Introduction

If you talk about the most versatile and widely used polymers in the world then polyethylene will top the list. The advantages and applications are endless. However, to gain maximum advantage you should know which of polyethylene to use, when to use and which technique to manufacture from it.

This blog explains polyethylene from its basics to everything about it. The manufacturing process, advantages and disadvantages leaves behind nothing unexplainable.

What is Polyethylene Plastic？

You must have heard the word polythene in your daily life many times. Well both polythene and polyethylene are the same. Also known as polyethylene, polyethylene is the most common type of plastic used in the world.

Polyethylene plastic has both industrial and commercial uses. However, the most common use of polyethylene is in the packaging industry. Plastic films, plastic bags, bottles and containers all use polyethylene plastic in their manufacturing.

Polyethylene is a thermoplastic. Thermoplastic is a plastic that changes its shape when exposed to heat. Its thermoplastic property is the major reason behind its versatility. Polyethylene has a linear structure. Its chemical formula is (C2H4) n.

You can get an idea of the immense use of polyethylene plastic in the world from the fact that every year 100 million tons of polyethylene plastic are produced for several purposes.

How is PE made?

The process of manufacturing polyethylene plastic is known as polymerization. Polymerization of ethylene leads to the production of polyethylene plastic. This process takes place with the help of an initiator such as oxygen or peroxide. A number of catalysts speed up the polymerization process.

The manufacturing of PE is divided into three types. These three types are based on the three different types of pressure i.e.:

• High pressure production method

• Medium Pressure production method

• Low pressure production method

Let’s have a look at each production method in detail:

1. High Pressure Production Method

As the name indicates the high-pressure method is carried out under high pressure and temperature in a reactor. The process starts with the help of an initiator. The initiator is mostly oxygen or peroxide. The pressure range during the process is 100-300MPa and the temperature range is 200-300 degree Celsius.

Ethylene is introduced into the reactor under secondary pressure. The initiator then starts the polymerization process. At the end of the process there might be some residual or unreacted ethylene left in the reactor. This ethylene is recovered and recycled.

The reactor used in the high-pressure method can be of two types i.e.

• Tubular reactor

• Kettle Reactor

The production capacity of the kettle reactor is greater than tubular reactor. The catalyst used in this process is titanium (lull) chloride which is also known as Ziegler-Natta Catalyst.

2. Medium Pressure Production Method

The medium pressure production method is different from the high-pressure production method because of two reasons. The first reason is of course it uses medium pressure. The second reason is that it uses chromium as a catalyst supported silica gel.

Medium pressure production takes place inside a loop reactor. It is mainly used for the production of high and very low-density polyethylene.

3. Low Pressure Production Method

The pressure production method is further differentiated into three categories:

• Slurry Method

• Solution Method

• Gas phase method

The pressure during the low-pressure production method is maintained as low as 2MPa. The general steps during all three types are almost the same. The first step is preparation of ethylene molecule the catalyst, the second step is of course the polymerization of ethylene and the last step is granulation.

Common Application of Polyethylene

Polyethylene has several industrial and commercial uses. Afterall it is the most widely used plastic in the entire world. The main reason behind its widespread use is its versatility and thermodynamic properties. In this section we shall have a look at the several uses of polyethylene.

1. Packaging

This is the most widespread use of polyethylene. Plastic packaging is the most common application of polyethylene. Among the huge variety of packaging materials made from PE are plastic bags, plastic films, geomembranes, plastic bottles and containers. Have you ever thought about why polyethylene is used in packaging materials? It is because it has:

• Low density

• Chemical resistance

• Impermeable to water

• High resistance to wear and tear

In the packaging industry the market value of polyethylene is very high. The food packaging industry also uses polyethylene for storage purposes. The main reason behind its use is its chemical composition and underactivity. It does not react with the food substances and keep food preserved in its original form. It is used in the production of crates, jugs, trays and food containers.

2. Post Radiation Treatment

After undergoing radiation treatment polyethylene develops many physical properties. It becomes stronger and more resilient to environmental pressure. It is not easy to deform and becomes more elastic. Its practicality increases because of increased insulation to electricity.

The physical properties that polyethylene gets after radiation treatment make it suitable for a variety of applications. These applications include:

• Using polyethylene for the insulation of transformers and capacitors

• Using it in high temperature aircraft parts

3. Chemical Resistant Materials

Polyethylene is used in the manufacturing of pipes and anti-corrosion lining because of its chemical resistance. Because of low water absorption and excellent chemical resistance, it is also used in fittings.

