion speed such that the filament flows smoothly without any defects.

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Table 2. Parameters used for extrusion

Plastic Used: ABS

Extruder: Single Screw

Screw Design: Barrier Screw

20 − 40 𝐿/𝐷

Compression Ratio: 2.75: 1

Cylinder Temperatures:

𝑇𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑜𝑓 𝑍𝑜𝑛𝑒 1, ℃ 𝑇𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑜𝑓 𝑍𝑜𝑛𝑒 2, ℃ 𝑇𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑜𝑓 𝑍𝑜𝑛𝑒 3, ℃ 𝑇𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑜𝑓 𝑍𝑜𝑛𝑒 4, ℃ 𝑇𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑜𝑓 𝑍𝑜𝑛𝑒 5, ℃ 𝑇𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑜𝑓 𝑍𝑜𝑛𝑒 6, ℃

215 220 230 230 233 19

Melt Temperature: 200 − 240℃

Extrusion Speed 30 𝑅𝑃𝑀

The filament is checked for any defects like rough surfaces and diameter variations. Since the filament was pulled and rolled using hands, there were some defects on the surfaces and diameter of the filament. The filament was still suitable for 3D printing.

Figure 13. Recycled filament on first cycle and third cycle

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3.2. 3D Printing

Figure 14. Creality CR-10S and the samples printed at Arcada UAS

After the recycled filament samples are ready, it is now time to print the dogbone or tensile test piece. The dogbones were printed using Creality CR-10S printer at Arcada. CR-10 is an open 3D printer that has no encloser. It has an LCD screen and control knob to control various parameters of the print. The samples printed are shown in the above picture.

4. TESTING METHODS

4.1. Tensile Test

The tensile was conducted using tensile testometric device inside Arcada lab. Three different samples of each virgin ABS and recycled ABS were tested. The samples were tested in the testometric device, and the data were gathered into an Excel spreadsheet. The data was used to calculate various properties of material including the elastic modulus, yield strength, ultimate tensile strength. The data was then plotted on engineering stress-strain curves to compare the samples.

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Figure 15. Tensile Test of ABS

To begin with the test, width, thickness and gage length were determined. The load cell was set to zero to ensure that the software only measured the tensile load applied to the specimen. The specimen was loaded into the jaws of the testometric machine such that specimen was equally spaced between the two clamps. The test was started, and the specimen was loaded, resulting in a measurable strain. The upper jaw was set to move upward at 100 mm/min. The samples were pulled at a constant rate of 100 mm/min. The data was gathered using the software, and loaded into a spreadsheet. The test continued until fracture, where the software stopped the moving crosshead. The specimen was removed, and the jaws were reset to the initial position to start another tensile test. The testing procedure was repeated for the rest of the specimens.

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4.2. Melt Flow Index

The MFI test was conducted using noselab’s Extrusion Plastometer device inside Arcada lab. An ISO 1133:2005 Standard for ABS was used to perform the experiment. To begin with the experiment, the extrusion plastometer was preheated to 260℃. Then, 6 grams of pelletized sample was placed into the barrel. On top of the sample, a piston was placed and above the piston, a defined weight of 5 kg was kept. As the plastic starts to melt, the applied weight pushes the molten plastic through a die. The cut-off time was set to 30 seconds. After every cut-off time, the mass deposited was weighed to calculate the MFI value.

𝑀𝐹𝐼 (260℃/5 𝑘𝑔) = 𝑚 𝑡 × 1

60 𝑠 × 10

Where, m is the mass of the sample deposited and t is the cut-off time in seconds.

Figure 16. Melt flow index test

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5. RESULTS

5.1. Extrusion

Table 3. Extrusion parameters and results

Experiment 1 Experiment 2 Experiment 3

Zones Temperature 5 to 1 respectively

(℃)

226-236-216-231-215 228-231-230-225-209 230-230-228-225-220

Extrusion Speed 20 rpm 30 rpm 30 rpm

Cooling Method Water bath Water bath Water bath

Drying No drying Drying at 80℃ for 20

mins

Drying at 80℃ for 30 mins

Outcome Moisture or water

droplets present inside the sample, varying diameter of

filament

Varying diameter of filament, presence of few impurities

Smooth surface with no or very less contamination, few diameter variations

5.2. Tensile Testing

The data obtained from the tensile test was plotted into Excel to obtain engineering stress-strain graph. The graph can be used to calculate and compare young’s modulus, elongation at break and ultimate tensile stress.

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Figure 17. Tensile test comparison between virgin ABS and recycled ABS

From the graph, it is clear that the Young’s modulus value for virgin ABS and recycled ABS are nearly equal. But recycled ABS is more fragile or less ductile than virgin ABS. Virgin ABS absorbs large amount of energy before breaking than recycled ABS.

The table below shows comparison of Young’s modulus, stress at yield and strain at yield values between virgin ABS and recycled ABS:

Table 4. Tensile test results

Youngs Modulus (Average)

Stress at Yield (Average)

Strain at Yield (Average)

Virgin ABS 1.94 MPa 37.12 MPa 3.2%

Recycled ABS 1.88 MPa 36.49 MPa 3%

0 5 10 15 20 25 30 35 40

0 1 2 3 4 5 6 7 8

Stress (MPa)

%Strain

Tensile Test

Virgin ABS Recycled ABS

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5.3. Melt Flow Index

The table below shows the melt flow index values of virgin ABS and its comparison with recycled samples. It is seen from the result that the MFI value of ABS decreases upon successive recycling and processing. This might be due to addition of impurities and branching of polymer chains upon each recycling.

Table 5. Result of MFI test (average)

Virgin ABS (260℃/5 kg)

(g/10 min)

Recycled ABS (1^st Cycle) (260℃/5 kg)

(g/10 min)

Recycled ABS (2^nd Cycle) (260℃/5 kg)

(g/10 min)

Recycled ABS (3^rd Cycle) (260℃/5 kg)

(g/10 min)

40 40 38.4 37.8

6. DISCUSSION

6.1. Extrusion Properties and 3D Printing

Extrusion of good profile filament is vital for 3D printing process. Significant number of trials each with slightly different parameters and processes were tried. Since water bath was used for cleaning, in initial extrusions, several water droplets or moisture were trapped inside the filament.

Moreover, the filament was very rough and had varying diameters. In second attempt, the extrusion temperature and extrusion speed were raised. The filaments still had some moisture and few rough surfaces. To remove the moisture, the filament was dried at 80℃ for 20 mins. This removes a lot of moisture but presence of impurities was still visible. These might have contributed to surface roughness of the filament. In third attempt, to remove the impurities, the filament was dried at 80℃ for 30 mins and also the extrusion temperature was raised a bit. This resulted in filament with smooth surface, with no or very less contamination and few diameter variations. This filament was considered satisfactory to be used in 3D printing.

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24 During 3D printing, the initial samples were not printed well. Since the recycled filament samples had inconsistent diameter and were a bit moist, a section of the print was very thin or under extrusion. There were visible gaps or tear in the print.

Figure 18. Failed print and proper print comparison

To solve this issues, the filament diameter was checked for any inconsistency. Too thin or too thick sections were removed. The print temperature and speed were properly checked to print hotter and slower. Finally, the print was smooth without any issues.

6.2. Mechanical Properties

Mechanical properties of materials were analyzed by doing a tensile test. It is seen from the Figure 17 and Table 4, Young’s modulus value for virgin ABS sample and recycled ABS sample are nearly equal i.e. 1.94 MPa and 1.88 MPa respectively. It is also seen that the stress and strain at yield value for virgin ABS sample and recycled ABS sample are nearly equal. But it is clearly seen in Figure 17 that virgin ABS sample undergo very long plastic deformation and absorbs large amount of energy before breaking than recycled ABS sample. Recycled ABS samples are strong and can handle same amount of stress as virgin ABS samples but cannot handle larger torsion or flexing. So, recycled ABS can be used to make most of the plastic products that do not undergo much torsion or flexing.

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25

6.3. Flow Properties

From the MFI test results shown in table 5, it is seen that the MFI value of the virgin ABS is 40 gm/10 min. Upon first recycling, the MFI value stays the same. On 2^nd and 3^rd cycle, the MFI value decreases slightly to 38.4 and 37.8 gm/10 mins respectively.

Since virgin ABS samples have higher MFR value, it tells virgin sample has lower molecular weight and low viscosity but higher flow rate. On the other hand, the recycled samples with a bit lower MFR value means, the recycled sample has higher molecular weight, higher viscosity and lower flow rate. The decrease in MFI value with every cycle means that upon each recycling, there is some chance of contamination. This contamination might have led to branching of molecular chains and thus leading to lower flow rate.

7. CONCLUSION

This thesis shows that there were minor changes in mechanical or flow properties of ABS on recycling. Recycling has some effects on materials mechanical and flow properties. During each recycling step, there is a huge chance of contamination. This contamination leads to the change in chemical and molecular properties of plastics. However, it also shows that ABS plastics can be recycled and used for many cycles before being marked as waste.