4. Electrical Insulation

Polyethylene is highly resistant to moisture. It is a very stable plastic. It has high dielectric properties. These are the main reasons that make it suitable to use electrical insulation. It is used for insulation purposes in both electrical and non-electrical engineering applications.

When used in electrical cables it solves the problems related to electrical discharges. It is one of the top plastic materials used in electrical insulation applications.

5. Medical Tubing

Polyethylene has several applications in the medical industry as well. The catheter tubing which is the most widely used object in the medical industry is made from PE. But why is PE used in the manufacturing of catheter tubing?

It is because polyethylene is light weight and chemically inert. Not just it is flexible but it can retain its flexibility for longer time.

Chemical Properties of Polyethylene

The chemical properties of polyethylene are amazing. This is the main reason behind the versatile and widespread use of the plastic in several industrial applications. In this section we shall analyze the chemical properties of polyethylene one by one.

1. Acid Resistant

At room temperature polyethylene is stable and non-reactive to a variety of acids, amines and bases. Other than Sulphur acid and nitric acid it does not react with hydrochloric acid, hydrofluoric acid, sodium hydroxide and potassium hydroxide. This makes PE a very stable material.

2. UV Resistant

UV reacts to ultraviolet radiation. It reacts to ozone decomposition, photo-oxidation and thermal oxidation. However, it does give a shielding effect when exposed to light. This is because of the Carbon inside PE.

3. Solvent Resistant

Since it is non-reactive to a variety of acids and bases at room temperature, PE does not react with acids and base solvents at room temperature as well. It remains insoluble in any general solvent at room temperature.

However, under high temperature PE becomes soluble in aromatic hydrocarbons such as xylene or toluene.

Other Chemical Properties

The chemical properties of PE depend upon its molecular structure and density. All the different types of PE have different in density range. They are also produced through different manufacturing methods.

A lot of chemical properties of PE make it resembles paraffin. However, they are both not same.PE is made of non-polar saturated hydrocarbons with high molecular weight. This property makes it resemble paraffin.

PE is considered to be partially crystalline plastic. The crystalline nature of the plastic is because of the symmetric arrangement of the individual PE macromolecules. Crystallinity of the plastic is directly proportional to its density and molecular weight.

PE has poor resistance to heat since it is a thermoplastic. It also degenerates under environmental stress be it mechanical or chemical.

Physical Properties of Polyethylene

1. Texture

PE has a white waxy texture. It is translucent in nature. It is soft and tough at the same time. It is lighter than water and nontoxic in nature. It becomes more transparent as it crystallizes.

2. Melting Point

The melting point of PE is different for different types. High density polyethylene and medium density polyethylene has a melting point of 120-180 degree Celsius. Low density polyethylene has a melting point between 105-115-degree Celsius range.

3. Conductivity

PE offers high resistance to electric current. It is therefore known to be a very good insulator.

4. Mechanical Strength

When compared to other plastics PE has less mechanical strength. This makes the plastic flexible and malleable. It is less rigid and hard as compared to other types of plastics.

5. Ductility

PE has high impact strength and is known to be extremely ductile in nature.

6. Flammability

PE is a flammable material. When it comes in contact with fire it burns in an aggressive manner.

Common Types of PE and their Properties

The classification of polyethylene is done on the basis of density of plastic and the degree of branching its structure. The reason is that both these characteristics lay a Styron impact on the mechanical properties of the polyethylene. It is therefore clear that different types of polyethylene have different mechanical properties. In this section we shall discuss the various types of polyethylene.

1. Ultra-High Molecular Weight Polyethylene (UHMWPE) :

Ultra-High Molecular Weight Polyethylene (UHMWPE) is distinct from types of polyethylene. It is because it has no branching. It only has a linear structure. Also, as the name implies it has a very high molecular weight. Its molecular weight exceeds 1.5 million.

UHMWPE is extremely strong plastic. It offers high resistance to environmental stress and abrasion. Its molecular structure closely resembles the molecular structure of HDPE.

2. Low Density Polyethylene (LDPE):

Low density polyethylene (LDPE) is also known by the name of high-pressure polyethylene. It has a unique texture. It appears as a milky structure with white resin like granules.

It has a highly branched molecular structure. This structure is the reason behind its flexibility, electrical insulation, elongation, breathability (to some extent) and transparency.

LDPE is used in the packaging of food products. A major advantage of LDPE is that it is recyclable making it an environmentally friendly option. The density of LDPE is less than water.