In conclusion, recycling of plastic wastes is vital for the sustainability of materials and environment. If the technology is good enough, we can recycle large volume of plastic waste that was actually supposed to be dumped into the landfills. These plastic waste can be used as a raw material for other production lines. 3D printing is one of the promising technology that can be used to manufacture products out of recycled plastics. Through a series of recycling processes, plastic wastes can be recycled to be used as raw material or filaments for 3D printing.

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References

A. D. JENKINS (UK), P. K. (. R. R. F. T. S. (. U. W. S. (., 1996. GLOSSARY OF BASIC TERMS IN POLYMER SCIENCE. 68(12), pp. 2287-2311.

Axel Barrett, 2020. 3D Printing in Circular Economy. [Online]

Available at: https://bioplasticsnews.com/2020/04/06/3d-printing-circular-economy/

[Accessed 22 9 2020].

Chakravorty, D., 2017. STL File Format for 3D Printing – Simply Explained. [Online]

Available at: https://all3dp.com/what-is-stl-file-format-extension-3d-printing/#pointone [Accessed 20 9 2019].

Compactor Management Company, 2017-18. Processes, Stages, and Benefits of Plastic Recycling.

[Online]

Available at: https://www.norcalcompactors.net/processes-stages-benefits-plastic-recycling/

[Accessed 12 April 2019].

European Commission, 2019. How much plastic packaging waste do we recycle? [Online]

Available at: https://ec.europa.eu/eurostat/web/products-eurostat-news/-/DDN-20191105- 2#:~:text=In%20the%20EU%2C%20an%20estimated,waste%20was%20recycled%20in%20201 7.&text=Compared%20with%202005%2C%20the%20recycling,to%2042%25%20in%202017).

[Accessed 20 9 2020].

Hajifathaliha, S., 2020. A Sustainable Approach in Additive Manufacturing, s.l.: s.n.

Helsinki Region Environmental Services (HSY), 2019. Circular Economy. [Online]

Available at: http://vara.hsy.fi/hsy/en/experts/climatechange/pages/circular-economy.html [Accessed 20 9 2020].

Hod Lipson, M. K., 2010. Fabricated New World of 3D Printing. 1st Edition ed. s.l.:John Wiley

& Sons, Incorporated.

Iunolainen, E., 2017. Suitability of recycled PP for 3D printing filament, Helsinki: s.n.

Luiz Gustavo Barbosa, M. P. G. H. C., 2017. Analysis of Impact and Tensile Properties of Recycled Polypropylene. International Journal of Materials Engineering, 7(6), p. 118.

Maria Cristina Tanzi, S. F. a. G. C., 2019. Foundations of Biomaterials Engineering. s.l.:Elsevier Ltd..

Nipun, 2015. Difference Between Yield Strength and Tensile Strength. [Online]

Available at: https://pediaa.com/difference-between-yield-strength-and-tensile-strength/

[Accessed 19 10 2020].

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27 Omnexus, 2020. Acrylonitrile Butadiene Styrene (ABS) and its Features. [Online]

Available at: https://omnexus.specialchem.com/selection-guide/acrylonitrile-butadiene-styrene- abs-plastic

[Accessed 22 9 2020].

plastikcity.co.uk, 2018. ASTM D638 Tensile Testing of Plastics. [Online]

Available at: https://www.plastikcity.co.uk/blog/tensile-testing-of-plastics/

[Accessed 19 10 2020].

Polymer Solutions News Team, 2019. Melt Flow Index Testing. [Online]

Available at: https://www.polymersolutions.com/blog/melt-flow-index-testing/

[Accessed 14 10 2020].

polymerdatabase.com, 2015-2020. Polymer Properties Database. [Online]

Available at: https://polymerdatabase.com

[Accessed 20 10 2020].

TechMiny, 2018. Extrusion moulding process for plastic machining. [Online]

Available at: https://techminy.com/extrusion-moulding/

[Accessed 22 9 2020].

WhiteClouds, 2019. Fused Deposition Modeling (FDM). [Online]

Available at: https://www.whiteclouds.com/3DPedia/fdm.html

[Accessed 16 5 2019].

yle News, 2019. Plastic recycling in big cities doubles in 2019. [Online]

Available at:

https://yle.fi/uutiset/osasto/news/plastic_recycling_in_big_cities_doubles_in_2019/11135850 [Accessed 20 9 2020].

A Sustainable Approach In Additive Manufacturing With Recycled ABS