3. Linear Low-Density Polyethylene (LLDPE):

Both the formation and the structure of linear low-density polyethylene is very unique. The copolymerization between the ethylene molecules and a-olefins causes the formation of LLDPE.Alongwith the linear ethylene backbone the structure has short branches of the copolymer.

LLDPE is stronger as compared to LDPE. When it comes to resistance to cracks and abrasion and environmental stress LLDPE is more resistant than LDPE. It has a high softening and melting temperature as well. It is stronger than LDPE.

Both shrink wrap and stretch wrap use LLDPE in their manufacturing. It is popular for having low density and clarity.

4. High Density Polyethylene (HDPE):

Unlike low density polyethylene, high density polyethylene is also known as low pressure polyethylene. It has an opaque white wax like appearance.

HDPE is a very good insulator to electric current. It also offers strong resistance to acids, alkalis and organic solvents. When the temperature is low it maintains a certain amount of toughness. As compared to LDPE it has high tensile strength, surface hardness and rigidity.

HDPE is the most common type of polyethylene available. Products such as milk jugs, detergent bottles and cutting boards are all made of HDPE. It is a durable and versatile material.

Why Choose Polyethylene for CNC Machining?

Among all the types of polyethylene discussed in this blog high density polyethylene is the most used plastic. There are several reasons behind it being a popular choice for CNC machining. First of all, it guarantees machined parts with high precision.

HDPE is versatile in nature and has exceptional strength to its high-density material to ratio. Not only is it strong but also offers great flexibility and chemical stability with low friction. HDPE is used in several CNC applications such as NC turning, CNC milling, CNC routing and CNC drilling.

Another major advantage of using HDPE for CNC applications is that it is environmentally friendly.

Why Choose Polyethylene in Plastic Molding？

Using Polyethylene for plastic molding is very convenient for manufacturers. It is because it comes in the form of pellets. Depending upon what type of finished product is required it goes through a molding process. That means for different finished products there are different molding techniques.

In this section we shall have a look at the various plastic molding techniques that can be applied to PE:

1. Injection Molding

In plastic molding injection molding holds a prominent spot. A hot steaming liquid which in this case is molten PE is poured inside a mold. It is then allowed to cool down. The mold is opened and the product is extracted in solid form.

Injection molding is economical for bulk production. For low production it is a costly process as the cost of molds is usually high. Molds are made of aluminum or steel.

2. Blow Molding

Blow molding technique in plastic molding is used when you want to manufacture hollow parts with thin walls. In this technique you heat the plastic first and then blow it like a balloon. Again, you need a mold for this purpose. The liquid expands against the wall of the mold as air gets filled inside.

Use this technique when achievement of perfect shape is your requirement. This technique is very time saving. If your business requires hundreds and thousands of plastic bottle production on a daily basis then this is the perfect technique for you to choose.

3. Compression Molding

The working of compression molding is the same as its name. A hot liquid is poured inside a mold and is compressed. Compression continues unless the liquid assumes the shape of the mold.

PE plastic in this case comes in the form of sheets. First heat is used to melt it in the mold and later to retain the shape. Finally, it is cooled, trimmed and removed.

Compression molding is widely used in the automotive industry for the manufacturing of plastic parts.

4. Extrusion Molding

Another method for molding PE plastic is extrusion molding. The process is similar to injection molding. What makes it different from injection molding is the fact that instead of a mold it uses a die.

In this process hot molten plastic passes through a die. It is actually the die that determines the shape of the final product.

Pipes, straws and hoses use this technique for their manufacturing.

5. Rotational Molding

Rotational molding is also known as roto molding. In this technique plastic in the form of powder or liquid is placed inside a mold. The mold keeps rotating inside the oven until the resin or liquid forms a coating on the inside of the mold.

Rotational molding is a very cost-effective process because it produces minimal waste. It is used for the production of large hollow plastic components. PE with rotational molding can be used to manufacture pet houses, recycle bins, road cones etc.

Applications of Polyethylene in Perfume Packaging?

The perfume industry is all about fragrances and packaging. This is where polyethylene comes into play. Glass perfume bottles are very popular in the perfume manufacturing industry. Glass perfume bottle manufacturers design and produce bottles of various colors and designs that match with consumer’s demands.

Polyethylene naphtholate is used as a substitute for glass in perfume packaging. It is because of its molding ability, you can mold polyethylene naphtholate into two parts and then join the two parts together. This is possible with the help of injection blowing and extrusion blowing.

PET, which is Polyethylene terephthalate, is also a popular material for perfume packaging. But what qualities make it suitable for perfume packaging?

Perfume bottles made with PET are known for their clarity. They are also recyclable there causing no hazard to the environment.

Other than perfume Polyethylene is also used for the packaging of cosmetics and personal care products. It is considered to be a durable material that also preserves the components inside it.

The Difference Between Polypropylene and Polystyrene

Although both polyethylene and polystyrene have quite similar characteristics. Not only are they both very popular polymers but also, they are both strong, flexible and light weight. Certain distinctive features between the two create visible differences among them. In this section we shall have a look at the differences between polyethylene and polystyrene:

1. Strength

Although both polystyrene and polyethylene have almost similar strength yet when making a comparison between them certain forms of polyethylene are stronger. HDPE and UHMW are stronger than polystyrene. This makes them more suitable for applications such as construction packaging.

2. Malleability

Polystyrene can more easily be formed into various shapes and forms making it more malleable than polyethylene. If you have to choose between the two for engineering packaging then polystyrene is a better option to choose.

3. Availability

It depends upon your business what form of polymer chains polystyrene of polyethylene you are looking for. Both polystyrene and polyethylene are present in the form of films and sheets. However, if you want a polymer in foam form then only polystyrene is present in form.

In case your business demands the polymer to be present in fibrous form then you should choose polyethylene.

4. Electrical Insulation

Both synthetic polymers that are used for packaging. Again, it depends upon your business what type of business requirement you have. If your business demands packaging of electrical products that require packaging high electrical insulation then you should choose polystyrene.

You should choose polyethylene if you want a sustainable packaging film solution that’s ecofriendly and can protect your products during long transits.

Advantages of Using Polyethylene

A lot of advantages of polyethylene have been mentioned in this blog already. Polyethylene is ideal for packaging, it is flexible and it offers electrical insulation. In this section we shall analyze the advantages of polyethylene in detail one by one.

1. Recyclable

Polyethylene is a recyclable material. Manufacturing a new product is costly and time consuming. Whereas recycling a product is not just less costly because you already have the raw materials available but also environmentally friendly.

2. Water Resistant

A major factor that adds to the durability of polyethylene is that it is water resistant. This is one of the main reasons why polyethylene is an ideal material for packaging purposes.

3. Electrical Insulator

It is a really good insulator of electric current. However, it is prone to electrostatic current. Addition of antistatic agents can prevent the material from becoming electrostatically charged.

4. Assured Protection

Polyethylene is leak proof. When used for packaging purposes it provides assured protection to the components inside it. It is an amazing product for heat sealing. It means you can wrap it around a product and make it airtight.

In the electronics industry polyethylene provides extra protection to electronic components from moisture and tampering.

5. High Rigidity

Polyethylene plastics are moisture resistant and strong. This is one of the reasons that they are used to manufacture milk cartons, vegetable oil bottles and water bottles with caps. When it comes to excellent rigidity PE wears the crown.

6. Cost Effective

An important requirement for manufacturers is to save cost of production. Polyethylene meets all the standards of a cost-effective material. Consider the example of High-density polyethylene (HDPE). HDPE is not just easy to process but also very easy on the pocket. It has an opaque appearance. Shampoo bottles, flower pots and lotion bottles are all made of HDPE.

7. Highly Versatile Material

When it comes to versatility and adaptability PE is unbeatable among other materials. You can adapt it to your requirements in terms of material, thickness, color and clarity. It is your choice if you want to make your product visible through the package or not.

Disadvantages of Polyethylene

We have discussed several advantages of PE. However, it’s not possible that something doesn’t have any drawbacks. Therefore, in this section we shall discuss the disadvantages associated with the use PE:

1. Non-Biodegradable

PE is non-biodegradable’s disposal of PE requires traditional methods such as incineration and landfilling. Not only are these two processes very costly but also unsustainable. This raises concerns about environmental safety and protection. It takes a long time to break down. It can even take decades.

2. Threat to Natural Resources:

The source of PE is petroleum and natural gas. Although both resources are abundant in nature, they are finite. These natural resources have several other applications as well.Therefore, the usage of natural gas and petroleum for manufacturing PE is a threat.

3. Global Warming

The emission of greenhouse gases is contributing a lot to global warming and climate change. The manufacturing of PE leads to the emission of a lot of carbon dioxide which is also a greenhouse gas.

Conclusion

No doubt the versatility, flexibility and durability of PE is unquestionable. PE has an important role in every industry. From automotive to perfume industry and especially the packaging industry PE has its applications everywhere. Moreover, the variety of PE types, each of them with different properties increase the versatility of PE.